DE2729764A1 - Gasification of solid fuels - with combustion of the ash in oxygen and recycling of the hot gas produced - Google Patents

Abstract

Gasification of carbonaceous fuels with air and/or O2, steam and CO2 in a fluidised bed generator, in which ash contg. unburnt carbon, taken from the product gas and from the generator, is burnt in a fluidised bed of ash at below the m.pt. of the ash. The combustion gas contg. mostly CO2 is recycled to the generator as a addnl. gasifying agent and heat carrier. Efficiency is improved by almost complete use of the unburnt carbon, and disposal of the ash simplified. Maintenance of the ash bed at below its m.pt. reduces demands made on the construction material, and avoids molten droplets of slag which deposit in the equipment. Unpurified water, e.g. condensate, from the process can be sprayed into the ash during combustion to produce superheated steam for use in the generator.

Description

The invention relates to a method for gasifying coal

Substance-containing material with oxygen or air or with oxygen enriched air and water vapor and / or C02 in a fluidized bed generator with a post-gasification zone located at high temperatures in the fluidized bed in the range of about 800 to 1200 OC to a hydrogen, carbon monoxide and carbonaceous one Product gas containing ash particles, separation of the ash particles from the product gas, Combustion of the carbon-containing ash with oxygen to form carbon dioxide combustion gas containing and a substantially carbon-free residue and use of the combustion gas as a further gasification agent and heat carrier in the fluidized bed generator.

In coal gasification in a fluidized bed generator according to Winkler Ash particles containing carbon are discharged from the generator with the raw product gas, as a result, part of the carbon used is lost for gasification. This The higher the ash content of the coal used, the greater the loss. There Ash-rich coals are particularly suitable for gasification because of their low price, would it be from Advantage, the underutilization caused by the ash discharge to reduce or even eliminate the coal used.

Some of the carbon in the gasification residues is graphitic Form before which is combustible, but compared to gasification is relatively slow to react, the following processes are known, To take advantage of the carbon content of the fly ash: 1. The carbon-containing fly ash is separated in the hot cyclones downstream of the generator and into the generator returned. These ash particles become very fast because of their small size in turn discharged, and since their carbon content, especially during gasification of hard coals, present predominantly as graphite, can also be used with multiple recirculation in the carburetor no satisfactory reduction of the Reach the carbon content of the ash particles.

2. The ash particles separated from the product gas stream are together with another fuel, e.g. coal dust, in conventional steam generators burned. The steam generated in this way is mostly used for coal gasification formed carbon monoxide in a special plant to conquer or the turbines to operate the product gas compressors.

3. Finally, it is known to contain the deposited carbonaceous Burning flue dust in a melting chamber with oxygen with the addition of steam and add the hot combustion gas to the generator as a gasification agent.

Working above the ash melting point, i.e. depending on the composition the ash in the temperature range from 1400 to 1800 OC, makes high demands the material of the melting chamber. In addition, precautions must be taken to avoid fine slag droplets from the combustion gas from the melting chamber are discharged and lead to caking in the subsequent pipeline. At the very high temperatures prevailing in the melting chamber, it evaporates Part of the ash and condenses again in the relatively colder parts of the plant in the form of an aerosol. The aerosol particles are very difficult to get out of the product gas are removed and cause operational difficulties in the downstream Systems, e.g. in product gas compressors.

The present invention aims to improve carbon utilization in coal gasification in the fluidized bed by utilizing the carbon content the ashes.

In particular, the gasification efficiency, i.e. the ratio the bound heat in the gas to the bound heat in the spent coal the utilization of the carbon content of the ash can be increased. Also can the impurities removed from the product gas are also eliminated in an environmentally neutral manner will.

According to the invention, this object is achieved in the method mentioned at the outset solved in that one separated from the product gas and from the fluidized bed generator immediately discharged carbon-containing ash in a special, essentially fluidized bed consisting of burned-out ash at temperatures below the Ash melting point burns. A higher percentage is preferably used for combustion Oxygen. Due to the increased oxygen concentration achieved in this way and the comparatively higher temperature than in the gasification fluidized bed succeeds in reducing the carbon content the ash, which is about 20 to 50% by weight, to less than 10% by weight, preferably less than 5% by weight.

Since the im. Generator not gasified often over 10% of the carbon is contained in the coal used, results in the Combustion according to the invention a significant improvement in the gasification efficiency.

The carbon contained in the ashes is burned to carbon dioxide, that in addition to the oxygen and water vapor as a gasification agent to the fluidized bed generator is fed. The temperature of the fluidized bed ash is expediently maintained in the range between the gasification temperature of the generator and the melting or sintering temperature of the ash. The burnt-out ash is made from the ash fluidized bed withdrawn and repelled from the process after their heat has been used. The conduit speed in the ash fluidized bed is up to about 50% of the maximum superficial velocity in the gasification reactor. The superficial velocity of the crude product gas in the gasification reactor is well above the point of beginning Resuspension and generally ranges up to about 6 m / s depending on the Operating pressure.

According to the preferred embodiment of the method according to the invention one splashes water, preferably contaminated condensation water from the product gas cooling and wet dedusting in the ash fluidized bed and introduces the generated water vapor Combustion gas as a gasification agent and heat carrier in the fluidized bed generator to. The injected water and the water in it evaporate in the fluidized ash bed contained impurities from the further processing of the product gas, such as e.g. sulfur compounds, cyanides, the finest fly ash, etc., are used in the high Temperatures burned with the oxygen. The sulfur contained in the fly ash and the sulfur compounds contained in wastewater provide sulfur dioxide, the gets into the gasification zone with the combustion gas and becomes hydrogen sulfide there is reduced, which in turn can be eliminated using known methods in an environmentally friendly manner can. Through the use of contaminated wastewater in the Aschewi: -belschicht becomes hence the purification of these waters for the purpose of reuse or repulsion avoided. The addition of water to the ash fluidized bed increases the temperature the fluidized bed is steamed and the ash temperature is kept below the sintering temperature. In this embodiment, the combustion gas contains water vapor, in contrast to that caused by the product gas heat in generated in a waste heat boiler Water vapor is very highly superheated and, as a result, the gasification is considerable Part of the heat needed, so that the oxygen supply to the generator and so that coal combustion, which only serves to generate heat, can be reduced. In contrast, there is the temperature of the steam from the product gas containing the H2S Heated waste heat boiler is limited to 300 to 400 OC because of higher steam overheating is limited by the material properties of the heater. The inventive Processes with the addition of water to the ash fluidized bed allow the difficult to gasify Carbon content of the ash in steam and carbon dioxide of higher temperature than to convert the gasification temperature and so by supplying this gasification agent to the gasification reactor the combustion required to maintain the temperature of the gasification to reduce the amount of coal.

According to a further embodiment of the method according to the invention one introduces water vapor into the ash fluidized bed and leads it to more direct Overheating of the gasification generator too. This water vapor can, for example, in Waste heat boilers are generated by the sensible heat of the product gas, so that in In the fluidized bed of ash, only the superheating heat is absorbed by the steam. on In this way, a larger amount of the strongly superheated steam can be provided are as if the highly superheated steam in the ash fluidized bed directly from water is produced.

According to a further form of implementation of the method according to the invention one introduces carbon dioxide into the ash fluidized bed and leads it to more direct Heating up the gasification generator. This carbon dioxide can, for example, from the product gas can be obtained.

According to the preferred embodiment of the method according to the invention it is also provided that the temperature of the fluidized bed ash in the area holds from about 1000 to 1300 OC. The temperature depends on the ash composition away. In the case of strongly alkaline or strongly acidic ashes, depending on the composition Vortex temperatures considerably above 1300 OC up to 1500 OC are also used without causing sintering phenomena. The temperature of the ash fluidized bed can be set by the ratio of the H20 and 02 or C02 and 02 used will.

The method according to the invention is described below with reference to the drawing described in more detail in the flow diagram of a plant for carrying out the process is shown.

The gasification reactor 1 is supplied with coal in the grain size range through line 2b fed from 0 to 8 mm. In the lower part of the reactor is carried out over the perimeter distributed nozzles introduced oxygen and steam. The feed to the nozzles takes place through the oxygen line 2a and the steam line 3.

In addition, the generator through line 13 is a carbon dioxide / Water vapor mixture supplied, which serves as a heat transfer medium and gasification medium and its production is described below. A is formed in the lower part of the generator 1 Coal fluidized bed la, in which a substantial part of the feed through line 2b Coal is gasified. The larger particles of the carbonaceous particles formed in the process Ashes fall through the cone tip into the discharge device (not shown) and are withdrawn through line 12. A significant part of the partially gasified coal is carried up by the fluidized medium from the fluidized bed 1a. To further Gasification of the carbon still contained in these particles is caused by silver Nozzles (not shown) distributed around the circumference of the generator by means of line 2 oxygen fed. The carbon gasification therefore settles in the upper part of the generator away.

The gas leaving the generator 1 through line 4 contains considerable amounts of gas Quantities of carbon-containing fly ash, the coarsest part of which in the hot cyclone 5 the gas is deposited.

The generator gas, which is loaded with finer ash particles, travels on through line 7 in the waste heat boiler 8, in which a cooling of the gas to about 150 to 300 OC and a further separation of ash particles takes place. The gas flows through then another cyclone 9, working at 150 to 300 OC, in which the largest Part of the remaining ash still contained in the gas is deposited. The one in the hot cyclone 5, the waste heat boiler 8 and the cyclone 9 is collected through the lines a 6, 8a and 9 discharged, combined and passed through line 10 in the fluidized bed combustion chamber 11.

In the combustion chamber 11 is brought up through line 10 carbon-containing Ash and the directly discharged from the generator 1, crushed in the mill 17, and carbonaceous ash supplied through line 18 in a fluidized bed 11a burned with oxygen supplied through line 16. Besides the oxygen the fluidized bed 11a is fed through line 15 contaminated wastewater, the originates from the wet cleaning of the product gas, not shown. In the fluidized bed 11a, the carbon content of the ash is largely burned to carbon dioxide and the water fed in with combustion or decomposition of the contaminants it contains evaporates. The result is one consisting essentially of carbon dioxide and water vapor Gas mixture, possibly entrained after a separation (not shown) Ash particles through line 13 as an additional gasification medium in the gasification generator 1 is introduced.

The ash burned out in the fluidized bed 11a is passed through conduction 14 discharged.

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Claims (6)

Method for the gasification of carbonaceous material claims 1. Process for gasifying carbonaceous material with oxygen, air or with O2 enriched air and water vapor and / or C02 in a fluidized bed generator with a post-gasification zone located above the fluidized bed at temperatures in the range of about 800 to 1200 OC to a hydrogen, carbon monoxide and carbonaceous one Product gas containing ash particles, separation of the carbon-containing ash particles from the product gas, burning the carbonaceous ash with oxygen underneath Formation of a combustion gas containing carbon dioxide and one essentially carbon-free residue and use of the combustion gas as a further gasification agent and heat transfer medium in the fluidized bed generator, characterized in that the separated from the product gas and directly from the fluidized bed generator discharged carbonaceous ash in a substantially burned out Ash existing fluidized bed at temperatures below the ash melting point burns. 2. The method according to claim 1, characterized in that one uses water, preferably contaminated water from cooling and wet cleaning of the product gas, is injected into the ash vortex layer and the combustion gas containing water vapor supplies the fluidized bed generator as a gasification agent. 3. The method according to claim 1 or 2, characterized in that one Introduces water vapor into the ash fluidized bed and, after direct overheating, the Fluidized bed generator feeds. 4. The method according to any one of claims 1 to 3, characterized in that that one introduces carbonic acid into the ash fluidized bed and after direct heating feeds the fluidized bed generator. 5. The method according to any one of claims 1 to 4, characterized in that that the temperature of the fluidized bed ash in the range of about 1000 to 1300 OC holds. 6. The method according to any one of claims 1 to 5, characterized in that that one of the combustion gas on the way from the ash fluidized bed to the coal gasification fluidized bed suspended ash particles separated without a significant decrease in the gas temperature.