Patent Application
20200248084
There is a well-known global issue with waste disposal, particularly of large volume consumer products such as plastics, tires, textiles and other polymers that are not considered biodegradable within acceptable temporal limits. There is a public desire to incorporate these types of wastes into new products through recycling, reuse, or otherwise reducing the amount of waste generated.
A variety of means for the recycle, reuse, or reduction of waste stocks such as biomass, solid municipal waste, plastics, and paper have been articulated, among which is the gasification of such waste stocks. In such proposals, waste gasifiers which typically are air supplied fluidized bed gasifiers that can readily accept a variety of component sizes and types have been proposed or used. Such waste gasifiers typically operate at low to medium temperatures in the range of 500° C. to 1000° C. using air as an oxidizer, and given the lower operating temperature, incomplete oxidation reactions occur resulting the generating of high quantities of residues that can appear in both the gas phase (syngas stream) and bottoms solid phase; e.g. tarry substances. The types of residues and their quantity will vary depending on the feedstock composition. Further, while waste gasifiers have the advantage of accepting a highly variable composition of feedstocks, the resulting syngas compositions are also widely variable over time rendering them unusable for making chemicals without installation of expensive post treatments systems to clean up and purify the syngas streams existing the gasifier vessel. Even with purification processes, the hydrogen/carbon monoxide/carbon dioxide ratios will remain highly variable. As a result of the expense to install systems to purify the syngas stream exiting the gasifier vessel suitable for chemicals synthesis, or their compositional variability, or their low throughput, or by reason of a combination of these factors, waste gasifier generated syngas streams are typically used to generate energy, e.g. steam or electricity.
Tires have been investigated as a feed to a gasifier. In many instances, the gasifier is a fluidized or fixed bed type, and the processes described generate high amounts of sulfur or tar, or do not efficiently generate a large output of consistent syngas composition within levels air permitted limits.
We desire to reduce ensure a consistent and reliable syngas composition that continues to remain within limits established by air permits on an existing gasifier. It is desirable to conduct the operations efficiently, in a stable manner, and on a commercial scale.
There is now provided a gasification process comprising gasifying a feedstock stream comprising post-consumer tires and a solid fossil fuel in an existing gasifier for which one or more environmental air permits are granted before feeding said tires, at least one of said permits limiting the content of one or more gaseous compounds in all gases generated from the gasifier, wherein the gasification process is operated in a manner that does not require a new environmental air permit or an exception to an existing environmental permit for any gases generated from the gasifier.
Unless otherwise stated, reference the weight of the feedstock stream includes all solids, and if present liquids, fed to the gasifier, and unless otherwise stated, does not include the weight of any gases in the feedstock stream as fed to the injector or gasifier.
For purposes of classifying materials in the feedstock stream, a fossil fuel used is coal, petcoke, or any other solid at 25° C. and 1 atmosphere that is a byproduct from refining oil or petroleum. The fossil fuel portion of the feedstock stream is to be distinguished from post-consumer materials such as tires, even if those post-consumer materials are carbonaceous and derived from raw materials obtained from refining crude oil.
Post-consumer tires have presented a disposal problem because they are not biodegradable, they are vulcanized making their depolymerization impractical and economically unfeasible, and they contain steel wire. At lower temperatures, tires can incompletely combust to produce tarry products.
Generally, in a synthesis gas operation the feedstock stream comprised of finely particulated fossil fuel sources (e.g. coal, petcoke) and particulated rubber tires, and optionally water and other chemical additives, are injected along with an oxidizer gas into gasification reaction zone or chamber of a synthesis gas generator (gasifier). A hot gas stream is produced in the reaction zone, desirably refractory lined, at high temperature and pressure generating a molten slag, ash, soot, and gases including hydrogen, carbon monoxide, carbon dioxide and can include other gases such as methane, hydrogen sulfide and nitrogen depending on the fuel source and reaction conditions. The hot gas stream is produced in the reaction zone is cooled using a syngas cooler or in a quench water bath at the base of the gasifier which also solidifies ash and slag and separates solids from the gases. The quench water bath also acts as a seal to maintain the internal temperature and pressure in the reactor while the slag, soot and ash are removed into a lock hopper. The cooled product gas stream removed from the gasifier (the raw syngas stream) is further treated with a scrubber to remove remaining solids, and then further treated to remove acid gas (e.g. hydrogen sulfide) after optionally further cooling and shifting the ratio of carbon monoxide to hydrogen.
The post-consumer tires employed in the feedstock stream are tires that (i) have been used at least once for its intended application for any duration of time regardless of wear, and (ii) scrap, and (iii) out of specification tires that have not been used. While the latter two categories are generally considered pre-consumer tires, they are deemed for purposes of this invention to be included as a “post-consumer tire” since such tires are not usable by the consumer, and are not biodegradable, and may find their way into the same supply stream as used tires. Suitable sources of post-consumer tires in category (i) include those used on passenger cars, light trucks (vans, pick-up trucks, light utility vehicles), heavy trucks and buses, and other such as bicycle, motor cycle, agriculture, air plane, construction, and mining.
In one embodiment, the pre-ground tires comprise an average of at least 70 wt. % truck and bus tires, based on the weight of the tires used in the feedstock stream and based over any three-day period. In another embodiment, the tires are at least 70 wt. % passenger car and light truck tires, based on the weight of the tires used in the feedstock stream.
The rubber tires, as a co-fuel in a feedstock stream, have the advantage of not requiring thermal treatment prior to their introduction into the gasification zone or their introduction to one or more components of a feedstock stream. Unlike wood or grain which typically requires a thermal treatment beyond drying such as torrefaction, the tires do not receive a thermal treatment (above their pyrolysis temperature or above 150° C., or above 110° C., or above 100° C., or above 90° C., or above 80° C., or above 60° C., or above 58° C. or above their nominal temperature at their ambient conditions), or are not torrefied, prior to their introduction into the gasification zone. Further, unlike many biomass feedstocks which reduce the cold gas efficiency of the reactor and generate higher amounts of CO2 and water which reduce the gasifier efficiency, tires can be co-fed with other solid fossil fuels as they are more similar in composition while substantially maintaining the gasifier efficiency and cold gas efficiency. It is to be noted that the tires can be dried before their introduction into the feedstock stream, however, this would not be necessary in a slurry-based feedstock stream.
The process is flexible to permit the introduction of a wide range of tires. The composition of the tires is not particularly limited. The post-consumer will generally have two components: the elastomer and the cord. The cord can contain metal such as steel, or natural fibers such as cotton or silk, or synthetic fibers such as nylon and aramids. The elastomer is generally natural rubber or a synthetic rubber such as butadiene-based rubber, styrene-butadiene copolymer-based rubber, or butyl rubbers optionally halogenated, nitride rubber, isoprene rubber, neoprene rubber polysulphide rubber, and mixtures thereof. Other common materials found in tires include carbon black and silica, antioxidants, antiozonants, and curing systems such as sulfur and zinc oxide used in vulcanizing the rubber. The total amount of carbon (free or fixed) in all materials added to the solid fossil fuel, or in the tires, is at least 70 wt. %, or at least 75 wt. %, or at least 80 wt. %. The total amount of material in the pre-ground tires, other than the cord and elastomer and carbon black, is generally not more 7 wt. %, or not more than 6 wt. %, or not more than 5 wt. %, or not more than 4 wt. %, based on the weight of the tires.
In an embodiment, at least 50 wt. %, or at least 70 wt. %, or at least 80 wt. %, or at least 90 wt. % of the tires are vulcanized. In another embodiment, the pre-ground tires used in the feedstock stream have an average fixed carbon content of at least 60 wt. %, or at least 70 wt. %, or at least 75 wt. %, or at least 80 wt. %, based on the weight of the pre-ground tires.
The pre-ground tires may have an average sulfur content of at least 0.1 wt. %, or at least 0.2 wt. %, or at least 0.5 wt. %, or at least 0.8 wt. %, or at least 1 wt. %, or at least 1.2 wt. %, or at least 1.4 wt. %, based on the weight of the pre-ground tires. The upper amount is not particularly limited, but generally will be lower than 5 wt. %, or up to 4 wt. %, or up to 3 wt. %, or up to 2.5 wt. %, or up to 2 wt. %, based on the weight of the pre-ground tires.
The pre-ground tires may have an average ash content of at least 1 wt. %, or at least 2 wt. %, or at least 3 wt. %, or at least 4 wt. %, and up to 15 wt. %, or up to 12 wt. %, or up to 10 wt. %, or up to 8 wt. %. The tire ash content is similar to the typical ash content of coal used for gasification which may range from 3-10 wt. %, more typically in the 4-7 wt. % range.
In another embodiment, the average content of minerals, metals and elements other than carbon, hydrogen, oxygen, nitrogen, and sulfur, in the pre-ground tires is at least 0.5 wt. %, or at least 0.8 wt. %, or at least 1 wt. %, or at least 1.2 wt. %, or at least 1.5 wt. %, or at least 1.8 wt. %, or at least 2 wt. %, or at least 2.3 wt. %, or at least 2.5 wt. %, or at least 2.8 wt. %, or at least 3 wt. %, based on the weight of the pre-ground tires. The upper amount is not particularly limited, although an excessive amount of metals and minerals at high concentrations can result in excessive accumulation of solids in the quench zone of a gasifier that must be removed, and therefore, should generally not exceed 8 wt. %, or not exceed 7 wt. %, or not exceed 6 wt. %, or not exceed 5 wt. %, or not exceed 4.5 wt. %, or not exceed 4 wt. %, or not exceed 3.8 wt. %.
The post-consumer tires (hereinafter referred to as “tires” for convenience) charged to the gasifier have been treated by at least one granulation step to reduce the size of the tires from either their original form or from their form as shredded/chipped tires having an average size of ¼ inch or more in their longest dimension. Desirably, the tires, prior to arrival at a gasification facility, have been treated with a first pass of granulation or shredding from the original form of the tire in order to separate coarse metal and textile belts/wires from the rubber prior to their arrival to the gasification facility and make it feasible to conduct fine granulation. The coarsely granulated tires are then further finely granulated, and optionally further pulverizing or milling, to the final desired particle size. The gasification facility can receive pre-granulated tires at their final particle size, or can receive coarsely ground tires and the operator/owner of the gasification facility can conduct the granulation step(s) necessary to obtain the desired particle size present in the feedstock stream.
The tires are pre-ground prior to addition to other fossil fuels, meaning they are ground, and optionally but desirably sieved, to the final particle size prior to combining them with coal or pet-coke. As explained below, the tires in their original size, or as coarsely ground (e.g. average of ¼ inch or more in their largest dimension or even 0.5 inches or more), cannot be processed through an entrained flow coal gasifier. Further, the elasticity of the tires makes them unsuited for co-granulating with more hard and brittle carbonaceous fuel sources like coal or pet coke.
The tires are pre-ground to a suitable particle size, optionally sieved, and then combined with one or more fossil fuel components of the feedstock stream at any location prior to introducing the feedstock stream into gasification zone within the gasifier. As noted above, tires are not easily ground concurrently in the same equipment used to grind coal, particularly in a slurry, since the tires are soft, elastic and non-friable. However, the coal grinding equipment will provide an excellent source of energy for mixing pre-ground tires with the fossil fuel while reducing the size of the coal particles. Therefore, one of the desirable locations for combining pre-ground tires having a target size for feeding into the gasifier is into the equipment used for grinding the other carbonaceous fossil fuel sources (e.g. coal, pet-coke). This location is particularly attractive in a slurry fed gasifier because it is desirable to use a feed having the highest stable solids concentration possible, and at higher solids concentration, the viscosity of the slurry is also high. The torque and shear forces employed in fossil fuel grinding equipment is high, and coupled with the shear thinning behavior of a coal slurry, good mixing of the pre-ground tires with the ground fossil fuel can be obtained in the fossil fuel grinding equipment.
Other locations for combining pre-ground tires with fossil fuel sources can be onto the fossil fuel loaded on the main fossil fuel belt feeding a grinder, or onto the main fossil fuel belt feeding a grinder before the fossil fuel is loaded onto the belt, or into a fossil fuel slurry storage tank containing a slurry of fossil fuel ground to the final size, particularly if the storage tank is agitated.
The fossil fuel (coal or petcoke) and the tires are ground or milled for multiple purposes. The tires must be ground to a small size as does the fossil fuel source to (i) allow for faster reaction once inside the gasifier due to mass transfer limitations, (ii) to create a slurry that is stable, fluid and flowable at high concentrations of coal to water, and (iii) to pass through processing equipment such as high-pressure pumps, valves, and feed injectors that have tight clearances. Typically, this means that the solids in the feedstock, including the tires, are ground to a particle size in which at least 90% of the particles are 2 mm or smaller.
The tires are desirably ground to a particle size that, after optional sieving, is acceptable for gasifying within the design parameters of the gasifier. Desirably, the particle size of the tires used in the feedstock, or as fed to or combined with a solid fuel, is 2 mm and smaller or constitute those particles passing through a 10 mesh, or 1.7 mm or smaller (those particles passing through a 12 mesh), or 1.4 mm or smaller (those particles passing through a 14 mesh), or 1.2 mm or smaller (those particles passing through a 16 mesh), or 1 mm or smaller (those particles passing through a 18 mesh), or 0.85 mm or smaller (those particles passing through a 20 mesh), or 0.7 mm or smaller (those particles passing through a 25 mesh) or 0.6 mm or smaller (those particles passing through a 30 mesh), or 0.5 mm or smaller (those particles passing through a 35 mesh), or 0.4 mm or smaller (those particles passing through a 40 mesh), or 0.35 mm or smaller (those particles passing through a 45 mesh), or 0.3 mm or smaller (those particles passing through a 50 mesh), or 0.25 mm or smaller (those particles passing through a 60 mesh), or 0.15 mm or smaller (those particles passing through a 100 mesh), or 0.1 mm or smaller (those particles passing through a 140 mesh), or 0.07 mm or smaller (those particles passing through a 200 mesh), or 0.044 mm or smaller (those particles passing through a 325 mesh), or 0.037 mm or smaller (those particles passing through a 400 mesh). In another embodiment, the size of the ground tire particles is at least 0.037 mm (or 90% retained on a 400 mesh). The sample of pre-ground tires will be considered to be within a stated particle size limit if 90 vol. % of the sample is within the stated limits.
In one embodiment, the particle size of the pre-ground rubber tires as used in the feedstock composition is 0.1 mm or smaller (or those particles passing through a 140 mesh), or 0.7 mm or smaller (those particles passing through a 200 mesh), or 0.044 mm or smaller (those particles passing through a 325 mesh), or 0.037 mm or smaller (those particles passing through a 400 mesh).
In another embodiment, the particle sizes of rubber and the fossil fuels can be sufficiently matched to retain the stability of the slurry and avoid a coal/rubber separation at high solids concentrations prior to entering the gasification zone in the gasifier. A feedstock stream that phase separates, whether between solids/liquid or rubber/fossil fuel, can plug lines, created localized zones of gasified rubber, create inconsistent ratios of fossil fuel/tire, and can impact the consistency of the syngas composition. Variables to consider for determining the optimal particle size of the ground tires include the bulk density of the ground coal, the concentration of all solids in the slurry if a slurry is used, the effectiveness of any additives employed such as surfactants/stabilizers/viscosity modifiers, and the velocity and turbulence of the feedstock stream to the gasifier and through the injector nozzles.
In one embodiment, the bulk density of the ground tires without compaction (loose) after final grinding is within 150%, or within 110%, or within 100%, or within 75%, or within 60%, or within 55%, or within 50%, or within 45%, or within 40%, or within 35% of the loose bulk density of the ground fossil fuel after its final grinding. For example, if the granulated coal has a loose bulk density of 40 lbs/ft3 and the granulated tires have a loose bulk density of 33 lbs/ft3, the bulk density of the tires would be within 21% of the ground coal. For measurement purposes, the bulk density of the pre-ground tires and the fossil fuel after final grinding is determined dry (without addition of water) even though they are ultimately used as a slurry.
In an alternative embodiment or in addition to any other embodiment described herein, the maximum particle size of the ground rubber tires is selected to be similar (below or above) to the maximum particle size of the ground coal. The maximum particle size of the ground rubber tires is desirably within (meaning below or above) 50%, or within 45%, or within 40%, or within 35%, or within 30%, or within 25%, or within 20%, or within 15%, or within 10%, or within 5% of the maximum particle size of the ground coal. The maximum particle size is not determined as the maximum size of the particle distribution but rather by sieving through meshes. The maximum particle size is determined as the first mesh which allows at least 90 volume % of a sample of the ground particles to pass. For example, if less than 90 volume % of a sample passes through a 300 mesh, then a 100 mesh, a 50 mesh, a 30 mesh, a 16 mesh, but succeeds at a 14 mesh, then the maximum particle size of that sample is deemed to correspond to the first mesh size that allowed at least 90 volume % to pass through, and in this case, a 14 mesh corresponding to a maximum particle size of 1.4 mm.
The amount of ground tires present in the feedstock stream can range from 0.1 wt. % to 50 wt. %, desirably from 0.1 wt. % to 25 wt. %, based on the weight of all solids. The pre-ground tires at a concentration of less than 25 wt. %, or not more than 20 wt. %, or not more than 15 wt. %, or not more than 5 wt. %, based on the weight of the solids in the feedstock stream, can be incorporated into the feedstock stream without substantially impacting the reaction time, the flowability, the stability, or the physical processing of the feedstock stream feeding into the gasifier and inside the gasifier. The tire content can be at least 0.25 wt. %, or at least 0.5 wt. %, or at least 0.75 wt. %, or at least 1 wt. %, or at least 1.5 wt. %, or at least 1.75 wt. %, or at least 2 wt. %, or at least 2.5 wt. %, or at least 3 wt. %, or at least 3.5 wt. %, or at least 4 wt. %, or at least 4.5 wt. %, or at least 5 wt. %, or at least 6 wt. % or at least 10 wt. %, or at least 13 wt. %, or at least 15 wt. %, or at least 18 wt. %, based on the weight of all solids. Desirably, the content of ground tire present in the feedstock stream is from 0.25 wt. % to 15 wt. %, or from 0.25 wt. % to 13 wt. %, or from 0.25 wt. % to 10 wt. %, or from 0.25 wt. % to 8 wt. %, or from 0.25 wt. % to 6 wt. %, or from 0.25 wt. % to 5 wt. %, or from 0.25 wt. % to 4 wt. %, or from 0.25 wt. % to 3 wt. %, or from 0.25 wt. % to 2.5 wt. %, or from 0.5 wt. % to 15 wt. %, or from 0.5 wt. % to 13 wt. %, or from 0.5 wt. % to 10 wt. %, or from 0.5 wt. % to 8 wt. %, or from 0.5 wt. % to 6 wt. %, or from 0.5 wt. % to 5 wt. %, or from 0.5 wt. % to 4 wt. %, or from 0.5 wt. % to 3 wt. %, or from 0.5 wt. % to 2.5 wt. %, or from 1 wt. % to 15 wt. %, or from 1 wt. % to 13 wt. %, or from 1 wt. % to 10 wt. %, or from 1 wt. % to 8 wt. %, or from 1 wt. % to 6 wt. %, or from 1 wt. % to 5 wt. %, or from 1 wt. % to 4 wt. %, or from 1 wt. % to 3 wt. %, or from 1 wt. % to 2.5 wt. % each based on the weight of the solids in the feedstock stream.
The pre-ground tires are desirably isolated as a ground tire feed for ultimate destination to be mixed with one or more components of the feedstock stream. In one embodiment, at least 80 wt. %, or at least 85 wt. %, or at least 90 wt. %, or at least 95 wt. %, or at least 96 wt. %, or at least 97 wt. %, or at least 98 wt. %, or at least 99 wt. %, or at least 99.5 wt. %, or 100 wt. % of all post-consumer recycle content in the feedstock stream fed into the gasifier is ground tires, which includes both the rubber and the components that were contained in the tires (e.g. steel, metals, sulfur and elements other than rubber found in tires). In another embodiment, at least 80 wt. %, or at least 85 wt. %, or at least 90 wt. %, or at least 95 wt. %, or at least 96 wt. %, or at least 97 wt. %, or at least 98 wt. %, or at least 99 wt. %, or at least 99.5 wt. %, or 100 wt. % of all feedstock other than solid fossil fuels in the feedstock stream fed into the gasifier is pre-ground tires, which includes both the rubber and the components that were contained in the tires (e.g. steel, metals, sulfur and elements other than rubber found in tires).
The post-consumer pre-ground tires will, even after final grinding, contain some level of materials other than rubber, such as metals, traces of textile cord/belting or steel wires particles, or other materials. The quantity of such materials in the pre-ground tires that feed into the feedstock stream, other than rubber, is desirably less than 8 wt. %, or not more than 6 wt. %, or not more than 5 wt. %, or not more than 4 wt. %, or not more than 3.5 wt. %, or not more than 2 wt. %, or not more than 1.5 wt. %, or not more than 1 wt. %, or not more than 0.75 wt. %, or not more than 0.5 wt. %. based on the weight of the pre-ground tire particles.
Coal contains a quantity of ash that also contains elements other than carbon, oxygen, and hydrogen. The quantity of elements other than carbon, hydrogen, oxygen, and sulfur in the feedstock stream is desirably not more than 9 wt. %, or not more than 8.5 wt. %, or not more than 8 wt. %, or not more than 7.5 wt. %, or not more than 7 wt. %, or not more than 7.5 wt. %, or not more than 7 wt. %, or not more than 6.5 wt. %, or not more than 6 wt. %, or not more than 5.5 wt. %, or not more than 5 wt. %, or not more than 4.5 wt. %, based on the weight of all dry solids in the feedstock stream, or alternatively based on the weight of the feedstock stream.
Coal contains a quantity of ash that also contains elements other than carbon, oxygen, and hydrogen. The quantity of elements other than carbon, hydrogen, and oxygen in the feedstock stream is desirably not more than 15 wt. %, or not more than 12 wt. %, or not more than 10 wt. %, or not more than 9 wt. %, or not more than 8.5 wt. %, or not more than 8 wt. %, or not more than 7.5 wt. %, or not more than 7 wt. %, or not more than 7.5 wt. %, or not more than 7 wt. %, or not more than 6.5 wt. %, or not more than 6 wt. %, or not more than 5.5 wt. %, or not more than 5 wt. %, or not more than 4.5 wt. %, based on the weight of all dry solids in the feedstock stream, or alternatively based on the weight of the feedstock stream.
In one embodiment, the average quantity of zinc in the pre-ground rubber tire feed is less than 4 wt. %, or not more than 3.5 wt. %, or not more than 3 wt. %, or not more than 2.5 wt. %, or not more than 2.2 wt. %, or not more than 2.0 wt. %, based on the weight of the pre-ground rubber tires to be used in the feedstock stream.
Unlike the highly variable content of material in a municipal solid waste stream resulting in variability to the syngas composition and output, the post recycle composition of tires in the feedstock stream in the present invention is substantially consistent over time as a rubber tire content and its amount can also be controlled to be consistent, thereby reducing fluctuations in the syngas composition and output and without impacting the operations of the gasifier. Tires, being mostly organic material with a similar carbon content, will gasify as well or better than coal. The caloric heat value of rubber tires is also similar to or better than that of coal, making it an attractive co-feed constituent with coal. For example, standard passenger tires have a heat value in the range of 13,000 to 15,000 BTU/lb (30 MJ/Kg-35 MJ/Kg), while bituminous coal can have a heat value in a range of 12,500 to 13,300 BTU/lb (29-31 MJ/Kg). Further, any ash or non-organic material will be melted and vitrified into the ash matrix that is produced from the inorganics in the coal. Therefore, the tires can be viewed as a direct replacement for coal in the feed process.
The concentration of solids (e.g. fossil fuel and tires) in the feedstock stream should not exceed the stability limits of the slurry, or the ability to pump or feed the feedstock at the target solids concentration to the gasifier. Desirably, the solids content of the slurry should be at least 50 wt. %, or at least 55 wt. %, or at least 60 wt. %, or at least 62 wt. %, or at least 65 wt. %, or at least 68 wt. %, or at least 69 wt. %, or at least 70 wt. %, or at least 75 wt. %, the remainder being a liquid phase that can include water and liquid additives. The upper limit is not particularly limited because it is dependent upon the gasifier design. However, given the practical pumpability limits of a solid fossil fuels feed and maintaining a homogeneous distribution of solids in the slurry, the solids content for a solid fossil slurry fed slagging gasifier desirably should not exceed 75 wt. %, or 73 wt. %, the remainder being a liquid phase that can include water and liquid additives (as noted above, gases are not included in the calculation of weight percentages).
The feedstock stream is desirably stable at 5 minutes, or even 10 minutes, or even 15 minutes, or even 20 minutes, or even ½ hour, or even 1 hour, or even two hours. A feedstock slurry is deemed stable if its initial viscosity is 100,000 cP or less. The initial viscosity can be obtained by the following method. A 500-600 g of a well-mixed sample is allowed to stand still in a 600 mL liter glass beaker at ambient conditions (e.g. 25° C. and about 1 atm). A Brookfield R/S Rheometer equipped with V80-40 vane operating at a shear rate of 1.83/s is submerged into the slurry to the bottom of the beaker after the slurry is well mixed (e.g. a homogeneous distribution of solids was formed). After a designated period of time, a viscosity reading is obtained at the start of rotation, which is the initial viscosity reading. The slurry is considered to be stable if the initial reading on starting a viscosity measurement is not more than 100,000 cP at the designated period of time. Alternatively, the same procedure can be used with a Brookfield viscometer with an LV-2 spindle rotating at a rate of 0.5 rpm. Since different viscosity value will be obtained using the different equipment, the type of equipment used should be reported. However, regardless of the differences, the slurry is considered stable under either method only if its viscosity is not more than 100,000 cP at the reported time.
The quantity of solids in the feedstock stream and their particle size are adjusted to maximize the solids content while maintaining a stable and pumpable slurry. A pumpable slurry is one which has a viscosity under 30,000 cP, or not more than 25,000 cP, or not more than 23,000 cP, and desirably not more than 20,000 cP, or not more than 18,000 cP, or not more than 15,000 cP, or not more than 13,000 cP, in each case at ambient conditions (e.g. 25° C. and 1 atm). At higher viscosities, the slurry becomes too thick to practically pump. The viscosity measurement to determine the pumpability of the slurry is taken by mixing a sample of the slurry until a homogeneous distribution of particles is obtained, thereafter immediately submerging a Brookfield viscometer with an LV-2 spindle rotating at a rate of 0.5 rpm into the well mixed slurry and taking a reading without delay. Alternatively, a Brookfield R/S rheometer with V80-40 vane spindle operating at a shear rate of 1.83/s can be used. The method of measurement is reported since the measured values between the two rheometers at their difference shear rates will generate different values. However, the cP values stated above apply to either of the rheometer devices and procedures.
Conventional rubber tires granulators can be used to obtain the desires particle size. These can include systems for shredding the tires using high capacity shredders to chips, systems for loosening and separating the textile and steel wires through magnetic and screening technology, followed by granulation which also involves some loosening and separation of the steel and textile material in a tire and if necessary, a fine/powder granulator can be used in a last step. The steel material can be magnetically separated before or after sieving, and the textile balls can be physically separated after sieving. For the last step, the fine/powder granulators can be in communication with a conveying system to transport the granulated tires to a storage vessel from which the granulated tires can be fed to any location for making the feedstock stream, or the granulated particles can be fed continuously from the fine granulator to the desired location for making the feedstock stream. The feed of granulated tire particles from a storage vessel can be in a batch mode or in a continuous mode.
The carbonaceous materials, e.g. fossil fuel and rubber tires, are advantageously loose and not densified by mechanical or chemical means after granulation (other than natural compaction that may result from storage under its own weight). For example, coal chunks are granulated in the presence of water and not thereafter compacted, and rubber tires are fine ground/pulverized without densification operations prior to their addition into water.
The coal must be ground prior to feeding into a gasifier to achieve an acceptable particle size for the reasons noted above. These same considerations apply to the tire granulates, although as noted above, since the coal grinding equipment is not suitable to grind tires, the tires must be pre-ground prior to combining them to the feedstock composition or before adding to the coal grinding equipment.
The coal is typically ground to a size of 2 mm or less, and can be ground to any of the sizes noted above with respect to the granulated tire particle sizes. The small size of the coal and rubber tire particles is important to assure a uniform suspension in the liquid vehicle which will not settle out, to allow sufficient motion relative to the gaseous reactants, to assure substantially complete gasification, and to provide pumpable slurries of high solids content with a minimum of grinding.
The quality of the coal employed is not limited. Anthracite, bituminous, sub-bituminous, brown coal, and lignite coal can be sources of coal feedstock. To increase the thermal efficiency of the reactor, the coal employed desirably has a carbon content that exceeds 35 wt. %, or at least 42 wt. %, based on the weight of the coal. Accordingly, bituminous or anthracite coal is desirable due to their higher energy content.
In another embodiment, the fixed carbon content in the solid fossil fuel employed in the feedstock stream is similar to fixed carbon content of the cumulative amount of all other solids in the feedstock stream. The fixed carbon content is understood by those of skill in the art and is the combustible solids remaining (other than ash) after the coal is heated and volatiles removed. It can be determined by subtracting the percentages of moisture, volatile matter, and ash from a sample. If a solid is employed with a large mismatch in fixed carbon content, variations in syngas composition can be experienced outside of desirable limits. For example, a solid that has a very low fixed carbon content could, in an entrainment flow high temperature gasifier, gasify more readily than coal proceed from making carbon monoxide to generating more carbon dioxide within the residence time experienced by coal, while a co-feed of solids having a much higher fixed carbon content that coal would take longer to gasify and generate more unconverted solids. The degree of syngas compositional variations that can be tolerated will depend on the use of the syngas, and in the case of making chemicals, it is desirably to minimize the factors that could cause wider syngas compositional variations. Accordingly, in one embodiment, the fixed carbon content of solids other than solid fossil fuels is within +/−10 percentage digits, or within +/−9 percentage digits, or within +/−8 percentage digits, or within +/−7 percentage digits, or within +/−6 percentage digits, or within +/−5 percentage digits, or within +/−4 percentage digits, or within +/−3 percentage digits, or within +/−percentage digits, or within +1-1 percentage digits of the fixed carbon content of the solid fossil fuels in the feedstock composition. For example, a fixed carbon content of tires at 35% and a fixed carbon content of coal at 37.2% would be within 3 percentage digits of each other.
Sulfur is also typically present in solid fossil fuels. Desirably, the content of sulfur is less than 5 wt. %, not more than 4 wt. %, or not more than 3 wt. %, or not more than 2.5 wt. %, and also can contain a measure of sulfur, such as at least 0.25 wt. %, or at least 0.5 wt. %, or at least 0.75 wt. %.
It is also desirable to employ coal with a low inherent moisture content to improve the thermal efficiency of the gasifier. Using coal having moisture contents less than 25 wt. % or less than 20 wt. % or less than 15 wt. % or not more than 10 wt. % or not more than 8 wt. % without the application of external artificially applied heat is desirable.
Desirably, the coal feedstock has a heat value of at least 11,000 BTU/lb, or at least 11,500 BTU/lb, or at least 12,500 BTU/lb, or at least 13,000 BTU/lb, or at least 13,500 BTU/lb, or at least 14,000 BTU/lb, or at least 14,250 BTU/lb, or at least 14,500 BTU/lb.
While it is possible that the feedstock stream may contain minor amounts of liquid hydrocarbon oils leached from tires or coal, the feedstock stream desirably contains less than 5 wt. %, or not more than 3 wt. %, or not more than 1 wt. %, or not more than 0.1 wt. % liquid (at ambient conditions) non-oxygenated hydrocarbon petroleum oils introduced as such into the feedstock stream. Desirably, the feedstock stream contains less than 2 wt. %, or not more than 1 wt. %, or no added liquid fraction from refining crude oil or reforming any such fraction. Desirably, the quantity of liquids in the feedstock stream is other than the solids content. The content of liquids, or the content of water, present in the feedstock stream is desirably not more than 50 wt. %, or not more than 35 wt. %, or not more than 32 wt. %, or not more than 31 wt. %, or not more than 30 wt. %, based on the weight of the feedstock stream. Desirably, in each case, the content of liquids or water in the feedstock stream is desirably at least 10 wt. %, or at least 15 wt. %, or at least 20 wt. %, or at least 25 wt. %, or at least 27 wt. %, or at least 30 wt. %, based on the weight of the feedstock stream. Desirably, the liquids present in the feedstock stream contain at least 95 wt. % water, or at least 96 wt. % water, or at least 97 wt. % water, or at least 98 wt. % water, or at least 99 wt. % water, based on the weight of all liquids fed to the gasifier. In another embodiment, other than chemical additives that are chemically synthesized and contain oxygen or sulfur or nitrogen atoms, the liquid content of the feedstock stream is at least 96 wt. % water, or at least 97 wt. % water, or at least 98 wt. % water, or at least 99 wt. % water, based on the weight of all liquids fed to the gasifier.
The feedstock stream comprises at least ground coal and ground tires. Desirably, the feedstock stream also comprises water. The amount of water in the feedstock stream can range from 0 wt. % up to 50 wt. %, or from 10 wt. % to 40 wt. %, or from 20 wt. % to 35 wt. %. The feedstock stream is desirably a slurry containing water.
In addition to coal, water, and rubber tires, other additives can be added to and contained in the feedstock stream, such as viscosity modifiers and pH modifiers. The total quantity of additives can range from 0.01 wt. % to 5 wt. %, or from 0.05 wt. % to 5 wt. %, or from 0.05 to 3 wt. %, or from 0.5 to 2.5 wt. %, based on the weight of the feedstock stream. The quantity of any individual additive can also be within these stated ranges.
The viscosity modifiers (which includes surfactants) can improve the solids concentration in the slurry. Examples of viscosity modifiers include:
More specific examples of alkyl-substituted aminobutyric acid surfactants include N-coco-beta-aminobutyric acid, N-tallow-beta-aminobutyric acid, N-lauryl-beta-aminobutyric acid, and N-oleyl-beta-aminobutyric acid. N-coco-beta-aminobutyric acid.
More specific examples of alkyl-substituted polyethoxylated amide surfactant include polyoxyethylene oleamide, polyoxyethylene tallowamide, polyoxyethylene laurylamide, and polyoxyethylene cocoamide, with 5-50 polyoxyethylene moieties being present.
More specific examples of the alkyl-substituted polyethoxylated quaternary ammonium salt surfactant include methylbis (2-hydroxyethyl) cocoammonium chloride, methylpolyoxyethylene cocoammonium chloride, methylbis (2-hydroxyethyl) oleylammonium chloride, methylpolyoxyethylene oleylammonium chloride, methylbis (2-hydroxyethyl) octadecylammonium chloride, and methylpolyoxyethylene octadecylammonium chloride.
More specific examples of sulfonates include sulfonated formaldehyde condensates, naphthalene sulfonate formaldehyde condensates, benzene sulfonate-phenol-formaldehyde condensates, and lingosulfonates.
More specific examples of phosphate salts include trisodium phosphate, potassium phosphate, ammonium phosphate, sodium tripolyphosphate or potassium tripolyphosphate.
Examples of polyoxyalkylene anionic or nonionic surfactants have 1 or more repeating units derived from ethylene oxide or propylene oxide, or 1-200 oxyalkylene units.
Desirably, the surfactant is an anionic surfactant, such as salts of an organic sulfonic acid. Examples are calcium, sodium and ammonium salts of organic sulfonic acids such as 2,6-dihydroxy naphthalene sulfonic acid, lignite sulfonic acid, and ammonium lignosulfonate.
Examples of pH modifiers include aqueous alkali metal and alkaline earth hydroxides such as sodium hydroxide, and ammonium compounds such as 20-50 wt. % aqueous ammonium hydroxide solutions. The aqueous ammonium hydroxide solution can be added directly to the feedstock composition prior to entry into the gasifier, such as in the coal grinding equipment or any downstream vessels containing the slurry.
The atomic ratio of total oxygen to carbon entering the gasification zone can be a value in the range of 0.70 to less than 2, or from 0.9 to 1.9, or from 0.9 to 1.8, or from 0.9 to 1.5, or from 0.9 to 1.4, or from 0.9 to 1.2, or from 1 to 1.9, or from 1 to 1.8, or from 1 to 1.5, or from 1 to 1.2, or from 1.05 to 1.9, or from 1.05 to 1.8, or from 1.05 to 1.5, or from 1.05 to 1.2. The atomic ratio of free oxygen to carbon entering the gasification zone can also be within these same values. The weight ratio of both total oxygen and free oxygen to carbon in pounds entering the gasification zone can also each be within these stated values.
The total carbon content in the feedstock stream is at least 40 wt. %, or at least 45 wt. %, or at least 50 wt. %, or at least 55 wt. %, or at least 60 wt. %, or at least 65 wt. %, and desirably at least 70 wt. %, or at least 75 wt. %, or at least 80 wt. %, or at least 85 wt. %, or at least 90 wt. %, each based on the total solids content. High carbon contents contribute to fuel sources with higher heat values and promote improved reactor efficiency.
The feedstock stream is desirably injected along with an oxidizer into the refractory-lined combustion chamber of the synthesis gas generating gasifier. The feedstock stream (desirably a slurry) and oxidizer are desirably sprayed through an injector into a gasification zone that is under significant pressure, typically about 500 psig or more, or 600 psig or more, or 800 psig or more, or 1000 psig or more. The velocity or flow rate of the feedstock and oxidizer streams ejected from the injector nozzle into the combustion chamber will exceed the rate of flame propagation to avoid backflash.
In one embodiment of the invention, advantageously only one feedstock stream is charged to the gasifier or gasification zone, or in other words, all sources of carbon fuel are fed to the gasifier in only one stream. In another embodiment, only one feedstock stream is necessary or employed to produce a syngas or product stream that is a raw material to synthesize a chemical compound.
In another embodiment, a chemical is made from a first syngas sourced from a first gasifier fed with a first feedstock stream containing coal and the first syngas stream is not combined with a second syngas sourced from any other gasifier fed with second feedstock stream where the coal content between the first and second feedstock streams differs by more than 20%, or more than 10%, or more than 5%. For example, a first syngas stream generated from a first feedstock stream containing 90 wt. % coal would not be combined with a syngas stream generated from a different gasifier fed with a feedstock stream containing 70 wt. % coal or no coal, but could be combined with one containing 72 wt. % coal or more.
Prior to entry into the gasifier, the feedstock stream may be subjected to a variety of other optional processes. For example, the coal-rubber slurry can flow through a thickener in which excess water is eliminated from the slurry to obtain the final desired solids concentration of the slurry entering into the gasifier vessel. Additionally, the feedstock stream may be pre-heated to prior to entry into the gasifier. In this embodiment, the feedstock stream is heated to a temperature below the boiling point of water at the operating pressure existing in reaction zone. The preheater, when employed, reduces the heat load on the gasifier and improves the efficiency of utilization of both fuel and oxygen. In this embodiment, all of the water required for the generation of synthesis gas in reaction zone is supplied in liquid phase. When petroleum coke is employed as fuel for the gas generator, part of the water, e.g., from 1 to about 90 percent by weight based on the weight of water, may be vaporized in the slurry feed preheater or combined with the oxidizing stream as vaporized water.
The oxidizer is desirably an oxidizing gas that can include air, and desirably is a gas enriched in oxygen at quantities greater than that found in air. The reaction of oxygen and solid fossil fuel is exothermic. Desirably, the oxidant gas contains at least 25 mole % oxygen, or at least 35 mole %, or at least 40 mole %, or at least 50 mol %, or at least 70 mole %, or at least 85 mole %, or at least 90 mole %, or at least 95 mole %, or at least 97 mole %, or at least 98 mole % oxygen, or at least 99 mole %, or at least 99.5 mole % based on all moles in the oxidant gas stream injected into the reaction (combustion) zone of the gasifier. In another embodiment, the combined concentration of oxygen in all gases supplied to the gasification zone is also in the above stated amount. The particular amount of oxygen as supplied to the reaction zone is desirably sufficient to obtain near or maximum yields of carbon monoxide and hydrogen obtained from the gasification reaction relative to the components in the feedstock stream, considering the amount relative to the feedstock stream, and the amount of feedstock charged, the process conditions, and the reactor design.
In one embodiment, steam is not supplied to the gasification zone. The amount of water in a slurry fed system is typically more than sufficient a co-reactant and heat sink to regulate the gasification temperature. The addition of stream in a slurry fed gasifier will generally unduly withdraw heat from the reaction zone and reduce its efficiency.
Other reducible oxygen-containing gases may be supplied to the reaction zone, for example, carbon dioxide, nitrogen, or simply air. In one embodiment, no gas stream enriched in carbon dioxide or nitrogen (e.g. greater than the molar quantity found in air, or greater than 2 mole %, or greater than 5 mole %, or greater than 10 mole %, or greater than 40 mole %) is charged into the gasifier. Many of these gases serve as carrier gases to propel a dry feed to a gasification zone. Due to the pressure within the gasification zone, these carrier gases are compressed to provide the motive force for introduction into the gasification zone. The expenditure of energy and equipment for compressing carrier gases to the feedstock stream is avoided is a slurry feed. Accordingly, in another embodiment, the feedstock stream containing at least pre-ground tires and ground solid fossil fuel flowing to the gasifier, or this feedstock stream introduced to an injector or charge pipe, or this feedstock stream introduced into the gasification zone, or a combination of all the above, does not contain gases compressed in equipment for gas compression. Alternatively, or in addition, other than the oxygen rich stream described above, no gas compressed in equipment for gas compression is fed to the gasification zone or even to the gasifier. It is noteworthy that high pressure charge pumps that process the slurry feed for introduction into the gasification zone are not considered gas compressing equipment.
Desirably, no gas stream containing more than 0.03 mole %, or more than 0.02 mole %, or more than 0.01 mole % carbon dioxide is charged to the gasifier or gasification zone. In another embodiment, no gas stream containing more than 77 mole %, or more than 70 mole %, or more than 50 mole %, or more than 30 mole %, or more than 10 mole %, or more than 5 mole %, or more than 3 mole % nitrogen is charged to the gasifier or gasification zone. In another embodiment, steam is not charged into the gasification zone or to the gasifier. In yet another embodiment, a gaseous hydrogen stream (e.g. one containing more than 0.1 mole % hydrogen, or more than 0.5 mole %, or more than 1 mole %, or more than 5 mole %) is not charged to the gasifier or to the gasification zone. In another embodiment, a stream of methane gas (e.g. one containing more than 0.1 mole % methane, or more than 0.5 mole %, or more than 1 mole %, or more than 5 mole % methane) is not charged to the gasifier or to the gasification zone. In another embodiment, the only gaseous stream introduced to the gasification zone is an oxygen rich gas stream as described above.
The gasification process desirably employed is a partial oxidation gasification reaction. To enhance the production of hydrogen and carbon monoxide, the oxidation process involves partial, rather than complete, oxidization of the fossil fuel and tires and therefore is desirably operated in an oxygen-lean environment, relative to the amount needed to completely oxidize 100% of the carbon and hydrogen bonds. The total oxygen requirements for the gasifier is desirably at least 5%, or at least 10%, or at least 15%, or at least 20%, in excess of the amount theoretically required to convert the carbon content of the solid fuel and tires to carbon monoxide. In general, satisfactory operation may be obtained with a total oxygen supply of 10 to 80 percent in excess of the theoretical requirements. An example of a suitable amount of oxygen per pound of carbon is in the range of 0.4 to about 3.0-pound free oxygen per pound of carbon, or from 0.6 to 2.5, or from 0.9 to 2.5, or from 1 to 2.5, or from 1.1 to 2.5, or from 1.2 to 2.5 pounds of free oxygen per pound of carbon.
Mixing of the feedstock stream and the oxidant is desirably accomplished entirely within the reaction zone by introducing the separate streams of feedstock and oxidant so that they impinge upon each other within the reaction zone. Desirably, the oxidant stream is introduced into the reaction zone of the gasifier as high velocity to both exceed the rate of flame propagation and to improve mixing with the feedstock stream. The oxidant is desirably injected into the gasification zone in the range of 25 to 500 feet per second, or 50 to 400 ft/s, or 100 to 400 ft/s. These values would be the velocity of the gaseous oxidizing stream at the injector-gasification zone interface, or the injector tip velocity.
One method for increasing the velocity of the oxidant feed to the gasification zone is by reducing the diameter of the oxidant annulus near the tip of the injector or injector. Near the tip of the injector the annular passage converges inwardly in the shape of a hollow cone as shown in
The velocity of the feedstock slurry is determined by the desired throughput of syngas generation. Suitable examples of feedstock velocity introduced into gasification zone prior to contact with the oxidizing agent is in the range of 5 to 50 feet per second.
The feedstock stream and the oxidant can optionally be preheated to a temperature above about 200° C., or at least 300° C., or at least 400° C. Advantageously the gasification process employed does not require preheating the feedstock stream to efficiently gasifying the fuel, and a pre-heat treatment step would result in lowering the energy efficiency of the process. Desirably, the feedstock stream, and optionally the oxidant, are not preheated prior to their introduction into the gasifier. A preheat treatment step would be contacting the feedstock stream or oxidant with equipment that raises the temperature of the feedstock stream sufficiently such that the temperature of the feedstock stream or oxidant stream is above 200° C., or above 190° C., or above 170° C., or above 150° C., or above 130° C., or above 110° C., or above 100° C., or above 98° C., or above 90° C., or above 80° C., or above 70° C., or above 60° C., immediately prior to introduction into a injector on the gasifier. For example, while coal can be dried with hot air above 200° C., this step would not be considered a preheat of the feedstock stream if the feedstock stream is below 200° C. upon its introduction into the injector.
In another embodiment, no thermal energy (other than incidental heat from processing equipment such as mills, grinders or pumps) is applied to the feedstock stream containing both tires and the solid fossil fuel, or to the oxidant stream, at any point prior to its introduction into the injector, or gasifier, or gasification zone (other than the temperature increase experienced in a injector) that would increase the temperature of the stream by more than 180° C., or more than 170° C., or more than 160° C., or more than 150° C., or more than 140° C., or more than 130° C., or more than 120° C., or more than 110° C., or more than 100° C., or more than 90° C., or more than 80° C., or more than 70° C., or more than 60° C., or more than 50° C., or more than 40° C., or more than 30° C.
The process of the invention employs a gasification process, which is distinct from pyrolysis (which is a thermal process that degrades a fuel source in the absence of air or oxygen) or plasma processes in that gasification does not employ a plasma arc.
Desirably, the type of gasification technology employed is a partial oxidation entrained flow gasifier that generates syngas. This technology is distinct from fixed bed (alternatively called moving bed) gasifiers and from fluidized bed gasifiers. In fixed bed (or moving bed gasifiers), the feedstock stream moves in a countercurrent flow with the oxidant gas, and the oxidant gas typically employed is air. The feedstock stream falls into the gasification chamber, accumulates, and forms a bed of feedstock. Air (or alternatively oxygen) flows from the bottom of the gasifier up through the bed of feedstock material continuously while fresh feedstock continuously falls down from the top by gravity to refresh the bed as it is being combusted. The combustion temperatures are typically below the fusion temperature of the ash and are non-slagging. Whether the fixed bed operated in countercurrent flow or in some instances in co-current flow, the fixed bed reaction process generates high amount of tars, oils, and methane produced by pyrolysis of the feedstock in the bed, thereby both contaminating the sygnas produced and the gasifier. The contaminated syngas requires significant effort and cost to remove tarry residues that would condense once the syngas is cooled, and because of this, such syngas streams are generally not used to make chemicals and is instead used in direct heating applications. In a fluidized bed, the feedstock material in the gasification zone is fluidized by action of the oxidant flowing through the bed at a high enough velocity to fluidize the particles in the bed. In a fluidized bed, the homogeneous reaction temperatures and low reaction temperatures in the gasification zone also promotes the production of high amounts of unreacted feedstock material and low carbon conversion, and operating temperatures in the fluidized bed are typically between 800-1000° C. Further, in a fluidized bed it is important to operate below slagging conditions to maintain the fluidization of the feedstock particles which would otherwise stick to the slag and agglomerate. By employing an entrained flow gasification, these deficiencies present with fixed (or moving bed) and fluidized bed gasifiers that are typically used to process waste materials is overcome.
In one embodiment, the feedstock stream is introduced at the top ⅛ section of the gasifier, desirably at the top 1/12 of the gasifier height defined by the gasifier shell (not including the injector height protruding from the top of the shell or pipes protruding from the bottom of the shell). The feedstock stream is desirably not introduced into a side wall of the gasifier. In another embodiment, the feedstock stream is not a tangential feed injector.
In another embodiment, oxidant is introduced at the top ⅛ section of the gasifier, desirably at the top 1/12 of the gasifier height defined by the gasifier shell. The oxidant is desirably not introduced into the side wall of the reactor or bottom of the reactor. In another embodiment, both the feedstock stream and oxidant are introduced at the top ⅛ section of the gasifier, desirably at the top 1/12 of the gasifier height defined by the gasifier shell. Desirably, the oxidant and feedstock stream are fed co-currently to ensure good mixing. In this regard, a co-current feed means that the axis of the feedstock and oxidant streams are substantially parallel (e.g. not more than a 25° deviation, or not more than a 20°, or not more than a 15°, or not more than a 10°, or not more than a 8°, or not more than a 6°, or not more than a 4°, or not more than a 2°, or not more than a 1° deviation from each other) and in the same direction.
The feedstock and oxidant streams are desirably introduced into the gasification zone through one or more injector nozzles. Desirably, the gasifier is equipped with at least one of the injector nozzles in which through that injector nozzle both a feedstock stream and an oxidant stream are introduced into the gasification zone.
While the feedstock stream can be a dry feed or a slurry feed, the feedstock stream is desirably a slurry. The syngas produced in the gasification process is desirably used at least in part for making chemicals. Many synthesis processes for making chemicals are at high pressure, and to avoid energy input into pressurizing the syngas stream, desirably the gasifier is also run at high pressure, particularly when the syngas stream is directly or indirectly in gaseous communication with a vessel in which a chemical is synthesized. Dry feeds to a gasifier operating at high pressure are specially treated to ensure that the feed can be effectively blown and injected into the high-pressure gasification zone. Some techniques include entraining a flow of nitrogen at high pressure and velocity, which tends to dilute the syngas stream and reduce the concentration of desirably components such as carbon monoxide and hydrogen. Other carrier or motive gases include carbon monoxide, but like nitrogen, these gases are compressed before feeding into or compressed with the solid fossil fuels, adding to the energy requirements and capital cost of feed lock hoppers and/or compressing equipment. To deal with these issues, many dry feed gasifiers will operate at lower pressures, which for the mere production of electricity is sufficient, but is undesirable for gasifiers producing a syngas stream for making chemicals. With a slurry feed, a motive gas is not necessary and can readily be fed to a high-pressure gasifier that produces syngas as high pressure, which is desirable for making chemicals. In one embodiment, the feedstock stream is not processed through a lock hopper prior to entering an injector or entering the gasification zone. In another embodiment, the feedstock composition containing ground tires and solid fossil fuel is not pressurized in a lock hopper.
Desirably, the gasifier is non-catalytic, meaning that gasifier does not contain a catalyst bed, and desirably the gasification process is non-catalytic, meaning that a catalyst is not introduced into the gasification zone as a discrete unbound catalyst (as opposed to captive metals in the tires or solid fossil fuel that can incidentally have catalytic activity). The gasification process in the reaction zone is desirably conducted in the absence of added catalysts and contains no catalyst bed. The gasification process is also desirably a slagging gasification process; that is, operated under slagging conditions (well above the fusion temperature of ash) such that a molten slag is formed in the gasification zone and runs along and down the refractory walls.
In another embodiment, the gasifier is not designed to contain a pyrolysis zone. Desirably, the gasifier is not designed to contain a combustion zone. Most preferably, the gasifier is designed to not contain, or does not contain, either a combustion zone or a pyrolysis zone. The pyrolysis zone incompletely consumes the fuel source leading to potentially high amounts of ash, char, and tarry products. A combustion zone, while absent in tars, produces high amounts of CO2 and lower amounts of the more desirably carbon monoxide and hydrogen. Desirably, the gasifier is a single stage reactor, meaning that there is only one zone for conversion of the carbon in the feedstock to gases within the gasifier shell.
The gasification zone is void or empty space defined by walls in which oxidation reactions occur and allow gases to form within the space. Desirably, gasification zone does not have a bath of molten material or molten material that accumulates at the bottom of the gasification zone to form a bath. The gasification zone is desirably not enclosed on the bottom but rather is in gaseous communication with other zones below the gasification zone. Slag, while molten, does not accumulate at the bottom of the gasification zone but rather runs down the sides of the refractory and into a zone below the gasification zone, such as a quench zone to solidify the slag.
The flow of hot raw syngas in the gasifier desirably is vertically downward, or a down-flow reactor. Desirably, the flow of syngas generated in the gasifier is downward from the highest point of injecting the feedstock stream, desirably from the point of all feedstock stream locations. In another embodiment, the location for withdrawing the syngas stream from the gasifier is lower that at least one location for introducing the feedstock stream, desirably lower than all locations for introducing a feedstock stream.
The gasifier desirably contains refractory lining in the gasification zone. While a steam generating membrane or jacket between the gasifier wall and the surfaces facing the gasification zone can be employed, desirably the gasifier does not contain a membrane wall, or a steam generating membrane, or a steam jacket in the gasification zone or between inner surfaces facing the gasification zone and the gasifier shell walls as this removes heat from the gasification zone. Desirably, the gasification zone is lined with refractory, and optionally there is no air or steam or water jacket between the refractory lining the gasification zone (or optionally in any reaction zone such as combustion or pyrolysis) and the outer shell of the gasifier.
The gasification process is desirably a continuous process meaning that the gasifier operates in a continuous mode. The inclusion of pre-granulated tires into the feedstock stream can be intermittent or continuous provided that a continuous feed of fossil fuel is fed to the gasifier since the gasification process in the gasifier is in a continuous mode. By a continuous mode for gasifier operation is meant that the gasification process is continuous for at least 1 month, or at least 6 months, or at least 1 year. Desirably, the inclusion of granulated tires in the feedstock stream is continuous for at least 1 day, or at least 3 days, or at least 14 days, or at least 1 month, or at least 6 months, or at least 1 year. A process is deemed continuous despite shut-downs due to maintenance or repair.
The feedstock can be fed into the gasification zone through one or more injectors. In one embodiment, the gasifier contains only one injector. In another embodiment, the gasifier contains only one location for introducing feedstock. Typically, the injector nozzle serving the gasification chamber is configured to have the feedstock stream concentrically surround the oxidizer gas stream along the axial core of the nozzle. Optionally, the oxidizer gas stream can also surround the feedstock stream annulus as a larger, substantially concentric annulus. Radially surrounding an outer wall of the outer oxidizer gas channel can be an annular cooling water jacket terminated with a substantially flat end-face heat sink aligned in a plane substantially perpendicular to the nozzle discharge axis. Cool water is conducted from outside the combustion chamber into direct contact with the backside of the heat sink end-face for conductive heat extraction.
The reaction between the hydrocarbon and oxygen should take place entirely outside the injector proper to prevent localized concentration of combustible mixtures at or near the surfaces of the injector elements.
The gasification zone, and optionally all reaction zones in the gasifier are operated at a temperature in the range of at least 1000° C., or at least 1100° C., or at least 1200° C., or at least 1250° C., or at least 1300° C., and up to about 2500° C., or up to 2000° C., or up to 1800° C., or up to 1600° C., each of which are well above the fusion temperature of ash and are desirably operated to form a molten slag in the reaction zone. In one embodiment, the reaction temperature is desirably autogenous. Advantageously, the gasifier operating in steady state mode is at an autogenous temperature and does not require application of external energy sources to heat the gasification zone.
In one embodiment, the gasifier does not contain a zone within the gasifier shell to dry feedstock such as the coal, pet-coke, or tires prior to gasification. The increase in temperature within the injector is not considered a zone for drying.
Desirably, the gasification zone is not under negative pressure during operations, but rather is under positive pressure during operation. The gasification zone is desirably not equipped with any aspirator or other device to create a negative pressure under steady state operation.
The gasifier is operated at a pressure within the gasification zone (or combustion chamber) of at least 200 psig (1.38 MPa), or at least 300 psig (2.06 MPa), or at least 350 psig (2.41 MPa), and desirably at least 400 psig (2.76 MPa), or at least 420 psig (2.89 MPa), or at least 450 psig (3.10 MPa), or at least 475 psig (3.27 MPa), or at least 500 psig (3.44 MPa), or at least 550 psig (3.79 MPa), or at least 600 psig (4.13 MPa), or at least 650 psig (4.48 MPa), or at least 700 psig (4.82 MPa), or at least 750 psig (5.17 MPa), or at least 800 psig (5.51 MPa), or at least 900 psig (6.2 MPa), or at least 1000 psig (6.89 MPa), or at least 1100 psig (7.58 MPa), or at least 1200 psig (8.2 MPa). The particular operating pressure on the high end is regulated with a variety of considerations, including operating efficiency, the operating pressures needed in chemical synthesis reactors particularly with integrated plants, and process chemistry. Suitable operating pressures in the gasification zone on the high end need not exceed 1300 psig (8.96 MPa), or need not exceed 1250 psig (8.61 MPa), or need not exceed 1200 psig (8.27 MPa), or need not exceed 1150 psig (7.92 MPa), or need not exceed 1100 psig (7.58 MPa), or need not exceed 1050 psig (7.23 MPa), or need not exceed 1000 psig (6.89 MPa), or need not exceed 900 psig (6.2 MPa), or need not exceed 800 psig (5.51 MPa), or need not exceed 750 psig (5.17 MPa). Examples of suitable desirably ranges include 400 to 1000, or 425 to 900, or 450 to 900, or 475 to 900, or 500 to 900, or 550 to 900, or 600 to 900, or 650 to 900, or 400 to 800, or 425 to 800, or 450 to 800, or 475 to 800, or 500 to 800, or 550 to 800, or 600 to 800, or 650 to 800, or 400 to 750, or 425 to 750, or 450 to 750, or 475 to 750, or 500 to 750, or 550 to 750, each in psig.
Desirably, the average residence time of gases in the gasifier reactor is desirably very short to increase throughput. Since the gasifier is desirably operated at high temperature and pressure, substantially complete conversion of the feedstock to gases can occur in a very short time frame. The average residence time of the gases in the gasifier can be as short as less than 30 seconds, or not more than 25 seconds, or not more than 20 seconds, or not more than 15 seconds, or not more than 10 seconds, or not more than 7 seconds. Desirably, the average residence time of gases in all zones designed for conversion of feedstock material to gases is also quite short, e.g. less than 25 seconds, or not more than 15 seconds, or not more than 10 seconds, or not more than 7 seconds, or not more than 4 seconds. In these time frames, at least 85 wt. %, or at least or more than 90 wt. %, or at least 92 wt. %, or at least 94 wt. % of the solids in the feedstock can be converted to gases (substances which remain as a gas if the gas stream were cooled to 25° C. and 1 atm) and liquid (substances which are in liquid state if the gas stream is cooled to 25° C. and 1 atm such as water), or more than 93 wt. %, or more than 95 wt. %, or more than 96 wt. %, or more than 97 wt. %, or more than 98 wt. %, or more than 99 wt. %, or more than 99.5 wt. %.
A portion of ash and/or char in the gasifier can be entrained in the hot raw syngas stream leaving the gasification reaction zone. Ash particles in the raw syngas stream within the gasifier are particles which have not reached the melting temperature of the mineral matter in the solid fuel. Slag is substantially molten ash or molten ash which has solidified into glassy particles and remains within the gasifier. Slag is molten until quenched and then form beads of fused mineral matter. Char are porous particles that are devolatilized and partially combusted (incompletely converted) fuel particles. The particulate matter gathered in the bottom part of the reactor, or the quench zone, are predominately slag (e.g. above 80 wt. % slag) and the remainder is char and ash. Desirably, only trace amounts of tar or no tar is present in the gasifier, or in the quench zone, or in the gasification zone, or present in the hot raw syngas within the gasifier, or present in the raw syngas discharged from the gasifier (which can be determined by the amount of tar condensing from the syngas stream when cooled to a temperature below 50° C.). Trace amounts are less than 0.1 wt. % (or less than 0.05 wt. % or less than 0.01 wt. %) of solids present in the gasifier, or less than 0.05 volume %, or not more than 0.01 vol %, or not more than 0.005 vol %, or not more than 0.001 volume %, or not more than 0.0005 vol %, or not more than 0.0001 vol % in the raw syngas stream discharged from the gasifier.
In another embodiment, the process does not increase the amount of tar to a substantial extent relative to the same process except replacing the tires with the same amount and type of solid fossil fuel used in the mixed feedstock composition.
The quantity of tar generated in the process with the mixed feedstock is less than 10% higher, or less than 5% higher, or less than 3% higher, or less than 2% higher, or not higher at all, than the amount of tar generated with the same feedstock replacing the tires with the same solid fossil fuel under the same conditions.
To avoid fouling downstream equipment from the gasifier (scrubbers, CO/H2 shift reactors, acid gas removal, chemical synthesis), and the piping in-between, the syngas stream should have low or no tar content. The syngas stream as discharged from the gasifier desirably contains no or less than 4 wt. %, or less than 3 wt. %, or not more than 2 wt. %, or not more than 1 wt. %, or not more than 0.5 wt. %, or not more than 0.2 wt. %, or not more than 0.1 wt. %, or not more than 0.08 wt. %, or not more than 0.05 wt. %, or not more than 0.02 wt. %, or not more than 0.01 wt. %, or nor more than 0.005 wt. % tar, based on the weight of all condensable solids in the syngas stream. For purposes of measurement, condensable solids are those compounds and elements that condense at a temperature of 15° C./1 atm.
In another embodiment, the tar present, if at all, in the syngas stream discharged from the gasifier is less than 10 g/m3 of the syngas discharged, or not more than 9 g/m3, or not more than 8 g/m3, or not more than 7 g/m3,or not more than 6 g/m3, or not more than 5 g/m3, or not more than 4 g/m3, or not more than 3 g/m3, or not more than 2 g/m3, and desirably not more than 1 g/m3, or not more than 0.8 g/m3, or not more than 0.75 g/m3, or not more than 0.7 g/m3, or not more than 0.6 g/m3, or not more than 0.55 g/m3, or not more than 0.45 g/m3, or not more than 0.4 g/m3, or not more than 0.3 g/m3, or not more than 0.2 g/m3, or not more than 0.1 g/m3, or not more than 0.05 g/m3, or not more than 0.01 g/m3, or not more than 0.005 g/m3, or not more than 0.001 g/m3, or not more than 0.0005 g/m3, in each case Normal (15° C./1 atm). For purposes of measurement, the tars are those tars that would condense at a temperature of 15° C./1 atm, and includes primary, secondary and tertiary tars, and are aromatic organic compounds and other than ash, char, soot, or dust. Examples of tar products include naphthalenes, cresols, xylenols, anthracenes, phenanthrenes, phenols, benzene, toluene, pyridine, catechols, biphenyls, benzofurans, benzaldehydes, acenaphthylenes, fluorenes, naphthofurans, benzanthracenes, pyrenes, acephenanthrylenes, benzopyrenes, and other high molecular weight aromatic polynuclear compounds. The tar content can be determined by GC-MSD.
In another embodiment, the tar yield of the gasifier (combination of tar in syngas and tar in reactor bottoms and in or on the ash, char, and slag) is not more than 4 wt. %, or not more than 3 wt. %, or not more than 2.5 wt. %, or not more than 2.0 wt. %, or not more than 1.8 wt. %, or not more than 1.5 wt. %, or not more than 1.25 wt. %, or not more than 1 wt. %, or not more than 0.9 wt. %, or not more than 0.8 wt. %, or not more than 0.7 wt. %, or not more than 0.5 wt. %, or not more than 0.3 wt. %, or not more than 0.2 wt. %, or not more than 0.1 wt. %, or not more than 0.05 wt. %, or not more than 0.01 wt. %, or not more than 0.005 wt. %, or not more than 0.001 wt. %, or not more than 0.0005 wt. %, or not more than 0.0001 wt. %, based on the weight of solids in the feedstock stream fed to the gasification zone.
Because of the gasification technique employed, the amount of char generated by gasifying the tire-solid fossil fuel feedstock stream can remain within acceptable limits. For example, the amount of char (or incompletely converted carbon in the feedstock) generated by conversion of the carbon sources in the feedstock stream is not more than 15 wt. %, or not more than 12 wt. %, or not more than 10 wt. %, or not more than 8 wt. %, or not more than 5 wt. %, or not more than 4.5 wt. %, or not more than 4 wt. %, or not more than 3.5 wt. %, or not more than 3 wt. %, or not more than 2.8 wt. %, or not more than 2.5 wt. %, or not more than 2.3 wt. %, or not more than 4.5 wt. %, or not more than 4.5 wt. %, or not more than 4.5 wt. %.
In the process, char can be recycled back to the feedstock stream. In another embodiment, the efficiencies and features of the invention can be obtained without recycling char back to the gasification zone.
The total amount of char (or incompletely converted carbon in the feedstock) and slag generated in the gasifier or by the process is desirably not more than 20 wt. %, or not more than 17 wt. %, or not more than 15 wt. %, or not more than 13 wt. %, or not more than 10 wt. %, or not more than 9 wt. %, or not more than 8.9 wt. %, or not more than 8.5 wt. %, or not more than 8.3 wt. %, or not more than 8 wt. %, or not more than 7.9 wt. %, or not more than 7.5 wt. %, or not more than 7.3 wt. %, or not more than 7 wt. %, or not more than 6.9 wt. %, or not more than 6.5 wt. %, or not more than 6.3 wt. %, or not more than 6 wt. %, or not more than 5.9 wt. %, or not more than 5.5 wt. %, in each case based on the weight of the solids in the feedstock stream. In another embodiment, the same values apply with respect to the total amount of ash, slag, and char generated in the gasifier or by the process, based on the weight of the solids in the feedstock stream. In another embodiment, the same values apply with respect to the total amount of ash, slag, char and tar generated in the gasifier or by the process, based on the weight of the solids in the feedstock stream.
The raw syngas stream flows from the gasification zone to a quench zone at the bottom of the gasifier where the slag and raw syngas stream are cooled, generally to a temperature below 550° C., or below 500° C., or below 450° C. The quench zone contains water in a liquid state. The hot syngas from the gasification zone may be cooled by directly contacting the syngas stream with liquid water. The syngas stream can be bubbled through the pool of liquid water, or merely contact the surface of the water pool. In addition, the hot syngas stream may be cooled in a water jacketed chamber having a height that above the top surface of the water pool to allow the hot syngas to both contact the water pool and be cooled in the water jacketed chamber. Molten slag is solidified by the quench water and most of the ash, slag and char are transferred to the water in the quench tank. The partially cooled gas stream, having passed through the water in the quench zone, may be then discharged from the gasifier as a raw syngas stream and passed through a water scrubbing operation to remove any remaining entrained particulate matter.
The pressure in the quench zone is substantially the same as the pressure in the gasification zone located above the water level in the gasifier, and a portion of the quench water and solids at the bottom of the quench tank is removed by way of a lock hopper system. A stream of quench water carrying fine particles exits the gasifier quench zone in response to a liquid level controller and can be directed to a settler. The solids and water from the lock hopper may then flow into a water sump or settler where optionally the coarse particulate solids may be removed by screens or filter thereby producing a dispersion of fine particulate solids.
The raw gas stream discharged from the gasification vessel includes such gasses as hydrogen, carbon monoxide, carbon dioxide and can include other gases such as methane, hydrogen sulfide and nitrogen depending on the fuel source and reaction conditions. Carbon dioxide in the raw syngas stream discharged from the gasification vessel is desirably present in an amount of less than 20 mole %, or less than 18 mole %, or less than 15 mole %, or less than 13 mole %, or not more than 11 mole %, based on all moles of gases in the stream. Some nitrogen and argon can be present in the raw syngas stream depending upon the purity of the fuel and oxygen supplied to the process.
In one embodiment, the raw syngas stream (the stream discharged from the gasifier and before any further treatment by way of scrubbing, shift, or acid gas removal) can have the following composition in mole % on a dry basis and based on the moles of all gases (elements or compounds in gaseous state at 25° C. and 1 atm) in the raw syngas stream:
The gas components can be determined by FID-GC and TCD-GC or any other method recognized for analyzing the components of a gas stream.
The molar hydrogen/carbon monoxide ratio is desirably at least 0.65, or at least 0.68, or at least 0.7, or at least 0.73, or at least 0.75, or at least 0.78, or at least 0.8, or at least 0.85, or at least 0.88, or at least 0.9, or at least 0.93, or at least 0.95, or at least 0.98, or at least 1.
The total amount of hydrogen and carbon monoxide on a relative to the total amount of syngas discharged from the gasifier on a dry basis is high, on the order of greater than 70 mole %, or at least 73 mole %, or at least 75 mole %, or at least 77 mole %, or at least 79 mole %, or at least 80 mole %, based on the syngas discharged.
In another embodiment, the dry syngas production expressed as gas volume discharged from the gasifier per kg of solid fuel (e.g. tires and coal) charged to all locations on the gasifier is at least 1.7, or at least 1.75, or at least 1.8, or at least 1.85, or at least 1.87, or at least 1.9, or at least 1.95, or at least 1.97, or at least 2.0, in each case as N m3gas/kgsolids fed
The carbon conversion efficiency in one pass is good and can be calculated according to the following formula:
The carbon conversion efficiency in the process in one pass can be at least 70%, or at least 73%, or at least 75%, or at least 77%, or at least 80%, or at least 82%, or at least 85%, or at least 88%, or at least 90%, or at least 93%.
In another embodiment, the raw syngas stream contains particulate solids in an amount of greater than 0 wt. % up to 30 wt. %, or greater than 0 wt. % up to 10 wt. %, or greater than 0 wt. % up to 5 wt. %, or greater than 0 wt. % up to 1 wt. %, or greater than 0 wt. % up to 0.5 wt. %, or greater than 0 wt. % up to 0.3 wt. %, or greater than 0 wt. % up to 0.2 wt. %, or greater than 0 wt. % up to 0.1 wt. %, or greater than 0 wt. % up to 0.05 wt. %, each based on the weight of solids in the feedstock stream. The amount of particulate solids in this case is determined by cooling the syngas stream to a temperature of below 200° C., such as would occur in a scrubbing operation.
The cold gas efficiency of the process using the mixed tire/solid fossil fuel as a percent can be calculated as:
The cold gas efficiency is at least 60%, or at least 65%, or at least 66%, or at least 67%, or at least 68%, or at least 69%, or desirably at least 70%, or at least 71%, or at least 72%, or at least 73%, or at least 74%, or at least 75%, or at least 76%, or at least 77%, or at least 78%, or at least 79%.
In one embodiment, hydrogen and carbon monoxide from the raw syngas stream discharged from the gasifier or from a scrubbed or purified syngas stream are not recycled or recirculated back to a gasification zone in a gasifier. Desirably, carbon dioxide from the raw syngas stream discharged from the gasifier or from a scrubbed or purified syngas stream is not recycled or recirculated back to a gasification zone in a gasifier. Desirably, no portion of the syngas stream discharged from the gasifier or from a scrubbed or purified syngas stream is recycled or recirculated back to a gasification zone in a gasifier. In another embodiment, no portion of the syngas discharged from the gasifier is used to heat the gasifier. Desirably, no portion of the syngas made in the gasifier is burned to dry the solid fossil fuel.
The feedstock stream is gasified with the oxidizer such as oxygen desirably in an entrained flow reaction zone under conditions sufficient to generate a molten slag and ash. The molten slag and ash are separated from the syngas and quench cooled and solidified. In a partial oxidation reactor, the coal/rubber tire/water mixture is injected with oxygen and the coal/rubber will react with oxygen to generate a variety of gases, including carbon monoxide and hydrogen (syngas). The molten slag and unreacted carbon/rubber tires accumulate into a pool of water in the quench zone at the bottom part of the reactor to cool and solidify these residues.
In one embodiment, the slag discharged from the gasifier as a solid. Slag is cooled and solidified within the gasifier in a quench zone within the shell of the gasifier, and is discharged from the gasifier shell as a solid. The same applies to ash and char. These solids discharged from the gasifier are accumulated into a lock hopper which can then be emptied. The lock hopper is generally isolated from the gasifier and the quench zone within the gasifier.
The process can be practiced on an industrial scale and on a scale sufficient to provide syngas as a raw material to make chemicals on an industrial scale. At least 300 tons/day, or at least 500 t/d, or at least 750 t/d, or at least 850 t/d, or at least 1000 t/d, or at least 1250 t/d, and desirably at least 1500 t/d, or at least 1750 t/d, or even at least 2000 t/d of solids can be fed to the gasifier. The gasifier is desirably not designed to be mobile and is fixed to the ground, and desirably stationary during operations.
The syngas compositional variability produced by gasifying the feedstock containing the solid fossil fuel and tires is quite low over time. In one embodiment, the compositional variability of the syngas stream is low during a time period when the feedstock stream contains the solid fossil fuel and the pre-ground tires. The compositional variability of the syngas stream can be determined by taking at least 6 measurements of the concentration of the relevant gaseous compound in moles in equal time sub-periods across the entire time that the feedstock solids content is consistent and contain tires, such entire time not to exceed 12 days. The mean concentration of the gaseous compound is determined over the 6 measurements. The absolute value of the difference between the number farthest away from the mean and the mean number is determined and divided into the mean number×100 to obtain a percent compositional variability.
The compositional variability of any one of:
In another embodiment, variability of the syngas stream generated by the mixed feedstock containing tires (“mixed case”) is compared to the benchmark variability of the syngas stream generated from the same feedstock without the tires and its amount replaced by a corresponding amount of the same fossil fuel (“solid fossil fuel only case”) and processed under the same conditions to obtain a % switching variability, or in other words, the syngas variability generated by switching between the two feedstock compositions. The variation of the mixed case can be less than, or no different than, or if higher can be similar to the variation of the solid fossil fuel only case. The time periods to determine variations is set by the shorter of a 12-day period or the time that tires are present in the feedstock composition, and that time period is the same time period used for taking measurements in the solid fossil fuels only case. The measurements for the solid fossil fuels only case are taken within 1 month before feeding a feedstock containing tires to the gasifier or after the expiration of feeding a feedstock containing tires to the gasifier. The variations in syngas composition made by each of the streams is measured according to the procedures states above. The syngas mixed case variability is less than, or the same as, or not more than 15%, or not more than 10%, or not more than 5%, or not more than 4%, or not more than 3%, or not more than 2%, or not more than 1%, or not more than 0.5%, or not more than 0.25% of the syngas solid fossil fuel only case. This can be calculated as:
where % SW is percent syngas switching variability on one or more measured ingredients in the syngas composition; and
Vm is the syngas compositional variability using the mixed stream containing post-consumer tires and the fossil fuel; and
Vff is the syngas compositional variability using the fossil fuel only stream, where the solids concentration is the same in both cases, the fossil fuel is the same in both cases, and the feedstocks are gasified under the same conditions, other than temperature fluctuations which may autogeneously differ as a result of having tires in the feedstock, and the variabilities are with respect to any one or more of the syngas compounds identified above. In the event that the % SV is negative, then the syngas mixed case variability is less than the syngas solid fossil fuel only case.
In another embodiment, there is provided a continuous process for feeding a gasifier with a continuous feedstock composition containing solid fossil fuel and intermittently feeding a feedstock composition containing post-consumer tires and solid fossil fuel, while maintaining a negative, zero, or minimal syngas compositional switching variability over time frames that includes feedstocks with and without the post-consumer waste material using syngas produced using feedstocks without the post-consumer waste material as the benchmark. For example, switching frequency between feedstocks without the post-consumer tires (FF only) and the identical feedstocks except replacing a portion of the solids with the post-consumer tires (Mixed) can be at least 52×/yr, or at least 48×/yr, or at least 36×/yr, or at least 24×/yr, or at least 12×/yr, or at least 6×/yr, or at least 4×/yr, or at least 2×/yr, or at least 1×/yr, or at least 1×/2yr, and up to 3×/2yr, without incurring a syngas switching variability beyond the percentages express above. One switch is counted as the number of times in a period that the Mixed feedstock is used.
To illustrate an example of the overall process, reference made to
The grinder can also be equipped with a classifier to remove particles above the target maximum particle size. An example of a classifier is a vibrating sieve or a weir spiral classifier.
The coal grinder zone (which includes at least the grinding equipment, feed mechanisms to the grinder, and any classifiers) is a convenient location for combining pre-ground rubber tire particles through line 4 to the coal. The desired amount of coal and tires can be combined onto a weigh belt or separately fed though their dedicated weigh belts that feed the grinding apparatus. The water slurry of ground coal and rubber tires is discharged through line 5 and pumped into a storage/charge tank 6 that is desirably agitated to retain a uniform slurry suspension. Alternatively, or in addition to the grinder 2 location, pre-ground rubber tires can be added into the charge/storage tank 6 through line 7, particularly when this tank is agitated.
The feedstock stream is discharged from tank 6 directly or indirectly to the gasifier 9 through line 8 into the injector 10 in which the coal/rubber/water slurry is co-injected with an oxygen-rich gas from line 11 into the gasification reaction zone 12 where combustion takes place. The injector 10 may optionally be cooled with a water line 13 feeding a jacket on the injector and discharged through line 14. After start-up and in a steady state, the reaction in the reaction zone 12 takes place spontaneously at an autogenous temperature in the ranges noted above, e.g. 1200° C. to 1600° C. and at a pressure in the ranges note above, e.g. 10-100 atmospheres. The gaseous reaction products of the partial oxidation reaction include carbon monoxide, hydrogen, with lesser amounts of carbon dioxide and hydrogen sulfide. Molten ash, unconverted coal or rubber, and slag may also be present in the reaction zone 12.
The gasifier 9 is illustrated in more detail in
Turning back to
The temperature of the raw syngas stream exiting the gasification vessel through line 16 can be within a range of 150° C. to 700° C., or from 175° C. to 500° C. Desirably, the temperature of the raw syngas discharged from the gasifier is not more than 500° C., or less than 400° C., or not more than 390° C., or not more than 375° C., or not more than 350° C., or not more than 325° C., or not more than 310° C., or not more than 300° C., or not more than 295° C., or not more than 280° C., or not more than 270° C. The temperature of the raw syngas exiting the gasification vessel is substantially reduced from the temperature of the reaction product gases within the reaction zone. The temperature reduction between the gasification zone gas temperature (or alternatively all reaction zones if more than one stage is used) and the raw syngas temperature discharged from the gasifier vessel can be at least 300° C., or at least 400° C., or at least 450° C., or at least 500° C., or at least 550° C., or at least 600° C., or at least 650° C., or at least 700° C., or at least 800° C., or at least 900° C., or at least 1000° C., or at least 1050° C., or at least 1100° C.
As shown in
As shown in
Solids, including unconverted particulate coal, settle by gravity from the water in settling tank 24 and are drawn off through line 27 as a concentrated slurry of ash, unconverted coal and soot in water. This slurry may be optionally be recycled to grinding zone 2 via line 28. If desired, a portion of the slurry from line 27 may be diverted through line 29 into mix tank 6 to adjust the concentration of solids in the water-coal-rubber slurry feedstream charged to the gasifier. Also, as shown in
As shown in
Alternatively, or in addition, the quench water through line 33 feeding the quench water zone can supplied from a syngas scrubber downstream from the gasifier as shown in
If desired, high temperature surfactants can be added to the quench water directly into the quench zone/chamber. Examples of such surfactants include any one of the surfactants mentioned above to stabilize the feedstock stream, such as ammonium lignosulfonate or an equivalent surfactant which is thermally stable at temperatures of about 300° F. to about 600° F. Other surfactants include organic phosphates, sulfonates and amine surfactants. The surfactants are used to establish a stable suspension of soot in the water at the bottom of the quench chamber, where the soot concentration can be at least 1 wt. %, or in the range of about 3.0 weight % to about 15.0 weight %, each based on the weight of the water in the quench chamber. The concentration of active surfactants in the bottom of the quench zone can vary from about 0.01 weight % to about 0.30 weight %.
Also, as illustrated in
As shown in
In an alternative embodiment as shown in
In an alternate embodiment, as shown in
To illustrate one embodiment of an injector, reference is made to
A more detailed view of the injector is shown in
The internal nozzle shell 111 and intermediate nozzle shell 113 can both be axially adjustable relative to the outer nozzle shell 115 for the purpose flow capacity variation. As intermediate nozzle 113 is axially displaced from the conically tapered internal surface of outer nozzle 115, the outer discharge annulus 116 is enlarged to permit a greater oxygen gas flow. Similarly, as the outer tapered surface of the internal nozzle 111 is axially drawn toward the internally conical surface of the intermediate nozzle 113, the feedstock slurry discharge area 114 is reduced.
Surrounding the outer nozzle shell 115 is a coolant fluid jacket 110 having an annular end closure 119. A coolant fluid conduit 120 delivers a coolant, such as water, from the upper assembly supply port 100 in
The planar end of the cooling jacket 119 includes an annular surface 123 which is disposed facing the combustion chamber. Typically, the annular surface 123 of cooling jacket is composed of cobalt base metal alloy materials. Although cobalt is the preferred material of construction for the nozzle assembly 125, other high temperature melting point alloys, such as molybdenum or tantalum may also be used. The heat shield 124 is formed from a high temperature melting point material such as silicon nitride, silicon carbide, zirconia, molybdenum, tungsten or tantalum.
While this discussion was based on a injector and feed stream arrangement as previously described, it is understood that the injector may consist of only two passages for introducing and injecting the oxidant and feedstock stream, and they may be in any order with the feedstock stream passing through the central axial bore opening while the feedstock is fed through an annulus surrounding at least a portion of the central oxidant conduit, or the order may be reversed as described above.
An example of the operation of the gasifier and scrubber is illustrated in
The resulting mixture of gas and water formed in contactor 55 is directed into scrubber 59 through a dip leg 60 which extends downwardly into the lower portion of scrubber 59. The gas stream from contactor 55 also carries entrained solid particles of unconsumed fuel or ash. A body of water is maintained in the scrubber 59, the level of which may be controlled in any suitable manner, for example by means of a liquid level controller 61, shown diagrammatically. The dip leg 60 discharges the mixture of water and gas below the level of water contained in the scrubber 59. By discharging the mixture of gas and water through the open end of dip leg 60 into intimate contact with water, solid particles from the gas stream are trapped in the water.
Scrubber 59 is suitably in the form of a tower having an optionally packed section 62 above the point of entry of the gas stream from contactor 55. Water from line 63 is introduced into scrubber 59 above the level of the packing material 62. In packed section 62, the gas stream is intimately contacted with water in the presence of suitable packing material, such as ceramic shapes, effecting substantially complete removal of solid particles from the gas stream. Product gas, comprising carbon monoxide and hydrogen and containing water vapor, atmospheric gases, and carbon dioxide, is discharged from the upper end of scrubber 59 through line 64 at a temperature corresponding to the equilibrium vaporization temperature of water at the pressure existing in scrubber 59. Clean syngas from line 64 may be further processed, for example, for the production of higher concentrations of hydrogen by water-gas shift reaction and suitable downstream purification to remove sulfur.
Water from the lower portion of scrubber 59 is passed by pump 65 through line 56 to injectors 56 and 57. Clarified water from settler 66 also may be supplied to line 56 by pump 67 through line 68. Water is withdrawn from scrubber 59 by pump 69 and passed through valve 70 responsive to liquid level control 61 on the scrubber and passed into quench zone 71 via line 72 to control the liquid level in scrubber 59.
Any heavy solid particles removed from the gas stream in the dip leg 60 settling into water slurry are collected the water bath at the bottom of the scrubber 59 and discharged at the bottom leg 73 at periodic intervals through line 74 as controlled by valve 75.
Any suitable scrubber design can be used in the process. Other scrubber designs include a tray type contacting tower wherein the gases are counter currently contacted with water. Water is introduced into the scrubber at a point near the top of the tower.
In another embodiment, the type and quantity of fuel feeds, and the gasification process is desirably operated in a manner that gaseous products generated through co-gasification with post-consumer tires do not exceed existing environmental air permits. This can be accomplished by operating the gasification process at high temperatures (e.g. greater than 1100° C., or greater than 1200° C.) and at high pressures (e.g. greater than 40 bar, or greater than 50 bar) in a slagging environment. Desirably, the quantity of post-consumer tires employed in the feedstock is any one or more of the quantities already mentioned. Accordingly, the gasification process employing post-consumer tires as a feedstock material can be operated in a manner that does not require applying for or obtaining additional environmental air permits, or additional exceptions to existing environmental air permits, for the gaseous products produced from gasification. Desirably, the operating rate of the gasifier also remains within limits defined in any existing permit, including operating or any other environmental permits.
In one embodiment, the total sulfur content in the raw syngas stream discharged from the gasifier is 0.015 to 3.0, or 0.02 to 2, or 0.05 to 1.5, or 0.1 to 1, each in mole % based on total moles of the gases in the raw syngas stream. In another embodiment, the H2S content in the raw syngas stream discharged from the gasifier can be 0.01 to 2.0, or 0.05 to 1.5, or 0.1 to 1, or 0.1 to 0.5, each in mole % based on total moles of gases in the raw syngas stream. In another embodiment, the total sulfur content of the raw syngas stream discharged from the gasifier is within the limits established by an existing air permit on the gasifier.
In another embodiment, one or more of the gaseous compounds can be sold within the limits of the existing environmental permits or exceptions thereto. For example, gaseous sulfur compounds can be recovered as solid sulfur and sold within the existing permitted limits or exceptions thereto as such or converted to derivates of sulfur such as sulfuric acid.
Ground post-consumer rubber tires are milled to a nominal particle size between 1 mm and 0.5 mm. Coal is dried and crushed in a Retsch jaw crusher to a nominal size of <2 mm. A predetermined amount of water is added to a 4.5 L metal bucket. Ammonium lignosulfonate is added to the water in the metal bucket and mixed with a spatula until it is distributed evenly. Ground tires and coal are added to the water and ALS mixture in the metal bucket and then the blend is mixed by an overhead mixer. Aqueous ammonia is added to the slurry to adjust the pH to 8±0.2. After being well mixed, the sample is placed in the laboratory rod mill equipped with 5 stainless steel rods at ½″×9″, 8 rods at ⅝″×9″, 8 rods at ¾″×9″, 2 rods at 1″×9″, and 1 rod at 1 ¼″×9″. The slurry is milled for 1 hour at approximately 28 rpm (mill outside diameter=11.75 inches). The aqueous ammonia is again used to adjust the pH to 8±0.2 while the slurry is mixed by the overhead mixer. Each batch of slurry is made to be a total of approximately 3000 grams with approximately 69% solids with varying amounts of recycled materials as reported in Table 1 below. Viscosity and stability tests are conducted with the results listed in Table 1.
500-550 g samples of coal slurry are transferred to a 600 mL glass beaker to measure the viscosity and stability. The stability of each sample can be judged by visual observation. The slurry is well mixed to generate a homogeneous distribution of particles throughout the sample and letting the slurry sit undisturbed for a period of time. The slurry is then remixed. If a layer of particles separated out at the bottom of the beaker, the slurry will be difficult to remix, and it is then considered to have settled. Over a period of time, the slurries will have settling. However, the longer the amount of time required to settle determines whether the stability of the slurry is considered good, moderate, or poor. If the slurry settles before 5 minutes, it is considered poor.
In an alternative method, the stability of the slurry can be determined quantitively. The viscosities of the slurry samples are measured at room temperature using either a Brookfield viscometer with an LV-2 spindle rotating at a rate of 0.5 rpm (method A) or a Brookfield R/S rheometer with V80-40 vane spindle operating at a shear rate of 1.83/s (method B). An average of 3 viscosity measurements is reported.
The stability is measured, by either Method A or Method B, by submerging the spindle of the rheometer into the slurry at the bottom of the beaker after the slurry is well mixed to form a homogeneous distribution of solids. After a designated period of time, the viscosity is measured with the spindle at the bottom of the beaker. The viscosity increases with settling and the slurry is considered to have settled if the initial reading on starting a viscosity measurement is 100,000 cP. Thus, slurries are considered stable if the initial viscosity is 100,000 cP or less after standing still for 5 minutes.
The pumpability of a slurry is measured by Method A or Method B. The slurry is considered pumpable if the viscosity reading is 30,000 cP or less (desirably 25,000 or less or better is 20,000 or less) when taking a reading immediately after well mixing the slurry to form a homogeneous distribution of solids.
The results of stability are determined by visual observation, and the results of pumpability are reported in Table 1 in the viscosity column using Method A. Stability is determined at the 5-minute mark.
aMeasured by method A.
All mixtures show moderate to good stability, but the viscosity of the slurry at 18.6% rubber is nearly at the maximum value that can be reliably pumped into the gasifier. The viscosity of the slurry at 36.2% rubber is too high and would not be pumpable at 69% solids loading. The 18.6% slurry would be usable, more preferably at a slightly lower total solids loading. Loadings of 15% and below are acceptable for normal production uses. 100% is not stable (settled) and is very low total solids.
Batches of the coal/tire slurry are prepared as stated in Example 1 and in the amounts reported in Table 2. The results of stability and pumpability are reported below in Table 2 using Method B in each case. A report of “stable” in the stability column indicates a viscosity reading of less than 100,000 cP at the time period stated.
0%
All samples remained stable at 5 and 10 minutes. However, at a 20% of solids loading, the tires sample would be considered too viscous to be effectively pumpable.
Elemental analysis of the pre-ground tires is conducted, and the results are reported in Tables 3 and 4 below:
aBy CHN elemental analyzer
bBy Uniquant x-ray analysis
cBy difference
aCalculated from uniquant x-ray analysis of tires.
This application claims the benefit of U.S. Provisional Application No. 62/800,751 filed on Feb. 4, 2019; of which the entire contents are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62800751 | Feb 2019 | US |
