Method for syngas scrubbing and soot recovery

Abstract

A method for removing impurities from black water associated with a gasifier includes adding a flocculant to the black water to produce a black water and flocculant mixture; settling the black water and flocculant mixture in a gravity settler to separate the black water and flocculant mixture into clear water, a foam phase and a heavy phase, wherein the foam phase comprises soot, water, and air or gas, and the heavy phase comprises soot and water; removing clear water from the settled black water and flocculant mixture; collecting a thin slurry comprising the foam phase and the heavy phase; and phase separating the thin slurry in a high speed centrifuge to provide additional clear water and a thick slurry, wherein the black water is obtained from wet gas scrubbing of syngas.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 313,800, filed February 25, 2022, which is incorporated by reference herein in its entirety for all purposes.

[0002] Field The present technology relates to the removal and recovery of particulate impurities, such as soot, and removal of gaseous contaminants, such as halogenated acids, ammonia, and volatile heavy metals, from synthesis gas ("syngas") produced by a gasification reactor or gasifier, preferably a fixed-bed slagging countercurrent oxygen gasifier; compositions produced therefrom; and processes including same. The present technology also relates to the recovery of soot and other particulate impurities collected in wet gas scrubbing water in a form suitable for recycle to the gasifier, and to the recovery of clarified water of suitable quality for reuse in wet gas scrubbing. [Background technology]

[0003] background The adoption of gasifiers for heterogeneous waste has been hindered by significant limitations. Also, while the particulate carbonaceous by-products from clean wood gasifiers can be applied to land, this is not the case for heterogeneous waste or treated waste wood, which are classified as hazardous waste. There remains a great need for processes to remove particulate impurities, including carbonaceous and inorganic compounds such as soot, from syngas and / or scrubber water, such as those produced by gasification processes treating heterogeneous waste streams. There is also a need to remove a number of gaseous pollutants, depending on the composition of the heterogeneous feedstock. Summary of the Invention

[0004] overview In one aspect, a process is provided herein for effectively removing soot from syngas. In one embodiment, soot is removed from syngas to a level that makes the purified syngas, i.e., the soot-removed syngas, suitable for downstream conversion processes. Some end products that can be obtained from these conversion processes include, but are not limited to, hydrogen (H2), synthetic natural gas (CH4), methanol (CH3OH), ammonia (NH3), liquid fuels, and gaseous feedstocks for microbial fermentation to produce feed proteins, biodegradable polymers, or alcohol.

[0005] In another aspect, provided herein is a process for effectively removing soot from syngas wet scrubber water to a level suitable for recycling purified scrubber water, i.e., soot-removed scrubber water, and / or recovering soot from the scrubber water in a form suitable for recycling to the gasifier.

[0006] As used herein, "effectively remove" refers to removing an amount, e.g., an amount of soot, from other components, such as syngas or wet scrubber water, such that the purified syngas or water is suitable for a desired purpose. As used herein, "purified" refers to a component, such as syngas, water, such as wet scrubber water, or a mixture thereof, from which the soot has been effectively removed. As used herein, "removing" refers to removing at least a portion or more of the soot, such as removing a substantial amount of soot, substantially all of the soot, or virtually all of the soot.

[0007] In one embodiment, the synthesis gas is produced by a gasifier processing a heterogeneous waste stream. In one embodiment, the gasifier is a fixed bed gasifier. In another embodiment, the gasifier is an oxygen-blown gasifier. In another embodiment, the gasifier is a slagging gasifier.

[0008] In one embodiment, a process for removing soot from syngas is provided herein, which process comprises a dry separation process. Exemplary dry separation processes include, but are not limited to, settling chambers, cyclones, ceramic filters, fabric filters, candle filters, impingement plates, and electrostatic precipitators. In one embodiment, the dry separation process removes more than about 75%, preferably more than about 80%, and most preferably more than about 85% of the soot present in the pre-separation syngas, i.e., the syngas exiting the gasifier.

[0009] In one such embodiment, soot is removed from the syngas using a high temperature dry separation method. The soot collected by the described high temperature dry separation method can be recycled back to the gasifier with reduced contamination from condensable alkali salts such as K2O, KCl, Na2O, and NaCl. In one embodiment, due to the high carbon content of the collected soot, the soot can be mixed with the heterogeneous gasifier feedstock which increases the overall efficiency of the gasification process. Examples of exemplary blenders useful for mixing include, but are not limited to, ribbon blenders, pug mills, kneaders, or tumble blenders. In another embodiment, the soot can be pneumatically injected into the gasifier using a suitable lance or nozzle.

[0010] In another embodiment, provided herein is a process for removing soot remaining in semi-purified syngas as obtained after dry separation, including wet syngas scrubbing. When a dry sorbent scrubbing process is used to remove acid gases from a syngas stream, the wet scrubbing process also removes the spent sorbent from the gas by dissolving it in water. For example, the syngas can be contacted (e.g., passed through or exposed to) a dry sorbent, which can neutralize halogenated acids remaining in the syngas, such as a syngas that has been separated from particulate soot (e.g., by a hot cyclone or other device). Exemplary wet syngas scrubbing methods include, but are not limited to, Venturi scrubbers, plates, scrubber towers with random or structured packaging, spray columns, and wet electrostatic precipitators. In one embodiment, the wet syngas scrubbing process removes residual soot to about 0.1 g / Nm of purified syngas. 3 Less than about 0.05 g / Nm 3 less than about 0.01 g / Nm 3 The dry sorbent is removed to less than 1000 ppm. When using a dry sorbent process to remove acid gases, the concentration of dissolved salts in the wet scrubber water can be reached at a steady state by "blowdown" of a known amount of water and addition of fresh water. In one embodiment, the blowdown water can then be sent to an evaporation pond, or, if water recovery is important, treated by processes such as, but not limited to, reverse osmosis or crystallization followed by filtration, and the resulting clean water can be recycled back to the wet scrubber. The spent dry sorbent can be removed by a dry particulate collector, which can operate above the dew point of the syngas (e.g., syngas separated from particulate soot, such as by a cyclone or other device).

[0011] The present technology is directed, in part, to a process for recovering clean water by separating soot present in dirty scrubber water, also commonly referred to as "black water." In one embodiment, the recovered clean water is recycled to the wet gas scrubbing process. In another embodiment, the separated soot is suitable for recycling to the gasifier.

[0012] In one embodiment, the process includes separating the black water by a gravity separator, thereby allowing the clean water to be separated from the soot as a clear interlayer. In one embodiment, the clean water is continuously removed and recycled as needed. In another embodiment, the process further includes recovering one or more of a heavy phase containing wet soot that settles to the bottom of the gravity separator, a foam phase ("foam") that floats to the surface and contains soot, water, and entrained gas, and any combination of these two phases. Exemplary gravity separators include, but are not limited to, gravity settling chambers, high efficiency inclined plate gravity settlers, and froth flotation tanks or columns. Without being bound by theory, it is believed that the high porosity, low particle density, and hydrophobicity of soot promotes flotation and the formation of a foam phase in the presence of entrained gas that preferentially adheres to the soot due to its poor wettability.

[0013] In another embodiment, the process further comprises mixing a surface-active chemical (or surface-active agent) with the black water prior to separation by the gravity separator. In one embodiment, the surface-active chemical or agent is a surfactant. In another embodiment, the surfactant is an anionic surfactant. Non-limiting examples of such surfactants include Niaproof08 and ColaWet DOSS75. In another embodiment, the surfactant is a non-ionic surfactant. Non-limiting examples of such surfactants include DOW Ecosurf EH3, DOW Tergitol L61, Synperonic NCA 810, and Synperonic NCA 8300. In another embodiment, the surfactant is a cationic surfactant. In another embodiment, the surfactant is added in a range of about 0.1% to about 3% vol% (vol / vol), such as about 0.2 vol%, about 0.3 vol%, about 0.5 vol%, about 0.75 vol%, about 1 vol%, or about 2 vol%.

[0014] In another embodiment, the process further comprises mixing a flocculant with the black water prior to separation by the gravity separator. In another embodiment, the flocculant is added in the range of 10-20 parts per million by volume (ppmv), such as about 10 ppmv, 15 ppmv, or 20 ppmv. In another embodiment, a combination of surface active chemicals and flocculants (collectively referred to as "chemical modifiers") are mixed with the black water prior to separation by the gravity separator. The addition of surface active chemicals allows for more effective and / or faster separation, resulting in reduced equipment costs and greater clarity of the recycled water.

[0015] In another embodiment, the process further includes collecting from the gravity separator a heavy phase from the bottom layer of the gravity separator, comprising soot and water, and an upper foam phase layer from the top layer of the gravity separator, comprising soot, water, and entrained air or gas, or any combination of the two. Combining the two streams produces a dilute slurry comprising soot, water, and entrained air. In certain embodiments, the collection is accomplished using one or more of a nozzle, a weir, a skimmer, and a pump. In one embodiment, the collected dilute slurry is continuously fed to a high-speed centrifuge. In certain embodiments, the centrifuge operates at a gravitational force or "g-force" of greater than about 6,000 to about 10,000 g-force. In certain embodiments, the high-speed centrifuge separates the dilute slurry into a thick slurry underflow (e.g., where the concentration of soot in the thick slurry is about 5 to 10 times higher than the concentration in the thin slurry feed) and clear water from an overflow port of the high-speed centrifuge. In one embodiment, the clear water is recycled as clean scrubber water. In one embodiment, the high speed centrifuge is a disk stack centrifuge. In another embodiment, the high speed centrifuge is a decanter centrifuge. In another embodiment, the disk stack centrifuge is followed by a decanter centrifuge which further dewaters the thick slurry collected by the disk stack centrifuge. In another embodiment, the black water from the wet scrubber is fed directly to the high speed centrifuge without prior treatment in a gravity separator.

[0016] In one embodiment, the only phase collected from the overflow port of the high speed centrifuge, i.e., clear water, is clean or substantially clean water that is completely, i.e., for all practical purposes, separated from soot. Entrained gas present in the foam phase from the gravity separator that forms part of the dilute slurry fed to the centrifuge is exhausted from the centrifuge. Surprisingly, it has been found that the foam phase is very persistent and difficult to separate in a high speed laboratory swing tube centrifuge, yet when processed in an industrial disc stack centrifuge, clean water is produced without any solids being carried over. Without wishing to be bound by theory, it is believed that the interaction of the soot and entrained air in the foam with the closely spaced separating discs of the centrifuge, typically spaced about 1-2 mm apart, results in effective degassing and wetting of the soot, which causes the foam to break down and the soot to flow into the thick slurry, releasing the trapped gas that is exhausted from the centrifuge.

[0017] In one embodiment, the thickened slurry recovered from the centrifuge is recycled directly to the gasifier and mixed with the heterogeneous waste prior to being fed to the gasifier. Exemplary blenders useful for mixing include, but are not limited to, ribbon blenders, pug mills, kneaders, or tumble blenders. In another embodiment, the thickened slurry recovered from the centrifuge is recycled to the gasifier using a slurry pump and injected into the gasifier using an appropriate lance or nozzle.

[0018] In another embodiment, the thickened slurry recovered from the centrifuge is further dewatered with a suitable dewatering device. Dewatering improves the energy efficiency of the gasifier by reducing the parasitic heat load required to heat and evaporate the additional water present in the thickened slurry. Exemplary dewatering devices include, but are not limited to, rotary vacuum filters, vacuum belt filters, candle filters, filter presses, decanter centrifuges, or thermal dryers. In one embodiment, the thickened slurry is mixed with the heterogeneous waste and co-processed in a waste feed dryer before being fed to the gasifier. In another embodiment, the thickened slurry is dried separately using a dedicated dryer, such as, but not limited to, a heated rotary drum dryer.

[0019] In another aspect, a method is provided for removing gaseous pollutants from syngas using a dry separation process. Dry gas scrubbing processes have distinct advantages over wet gas scrubbing because they avoid condensation conditions that increase corrosion when halogenated acids, particularly HCl, are present in the syngas. In another embodiment, HCl is removed by a combination of dry and wet gas scrubbing processes. HCl gas present in syngas can be removed by reacting the gas with solid sorbents such as alkali (Na, K) or alkaline earth (Ca) carbonates or oxides at moderate to high temperatures (200-850° C.). Examples of sorbents include, but are not limited to, sodium bicarbonate or minerals such as trona, nahcolite, shortite, or dawsonite.

[0020] In one embodiment, the sorbent is injected directly into the gas stream or reacted with the gas stream in a fluidized bed. This reaction produces salts that can then be removed using wet or dry separation methods, including but not limited to high temperature candle filters, baghouse filters, high temperature cyclone separators, Venturi scrubbers, plates, scrubber towers with random or structured packaging, spray columns, and wet electrostatic precipitators. The final concentration of HCl in the syngas is reduced to 5 ppm or less, preferably less than 1 ppm. In another embodiment, the syngas can be passed through a fixed bed of sorbent pellets, where the spent sorbent is removed and replaced with new sorbent, either continuously or as a batch process.

[0021] These and other embodiments may be applied to the general purpose of converting multiple different waste streams into clean syngas, with soot being separated from the syngas and recovered from the black water and recycled to the gasifier, while also recovering clarified water that is recycled and reused for wet gas scrubbing.

[0022] In another aspect, provided herein is a purified (also called clean) or semi-purified syngas composition. In another aspect, provided herein is a purified water, such as a scrubber water composition.

[0023] The clean syngas can be converted into multiple end products, including, but not limited to, hydrogen (H2), synthetic natural gas (CH4), methanol (CH3OH), ammonia (NH3), liquid fuels, and gaseous feedstock for microbial fermentation to produce feed proteins, biodegradable polymers, or alcohol. In another embodiment, a CO2 by-product having a purity of greater than about 95%, preferably greater than about 99.5%, is recovered from the purge gas or tail gas after converting the syngas into products.

[0024] The following disclosure provides, among other things, these and other aspects of the invention, as well as non-limiting examples of various embodiments of the invention. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a diagram of a dry gas scrubbing process in which soot produced in the gasifier and spent sorbent in solid form are removed from the gas stream using a dry separation method. [Diagram 2] FIG. 1 is a diagram of a process flowsheet including a venturi scrubber and a packed bed scrubber tower used in wet syngas scrubbing. [Diagram 3] FIG. 1 is a process flowsheet including a venturi scrubber and a packed bed scrubber in combination with a settling tank and a centrifuge to recover soot, according to various embodiments. [Figure 4] Applicable to various examples, photograph of a graduated cylinder after 5 minutes of gravity separation of soot from wet gas scrubber water. [Diagram 5] 3A-3C are photographs of a dilute slurry fed into a disc stack centrifuge and clear water resulting from the disc stack centrifuge used for soot separation, according to various embodiments. [Figure 6] 3 is a photograph of the Venturi scrubber tank from the flowsheet shown in FIG. 2 showing a thick layer of foam containing soot, water, and entrained gases. [Figure 7] 4 is a photograph of the Venturi scrubber tank from the flowsheet shown in FIG. 3 showing effective removal of bubbles when incorporating a settling tank and centrifuge to remove soot, according to various embodiments. [Figure 8] 1 is a photograph showing the effect of several different Baker Hughes flocculants selected to improve gravity solids separation of soot and promote their distribution into the foam phase, according to various embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Detailed Description In this specification and the claims that follow, reference will be made to a number of terms that have the following meanings. It should be noted that the specific embodiments are not intended as exhaustive descriptions or as limitations to the broader aspects discussed herein. An aspect described in conjunction with a specific embodiment is not necessarily limited to that embodiment and can be implemented in any other embodiment(s).

[0027] The terms "approximately," "about," "substantially," and similar terms used in connection with numerical ranges herein will be understood by those of ordinary skill in the art and will vary to some extent depending on the context in which they are used. Where there is a use of a term that is not clear to a person of ordinary skill in the art given the context in which it is used, the term will be plus or minus 10% of the disclosed value. When "approximately," "about," "substantially," and similar terms are applied to structural features (e.g., to describe its shape, size, orientation, direction, etc.), these terms are intended to cover slight variations in the structure that may result, for example, from the manufacturing or assembly process, and are intended to have a broad meaning consistent with common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. Thus, these terms should be interpreted as indicating that non-substantial or insignificant modifications or variations of the described and claimed subject matter are considered to be within the scope of the disclosure set forth in the appended claims.

[0028] Use of the terms "a," "an," "the," and similar referents in the context of describing elements (particularly in the context of the appended claims) should be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values ​​herein is merely intended to serve as a shorthand method of referring individually to each individual value falling within the range, unless otherwise indicated herein, and each individual value is incorporated into the specification as if it were individually set forth herein. All methods described herein can be performed in any suitable order, unless otherwise indicated herein or clearly contradicted by context. The use of any examples or exemplary language (e.g., "etc.") provided herein is merely for the purpose of better understanding the embodiments and does not limit the scope of the claims, unless otherwise stated. No language in the specification should be construed as indicating any non-claimed element as required.

[0029] "Black water" refers to wastewater resulting from wet syngas scrubbing unit operations specifically designed to remove particulate solids, including, but not limited to, Venturi scrubbers, tower scrubbers, and wet electrostatic precipitators. The solids-laden dirty scrubber water resulting from these unit operations is typically deep black in color due to the presence of suspended soot particles.

[0030] "Chemical Modifiers" refers collectively to any combination of surfactants and / or flocculants selected for the purpose of improving the performance (i.e., increasing the rate and / or quality) of unit operations used to separate particulate solids from black water. These unit operations include, but are not limited to, gravity separation, centrifugation, filtration, and flotation processes.

[0031] "Thick Slurry" refers to the underflow collected by high speed centrifuges that process dilute slurries. Thick slurries contain wet soot and water and essentially no entrained air or gas. The soot in a thick slurry is typically about 5 to 10 times more concentrated than the soot present in the dilute slurry.

[0032] "Lean slurry" refers to the combination of the heavy and foam phases collected from the bottom and top layers, respectively, of a gravity separator used to separate black water. The heavy phase includes soot particles that sink to the bottom and water. The foam phase includes soot, water, and entrained gas or air, and the foam collects in the top layer because its combined density is less than that of water. The lean slurry includes soot, water, and entrained gas or air, with the soot concentration being about 1 to about 10% by weight.

[0033] "Envelope density" refers to the density of a porous solid particle whose voids are filled with air or gas. This density represents the weight of the particle contributed by the skeletal solid divided by the total envelope volume of the particle. As a non-limiting example, a skeletal density of 2.0 g / cm 3 A solid particle with a porosity of 50% has an envelope density of 1.0 g / cm, ignoring the small contribution of air. 3 become.

[0034] "Flocculating agent" refers to a substance that promotes the aggregation of fine particles present in a dispersion or emulsion by reducing the repulsive forces between these particles, thereby encouraging the particles to clump together into larger aggregates, also known as flocs, which then rise to the surface (floating) or sink to the bottom (sedimentation). Flocculating agents also accelerate the rate of floating or settling and improve the quality of separation of particles from a liquid.

[0035] "Gasification" refers to the gasification of coal, liquids, dust, and slurries, and the term also includes gasification of waste materials, such as gasification of heterogeneous waste materials. In lower temperature gasification (usually below about 1000°C), dry ash is produced as waste material. In higher temperature gasification, such as that performed by slagging gasifiers, these operate at temperatures above the melting point of the ash (usually above about 1400°C) and produce molten slag that is usually quenched. A gasifier or gasification reactor performs the gasification. Gasifiers include fixed bed, fluidized bed, circulating fluidized bed, and entrained bed gasifiers.

[0036] "Heterogeneous waste" refers to municipal solid waste ("MSW"), wood, agricultural waste, coal, petroleum coke, or hydrocarbon waste streams with various particle morphologies, such as, but not limited to, in the size range of 6 mm to 100 mm, outside the range that can be processed by existing fluidized bed, entrained bed, or fixed bed gasification processes. Heterogeneous waste feed to the gasifier includes any mixture of the above waste streams, whether fed to the gasifier in a single mixed stream or fed to the gasifier as separate feed streams sequentially or via separate feeders.

[0037] "Skeletal density" refers to the true density of the solid phase within a porous particle. This density corresponds to the density of a particle with zero porosity.

[0038] "Soot" refers to solid carbonaceous particles resulting from the partial oxidation of hydrocarbons and tar. Soot produced from a gasification process primarily contains about 80% to greater than 90% by weight carbonaceous material and typically less than about 10% to 20% by weight inorganic ash components.

[0039] "Surfactant" refers to any surface active chemical used to modify the surface chemistry and interactions between different phases which may include solids, liquids, gases, and any combination thereof. Non-limiting examples include detergents, foaming agents, emulsifiers, dispersing aids, and wetting agents.

[0040] "Synthesis gas" or "syngas" means the gaseous product of the gasification of heterogeneous wastes composed of CO, H2, CO2, H2O, CH4, higher hydrocarbons including C2, and condensable hydrocarbons heavier than C3 compounds (i.e., tar), and solids carried over with the synthesis gas, including carbonaceous soot and mineral ash components.

[0041] "Tar" refers to condensable hydrocarbons having more than three carbon atoms (C3), including, for example, but not limited to, oxygenated compounds formed during gasification from the gasification of heterogeneous waste.

[0042] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In one aspect, provided herein is a method or process for removing impurities from black water (e.g., dirty scrubber water) associated with a gasifier. The method can include adding a flocculant to the black water to produce a black water and flocculant mixture, and settling the black water and flocculant mixture in a gravity settler to separate the black water and flocculant mixture into clear water, a foam phase, and a heavy phase. The foam phase can include soot, water, air, or gas. The heavy phase can include soot and water. The method can include separating and / or removing the clear water from the settled black water and flocculant mixture. The method can include collecting a dilute slurry including a foam phase and a heavy phase. The method can include phase separating the dilute slurry. The dilute slurry can include a foam phase and a heavy phase. The method can include phase separating the dilute slurry in a high speed centrifuge to provide additional clear water and thick slurry. The black water is obtained from wet gas scrubbing of syngas. Black water can contain soot or gaseous contaminants such as halogenated acids, ammonia, or volatile heavy metals.

[0043] In one embodiment, the method or process further comprises recycling the clarified water for reuse as wet gas scrubbing water. In another embodiment, the method further comprises recycling the thickened slurry to a gasifier producing syngas. In another embodiment, the thickened slurry is recycled through an injection nozzle. In another embodiment, the thickened slurry is recycled including mixing with solid feed before being recycled to the gasifier. In another embodiment, the method further comprises dewatering the thickened slurry in a filter, membrane, centrifuge, or dryer before being recycled to the gasifier. In another embodiment, the method further comprises adding a surfactant to the wet gas scrubbing device. In another embodiment, the clarified water produced by the high speed centrifuge is substantially free of entrained gas, solids, or bubbles. In another embodiment, the wet gas scrubbing comprises scrubbing the syngas using one or more of a venturi scrubber, a column scrubber, and an auxiliary solid separator. In another embodiment, the auxiliary solid separator is a wet electrostatic precipitator. The auxiliary solid separator removes trace particulate impurities. In another embodiment, the phase separation is carried out in the absence of a surfactant.

[0044] In one embodiment, the synthesis gas is produced by a gasifier that gasifies heterogeneous waste. In one embodiment, the gasifier includes a tar breaking zone ("polishing section") integrated with the gasifier, preferably located in the upper zone of the gasifier. In one embodiment, the tar breaking zone includes one or more burners arranged around the periphery. In one embodiment, the one or more burners are arranged at multiple heights within the tar breaking zone. In certain embodiments, the burners operate at above stoichiometric oxygen levels. Stoichiometric oxygen refers to the molar ratio of oxygen to CO2 and HO required to completely combust one mole of fuel. As a non-limiting example, one mole of C x H y The stoichiometric requirement of O2 for burning hydrocarbons is equal to (x+y / 4) moles of O2.

[0045] In another embodiment, the heterogeneous waste requires no or substantially no pre-treatment, limited to removal of hazardous materials such as large items that cannot be shredded, metals, rocks, and explosives. In another embodiment, the heterogeneous waste requires only basic shredding to a preferred size range of about ¼ inch to about 2 inches (i.e., about 6 mm to about 50 mm). In another embodiment, the heterogeneous waste requires drying only if the moisture content is greater than about 20% by weight.

[0046] In another embodiment, the tar destruction zone has a residence time of at least about 2 seconds, and most preferably about 5 seconds, to achieve effective tar destruction. As used herein, effective tar destruction refers to the simultaneous destruction of all or substantially all of the tars and their simultaneous conversion to additional non-condensable syngas and tar-free residual particulate soot so that the syngas can be further processed in heat recovery and solids removal unit operations downstream of the gasifier without fouling from the residual tars condensing as the syngas temperature is reduced.

[0047] In another embodiment, the temperature of the tar destruction zone is at least about 2000° F. (1093° C.). In another embodiment, the temperature of the tar destruction zone is greater than about 2200° F. (1204° C.).

[0048] In one embodiment, the gasifier does not include a plasma torch. In another embodiment, the gasifier does not include a bed permeable additive. An illustrative example of a bed permeable additive is coke with a narrow particle size distribution. Plasma torches add cost and complexity and require very high parasitic electrical loads, thus negatively impacting the overall energy efficiency of the gasifier. Bed permeants such as high crush strength coal are costly and derived from non-renewable resources, thus increasing greenhouse gas emissions from the gasifier.

[0049] In another aspect, provided herein is a synthesis gas composition, also referred to simply as synthesis gas, and other such compositions. In one embodiment, the synthesis gas composition is provided by gasifying heterogeneous waste. In one embodiment, the synthesis gas composition exits the top of the polishing section of the gasifier. In another embodiment, the synthesis gas composition has a flow rate of about 5 g / Nm 3 In another embodiment, the synthesis gas composition preferably has a tar content of less than about 2 g / Nm 3 In another embodiment, the synthesis gas composition has a tar content of less than about 10 g / Nm 3 Less than 5 g / Nm 3 has a soot content of less than 100%.

[0050] In another embodiment, the syngas composition is soot-free or substantially soot-free. In another embodiment, soot is removed from the syngas produced by the gasifier at high temperatures using dry separation methods such as, but not limited to, cyclones, ceramic baghouses, electrostatic precipitators, or candle filters. In another embodiment, the soot is removed by a high-temperature cyclone before the syngas is cooled to less than about 900° C. to recover the condensed alkali salt-free soot, which is recycled to the gasifier feed. The cyclone can be a cylindrical or conical settling chamber that can cause the gas (e.g., syngas) to flow in a spiral or circular manner within the chamber. Particles (e.g., soot) within the gas can be moved by centrifugal force to the outer wall within the chamber of the cyclone and can be collected at the bottom of the cyclone. For example, the centrifugal force generated within the cyclone chamber can separate solid particulate matter within the gas from the gas, such that the gas can exit the cyclone (e.g., from the center or top of the cyclone) substantially free of particulate matter. For example, particulate soot can be removed from the syngas by dry separation of the particulate soot from the syngas using high temperature cyclones. The removed particulate soot can be provided (e.g., recycled) to, for example, a gasifier. By removing the soot at high temperatures, the alkali oxides remain as vapors in the gas stream carried from the gasifier, rather than depositing and contaminating the soot being separated or fouling piping or equipment. The minimum temperature for this separation depends on the composition of the alkali oxides carried from the gasifier (which can include Na2O and KO) and the vapor pressure of these compounds at the temperature in question.

[0051] The soot collected by the described dry separation method can be recycled back to the gasifier. In one embodiment, the soot can be mixed with the heterogeneous gasifier feedstock which increases the overall efficiency of the gasification process due to the high carbon content of the collected soot. Examples of exemplary blenders useful for mixing include, but are not limited to, ribbon blenders, pug mills, kneaders, or tumble blenders. In another embodiment, the soot can be pneumatically injected into the gasifier using a suitable lance or nozzle.

[0052] In some embodiments, soot in the syngas is substantially removed from the syngas using wet gas scrubbing to capture the soot in scrubber water or black water. In one embodiment, the black water is dewatered in a filter, centrifuge, hydrocyclone, flotation cell, or other suitable device to provide a thickened slurry containing the soot and residual water, which is recycled to the gasifier solids feeder. In another embodiment, the thickened slurry is circulated back to the gasifier and injected into the gasifier by an injection nozzle through one or more lances.

[0053] In one embodiment, the black water produced during wet gas scrubbing is conditioned or mixed with a surfactant and sent to a gravity settling chamber, a high efficiency inclined plate gravity settler, a froth flotation tank, or other gravity solids separator to separate the soot into a heavy phase that sinks to the bottom, an upper froth phase that floats on top, or a combination of both phases, and optionally further recover at least a portion of the water contained in the black water as a clear water layer that is substantially free of soot or other particulate solids. In another embodiment, the surfactant is a wetting agent selected to promote wetting of suspended particles and subsequent settling of the soot. As used herein, a wetting agent reduces the surface tension between a solid surface and a liquid to promote wetting.

[0054] In one embodiment, the black water is conditioned with a flocculant selected to promote gravity separation by agglomeration of particulate and soot particles, resulting in faster settling into the heavy phase and / or flotation into the upper froth phase.

[0055] In one embodiment, the thin slurry separated from the black water in the gravity separator is collected from the top and bottom layers, or any combination of these layers, and is further processed in a high speed centrifuge to separate at least a portion of the water contained in the slurry as clear water collected from the high speed centrifuge, while concentrating (i.e., increasing) the soot content of the slurry collected from the underflow of the high speed centrifuge as thick slurry. In one embodiment, the centrifuge is a disc stack centrifuge.

[0056] In one embodiment, the black water from the wet scrubber is sent directly to a high speed centrifuge which recovers clear water from the black water that is at least substantially free of solids while simultaneously collecting the soot as an underflow in the form of a thick slurry. In another embodiment, the clear water is recycled for use in the wet scrubber. In another embodiment, the thick slurry is recycled directly to the gasifier. In another embodiment, the thick slurry is dewatered using a belt filter, filter press, drum dryer, or other suitable equipment before being further recycled back to the gasifier.

[0057] In another aspect, a method is provided for removing gaseous contaminants (such as, for example, hydrochloric acid) from syngas using a dry separation process. When HCl is present in the syngas, a dry gas scrubbing process has a distinct advantage over wet gas scrubbing due to reduced corrosion of metal parts of downstream equipment and piping. Cl, even when quickly neutralized in a wet scrubber using a base such as NaOH or Na2CO3, is still present. - ions are known to play an important role in the pitting corrosion reactions of ferrous metals. They can be adsorbed or easily penetrate the passive oxide layer, compromising its integrity and accelerating electrochemical reactions. There are also strict limitations on the concentration of HCl gas delivered to downstream processes such as fuel cells, internal combustion engines, gas turbines, ammonia production, and methanol synthesis.

[0058] HCl gas present in the synthesis gas can be removed by reacting the gas with a solid sorbent such as an alkali (Na, K) or alkaline earth (Ca) carbonate or oxide at moderate to high temperatures (200-850°C). Examples of sorbents include, but are not limited to, sodium bicarbonate or minerals such as trona, nacolite, shortite, dawsonite. Depending on the final choice of sorbent used, some typical reactions of HCl with the sorbent are as follows: Na2CO3+2HCL → 2 NaCl+H2O+CO2 NaHCO3+HCl →NaCl+H2O+CO2 K2CO3+2HCl → 2KCl+H2O+CO2 CaCO3+2HCl →CaCl2+H2O+CO2 CaO+2HCl→CaCl2+H2O

[0059] In some embodiments, the sorbent is injected directly into the gas stream or reacted with the gas stream in a fluidized bed. This reaction produces salts that can then be removed using wet or dry separation methods, including but not limited to high temperature candle filters, baghouse filters, high temperature cyclone separators, Venturi scrubbers, plates, scrubber towers with random or structured packaging, and spray columns. In another embodiment, the synthesis gas can be passed through a fixed bed of sorbent pellets, where the spent sorbent is removed and replaced with fresh sorbent, either continuously or as a batch process. In another embodiment, the gas stream after injection of the sorbent is cooled to a temperature where the spent sorbent to be separated does not have a significant vapor pressure, allowing for more efficient separation using dry separation methods, such as, but not limited to, cyclones, baghouses, electrostatic precipitators, or candle filters.

[0060] In one embodiment, the soot- and HCl-free syngas is further converted to gaseous feedstocks for microbial fermentation to produce hydrogen, synthetic natural gas, methanol, ammonia, liquid fuels, and feed proteins, biodegradable polymers, or alcohol, including the syngas compositions provided herein (collectively, "end products"), or produced from the syngas compositions provided herein.

[0061] In one embodiment provided herein, a hydrogen end product having a purity of greater than about 99.9%, preferably greater than about 99.99%, is recovered from the synthesis gas.

[0062] In one embodiment provided herein, a CO2 by-product having a purity of greater than about 95%, preferably greater than about 99.5%, is recovered from the purge gas or tail gas remaining after conversion of syngas to end products.

[0063] Specific non-limiting advantages of the technology provided herein include the removal of all or substantially all soot from the syngas, in part by wet syngas scrubbing, and / or recapturing the soot in wet gas scrubber water or black water. Recycling and purification of black water is particularly difficult, given challenges such as the very hydrophobic nature of soot particles, which promotes the formation of a very persistent foam phase that can damage equipment such as pumps. An important advantage of the technology and methods provided herein is the ability to efficiently separate black water into a) a clarified water that is substantially free of solids that can be recycled as scrubber water, and b) a thick, partially dewatered slurry that can be recycled to the gasifier, avoiding the generation of waste streams and improving the overall yield of end products.

[0064] 1 shows an exemplary dry gas scrubbing flowsheet and equipment used in certain embodiments to remove soot and HCl from the synthesis gas produced by the gasifier. In a preferred embodiment, a gasifier with an integrated tar destruction zone or a separate tar destruction unit operation converts carbon-containing feedstocks, including but not limited to municipal solid waste ("MSW"), wood, agricultural waste, coal, petroleum coke or hydrocarbons, into a substantially tar-free synthesis gas ("syngas") composed of CO, H2, CO2, H2O, CH4, and non-condensable hydrocarbons of C2 and above, as well as particulate solids carried over with the synthesis gas, including carbonaceous soot and inorganic ash components.

[0065] In one embodiment, the syngas from the gasifier is quenched to about 800°C. At this temperature, there is no significant deposition of alkali oxides carried over from the gasifier. This is also close to the upper temperature limit before some proposed sorbents decompose. The soot in the syngas is separated at this high temperature using dry separation methods including, but not limited to, cyclones, ceramic filters, etc. In one embodiment, the soot is then recycled to the gasifier using a pneumatic lance or mixed with the gasifier feedstock to improve the overall efficiency of the gasifier. After this step, the selected sorbent is contacted with the syngas via, but not limited to, direct injection, fluidized bed, or fixed bed. In FIG. 1, direct injection is employed.

[0066] In one embodiment, the gas is then cooled using a waste heat boiler which generates steam that can be used for the rest of the plant, as shown in Figure 1. At a minimum, the temperature of the gas is reduced low enough that the salt formed by the reaction of the sorbent with the HCl gas does not have a significant vapor pressure. In another embodiment, this is accomplished by quenching with water instead of using a waste heat boiler.

[0067] In one embodiment shown in Figure 1, salts produced by the sorbent reaction are removed by a dry gas scrubbing step, such as, but not limited to, a cyclone, baghouse or candle filter. The syngas, substantially free of soot and HCl gas, is now sent for further processing or conversion to end products.

[0068] In another embodiment, instead of using dry gas separation to remove residual salts, wet gas scrubbing is used instead.

[0069] FIG. 2 shows a typical flowsheet and equipment used in certain embodiments during wet gas scrubbing to remove residual soot remaining in the syngas after upstream syngas heat recovery and dry particulate solids removal operations. Synthesis gas production from the gasifier and dry gas treatment are provided prior to wet gas scrubbing. In a preferred embodiment, a gasifier with an integrated tar destruction zone or separate tar destruction unit operation converts carbon-containing feedstocks, including but not limited to municipal solid waste ("MSW"), wood, agricultural waste, coal, petroleum coke or hydrocarbons, into a substantially tar-free synthesis gas ("syngas") comprised of CO, H2, CO2, H2O, CH4, and non-condensable hydrocarbons of C2 and above, as well as particulate solids carried over with the synthesis gas, including carbonaceous soot and inorganic ash components.

[0070] In one embodiment, the syngas exiting the gasifier is partially quenched with water to a temperature of about 800 to less than about 850°C and simultaneously further cooled to a temperature of about 200 to less than about 250°C before being heat recovered in a heat recovery boiler to produce steam. Without being bound by theory, quenching the syngas before entering the heat recovery equipment can significantly reduce fouling of heat exchange surfaces by reducing the stickiness of the ash that occurs at higher temperatures. In another embodiment, the syngas is quenched to a temperature of about 200 to about 250°C using water injection without any heat recovery. After heat recovery or quenching, a significant proportion of the soot and particulate matter, about 75% to about 85%, is removed from the syngas using dry syngas particulate removal methods, including but not limited to high temperature candle filters, baghouse filters, and high temperature cyclone separators. The syngas is then further purified using wet gas scrubbing methods to remove residual particulate solids and water soluble gaseous impurities, including but not limited to HCl, HF, and NH3.

[0071] As shown in FIG. 2, in certain embodiments, the syngas enters a Venturi scrubber where it is contacted at a high scrubber-to-gas ratio. The Venturi scrubber uses a large volume of scrubber water that is fed by a circulation pump in a co-current pattern to a high-pressure nozzle located upstream of the throat of the Venturi scrubber. As the gas enters the throat section, the liquid droplets are sheared by the high relative velocity difference between the gas and the liquid, further reducing their size. These small droplets have a large surface area per unit volume, which efficiently collects particulate impurities present in the syngas into the scrubber water. Water-soluble gaseous impurities, including but not limited to HCl, HF, and NH3, are also significantly removed from the syngas, with approximately 80%-95% of these impurities dissolving in the scrubber water.

[0072] In other embodiments, the gas is then sent to a packed bed scrubber where it is contacted with countercurrent water using multiple stages in a column with multiple spray nozzles, multiple gas / liquid contact plates, random packaging, structured packaging, or other suitable gas / liquid contacting internals. In some embodiments, the scrubber water is doped with chemicals including, but not limited to, surfactants, flocculants, or pH adjusters such as sulfuric acid or sodium hydroxide, or other suitable acids or bases, to further increase the removal efficiency of particulate and gaseous impurities to greater than about 95%, preferably greater than about 99%. The syngas exiting the wet gas scrubbing section of FIG. 2 is then further processed using well known techniques to remove additional trace impurities before being further processed and converted to products including, but not limited to, hydrogen (H2), synthetic natural gas (CH4), methanol (CH3OH), ammonia (NH3), liquid fuels, and gaseous feedstocks for microbial fermentation to produce feed proteins, biodegradable polymers, or alcohol.

[0073] The flow sheet of FIG. 2 shows an embodiment including two circulation pumps, one for the venturi scrubber and one for the packed bed scrubber. As will be appreciated by those skilled in the art, impurities accumulate in the circulation water and over time impede the efficient functioning of the equipment or the desired separation of the impurities from the synthesis gas. Here, the scrubber water containing particulate soot, dissolved water-soluble gaseous impurities, and mineral ash is commonly referred to as black water. To ensure continued satisfactory performance of the wet gas cleaning equipment, a certain amount of black water is purged and replaced with fresh make-up water. Considering the small particle size and hydrophobic nature of the soot particles, it is difficult to remove the suspended soot from this purge stream. The presence of toxic substances that may be present in the soot makes it even more difficult to discharge this stream as wastewater.

[0074] FIG. 3 is a schematic diagram of one embodiment of a wet gas scrubbing process improved to address the challenges associated with the treatment and recovery of soot and clean water from the black water purge, according to various embodiments. As shown in FIG. 3, the circulating black water is sent to a settling tank (an exemplary, non-limiting gravity separator). The venturi scrubber is equipped with an agitator to ensure good suspension of the soot so that all the soot is transferred to the settling tank instead of being accumulated in the venturi scrubber sump. In certain embodiments, appropriately selected chemical modifiers, such as flocculants or surfactants, are injected into the black water using a static mixer to ensure good dispersion before entering the settling tank. As used herein, a flocculant promotes the aggregation of fine suspended soot particles into larger aggregates to increase the speed and quality of separation of soot and clean water in the settling tank.

[0075] In some embodiments, the gravitational settling rate is increased to substantially separate the clear water from the soot-containing foam phase and heavy phase in less than about 5 minutes, preferably less than about 1 minute, in a 500 milliliter ("mL") graduated cylinder test shown as a non-limiting example in Figure 4. In one embodiment, the foam phase, which includes soot, water, and air, accumulates at the surface of the clear water. In another embodiment, the suspended soot settles to the heavy phase at the bottom of the clear water. In some embodiments, both the foam phase and the heavy phase are separated from the clear water.

[0076] Clear water is removed from the intermediate layer using suitable transfer pumps and sent to a clear water tank from where the pump is used to recycle the recovered clear water to the venturi scrubber and packed bed scrubber. The soot-containing foam phase is collected from the top layer of the clear water in the settling tank using suitable skimmer pumps and mixed with the heavy phase removed from the bottom layer of the settling tank. The combined foam and heavy phase streams produce a dilute slurry, typically in the range of about 20-30% of the total volume treated in the settling tank. Thus, an amount equivalent to about 70-80% of the volume of black water fed to the settling tank is recovered as clear water for reuse in wet gas scrubbing using simple gravity separation assisted by flocculants. The dilute slurry stream is then sent to a high speed disc stack centrifuge operating at a force of about 6,000-10,000 g. The centrifuge separates the dilute slurry feed into an underflow thick slurry and an overflow clear water that is substantially free of solids or foam, as shown in FIG. 5, where the beaker on the left is a photograph of the dilute slurry fed to the centrifuge, and the photograph on the right is the clear water collected from the centrifuge overflow. The thick slurry is typically less than about 5% by volume of the dilute slurry fed to the centrifuge, and preferably less than about 2% by volume. Thus, about 95% to more than 98% of the dilute slurry fed to the centrifuge can be recovered as clean water and sent to a clean water tank for reuse in the wet gas scrubbing process. FIG. 6 and FIG. 7 are comparative photographs of the contents of the venturi scrubber sump for the base case flowsheet shown in FIG. 2 and the modified flowsheet of FIG. 3, according to various embodiments. As can be seen, the significant foam phase that interferes with the operational stability of the wet gas scrubbing in FIG. 6 is substantially eliminated in FIG. 7, with no foam present at the surface and only a thin layer of hydrophobic solids.

[0077] In one embodiment, the thick slurry stream is recycled to the gasifier by mixing with a portion of the heterogeneous waste in a suitable mixer, including but not limited to a solid blender or pug mill, before being fed to the gasifier. In another embodiment, the thick slurry is recycled to the gasifier using a slurry pump and a modified lance that directly injects the slurry into the bed of material in the gasifier. In another embodiment, the thick slurry is further dewatered using suitable equipment, including but not limited to a belt filter, a vacuum drum filter, a filter press, a zwitterionic cross-flow membrane filter, a decanter centrifuge, or a drum dryer. Zwitterionic membranes comprise highly hydrophilic zwitterionic clusters that suppress fouling, since they only allow water to pass through the membrane and reject hydrophobic materials or solids. In one embodiment, a flocculant can be added to facilitate dewatering. In another embodiment, a filter aid can be added to the slurry to improve filtration performance. In some embodiments, the filter aid can be selected from materials useful as slagging additives in gasifiers, including but not limited to Ca(OH)2, CaCO3, silica-containing minerals such as natural clays or diatomaceous earth. The overall result is that substantially all of the syngas impurities recovered during the wet gas scrubbing are recycled to the gasifier and converted to additional syngas and slag without any waste being produced, while substantially all of the water is ultimately recovered for reuse in the wet gas scrubbing section.

[0078] Dilute slurry streams have proven very difficult to thicken using conventional centrifuges such as decanter centrifuges. Under the conditions tested, even a high speed laboratory swinging bucket centrifuge was unable to break up the foam phase, and soot-containing foam continued to remain on the surface even after extensive centrifugation. Direct filtration of the heavy phase or sludge has also proven very difficult. It was therefore very surprising that the high speed disk stack centrifuge achieved almost complete separation of the dilute slurry into a thick slurry, with no evidence of residual foam, and only clear water exiting the overflow port.

[0079] In certain embodiments, a surfactant that functions as a wetting agent is injected into the scrubber water pumped to the venturi scrubber and packed bed scrubber. The wetting agent reduces the surface tension between the water and the soot particle surface, promoting degassing and effective wetting, so that the soot is suspended uniformly in the venturi scrubber sump rather than accumulating as a problematic foam phase. In some embodiments, a process is provided herein for removing the foam phase. In this way, the foam phase cannot interfere with the efficient operation of the wet gas scrubbing by reducing pump performance, being carried over by the syngas, etc.

[0080] In another embodiment, a wet electrostatic precipitator ("WESP") is used downstream of the wet gas scrubbing flowsheet shown in Figure 3 to remove any residual soot or aerosol contaminants remaining in the syngas. In some embodiments, the black water resulting from the WESP scrubbing is sent to a settling tank and collected.

[0081] The invention thus generally described will be more readily understood by reference to the following examples, which are provided for purposes of illustration and are not intended to limit the invention. EXAMPLES

[0082] Example 1A: Use of Wetting Agents in Wet Gas Scrubbing Operations Six different surfactants, both anionic (Niaproof08 and ColaWet DOSS75) and non-ionic (DOW Ecosurf EH3, DOW Tergitol L61, Synperonic NCA810, and Synperonic NCA8300), were tested at various concentrations (e.g., two or more of 0.25vol%, 0.5vol%, 0.75vol%, 1vol% and 2%vol%). Samples were spiked with a defined amount of surfactant and then spun in a bench-scale centrifuge. Many of the surfactants improved the solids removal efficiency of the centrifuge when the correct dosage was used.

[0083] However, under the conditions tested, the flowsheet of Figure 3 with the jet ejector venturi scrubber caused additional foaming in the venturi sump due to the surfactant added water. This effect varied depending on the choice and concentration of surfactant used. In gas scrubbing layouts without jet venturi scrubbers, the addition of surfactant may still have operational advantages, but this example confirms the difficulty of effectively removing bubbles or foam caused by the presence of very small particle size hydrophobic solids along with water and gas in jet venturi scrubbers designed to create high shear and intimate surface contact between the gas and liquid phases.

[0084] Despite the above results, it was surprisingly observed that when surfactant-free black water was used in a larger disc stack centrifuge skid, only a single heavy solid phase was obtained with no clear liquid layer and no upper solid layer.

[0085] Example 1B: Characterization of soot in black water The properties of the particulate soot processed in Examples 1 and 2 were further characterized to demonstrate the effect of the particulate soot properties on the separation process. Table 1 graphs and tabulates a typical particle size distribution for the soot showing a volume average mean diameter of 11.7 microns and a number average mean diameter of 2.4 microns.

[0086] Table 1. Particle volume and size data This indicates that 30% of the total volume of the particles is less than 6.95 microns. TIFF2025508264000002.tif67128

[0087] Table 2 provides a proximate analysis of the collected soot particles and confirms that the carbon content is very high, 90% (w / w on a dry basis), with lower amounts of inorganic ash and volatile matter present.

[0088] (Table 2) Collected data on soot particles TIFF2025508264000003.tif37161

[0089] Soot with a high carbon content has a higher surface tension (i.e., more hydrophobic and less wettable). The porosity of the soot particles in this example was 60% as measured by Hg porosimetry. The true solid skeletal density was 1.838 g / cm3 as measured using the ASTM D2638 test method. 3 and the density of the particle or envelope is 0.735 g / cm 3 (i.e. 1.838g / cm 3 This was 40% of the total.

[0090] Example 2: Use of flocculants to improve gravity separation of solids from black water Flocculants promote the aggregation of small particles into larger particles ("flocs") and increase the rate at which the flocs settle or float, depending on whether their density is greater or less than that of the liquid medium. Several commercial flocculants from Baker Hughes were evaluated, and the results are shown in Figure 8. The flocculants were mixed with the samples and allowed to settle under gravity in a beaker. Comparing the flocculated samples to the control (far right), it is clear that each chemical has some effect both in terms of producing larger flocs and in terms of promoting the formation of a clear water layer that is substantially free of solids. In both cases, a significant proportion of solids was present in the foam phase, indicating that the flocculants accelerated phase separation but did not significantly affect particle degassing. Finally, FLW163 or Tretolite™ was selected for plant testing according to the flowsheet shown in Figure 3. The impact of the flocculants was quantified using, among others, a Clarity Wedge or a Water Turbidity Wedge, such as those available from www.chemworld.com. A reading of 1 represents a high particulate loading (no numbers on the scale) and a reading of 46 represents a low particulate loading and the water is nearly clear. The effect of selected flocculants on the performance of the gravity settling tank is shown in Table 4. The black water fed to the settling tank was completely turbid and barely visible with a Clarity Wedge reading of 1. During operation without flocculant, the settling tank produced a partially clear water layer with a Clarity Wedge reading of 12 (a thin black suspension to the naked eye with significant turbidity still present). Flocculant was then dosed into the black water being pumped to the settling tank using an in-line mixer. The turbidity of the clear water decreased and the Clarity Wedge reading improved to 42, or essentially clear with very little turbidity. The dilute slurry was processed in a high speed disc stack centrifuge, shown in the flowsheet in Figure 3, resulting in complete separation and essentially completely clear water emerging from the centrifuge with a Clarity Wedge reading of 46 (i.e., maximum clarity).In this example, the effectiveness of a separation method according to the flowsheet in FIG. 3 in combination with a flocculant was demonstrated to separate soot from black water to produce clarified water for reuse in wet gas scrubbing, and to allow the dewatered soot to be fed to a gasifier for conversion to additional synthesis gas.

[0091] (Table 3) Effect of flocculants on separation quality in settling tanks TIFF2025508264000004.tif20134

[0092] Example 3: Use of a Disc Stack Centrifuge to Separate a Dilute Slurry into Clear Water and a Thick Slurry The dilute slurry formed by the combination of the foam phase collected from the top layer of the gravity separator and the heavy phase collected from the bottom layer of the gravity separator contains soot, water, and entrained air or gas. The soot in the foam phase is hydrophobic, making it difficult to completely separate from the dilute slurry. When a sample of this dilute slurry was spun in a laboratory swing tube centrifuge, it did not separate well under the test conditions and did not produce a clear water layer.

[0093] However, when this same dilute slurry is fed into a high speed disk stack centrifuge, it has been observed to produce two exit streams, an overflow which is clear water essentially free of soot, and a thick slurry collected from the underflow which contains almost all of the soot present in the dilute slurry, as seen in Figure 5. Without wishing to be bound by theory, it is believed that the interaction of the soot and entrained air in the bubbles with the closely spaced separating disks of the disk stack centrifuge, typically spaced about 1-2 mm apart, results in effective degassing and wetting of the soot, thereby breaking down the bubbles into heavy soot and discharging it as a thick slurry, releasing trapped gases which are exhausted from the centrifuge.

[0094] Without wishing to be bound by theory, it is believed that after observing the surprising separation, the small particle size, hydrophobicity and high porosity of the solids result in significant entrapment of the gas and solids, forming a very persistent foam phase. It is further believed that the surprisingly effective degassing and foam separation in high speed disk stack centrifuges may be the result of intimate contact between the solids and the tilted disks that are very closely spaced, approximately 1-2 mm apart.

[0095] While particular embodiments have been shown and described, it is to be understood that changes and modifications can be made by those skilled in the art without departing from the technology in its broader aspects as defined in the appended claims.

[0096] The embodiments illustratively described herein may be suitably implemented in the absence of any element or elements, limitations, or limitations not specifically disclosed herein. Thus, for example, terms such as "comprising," "including," and "containing" are to be understood broadly and without limitation. Furthermore, the terms and expressions used herein are used as terms of description and not of limitation, and the use of such terms and expressions is not intended to exclude any equivalents of the features shown and described or portions thereof, but is recognized to be subject to various modifications within the scope of the claimed technology. In addition, the phrase "consisting essentially of" will be understood to include the elements specifically recited and additional elements that do not materially affect the basic and novel characteristics of the claimed technology. The phrase "consisting of" excludes any elements not specified.

[0097] The present disclosure should not be limited in terms of the specific embodiments described in this application. As will be apparent to those skilled in the art, many modifications and variations can be made without departing from the spirit and scope thereof. In addition to those recited herein, functionally equivalent methods and compositions within the scope of the present disclosure will be apparent to those skilled in the art from the foregoing description. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure should be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that the present disclosure is not limited to specific methods, reagents, compounds, compositions, or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0098] Additionally, where features or aspects of the disclosure are described in terms of a Markush group, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual members or subgroups of members of the Markush group.

[0099] As will be understood by those skilled in the art, for any or all purposes, especially in terms of providing a written description, all ranges disclosed herein also include any and all possible subranges and combinations of those subranges. Any recited range can be easily recognized as fully described and allowing the same range to be broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be easily broken down into a lower third, a middle third, an upper third, etc. As will also be understood by those skilled in the art, all language such as "up to," "at least," "greater than," "less than," etc. refers to a range that includes the recited numbers and can then be broken down into subranges as discussed above. Finally, as will be understood by those skilled in the art, a range includes each individual member.

[0100] All publications, patent applications, issued patents, and other references mentioned herein are herein incorporated by reference as if each individual publication, patent application, issued patent, or other reference was specifically and individually indicated to be incorporated by reference in its entirety. Definitions contained in any text incorporated by reference are excluded to the extent they conflict with definitions in this disclosure.

[0101] Other embodiments are within the scope of the following claims.

Claims

1. 1. A method for removing impurities from black water associated with a gasifier, comprising: adding a flocculant to the black water to produce a mixture of the black water and the flocculant; settling the black water and flocculant mixture in a gravity settler to separate the black water and flocculant mixture into clear water, a foam phase and a heavy phase, the foam phase comprising soot, water and air or gas, and the heavy phase comprising soot and water; removing the clear water from the settled black water and flocculant mixture; collecting a dilute slurry comprising the foam phase and the heavy phase; phase separating the thin slurry in a high speed centrifuge to provide further clarified water and a thick slurry; Including, The process wherein the black water is obtained from wet gas scrubbing of synthesis gas (syngas).

2. The method of claim 1 , wherein the impurities include soot and gaseous pollutants.

3. The method of claim 2 , wherein the gaseous contaminants include at least one of a halogenated acid, ammonia, or a volatile heavy metal.

4. 10. The method of claim 1 further comprising recycling the clarified water for reuse as wet gas scrubbing water.

5. The method of claim 1 further comprising recycling the thick slurry to the gasifier that produces the synthesis gas.

6. 6. The method of claim 5, wherein the thickened slurry is recycled through an injection nozzle.

7. 6. The method of claim 5, further comprising the step of mixing the thick slurry with a solid feed material prior to recycling the thick slurry to the gasifier.

8. 6. The method of claim 5, further comprising the step of dewatering the thickened slurry with at least one of a filter, a membrane, a centrifuge, or a dryer prior to recycling the thickened slurry to the gasifier.

9. 10. The method of claim 1 further comprising the step of adding a surface-active agent to the wet scrubber.

10. 10. The method of claim 1, wherein the clarified water produced by the high speed centrifuge is substantially free of entrained gases, solids and bubbles.

11. 10. The method of claim 1, wherein wet gas scrubbing comprises scrubbing the synthesis gas with one or more of a venturi scrubber, a column scrubber, and an auxiliary solids separator.

12. 12. The method of claim 11, wherein the auxiliary solids separation device is a wet electrostatic precipitator that removes trace particulate impurities, and black water obtained from the wet electrostatic precipitator is fed to the gravity settler.

13. The method of claim 1 , wherein the phase separation is carried out in the absence of a surfactant.

14. The method of claim 1 , wherein the high speed centrifuge is a disc stack centrifuge.

15. 1. A method for removing particulate soot from a gasifier syngas, comprising: dry separating the particulate soot from the synthesis gas by a high temperature cyclone; feeding the separated particulate soot by the high temperature cyclone to the gasifier for recycling the particulate soot; A method comprising:

16. 16. The method of claim 15, further comprising contacting the separated syngas with a dry adsorbent to neutralize halogenated acids in the separated syngas.

17. 17. The method of claim 16, further comprising removing spent dry sorbent with a dry particulate collector operating above the dew point of the separated syngas.

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