AU646755B2

AU646755B2 - Process for gasifying coal and apparatus for coal gasification

Info

Publication number: AU646755B2
Application number: AU21085/92A
Authority: AU
Inventors: Norio Arashi; Shuntaro Koyama; Yoshiki Noguchi; Sadao Takahashi
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1991-09-20
Filing date: 1992-08-18
Publication date: 1994-03-03
Anticipated expiration: 2012-08-18
Also published as: CA2076884C; DE4230819C2; AU2108592A; JPH0578671A; CA2076884A1; DE4230819A1

Description

646755

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S): Hitachi, Ltd.

ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

INVENTION TITLE: Process for gasifying coal and apparatus for coal gasification f..

0.

The following statement is a full description of of performing it known to me/us:this invention, including the best method ft.

oe ft.

*n *r r 1 BACKGROUND OF THE INVENTION 1) Field of the Invention The present invention relates to a process for gasifying coal to form a combustible gas rich in hydrogen from coal, an apparatus for gasifying coal and a plant for coal gasification-combined power generation.

2) Prior Art On the basis of a recent'concept that CO 2 is a cause for a terrestrical greenhouse effect, various systems for using fossil fuels have been proposed.

A process for utilizing coal without any discharge of CO 2 to the atmosphere when combusted has been proposed by Meyer Steinberg as a system, as S. disclosed in International Conference on Coal Science 'TEA), 1059-1062 (1989).

The process comprises gasifying coal in a .i hydrogen atmosphere at a high temperature and a high pressure, thereby forming CH 4 decomposing the CH 4 into C and a H 2 gas in a reactor using a catalyst at a high temperature and a high pressure, thereby obtaining a H 2 gas on one hand and removing C as carbon black on the other hand, and using only the H 2 gas as a ful., The above-mentioned prior art is a two-stage system of once forming CH 4 and thermally decomposing

CH

4 in a reactor using a catalyst at a high temperat,.e la- 1 and a high pressure, where a H 2 gas is not obtained directly from coal. Thus, two reactors, i.e. a gasification unit for forming CH 4 from coal and a unit for decomposing CH 4 to C and a H 2 gas, are required, and the carbon black formed by the decomposition of CH 4 is in a fine particulate form, necessitating a technique for separating and recovering the carbon black.

SUMMARY OF THE INVENTION An object of the present invention is to provide a process and an apparatus for gasifying coal, which can form a H 2 rich gas with less CO 2 discharge directly from coal, and also a process and a plant for power generation, utilizing the gasification process.

The present process for gasifying coal comprises exposing coal to an atmosphere heated to a gasification temperature for 0.1 to 1 second, thereby forming a combustible gas containing hydrogen as a main component.

Specifically, the process comprises heating 20 coal up to a gasification temperature at a rate of 103 to 10 OC/second and maintaining the coal at the gasification temperature for 0.1 to 1 second.

Coal may be passed through a transfer pipe at a rate of 103 to 10 4 0C/second and heated to the gasification temperature for 0.1 to 1 second on the way of the passing.

When coal is heated to the gasification 2 1 temperature in an oxygen gas-free state, a gas very rich in hydrogen with less CO and CO 2 can be obtained.

An oxygen gas can be present in accordance with restriction values of CO and CO 2 in the gas formed by coal gasification. In that case, it is Crsirable that the oxygen gas is present in such a range that a ratio of fed oxygen to fed coal by weight is not more than 0.3. It is desirable to feed air or oxygen gas.

In order to increase the amount of formed oxygen, it is possible to heat coal in a moisture absorbed state to the gasification temperature.

The gasification temperature is desirably in a range of 1,400 to 1,700 0 C. Too higher a gasification temperature will deteriorate materials of the heating 15 unit.

Once coal is maintained in the atmosphere heated to the gasification temperature for 0.1 to 1 second, it is desirable to discharge the gasification product from the heating atmosphere and cool the gasifi- 20 cation product to a lower temperature than the gasification temperature.

One example of the present apparatus for gasifying coal comprises a heating means of forming a heating atmosphere heated to a coal gasification temperature and a coal transfer means of transferring coal to the heating atmosphere and exposing the coal to the heating atmosphere for 0.1 to 1 second, Another example comprises a coal transfer 3 1 means of transferring coal particles at a rate of 103 to 10 4 C/second and a heating means of heating the coal particles to a gasification temperature for 0.1 to 1 second on the way of the transferring.

The apparatus may comprises a transfer pipe with both open ends, through which coal particles are transferred from one end to another, a coal transfer means of feeding the coal particles to the transfer pipe at a high rate of 10 to 10 4C/second, and an external heating means of heating the coal particles passing through the transfer pipe to a gasification temperature from the outside of the transfer pipe for 0.1 to 1 second.

S. It is preferable to feed at least a portion of 0*o 15 the hydrogen-rich gas formed by heating coal to the gasification temperature as a fuel to the coal heating means of the apparatus for coal gasification, whereby a gasification system of less CO 2 discharge can be provided.

20 The present process for coal gasificationcombined power generation comprises rapidly heating coal at a gasification temperature for a short time, thereby forming a combustible gas containing hdroqen as a main component, combusting the combustbl9 gas ai a fuel for the coal gasification, and then feeding the combustion gas to an electric generator-coupled gas turbine, thereby generating electric power.

One example of the present plant for coal 4- 1 gasification-combined power generation comprises a coal gasification unit for heating coal to a gasification temperature with a combustible gas as a fuel, thereby forming a combustible gas containing hydrogen as a main component, a heat exchanger for recovering steam through heat exchange with the combustible gas containing hydrogen as a main component, formed in the coal gasification unit, a coal-heating fuel feeding means for feeding the cooled combustible gas from the heat exchanger as a coal-heating fuel to the coal gasification unit, an electric generator-coupled gas turbine for generating electric power with a combustion gas discharged from the coal gasification unit, and an electric generator-coupled steam turbine for generating 15 electric power with the steam recovered in the heat exchanger.

Another example of the present plant for coal gasification-combined power generation comprises a coal gasification unit for heating coal to a gasification

S.

20 temperature with a combustible gas as a fuel, thereby forming a combustible gas containing hydrogen as a main component, a heat exchanger for recovering steam through heat exchange with the combustible gas, formed in the coal gasification unit, an electric generator-coupled gas turbine for generating electric power with a combustion gas from the heating of the coal in the coal gasification unit, and an electric generator-coupled stream turbine for generating electric power with the 5 -6steam recovered in the heat exchanger.

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on a finding that oniy H atoms can be selectively evolved from coal by selecting conditions such as a heating temperature, heating rate and heating time of coal particles in pyrolysis of moisture-free coal, pyrolysis of moisturecontaining coal and gasification with oxygen.

According to the present invention there is provided a process for gasifying coal, which comprises heating coal to a gasification temperature of 1,400° to 1,700 0 C at a temperature elevation rate of 103 to 10 4 C/sec. and maintaining the coal at the gasification temperature for 0.1 to 1 sec., and cooling the resulting gasification product.

The invention also provides an apparatus for gasifying coal, which comprises a means of heating coal to a gasification temperature of 1,4000 to 1,700°C at a temperature S. elevation rate of 10" to 10 8 sC/sec. and a means of maintaining the coal at the gasification temperature for 0.1 to 1 sec. and then cooling the resulting gasification product.

*o 20 The invention further provides a process for coal gasification-combined power generation, which comprises heating coal to a gasification temperature of 1,4000 to 1,700 0 C at a temperature elevation rate of 103 to 108C/sec. and maintaining the coal at the gasification temperature for 0.1 to 1 sec., thereby forming a combustible gas containing hydrogen as a main component, combusting the combustible gas as a fuel for the coal gasification, and then feeding the combustion gas to an electric generatorcoupled gas turbine, thereby generating electric power.

o The invention further provides a plant for coal gasification-combined power generation, which comprises a coal gasification unit for heating coal to a gasification temperature of 1,4000 to 1,7'0 0 C at a temperature elevation rate of 103 to 10sC/sec. and maintaining the coal at the gasification temperature for 0.1 to 1 sec. with a combustible gas as a fuel, thereby forming a combustible gas containing hydrogen as a main 9309G9,p\oper3aahiachicres,6 6a component, a heat exchanger for recovering steam through heat exchange with the combustible gas containing hydrogen as a main component, formed in the coal gasification unit, a coal-heating fuel feeding means for feeding the cooled combustible gas from the heat exchanger as a coal-heating fuel to the coal gasification unit, an electric generator-coupled gas turbine for generating electric power with a combustion gas discharged from the coal gasification unit, and an electric generator-coupled steam turbine for generating electric power with the steam recovered in the heat exchanger.

The invention still further provides a plant for coal gasification-combined power generation, which comprises a coal gasification unit for heating coal to a gasification temperature of 1,4000 to 1,700 0 C at a temperature elevation rate of 103 to 10sC/sec. with a combustible gas as a fuel, thereby forming a combustible gas containing hydrogen as a main component, a heat exchanger for recovering steam through heat exchange with the combustible gas, formed in the coal gasification unit, an electric generator-coupled gas turbine for generating electric power with a combustion gas from the heating of the coal in the coal gasification unit, and an electric generator-coupled steam turbine for generating electric power with the steam recovered in the heat exchanger.

;Pyrolysis of coal generates gases such as H2, CO, CO 2

CH

4

C

2 11- 4

C

3

H

8 etc. and oils, where the yields of the products depend on a heating temperature and a heating time.

As is well known, the higher the heating temperature, the lower the yields of oils and hydrocarbon gases of C, an C 3 and the higher the yield of H2. On the other hand, the longer the heating time, the larger the amount of gases evolved from coal, and the S secondary decomposition of thus formed gases and oils is promoted to increase the amount of such components as CO, H 2 and CH 4 By the present invention, H atoms can be selectively converted to a H2 gas by heating coal to a gasification temperature, preferably 1,400 0 C or higher at a heating rate of 103 to 10 4 C/second, maintaining the coal at that temperature for 0,1 to 1 second.

It seems that this phenomenon is due to differences in evolving rates of individual atom species 930909,p.opcr"cat,hilachi.rcs,6 1 in the primary decomposition of coal, that pyrolysis at a high temperature for a short time. Among C, H and 0 atom species of coal, H atom species is evolved as

H

2 molecules at first, and then hydrocarbons (CH 4

C

2

H

4

C

3

H

8 etc.), CO, CO 2 etc. are evolved. Thus, CO and CO 2 which are slowly evolved due to their nature, can be prevented from evolving by making the temperature higher, thereby increasing the yield of H 2 gas and making the time of pyrolysis shorter.

When moisture-containing coal is pyrolyzed at a temperature of 1,400 0 C or higher, steam and volatile matters are evolved, and the steam reacts with C of coaS to form a H 2 gas and CO. This reaction depends on a S..heating temperature and a heating time. At a higher 15 heating temperature, the moisture contained within the coal particles rapidly turns into steam, which reacts with C of coal when the steam is evolved from the interiors of coal particles. Thus, almost all amount of moisture contained in the coal particles can react with 20 C even for such a short pyrolysis time as less than one second. That is, the amount of the thus formed H 2 gas c" is larger than the content of H atoms in the coal. When coal is heated in an oxygen-fed state on the other hand, the yield of a H 2 gas is reduced, whereas the yields of CO and CO 2 are increased. When a ratio of fed oxygen to fed coal by weight (which will be hereinafter referred to as "an oxygen ratio") is not more than 0.3, at least 90% of the yield of a H 2 gas at zero oxygen 7 -8ratio (pyrolysis) can be obtained, and an inciease in the yield of CO 2 is very small, whereas that of CO is considerably increased. Thus, when the coal is heated in an oxygen fed state, gasifying of the coal at a temperature of 1,400 0 C or higher, and a heating rate of 103 to 10 4 0C/second should preferably occur with an oxygen ratio of 0 to 0.3, for a time of 0.1 to 1 second and successive cooling of the gasification products as a means of converting nearly 100% of H atoms in coal to a H 2 gas and allowing almost all amount of moisture contained in the coal to react with C.

Reasons for selecting a heating rate of 103 to 10 40 C/second and a heating temperature of 1,400°C or higher are to suppress secondary decomposition of volatile matters, increase the yield of a H 2 gas for a short time and allow almost all amount of the moisture contained in coal to react with C, as mentioned above. Reason for setting the oxygen ratio to the above-mentioned range is to change yields of a H 2 gas, and CO i and CO 2 in accordance to restriction of the amount of CO 2 to be discharged to the atmosphere or end uses. When the discharge restriction of CO 2 is loosened, oxygen may 15 be additionally supplied. When a gas of higher H 2 gas concentration, which contains Ssubstantially no CO2, is required, a zero oxygen ratio is preferable. When it is desired to form much CO with some reduction in the yield of a H 2 gas and with some increase in the yield of CO 2 it is desiable to additionally supply a small amount of

O*

0 931210,p\opcdhhitachO7.com,8 1 oxygen. At an oxygen ratio of more than 0.3, the yields of CO and CO2 are rapidly increased and the yield of a

H

2 gas is considerably lowered.

In the foregoing, oxygen is used as a coalgasifying agent, and air as an oxygen-containing gas can attain the same effect as above by controlling it by keeping a ratio of oxygen in the fed air to fed coal by weight within the above-mentioned oxygen ratio range.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a vertical cross-sectional view of a gasificaticn furnace for carrying out the present invention.

Fig. 2 is a cross-sectional view of the fixing part of a pipe-shaped refractory in a gasification 15 furnace for carrying out the present invention.

Fig. 3 is a schematic flow diagram of a combined power plant system, using a coal gasification product gas as a heating fuel to a gasification furnace.

.i Fig. 4 is a schematic flow diagram of a combined power plant system serving also to produce a feed gas to chemical synthesis.

Fig. 5 is a schematic flow diagram of a combined power plant system, using CH 4 or natural gas as a heating fuel to a gasification furnace.

PREFERRED EMBODIMENTS OF THE INVENTION Fig. 1 is a cross-sectional view showing the 9 1 structure of b gasification furnace for carrying out the present invention. A gasification furnace 10 is in such a structure that a pipe-shaped refractory 17 is provided through a furnace shell lined with refractory heatinsulating materials 19 and a combustion chamber 18 is provided between the refractory heat-insulating materials 19 and the pipe-shaped refractory 17, and a burner 14 and a combustion gas outlet 15 are provided at the furnace shell. A fuel 2 for heating the gasification furnace and air 3 are fed to the burner 14 to form a flame in the combustion chamber 18, thereby heating the pipe-shaped refractory 17, and combustion gas 11 is discharged through the combustion gas outlet 15 to the outside of the furnace. Since the combustion chamber 18 15 is surrounded with the refractory heat-insulating materials 19, heat radiation to the outside of the furnace can be prevented and the inside of the pipeshaped refractory 17 can be readily maintained at a high temperature such as 1,400 0 C or higher. Coal particles 1 20 and oxygen or an oxygen-containing gas 4 are fed into the pipe-shaped refractory 17 through a coal feed pipe 13 at an oxygen ratio of 0 to 0.3, and passed through a zone of the pipe-shaped refractory 17, whose inside temperature is 1,400°C or higher, for 0.1 to 1 second, and product gas/as are discharged through a product gas outlet 16 to the outside of the furnace.

Fig. 2 is a cross-sectional view showing the fixed part of the pipe-shaped refractory 17 at the 10 1 gasification furnace. The refractory insulating materials 19, which line the steel furnace shell 20 of the gasification furnace 10, are positioned at the outside of the pipe-shaped refractory 17 and are provided with a groove for inserting a packing material therein at both ends of the refractory heat-insulating materials 19, a heat-resistant packing material 23 is inserted into the groove, and a metallic packing ring 22 is provided on the packing material 23 and fixed to the steel furnace shell 20 by bolts 21. The heat-resistant packing material 23 is deformed in the groove by fastening the bolts 21 to seal the clearance between the refractory heat-insulating materials 19 and the pipeshaped refractory 17 and prevent leakage of the gas 15 formed in the pipe-shaped refractory 17 into the 4. see* combustion chamber 18 or leakage of the combustion gas into the pipe-shaped refractory 17.

Fig. 2 shows a structure of a combined power generation system which comprises gasifying coal in a 20 gasification furnace of above-mentioned structure, using the product gases as a fuel for heating the gasification furnace, and supplying the combustion gas to an electric 9 9 generator-coupled gas turbine, thereby generating e electric power, while leading steam obtained by heat recovery to an electric generator-coupled steam turbine, thereby also generating electric power, the electric generator being not shown in the drawing.

The present system comprises a gasification 11 1 plant section comprising a gasification furnace 10, a rough dust remover 30, a gas cooler, a precise dust remover 40, and a desulfurizer 50, and a power plant section comprising an electric generator-coupled gas turbine 70 for generating electric power with combustion gas 11 used for heating the gasification furnace 10, a steam heater 80 for heating steam 83 recovered by the gas cooler 35, an electric generator-coupled steam turbine 90 for generating electric power with the heated steam, and a condenser 100 for recovering the steam used for the power generation as cooling water (the electric generator being not shown in the drawing). Functions of the individual units are as follows: The gasification furnace is an externally heated reactor, wherein the heating is carried out with the heat of combustion 'f the purified gas 51 obtained S"by dust removal and desulfurization of the gas formed in the gasifications furnace 10. The purified gas 51 is combusted with compressed air 3' obtained by compressing atmospheric air 3 by a compressor 71 to maintain the interior of the gasification furnace 10 at a temperature of 1,400 0 C or higher. At the same time when coal particles 1 are fed to the gasification furnace oxygen or oxygen-containing gas 4 is fed thereto in an oxygen ratio of 0 to 0.3 to heat for 0.1 to 1 second.

Inside the gasification furnace 10, gasification of coal particles 1 proceeds, turning H of the coal particles 1 into a H2 gas. When the coal particles 1 contain 12 1 moisture, almost all amount of the moisture reacts with C of the carbon particles 1 to form a H 2 gas and CO.

Thus, the product gas 12 evolved from the gasification furnace 10 is a gas mixture containing a H 2 gas as the main component and CO. Since the'product gas 12 is at a high temperature and contains much unreacted char, coarse particulate char 32 is removed therefrom through a cyclone, etc. of the rough dust remover 30. Then, the produci; gas 31 removed from the coarse particulate char 32 is led to the gas cooler, through which cooling water 81 passes, to lower the temperature of the product gas and recover the cooling water 81 as steam 82.

The cooled product gas 36 is passed through the precise dust remover 40 to separate and remove fine particulate char 42, and the durt-removed product gas 41 S. is led to the desulfurizer 50 to remove H 2 S therefrom and obtain a purified gas 51. The purified gas 51 is used as a heating fuel to the gasification furnace and the combustion gas 11 is fed to the electric generator-coupled gas turbine and utilized to generate electric power. After the power generation, the gas is led to the steam heater 80 to heat steam 82 recovered in the gas cooler 35, and then discarded as a waste gas 72.

On the other hand, the steam heated in the steam heater 80 is fed to the electric generator-coupled steam turbine 90 to generate electric power, and after the power generation, the steam is led to the condenser 100 to recover the steam as water and the recovered 13 1 water is utilized again as cooling water 81.

In the present system, the coarse particulate char 32 and the fine particulate char 42 removed in the rough dust remover 30 and the precise dust remover respectively, contain much C, and thus the chars are buried underground as a char mixture 43 and stored therein as a future fuel resource. A desulfurizing agent of metal oxide is filled in the desulfurizer and reacts with H2S to form sulfides. The sulfides are withdrawn into a sulfurizing agent recovery tank :I and recovered as a spent desulfurizing agent 61.

Fig. 4 shows the structure of a combined power plant system serving also to produce a feed gas for chemical synthesis according to the present invention.

In the present system, only a difference in the structure from Fig. 3 is not to use the purified gas 51 as the heating fuel 2 to the gasification furnace 10, but to feed a heating fuel from the outside of the gasification plant system, thereby using all the amount of the purified gas 51 as a feed gas to chemical synthesis. In that case, CH 4 with less generation of CO2 at the combustion or a natural gas containing

CH

4 as the main component is used as the heating fuel 2 to the gasification furnace That is, CH 4 or a natural gas as the heating fuel 2 to the gasification furnace 10 is combusted with compressed air 3' to increase the inside temperature of the gasification furnace 10 to 1,400°C or higher, and 14 1 coal particles 1 and oxygen or oxygen-containing gas 4 are fed to the gasification furnace 10 in an oxygen ratio of 0 to 0.3, where a gas mixture containing a H 2 gas as the main component and CO is obtained as the product gas 12, as mentioned before. The product gas 12 is led to the rough dust remover 30, the gas cooler the precise dust remover 40 and the desulfurizer successively, to remove the unreacted solid matters and H 2S from the product gas 12 on one hand and recover steam 82 on the other hand, and the thus obtained purified gas 51 is used as a feed gas to chemical synthesis.

i. In the present system, the hot combustion gas 11 heated in the gasification furnace 10 is led to the electric generator-coupled gas turbine 70 to generate electric power, and after the power generation the gas *e is led to the steam heater 80 to heat the steam 82, and then discarded. On the other hand, the heated hot steam is utilized in the electric generator-coupled steam turbine 90 to generate electric power, and after the power generation, the steam is condensed to water in the condenser 100 and utilized as the cooling water 81.

Fig. 5 shows the structure of a combined power plant system, using CH 4 or a natural gas as a heating fuel to the gasification furnace. In the present system, only differences in the structure from the afore-mentioned power plant systems are to feed the combustion gas 11 of CH 4 or natural gas used for 15 1 heating the gasification furnace 10 to the electric generator-coupled gas turbine 70 to generate electric power on one hand, and to pass the gas 12 formed from coal particles 1 in the gasification furnace 10 to the rough dust remover 30, the gas cooler 35, the precise dust remover 40 and the desulfurizer 50 to remove the coarce particulate char 32, the fine particulate char 42 and H2S, thereby obtaining a purified gas, while recovering steam 82, on the other hand, and to feed the purified gas 51 is a gas turbine combustor 73 to undergo :combustion therein with a portion 3" of the compressed air discharged from the compressor 71, and feed the combustion gas to the electric generator-coupled gas turbine 70 to generate electric power. In the present system, after the power generation in the electric generator-coupled gas turbine 70, the exhaust gas is fed to the steam heater 80 and utilized for heating the steam 82. Steam is utilized for power generation in the electric generator-coupled steam turbine In the present power plant system, unreacted char containing much C is recovered, as mentioned before, and the char is buried underground and stored as a future fuel resource until a technique for separating and recovering CO 2 has been established. Thus, it is recommended to install the present confined power plant at coal mining sites and refill the recovered unreacted char into the subterraninean coal-excavated pits.

S16 1 Example 1

S.

S

The present invention will be explained below, referring to actual coal gasification results.

Coal particles having the following elemental analysis by weight) were made to absorb moisture to a moisture content of 6.92% by weight: C 65.65% H :5.00% N :1.35% 0 15.49% S :0.10% Ash 12.41% With the thus mositure-adjusted coal particles the present coal gasification process and the conventional coal gasification process were tested in an externally heated gasification furnace under the following conditions.

In the present process, gasification was carried out at 1,400 0 C and 1,600 0 C at a heating rate of 103 to 10 4 0C/second in oxygen ratios of 0 and 0.3 for a heating time of coal particles of 0.185 seconds to investigate yields of H 2 gas, CO and CO 2 per gram of coal after cooling.

In the conventional process, gasification was carried out at the same temperatures as those of the 2 present process at a heating rate of 10 2C/second in an oxygen ratio of 0.9 for a heating time of coal 17 S S 1 particles of 3 seconds, which had been regarded as most appropriate gasification conditions for producing CO as a combustible gas in highest yield to investigate yields of the gas, CO and CO 2 per gram of coal for comparison.

In both processes, the pressure of the gasification furnace was the atmospheric pressure.

Table 1 shows comparison in gas yields between the present process and the conventional process.

Table 1 Reaction Oxygen temp. ratio Gas yield (P/g) H2 CO 2

CO

0 0.604 0.007 0.274 1400 The present 0.3 0.563 0.048 0.570 gasification process 0 0.606 0.003 0.282 1600 0.3 0.581 0.017 0.651 The conven- 1400 0.9 0.339 0.276 0.730 tional gasification 1600 0.9 0.373 0.174 0.961 process Comparison of H 2 gas yield reveals the following facts. The theoretical the gas yield when all the amount of moisture contained in the coal particles reacts with C and all the amount of H atoms in the coal particles turns into a H 2 gas is 0.607 A/g. The H 2 gas yield in an oxygen ratio of zero is 0.6 a/g at a 18 1 temperature of 1,400°C or higher, and it has been confirmed that not only H atoms in the coal particles but also the moisture contained thein almost completely reacted with C to form the H 2 gas. The H 2 gas yield in an oxygen ratio of 0.3 is slightly smaller than that in an oxygen ratio of zero, but still is about 93% of the H 2 gas yield in an oxygen ratio of zero, which is much higher than that in the conventional process.

Comparison of CO 2 yield reveals that the

CO

2 yields in oxygen ratios of zero and 0.3 are much lower in the present process than those in the conventional process and it is evident that the present *9*e process produces substantially no CO 2 Since the CO yield increases with increasing amount of fed oxygen up to oxygen ratio of about 0.9, .i the CO yield of the present process in oxygen ratios of zero and 0.3 are lower than that in the conventional process. That is, in the present process the CO yield is lower at the coal gasification than that in the conventional process, but the H 2 gas yield is higher with no substantial formation of CO 2 Thus, when the product gas obtained by coal gasification by the present process is used as a heating fuel, the amount of CO 2 in the combustion gas can be much more reduced than when the product gas obtained by the conventional process is combusted, and thus the present process is an effective coal gasification process taking the terrestrical greenhouse effect into consideration.

19 1 Example 2 Coals having the following composition was ma~de to absorb moisture to a moisture contcnt of 5.15% and gasified under the same gasification conditions as in Example 1 and the results of gas yields in the present process and the conventional process are shown in Table 2.

C,

H

N

0

S

Ash 66. 12% 5.41% 0.87% 16.48% 0.20% 10. 92% *9 9 9 999 9 99 9.9.

9 99..

.9.9.9 9 9. 9 99 Table 2 99 99 .999 99 .9 9 4 99 99 9 99 9 4.9.

.9 9 .9 Reaction Oxygen Ga il 2g temp. ratio Gsyed(.g 0 C) IH2 CO 2

CO

0 0.610 0.005 0.273 1400 The present 0.3 0.582 0.017 0,636 gasification-____ process 0 0.635 0,~004 0.275 1600 0.3 0.612 0.010 0.660 The conven- 1400 0.9 0.320 0.222 0.838 tional gasi- I fic.ation 1600 0.9 0.348 0.180 0.9)45 pro~cess____ 20 1 The H 2 gas yields in oxygen ratios of zero and 0.3 are much higher in the present process than those in the conventional process. Theoretical H 2 gas yield when all the amount of moisture contained in the coal particles reacts with C and all the amount of H atoms in the coal particles is converted to a H 2 gas is about 0.638 2/g. The H 2 gas yield in an oxygen ratios of zero is 0.610 2/g or higher at temperatures of 1,400'C and 1,6000C in the present invention, and that in an oxygen of 0.3 is somewhat lower than that in an oxygen ratio of zero in the present invention, but is much higher than that in the conventional process.

Comparison of the CO 2 yield reveals that the

CO

2 yields in oxygen ratios of zero and 0.3 are considerably lower in the pressed invention than those in the conventional process, and thus the present invention is effective for reducing the CO2 yield.

*Comparison of CO yield reveals that the CO yields in oxygen ratios of zero and 0.3 are lower in the present invention than those in the conventional process. That is, in the present invention, the H 2 gas yield is increased and the CO and CO 2 yields are reduced, as compared with the conventional process und thus it is possible to largely reduce the amount of

CO

2 in the combustion gas produced by combustion of the product gas.

In the present coal gasification, the H 2 gas yield is higher and the CO and CO 2 yields are lower 21 1 than in the conventional coal gasification process.

Thus, when combustion of the product gas is utilized for bwer generation, the CO 2 yield in the combustion exhaust gas can be considerably reduced, as compared with the conventional process, and thus the present invention is effective for reducing a plant cost for removing CO 2 as the main cause for terrestrical greenhouse effect.

**o f 22

Claims

1. A process for gasifying coal, which comprises heating coal to a gasification temperature of 1,400° to 1,700 0 C at a temperature elevation rate of 103 to 10 4 0C/sec. and maintaining the coal at the gasification temperature for 0.1 to 1 sec., and cooling the resulting gasification product.

2 A process according to Claim 1, wherein the coal is heated to the gasification temperature in an oxygen gas-free state.

A process according to Claim 1, wherein the coal is heatr^ to the gasification t-mperature in the presence of an oxygen gas in a range that a ratio of fed oxygen to fed coal by weight is not more than 0.3.

4. A process according to Claim 1 or Claim 2, wherein the coal is heated to the gasification temperature in a moisture-absorbed state.

A process according to Claim 3, wherein air is fed as the oxygen gas. 20

6. An apparatus for gasifying coal, which comprises a mt ,ns of heating coal to a gasification temperature of 1,4000 to 1,700 0 C at a temperature elevation rate of 10 3 to 108lC/sec. and a means of maiitaining the coal at the gasification temperature for 0.1 to 1 sec. and then cooling the resulting gasification product.

7. An apparatus according to Claim E, wherein the means of heating coal to a gasification temperature comprises a transfer pipe with both open ends, through which coal is transferred from one end to another, the transfer pipe being heated externally. on e sc I

8. A process for coal gasification-combined power generation, which comprises heating coal to a gasification temperature of 1,4000 to 1,700 0 C at a temperature elevation rate of 103 to 10 80 C/sec. and maintaining the coal at the gasification temperature for 0.1 S to 1 sec., thereby forming a combustible gas containing hydrogen as a main component, 930909,p:\opci'kaIl,liachL.rcs,23 24 combusting the combustible gas as a fuel for ;he coal gasification, and then feeding the combustion gas to an electric generator-coupled gas turbine, thereby generating electric power.

9. A plant for coal gasification-combined power generation, which comprises a coal gasification unit for heating coal to a gasification temperature of 1,4000 to 1,700 0 C at a temperature elevation rate of 103 to 10 8 C/sec. and maintaining the coal at the gasification temperature for 0.1 to 1 sec. with a combustible gas as a fuel, thereby forming a combustible gas containing hydrogen as a main component, a heat exchanger for recovering steam through heat exchange with the combustible gas containing hydrogen as a main component, formed in the coal gasification unit, a coal-heating fuel feeding means for feeding the cooled combustible gas from the heat exchanger as a coal-heating fuel to the coal gasification unit, an electric generator-coupled gas turbine for generating electric power with a combustion gas discharged from the coal gasification unit, and an electric generator-coupled steam turbine for generating electric power with the steam -covered in the heat exchanger.

10. A plant for coal gasification-combined power generation, which comprises a coal gasification unit for heating coal to a gasification temperature of 1,4000 to 1,700°C at a temperature elevation rate of 103 to 10sC/sec. with a combustible gas as a fuel, thereby forming a combustible gas containing hydrogen as a main component, a heat exchanger for reco'rinj steam through heat exchange with the combustible gas, formed in the coal .asificf.tion unit, an electric generator-coupled gas turbine for generating electric power S with a c .ustion gas from the heating of the coal in the coal gasification unit, and an "ator-coupled steam turbine for generating electric power with the steam :ec..ered in the heat exchanger, Dated this 9th day of September, 1993 HITACHI, LTD. By its Patent Attorneys DAVIES COLLISON CAVE 930909,p:\opr\kat,hitach.res,24 ABSTRACT OF THE DISCLOSURE Coal is supplied to a gasification furnace heated to 1,400°C or higher and gasified for 0.1 to 1 second to form a hydrogen-rich gas, which is purified to a purified gas. The purified gas is used as a heating fuel to the gasification furnace, and the combustion gas is fed to an electrib generator-coupled gas turbnae to generate electric power. The steam recovered in a gas cooler is heated with the exhaust gas from the gas turbine and fed to an electric generator-coupled steam turbine to generate electric power. A hydrogen-rich gas with less CO is formed directly from coal thereby. 4 4. .46*