BG111515A - Three-stage installation for gasification of biomass using sand circulating flow with intermadiate mixing - Google Patents

Abstract

The installation is intended for the preparation of medium gas (XIII) from biomass (e.g., straw), whose ash softens at relatively low temperature. Biomass (1) passes through the pre-drier (1) and then undergoes rapid pyrolysis in the reactor (2) with circulating fluidized bed of circulating pyrolysis gas (II) and sand (III). The char is gasified in generator units (11) with air (VII) and steam (XI). In the third stage of the installation, the pyrolysis steam gas mixture (VI), purified from the ash (V), overheats first indirectly in the tubular furnace (14) with exhaust gas (lX) after the combustion of the generator gas (VIII) and then - directly in the converter furnace (16) by burning pyrolysis resin (XII), condensed from the pyrolysis steam (VI) in the gas cleaning system (18). To avoidoverruns heat, sand circulating between generator units (11) and pyrolysis reactor (2) via the intermediate temperature stage - agitator (5).

Description

THREE-STATE BIOMASS GASIFICATION INSTALLATION THROUGH INTERMIXED MIXED SAND FLOW

TECHNICAL FIELD

The invention relates to the production of medium-calorific fuel gas by thermal decomposition of low ash softening biomass due to the high content of alkaline and alkaline earth elements such as straw.

BACKGROUND OF THE INVENTION

Wood, like coal, contains very little alkaline and alkaline earth elements, so gasification uses medium temperature methods similar to those for coal gasification. In the fluidized bed method, using a single reactor and steam gasification at about 850 - 950 degrees Celsius, low calorific gas with a lower combustion heat of 5-6 MJ / standard cubic meter is obtained. With the same method and a two-reactor steam gasification scheme, an average-calorific 'gas gas with a lower combustion heat of about 13 MJ / standard cubic meter - Austrian patents AT405937B and AT507175B1 is obtained. In this scheme, steam gasification of the particles at 850 ° C is carried out in the first reactor, and in the second at 930 ° C, the charcoal residue of the first reactor is burned and the burned sand is returned to the first reactor. The resulting gas is purified and used in a gas-piston engine-generator.

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The straw has an initial ash deformation temperature of about 850 ° C and can be thermally treated at a maximum of about 760 ° C before its ash begins to adhere to the sand in the reactors, but at this temperature the Austrian method will be very low effective. In Denmark, a two-reactor method for the rapid pyrolysis of straw and the subsequent gasification of the charcoal residue is applied for the production of low-calorie straw from combustion in a steam boiler of a TPP - European Patent Application EP2284245A1 and European Patent EP1021499B1 published. In this scheme, rapid pyrolysis of finely chopped straw is carried out in the first reactor at 650 ° C, and in the second at 730 ° C an average gas gasification of the charcoal residue is carried out and the generated gas and the heated sand are returned to the first reactor. The mixture of gas and pyrolysis vapor is purified from the ashes in cyclones and then burned in a steam boiler. The first reactor is of the Circulating fluidized bed type, and the second is the fluidized bed type, in contrast to the Austrian method, where the first reactor is of the fluidized bed type and the second is of the "Circulating fluidized bed" type.

It is apparent from the prior art that there is no method of producing medium calorific biomass gas with low ash softening temperature. Medium-calorie gas is needed for economically viable distributed electricity generation through gas-piston engine-generators, since with it they have an electrical efficiency of about 38%. With low-calorie gas, their efficiency is about 34%, and larger and more expensive special engines should be used.

SUMMARY OF THE INVENTION

The invention is a three-stage biomass gasification installation which has a low initial ash deformation temperature, for example straw. The biomass is subjected to rapid pyrolysis in a circulating fluidized bed reactor and the charcoal residue is gasified into a fluidized bed steam generator. In the third stage of the installation, the gas-vapor mixture of the pyrolysis reactor is first indirectly heated in a tube furnace by combustion of the generator gas and then heated directly in a converter furnace by burning the pyrolysis resins condensed during the purification of the superheated steam-gas mixture.

Rapid pyrolysis should be carried out at a maximum of 570 ° C, since at this temperature, in addition to non-condensable combustible gases, mainly light resins are formed, which can then be converted into non-condensable combustible gases by overheating to about 850 ° C. During rapid pyrolysis at 650 ° C, mainly medium-sized resins are formed which require overheating at more than 1 000 ° C. This is technically difficult to implement and economically disadvantageous.

The minimum gasification temperature for the carbonized residue is about 730 ° C, and a pyrolysis reactor using the combustion sand from the gas generator produces a temperature drop of about 80 ° C in this sand. In order for rapid pyrolysis to be carried out at 570 ° C, the sand must be pre-cooled to 650 ° C without losing heat when cooled, and therefore it must circulate between the gas generator and the pyrolysis reactor via an intermediate temperature mixer step type "Circulating fluidized bed, which also comprises the essence of the invention. Two connected circulating sand circles and three temperature levels are obtained: 730 ° C in the gas generator, 650 ° C in the mixer and 570 ° C in the pyrolysis reactor.

According to FIG. 1, the first stage of the gasification installation consists of a drying unit 1, reactor type 2 "Circulating fluidized bed for rapid pyrolysis of finely divided biomass I, cyclones 3 and 4 and a sand mixer type 5" Circulating fluidized bed. Reversed pyrolysis gas II enters the bottom of the pyrolysis reactor 2, raises the sand and biomass into it and at about 570 ° C produces a vapor mixture and a charred residue (the so-called semi-coke). The stream III of sand and semi-coke goes through cyclone 4 to mixer 5, where the superheated steam XI mixes it with the hot stream IV of sand and ash coming from the gas generator 11. The mixed stream rises and half of the burnt sand and the semi-coke in it are sent through the cyclone 3 back to the pyrolysis reactor 2.

The second stage is an 11 fluidized bed fluidized bed gas generator. At the bottom, the second half of the sand and semi-coke in the mixer 5 is supplied through the cascade-connected cyclone 7, the mixing heat exchanger 9 and the cyclone 10. Steam XI from cyclones 3 and directed to cyclone 8 to remove ash V and then part of the steam is directed to the bottom of the gas generator. Air flow VII enters the bottom of the gas generator and creates a fluidized bed.

Part of the semi-coke is burned and at 730 ° C a gas is generated which goes into cyclone 12 and the circulating sand, heated and mixed with ash, returns to the mixer 5.

The third stage consists of the gas generator burner VIII, the tube furnace 14 for indirectly overheating the pyrolysis vapor VI, the humidifier 15 and the converter furnace 16 to directly heat the gas mixture to about 850 ° C by burning in the burner 17 of these pyrolysis resins which have not been decomposed during overheating and have condensed in the gas cleaning system 18.

The superheated pyrolysis vapor VI is directed to the gas purification system 18 and thereafter the recirculating gas II returns to the pyrolysis reactor 2 and the new pyrolysis gas XIII is burned into the engine of the generating unit 19. Exhaust gases from the engine and cyclone 10 enter the steam generator 20 and then go to the drying unit 1.

DESCRIPTION OF THE FIGURES Attached

Figure 1 is a general schematic diagram of a complete plant for the production of medium-calorific biomass gas with low ash softening temperature.

The complex includes a biomass drying unit, the proposed three-stage gasification installation, a gas treatment system, an electric generator unit and a steam generator unit.

Figure 2 is a detailed schematic diagram of the complex described in Figure 1.

EXAMPLE FOR THE IMPLEMENTATION OF THE INVENTION

The invention can be implemented in accordance with the schematic diagram of Figure 2, explained by the following two tables:

Table 1: Mass flows in the gas complex of FIG. 2

I - Biomass II - Reversible pyrolysis gas III - Sand, carbon biomass and ash IV - Sand and ash V - Ash VI - Reversible pyrolysis gas and new pyrolysis vapors VII - Air VIII - Gas from the gas generator IX - Exhaust gases X - Water XI - Water vapor XII - Pyrolysis oil XIII - Powder and water-soluble pyrolysis resins XIV - Fine powder, water and inorganic compounds XV - Reversed and new pyrolysis gas XVI - New pyrolysis gas

Table 2: Components of the gasification complex of FIG. 2

1 - Biomass receiving hopper 2 - Combustion chamber for exhaust gas 3 - Tubes 4 - Transport centrifugal fan 5 - Cyclone for separation of the dried biomass 6 - Screwdriver of feed hopper 7 - Pyrolysis reactor feed hopper 8 - Pyrolysis reactor screw dispenser 9 - Pyrolysis reactor 10 - Pyrolysis reactor inlet cyclone 11 - Sand mixer inlet cyclone 12 - Sand mixer 13 - Pyrolysis reactor ash cyclone 14 - Pyrolysis reactor ash hopper 15 - Steam collector from the sand mixer 16 - Sand cyclone for gas generator 17 - Sand mixer cyclone 18 - Sand mixer ash hopper 19 - Sand and exhaust gas mixer 20 - Inlet cyclone of the gas generator 21 - Screwdriver of gas generator 22 - Gas generator 23 - Sand mixer screw dispenser 24 - Gas generator cyclone 25 - Ash hopper from gas generator 26 - Gas generator burner 27 - Tube furnace for indirect overheating of pyrrole. money 28 - Pyrolysis money moisturizer 29 - Throttle choke 30 - Pyrolysis resin burner 31 - Converter furnace for direct overheating of money 32 - Circulating gas heater 33 - Maslen scrubber 34 - Pump for hot pyrolysis oil 35 - Circulating oil cooler 36 - Hot pyrolysis oil choke 37 - Pyrolysis oil cooler manifold 38 - Pyrolysis money trap cap 39 - Chilled pyrolysis oil pump 40 - Water scrubber 41 - Dust pools and resins dissolved in water 42 - Venturi scrubber 43 - Water vapor condenser and drip trap 44 - Dust, water and inorganic compounds 45 - Filters 46 - Pyrolysis gas compressor 47 - Compressed pyrolysis gas tank 48 - Throttle for circulating pyrolysis gas 49 - Gas throttle for engine generator 50 - Generator motor 51 - Steam boiler 52 - Water pump for the steam boiler 53 - Water tank for steam boiler 54 - Water vapor heater

The conversion of biomass to medium calorie gas goes through the following stages:

A) Drying of biomass: Finely chopped biomass I is fed into a receiving hopper 1. Cooled exhaust gases IX flow from the mixing chamber 2 and the biomass particles are drawn into the drying tubes 3. Following these tubes, the transport centrifugal fan 4 sends the mixture of dried biomass and humidified exhaust gas to cyclone 5 for biomass separation.

B) Biomass gasification of the invention:

B.1) Production of the pyrolysis gas-vapor mixture: The dried biomass enters through the auger dispenser 6 into the feed hopper 7 and from there through the auger dispenser 8 it enters the lower part of the pyrolysis reactor 9 type "Circulating fluidized bed, where from the incoming cyclone 10 also enters hot stream III of sand and charcoal biomass (semi-coke). At the bottom of the reactor enters at high speed reversed pyrolysis gas II, which swirls and carries the sand, dried and charred biomass to the top of the reactor. Ascending, the dried biomass absorbs heat from the burnt sand, is charred and a vapor-gas mixture consisting of non-condensable gases and condensing vapors of resins is released. The tip of the pyrolysis reactor is connected to the inlet cyclone 11 of the sand mixer 12 of type "Circulating fluidized bed. After cyclone 11, a lower stream of sand and semi-coke with reduced temperature enters the lower part of the mixer 12, and the circulating pyrolysis gas and the new vapor-gas mixture

• go to cyclone 13 to separate ash V in hopper 14. Also, at the bottom of the sand mixer 12 receives a hot stream IV of sand and ash from the gas generator 22 through a screw dispenser 23. At the bottom of the mixer 12 enters at high speed water vapor XI from the superheater 54, which raises and mixes the mass flows received from the pyrolysis reactor and from the gas generator. Half of the mixed stream passes through the inlet cyclone 10 of the pyrolysis reactor and after separation of the sand, semi-coke and a small part of the ash, the steam mixed with ash is directed to the water vapor collector 15 from the sand mixer.

B.2) Generation gas production: The other half of the flow in the mixer 12 enters the cyclone 16 to separate the sand for the gas generator 22. The water vapor goes to the collector 15 and from there all the water vapor XI passed through the mixer 12 goes to the cyclone 17 to separate the ash into the hopper 18. The sand and semi-coke separated in the cyclone 16 are directed to the mixing heat exchanger 19 for combustion with the exhaust gases IX from the tube furnace 27. From the next cyclone 20, the exhaust gases are directed to the superheater 54, and through the auger dispenser 21, the heated sand mixture enters the bottom of the gas generator 22, which is of the fluidized bed type. Just below it, part of the purified water vapor XI after cyclone 17 enters the gas generator. At the bottom of the gas generator enters air VII, which swirls the steam and sand mixture and burns some of the incoming char. The heat causes the remainder of the semi-coke to gasify and the resulting gas is sent to cyclone 24 to separate ash V in the hopper 25.

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B.Z) Overheating of the pyrolysis gas-vapor mixture to produce a medium-calorie gas: From cyclone 13, the ash-purified pyrolysis gas-vapor mixture is poisoned to humidifiers 28. This is followed by successive indirect overheating in the tube furnace 27 heated by the burner 26 for the gas generator VIII and direct overheating in the converter furnace 31, which enters the exhaust gases from the burner 30 for the pyrolysis resins XII. In order not to dilute the high-nitrogen pyrolysis gas, the burner could use oxygen-enriched air. The superheated steam and gas mixture VI then heats the circulating pyrolysis gas II in the heater 32 and is directed for purification.

C) Purification of the pyrolysis gas: In the oil scrubber 33, the decomposed pyrolysis resins are cooled and condensed, most of them draining from the bottom of the scrubber to the pump 34, which transports them to the reservoir 37, and the rest of the resins is trapped in the dropper 38 and it flows to the collector. From there pump 39 sends the resins to the burner 30. After passing through the water scrubber 40, the venturi scrubber 42, the condenser-trap 43 and one of the filters 45, the pyrolysis gas is pumped with the compressor 46 into the gas holder 47. From there, the amount of newly generated gas XVI is fed to the gas-piston engine-generator 50, and the circulating gas II is directed to the pyrolysis reactor 9. The exhaust from the engine enters the steam boiler 51 to generate steam XI. The steam enters the superheater 54, which is heated by the exhaust gases from the tube furnace 27 separated from the cyclone 20. The exhaust gases IX from the steam boiler 51 and from the superheater 54 enter the mixing chamber 2 and the production cycle is closed.

Claims (1)

Patent Claim Three-stage installation for gasification of biomass by circulating sand stream with intermediate mixing, realizing in various stages the processes of rapid pyrolysis, gasification of the charcoal residue after pyrolysis and overheating of the pyrolysis vapor, characterized in that according to FIG. 1 sand circulates between the pyrolysis reactor (2) and the gas generator (11) by means of an intermediate temperature step-mixer (5), whereby two connected circulating sand circles are formed and three temperature levels are obtained, thus at the temperature of the fast pyrolysis of biomass generates such pyrolysis vapors, which can be converted to medium-calorific gas by subsequent overheating without heat overflow.