Patent Application
20150052812
The present invention relates generally to the production of gaseous fuel from an organic-carbon-containing feedstock.
The vast majority of fuels are distilled from crude oil or obtained from natural gas pumped from limited underground reserves, or mined from coal. As the earth's crude oil supplies become more difficult and expensive to collect and there are growing concerns about the environmental effects of coal other than clean anthracite coal, the world-wide demand for energy is simultaneously growing. Over the next ten years, depletion of the remaining world's easily accessible crude oil reserves, natural gas reserves, and low-sulfur bituminous coal reserves will lead to a significant increase in cost for fuel obtained from crude oil, natural gas, and coal.
The search to find processes that can efficiently convert biomass to fuels and by-products suitable for transportation and/or heating is an important factor in meeting the ever-increasing demand for energy. In addition, processes that have solid byproducts that have improved utility are also increasingly in demand.
Biomass is a renewable organic-carbon-containing feedstock that contains plant cells and has shown promise as an economical source of fuel. However, this feedstock typically contains too much water and contaminants such as water-soluble salts to make it an economical alternative to common sources of fuel such as coal, petroleum, or natural gas.
Historically, through traditional mechanical/chemical processes, plants would give up a little less than 25 weight percent of their moisture. And, even if the plants were sun or kiln-dried, the natural and man-made chemicals and water-soluble salts that remain in the plant cells combine to create corrosion and disruptive glazes in furnaces. Also, the remaining moisture lowers the heat-producing MMBTU per ton energy density of the feedstock thus limiting a furnace's efficiency. Centuries of data obtained through experimentation with a multitude of biomass materials all support the conclusion that increasingly larger increments of energy are required to achieve increasingly smaller increments of bulk density improvement. Thus, municipal waste facilities that process organic-carbon-containing feedstock, a broader class of feedstock that includes materials that contain plant cells, generally operate in an energy deficient manner that costs municipalities money. Similarly, the energy needed to process agricultural waste, also included under the general term of organic-carbon-containing feedstock, for the waste to be an effective substitute for coal or petroleum are not commercial without some sort of governmental subsidies and generally contain unsatisfactory levels of either or both water or water-soluble salts. The cost to suitably transport and/or prepare such feedstock in a large enough volume to be commercially successful is expensive and currently uneconomical. Also, the suitable plant-cell-containing feedstock that is available in sufficient volume to be commercially useful generally has water-soluble salt contents that result in adverse fouling and contamination scenarios with conventional processes. Suitable land for growing a sufficient amount of energy crops to make economic sense typically are found in locations that result in high water-soluble salt content in the plant cells, i.e., often over 4000 mg/kg on a dry basis.
Attempts have been made to prepare organic-carbon-containing feedstock as a biogas, i.e., a gaseous renewable fuel or natural gas substitute, but these have not been economically viable as they generally contain high levels of carbon monoxide and carbon dioxide from retained intracellular water and water-soluble salts in the feedstock that reduces the energy density to well below that of natural gas. However, there remains a need for processed biogas as it is a clean renewable source of gaseous fuel if it could be made cost-effectively with a more substantial reduction in its content of water and water-soluble salt in its feedstock.
Gaseous fuels from renewable organic-carbon-containing feedstock are an important factor in meeting the ever-increasing demand for energy. The present invention fulfills these needs and provides various advantages over the prior art.
Embodiments of the present are directed to a composition from renewable unprocessed organic-carbon-containing feedstock and a process. The composition is a processed biogas composition, a gaseous renewable carbon fuel whose characteristics include an energy density of at least 700 BTU per standard cubic foot (BTU/cubic ft) or 26 megajoules per cubic meter (MJ//cubic meter), a carbon monoxide concentration of less than 20 vol %, a carbon dioxide concentration of less than 15 vol %. The composition is renewable and made with a system configured to convert unprocessed organic-carbon-containing feedstock into processed organic-carbon-containing material with a beneficiation sub-system, and subsequently to the processed biogas with an oxygen-deficient thermal sub-system.
The process of making the biogas composition comprises three steps. The first step is to input into a system, comprising a first and a second subsystem, a renewable unprocessed organic-carbon-containing feedstock that includes free water, intercellular water, intracellular water, intracellular water-soluble salts, and at least some plant cells comprising cell walls that include lignin, hemicellulose, and microfibrils within fibrils. The second step is to pass the unprocessed organic-carbon-containing feedstock through the first sub-system, a beneficiation sub-system process, in order to result in processed organic-carbon-containing feedstock having a water content of less than 20 wt % and a salt content that is reduced by at least 60 wt % on a dry basis from that of the unprocessed organic-carbon-containing feedstock. The third step is to pass the processed organic-carbon-containing feedstock through the second sub-system, an oxygen-deficient thermal sub-system process, to result in a processed biogas composition that is renewable and has an energy density of at least 700 BTU/cubic ft (26 MJ/cubic meter), a carbon monoxide concentration of less than 20 vol %, and a carbon dioxide concentration of less than 15 vol %.
The invention is a processed biogas that is a suitable renewable natural gas substitute for devices that use natural gas as a feedstock to generate heat or electricity such as, for example, furnaces and natural gas fired household devices. The low salt content of the processed organic-carbon-containing feedstock into the oxygen-deficient thermal sub-system substantially reduces adverse side reactions that may produce higher carbon monoxide and carbon dioxide concentrations in the resulting processed biogas. This makes the biogas from renewable feedstock a suitable substitute for natural gas, a material that is getting more expensive to acquire in both monetary and environmental cost. During the beneficiation section of the process, the substantial reduction of water-soluble salts reduces the adverse results that occur with the subsequent use of the processed organic-carbon-containing feedstock. In addition, energy needed to remove water from unprocessed organic-carbon-containing feedstock described above to a content of below 20 wt % and a substantial amount of the water-soluble salt with the invention is significantly less than for conventional processes. In some embodiments, the total cost per weight of the beneficiated feedstock is reduced by at least 60% of the cost to perform a similar task with known mechanical, physiochemical, or thermal processes to prepare renewable organic-carbon-containing feedstock for use in subsequent fuel making operations such as an oxygen-deficient thermal sub-system.
The above summary is not intended to describe each embodiment or every implementation of the present invention. Advantages and attainments, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings.
While the invention is amenable to various modifications and alternative forms, specifics have been shown by way of example in the drawings and will be described in detail below. It is to be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.
The processed biogas of the invention is a gaseous fuel made from passing beneficiated processed organic-carbon-containing feedstock through an oxygen-deficient thermal system. The processed biogas is similar to natural gas in energy density. The processed biogas of the invention has the advantages of coming from a renewable source, i.e., agricultural and plant materials, without the burdens of current biomass processes that are inefficient and result in gases having an unsatisfactorily low energy density and high concentration of carbon monoxide and carbon dioxide. There are several aspects of the invention that will be discussed: biogas, unprocessed renewable organic-carbon-containing feedstock, beneficiation sub-system, oxygen-deficient thermal sub-system, beneficiation sub-system process, and oxygen-deficient thermal sub-system process.
Gaseous fuel made from renewable organic-carbon-containing feedstock is referred to as processed biogas in this document. The processed biogas of the invention comprises a gaseous carbon fuel comprising an energy density of at least 700 BTU/cubic ft (26 MJ/cubic meter), a carbon monoxide concentration of less than 20 vol %, and a carbon dioxide concentration of less than 15 vol %. The processed biogas is made from unprocessed organic-carbon-containing feedstock that is converted into a processed organic-carbon-containing feedstock in a beneficiation sub-system, and that is then passed through an oxygen-deprived thermal sub-system. As used in this document, processed biogas is the gaseous product of the devolatization of beneficiated organic-carbon-containing feedstock. Organic-carbon-containing feedstock used to make the processed biogas of the invention can contain mixtures of more than one renewable feedstock.
Natural gas and crude oil are the sourced of the vast majority of fuels used today. These sources are obtained from limited underground reserves. As the earth's natural gas and crude oil supplies are depleted, the world-wide demand for energy is simultaneously growing. Over the next ten years, depletion of the remaining world's easily accessible natural gas and crude oil reserves will lead to a significant increase in cost for fuel obtained from them.
Natural gas is currently primarily obtained from underground deposits formed over millions of years in the form of anaerobic deposits, also called sweet crude for its low sulfur content, and tar sand deposits, also called sour crude for its high sulfur content. Besides, hydrocarbon gases, natural gas also contains as gaseous impurities carbon monoxide, carbon dioxide, water vapor, and hydrogen sulfide. It also may contain small amounts of helium and nitrogen. The energy density of natural gas is typically averages 1,000 BTU/cubic ft (39 MJ/cubic meter) and ranges from 850 to 1050 BTU/cubic ft (33 to 41 MJ/cubic meter).
Syngas, or synthesis gas, is a fuel gas mixture consisting primarily of hydrogen, carbon monoxide, and very often some carbon dioxide. It is commonly used as an intermediate in creating synthetic natural gas, synthetic petroleum, and products to drive gas turbines. Production methods include the gasification of carbon-containing biomass such as, for example, gasification of agricultural waste and municipal waste. However, syngas has less than half the energy density of natural gas and the carbon monoxide and carbon dioxide created are considered harmful contributors to global warming. Syngas has an energy density of less than 300 BTU/cubic ft (11 MJ/cubic meter).
The search to find processes that can efficiently convert renewable materials to fuels suitable for transportation, generation of electricity, and/or heating is an important factor in meeting the ever-increasing demand for energy. Methods and systems for efficiently converting organic-carbon-containing feedstock such as biomass into gaseous fuel with energy densities on the order at least that of natural gas are needed. The present invention fulfills these needs and provides various advantages over the prior art.
Biogas is a renewable gaseous fuel that can be regenerated in less than 50 years. Typically it refers to a mixture of gases produced by the breakdown of organic matter in the absence of oxygen. Biogas can be produced from regionally available raw materials such as recycled waste. It is a renewable energy source and in many cases exerts a very small carbon footprint.
Biogas is produced by anaerobic digestion with anaerobic bacteria or fermentation of biodegradable materials such as manure, sewage, municipal waste, green waste, plant material, and crops. It is primarily methane (CH4) and carbon dioxide (CO2) and may have small amounts of hydrogen sulfide (H2S), moisture, and siloxanes. The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used for any heating purpose, such as cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.
Biogas can also be made by oxygen-deficient thermal processes. These processes also result in biooil and biochar in the case of conventional thermal processes such as pyrolysis, or in biochar and biogas in the case of sublimation. In either case, the primary gas is methane with some ethane, propane, butane, and other non-condensable gases such as, for example, nitrogen.
Methane is important for electrical generation by burning it as a fuel in a gas turbine, gas reciprocating engine, or steam boiler. Compared to the hydrocarbon fuels, burning methane produces less carbon dioxide, a gas associated with global warming, for each unit of heat released. At about 891 kJ/mol, methane's heat of combustion is lower than any other hydrocarbon but the ratio of the heat of combustion to the molecular mass of 16 g/mo. (of which 12 g/mol is carbon) shows that methane, being the simplest hydrocarbon, produces more heat per mass unit, 55.7 kJ/g, than any other complex hydrocarbon. Methane as a fuel is generally known as natural gas because natural gas is predominately methane with lesser amounts of ethane, propane, and butane and has an energy density of between 850 and 1050 BTU/cubic ft (32 and 39 MJ/cubic meter). The energy density of the components of natural gas are 910 BTU/cubic ft (34 MJ/cubic meter) for methane, 1633 BTU/cubic ft (61 MJ/cubic meter) for ethane, 2371 BTU/cubic ft (88 MJ/cubic meter) for propane, and 2977 BTU/cubic ft (111 MJ/cubic meter) for butane. Typically natural gas contains at least 95 vol % hydrocarbons, generally comprising 75% methane, 15% ethane, 5% propane, and butane, and the remaining 5 vol % is non-fuel components including carbon dioxide, carbon monoxide, sulfur compounds, and nitrogen compounds.
Natural gas can be produced from virtually all forms of biomass. Natural gas can be converted from plant and animal residues ranging from fresh collections to collections many millions of years old. It can also be produced from man-made products such as, for example, plastics, and paper products. The question is generally not where one should go to look for a feedstock to produce natural gas but rather how to convert it.
In biogas made by thermal heat or infrared radiation (IR), the heat is absorbed on the surface of any organic-carbon-containing feedstock and then is re-radiated to the next level at a lower temperature. This process is repeated over and over again until the thermal radiation penetrates to the inner most part of the feedstock. All the material in the feedstock conduct or absorbs the thermal radiation at its surfaces and different materials that make up the feedstock conducts or absorb the IR at different rates. A delta temperature of several orders of magnitude can exist between the surface and the inner most layers or regions of the feedstock. As a result, the solid organic-carbon-containing feedstock locally passes through a liquid phase before it is volatilized. This variation in temperature may appear in a longitudinal direction as well as radial direction depending on the characteristics of the feedstock, the rate of heating, and the localization of the heat source. This variable heat transfer from the surface to the interior of the feedstock can cause cold and hot spots, thermal shocks, uneven surface and internal expansion cracks, fragmentation, eject surface material and create aerosols. All of this can result in microenvironments that cause side reactions with the creation of many different end products. These side reactions are not only created in the feedstock but also in the volatiles that evaporate from the feedstock and occupy the vapor space in the internal reactor environment before being collected.
A common thermal process, pyrolysis, produces biochar, liquids, and gases from biomass by heating the biomass in a low/no oxygen environment. The absence of oxygen prevents combustion. Typical yields are 60% bio-oil (from the condensable biogas), 20% biochar, and 20% non-condensable biogas. High temperature pyrolysis in the presence of limited stoichiometric oxygen is known as gasification, and produces primarily syngas. By comparison, slow pyrolysis can produce substantially more char, on the order of about 50%.
Another thermal process is a sublimation process that produces biochar and gases from biomass in a low/no oxygen environment. The absence of oxygen also prevents combustion. Typical yields are 70% biogas and 30% biochar. Sublimation can occur in a vertical manner that lends itself to heavier/denser biomass feedstock such as, for example, wood and a horizontal manner that lends itself to a lighter biomass feedstock such as, for example, wheat straw. The energy density of biogas from sublimation is up to 700 BTU/cubic ft (26 MJ/cubic meter).
In all of the above processes, substantial water is in all renewable organic-carbon-containing feedstock in the pyrolysis or gasification steps. This is because intracellular water is difficult to remove in organic-carbon-containing feedstock. As a result, there is an oxygen source from the water and the product biogas generally contains carbon monoxide at a concentration of over 30 to 40 vol % and carbon dioxide at a concentration of over 20 vol %. This has the further effect of reducing the energy density of the biogas to well below that of natural gas. In contrast, the processed biogas of the invention has an energy density that makes it a suitable substitute for natural gas with an energy density of at least 700 BTU/cubic ft (26 MJ/cubic meter), a carbon monoxide concentration of less than 20 vol %, and a carbon dioxide concentration of less than 15 vol %.
The energy density may vary in the processed biogas. Factors that affect the energy density are the relative concentrations of methane, ethane, propane, and butane. As the % of methane decreases relative to the % of the other gaseous hydrocarbons, the energy density of the processed biogas increases. Similarly as the concentration of carbon monoxide in the processed biogas decreases, the energy density increases. Some embodiments have a concentration of carbon monoxide that is less than 30 vol %, some less than 25 vol %, some less than 20 vol %, some less than 15 vol %, some less than 10 vol %, and some less than 5 vol %. In addition, as the concentration of carbon dioxide in the processed biogas decreases, the energy density increases. Some embodiments have a concentration of carbon dioxide that is no greater than 20 vol %, some no greater than 15 vol %, some no greater than 10 vol %, and some no greater than 5 vol %.
As a result of the above, the energy density of the processed biogas of the invention is at least 700 BTU/cubic ft (26 MJ/cubic meter) and can be as high as at least 2000 BTU/cubic ft (75 MJ/cubic meter). In some embodiments the energy density is at least 900 BTU/cubic ft (34 MJ/cubic meter); in some at least 1100 BTU/cubic ft (41 MJ/cubic meter); in some at least 1300 BTU/cubic ft (48 MJ/cubic meter); in some at least 1500 BTU/cubic ft (56 MJ/cubic meter); in some at least 1700 BTU/cubic ft (63 MJ/cubic meter); in some at least 1900 BTU/cubic ft (71 MJ/cubic meter); and in some at least 2100 BTU/cubic ft (78 MJ/cubic meter).
The energy density of processed biomass has a somewhat broad distribution of carbon content reflecting the nature of processed organic-carbon-containing feedstock discussed below. The carbon content ranges in a distribution from C1 to C4. This is in contrast to that of biogas made from the sublimation of renewable feedstock that is not organic-carbon-containing feedstock such as, for example, ground up tires that has a narrow distribution of carbon centering on C3-C4.
In some embodiments of the inventions, organic-carbon-containing feedstock used to make the processed biogas of the invention can contain mixtures of more than one renewable feedstock when the processed organic-carbon-containing feedstock is made to have substantially uniform energy densities regardless of the type of organic-carbon-containing feedstock used.
Cellulose bundles, interwoven by hemicellulose and lignin polymer strands, are the stuff that makes plants strong and proficient in retaining moisture. Cellulose has evolved over several billion years to resist being broken down by heat, chemicals, or microbes. In a plant cell wall, the bundles of cellulose molecules in the microfibrils provide the wall with tensile strength. The tensile strength of cellulose microfibrils is as high as 110 kg/mm2, or approximately 2.5 times that of the strongest steel in laboratory conditions. When cellulose is wetted, as in the cell walls, its tensile strength declines rapidly, significantly reducing its ability to provide mechanical support. But in biological systems, the cellulose skeleton is embedded in a matrix of pectin, hemicellulose, and lignin that act as waterproofing and strengthening material. That makes it difficult to produce fuels from renewable cellulose-containing biomass fast enough, cheap enough, or on a large enough scale to make economical sense. As used herein, organic-carbon-containing material means renewable plant-containing material that can be renewed in less than 50 years and includes plant material such as, for example herbaceous materials such as grasses, energy crops, and agricultural plant waste; woody materials such as tree parts, other woody waste, and discarded items made from wood such as broken furniture and railroad ties; and animal material containing undigested plant cells such as animal manure. Organic-carbon-containing material that is used as a feedstock in a process is called an organic-carbon-containing feedstock
Unprocessed organic-carbon-containing material, also referred to as renewable biomass, encompasses a wide array of organic materials as stated above. It is estimated that the U.S. alone generates billions of tons of organic-carbon-containing material annually. As used in this document, beneficiated organic-carbon-containing feedstock is processed organic-carbon-containing feedstock where the moisture content has been reduced, a significant amount of dissolved salts have been removed, and the energy density of the material has been increased. This processed feedstock can be used as input for processes that make several energy-producing products, including, for example, liquid hydrocarbon fuels, solid fuel to supplant coal, and synthetic natural gas.
As everyone in the business of making organic-carbon-containing feedstock is reminded, the energy balance is the metric that matters most. The amount of energy used to beneficiate organic-carbon-containing feedstock and, thus, the cost of that energy must be substantially offset by the overall improvement realized by the beneficiation process in the first place. For example, committing 1000 BTU to improve the heat content of the processed organic-carbon-containing feedstock by 1000 BTU, all other things being equal, does not make economic sense unless the concurrent removal of a significant amount of the water-soluble salt renders previously unusable organic-carbon-containing feedstock usable as a fuel substitute with inherent energy density greater than 7500 BTU/pound for some processes such as boilers.
As used herein, organic-carbon-containing feedstock comprises free water, intercellular water, intracellular water, intracellular water-salts, and at least some plant cells comprising cell walls that include lignin, hemicellulose, and cellulosic microfibrils within fibrils. In some embodiments, the water-soluble salt content of the unprocessed organic-carbon-containing feedstock is at least 4000 mg/kg on a dry basis. In other embodiments the salt content may be more than 1000 mg/kg, 2000 mg/kg, or 3000 mg/kg. The content is largely dependent on handling (e.g. forest products are often transported in salt-rich waterways such as the ocean in intracoastal waterways) or on the soil where the organic-carbon-containing material is grown. Regions that are land rich and more able to allow land use for growing energy crops in commercial quantities often have alkaline soils that result in organic-carbon-containing feedstock with water-soluble salt content of over 4000 mg/kg.
Water-soluble salts are undesirable in processes that use organic-carbon-containing feedstock to create fuels. The salt tends to shorten the operating life of equipment through corrosion, fouling, or slagging when combusted. Some boilers have standards that limit the concentration of salt in fuels to less than 1500 mg/kg and, in some cases, less than 500 mg/kg. This is to find a balance between availability of fuel for the boilers and expense of frequency of cleaning the equipment and replacing parts. If economical, less salt would be preferred. In fact, salt reduction through beneficiation is an enabling technology for the use of salt-laden biomass (e.g. hogged fuels, mesquite, and pinyon-junipers) in boilers. Salt also frequently poisons catalysts and inhibits bacteria or enzyme use in processes used for creating beneficial fuels. While some salt concentration is tolerated, desirably the salt levels should be as low as economically feasible.
The water-soluble salt and various forms of water are located in various regions in plant cells. As used herein, plant cells are composed of cell walls that include microfibril bundles within fibrils and include intracellular water and intracellular water-soluble salt.
Plant cells have a primary cell wall and a secondary cell wall. The secondary cell wall varies in thickness with type of plant and provides most of the strength of plant material.
The plant cells are separated from each other by intercellular water. An aggregate of plant cells are grouped together in plant fibers, each with a wall of cellulose that is wet on its outside with free water also known as surface moisture. The amount of water distributed within a specific organic-carbon-containing feedstock varies with the material. As an example, water is distributed in fresh bagasse from herbaceous plants as follows: about 50 wt % intracellular water, about 30 wt % intercellular water, and about 20 wt % free water. Bagasse is the fibrous matter that remains after sugarcane or sorghum stalks are crushed to extract their juice.
Conventional methods to beneficiate organic-carbon-containing feedstock include thermal processes, mechanical processes, and physiochemical processes. Thermal methods include heat treatments that involve pyrolysis and torrefaction. The thermal methods do not effectively remove entrained salts and only serve to concentrate them. Thus thermal processes are not acceptable for the creation of many energy related products such as organic-carbon-containing feedstock used as a fuel substitute to the likes of coal and petroleum. Additionally, all conventional thermal methods are energy intensive, leading to an unfavorable overall energy balance, and thus economically limiting in the commercial use of organic-carbon-containing feedstock as a renewable source of energy.
The mechanical method, also called pressure extrusion or densification, can be divided into two discrete processes where water and water-soluble salts are forcibly extruded from the organic-carbon-containing material. These two processes are intercellular and intracellular extrusion. The extrusion of intercellular water and intercellular water-soluble salt occurs at a moderate pressure, depending upon the freshness of the organic-carbon-containing material, particle size, initial moisture content, and the variety of organic-carbon-containing material. Appropriately sized particles of freshly cut herbaceous organic-carbon-containing feedstock with moisture content between 50 wt % and 60 wt % will begin extruding intercellular moisture at pressures as low as 1,000 psi and will continue until excessive pressure forces the moisture into the plant cells (essentially becoming intracellular moisture).
As the densification proceeds, higher pressures, and hence higher energy costs, are required to try to extrude intracellular water and intracellular water-soluble salt. However, stiff cell walls provide the biomass material with mechanical strength and are able to withstand high pressures without loss of structural integrity. In addition, the formation of impermeable felts that are more prevalent in weaker cell walled herbaceous material has been observed during compaction of different herbaceous biomass materials above a threshold pressure. This method is energy intensive. In addition, it can only remove up to 50 percent of the water-soluble salts on a dry basis (the intracellular salt remains) and is unable to reduce more than the water content to below 30 wt percent.
The felts are formed when long fibers form a weave and are bound together by very small particles of pith. Pith is a tissue found in plants and is composed of soft, spongy parenchyma cells, which store and transport water-soluble nutrients throughout the plant. Pith particles can hold 50 times their own weight in water. As the compression forces exerted during the compaction force water into the forming felts, the entrained pith particles collect moisture up to their capacity. As a result, the moisture content of any felt can approach 90%. When felts form during compaction, regardless of the forces applied, the overall moisture content of the compacted biomass will be substantially higher than it would have been otherwise had the felt not formed. The felt blocks the exit ports of the compaction device as well as segments perpendicular to the applied force, and the water is blocked from expulsion from the compaction device. The felt also blocks water passing through the plant fibers and plant cells resulting in some water passing back through cell wall pores into some plant cells. In addition, it can only remove up to 50 percent of the water-soluble salts on a dry basis and is unable to reduce more than the water content to below 30 wt percent.
The physiochemical method involves a chemical pretreatment of organic-carbon-containing feedstock and a pressure decompression prior to compaction to substantially improve the quality of densified biomass while also reducing the amount of energy required during compaction to achieve the desired bulk density. Chemically, biomass comprises mostly cellulose, hemicellulose, and lignin located in the secondary cell wall of relevant plant materials. The strands of cellulose and hemicellulose are cross-linked by lignin, forming a lignin-carbohydrate complex (LCC). The LCC produces the hydrophobic barrier to the elimination of intracellular water. In addition to the paper pulping process that solubilizes too much of the organic-carbon-containing material, conventional pre-treatments include acid hydrolysis, steam explosion, AFEX, alkaline wet oxidation, and ozone treatment. All of these processes, if not carefully engineered, can be can be expensive on a cost per product weight basis and are not designed to remove more than 25% water-soluble salt on a dry weight basis.
In addition, the energy density generally obtainable from an organic-carbon-containing material is dependent on its type, i.e., herbaceous, soft woody, and hard woody. Also mixing types in subsequent uses such as fuel for power plants is generally undesirable because the energy density of current processed organic-carbon-containing feedstock varies greatly with type of plant material.
As stated above, plant material can be further subdivided in to three sub classes, herbaceous, soft woody and hard woody, each with particular water retention mechanisms. All plant cells have a primary cell wall and a secondary cell wall. As stated earlier, the strength of the material comes mostly from the secondary cell wall, not the primary one. The secondary cell wall for even soft woody materials is thicker than for herbaceous material.
Herbaceous plants are relatively weak-walled plants, include corn, and have a maximum height of less than about 10 to 15 feet (about 3 to 5 meters (M)). While all plants contain pith particles, herbaceous plants retain most of their moisture through a high concentration of pith particles within the plant cells that hold water like balloons because these plants have relatively weak cell walls. Pressure merely deforms the balloons and does not cause the plant to give up its water. Herbaceous plants have about 50% of their water as intracellular water and have an energy density of unprocessed material at about 5.2 million BTUs per ton (MMBTU/ton) or 6 gigajoules per metric ton (GJ/MT). By comparison, pure carbon in the form of graphite has an energy density of 28 MMBTU/ton (33 GJ/MT) and, bituminous coal has an energy density of about 21 MMBTU/ton (25 GJ/MT)
Soft woody materials are more sturdy plants than herbaceous plants. Soft woody materials include pines and typically have a maximum height of between 50 and 60 feet (about 15 and 18 M). Their plant cells have stiffer walls and thus need less pith particles to retain moisture. Soft woody materials have about 50% of their water as intracellular water and have an energy density of about 13-14 MMBTU/ton (15-16 GJ/MT).
Hard woody materials are the most sturdy of plants, include oak, and typically have a maximum height of between 60 and 90 feet (18 and 27 M). They have cellulosic plant cells with the thickest secondary cell wall and thus need the least amount of pith particles to retain moisture. Hard woody materials have about 50% of their water as intracellular water and have an energy density of about 15 MMBTU/ton (18 GJ/MT).
There is a need in the energy industry for a system and method to allow the energy industry to use organic-carbon-containing material as a commercial alternative or adjunct fuel source. Much of the land available to grow renewable organic-carbon-containing material on a commercial scale also results in organic-carbon-containing material that has a higher than desired content of water-soluble salt that typically is at levels of at least 4000 mg/kg. Forest products in the Pacific Northwest are often transported via intracoastal waterways, exposing the biomass to salt from the ocean. Thus such a system and method must be able to remove sufficient levels of water-soluble salt to provide a suitable fuel substitute. As an example, boilers generally need salt contents of less than 1500 mg/kg to avoid costly maintenance related to high salt in the fuel. In addition, the energy and resulting cost to remove sufficient water to achieve an acceptable energy density must be low enough to make the organic-carbon-containing material feedstock a suitable alternative in processes to make coal or hydrocarbon fuel substitutes.
There is also a need for a process that can handle the various types of plants and arrive at processed organic-carbon-containing feedstock with similar energy densities.
The invention disclosed does allow the energy industry to use processed organic-carbon-containing material as a commercial alternative fuel source. Some embodiments of the invention remove almost all of the chemical contamination, man-made or natural, and lower the total water content to levels in the range of 5 wt % to 15 wt %. This allows the industries, such as the electric utility industry to blend the organic-carbon-containing feedstock on a ratio of up to 50 wt % processed organic-carbon-containing feedstock to 50 wt % coal with a substantial reduction in the amount of water-soluble salt and enjoy the same MMBTU/ton (GJ/MT) efficiency as coal at coal competitive prices. Literature has described organic-carbon-containing feedstock to coal ratios of up to 30%. A recent patent application publication, EP2580307 A2, has described a ratio of up to 50% by mechanical compaction under heat, but there was no explicit reduction in water-soluble salt content in the organic-carbon-containing feedstock. The invention disclosed herein explicitly comprises substantial water-soluble salt reduction through a reaction chamber with conditions tailored to each specific unprocessed organic-carbon-containing feedstock used. As discussed below, additional purposed rinse subsections and subsequent pressing algorithms in the compaction section of the Reaction Chamber may be beneficial to process organic-carbon-containing feedstock that has a particularly high content of water-soluble salt so that it may be used in a blend with coal that otherwise would be unavailable for burning in a coal boiler. This also includes, for example, hog fuel, mesquite, and Eastern red cedar.
In addition, the invention disclosed does permit different types of organic-carbon-containing feedstock to be processed, each at tailored conditions, to result in processed outputs having preselected energy densities. In some embodiments of the invention, more than one type of feedstock with different energy densities that range from 5.2 to 14 MMBTU/ton (6 to 16 GJ/MT) may be fed into the reaction chamber in series or through different reaction chambers in parallel. Because each type of organic-carbon-containing feedstock is processed under preselected tailored conditions, the resulting processed organic-carbon-containing feedstock for some embodiments of the system of the invention can have a substantially similar energy density. In some embodiments, the energy density is about 17 MMBTU/ton (20 GJ/MT). In others it is about 18, 19, or 20 MMBTU/ton (21, 22, or 23 GJ/MT). This offers a tremendous advantage for down-stream processes to be able to work with processed organic-carbon-containing feedstock having similar energy density regardless of the type used as well as substantially reduced water-soluble content.
The process of the invention uses a beneficiation sub-system to create the processed organic-carbon-containing feedstock that is a clean economical material to be used for creating a satisfactory coal substitute solid fuel from renewable biomass and a microwave subsystem for converting the processed organic-carbon-containing feedstock into the solid fuel char of the invention. The first subsystem will now be discussed.
The Beneficiation sub-system is used to make processed organic-carbon-containing feedstock comprises at least three elements, a transmission device, at least one reaction chamber, and a collection device. As used in this document, the beneficiation sub-system refers to the system that is used to convert unprocessed organic-carbon-containing feedstock into processed organic-carbon-containing feedstock.
The first element, the transmission device, is configured to convey into a reaction chamber unprocessed organic-carbon-containing feedstock comprising free water, intercellular water, intracellular water, intracellular water-soluble salt, and at least some plant cells comprising cell walls that include lignin, hemicellulose, and cellulosic microfibrils within fibrils. The transmission device may be any that is suitable to convey solid unprocessed organic-carbon-containing feedstock into the reaction chamber to obtain a consistent residence time of the feedstock in the reaction chamber. The transmission devices include such devices at augers that are well known in the chemical industry.
Particle size of the unprocessed organic-carbon-containing feedstock should be sufficiently small to permit a satisfactorily energy balance as the unprocessed organic-carbon-containing feedstock is passed through the system to create processed organic-carbon-containing feedstock. In some embodiments, the unprocessed organic-carbon-containing feedstock arrives at some nominal size. Herbaceous material such as, for example, energy crops and agricultural waste, should have a particle size where the longest dimension is less than 1 inch (2.5 cm). Preferably, most wood and wood waste that is freshly cut should have a longest length of less than 0.5 inches (1.3 cm). Preferably, old wood waste, especially resinous types of wood such as, for example pine, has a particle size with a longest dimension of less than 0.25 inches (about 0.6 cm) to obtain the optimum economic outcome, where throughput and energy/chemical consumption are weighed together.
Some embodiments of the system may also include a mastication chamber before the reaction chamber. This mastication chamber is configured to reduce particle size of the organic-carbon-containing feedstock to less than 1 inch (2.5 cm) as the longest dimension. This allows the organic-carbon-containing feedstock to arrive with particle sized having a longest dimension larger than 1 inch (2.5 cm).
Some embodiments of the system may also include a pretreatment chamber to remove contaminants that hinder creation of the passageways for intracellular water and water-soluble salts to pass from the cellulosic-fibril bundles. The chamber is configured to use for each organic-carbon-containing feedstock a particular set of conditions including time duration, temperature profile, and chemical content of pretreatment solution to at least initiate the dissolution of contaminates. The contaminants include resins, rosins, glue, and creosote. The solid slurry, including any incipient felts, may be collected for use as binders in the processed organic-carbon-containing feedstock that is the primary end product. Separate oils may be collected as a stand-alone product such as, for example, cedar oil.
The second element, the reaction chamber, includes at least one entrance passageway, at least one exit passageway, and at least three sections, a wet fibril disruption section, a vapor explosion section, and a compaction section. The first section, the wet fibril disruption section, is configured to break loose at least some of the lignin and hemicellulose between the cellulosic microfibrils in the fibril bundle to make at least some regions of cell wall more penetrable. This is accomplished by at least one of several means. The organic-carbon-containing feedstock is mixed with appropriate chemicals to permeate the plant fibrils and disrupt the lignin, hemicellulose, and LCC barriers. Additionally, the chemical treatment may also unbundle a portion of the cellulose fibrils and/or microfibrils, de-crystallizing and/or de-polymerizing it. Preferably, the chemicals are tailored for the specific organic-carbon-containing feedstock. In some embodiments, the chemical treatment comprises an aqueous solution containing a miscible volatile gas. The miscible gas may include one or more of ammonia, bicarbonate/carbonate, or oxygen. Some embodiments may include aqueous solutions of methanol, ammonium carbonate, or carbonic acid. The use of methanol, for example, may be desirable for organic-carbon-containing feedstock having a higher woody content to dissolve resins contained in the woody organic-carbon-containing feedstock to allow beneficiation chemicals better contact with the fibrils. After a predetermined residence time of mixing, the organic-carbon-containing feedstock may be steam driven, or conveyer by another means such as a piston, into the next section of the reaction chamber. In some embodiments, process conditions should be chosen to not dissolve more than 25 wt % of the lignin or hemicellulose as these are important contributors to the energy density of the processed organic-carbon-containing feedstock. Some embodiments of the system, depending on the specific organic-carbon-containing feedstock used, may have temperatures of at least 135° C., at least 165° C., or at least 180° C.; pressures of at least 260 psig, at least 280 psig, at least 375 psig, or at least 640 psig; and residence times of at least 15 minutes (min), 20 min, or 30 min.
The second section, the vapor explosion section, is in communication with the wet fibril disruption section. It at least is configured to volatilize plant fibril permeable fluid through rapid decompression to penetrate the more susceptible regions of the cell wall so as to create a porous organic-carbon-containing feedstock with cellulosic passageways for intracellular water and water-soluble salts to pass from the cellulosic-fibril bundles. The organic-carbon-containing feedstock is isolated, heated, pressurized with a volatile fluid comprising steam. The applied volatile chemicals and steam penetrate into the plant fibrils within the vapor explosion section due to the high temperature and pressure. After a predetermined residence time dictated by the specific organic-carbon-containing feedstock used, pressure is released rapidly from the reaction chamber by opening a fast-opening valve into an expansion chamber that may be designed to retain the gases, separate them, and reuse at least some of them in the process for increased energy/chemical efficiency. Some embodiments may have no expansion chamber where retention of gasses is not desired. Some embodiments of the system, depending on the specific organic-carbon-containing feedstock used, may have a specific pressure drop in psig of at least 230, at least 250, at least 345, or at least 600; and explosive durations of less than 500 milliseconds (ms), less than 300 ms, less than 200 ms, less than 100 ms, or less than 50 ms.
Some embodiments may include gas inlets into the wet fibril disruption section of the reaction chamber to deliver compressed air or other compressed gas such as, for example, oxygen. After delivery to the desired pressure, the inlet port would be closed and the heating for the reaction would proceed. Note that this could allow for at least one of three things: First, an increase in total pressure would make subsequent explosion more powerful. Second, an increase in oxygen content would increase the oxidation potential of the processed organic-carbon-containing feedstock where desirable. Third, a provision would be provided for mixing of organic-carbon-containing feedstock, water, and potentially other chemicals such as, for example, organic solvents, through bubbling action of gas through a perforated pipe at bottom of reaction chamber.
The net effect on the organic-carbon-containing feedstock of passing through the wet fibril disruption section and the vapor explosion section is the disruption of fibril cell walls both physically through pressure bursts and chemically through selective and minimal fibril cellulosic delinking, cellulose depolymerization and/or cellulose decrystallization. Chemical effects, such as hydrolysis of the cellulose, lignin, and hemicellulose also can occur. The resulting organic-carbon-containing feedstock particles exhibit an increase in the size and number of micropores in their fibrils and cell walls, and thus an increased surface area. The now porous organic-carbon-containing feedstock is expelled from the vapor explosion section into the next section.
The third section, the compaction section is in communication with the vapor explosion section. The compression section at least is configured to compress the porous organic-carbon-containing feedstock between pressure plates configured to minimize formation of felt that would close the reaction chamber exit passageway made to permit escape of intracellular and intercellular water, and intracellular and intercellular soluble salts. In this section, the principle process conditions for each organic-carbon-containing feedstock is the presence or absence of a raised pattern on the pressure plate, the starting water content, the processed water content, and final water content. The compaction section of the system of the invention requires a raised patterned surface on the pressure plates for feedstock comprising herbaceous plant material feedstock. However, the section may or may not require the raised pattern surface for processing soft woody or hard woody plant material feedstock depending on the specific material used and its freshness from harvest. Some embodiments of the system, depending on the specific organic-carbon-containing feedstock used, may have a starting water contents ranging from 70 to 80 wt %, from 45 to 55 wt % or from 40 to 50 wt %; and processed water content of from 4 to 15 wt % depending on actual targets desired.
The third element, the collection device, is in communication with the reaction chamber. The collection chamber at least is configured to separate non-fuel components from fuel components and to create a processed organic-carbon-containing feedstock. This feedstock has a water content of less than 20 wt % and a water-soluble salt content that is decreased by at least 60% on a dry basis. Some embodiments have the water content less than 20 wt % after allowing for surface moisture to air dry. Some embodiments have a processed organic-carbon-containing feedstock that has a water content of less than 15 wt %. Other embodiments have processed organic-carbon-containing feedstock that has a water content of less than 12 wt %, less than 10 wt %, less than 8 wt %, or less than 5 wt %. Some embodiments have a water-soluble salt content that is decreased by at least 65% on a dry basis. Other embodiments have a water-soluble salt content that is decreased by at least 70% on a dry basis, 75% on a dry basis, at least 80% on a dry basis, at least 85% on a dry basis, at least 90% on a dry basis, or at least 95% on a dry basis.
Some embodiments of the system may further include at least one rinsing subsection. This subsection is configured to flush at least some of the water-soluble salt from the porous organic-carbon-containing feedstock before it is passed to the compaction section. In some embodiments where the salt content is particularly high, such as brine-soaked hog fuel (wood chips, shavings, or residue from sawmills or grinding machine used to create it and also known as “hammer hogs”), the system is configured to have more than one rinsing subsection followed by another compaction section. The separated water, complete with dissolved water soluble salts, may be collected and treated for release into the surrounding environment or even reused in the field that is used to grow the renewable organic-carbon-containing feedstock. The salts in this water are likely to include constituents purposefully added to the crops such as fertilizer and pesticides.
The beneficiation sub-system of the invention can better be understood through depiction of several figures.
As stated above, the pressure plates in the compaction section are configured to minimize felt formation. Felt is an agglomeration of interwoven fibers that interweave to form an impermeable barrier that stops water and water-soluble salts entrained in that water from passing through the exit ports of the compaction section. Additionally, any pith particles that survived the beneficiation process in the first two sections of reaction chamber can be entrained in the felt to absorb water, thereby preventing expulsion of the water during pressing. Therefore, felt formation traps a significant fraction of the water and salts from being extruded from the interior of biomass being compressed.
Some embodiments achieve the processed organic-carbon-containing feedstock water content and water-soluble salt reduction over unprocessed organic-carbon-containing feedstock with a cost that is less than 60% that of the cost per weight of processed organic-carbon-containing feedstock from known mechanical, known physiochemical, or known thermal processes. In these embodiments, the reaction chamber is configured to operate at conditions tailored for each unprocessed organic-carbon-containing feedstock and the system is further engineered to re-capture and reuse heat to minimize the energy consumed to lead to a particular set of processed organic-carbon-containing feedstock properties. The reaction chamber sections are further configured as follows. The wet fibril disruption section is further configured to use fibril disruption conditions tailored for each organic-carbon-containing feedstock and that comprise at least a solvent medium, time duration, temperature profile, and pressure profile for each organic-carbon-containing feedstock. The second section, the vapor explosion section, is configured to use explosion conditions tailored for each organic-carbon-containing feedstock and that comprise at least pressure drop, temperature profile, and explosion duration to form volatile plant fibril permeable fluid explosions within the plant cells. The third section, the compaction section, is configured to use compaction conditions tailored for each organic-carbon-containing feedstock and pressure, pressure plate configuration, residence time, and pressure versus time profile.
The importance of tailoring process conditions to each organic-carbon-containing feedstock is illustrated by the following discussion on the viscoelastic/viscoplastic properties of plant fibrils. Besides the differences among plants in their cell wall configuration, depending on whether they are herbaceous, soft woody or hard woody, plants demonstrate to a varying degree some interesting physical properties. Organic-carbon-containing material demonstrates both elastic and plastic properties, with a degree that depends on both the specific variety of plant and its condition such as, for example, whether it is fresh or old. The physics that governs the elastic/plastic relationship of viscoelastic/viscoplastic materials is quite complex. Unlike purely elastic substances, a viscoelastic substance has an elastic component and a viscous component. Similarly, a viscoplastic material has a plastic component and a viscous component. The speed of pressing a viscoelastic substance gives the substance a strain rate dependence on the time until the material's elastic limit is reached. Once the elastic limit is exceeded, the fibrils in the material begin to suffer plastic, i.e., Permanent, deformation.
An example of how the compaction cycle is optimized for one organic-carbon-containing feedstock to minimize energy consumption to achieve targeted product values follows. Through experimentation, a balance is made between energy consumed and energy density achieved.
In a similar manner, energy consumption can be optimized during the wet fibril disruption and the vapor explosion parts of the system. Chemical pretreatment prior to compaction will further improve the quality of the product and also reduce the net energy consumption. For comparison purposes, the pressure applied to achieve a bulk density multiplier of “10” in
Multiple reaction chambers may be used in parallel to simulate a continuous process.
The oxygen-deficient thermal sub-system is used to convert the processed organic-carbon-containing feedstock from the beneficiation sub-system into the clean porous processed biochar of the invention. In its broadest understanding, the oxygen-deficient thermal sub-system comprises a reaction chamber configured to heat processed organic-carbon-containing feedstock in an atmosphere that contains less than 5 percent oxygen to a temperature sufficient to convert at least some processed organic-carbon-containing feedstock into processed biogas and processed biochar. In some embodiments, the atmosphere contains less than 4 percent oxygen, in some less than 3 percent oxygen, and in some less than 2 percent oxygen. The sub-system further comprises at least two aspects that are suitable for the invention—a conventional pyrolysis oxygen-deficient thermal system, and a sublimation oxygen-deficient thermal sub-system.
The common pyrolysis oxygen-deficient thermal sub-system produces biochar, liquids, and gases from biomass by heating the biomass in a low/no oxygen environment. The absence of oxygen prevents combustion. The relative yield of products from pyrolysis varies with temperature. Temperatures of 400-500° C. (752-932° F.) produce more char, while temperatures above 700° C. (1,292° F.) favor the yield of liquid and gas fuel components. Pyrolysis occurs more quickly at the higher temperatures, typically requiring seconds instead of hours. Typical yields are 60% bio-oil (from condensable gases), 20% biochar, and 20% non-condensable gases. In the presence of limited stoichiometric oxygen concentration, high temperature pyrolysis is also known as gasification, and produces primarily syngas. By comparison, slow pyrolysis can produce some biogas, on the order of about 20%. The main benefit from the invention is that the resulting processed biogas made with processed organic-carbon-containing feedstock has a biogas content that is at least 30 vol %; in some embodiments at least 40 vol %; in some at least 50 vol %.
Another oxygen-deficient thermal sub-system is sublimation oxygen-deficient thermal sub-system. Unlike the pyrolysis sub-system, the feedstock in the sublimation sub-system does not pass through a liquid phase and the products are only fuel gases and processed biochar.
The following description relates to approaches for processing organic-carbon-containing feedstock into processed biogas fuel and a processed biochar fuel by a sublimation sub-system. The processed biogas fuel is primarily methane but also may include ethane, propane, and butane depending on the nature of the organic-carbon-containing feedstock and the residence times employed during the sublimation process. Processed biochar fuel is the solid carbon-based residue that is unable to be converted into processed biogas fuel. Alternatively, system conditions may be adjusted to preferentially create more than the minimum processed biochar or more than the minimum processed biogas.
The sublimation sub-system is a high temperature sub-system configured to convert a solid renewable biomass to processed biogas and processed biochar cleanly without passing through a liquid state, a passage that can result in many side reactions discussed above under gasification. The key to sublimation is to expose the solid to a high temperature in the absence of free water and in a substantially oxygen free atmosphere. Under sublimation, the methane groups and higher carbon groups such as ethane, propane, and butane, rejoin after being deconstructed from a carbon chain in the feedstock without breaking down to carbon dioxide and water. The key to achieving even higher energy densities and lower concentrations of carbon dioxide and carbon monoxide in the processed biogas is through use of unprocessed organic-carbon-containing feedstock being processed in the beneficiation sub-system,
As a result, the processed biogas of the invention has an energy density of at least 700 BTU/cubic ft (26 MJ/cubic meter), a carbon monoxide concentration of less than 20 vol %, and a carbon dioxide concentration of less than 15 vol %. This is significantly better than the biogas made with unprocessed organic-carbon-dioxide feedstock in the sublimation sub-process—an energy density of less than 600 BTU/cubic ft (22 MJ/cubic meter), a carbon monoxide concentration of at least 40 vol %, and a carbon dioxide concentration of at least 20 vol %. For processed biogas, in some embodiments, the energy density may exceed that of natural gas as the processed biogas is constructed to have increased concentrations of ethane, propane, and butane; materials that have a higher energy density than methane.
The sublimation system can be further illustrated by a horizontal sublimation system and a vertical sublimation system. Other orientation s may be contemplated.
The horizontal sublimation oxygen-deficient thermal sub-system comprises four elements. The first is a hot box configured to be able to (1) heat from an ambient temperature to an operating sublimation temperature, (2) maintain an initial operating sublimation temperature and a final operating sublimation temperature that are stable within less than ±10° C., and (3) cool from operating sublimation temperatures to an ambient temperature. All without leaking any oxygen into the hot box and having at least one heat source in communication with the interior of the hot box to supply heat as needed. The second element is at least one substantially horizontal reaction chamber largely located within the hot box and having a surface. The reaction chamber is configured to heat the processed organic-carbon-containing feedstock without external catalyst or additional water to an operating sublimation temperature in a time frame that is short enough to sublime at least part of the processed organic-carbon-containing feedstock without creating substantially any liquid. The reaction chamber is also configured to heat from an ambient temperature to an operating sublimation temperature, operate at a sublimation temperature, and cool from an operating sublimation temperature to an ambient temperature without leaking any product gas fuel into the surrounding hot box, and comprising an input end outside the hot box. The reaction chamber is further configured to receive compressed feedstock through an input line and an output end outside the hot box and configured to discharge product gas fuel gas through a discharge line and solid char fuel through an output line. The third element is a first powered transport mechanism that is located within the reaction chamber and is configured to convey sublimation products of the processed organic-carbon-containing feedstock through the reaction chamber as the processed organic-carbon-containing feedstock is transformed into processed biogas and processed biochar. The fourth element is a gas-tight element on both the input line and output line and configured to prevent hot processed biogas from adversely escaping from the reaction chamber.
The overall process will now be discussed for using a substantially horizontal sublimator to efficiently convert processed carbon-containing feedstock to product biogas fuel and solid processed biochar fuel. The process will be discussed briefly for an embodiment that needs processed organic-carbon-containing feedstock preparation, drying and compression, and uses an apparatus with two reaction chambers and burners to deliver sublimation heat. In some embodiments, the beneficiation sub-system is attached directly to horizontal sublimation oxygen-deficient thermal sub-system and the processed organic-carbon-containing feedstock needs little if any preparation, drying, and compression. In some embodiments, the desired properties of the processed organic-carbon-containing feedstock are such that at least some additional preparation, drying and or compression are desirable. Briefly, the sublimation sub-system of this embodiment of the invention is configured to be able to perform a preparation step, a drying step, a compression step, a sublimation step, and a separation step. Processed organic-carbon-containing feedstock preparation will be dictated by the physical characteristics of the processed organic-carbon-containing feedstock being considered for processing/conversion such as its water content and physical characteristics such as size and thickness. Size reduction of carbon-containing feedstock will enhance the compressibility of the processed organic-carbon-containing feedstock to allow for maximum throughput in the reaction chamber. In some embodiments, sizes are of a volume that is less than the equivalent of a cube about 2 cm (about 0.75 in) on a side with a length in any one direction of no more than about 5 cm (about 2 in).
After the processed organic-carbon-containing feedstock is properly prepared, it will then pass through a gas-tight element on an input line into a substantially horizontal drying chamber with an internal auger and be treated with recycled heat from the downstream process to drive off as much free water as possible. Reducing the free water content will increase the heat absorption by the processed organic-carbon-containing feedstock and reduce the amount of oxygen present by the water inside the sublimation reaction chamber and the finished product biogas fuel and processed biochar. Reducing the free water and the oxygen will result in less carbon dioxide and carbon monoxide in the processed biogas fuel. Less carbon dioxide and carbon monoxide byproduct is desirable because it increases the energy content of the processed biogas.
After the drying chamber, the processed organic-carbon-containing feedstock will pass into a compression chamber containing a compression screw that is designed to compress the carbon-containing feedstock to the desired density. This compression further decreases any free water remaining. It also removes entrained air in the processed organic-carbon-containing feedstock that also will minimize the oxygen present in the sublimation reaction chamber. This dewatered, de-aired, and densified carbon-containing feedstock will enter the reaction chamber.
The compression chamber develops a feedstock plug at its exit that enters the reaction chamber. This plug acts as a partial barrier or seal so a minimal amount of gases produced in the reaction chamber backflow and escape. The gas-tight element on the input line prevents the rest of the gases from escaping the system.
In the embodiment being discussed, the sublimation sub-system has a physical plant that is a three dimensional, rectangular box with an internal substantially horizontal reaction chamber running along the top, a drop passage, and then a second substantially horizontal reaction chamber in the reverse direction of the top reaction chamber. Each reaction chamber contains its own auger for transporting the feedstock, is continuous, and is completely sealed against the escape of any hot product gas fuel.
In this embodiment, burners are external to the heating box but attached to it and will heat the space between the inside wall of the heating box and the outside walls of the reaction chamber configuration so that there will be no intermingling of the heated transfer air heating the external surface of the reaction chamber and the contents of the processed organic-carbon-containing feedstock in the reaction chamber undergoing sublimation. All the internal surfaces of the heating box are lined with high thermal insulating material so as to minimize heat loss and minimize the internal reactor air space.
After the compression screw, the processed organic-carbon-containing feedstock plug now enters the reaction chamber. The reaction chamber containing an auger inside of it that may be inside of a tube vented to a head space above the tube but within the reaction chamber for aggregation of the gases that are generated. The auger propels and rotates the processed organic-carbon-containing feedstock so that it is evenly exposed to the sidewalls of the tube or reaction chamber for efficient heat exchange and to ‘turn over’ the feedstock for even heating. The reaction chamber is heated from the outside surface of the reaction chamber so the transfer heats the air and any combustion products from the burners do not get intermingled with the processed organic-carbon-containing feedstock and/or product gas fuel or processed biogas. The reaction chamber is constructed to prevent the leaking out of any hot gases.
The processed organic-carbon-containing feedstock is then augured down the length of the reaction chamber. At the end of the reaction chamber, the carbon-containing feedstock drops down into a second augured reaction chamber that is of the same design as the first reactor tube. The configuration of the three chambers, including the connecting passage, looks like a U rotated 90 degrees to the left.
The processed organic-carbon-containing feedstock has now been reduced to devolatilized carbon and volatile gases. The volatile gases are passing and mixing with the hot carbon surfaces and reacting with it to form a hot product gas fuel. The residence time in both of the reaction chambers allows the volatile gases created during the sublimation to deconstruct down to a structure approaching that of methane and move down the reaction chambers.
At the end of the second reactor chamber are two outlets. One outlet is for the devolatized carbon to pass through a gas-tight mechanism and be collected as solid biochar fuel and the second outlet is for the product processed biogas to be captured. The product gas exits the reaction chamber, is filtered and the final product processed biogas product fuel is then stored.
More specifically, the apparatus aspect of the invention comprises a system that includes a hot box, at least one reaction chamber, a first powered transport mechanism, and gas-tight elements. The hot box is configured to be able to heat from an ambient temperature to an operating sublimation temperature, maintain an initial operating sublimation temperature and a final operating sublimation temperature that are stable within less than ±10° C., and cool from operating sublimation temperatures to an ambient temperature without leaking any oxygen into the hot box and having at least one heat source in communication with the interior of the hot box to supply heat as needed.
The temperature needed to sublime processed organic-carbon-containing feedstock depends on the individual feedstock. If an operating temperature is too low, a liquid forms during the phase change from solid to gas with accompanying adverse reactions discussed above and associated with gasification processes. If the temperature is too high, energy is wasted in an already endothermic reaction. Operating sublimation temperatures are typically between 600° C. and 850° C. More common low density processed organic-carbon-containing feedstock have operating sublimation temperatures between 650° C. and 750° C.
For the above reasons, the operating temperature in the reaction chamber should be reasonably stable during operation of the apparatus. In some embodiments where the reaction chamber has a shorter length and the flowrate of the processed organic-carbon-containing feedstock is smaller, the operating temperature may be substantially constant within less than ±10° C. In other embodiments having a longer residence time and a larger processed organic-carbon-containing feedstock throughput, the reaction chamber may not be constant but rather forms a profile through the reaction chamber drops from the beginning to the end. In these embodiments, for energy efficiency reasons, the individual temperatures of the temperature profile through the reaction chamber should be stable during operation within less than ±10° C.
The heat source must be able to heat the inside of the hot box to a stable operating sublimation temperature and maintain that temperature during the operation of the apparatus. Heat sources may include any that can provide sufficient heat and include, for example, infrared sources, laser sources and combustion sources. Embodiments that use combustion sources have the additional advantage in that they can be fueled by some of the product biogas fuel such that they require no additional energy from external sources. Such embodiments may be self-sufficient during operation with as little as 10 percent of the product gas fuel that is created in the apparatus. Some embodiments may be self-sufficient with as little as 7 percent and some with as little as 5 percent. This is due to the high-energy content of the product gas fuel and the variable amounts of energy needed to process different feedstock.
The at least one reaction chamber is substantially horizontal, located largely within the hot box, has a surface, and is configured to heat the processed organic-carbon-containing feedstock without external catalyst or additional water to an operating sublimation temperature in a time frame that is short enough to sublime at least part of the processed organic-carbon-containing feedstock without creating substantially any liquid. Also, it is configured to heat from an ambient temperature to an operating sublimation temperature, operate at a sublimation temperature, and cool from an operating sublimation temperature to an ambient temperature without leaking any product processed biogas fuel into the surrounding hot box. Further, it comprises an input end outside the hot box and configured to receive compressed feedstock through an input line and an output end outside the hot box and configured to discharge product processed biogas fuel through a pressure-isolation element and processed biochar fuel through an output line.
Sublimation is a reaction that strips smaller gaseous hydrocarbons from an organic-carbon-based feedstock and more particularly in the case of the invention from a processed organic-carbon-based feedstock. In the invention, the gas collects as a processed biogas fuel as it interacts with processed biochar fuel residue. Thus, there is no need for expensive external catalysts and subsequent elaborate reforming operations to create the processed biogas fuel. In addition, the sublimation of the invention is conducted in the presence of minimal oxygen since any oxygen reacts to cause non-fuel reaction products such as carbon dioxide. Thus it is desirable to not use superheated steam in contact with the processed organic-carbon-containing feedstock to achieve operating sublimation temperature. Some oxygen that is interstitially locked in the cells may be in the processed organic-carbon-containing feedstock. Also, some oxygen may enter the reaction chamber because of potentially incomplete drying when that drying step is desirable. Both of these sources of potential oxygen sources should be mitigated by the beneficiation pre-processing: cell walls broken exposing interstitial water and oxygen to expulsion and also a good pre-drying process. Thus, these sources of oxygen comprise a small portion and contribute to less than 5 percent of the gaseous product and often less than 3 percent or 2 percent depending on the particular processed organic-carbon-containing feedstock used.
To avoid passing through the liquid phase, the solid surface of the processed organic-carbon-containing feedstock should reach the sublimation temperature immediately. In some embodiments, this is within 1 millisecond. In some embodiments, the time is within less than 0.1 millisecond. In still others it is within less than 0.01 millisecond.
Some embodiments have a single reaction chamber. These are constructed to withstand the temperature changes associated with passing from ambient to operating sublimation temperatures during start up operation and the reverse during shutdown operations. Features may include thicker walls and/or the use of supporting elements such as gussets where the conversion part of the reaction is in communication with the side of the hot box.
The first powered transport mechanism is located within the reaction chamber and is configured to convey sublimation products of the processed organic-carbon-containing feedstock through the reaction chamber as the processed organic-carbon-containing feedstock is transformed into product gas fuel and solid char fuel. Some embodiments have a reaction chamber that comprises a tube containing the first powered transport mechanism. The reaction chamber also has a head-space in communication with the tube for the collection of product processed biogas fuel as it is created. The first powered transport mechanism is configured to advance the solid portions of the processed organic-carbon-containing feedstock, particularly the low-density forms of the processed organic-carbon-containing feedstock. It is also configured to assist intermixing with the heat of the surface of the reaction chamber to assist in maintaining a stable operating sublimation temperature in contact with the solid parts of the feedstock as product processed biogas fuel continues to be removed from the solid parts of the feedstock. The first transport mechanism is one that is able to effectively operate at a sublimation temperature and not be adversely impaired by thermal expansion and contraction during the starting up and cooling down phases of operation. One example of an effective first transport mechanism is in an augur.
The gas-tight element is on both the input line and output line and configured to prevent hot product fuel processed biogas from adversely escaping from the reaction chamber. Leaks that permit product processed biogas fuel to exit the reaction chamber in an unregulated manner can cause a serious safety concern. Combustible product processed biogas fuel in the presence of hot surfaces can cause fires and explosions. Examples of gas-tight elements effective for this purpose at the temperatures discussed are a rotary valve, a rotary vacuum valve, and actuated double-gate valve. Alternatively, a more expensive configuration may include a box surrounding the sublimation sub-system inputs and outputs with purge nitrogen under a positive pressure in the box to keep any escaping gas from becoming hazardous.
The operating pressure in the reaction chamber may be protected from adverse instability from the product processed biogas fuel leaving in its discharge line by passing the product gas fuel through a pressure isolation element. This helps maintain the stable sublimation conditions within the reaction chamber. Pressure isolation elements include, for example, bubblers and cyclones to maintain pressure in the reaction chamber. Alternatively, the pressure in the reaction chamber may be controlled through the product processed biogas fuel being discharged into gas tight holding tanks.
Some embodiments of the system have at least two substantially horizontal reaction chambers that are in communication with each other in series, and the first powered transport mechanism has a part of a shaft that extends outside each reaction chamber and the hot box. Embodiments with more than one reaction chamber in series provide systems able to process higher amounts of carbon-containing feedstock with similar footprints to that of some systems having a single reaction chamber. These embodiments further comprise an adjustable sealing element located outside the hot box at the region of the hot box surrounding a collar about the extended part of the first powered transport mechanism. The adjustable sealing element is configured to prevent the adverse entry from outside the hot box of external oxygen entering the hot box during changing temperatures of startup and shutdown operations, and during steady-state sublimation operation. Leaks that permit oxygen to enter the hot box from the outside or product gas fuel to enter from the reaction chamber can cause undesirably large fluctuations in the operating sublimation temperature. They represent an additional and uncontrolled source of heat when they combust.
Each sealing element comprises an adjustable plate and an adjustable seal to permit satisfactory exclusion of additional undesirable oxygen leaking into the hot box or reaction chamber through undesirable leaks created during thermal expansion and contraction of elements of the system during startup and shutdown operations. The adjustable plate comprises a substantially vertical plate that is adjustably attached to the hot box and configured to vertically move the collar about the extended part of the shaft of the first powered transport mechanism to prevent adverse contact between collar and the shaft. The adjustable seal is in communication with the adjusting plate, located about the extended portion of the shaft of the first powered transport mechanism and comprises a cone and rope configuration designed to maintain a gas-tight seal about the shaft of the first powered transport mechanism as it extends from the hot box.
The residence time in the reaction chamber varies with the nature of the processed organic-carbon-containing feedstock and the quantity being processed. Typically, between at least 50 percent by weight and over 90 percent by weight of processed organic-carbon-containing feedstock can be converted into product gas fuel with the remainder being solid char fuel having an energy density similar to coal. Longer residence times allow more methane units to reassociate from the disassociated gas and may result in a higher conversion to product gas fuel approaching over 70 weight percent to over 90 weight percent. Residence times may range from less than 10 minutes in some embodiments to less than 5 minutes in some embodiments to less than 2 minutes in some embodiments. Excessively long residence times have no adverse effect on the conversion once the theoretical conversion is substantially achieved.
In some embodiments the reactor chambers further comprise manifolds attached to the outside of the reaction chambers within the hot box. The reaction chamber surface and the manifold are configured to allow dissociated gas to pass between the reaction chamber and the manifold to increase the time the disassociated gas is exposed to sublimation temperatures. In some cases, this additional time may result in dissociating gases that have longer carbon-carbon structured chains such as, for example, ethane, propane, and butane, to further disassociate into methane.
Some embodiments of the system of the invention further comprise a vertical support within the hot box and further beneath the substantially horizontal reaction chamber to support its weight during startup, shutdown, and operating conditions where thick reaction chamber walls and support elements such as gussets are not desirable or not feasible to provide adequate support. Generally, the vertical support is configured to be dimensionally stable to within about 2.5 cm (about one inch) in the vertical direction over temperature variations between ambient temperature and about 850° C. that may occur during the startup, operation, and shutdown of the substantially horizontal reaction chamber.
Vertical dimensional stability is achieved by the use of insulation in combination with the use of cooling material flowing through the support in addition to the use of insulation. The cooling material is that commonly associated with cooling and includes, for example, water; refrigerants such as halogenated gas, carbon tetrachloride, chlorofluorocarbons, hydrochlorofluorocarbons, ammonia, carbon dioxide, ethane, propane, ether, and dimethylether; gaseous coolants such as air, hydrogen, inert gases, and sulfur hexafluoride; liquid coolants such as water, ethylene glycol, diethylene glycol, propylene glycol, and Freon® by DuPont; and solid coolants such as dry ice.
Cooling materials may pass through or around a vertical support in any manner that maintains the desired vertical dimensional stability. When the vertical support is not cooled, thermal expansions may result in vertical expansions of several inches. This is enough to cause welds in the supported reaction chamber to break and leak product gas fuel into the hot box or out into the environment. As discussed above, this can cause a safety issue and can adversely destabilize the operating temperature profile in the reaction chamber. Some embodiments may have the cooling material pass horizontally along the vertical support walls near the hot reaction chamber that is being supported. Some embodiments may have cooling material flow vertically up into the shaft of the vertical support. Other configurations are also possible as long as they limit vertical thermal expansion sufficiently to not cause leaks in welds in the reaction chamber.
Some embodiments of the system may further comprise a preparation chamber that is outside the hot box. This is useful when carbon-containing feedstock is not supplied in a dried and compressed manner. The preparation chamber is in communication with the substantially horizontal reaction chamber, is configured to remove some free water and oxygen from the processed organic-carbon-containing feedstock, and is configured to compress the processed organic-carbon-containing feedstock into a plug before it enters the substantially horizontal reaction chamber.
The preparation chamber also comprises a second powered transport mechanism that is located partly within the preparation chamber and has a part that extends outside the preparation chamber. The preparation chamber is configured to perform one or more of moving the processed organic-carbon-containing feedstock through the preparation chamber and compressing the processed organic-carbon-containing feedstock within the preparation chamber as it is dried of more free water.
Heat may be supplied internally for the drying function. In some embodiments, the heat used to dry the processed organic-carbon-containing feedstock comes from the combustion gasses in the hot box. In some embodiments, the heat may come from at least one of the hot product gas fuel and the solid char fuel through heat conveyance devices such as, for example, heat exchangers.
In some embodiments, the preparation chamber may be subdivided into a drying chamber and a compression chamber where additional drying may occur. The compression chamber may be equipped with its own second powered transport mechanism. The drying chamber may be equipped with its own third powered transport mechanism. In this embodiment, the drying chamber or pre-preparation chamber is in communication with the compression chamber or preparation chamber and is configured to reduce the particle size of low density processed organic-carbon-containing feedstock to a size and remove the bulk of initial water and trapped air to permit the processed organic-carbon-containing feedstock to be more easily conveyed through the preparation chamber of the system, more easily compressed there without entraining oxygen or water, and more easily heated there to a sublimation temperature without permitting the formation of a liquid phase. In this embodiment, a third powered transport mechanism that precedes and is in communication with the pre-preparation chamber, has a part that extends outside the pre-preparation chamber. The mechanism is configured to perform one or more of moving the processed organic-carbon-containing feedstock through the pre-preparation chamber and compressing the processed organic-carbon-containing feedstock within the pre-preparation chamber in more manageable sized particles.
In both cases, the individual transport mechanisms are to advance processed organic-carbon-containing feedstock forward into a condition for sublimation. One example of a transport mechanism is an augur but others are suitable if they accomplish the desired function.
The system of the invention may further comprise various units to prepare the processed organic-carbon-containing feedstock into a condition to be used by the system of the invention. Various feedstock must have their size reduced as discussed above to dimensions that can be dried, compressed, and sublimated in a timely manner. By way of illustration, tires must be reduced to tire crumbs and straws or stalks must be reduced to shapes that are more readily conveyed through the preparation chamber of the system, more easily compressed there without entraining oxygen or water, and more easily heated there to a sublimation temperature without permitting the formation of a liquid phase. Units may include, for example, devices that grind, chop, slice, or cut.
The high temperature adjustable seal and plate that is shown in
The high temperature vertical support stand that is shown in
Another embodiment of the invention involves a process for converting a carbon-containing compound to product gas fuel and solid char fuel. The process comprises at least four steps. The first step is inputting processed organic-carbon-containing feedstock into a substantially horizontal sublimating reaction chamber largely contained within a hot box and configured to be able to heat from an ambient temperature to an operating sublimation temperature, operate at a sublimation temperature, and cool from an operating sublimation temperature to an ambient temperature without leaking any hot product gas fuel from the reaction chamber into the hot box or atmosphere, or leaking any oxygen from outside the hot box into the hot box. The second step is heating processed organic-carbon-containing feedstock to a sublimating temperature before it is able to form a liquid phase. The third step is maintaining the temperature at a sublimation temperature for a residence time that is as long a time as needed to convert the carbon-containing feedstock to product gas fuel and solid char fuel. The fourth step is separating the product gas fuel from the solid char fuel.
Heat generated by the process may be used in various ways. Some embodiments may use direct heated combustion gases from the hot box to a pre-preparation chamber to dry the processed organic-carbon-containing feedstock before it enters a preparation chamber for compression, if needed, and a sublimation chamber. Some embodiments may use the heat for other purposes such as heating buildings.
Heat used to sublimate the feedstock may be supplied by combusting part of the product fuel gas. Sublimation temperatures can be maintained with a small fraction of the product gas fuel being used as fuel for burners as discussed above.
The vertical sublimation oxygen-deficient thermal sub-system comprises three elements, a vertical reaction chamber, a first powered transport mechanism, and a self-adjusting seal. The first, at least one substantially vertical reaction chamber, is configured to heat the processed organic-carbon-containing feedstock without external catalyst or additional water, carbon dioxide, or carbon monoxide, to an operating sublimation temperature in a time frame that is short enough to sublime at least part of the processed organic-carbon-containing feedstock without creating substantially any liquid. The second, the first powered transport mechanism, is located partly within the reaction chamber, has an extended part that extends outside the reaction chamber, and is configured to convey sublimation products of the processed organic-carbon-containing feedstock through the reaction chamber as the processed organic-carbon-containing feedstock is transformed into processed biogas and processed biochar. The third, the self-adjusting seal, is configured to continuously contain the processed biogas within the reaction chamber at the region surrounding the extended part of the powered transport mechanism during changing temperatures of startup and shutdown operations, and during steady-state sublimation temperature during operation.
To better understand this sub-system, the vertical sublimation sub-system will be discussed with reference at times to a particular embodiment or embodiments. However, it is understood that other embodiments may be used as long as they perform the sublimation desired.
The vertical sublimation oxygen-deficient thermal sub-system is designed for processing high-density feedstock. High density means that the feedstock has a high weight per unit volume. Feedstock preparation will be dictated by characteristics of the processed organic-carbon-containing feedstock such as size or thickness, and density of the processed organic-carbon-containing feedstock from the beneficiation sub-system. In general the desirable size or thickness is on the order of less than 0.5 inch (13 mm) in the longest dimension of the particle. The particle size is important in the vertical sub-system because denser materials take more time to heat thoroughly from the particle surface to its internal midpoint. Volatile gases are formed at the midpoint or center of the particle and have to travel to the surface of the particle where they are released into the reaction chamber environment. The sublimed gas should be created as quickly as possible and stay in the gas phase at all times for best conversion of the processed organic-carbon-containing feedstock into processed biogas and processed biochar. A high-density feedstock allows the particles to fall through the reaction chamber and reach the bottom where they are eventually separated in to the gas and solid forms. At times, the processed organic-carbon-containing feedstock may have to be further compressed to achieve desired density and further manipulated to achieve desired particles sizes.
After the processed organic-carbon-containing feedstock is properly prepared, it is conveyer to the top of the vertical sub-system by such as, for example, an auger or some other material conveying device. During the transportation of the feedstock, heat may be recycled from downstream processes to maximize removal of any free water. Then the feedstock is deposited into a hopper of a compression auger. The compression auger reduces the free water and entrained air content. This will increase the heat absorption by the feedstock and reduce the amount of oxygen present. Reducing the oxygen content that comes from the water and air will result in less carbon dioxide and carbon monoxide in the produced biogas and less contaminants in the processed biochar. A feedstock plug or seal is created at the end of the compression screw at the entrance point to the reaction chamber. Thus, when the feedstock enters the reaction chamber, the processed biogas that is created does not travel back and escape to create a hazardous situation.
As the feedstock enters the reaction chamber, the feedstock is immediately subjected to a stream of superheated gas that sublimes the volatiles from the feedstock. As the volatilized gas and the devolatized feedstock, now reduced to carbon, falls the length of the reaction chamber tube, the volatilized gas and the carbon solid intermingle, react, and gain momentum. At the bottom of the shared common reaction chamber tube, the devolatilized carbon drops down into a collection hopper and the gas stream is split into two streams that move laterally over and up two reaction chamber tubes on either side of the common down tube. The reaction chamber looks like two of the letters “O” that are connected in the middle. The two up tubes of the reaction chamber now carry the hot gas upward and assisted by a turbine fan. Two-thirds of the way up each of the two up-tubes is a super-heater that raises the temperature of the gas. It is more economical to super heat just the gas than to heat the incoming feedstock. The super heated gas is now reaching the top of the up reaction chamber tubes and is directed from the top of each up tube, laterally, over to the top of the shared common down tube where the entrance of the feedstock is located. The super heated gas then is used to sublime the incoming feedstock and everything repeats itself in the down tube in a closed loop cycle. When the tubes in the reaction chamber are in equilibrium and balanced, the processed biogas is pulled through an outlet at the top of one of the upward reaction tubes, cooled, and stored as processed biogas. The carbon exits the bottom of the common middle tube and is transported by auger, cooled, and collected for storage as processed biochar.
The reaction chamber in the sub-system is a three dimensional, rectangular box with the longest side perpendicular to the ground. On the topside is a compression screw and feedstock entrance port. On the bottom side is a collection cone with an exit auger at the bottom of the cone for produced biochar.
Inside the reaction chamber heater box are three connected and continuous tubes with the middle tube shared between the two outside tubes such that the three tubes act as one tube. The middle tube acts as a down draft while the two outside tubes act as updrafts. In this configuration, the feedstock inters at the top of the middle tube and free falls as the feedstock traverses the length of the tube. This is where the sublimation of the feedstock occurs. There is a junction at the bottom of the middle tube where the tube makes two lateral splits. At the end of each lateral split, a tube continues up on both sides of the middle tube. Thus, all three reaction chamber tubes are continuous and sealed so that the reaction chamber remains isolated from outside contaminants and only contains the feedstock that is to be processed. No external air, steam, or catalyst is introduced.
On the outside of the reaction chamber, but connected to it, are two burners that heat the space between the inside of the outside box wall and the outside of the inside wall of the internal tube configuration. This space is heavily insulated and keeps the reaction chamber environment at a minimum temperature.
In operation, the sublimated feedstock at the bottom of the middle downdraft tube of the reaction chamber has separated into a devolatilized carbon and processed biogas. The stream of processed biogas splits and travels laterally to the outside updraft reaction chamber tubes. The devolatilized carbon settles into the collection cone and is removed by an auger. The devolatilized carbon is still in the heated reaction chamber environment so this acts as a polishing step to make sure all of the volatile gases that can be created will be captured and continue in the subliming process through the reaction chamber updraft tubes. After some residence time, the carbon can be passed through an auger into a cooling chamber and then stored as processed biochar. Residence time depends on the nature and volume of the processed organic-carbon-containing feedstock. Shorter residence times yield longer chain hydrocarbon gases and a processed biogas with a higher energy density. In some embodiments, the residence time is less than 10 minutes, in some less than 7 minutes, in some less than 5 minutes, in some less than 3 minutes, and in some less than 2 minutes.
At the split at the bottom of the middle downdraft tube the carbon drops out and only the processed biogas continues to travel laterally to the outside updraft tubes of the reaction chamber. The product processed biogas travels up the updraft tubes carried by their own inertia from traversing the downdraft tube with some optional assistance by a turbine fan placed at the top of the updraft tubes. Attached on the outside wall of both updraft tubes but still inside of the external wall of the reaction chamber box is laced one super heater on each outside tube. During startup, as the processed biogas traverses the updraft tube back to the top of the top part of the reaction chamber tubes, it passes through the super heaters and the temperature in the reaction chamber is increased to a preselected temperature that is the desired equilibrium temperature. It is more economical to super heat just the processed biogas than the input processed organic-carbon-containing feedstock. The superheating assists in the further dissociation of the processed biogas when it comes in contact with the devolatilized carbon in the downdraft tube.
As the two superheated processed biogas streams reach the top of the two outside tubes, they are comingled with the fresh incoming feedstock as it enters the middle downdraft tube and sublime that feedstock. The cycle of the fresh feedstock coming into the reaction chamber, the fresh feedstock mixing with the superheated processed biogas and the mixture entering the reaction chamber tubes completes the reaction processing cycle. When the reaction reaches equilibrium and balance, more feedstock is added and both processed biochar and processed biogas is removed according to predetermined production rates.
The invention also comprises a process for making processed biogas. The process includes two aspects of the beneficiation process for making processed carbon-containing feedstock with the beneficiation sub-system discussed above and three aspects of the oxygen-deficient thermal process for converting the processed carbon-containing feedstock into processed biogas. Specifically, the process is one of making a gaseous fuel with three steps. The first is to input into a system, comprising a first sub-system and a second sub-system, an unprocessed organic-carbon-containing feedstock that includes free water, intercellular water, intracellular water, intracellular water-soluble salts, and at least some plant cells comprising cell walls that include lignin, hemicellulose, and microfibrils within fibrils. The second step is to pass the unprocessed organic-carbon-containing feedstock through the first sub-system, a beneficiation sub-system, to make processed organic-carbon-containing feedstock. The third step is to pass the processed organic-carbon-containing feedstock through an oxygen-deficient thermal sub-system to convert the processed organic-carbon-containing feedstock into the gaseous processed biogas fuel.
The beneficiation process step comprises the step of passing unprocessed organic-carbon-containing feedstock through a beneficiation sub-system process to result in processed organic-carbon-containing feedstock having a water content of less than 20 wt % and a salt content that is reduced by at least 60 wt % on a dry basis from that of the unprocessed organic-carbon-containing feedstock. There are two aspects of the beneficiation sub-system process. The first focuses on the properties of the processed organic-carbon-containing feedstock and the second focuses on the energy efficiency of the process of the invention over that of currently known processes for converting unprocessed organic-carbon-containing feedstock into processed organic-carbon-containing feedstock suitable for use with downstream fuel producing systems. Both use the beneficiation sub-system disclosed above.
The first aspect of the beneficiation process step of the invention comprises four steps. The first step is inputting into a reaction chamber unprocessed organic-carbon-containing feedstock comprising free water, intercellular water, intracellular water, intracellular water-soluble salts, and at least some plant cells comprising cell walls that include lignin, hemicellulose, and microfibrils within fibrils. Some embodiments have unprocessed organic-carbon-containing feedstock that comprises water-soluble salts having a content of at least 4000 mg/kg on a dry basis.
The second step is exposing the feedstock to hot solvent under pressure for a time at conditions specific to the feedstock to make at least some regions of the cell walls comprising crystallized cellulosic fibrils, lignin, and hemicellulose more able to be penetratable by water-soluble salts without dissolving more than 25 percent of the lignin and hemicellulose. As mentioned above, this is accomplished by one or more of unbundling regions of at least some fibrils, depolymerizing at least some strands of lignin and/or hemicellulose, or detaching them from the cellulose fibrils, thereby disrupting their interweaving of the fibrils. In addition, the cellulose fibrils and microfibrils can be partially depolymerized and/or decrystallized.
The third step is rapidly removing the elevated pressure so as to penetrate the more penetrable regions with intracellular escaping gases to create porous feedstock with open pores in at least some plant cell walls. In some embodiments the pressure is removed to about atmospheric pressure in less than 500 milliseconds (ms), less than 300 ms, less than 200 ms, less than 100 ms, or less than 50 ms.
The fourth step is pressing the porous feedstock with conditions that include an adjustable compaction pressure versus time profile and compaction time duration, and between pressure plates configured to prevent felt from forming and blocking escape from the reaction chamber of intracellular and intercellular water and intracellular water-soluble salts, and to create processed organic-carbon-containing feedstock that has a water content of less than 20 wt % and a water-soluble salt content that is decreased by at least 60% on a dry basis that of the unprocessed organic-carbon-containing feedstock. In some embodiments, the water content is measured after subsequent air-drying to remove remaining surface water. In some embodiments, the pressure plate has a pattern that is adapted to particular organic-carbon-containing feedstock based on its predilection to form felts and pith content as discussed above. In some embodiments, the pressure amount and pressure plate configuration is chosen to meet targeted processed organic-carbon-containing feedstock goals for particular unprocessed organic-carbon-containing feedstock. In some embodiments, the pressure is applied in steps of increasing pressure, with time increments of various lengths depending on biomass input to allow the fibers to relax and more water-soluble salt to be squeezed out in a more energy efficient manner. In some embodiments, clean water is reintroduced into the biomass as a rinse and to solubilize the water-soluble slats before the fourth step begins.
The process may further comprise a fifth step, prewashing the unprocessed organic-carbon-containing feedstock before it enters the reaction chamber with a particular set of conditions for each organic-carbon-containing feedstock that includes time duration, temperature profile, and chemical content of pretreatment solution to at least initiate the dissolution of contaminates that hinder creation of the cell wall passageways for intracellular water and intracellular water-soluble salts to pass outward from the interior of the plant cells.
The process may further comprise a sixth step, masticating. The unprocessed organic-carbon-containing feedstock is masticated into particles having a longest dimension of less than 1 inch (2.5 centimeters) before it enters the reaction chamber.
The process may further comprise a seventh step, separating out the contaminants. This step involves the separating out of at least oils, waxes, and volatile organic compounds from the porous feedstock with solvents less polar than water.
As with the system aspect, the unprocessed organic-carbon-containing feedstock may comprise at least two from a group consisting of an herbaceous plant material, a soft woody plant material, and a hard woody plant material that are processed in series or in separate parallel reaction chambers. In addition, in some embodiments, the energy density of each plant material in the processed organic-carbon-containing feedstock may be substantially the same. In some embodiments, the organic-carbon-containing feedstock comprises at least two from the group consisting of an herbaceous plant material, a soft woody plant material, and a hard woody plant material, and wherein the energy density of each plant material in the processed organic-carbon-containing feedstock is at least 17 MMBTU/ton (20 GJ/MT).
The second aspect is similar to the first except steps have an efficiency feature and the resulting processed organic-carbon-containing feedstock has a cost feature. The second aspect also comprises four steps. The first step is inputting into a reaction chamber organic-carbon-containing feedstock comprising free water, intercellular water, intracellular water, intracellular water-salts, and at least some plant cells comprising lignin, hemicellulose, and fibrils within fibril bundles. Each step emphasizes more specific conditions aimed at energy and material conservation. The second step is exposing the feedstock to hot solvent under pressure for a time at conditions specific to the feedstock to swell and unbundle the cellular chambers comprising partially crystallized cellulosic fibril bundles, lignin, hemicellulose, and water-soluble salts without dissolving more than 25 percent of the lignin and to decrystallize at least some of the cellulosic bundles. The third step is removing the pressure to create porous feedstock with open pores in its cellulosic chambers. After possibly mixing with fresh water to rinse the material and solubilize the water-salts, the fourth step is pressing the porous feedstock with an adjustable compaction pressure versus time profile and compaction duration between pressure plates configured to prevent felt from forming and blocking escape from the reaction chamber of intracellular and intercellular water and intracellular water-soluble salts, and to create a processed organic-carbon-containing feedstock that has a water content of less than 20 wt %, a water-soluble salt content that is decreased by at least 60 wt % on a dry basis, and a cost per weight of removing the water and the water-soluble salt is reduced to less than 60% of the cost per weight of similar water removal from known mechanical, known physiochemical, or known thermal processes.
Energy efficiencies are achieved in part by tailoring process conditions to specific organic-carbon-containing feedstock as discussed above. Some embodiments use systems engineered to re-capture and reuse heat to further reduce the cost per ton of the processed organic-carbon-containing feedstock. Some embodiments remove surface or free water left from the processing of the organic-carbon-containing feedstock with air drying, a process that takes time but has no additional energy cost.
The oxygen-deficient thermal sub-system process step comprises passing the processed organic-carbon-containing feedstock through an oxygen-deficient sub-system process to result in a processed biogas fuel composition having an energy density of at least 700 BTU/cubic ft (26 MJ/cubic meter), a carbon monoxide concentration of less than 20 vol %, and a carbon dioxide concentration of less than 15 vol %.
In the broadest perspective the process comprises three steps. The first step is to input into a system, comprising a first and a second subsystem, an unprocessed organic-carbon-containing feedstock that includes free water, intercellular water, intracellular water, intracellular water-soluble salts, and at least some plant cells comprising cell walls that include lignin, hemicellulose, and microfibrils within fibrils. The second step is to pass the unprocessed organic-carbon-containing feedstock through the first sub-system, a beneficiation sub-system process, to result in processed organic-carbon-containing feedstock having a water content of less than 20 wt % and a salt content that is reduced by at least 60 wt % on a dry basis from that of the unprocessed organic-carbon-containing feedstock. The third step is to pass the processed organic-carbon-containing feedstock through the second sub-system, an oxygen-deficient thermal sub-system process, to result in a processed biogas composition having an energy density of at least 700 BTU/cubic ft (26 MJ/cubic meter), a carbon monoxide concentration of less than 20 vol %, and a carbon dioxide concentration of less than 15 vol %.
The process that uses the horizontal oxygen-deficient thermal sub-system involves four steps. The first step is to input processed organic-carbon-containing feedstock into a substantially horizontal sublimating reaction chamber largely contained within a hot box. The reaction chamber is configured to be able to (1) heat from an ambient temperature to an operating sublimation temperature, (2) operate at a sublimation temperature, and (3) cool from an operating sublimation temperature to an ambient temperature. This is done without leaking any hot product gas fuel from the reaction chamber into the hot box or atmosphere, or leaking any oxygen from outside the hot box into the hot box. The second step is to heat the processed organic-carbon-containing feedstock to a sublimating temperature before it is able to form a liquid phase. The third step is to maintain the temperature at a sublimation temperature for a residence time that is as long a time as needed to convert the processed organic-carbon-containing feedstock to processed biogas and processed biochar. The fourth step is to separate the processed biogas from the processed biochar.
These steps are depicted in
In some embodiments the process may use a horizontal sublimation sub-system, depending on its size, wherein the substantially horizontal sublimating reaction chamber is supported by a vertical support. It is beneath the substantially horizontal reaction chamber. It is also configures to be dimensionally stable in the vertical direction over temperature variations of from ambient temperature to about 850° C. that may occur during the startup, operating, and shutdown operations of the substantially horizontal reaction chamber.
The process that uses the vertical oxygen-deficient thermal sub-system involves four steps. This is depicted in
Various modifications and additions can be made to the preferred embodiments discussed hereinabove without departing from the scope of the present invention. Accordingly, the scope of the present invention should not be limited by the particular embodiments described above, but should be defined only by the claims set forth below and equivalents thereof.
| Number | Date | Country | |
|---|---|---|---|
| 61867952 | Aug 2013 | US | |
| 61971329 | Mar 2014 | US | |
| 61974876 | Apr 2014 | US |
