EP0333991B1 - Process for conveying finely granulated to powdered fuel into high pressure gasification reactor - Google Patents

Description

The invention relates to a method for conveying a fine-grained to dusty fuel in a gasification reactor under increased pressure, in which the fuel to be gasified is conveyed pneumatically from the processing system into a storage container provided with a filter and from there into the gravity flow into a lock container from which the combustion of the gasification reactor is fed via an allotment container, the lock container being alternately pressurized and relaxed again and a combustible gas being used both for pressurizing the lock container and the allotment container and for supplying the fuel to the burners of the gasification reactor .

For the conveyance of fine-grained to dusty fuels in a gasification reactor under increased pressure, a method of operation has been known for a long time, in which the fuel to be gasified is brought to gasification pressure in a lock tank by exposure to a gas and from there via an allotment tank with the help of a Carrier gas stream is fed to the burners of the gasification reactor, the lock container being alternately pressurized and expanded again. EP-B1-0101098 describes a variant of this method, in which the lock container is covered with nitrogen or technical carbon dioxide, while as the conveying gas for the Transporting the fuel from the supply container to the burners of the gasification reactor, a combustible gas is used, which can also be a gas of our own generation. It is provided here that the fuel is kept in the fluidized state in the metering system. DE-A-2831208 relates to another variant of this method, in which both the pressurization of the lock container and the distribution container as well as a combustible gas is used for supplying the fuel to the burners of the gasification reactor. In this case too, the fuel is transferred to a fluidized bed in the supply container and is fed to the burners of the gasification reactor in the fluidized state.

The fact that in this case the lock container is charged with inert gas and the supply container with combustible gas, means that a mixed gas is displaced from these containers during the filling process, which contains both inert gas components and combustible gas components. The further use of this gas, for example in the coal processing plant, is therefore made more difficult by the safety measures required in this case. Likewise, for safety reasons, it is not readily possible to discharge this gas into the atmosphere. The high content of inert gas components also makes it practically impossible to destroy or recycle this gas without the use of additional fuels.

The invention is therefore based on the object of further developing the method of the type mentioned in such a way that the disadvantages described above are avoided and at the same time a complete return of all the gases displaced from the containers during the filling process is made possible.

The method used to achieve this object is characterized in that the volumetric flow of combustible gas supplied to the lock container and distribution container is adapted exclusively to the need for pressure build-up, pressure maintenance and supply of the fuel to the gasification reactor and a fluidized bed-like loosening of the fuel bed in the lock container and distribution container is omitted.

By using this method of working it is not only possible to avoid the disadvantages described above. At the same time, in contrast to the removal of fuel from a fluidized bed, it is also ensured that the level of the bulk material in the feed container has no direct influence on the procedural conditions of the discharge. In the interest of economic operation, it is only necessary to ensure that the mass flow entering the distribution container is approximately equal to the emerging mass flow in order to utilize the conveying gas from the subsequent supply for pressure maintenance in and the pneumatic metering from the distribution container to the gasification reactor as losslessly as possible can.

Basically, two variants are possible for carrying out the method according to the invention:

In the first variant, the partial oxidation raw gas generated in the gasification reactor is further processed into synthesis gas by the subsequent gas treatment. In this case, dust-free and dry carbon dioxide is used as the inert conveying gas, which can possibly also originate from the CO₂ scrubbing of the partial oxidation raw gas required for the synthesis gas production. The carbon dioxide used is discharged into the atmosphere after it has left the cyclone filter after appropriate cleaning. The gases displaced from the lock tank and the feed tank during the filling process, on the other hand, are returned to the process and added to the partial oxidation raw gas generated before the gas treatment thereof. As combustible gas for the loading of the lock container and the distribution container as well as for the supply of the fuel to the burners, a partial flow of the already dried and dust-free synthesis gas can preferably be used. However, a residual gas, such as from ammonia synthesis, can also be used for this purpose. If this is a residual gas containing SO₂, such as the residual gas containing SO₂ and COS from gas treatment, the gas must be kept at a temperature which is significantly above the dew point in order to avoid corrosion. In deviation from the procedure described above, it may be appropriate in this case to add the gas returned to the process directly at the burner in order to safely and completely reduce the SO₂ content with the fuel in the reaction zone of the gasification reactor.

In the second variant, the partial oxidation gas generated in the gasification reactor is used as fuel gas for the gas turbine of a downstream gas-steam turbine power plant. This way of working does not focus on relieving the gasification process of inert ballast gas, but on reducing the compressor capacity for the gases required in the system. In this case, nitrogen is therefore used as the inert conveying gas. This can preferably be a relatively impure nitrogen with an oxygen content of 3-5% by volume, which is obtained as a by-product in the air separation plant, which supplies the oxygen required for the gasification. The nitrogen used as the inert conveying gas is after the delivery and separation of the fuel in the cyclone filter together with the expansion gas from the lock tank and the feed tank of the gas turbine of the downstream Teten gas-steam turbine power plant supplied. In this case, a partial stream of the cleaned partial oxidation gas and / or a residual gas can be used as the combustible gas for the loading of the lock container and the supply container and the supply of the fuel to the burners.

Fig. 1

ein Fließschema für die Verfahrensvariante, bei der das erzeugte Partialoxidationsrohgas zu Synthesegas weiterverarbeitet werden soll und

Fig. 2

ein Fließschema für die Verfahrensvariante, bei der das erzeugte Partialoxidationsrohgas als Brenngas für die Gasturbine eines nachgeschalteten Gas-Dampfturbinenkraftwerkes verwendet werden soll.

Further details of the method according to the invention result from the present subclaims and are to be explained below on the basis of the flow diagrams shown in the figures. Here show:

Fig. 1

a flow diagram for the process variant in which the partial oxidation crude gas generated is to be further processed to synthesis gas and

Fig. 2

a flow diagram for the process variant in which the partial oxidation raw gas generated is to be used as fuel gas for the gas turbine of a downstream gas-steam turbine power plant.

In the flow diagram shown in FIG. 1, the fine-cored to dust-like fuel from the storage bunker 1 of the processing plant is conveyed pneumatically into the cyclone filter 3 at a low pressure of 2-4 bar by means of carbon dioxide as an inert conveying gas. The cyclone filter 3 has an expanded separation space 4. The carbon dioxide required for the production is introduced into the system via line 5 and leaves the almost pressure-free cyclone filter 3 via line 6. After passing through a filter 7 or a molecular seal, it can enter the system Atmosphere. The fuel, which is collected in the separating chamber 4 almost without pressure and supplemented by constant subsequent delivery, reaches the almost pressure-less lock container 9 by gravity flow via the line 8. To avoid bridging at the outlet of the separating chamber 4, additional carbon dioxide is blown into the area of the outlet via the line 10. During the filling process, there is practically no excess pressure in the lock container 9. However, the container is filled with combustible gas, which is displaced by the incoming fuel and flows off via line 11. After being cleaned in the filter 65, this displaced gas passes through the line 12 into the gasometer 13, which operates at a slight excess pressure. However, this overpressure must always be somewhat lower than the operating pressure in the cyclone filter 3, so that combustible gas in countercurrent to the fuel never reaches the separating chamber 4 and the associated cyclone filter 3 from the lock container 9. However, system-related contamination of the combustible gas drawn off via line 11 with up to 25% by volume of carbon dioxide is permitted.

After the lock container 9 has been filled to the required extent with fuel, the fuel supply is interrupted by closing the valve 14 in the line 8 and at the same time the valve 15 in the line 11 is also closed. The lock container 9 is now brought to the same pressure as the supply container 16. This is done by supplying a combustible gas via lines 17 and 18. The combustible gas which has been involved has already been explained above. As can be seen from the illustration, this gas is simultaneously into the lock tank from above and below 9 blown in. The line 17 has a plurality of outlet openings which, in the region of the funnel-shaped taper, open into the lock container 9 and are distributed uniformly over the circumference. The gas supply via lines 17 and 18 can be regulated by valves 19 and 20. By this gas supply, the gas mixture present in the lock container 9 after the end of the unpressurized filling process, which can still contain a maximum of 25 vol.% CO₂, is diluted so much by the combustible gas supplied that the inert gas portion (CO₂ portion) finally at the for Process usual operating pressures is not more than 1 vol .-%. As soon as the pressure in the lock container 9 almost corresponds to the pressure in the supply container 16, the valve 19 in the line 17 is closed and the fine adjustment of the pressure control takes place via the valve 20 in the line 18 for the gas supply and the valve 21 in the line 22 for the Gas removal. To empty the lock container 9, the valve 23 in the line 24 is opened. Likewise, the valve 25 in the pressure compensation line 26 is opened, so that gas can flow into the lock container 9 in accordance with the fuel outlet. As soon as the valves 23 and 25 are open and fuel flows out of the lock container 9, the valve 64 in the line 63 is also opened, so that additional flammable gas can flow through this line to avoid bridging when the fuel flows out of the lock container 9. This gas reduces the bulk density of the fuel-gas mixture by 10-20%. Basically, the gas supply is limited so that a fluidized bed-like loosening of the fuel is avoided.

The fuel flowing under the influence of gravity into the distribution container 16 displaces the combustible gas located there above the fuel residue, which can escape from the distribution container 16 via the line 27. The majority of the displaced gas is introduced into the lock container 9 via the pressure compensation line 26, while a small part can get into the line 22 with the valve 28 open and from there into the buffer container 29. As a result of mixing the gas in the lock container 9 after the pressure build-up with the gas stream supplied via the pressure compensation line 26, the proportion of inert gas (CO₂ content) in the combustible gas located above the fuel bed in the distribution container 16 decreases after the filling process of the distribution container so far that it only is still about 0.5% by volume. After the lock container 9 has been completely emptied, the valves 20, 23, 25 and 64 are closed, while at the same time the valve 21 is opened in the buffer container 29 to relieve the lock container 9. Before the release of the lock container 9, a pressure prevails in the buffer container 29 which corresponds to approximately 15% of the pressure in the lock container 9. As a result of the expansion, the pressure in the lock container 9 is reduced by approximately 66% to, for example, 9 bar. The majority of the combustible gas from the lock container 9 is therefore recovered at a high pressure level and can be withdrawn from the buffer container 29 via the line 30. After appropriate compression in the compressor 31, the gas is added via line 32 to the partial oxidation raw gas generated before the gas treatment 33. As the last step to relieve the lock container 9, the valve 15 in the line 11 is opened and the remaining gas with predominantly combustible constituents via the filter 65 and the line 12 passed into the gasometer 13. The fuel dust separated in the filter 65 is returned to the lock container 9 by a partial flow of the carbon dioxide from the line 5, which is supplied via the line 34. For this purpose, the valve 37 in the line 36 is temporarily opened when the lock container 9 is just depressurized before filling. The gas collected in the gasometer 13 can be drawn off via the line 38 and fed to the compressor 39, which runs on the same shaft as the compressor 31. This gas is then added via line 40 to the gas stream in line 30. If necessary, all or part of the gas drawn off via line 38 can also be fed via line 66 to another use, for example as fuel gas.

The fuel in the supply container 16 is metered via line 41 to the burners of the gasification reactor 42. This metering does not take place under the influence of gravity, but rather through the pressure difference between the feed tank 16 and the gasification reactor 42 which determines the mass flow. This pressure difference is generated by supplying combustible gas to the feed tank 16 via the lines 43, 44 and 45, the valves 46, 47 and 48 are opened accordingly. The gas flow that is supplied via line 44 covers approximately two thirds of the requirement. The introduction into the allotment container 16 takes place via a plurality of outlet openings which, in the region of the funnel-shaped taper, open out into the allotment container 16 evenly distributed over the circumference. The gas flow in line 45 is used primarily to avoid bridging when the fuel flows out of the supply container 16 this gas flow also achieves a reduction in the bulk density, but a fluidized bed-like loosening of the fuel is to be avoided. The amount of gas supplied through line 43 primarily serves to compensate for the volume when fuel is removed from the supply container 16, unless a corresponding amount of fuel flows in from the lock container 9 at the same time. However, if this is the case, then valve 46 in line 43 generally remains closed. The valve 49 in the connector 50, which connects the supply container 16 to the line 41, is of course open during the removal of fuel from the supply container 16.

The partial oxidation crude gas generated in the gasification reactor 42 is cooled in the waste heat boiler 51, which forms a structural unit with the gasification reactor 42, and then passes via line 52 into the individual stages of the gas treatment 33, in which the partial oxidation gas is converted into synthesis gas. Since these are process steps which are known per se and are generally customary in technology and which are not the subject of the present invention, there is no need to go into them in greater detail. The synthesis gas generated is withdrawn via line 53 and used for further use. A partial stream of this gas can be branched off via line 54. This partial flow is brought to the required pressure by gradual compression in the compressors 55 and 56 and then passes via line 57 to line 58, from which lines 17, 18, 63, 43, 44 and 45 depart.

Alternatively, for example, the SO₂- and COS-containing residual gas from the gas treatment 33 can be fed via line 59 to the compressors 55 and 56 and then returned to the process in the manner described above. The heat exchanger 60 is used to set the temperature of the recirculated gas flow. The oxygen or an oxygen-water vapor mixture required for the gasification is introduced into the gasification reactor 42 through the line 61. The burners of the gasification reactor 42 are designed so that they do not allow the oxygen or the oxygen-water vapor mixture to flow back into the line 41. There is no need to go into details of the gasification reactor 42 here, since this can also be a known construction. It is preferable to choose a reactor type in which the gasification takes place in a cloud of airborne dust.

Normally, no synthesis gas or residual gas and no carbon dioxide are available when the plant is started up. The lock system is then temporarily supplied with nitrogen, which is supplied via line 62. During the start-up phase, the gas supply to the gasometer 13 and to the buffer tank 29 is blocked and the expansion gases are flared.

The flow diagram in FIG. 1 does not show that a filter can be arranged in the gas path between the lock container 9 and the buffer container 29, through which the expansion gases are freed of entrained fuel particles. The filter is then flushed again at the next pressure build-up by the combustible gas flowing into the lock container 9. In the flow chart is also not shown that when using a large gasification reactor 2 with throughputs of> 10 t of fuel per hour, two or more lock tanks 9 can optionally be provided, which are filled and emptied at different times. As a result, the fuel supply is evened out to the supply container 16, which in this case, like the gasometer 13 and the buffer container 29, is only provided once.

2 shows the flow diagram for the process variant in which the partial oxidation raw gas generated is to be used as fuel gas for the gas turbine of a gas-steam turbine power station connected downstream. This flowchart is essentially the same as the flowchart in FIG. 1, and the same reference numbers naturally have the same meaning in both flowcharts. Therefore, a detailed explanation of this flow diagram with reference to the above explanations can be dispensed with. In this case, since the focus is not on relieving the gasification process of inert fiber, but rather on reducing the compressor output, nitrogen is fed into the system as an inert conveying gas via line 5. This can preferably be impure nitrogen with an oxygen content of 3-5% by volume, which is obtained as a by-product in the air separation plant, which supplies the oxygen required for the gasification. Through this nitrogen, the fuel is pneumatically transported from the storage bunker 1 via the line 2 to the cyclone filter 3, in which the fuel is separated from the nitrogen. The nitrogen withdrawn via line 6 is in this The trap is not discharged into the atmosphere, but goes into the gasometer 13. In this case, the combustible gas which is displaced via line 11 when filling the lock container 9 reaches the cyclone filter 3 and is introduced together with the nitrogen via line 6 into the gasometer 13 . From this, the gas mixture is withdrawn via line 38. After appropriate compression in the compressors 31 and 39, it is fed together with the gas withdrawn from the buffer tank 29 via line 32 to the combustion chamber of the gas turbine of the gas-steam turbine power station connected downstream. The partial oxidation gas generated also gets there, which is drawn off via line 53 following gas treatment 33. In this case, the steam generated in the waste heat boiler 51 can be used in the steam turbine of the gas-steam turbine power plant, if appropriate after corresponding overheating.

Claims (3)

1. Process for conveying finely granulated to powdered fuel into a high-pressure gasification reactor, in which the fuel to be gasified is pneumatically conveyed from the dressing plant into a stock vessel provided with a filter and passes from there by gravity flow into a transfer vessel, from which it is fed via a metering vessel to the burners of the gasification reactor, the transfer vessel being alternately pressurised and let down again, and a combustible gas being used for the pressurising of the transfer vessel and metering vessel and also for feeding the fuel to the burners of the gasification reactor, characterised in that the volumetric flow of combustible gas fed to the transfer vessel and metering vessel is adjusted exclusively to the requirement for building up and maintaining the pressure and for feeding the fuel to the gasification reactor, and there is no loosening, similar to a fluidised bed, of the bulk fuel in the transfer vessel and metering vessel.

2. Process according to Claim 1, characterised in that, if the generated crude partial oxidation gas is further processed to synthesis gas, dust-free and dry carbon dioxide, which has been separated off from the generated crude partial oxidation gas, is used for the pneumatic conveyance of the fuel from the dressing plant to the stock vessel designed as a cyclone filter with a widened precipitation space, and that a part stream of the generated synthesis gas is used for pressurising the transfer vessel and metering vessel and for feeding the fuel to the burners of the gasification reactor, the gas displaced from the transfer vessel and metering vessel during the filling step being recycled into the process and being added to the crude partial oxidation gas before the latter is subjected to a gas treatment.

3. Process according to Claim 1, characterised in that, if the generated crude partial oxidation gas is used as fuel gas in a gas turbine, the nitrogen arising as a by-product in the air separation plant of the gasification reactor is used for the pneumatic conveyance of the fuel from the dressing plant to the stock vessel designed as a cyclone filter with a widened precipitation space, and that a part stream of the purified partial oxidation gas and/or a residual gas is used for pressurising the transfer vessel and metering vessel and for feeding the fuel to the burners of the gasification, reactor, the gas displaced from the transfer vessel and metering vessel during the filling step being fed, together with the nitrogen arising after the precipitation of the fuel in the cyclone filter, to the combustion chamber of the gas turbine.

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