A METHOD FOR PROCESSING CONDENSED FUEL BY MEANS OF GASIFICATION

Abstract: The invention pertains to methods to process low-grade condensed fuels, primarily highly humid ones by means of pyrolysis and gasification of their organic part so as to produce liquid hydrocarbon products of pyrolysis and fuel gas, which are used for energy generation. The method can be used for environmentally friendly processing/disposal of poorly combustible wastes. The fuel is charged in a gasifier reactor type of a shaft kiln, possibly together with a solid incombustible material countercurrently to an oxygen-containing gasifying agent and combustible components of the charge are gasified. Smoke gases are introduced in the gasifying agent. The maximum temperature in the reactor is controlled within 800 to 1300 DEG C by means of variation of the fraction of the smoke gas in the gasifying agent; the oxygen content in the gasifying agent is controlled within 2 to 18 % vol.

Description: A METHOD FOR PROCESSING CONDENSED FUEL BY MEANS OF GASIFICATION This invention pertains to methods for processing various condensed fuels, primarily highly humid ones, such as solid municipal waste, biomass wastes, sludges and slurries, coal by means of pyrolysis and gasification of their organic part so as to produce hydrocarbon products of pyrolysis and fuel gas, which are used for energy generation. The method can be used for environmentally friendly and energy efficient processing/disposal of poorly combustible wastes . A number of methods for incineration of combustible wastes with energy generation is known. Among those, distinguished by their environmental friendliness are the methods based on two-stage processing, first gasification and then combustion of the product gas. For processing of oil shale this scheme is described in the patents US-A-2 796 390 (Elliott) and US-A 2 798 032 (Martin et al . ) . Generally, the gasification of organic fuels in counterflow of a gasifying agent can be presented as follows . The gasifying agent containing oxygen and possibly water and/or carbon dioxide enters the combustion zone wherein oxygen reacts at 900—1500°C with the carbon of solid fuel in the form of char. The gasifying agent is fed to the reactor countercurrently to the fuel so that the oxidant gas at least partially is passed through a layer of solid combustion products (ashes) that already do not contain carbon. In this zone, solid combustion products cool down and the gasifying agent, correspondingly, heats before it enters the combustion zone. In the combustion zone, the oxygen of the gasifying agent is totally consumed and hot gaseous combustion products, including carbon dioxide and water, enter the next zone of the charge, which is called reduction zone, where carbon dioxide and steam react with the carbon of fuel yielding combustible gases. The sensible heat of the gases heated in the combustion zone is partially consumed in these reduction reactions. The temperature of the gas flow drops as the gas filters through the fuel and lends to the latter its sensible heat. The fuel heated in oxygen-free environment is pyrolyzed yielding char, pyrolysis tars, and combustible gases. The product gas is passed through fresh fuel so as to cool down the gas while fuel is heated and dried. Finally, the product gas (containing steam, hydrocarbon vapors, and tars) is withdrawn for further use. A method described in patent RU-2079051 (Manelis et al . ) proposes gasification of solid municipal waste in a countercurrent of a gasifying agent containing oxygen and also water and/or carbon dioxide. The maximum temperature in the combustion zone (i.e., maximum temperature in the reactor) is controlled within 700 to 1400°C (preferably 1000 to 1200°C) while the temperature of the product gas at the reactor outlet is maintained below 400°C (preferably under 250°C) . The temperature regime of the process is controlled through variation at least one of the following parameters, mass fraction of oxygen in the gasifying agent "a", mass fraction of incombustibles in the fuel charge "J ", mass fraction of combustibles in the fuel charge "c", while the ratio A = ab/c is maintained within 0.1 to 4.0. Preferably, A is maintained within 0.15 < A < 1.0. For gasification of coal and other carbonaceous fuels similar processing scheme is disclosed in patent RU-1761777 (Manelis et al . ) Analogous countercurrent scheme is also applicable to processing hydrocarbons (e.g., oil slurries) as disclosed in patent application RU- 96/119443 (Manelis et al . ) provided that slurries are charged together with a solid incombustible material. In all abovementioned cases, introduction of water (carbon dioxide) in the gasifying agent provides means to enhance content of hydrogen (carbon monoxide) in the product gas and to reduce the temperature in the combustion zone. On the other hand, supply of steam necessitates introduction of additional equipment in the installation. Besides, a general drawback of the aforementioned methods when applied to gasification of humid fuel is unavoidable addition of steam to the product gas. The latter is diluted with steam, which further increases heat losses with the smoke gas and reduces energy efficiency of the boiler and of the process in general . The objective of this invention is to perform pyrolysis and gasification of condensed fuels without external heat supply, with high energy efficiency and high yield of valuable products, (pyrolysis tars and combustible gases) . This invention provides a method for processing condensed combustibles that includes : charging in the reactor a mixture that possibly contains pieces of solid incombustible material and at least partially consists of combustible components so as to pyrolyze and gasify the latter; - establishing gas flow through said charge by means of supply into said reactor, into a zone where solid processing products accumulate, of a gasifying agent containing oxygen, steam and carbon dioxide, withdrawal of gaseous and liquid processing products, the successive cross-sections of said charge successively enter the zones of heating, pyrolysis, coking, gasification, and cooling; - discharging solid residue of processing from the reactor; and burning at least part of the combustible gas, which is distinguished by that the smoke gas formed in burning of combustible gas is introduced into gasifying agent, the oxygen content in the gasifying agent preferably being maintained within 2 to 18% by volume. Thus it is possible to combine relatively high combustibility of the product gas with high energy efficiency of the process. In order to secure uniform distribution of the gasifying agent over the reactor cross-section one can introduce in the charge pieces of incombustible material predominantly with mesh size less than 200 mm. This also provides possibility to compensate dilution of the gasifying agent with the nitrogen of the smoke gas. The heat exchange with solid incombustible material provides a possibility to preheat the gasifying agent and thus to increase the temperature in the gasification zone . _ The regulation limits for the aforementioned parameters can be found experimentally for each particular case depending on the fuel composition. The gasifying agent is supplied to the part of the reactor where solid products of processing accumulate so as to pass gas flow through the layer of these products. The gasifying agent or its constituents can be supplied in one stream or in distributed mode. In particular, air and smoke gases can be supplied via their own separate inlets. The mixture charged enters the preheating zone wherein it heats to 300°C owing to heat exchange with the combustible product gas. The product gas is withdrawn from the preheating zone. Here the name product gas refers to aerosol comprising pyrolysis tars as vapors and fine droplets and generator gas incorporating carbon monoxide and dioxide, steam, hydrogen, methane, ethylene, propane, and other gases. Further the charge enters the pyrolysis zone, where it heats to 300 - 500°C due to heat exchange with gas flow and combustible materials pyrolyze emitting volatiles to the gas and forming carbonaceous residue. Further the mixture containing pyrolyzed waste enters the coking zone where coke is formed from the organic matter of waste at 500 - 800°C. Further the mixture containing coked combustibles enters the gasification (combustion) zone where preheated gasifying agent reacts with the coke at 800 - 1300°C to yield combustible gas and solid residue of combustion. Finally, the solid residue enters the cooling zone where owing to heat exchange of the solid residue with countercurrently supplied gasifying agent the latter is preheated. The above classification of the zones is in part arbitrary, they might be defined alternatively, say according to gas temperature or composition and state of the reactants. However, for any notation chosen the distinctive feature that owing to counterflow of the gas and the charge, the gasifying agent (oxidant gas) preheats due to heat exchange with the solid residue and further hot gaseous products lend their heat to fresh mixture charged into reactor. Upon completion of the process solid residue of processing is discharged from the reactor. This residue can be processed, e.g., on a sieve and pieces of solid incombustible material isolated from the residue can be used for preparation of processing mixture. In particular, this applies to recycling of solid material intentionally introduced in the mixture. The product gas withdrawn from the reactor can be burnt directly in a gas burner of power- generating utility. It also can be cleansed or processed according to known technologies. Thus, pyrolysis oils can be condensed and used as a hydrocarbon feedstock and uncondensed gas as a fuel gas . The smoke gas can be supplied as a component of gasifying agent either directly, or, alternatively, after being used for preliminary drying of the waste. In the latter case one can achieve both lower humidity of the waste charged into reactor and reduce overall volume of recycled smoke gas; correspondingly higher becomes combustion temperature of the product gas. Thus, unlikely to the methods known from the previous art, this invention makes possible pyrolysis and gasification of low-grade condensed fuels without additional heat supply and with high energy efficiency. The energy necessary to support the process is supplied by combustion of a fraction of combustible part of the waste. Introduction of steam and carbon dioxide from the smoke gas provides a possibility to enhance content of combustible components (hydrogen and carbon monoxide) in the product gas, while use of the smoke gas allows one to avoid additional energy expenditure to produce steam, only water contained in the waste is used in the process. The figure schematically presents a possible materialization of the process. Waste "W" is prepared in crasher 1, further in mixer 2 it is mixed with solid incombustible material "I" and then charged into shaft kiln reactor 4 through lock 3 at its upper part. In reactor 4 the mixture successively passes through heating zone 5, pyrolysis zone 6, combustion zone 7, and cooling zone 8. Solid processing residue "R" is continuously discharged via lock 9 with the rate controlled so as to maintain combustion zone at certain elevation from the reactor bottom. The solid residue is fractionated on sieve 10 and part of it is recycled as solid material mixed with waste and the rest of solid residue is directed for further processing or disposal. Air "A x " is supplied by fan 11 to the lower part of the reactor. To the same zone exhaust fan 12 supplies smoke gas "S". The product gas "G" is withdrawn from the upper part of the reactor and directed to gas cleansing unit 13. In the condenser liquid products "C" are isolated from the product gas. The product gas is directed for combustion with air "A 2 " in steam boiler 14. A fraction of smoke gas "S" is directed to drier 15, where waste "W" is dried with the heat of smoke gas. The temperatures in respective zones are measured continuously and when the temperatures deviate from prescribed optimal values, the control parameters are adjusted. In case the temperature in the combustion zone exceeds the prescribed limits the fraction of smoke gases in the gasifying agent is increased, correspondingly higher becomes content of steam and carbon dioxide in the gasifying agent and greater contribution of endothermic reactions C + C0 2 → 2 CO C + H 2 0 → CO + H 2 and temperature in the combustion zone drops. Alternatively, when the temperature in the combustion zone falls below prescribed limits the fraction of smoke gases in the gasifying agent is reduced. The concentration of oxygen in the gasifying agent is maintained within 2 to 18% by volume; when the oxygen concentration falls below said limit, this results in excessive dilution of the product gas with nitrogen of the smoke gas and this hampers combustion of the fuel gas, whereas at higher oxygen concentration there is insufficient yield of hydrogen and carbon monoxide according to aforementioned reactions. The other features and advantages of this invention are disclosed in the following nonrestrictive examples. Example (1) . Processed is solid municipal waste of the 8 following composition (wt.%): paper and cardboard 38.2, food residues 28.6, wood and leaves 1.8, textiles 4.9, leather and rubber 0.6, polymers 7.0, bones 1.0, metals 4.0, glass and stones 5.1, fines 9.1, having humidity 47% and calorific value of 5.87 GJ/t. The composition of dry mass is : C - 32.25%, H - 4.46%, O - 25.78%, N - 0.93%, S - 0.32%, ash - 33.26%. This composition is typical of solid municipal waste (SMW) of Moscow. 1A. SMW is gasified with addition of 10 wt.% of solid inert material in the processing mixture and supply of the gasifying agent comprising 200 g steam per 1 kg of air. The product gas is burnt with supply of secondary air so as to maintain volume concentration of oxygen in the smoke gas at 2% (on dry gas basis; i.e. overall stoichiometric ratio of oxygen is 1.1) . Total air consumption (sum of that fed as gasifying agent constituent and secondary air fed to the gas burner) is 2.8 t per ton of SMW. For the specified parameters of gasification 170 kg of steam is consumed for gasification of 1 t SMW. The smoke gas produced comprises (vol. %) : N 2 - 53.9, C0 2 - 11.0, 0 2 -1.3, Ar - 0.6, H 2 0 - 33.2%; yield of smoke gas is 3190 nm 3 per ton of SMW. IB. SMW is gasified as in 1A but with gasifying agent composed of smoke gas and air in 11:10 volume ratio. The smoke gas produced comprises (vol. %) : N 2 - 57.8, C0 2 - 11.8, 0 2 -1.3, Ar - 0.7, H 2 0 - 21.3; yield of smoke gas is 2980 nm 3 per ton of SMW. 1C. SMW is gasified as in IB but with gasifying agent composed of smoke gas and air in 7:10 volume ratio, the smoke gas withdrawn from boiler at 250°C, being directed for drying of SMW. Smoke gas dries ca. 50 kg of water from a ton of SMW. This water as steam enters the gasifying agent The composition of the smoke gas and yield of the smoke gas are the same as in IB. The heat loss with smoke gas (primarily as the condensation heat of the steam in the smoke gas in 1A is ~ 500 MJ/ton of SMW higher than that in 1B,C. Example (2) . Processed is biomass waste having humidity of 35% and ash content of 10% per total mass; the calorific value of the waste is 9.6 GJ/t. 2A. The waste is gasified with addition of 20 wt.% of solid inert material in the processing mixture and supply of the gasifying agent comprising 200 g steam per 1 kg of air. The product gas is burnt with supply of secondary air at 1.1 overall stoichiometric ratio of oxygen. The smoke gas produced comprises (vol. %) : N 2 - 57.8, C0 2 - 12.8, 0 2 -1.5, Ar - 0.7, H 2 0 - 27.8%; yield of smoke gas is 3620 nm 3 per ton of fuel . 2B. The waste is gasified as in 1A but with gasifying agent composed of smoke gas and air in 8:10 volume ratio. The smoke gas produced comprises (vol. %) : N 2 - 60.1, C0 2 - 13.3, 0 2 - 1.5, Ar - 0.7, H 2 0 - 23.5; yield of smoke gas is 3485 nm 3 per ton of SMW. 2C. The waste is gasified as in 2B but with gasifying agent composed of smoke gas and air in 5:10 volume ratio, the smoke gas withdrawn from boiler at 250°C, being directed for drying of SMW. Smoke gas dries ca. 30 kg of water from a ton of SMW. This water as steam enters the gasifying agent The composition of the smoke gas and yield of the smoke gas are the same as in 2B. The heat loss with smoke gas per ton of waste in 2A is ~ 350 MJ higher than that in 2B,C. Example (3) . Processed is oil slurry having humidity of 30% hydrocarbon content 60%, and ash content of 10% per total mass; the calorific value of the slurry is 10 22 . 6 GJ/t . 3A. The slurry is gasified in mixture comprising 30 wt.% of slurry and 70% of solid inert material in the processing mixture and supply of the gasifying agent comprising 100 g steam per 1 kg of air. For each ton of slurry processed 200 kg of oil is condensed from the product gas and uncondensed gas is burnt with supply of secondary air at 1.1 overall stoichiometric ratio of oxygen. The smoke gas produced comprises (vol. %) : N 2 - 69.8, C0 2 - 13.8, 0 2 -1.7, Ar - 0.8, H 2 0 - 13; yield of smoke gas is 5560 nm 3 per ton of fuel . 3B. The waste is gasified as in 3A but with gasifying agent composed of smoke gas and air in 1:1 volume ratio. The smoke gas produced comprises (vol. %) : N 2 - 71.5, C0 2 - 14.1, 0 2 - 1.7, Ar - 0.8, H 2 0 - 11.9; yield of smoke gas is 5430 nm 3 per ton of slurry. The heat loss with smoke gas per ton of waste in 3A is ~ 270 MJ higher than that in 3B. Example (4) . Processed is brown coal having humidity of 29%, 41% content of combustibles, and ash content of 30% per total mass. 4A. The coal is gasified with supply of the gasifying agent comprising 300 g steam per 1 kg of air. The product gas is burnt with supply of secondary air at 1.1 overall stoichiometric ratio of oxygen. The smoke gas produced comprises (vol. %) : N 2 - 60.2, CO- - 10.9, 0 2 -1.5, Ar - 0.7, H 2 0 - 26.2, S0 2 - 0.5; yield of smoke gas is 4500 nm 3 per ton of fuel. 4B. The coal is gasified as in 4A but with gasifying agent composed of smoke gas and air in 1:1 volume ratio. The smoke gas withdrawn from boiler at 250°C, being directed for drying of coal. Smoke gas dries ca. 65 kg of water from a ton of coal. The smoke gas produced comprises (vol. %) : N 2 - 65.7, C0 2 - 11.9, 11 0 2 - 1.6, Ar - 0.7, H 2 0 - 19.2, S0 2 - 0.3; yield of smoke gas is - 4120 per ton of coal. The heat loss with smoke gas per ton of coal in 4A is ~ 800 MJ higher than that in 4B . A comparison of the above examples shows that use of smoke gases as a component of the gasifying agent in gasification of combustible wastes provides a possibility to enhance energy efficiency of the process, as compared with the use of steam from external source, since heat loss with smoke gases becomes less. Additionally to that this allows one to exclude special apparatus for steam production. Use of the smoke gas for preliminary partial drying of the fuel provides possibility to reduce volume of the smoke gas recycled and enhances the temperature of combustion of the product gas in burner.

Claims: 12 CLAIMS 1. A method for processing materials that at least partially comprise combustibles, which includes charging in the reactor of a mixture that is at least partially composed of combustible materials; establishing of a gas flow through said mixture by means of supplying to said reactor a gasifying agent, containing oxygen, carbon dioxide, and water; and withdrawal of gaseous and liquid products of processing from the reactor wherein successive cross- sections of said charge successively stay in the zones of heating, pyrolysis, coking, gasification, and cooling; control of the temperature in the combustion zone within 800 - 1300 °C; discharging from the reactor solid products of processing; burning of at least part of the combustible gas produced, charact eri sed in that smoke gas, preferably in mixture with air, is used as the gasifying agent. 2. A method according to Claim 1, charac t eri sed in that the oxygen concentration in the gasifying agent is maintained within 2 to 18 vol . % . 3. A method according to anyone of Claims 1, 2, charac t eri sed in that the maximum temperature in the reactor is maintained constant by means of adjustment of the fraction of the smoke gas in the gasifying agent supplied to the reactor. 4. A method according to anyone of Claims 1- 3, characteri sed in that at least part of said smoke gases is directed for drying of raw material, the steam evaporated in drying being incorporated in the gasifying agent.

Inventors: FOURSOV VICTOR P, MANELIS GEORGI B, POLIANTCHIK EVGUENI V, FOURSOV, VICTOR P., MANELIS, GEORGI B., POLIANTCHIK, EVGUENI V.
Applicants: FIOTER OY, FOURSOV VICTOR P, MANELIS GEORGI B, POLIANTCHIK EVGUENI V, FOURSOV, VICTOR P., MANELIS, GEORGI B., POLIANTCHIK, EVGUENI V.
Application year: 1999
Main classification: C10J3
IPC codes: C10J3, F23G5