Patent Application
20180086994
The present invention pertains to the field of gasification of carbonaceous feedstock/fuel, and in particular to a process and system for conversion of carbonaceous fuel materials into clean high quality syngas substantially devoid of tars and for the production of clean ash substantially devoid of carbon content.
Gasification can convert carbon-containing materials to useful chemical products. These chemical products typically involve synthesis gas (syngas), which can be further combusted to produce electricity, or chemically reacted to produce oxygenates or hydrocarbons in catalytic systems.
Several types of gasification and pyrolysis methods and apparatuses have been developed to achieve efficient conversion of biomass into clean gaseous products. Many of the gasification processes known in the art have failed due to insufficient attention to low tar production or efficient tar destructions.
Existing downdraft gasifiers require very high quality wood fuels or biomass, such as ash free wood blocks or high quality wood chips, and cannot be scaled up to economically attractive scales without severely increased tar production. Multi-stage downdraft gasifiers which comprise separate zones for fuel pyrolysis, partial oxidation, and reduction of bed gas, have also been developed, however such gasifiers known in the art also result in substantial amount of tar production, significant tar levels retained in the syngas and the ash also containing very high levels of unconverted carbon content
CZ Patent No. 295171 discloses a biomass gasifier comprising vertically oriented mutually nested cylindrical containers and a horizontal rotating table top, which is equipped in its center with a perforated conical grate and char table to separate the pyrolysis gases and char. The char is transferred tangentially from the rotating table and directed to a container for removal under the table. This gasifier is structurally complicated, and is known for its poor controllability and flexibility of performance, and lacks any reduction zone to reduce tar content in the product gases.
PCT Publication No. 2015/090251 discloses a device (1) for the mufti-stage gasification of carbonaceous fuels (2), which comprises a hermetically sealed vertical container (3) which is fitted with insulation (4). Inside vertical container (3) is pyrolysis chamber which is adapted for filling with carbonaceous fuel (2) from above of the container (3). Under pyrolysis chamber is in the container (3) a partial oxidation chamber (7) for oxidation of the pyrolysis product which is delimited by a refractory casing (8) and the partial oxidation chamber (7) is followed by a reduction zone (10) for chemical reduction of oxidized product gas (11).
The devices/systems of CZ 295,171 and WO 2015/090251, result in considerable amount of tar in the product gases, which in turn clogs the cleaning devices used to clean the product gases. Further the WO 2015/090251 has no means to effectively manage the reduction reactions and failed to produce consistent flow and quality of syngas
Therefore, a need exists for a process and system for gasification of carbonaceous material to form consistent clean product gases, such as syngas, while substantially reduced tar contents.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.
An object of the present invention is to provide a process for concerting carbonaceous fuel material into law tar syngas.
In accordance with an aspect of the present invention, there is provided a continuous multi-stage vertically sequenced gasification process for conversion of solid carbonaceous fuel material into clean (low tar) syngas in a gasifier comprising:
As used herein, the term “about” refers to a +/−10% variation from the nominal value. It is to be understood that such a variation is always included in a given value provided herein, whether or not it is specifically referred to.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
In one aspect of the present invention, there is provided a continuous multi-stage vertically sequenced gasification process for conversion of solid carbonaceous fuel material into clean (low tar) syngas in a gasifier comprising a pyrolysis zone, a partial oxidation zone located vertically downstream of the pyrolysis zone, and a reduction zone located vertically downstream of the partial oxidation zone and comprising an inwardly and downwardly angled perforated floor/base and a deflector located in the center of the floor. The angle of the floor is greater than 0° to greater than the angle of material repose, shown as Ø in
The process of the present invention is carried out by feeding the carbonaceous fuel material through the upper portion of the pyrolysis zone vertically downward towards the lower portion of the pyrolysis zone, while pyrolyzing the fuel into pyrolysis vapours comprising tar, and pyrolysis residue comprising char containing ash and carbon. A first oxidant is optionally added to the lower portion of the pyrolysis zone to achieve a temperature greater than 200° C.
The pyrolysis vapours are directed to the partial oxidation (POX) zone, and the pyrolysis residue formed in the pyrolysis zone is directed downwardly to the reduction zone via a separation member positioned between the pyrolysis zone and the partial oxidation zone. The separation member comprises a plurality of vertically inclined perforations/slanted vents to allow the pyrolysis vapours only into the partial oxidation zone. A second oxidant is then added in the partial oxidation zone to achieve a temperature greater than 900° C. to reform the pyrolysis vapours into raw syngas containing significantly reduced levels of tar.
A bed of pyrolysis residue having a uniform depth is formed on the floor/base of the reduction zone, and the raw syngas primarily formed in the partial oxidation zone and optionally in the pyrolysis zone is passed downward through the pyrolysis residue (char) bed to carry out an endothermic reaction between CO2 and H2O in the syngas and carbon of the char in the pyrolysis residue bed, while controlling the reduction zone pressure drop, resident time and syngas flow space velocity during the endothermic reaction to form substantially tar free raw syngas, to reduce carbon content in the pyrolysis residue, and to reduce the temperature of raw syngas as compared to the temperature of the partial oxidation zone. The substantially tar free raw syngas is then moved in upward counter-current flow in indirect thermal contact with the pyrolysis zone, to heat the pyrolysis zone and subsequently cool the substantially tar free syngas before collecting same.
The process of the present invention can be performed entirely in one chamber, or in separate chambers or a combination of chambers in a vertical configuration.
In one embodiment, the lower portion of the pyrolysis zone has a perimeter greater than that of the upper portion. In one embodiment, pyrolysis zone is provided with a gradually increasing perimeter towards the lower portion.
In one embodiment, the separation member is an inverted or inclined hemispherical or conical ceramic heated membrane.
In one embodiment of the present invention, the process is carried out under pressure, preferably greater than full vacuum and less than 600 psig, more preferably between atmospheric pressure and 100 psi.
In one embodiment of the process of the present invention, the first and second oxidants comprise air, enriched air, oxygen with purity greater than 85 wt %, oxygen with purity greater than 95 wt %, or a combination thereof. In one embodiment, the first oxidant and/or the second oxidant further comprises H2O (steam) and/or CO2.
In one embodiment, the first oxidant and the second are same. In one embodiment, the first oxidant and the second are of different compositions.
In one embodiment, the first oxidant comprises air, enriched air, oxygen with purity greater than 85 wt %, oxygen with purity greater than 95 wt %, or a combination thereof, and the second oxidant comprises at least one of air, enriched air, oxygen with purity greater than 85 wt %, oxygen with purity greater than 95 wt %, premixed with H2O and/or CO2.
In one embodiment of the process of the present invention, the syngas composition formed has a H2:CO ratio from about 0.5 to about 1.5, preferably about 0.8 to about 1.0.
In one embodiment of the process of the present invention, the carbonaceous fuel material comprises biomass fuel selected from wood chips, railway tie chips, waste wood, forestry waste, sewage sludge, pet coke, coal, Municipal Solid Waste (MSW), Refuse-derived Fuel (RDF), or any combination.
In one embodiment of the process of the present invention, the biomass fuel is formed by a chipping, shredding, extrusion, mechanical processing, compacting, pelletizing, granulating, or crushing process. In one embodiment, the biofuel sprayed with, coated with or impregnated with liquid or solid carbonaceous materials is used.
In one embodiment of the process of the present invention, the POX stage temperature is greater than 1250° C., or greater than the ash fusion temperature to create liquid slag.
In one embodiment of the present invention, the process further comprises adding an additional slag separation chamber to remove and quench the liquid slag to form a non-leachable by-product for safe disposal.
In one embodiment of the present invention, the process further comprises processing and cooling the tar free syngas to be used for electric power generation and chemical production, such as methanol, DME gasoline, and Fischer Tropsch liquids, such as syndiesel, synthetic jet fuel and synthetic wax.
In another aspect of the present invention, there is provided an apparatus for a continuous multi-stage vertically sequenced gasification process for conversion of solid carbonaceous fuel material into clean (low tar) syngas. The apparatus of the present invention comprises a pyrolysis zone, a partial oxidation zone located vertically downstream of the pyrolysis zone for conversion of pyrolysis vapours into syngas, and a reduction zone located vertically downstream of the partial oxidation zone. A separation member is positioned between the pyrolysis zone and the partial oxidation zone, which comprises a plurality of vertically inclined vents to allow pyrolysis vapours into the partial oxidation zone, and the separation member is configured to direct the pyrolysis residue into the reduction zone. The apparatus further comprises an outlet for ash, positioned downstream of the reduction zone, and an outlet for the syngas positioned after the reduction zone. The reduction zone is provided with an inwardly and downwardly angled perforated floor and a deflector/diffuser located in the center of the floor, and configured to form a bed of pyrolysis residue having a uniform depth and radial width.
In one embodiment of the apparatus of the present invention, the pyrolysis zone, the partial oxidation zone and the reduction zone are comprised with one container/chamber.
In one embodiment of the apparatus of the present invention, the lower portion of the pyrolysis zone has a perimeter greater than that of the upper portion. In one embodiment, the pyrolysis zone has gradually increasing perimeter towards the lower portion.
In one embodiment of the invention, the apparatus further comprises an outer shell having a shell inlet in communication with the syngas outlet, and a shell outlet, wherein the outer shell encircles/surrounds the pyrolysis zone, the partial oxidation zone and the reduction zone to form a channel for flow of the syngas toward the shell outlet. In one embodiment, the shell outlet is provided on an upper portion of the shell to allow the syngas to move upward in the channel to provide indirect thermal contact between the syngas and the pyrolysis zone.
In one embodiment of the apparatus of the present invention, the pyrolysis zone, the partial oxidation zone and the reduction zone are comprised within separate containers/chambers.
Further details relating to the apparatus and the process of the present invention are as follows.
With reference to
BioFuel+heat energy+optional oxidant→H2+CH4+CO2+reduced char
The pyrolysis vapours generally contain relatively high portion of volatile organic tars derived from the pyrolysis process, which normally causes significant plugging and fowling problems if condensed and cooled in downstream systems, resulting in very low gasifier reliability and on-stream performance.
As the carbonaceous fuel material/biofuel advances vertically towards the lower portion of the vertical Pyrolysis stage (30), the fuel will reduce by more than 70% weight to char or commonly known as “wood coal” with significantly lower density than the feed biofuel. The novel vertical configuration with increasing perimeter, disclosed in the present application allows gravity to drive the biofuel consistently and uniformly advance vertically through the pyrolysis stage. This inherently provides for stable and consistent production of syngas. In one embodiment of the invention, any or all portions of the pyrolysis chamber walls slope slightly and/or gradually outward from the top of the biomass fill level to the lowest point where reduced char is present, where the bottom of the chamber is larger in area/perimeter than the top of the chamber. This allows the biomass material to advance without holdup and bridging, which further provides for continuous stable flow of advancing biofuel and produced syngas.
The Pyrolysis zone (30) and POX zone (40) are separated by a separation member (65), such as an inverted or inclined hemispherical or conical ceramic heated membrane as shown in
A suitable rotating mechanical spreader, well known to those skilled in the art is placed at the surface of the pyrolysis zone 20 to evenly spread the biomass feed (10) into the top of the pyrolysis zone. The equal or even height of the biomass allows the reducing biomass to flow consistently and stably through pyrolysis stage and produce a very desirable stable flow of syngas.
A second oxidant (100), whether pure or mixed, is added below the heated membrane (65) in the POX zone (40), to create a partial oxidization temperature of greater than 900° C., more preferred greater than 1000° C., up to 1250° C. for non-slagging, and greater than 1250° C. or an ash fusion temperature for slagging. Pyrolysis vapours pass through vertically inclined passages/slanted vents (70) from pyrolysis zone and are partially oxidized with the second pure oxidant or mixed oxidant to reform the pyrolysis gas to raw syngas consisting primarily of CO, CO2 and H2, with lower concentrations of CH4, N2, and Ar, and significantly reduced concentrations of tar. The composition of inerts in the raw syngas is dependent primarily on composition and quality of oxidant.
The pure or mixed oxidant can be air (containing nitrogen), enriched air (containing lower portion of nitrogen), O2 of relatively high purity (>85 wt % O2, preferred greater than 95 wt % and more preferred greater than 98 wt % to avoid inefficient inert purging), air or O2 mixed with CO2 and/or steam (H2O). The presence/addition of H2O and CO2 in the pyrolysis zone enhances the decomposition and cracking of the primary and/or secondary tars. The CO2 and H2O can be premixed with second oxidant and used in POX zone to control temperature if O2 or enriched air is used. Optionally, external methane CH4 can also be mixed into oxidant or added separately, to add heat energy to control POX zone temperature if needed.
The reduction zone in the present invention comprises an inwardly and downwardly angled perforated floor/base (125) and a deflector/diffuser (110) located in the center of the floor/base. The deflector can be of any size and shape (such as conical or cylindrical). The perforated floor/base is spaced at a predetermined distance (D) from the separation member as shown in
With the uniform char bed (120) having uniform depth (d) and width (h), the raw syngas flow space velocity is consistent and pressure drop is low and consistent, to maximize the benefits and effect of the endothermic reaction in the reduction zone. Raw syngas vapours (90) rich in CO2 and/or steam (H2O) and containing a reduced concentration of tars passes in contact with the uniform hot bed (120) of carbon rich ash/char whereby following reactions occur;
C+CO2→2CO ΔH=+13.369 kJ/kg (1)
C+H2O→CO+H2 ΔH=+9.846 kJ/kg (2)
The high temperatures of the POX raw syngas carries sufficient physical enthalpy, CO2 and/or H2O to drive the endothermic carbonization reactions. Higher feed concentrations and varied amounts of CO2 and steam (H2O) can be added to the second oxidant in stage 2 to optimize the reactions (1) and (2) in stage 3, maximize tertiary tar decomposition and maximize carbon conversion from the char. Feed levels of CO2 and H2O greater than the stoichiometric levels, can also be added to the oxidant to cool the temperature of the POX zone to below 1250° C., if the oxidant used is concentrated O2, with low or no levels of N2.
A suitable mechanical spreader (not shown), well known to those skilled in the art can be added at the char bed to evenly spread and maintain a consistent depth of the char bed. In one In a further embodiment, the floor of the reduction zone is formed of a bed support screen (125), which is continuously or intermittently physically rotated and/or agitated to continuously assist with the vertical transfer of the clean ash to a lower bed (150) for removal. A suitable ash level controller can be used to maintain a consistent ash level on screen. Additional ash agitator means, flow gates, and cooling system is provided to cool and physically remove the clean ash (160) from the lower proximity of the gasifier.
The raw syngas (90), containing reduced level of tars at a temperature greater than 900° C., is directed vertically downward through the evenly distributed char bed (120) in the Reduction zone. This results in the following very desirable benefits;
The inventors of the present invention have surprisingly found that the configuration of the separation member to direct the pyrolysis residue/char into the reduction zone and its placement at a predetermined vertical distance (D) from the inwardly downwardly angled perforated floor (having an angle greater than 0° to greater than the angle of material repose shown as Ø, preferred to be about 20° to 40° for most ash char compositions) of the reduction zone, which is provided with agitation (typically in form of continuous or intermittent rotation, and/or oscillation vibration as an example), and a deflector located in the center of the floor, results in the formation of a reduction bed of pyrolysis residue having a uniform depth (d), and width (h).
The uniform bed provides the critical uniform pressure drop and flow distribution of the raw syngas from the pyrolysis zone over the entire residue or char bed which facilitates consistent flow and consistent quality of raw syngas and clean ash.
The uniform pyrolysis residue bed promotes an efficient endothermic reaction between CO2 and H2O in the syngas and carbon content in the pyrolysis residue, and by controlling the reduction zone residence time and syngas flow space velocity during the endothermic reaction without any risk of channeling, results in the formation of substantially tar free raw syngas, reduction of carbon content in the pyrolysis residue, and reduction in the temperature of raw syngas as compared to the temperature of the partial oxidation zone.
In one embodiment, the CO2 and H2O accelerate the decomposition of the tars producing substantially tar free syngas comprising less than 200 ppm of tar. In one embodiment tar is less than 100 ppm, further in one embodiment, tar is less than 50 ppm. In one embodiment, substantially tar free syngas comprises less than 10 ppm of tar.
In the embodiment, when the Stage 2 temperature is operated above ash fusion temperature, typically above 1200° C., then a liquid slag is formed, which can be separated, quenched and converted to vitrified solid which is non-leachable and safe to dispose in normal means. The ash, in whatever form, is removed from the gasifier and cooled for storage and disposal.
As depicted in
In the embodiment depicted in
As shown in
Typical feed streams 2 may include chipped, pelletized, shredded or mechanically processed wood, construction wood waste, coal, petcoke, forestry waste wood with or without green and bark material, solid sewage sludge, selected municipal solid waste (MSW), controlled refuse-derived fuel (RDF) containing specific compositions of plastic and biomass, agricultural waste, or any blended or combinations of above materials. The Heating Value of these materials range from 3000 to 6000 BTU/lb for MSW, to 7000 BTU/lb for RDF, to 7000 BTU/lb for wood chips, to 10000 BTU/lb for coal, to 13000 BTU/lb for petcoke. In a further embodiment, the biomass fuel can be sprayed, coated with or impregnated with liquid or solid carbonaceous materials to enhance the gasifier process. All biomass feed materials may contain moisture levels of 0 to 50 wt % whereby waste heat from gasifier is used to dry materials to 5 to 15 wt %, preferred to 10 to 12 wt % before being fed 10 to gasifier. Integrated drying means using excess low level heat energy from the Biomass Gasifier process increases the overall thermal efficiency of the unit. Moisture content of biomass may vary from summer to winter seasons. The biomass material is typically sized from +1 mm to −100 mm, well known to those skilled in the art to facilitate favorable material handling and flowing properties.
The physical size or shape of each gasifier process stage and zone can vary and be adjusted by those skilled in the art and may or may not be physically the same for each stage. The key is that the stages and zones are configured in the correct sequence, or more preferred, correct vertical sequence to achieve the desired results as disclosed.
The biomass gasification process may be performed in separate vessels or groupings of vessels or more preferred, in a single vessel as long as the process sequence and vertical flow sequence is performed as disclosed to create the novel desired process performance.
The process may be operated at any pressure to accommodate the economic integration with the downstream processes or the biomass gasification process must be suitably equipped with syngas compression means. By way of example the process can be operated at slightly vacuum conditions to near atmospheric pressure for electric power generation applications, where a clean syngas booster blower fan is used to create 1 to 10 psig pressure to feed to the syngas engines driving electric generators. In another example, the biomass gasifier process may operate at 10 to 100 psig, feeding syngas to a suitable gas compressor, well known by those skilled in the art, to boost the pressure to 300 to 500 psig to process in a Fischer-Tropsch unit for production of synthetic products, such as syndiesel.
Other features, such as various syngas cleanup unit operations, including unit operations such as a high efficiency, high temperature particulate separator or ceramic filter are added to remove fine particles from the raw syngas. These features may be integrated directly into the gasifier unit or be installed directly downstream of the gasifier to effect the process.
It is obvious that the foregoing embodiments of the invention are examples and can be varied in many ways. Such present or future variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
This application claims benefit of U.S. Provisional Patent Application No. 62/401,711 filed Sep. 29, 2016, which is hereby incorporated by reference as part of the present disclosure.
| Number | Date | Country | |
|---|---|---|---|
| 62401711 | Sep 2016 | US |
