Patent Application
20120116135
None.
The present invention relates generally to the conversion of biomass to fuel range hydrocarbons.
Due to governmental legislation as mandated in the Renewable Fuels Standards (RFS), the use of renewable energy sources is becoming increasingly necessary to reduce emissions of carbon based fuels and provide alternatives to petroleum based energy and feedstock. One of the alternatives being explored is the use of biomass. Biomass is any carbon containing material derived from living or formerly living organisms, such as wood, wood waste, crops, crop waste, waste, and animal waste.
Pyrolysis is the chemical decomposition of organic materials by heating in the absence of oxygen or other reagents. Pyrolysis can be used to convert biomass (such as lignocellulosic biomass) into pyrolysis oil or so-called bio-oil. The bio-oils obtained by pyrolysis of biomass or waste have received attention recently as an alternative source of fuel.
Generally, the pyrolysis of biomass produces four primary products, namely water, “bio-oil,” also known as “pyrolysis oil,” char, and various gases (H2, CO, CO2, CH4, and other light organic compounds) that do not condense, except under extreme conditions. For exemplary purposes, the pyrolysis decomposition products of wood from white spruce and poplar trees are shown in Table 1.
Fast pyrolysis is one method for the conversion of biomass to bio-oil. Fast pyrolysis is the rapid thermal decomposition of organic compounds in the absence of atmospheric or added oxygen to produce liquids, char, and gas.
Fast pyrolysis affords operation at atmospheric pressure, moderate temperatures, and with low or no water usage. Pyrolysis oil yields typically range from 50-75% mass of input biomass and are heavily feedstock dependent.
The major advantage of these fuels is that they are CO2 neutral and contain a very low fraction of bonded sulfur and nitrogen. Thus, they contribute very little to the emission of greenhouse gases or other regulated air pollutants.
There has been a considerable effort in the past to develop pyrolysis processes for the conversion of biomass and waste to liquids for the express purpose of producing renewable liquid fuels suitable for use in boilers, gas turbines and diesel engines.
However, pyrolysis oil obtained from a biomass fast pyrolysis process is a chemically-complex mixture of compounds including water, light volatiles, and non-volatiles. Such oil is in general of relatively low quality and has a number of negative properties such as high acidity (which can lead to corrosion problems), substantial water content (usually in the range of 15% to 30%), variable viscosity, low heating values (about half that of diesel fuel), low cetane number, etc. These negative properties are related to the oxygenated compounds contained in bio-oils. The oxygen content of pyrolysis oil is approximately 45 wt %. In general, pyrolysis oil has a total acid number (TAN) value of approximately 100. The desired TAN value for transportation fuel is less than 10.
There has been a considerable effort in the past to address the high TAN problem in pyrolysis oils by post treatment or upgrading them before they are used as a fuel. Most of these treatment methods involve the removal of oxygen. Particular attention has been focused on hydrotreating using conventional petroleum catalysts, such as cobalt-molybdenum or nickel-molybdenum on alumina, to produce essentially oxygen-free naphthas. Since pyrolysis liquids typically contain between 30 to 50 wt % of oxygen, complete removal of oxygen requires a substantial consumption of hydrogen which represents a major and sometimes prohibitive cost.
Therefore, developing a new and energy saving method or process for improving quality of pyrolysis oil would be a significant contribution to the art.
This invention discloses a heat integrated and energy saving process for producing high quality pyrolysis oil from biomass by utilizing a torrefaction pretreatment step for biomass pyrolysis processing wherein the pretreatment step improves the quality of the pyrolysis oil by reducing acidity. This invention further utilizes the gaseous product of the torrefaction step through a combustion process for heat production and recovery.
In one embodiment of the current invention, there is disclosed a process for producing a pyrolysis oil product from a biomass feedstock comprising at least the following steps: a) a step of subjecting a biomass feedstock to thermal treatment in a reactor A under a torrefaction reaction condition to produce a mixture product comprising a solid product and a gaseous product; b) a step of subjecting the solid product produced from step a) in a reactor B under a pyrolysis reaction condition to produce a product comprising pyrolysis oil product; c) a step of subjecting the gaseous product produced from step a) in a reactor C under a combustion reaction condition to produce a product comprising CO2, H2O and heat; and d) a step of recovering and feeding the heat produced from step c) to heat an object selected from a group consisting of the biomass feedstock, the solid product from step a), the gaseous product from step a), the pyrolysis products, the reactor A, the reactor B, and any combination thereof.
A more complete understanding of the present invention and benefit thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings in which:
Embodiments of the invention disclose a heat integrated and energy saving process for producing high quality pyrolysis oil from biomass. This invention utilizes a torrefaction pretreatment step for biomass pyrolysis process wherein the pretreatment step improves the quality of the pyrolysis oil by reducing acidity. This invention further utilizes the gaseous product of the torrefaction step through a combustion process for heat production and recovery.
As used herein, the term “biomass” includes any renewable source (living or formerly living), but does not include oil, natural gas, and/or petroleum. Biomass thus includes but is not limited to wood, paper, crops, animal and plant fats, biological waste, algae, and the mixture thereof.
According to one embodiment of the invention, there is disclosed a step of subjecting a biomass feedstock to a thermal treatment in a reactor A under a torrefaction reaction condition to produce a product comprising a solid product and a gaseous product.
According to one embodiment of the invention, the torrefaction process consists of a slow heating of the biomass feedstock in an inert atmosphere to produce a solid product that has lower hemicellulose content, higher energy density, much lower moisture content (<3 wt %), and lower resistance to fracture (higher brittleness) in comparison with the initial biomass material. In addition to the solid product, the torrefaction of the biomass also produces gaseous product which may comprise CO2, CO, H2O, H2, C1/C2/C3 hydrocarbons, acetic acid, formic acid and other light organic compounds.
Any standard torrefaction reactor can be used to torrefy the biomass feedstock. Exemplary reactor configurations include without limitations auger reactors, ablative reactors, rotating cones, fluidized-bed reactors (e.g. circulating fluidized bed reactors), entrained-flow reactors, vacuum moving-bed reactors, transported-bed reactors, and fixed-bed reactors.
Any standard torrefaction reaction condition can be used to torrefy the biomass feedstock in the torrefaction reactor. One skilled in the art can readily select a combination of temperature, pressure, and residence time that produces a torrefied product. In some embodiments, the torrefaction reaction condition includes a temperature ranging from 180 to 350° C. with a residence time ranging from 1 minute to 24 hours. In some other embodiments, the torrefaction reaction condition includes a temperature ranging from 220 to 280° C. with a residence time ranging from 5 to 20 minutes.
A variety of pressures can be used for torrefaction, such as atmospheric pressure or ranging as high as 500 psi. Torrefaction typically operates in pressures ranging from vacuum pressures of −3 psi to above atmospheric pressure of 15 psi.
In one embodiment of the invention, torrefaction is carried out in the presence of a catalyst material selected from a group consisting of solid acid catalysts such as ZSM-5, solid base catalysts such Hydrotalcite, silica catalysts such as Diatomite, silica-alumina catalysts such as Kaolin, Group B metal oxide catalysts such as Ammonium Molybdate, pyrolytic char and any combination thereof.
In one embodiment of the invention, the torrefaction reaction is carried out in the absence of diatomic oxygen in an inert gas atmosphere such as nitrogen, argon, steam, carbon oxides, etc. In another embodiment of the invention, the torrefaction reaction is carried out in a reducing gas atmosphere (e.g., a gas atmosphere comprises carbon monoxide). Also, torrefaction may be carried out with other reactants such as hydrogen, ammonia, etc.
The torrefied biomass according to various embodiments of the invention may be added to a pyrolysis reactor for further processing. In another embodiment of the invention, the torrefied biomass is pyrolyzed in a pyrolysis reactor under a pyrolysis reaction condition to form a pyrolysis oil product.
Pyrolysis, which is the thermal decomposition of a substance into its elemental components and/or smaller molecules, is used in various methods developed for producing hydrocarbons, including but not limited to hydrocarbon fuels, from biomass. Pyrolysis requires moderate temperatures, generally greater than 325° C., such that the feed material is sufficiently decomposed to produce products which may be used as hydrocarbon building blocks.
Embodiments of the inventive process use any standard pyrolysis reactor providing sufficient heat to pyrolyze torrefied biomass feedstock, including without limitation, auger reactors, ablative reactors, a bubbling fluidized bed reactor, circulating fluidized bed, transport reactors, rotating cone pyrolyzers, vacuum pyrolyzers, and the like.
Any standard pyrolysis reaction condition can be used to pyrolyze the torrefied biomass feedstock in a pyrolysis reactor. One skilled in the art can readily select a combination of temperature, pressure, and residence time that produces a pyrolyzed product. In some embodiments, the pyrolysis reaction condition includes a temperature ranging from 375 to 700° C. with a residence time ranging from 0.01 to 200 seconds. In some other embodiments, the pyrolysis reaction condition includes a temperature ranging from 425 to 525° C. with a residence time ranging from 0.5 to 2 seconds.
A variety of pressures can be used for pyrolysis such as atmospheric pressure or greater. In some embodiments, the pyrolytic pressure ranges from vacuum conditions to 1000 psi. In other embodiments, the reaction pressure during pyrolysis can range from typical atmospheric pressure up to 300 psi.
In some embodiments, the pyrolysis reaction is carried out in the presence of a catalyst material selected from a group consisting of solid acid catalysts such as ZSM-5, solid base catalysts such Hydrotalcite, silica catalysts such as Diatomite, silica-alumina catalysts such as Kaolin, Group B metal oxide catalysts such as Ammonium Molybdate, pyrolytic char and any combination thereof.
According to various embodiments of the invention, the gaseous product from the torrefaction reactor may be sent to a combustion reactor for further processing. In some embodiments, the gaseous product is combusted in the combustion reactor under a combustion reaction condition to form a product comprising CO2 and heat.
Any standard combustion reaction condition can be used to combust the gaseous product from the torrefaction step in a combustion reactor. One skilled in the art can readily select a combination of temperature, pressure, and residence time that produces a combustion product. In some embodiments, the combustion reaction condition includes a temperature ranging from 100 to 3000° C. In some other embodiments, the combustion reaction condition includes a temperature ranging from 400 to 1200° C.
Combustion is the burning reaction of fuel reactants with oxygen for the production of heat and light. In one embodiment, the produced gases from torrefaction are reacted with diatomic oxygen or oxygen containing air for the purpose of heat utilization during torrefaction and/or pyrolysis. Composition of the gas includes, but is not limited to, H2, CO, CO2, H2O, CH4, C2H2, C2H4, C2H6, C3H8, acetic acid, formic acid and other light organic compounds. Other gases that may also be present include O2, N2, and Ar as well as others.
Embodiments of the inventive process use any standard combustion reactor to combust the gaseous product from the torrefaction step, including without limitation, furnaces, combustion fluid beds, combustion fixed beds, gas turbines, kilns, gas burners, boilers, and others.
A variety of pressures can be used for combustion such as atmospheric pressure or greater. In some embodiments, the combustion pressure ranges from near atmospheric conditions to 300 psi. In other embodiments, the reaction pressure during combustion is near atmospheric pressure.
In one embodiment, the yield of gaseous product from torrefaction step is 0.1-70 wt % of raw biomass. The gaseous product comprises CO2, CO, H2O, H2, C1/C2/C3 hydrocarbons, acetic acid, formic acid and other light organic compounds. In one embodiment, the concentration of the CO2 in the gaseous product ranges from 0 to 85 vol %, while the concentration of the CO in the gaseous product is in the range of 0 to 40 vol %. The concentration of H2O in the gaseous product is in the range of 0 to 95 vol %. The total amount of H2, C1/C2/C3 hydrocarbons, acetic acid, formic acid and other light organic compounds is in the range of 0 to 70 vol %. In a different embodiment, the concentration of the CO2 in the gaseous product ranges from 5 to 50 vol %, while the concentration of the CO in the gaseous product is in the range of 0-30 vol %. The concentration of H2O in the gaseous product is in the range of 30-80 vol %. The total amount of H2, C1/C2/C3 hydrocarbons, acetic acid, formic acid and other light organic compounds is normally below 50 vol %.
The gaseous product of torrefaction can not be directly released to the atmosphere mainly due to the high concentration of CO and organic compounds in the stream. One embodiment of the current invention converts (via e.g. combustion) CO and organic compounds into CO2 which can then be directly released to the atmosphere without violating environmental regulations (e.g., CO emission specification). Depending on local emission regulations, some extra treatment might need to be placed downstream of the combustion reactor.
Since the reactions of torrefaction and pyrolysis are endothermic, to maintain normal operation and desired product quality, heat must be supplied constantly to these two reactions. According to one embodiment of the invention, the heat produced from torrefaction gaseous product combustion may be utilized for the torrefaction and/or pyrolysis reactions. The produced gas can initially be combusted in a combustion reactor providing heat for torrefaction and/or pyrolysis reactions through a heat carrier, such as solid catalyst, sand, steam, and flue gas. For example, the produced torrefaction gaseous products can be combusted in a fluidized bed or fast transport bed containing solid catalyst or other solid particles. The heated catalyst or solid particles can then be used to provide heat for the endothermic torrefaction and/or pyrolysis reactions. According to one embodiment of the invention, the heat from combustion of torrefaction gaseous products can be utilized to pre-heat the feedstocks of the torrefaction and/or pyrolysis reactors, or to directly heat the reactors in order to maintain reaction temperature. The heat produced from combustion of torrefaction gaseous products can also be recovered to generate some products, such as process steam and electricity. These process steam and electricity products not only may be used to provide heat for the torrefaction and/or pyrolysis processes, but also may be utilized for other processes.
According to one embodiment of the invention, the torrefaction and/or pyrolysis process described above is carried out in the presence of a carrier gas stream, including but not limited N2, He, CO2, and Ar, and the heat from combustion of torrefaction gaseous products can be utilized to pre-heat the biomass feedstocks, the carrier gas stream, or the reactors directly in order to maintain reaction temperature.
The final pyrolysis oil product obtained according to some embodiments of the present invention has a TAN number between 80 and 200. The pyrolysis oil product obtained according to some other embodiments of the present invention has a TAN number between less than 20 and 50.
The following examples of certain embodiments of the invention are given. Each example is provided by way of explanation of the invention, one of many embodiments of the invention, and the following examples should not be read to limit, or define, the scope of the invention.
The comparison study of the process of torrefaction prior to pyrolysis has been performed in a micropyrolysis unit. The reactions were carried out at torrefaction temperatures ranging from 179 to 321° C. and pyrolysis temperatures ranging from 379 to 521° C. with no catalyst loading. In addition, a wide variety of biomass was tested including red oak, switchgrass, miscanthus, and corn stover pellets. Comparative pyrolysis tests were run without the torrefaction pretreatment at the same pyrolysis temperatures.
The experimental results indicating the reduction of acetic acid in the pyrolysis product due to torrefaction are shown as follows:
1Mass of acetic acid over mass of biomass
2Acetic acid peak area over total peak area by GC/MS
3Torrefaction - pyrolysis acetic acid level relative to pyrolysis acetic acid level
The result above shows that the acetic acid concentration in pyrolysis oil products was reduced by 18 to 39% with this pretreatment, compared to that from un-torrefied biomass. The resulting pyrolysis oil would have a similar reduction in TAN (total acid number) value as ˜80% of the TAN is due to acetic acid in pyrolysis oils.
As illustrated in
As discussed above, the pyrolysis oil obtained from biomass fast pyrolysis process is of relatively low quality. In general, pyrolysis oil has TAN value of approximately 100. The desired TAN value for transportation fuel is less than 10.
The results above show that using torrefied biomass as a pretreated feed for pyrolysis helps reduce TAN (total acid number) of the pyrolysis oil product. The pretreatment by torrefaction according to the current invention helps to significantly reduce the TAN value of the pyrolysis oil product by 25%. This is mainly attributed to the release of acetic acid in the torrefaction step.
The step of torrefaction and a heat generation and recovery step may be easily integrated with the pyrolysis step. The biomass pretreatment by torrefaction improves the biomass feed quality of pyrolysis step and therefore resulting in higher quality of pyrolysis oil product including low TAN value. The heat generation and recovery step convert the gaseous product from the torrefaction step into heat which can be recovered and utilized for torrefaction and/or pyrolysis. The heat produced as described can also be recovered to produce process steam and electricity. Therefore, this heat-integrated process according to the current invention helps to improve the pyrolysis oil produce and reduce the energy consumption and operating costs.
It should be noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a composition containing “a compound” includes a mixture of two or more compounds. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. It should also be noted that, as used in this specification and the appended claims, the phrase “configured” describes a system, apparatus, or other structure that is constructed or configured to perform a particular task or adopt a particular configuration to. The phrase “configured” can be used interchangeably with other similar phrases such as arranged and configured, constructed and arranged, constructed, manufactured and arranged, and the like.
Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims whiles the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents. In closing, it should be noted that each and every claim below is hereby incorporated into this detailed description or specification as an additional embodiments of the present invention.
This application is a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61/411,531, filed Nov. 9, 2010, entitled “HEAT INTEGRATED PROCESS FOR PRODUCING HIGH QUALITY PYROLYSIS OIL FROM BIOMASS,” which is incorporated herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61411531 | Nov 2010 | US |
