DE3130031A1 - METHOD FOR GASIFYING COAL - Google Patents

Description

The invention relates to a method for gasifying coal with oxygen, air or oxygen-enriched air and water vapor and / or carbon dioxide in a first gasification stage, preferably in a Winkler generator, at temperatures below the slag softening point in the range from about 800 to 1200 ⁰ C and pressures in the range from 1 to 100 bar with the formation of a gas containing hydrogen, carbon monoxide and carbon-containing fines and further gasification of the carbon-containing fines in a second gasification stage.

In the case of coal gasification in a fluidized bed, for example in a Winkler generator, carbon-containing fine material is discharged from the generator with the raw product gas, as a result of which part of the carbon used for the gasification is lost. In the case of reactive coals, such as lignite, this proportion in the ash can be 20 % , in the case of less reactive coals, such as hard coal, up to 50 %. The higher the ash content of the coal used, the greater the loss. Since ash-rich coals are particularly suitable for gasification because of their low price, it would be advantageous to reduce or even eliminate the underutilization of the coal used due to the discharge of fines. The carbon in this partially gasified discharge is partly in graphitic form and is indeed combustible, but is relatively inert when gasified.

The following measures are known in order to recycle the carbon content of the partially gasified fines

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respectively:

1. The carbon-containing discharge is in the fluidized bed generator downstream hot cyclones separated and fed back into the generator. These returned ash particles are due to their small size very quickly again discharged, and there Their carbon content, especially in the gasification of hard coal, is predominantly in the form of graphite that is not very reactive even with multiple recirculation in the carburetor no significant Achieve increase in carbon utilization.

2. The ash particles separated from the product gas are used together with another fuel, e.g. coal dust, in conventional Burned steam generators. The steam generated in this way is mostly used to remove the carbon monoxide formed during coal gasification to convert or drive turbines in a special system.

The present invention aims to improve the carbon utilization in coal gasification in the fluidized bed, especially in the Winkler generator, by utilizing the carbon content of the flue dust discharge for gasification through the formation of mainly more carbon monoxide and hydrogen. In addition, the degree of gasification, i.e. the ratio the heat contained in the product gas can be increased to the heat bound in the coal used. After all, supposed to environmentally harmful accompanying substances in coal, such as sulfur compounds, be brought into a harmless, landfillable form.

According to the invention, this object is achieved in the above-mentioned method in that in the second gasification stage the carbonaceous fine material is gasified in a vortex gasifier at temperatures above the slag flow point, preferably at temperatures between 1450 and 1850 ⁰ C, and thereby the total degree of carbon gasification of both Increases levels to over 90 % . An essential feature of the invention is therefore the gasification of the relatively inert carbon of the fines discharge of the first gasification stage with the formation of liquid slag in a vortex gasifier. The fines / gasification agent flow is introduced tangentially into the vortex gasification chamber, so that a spiral gas flow of high speed is formed in the chamber. At the high temperatures prevailing in the vortex chamber, the inert carbon of the fly ash particles from the first gasification stage is almost completely gasified. It was found that the fly ash particles constantly lose size on their path in the vortex chamber and form slag droplets which, under the action of the centrifugal force prevailing in the vortex, are thrown onto the inner wall of the vortex chamber, so that a film of slag forms on the wall. The film runs off the wall continuously. The liquid slag collected on the gently sloping floor drains into a second chamber that is under the same pressure as the vortex gasification chamber. The wall material of the vortex gasifier can consist of silicon carbide, for example. As a result, the carbon content of the fly ash particles is largely gasified, so that the slag running off from the vortex chamber has a very low residual carbon content

having. The total degree of gasification is significantly increased, for example from 70 to 75 % for a Winkler generator alone to over 90 %, preferably to over 95 ^° L. It is particularly surprising that despite the comparatively small volume of the vortex gasifier and thus a short residence time of the gasification components In the gasifier, the greatest possible separation of slag droplets from the gas is achieved.

According to the preferred embodiment of the invention, the carbon-containing fine material is separated from the exhaust gas from the first gasification stage and is introduced into the vortex gasifier together with fresh gasification agent. This intermediate separation of the discharge from the first gasification stage results in the vortex gasifier operating independently of the first gasification stage. In particular, for a given capacity of the overall system, the vortex gasifier can be reduced in size, since the gas throughput is significantly lower than when the vortex gasifier is directly coupled to the first gasification stage. The extent of gasification can be distributed very differently between the two gasification stages. In general, most of the gasification will take place in the first stage. In special cases, however, serving as a first stage fluidized bed can be used mainly for drying, crushing and degasification and only to a small extent for the gasification of coal discontinued, so that then aer major part of the gasification takes place in the fluidized carburetor.

You can use the vortex carburetor in addition to the fines

discharge of the first stage also ground coal and / or ash from the bottom discharge of the first gasification stage, in particular one Winkler generator. It may be necessary for fly ashes with a carbon content less than about 40 to 60% by weight be able to burn a fuel in addition to the fly ash. This fuel is expediently ground coal. if Ash from the bottom discharge of the Winkler generator and the vortex gasifier is fed, the simultaneous feed of fine coal is generally required, since this ash is lower in carbon than Fly ash is. It can also be used to increase the level of sulfur binding into the slag and / or to lower the slag pour point Lime and / or dolomite in finely divided form in the vortex gasifier be blown in.

According to the preferred embodiment of the method, the gas flowing out of the vortex gasifier is rapidly cooled to below the slag flow point, fly ash separates from the gas off and pneumatically returns it to the vortex carburetor. The rapid cooling of the gas exiting the vortex gasifier is expediently carried out by indirect heat exchange with boiler feed water. As far as the gas is fine, fine slag droplets has discharged from the vortex carburetor, these solidify through cooling in the gas flow without causing caking in the pipeline. This relatively small amount of finely divided solids is then separated in a hot cyclone before the gas is further cooled, e.g. in a waste heat boiler. The pneumatic Return of the separated fly ash can for example

take place with cooled raw gas from the vortex gasifier, however gasification agent can also be used for this purpose.

Preferably one combines the carburetor from the vortex outflowing gas after cooling and airborne dust separation with the product gas of the first gasification stage after its cooling and Fine material separation. The combination expediently takes place after the two gas streams have passed through separate waste heat boilers and other cooling units have approximately the same temperature. This association is recommended if the carburetor from the vortex outflowing gas can be fed to the same utilization as the product gas of the first gasification stage.

According to the preferred embodiment of the process according to the invention, the fine material with the gasification agent is introduced tangentially into a vortex gasification chamber with an essentially vertical axis and the gas formed is eccentrically axially upwards and the liquid slag axially downwards from the chamber. The fines / gasifying agent mixture moves in the gasifier essentially on a spiral path. The gas that is formed flows to the eccentric outlet nozzle in the ceiling of the gasification chamber, while most of the slag droplets formed from the fine material are thrown onto the wall and flow from there to the central slag outlet in the bottom of the gasification chamber. The main gasification agent used is preheated air, air enriched with oxygen or technical oxygen. Besides that, you can also

Carbon dioxide and, if necessary, steam are used, surprisingly it has been shown that the carbon entering the gasifier as fine material is almost completely converted into the gas phase and the liquid slag is very low in carbon. Despite the low The height and the small volume of the vortex carburetor takes place accordingly an almost complete carbon gasification in the gas space.

Appropriately, the carburetor from the vortex draining slag granulated by contact with water and cooled. For this purpose, the slag flows out of the vortex gasifier into a second chamber below, in which it is sprayed with water. The water / granulate mixture collected in the second chamber is withdrawn from time to time into a third chamber. The greater part of the slag is obtained in a granulated form and glazed form from which harmful substances such as sulfur compounds are no longer washed out. This slag is therefore Can be dumped and is suitable for use in road construction and as an aggregate in the construction sector. The vortex carburetor works in the same way like the first gasification stage under pressure, this third chamber also serves as a pressure lock for slag discharge.

In another embodiment of the method according to the invention, that which leaves the first gasification stage is carried out Gas with the contained fine material together with further gasification agent, preferably air and / or oxygen, directly to the Vortex carburetor closed. With this direct coupling of the vortex carburetor at the first gasification stage the vortex carburetor is natural

according to an increased gas throughput compared to the first gasification stage · The system costs for gas cooling and solids separation from the gas are reduced, however, since none separate treatment of the gases from the two gasification stages is required.

Two embodiments of the method according to the invention are described in more detail below with reference to the drawing. It demonstrate

FIG. 1 shows a schematic flow diagram of a plant for carrying out the method according to the invention with intermediate separation the fines discharged from the first gasification stage;

Figure 2 is a schematic flow diagram of the vortex gasifier with the associated apparatus, insofar as these are not shown in FIG. 1;

FIG. 3 shows a schematic flow diagram of a plant for carrying out the method according to the invention without intermediate separation the fines discharged from the first gasification stage from the gas;

Figure 4 is a horizontal section of the vortex carburetor, which is used in the method according to the invention; and

Figure 5 is an axial section of the vortex carburetor according to Figure 4 with the downstream containers for cooling,

Granulation and discharge of the slag.

In the embodiment according to FIG. 1, coal in the grain size range from 0 to 8 mm is filled into a lock container 31 via a container 30, covered there with C0 ₂ / N ₂ and then fed into the charging container 32 in batches. From the charging container 32, the coal is continuously conveyed by a screw 33 into a fluidized bed gasifier 34 at a pressure of 4 bar, to which gasification agents, ie steam and preheated air / oxygen, are fed through line 35 at several points (not shown). In the fluidized-bed gasifier 34, in addition to drying and grain size reduction, partial gasification of the coal fed in takes place. The low-carbon ash that collects in the lower part of the gasifier is alternately ^{discharged by the screw 36 into two lock containers 37 a} , 37, relaxed and discharged from the process. The gas generated in the gasifier 34 passes with the fine material discharged from the gasifier through the gas line 38 into the waste heat boiler. There, part of the fine material contained in the gas is separated off and collected in the lock container 40. After the waste heat boiler, the gas flows through a cyclone 41, in which further fine material is separated, which is collected in the lock container 42. The gas is then washed with water in a venturi system 43 for further purification, and then water droplets are separated from the gas in a separator 44. Then the raw gas is released from the plant for further processing. The fine material collected in the lock containers 40, 42 is in

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a vortex gasification system 50 gasified, the following in more detail is explained. The raw gas generated in this way is combined with the purified raw gas from the first gasification stage; the educated Slag is released from the process in granulated form.

According to FIG. 2, the separated fine material, possibly mixed with finely ground coal, is metered from a fine material container into an ejector 52 which is operated with, for example, air / carbon dioxide. Through the flow of propellant, the fine material is conveyed into a feed fluidized bed 53, from which it is blown tangentially into the fluidized bed gasifier in a controlled manner with the propellant flow. In order to achieve intensive gasification conditions, the vortex gasifier 20 is supplied with preheated air and / or oxygen as a gasification agent. As already mentioned above, with the fine material discharged from the first stage, finely ground coal can also be fed into the vortex gasifier ^{via the apparatuses 51 a} , 52 ^a. In the vortex gasifier 54, the carbonaceous material is largely gasified above the slag melting point. The liquid slag collects on the bottom, runs into the container 22 and is withdrawn from the system via the lock container 26, as will be explained in more detail below. The gas generated in the vortex gasifier 20 first flows through a cooler 54, in which it is cooled below the slag melting point, so that the small proportion of the small slag droplets discharged from the gasifier 20 solidifies in the gas flow. The gas flow then passes through a cyclone 55 in which solid material is separated out. The separated solid material passes through the lock

container 56,57 to a loading apparatus 58, with which the separated Material is fed into a product gas stream through which it is pneumatically returned to the vortex gasifier 20 will. The gas stream purified in this way then passes through a waste heat boiler in a manner similar to that of the product gas from the fluidized bed gasifier 59 as well as a venturi scrubber 60 exposed to water and a downstream separator 61 for wet cleaning. Then the gas, as mentioned above, is combined with the main gas flow from the fluidized bed gasifier. But it can also be in a combustion chamber are burned, with the combustion gases of which a turbine is applied.

In FIG. 3, the same reference numerals as in FIGS. 1 and 2 have been used for the same apparatus. In this embodiment, the gas leaving the fluidized bed gasifier 34 and loaded with fine material flows through line 38 directly into the fluidized bed gasifier 20, which in this case must be made much larger than in the embodiment of the method according to FIG. 1. Otherwise, the slag from the fluidized bed gasifier 20 drawn off and granulated in the same way, as shown in FIG. The gas flow from the vortex gasifier 20 is fed after the cooler 54 and the solids separation in the cyclone 55 to a waste heat system 39 in which most of the heat content of the gas is used to generate steam. Here, as in the embodiment according to FIG. 1, further solid matter is deposited, which is collected in the container 40 and, like the solid material deposited in the cyclone, by means of a rotary valve 40 ^a

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is fed into an ejector 40 in a gas stream that the The separated material is pneumatically returned to the vortex gasifier 20. The gas is then as in the embodiment of Figure 1 in washed in the venturi scrubber 43, freed of entrained droplets in the separator 44 and released as product gas.

According to FIGS. 4 and 5, the vortex gasifier has a tangential connection 20 ^a , to which the fly ash / gasification agent mixture is fed through line 16. The mixture moves in the gasifier on a spiral path to the eccentrically arranged gas outlet nozzle 20, whereby the fly ash particles are exposed to the intensive gasification conditions under which their carbon content is largely gasified and the particles 28 lose size and pass into the liquid state. While the gas leaves the vortex gasifier through nozzle 20 and is discharged through line 18, the liquid slag collects on the gasifier bottom 20, which is slightly inclined to the gasifier axis. The liquid slag flows through the nozzle 20 ^c into the container 22 and is intensely sprayed with water through the nozzles 23 so that the slag is quenched and granulated. The water is fed to the nozzles 23 through the ring line 24. The container 22, which is under the same pressure as the vortex gasifier 20, is emptied into the container 26 from time to time. If the vortex gasifier 20 is operated under excess pressure, the container 26 can serve as a pressure lock using the valves 25 and 27.

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example

In a Winkler generator, 10000 kg / h of hard coal with an ash content of 25% by weight and a carbon content of 58.5% by weight are produced at 1200 ^° C. with 5 t / h of steam and 3500 Nm / h of 98% strength Oxygen gasified at about 4 bar. 600 kg / h of generator ash with 15% by weight of carbon are discharged from the generator; 3620 kg / h of fly ash with 45% by weight of carbon escape with the product gas. 3260 kg / h of fly ash are separated from the product gas in a waste heat boiler and a cyclone, ^{and are gasified in a vortex gasifier at 1800 °} C. and 4 bar with 98% oxygen with the addition of steam. 1830 kg / h of liquid slag with a carbon content of about 2% by weight run off the vortex gasifier. The total degree of carbon gasification is 95%, that of the Winkler generator alone is around 71%.

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Claims (1)

• ο. «.» Davy McKee AG
6000 Frankfurt 60 Process for the gasification of coal Claims "1". Process for gasifying coal with oxygen, air or air enriched with oxygen and water vapor and / or carbon dioxide in a first gasification stage, preferably in a Winkler generator, at temperatures below the slag softening point in the range of about 800 to 1200 ⁰ C and pressures in the range from 1 to 100 bar with the formation of a gas containing hydrogen, carbon monoxide and carbonaceous fine material and further gasification of the carbonaceous fine material in a second gasification stage, characterized in that the carbonaceous fine material is gasified in a vortex at temperatures above the slag flow point, preferably at temperatures between 1450 and 1850 ⁰ C, gasified and thereby increases the total degree of carbon gasification of both stages to over 90! 2, method according to claim 1, characterized in, that the carbonaceous fines from the gas of the first Separates gasification stage and introduces carburetor with fresh gasifying agent into the vortex. 3. The method according to claim 1 or 2, characterized in that that the vortex carburetor additionally ground fine coal and / or ash from the first gasification stage. 4. The method according to any one of claims 1 to 3, characterized in that the gasifier flowing off from the vortex Gas cools quickly to below the slag flow point, fly ash is separated from the gas and the separated fly ash is pneumatically returned to the vortex gasifier. 5. The method according to any one of claims 2 to 4, characterized characterized in that one carburetor flowing out of the vortex Gas after cooling and separation of fly ash with the product gas the first gasification stage after its cooling and fines separation. 6. The method according to any one of claims 1 to 5, characterized in that the fines with the gasification agent introduces tangentially into a vortex gasification chamber with a substantially vertical axis, the gas eccentrically axially upwards and discharges the liquid slag axially downwards from the chamber. 7. The method according to any one of claims 1 to 6, characterized in that 'one of the carburetor running out of the vortex Slag granulates and cools by contact with water and so transferred into a glazed form. 8. The method according to claim 1, characterized in that the gas leaving the first gasification stage with the contained fine material together with other gasifying agent directly the vortex carburetor supplies.