GB2156843A

GB2156843A - Method and apparatus for feeding coal in an integrated power and coal gasification plant

Info

Publication number: GB2156843A
Application number: GB8503308A
Authority: GB
Inventors: Nobuo Nagasaki; Yoshiki Noguchi
Original assignee: Hitachi Engineering Co Ltd; Hitachi Ltd
Current assignee: Hitachi Engineering Co Ltd; Hitachi Ltd
Priority date: 1984-02-10
Filing date: 1985-02-08
Publication date: 1985-10-16
Also published as: DE3504593A1; GB8503308D0

Abstract

An integrated power and coal gasification plant comprises a gasifier in which coal is gasified with air, a gas purifier in which the combustible gas is purified and then fed to a burner which drives a gas turbine; gas inactive against coal is separated from the coal in the gasifier pressurized pressurized and used for feeding the coal to the gasifier. This gives a reduced risk of backfire, which could cause an explosion in the line feeding the coal into the gasifier.

Description

SPECIFICATION Method and apparatus for feeding coal in an integrated power and coal gasification plant This invention relates to method and apparatus for feeding coal in an integrated power and coal gasification plant, for example, a method of feeding dry coal into a pressurized gasifier.

In an integrated power and coal gasification plant, gasified coal fuel is pressurized and fed to a gas turbine burner. it is possible to gasify coal in a gasifier which works under pressure in order to increase the total heat efficiency of the power plant and to make the gasifier compact. In such a gasifier coal with pressurized nitrogen would be fed into the gasifier so that backfire of the coal or its resulting explosion does not take place in the line feeding the coal into the gasifier if the pressure in the feeding line became lower than that in the gasifier. The applicants are not aware of a direct disclosure of this but the idea of pressurizing nitrogen obtained from an air decomposition device is shown in e.g. U.S. Patent 4250704. However, such an apparatus has problems such as high cost and power consumption with employment of nitrogen as mentioned above to feed the coal.

The present inventon seeks to provide a method and apparatus for feeding coal in an integrated power and coal gasification plant in which the risk of backfire of the coal, and the resulting explosion, is reduced without needing high power consumption for feeding the coal into the gasifier. The invention achieves this by feeding coal with pressurized inactive gas which can be separated from the coal gasification plant. The inactive gas may be gas comprising mainly carbon dioxide separated from a gas purification device, talegas generated in a sulphur removal device, steam generated in the gasifier or part of purified gas. "Inactive gas" here means gas inactive against coal.

According to this invention not only backfire of coal and its resulting explosion in the line feeding coal into the gasifier may be avoided but also the power consumption necessary to get the inactive gas may easily be reduced since the inactive gas, produced in the coal gasification plant, is used.

Embodiments of the invention will now be described, in detail, by way of example, with reference to the accompanying drawings, in which: Figure I is a flow diagram of a first embodiment of an integrated power and coal gasification plant according to the present invention, Figures 2, 3, and 4 are flow diagrams respectively showing other embodiments, Figure 5 is a graph showing power consumption in each embodiment.

Referring first to Fig. 1, coal 1 is gasified with air 44 in a gasifier (a gasification device2) 10 under pressure such as 20 to 70 kg/cm2.

Thus gasified fuel 11 (combustible gas) is purified and then burnt in a burner 38, resulting in the driving of a gas turbine 90 and the generation of electric power by a generator 92. Exhaust gas 45 from the gas turbine 90 is led to an exhaust gas boiler 46. Steam 55, 56 produced in this boiler 46 drives a steam turbine 58, resulting in further electric power by a generator 59. In this embodiment carbon dioxide 60 separated from a gas purification device is used to feed coal into the gasifier 10.

Thus pulverized dry coal 1 is fed to a coal store tank 2 and then to a lockhopper 3. The lockhopper 3 is provided with an inlet valve and an outlet valve (not shown) on the inlet side and on the outlet side of the lockhopper 3 respectively. First the outlet valve is closed and then pressurized carbon dioxide is fed into the lockhopper 3 so that the coal inside the lockhopper 3 can be pressurized to a predetermined pressure. After completion of this pressurization the pressurized coal can be fed into the gasifier 10 through a feed tank 4 by closing the inlet valve of the lockhopper 3 and opening its outlet valve. A plurality of lockhoppers may be provided, one per gasifier, so that the pulverized coal can be fed continuously by changing from one lockhopper to another.

The pulverized coal is gasified under a pressure of e.g. 20 to 70 kg/cm2. Air 44 is used as the gasifying agent. The gas 11 thus produced is cooled in a steam generating device 1 5 where the sensible heat of the gas 11 is recovered in the form of steam. Gas 1 9 having passed the steam generating device 1 5 is cooled by an heat exchanger 20 whose medium is purified gas 76 as mentioned below. Cooled gas 21 is led to a dust removal device 22 and then dust removed gas 27 is led to a sulphide removal device 23, thereby producing purified gas 28. In fact, the sulphide is absorbed by an absorbing agent which circulates through a reproducing tower 24, a pump 25 and the sulphide removal device 23 so that the same agent can be used repeatedly, removing the sulphide, i.e. the components containing sulphur from the agent.The sulphide 31 thus removed is partly converted in the form of sulphur at a sulphur recovering device 32 and the sulphur is removed through the line 34. Talegas left not converted in the solid form of the sulphur is burnt at a burner 35 and thus burnt talegas including sulphide is exhausted together with the exhausted gas 67 of the exhaust gas boiler 46.

The purified gas 28 is led to a carbon dioxide removal tower 75 where carbon dioxide contained in the purified gas 28 is removed by an absorbing agent circulating through a reproducing tower 77, a pump 79 and the carbon dioxide removal tower 75 so that the same agent can be used repeatedly, removing the carbon dioxide from the agent in the heated reproducing tower 77 whose pressure is reduced. The carbon dioxide 80 produced in the reproducing tower 77 is led to a precise sulphur removal device 95, pressurized by a compressor 81 and then fed to the lockhoppers 3. The precise sulphur removal device 95 serves to reduce the amount of the sulphur contained to about 1 ppm, which helps avoid corrosion of the compressor 81, the lockhoppers 3 and the feed tank 4. This device 95 comprises a converter from carbon sulphide to hydrogen sulphide, and a reactor filled with oxidized zinc.

The purified gas 76, from which carbon dioxide has been removed by the carbon dioxide removal device 75, is heated by the heat exchanger 20, burnt at the burner 38 and supplied to the gas turbine 90 as gas having high temperature.

The air 44 which serves as the gasifying agent is produced so that part of the air 40 compressed by a gas turbine compressor 91 is extracted, then cooled by a heat exchanger 41 whose medium is feed water 62 and further pressurized by a compressor 43 to the pressure necessary for the gasifier 10.

In this power system is a heat recovery system in which sensible heat of the exhaust gas 45 of the gas turbine 90 is recovered by means of the exhaust gas boiler 46 and sensible heat of the gas 11 by the steam generating device 1 5. Steam generated by the heat recovery system is heated further by a superheater 47 and fed to the steam turbine 58. The steam having passed the steam turbine 58 condenses after being cooled by a condenser 60 and is fed to the exhaust gas boiler 46 by a pump 61 as feed water 62.

A second embodiment of the present invention is shown in Fig. 2. This embodiment is generally similar to the first embodiment except talegas 33 produced in a sulphur recovering device 32 is basically used as the inactive gas to feed the coal. That is, the talegas 33 is changed to a gas containing mainly nitrogen and carbon dioxide by oxidation treatment at a catalyst burner 68, then led to a heat exchanger 70, pressurized by a compressor 72 and fed to the lockhoppers 3.

The catalyst burner 68 enables spontaneous combustion of the talegas 33 using less air, thereby producing gas inactive against coal and containing mainly carbon monoxide. Furthermore, since carbon monoxide, hydrogen and hydrogen sulphide can be burnt spontaneously due to the catalyst burner, the oxygen concentration can be decreased remarkably.

A third embodiment is shown in Fig. 3.

Again this is similar to the first embodiment except that reaction heat generated in the gasifier can be recovered in the form of steam converted from water 1 3. In this embodiment, saturated vapour whose pressure is relatively low, e.g. 40 kg/cm2, is heated by the steam generating device 15, e.g. 350"C and fed to the lockhoppers 3. The vapour having a temperature of 350"C is inactive against coal. In addition, condensation of the vapour does not take place in the line feeding the coal into the gasifier even under heat radiation.

Fig. 4 shows a fourth embodiment. In this embodiment sulphide of the purified gas 28 is removed further by a precise sulphur removal device 95 and thus treated gas 6 is fed to the lockhoppers 3. According to this embodiment power consumption to get gas to feed the coal is small compared with the first three embodiments because the purified gas 28 is already in the pressurized state. The fourth embodiment is otherwise similar to the first embodiment.

Fig. 5 shows comparison results of power consumption in each embodiment, as well as in a possible prior art system. In the prior art two kinds of power consumption are required, i.e. power 100 to drive an air decomposition device and power 101 to compress nitrogen before feeding it into the lockhoppers. Powers 103, 104, 106, and 107 shows powers to compress gas used to feed the coal respectively. Power 102 represents power necessary for the carbon dioxide removal device 75. The amount of power consumption corresponds to a power plant whose output power is 1000 MW.

Claims

1. A method for feeding coal in an integrated power and coal gasification plant, having a coal gasification system which includes a gasifier for producing a combustible gas by reaction of the coal with air under a predetermined pressure and a gas purification device for purifying the combustible gas, and a gas turbine system including a gas turbine using the purified combustible gas from the coal gasification plant, wherein gas inactive against the coal is separated from the coal gasification plant, the inactive gas is pressurized, and the coal is fed into the gasifier by means of the pressurized inactive gas.

2. A method according to claim 1, wherein the inactive gas is gas containing mainly carbon dioxide separated from the gas purification device.

3. A method according to claim 1, wherein the inactive gas is talegas generated in a sulphur removal device which constitutes the gas purification device.

4. A method according to claim 1, wheren the inactive gas is steam generated by means of reaction heat or the gasifier.

5. A method according to claim 4, wherein the steam is further heated such that the steam remains inactive against the coal.

6. A method according to claim 1, wherein the inactive gas is part of the purified combustible gas.

7. A method according to any one of claims 1 to 6, wherein the coal is pulverized dry coal.

8. A method for feeding coal in an integrated power and coal gasification plant, substantially as any one herein described with reference to Figs. 1 to 4 of the accompanying drawings.

9. An apparatus for feeding coal in an integrated power and coal gasification plant, having a coal gasification system which includes a gasifier for producing a combustible gas by reaction of the coal with air under a predetermined pressure, a gas purification device for purifying the combustible gas, a feeding device for feeding the coal into the gasifier, and a gas turbine plant including a gas turbine using the purified combustible gas from the coal gasification plant, wherein the apparatus includes means for separating gas inactive against the coal from the coal gasification system, a compressor for compressing the inactive gas, and means for leading the compressed inactive gas to said feeding device.

10. An apparatus according to claim 9, wherein the gas purification device comprises means for removing dust, sulphide and carbon dioxide from the combustible gas, there is provided means for leading the carbon dioxide to the compressor as said inactive gas.

11. An apparatus according to claim 9, wherein the gas purification device includes means for removing dust and sulphide from the combustible gas and means for removing sulphur from the sulphide and producing talegas, and there is provided means for leading the talegas to the compressor.

1 2. An apparatus according to any one of claims 9 to 11, having means for leading part of the gas purified in the gas purification device to the compressor to permit the purified gas to be used as the inactive gas.

1 3. An apparatus for feeding coal in an integrated power and coal gasification plant substantially as herein described with reference to and as illustrated in any one of Fig. 1 to 4 of the accompanying drawings.