AU730980B2

AU730980B2 - Coal gasification apparatus and a coal gasification hybrid power generation system

Info

Publication number: AU730980B2
Application number: AU27900/97A
Authority: AU
Inventors: Eiji Kida; Syntaro Koyama; Takanori Kudou; Atsushi Morihara; Yoshio Naganuma; Yoshiki Noguchi; Sadao Takahashi; Shinji Tanaka
Original assignee: Babcock Hitachi KK; Hitachi Ltd
Current assignee: Hitachi Ltd; Mitsubishi Power Ltd
Priority date: 1996-05-20
Filing date: 1997-05-19
Publication date: 2001-03-22
Anticipated expiration: 2017-05-19
Also published as: WO1997044412A1; JP4150937B2; KR20000015802A; AU2790097A; CN1221446A

Description

TITLE OF THE INVENTION COAL GASIFICATION APPARATUS AND A COAL GASIFICATION HYBRID POWER GENERATION SYSTEM BACKGROUND OF THE INVENTION The present invention relates to a coal gasification hybrid power generating system, wherein the power is generated by supplying fuel gasified by coal gasification apparatus to gas turbines, in particular, to the coal gasification apparatus and a method of coal gasification.

As a system for releasing an energy from coal and generating electric power therefrom, a system, wherein coal is converted to heat energy by combustion, and the energy is recovered after generating steam, is most widely utilized at present.

On the other hand, the coal gasification is a system, wherein coal is not directly used for combustion, but converted to a combustible gas by a gasification reaction with an oxidizing agent, and the combustible gas is i directly supplied to a power generating apparatus such o as gas turbines and fuel cells in order to convert to the oooo energy. Furthermore, the heat generated by the above process is converted to an electric energy by supplying S 25 the heat to steam turbines.

The above system has a better efficiency in comparison Rwith a conventional power generating system, wherein power is generated by steam which is generated by direct combustion of coal, because gas turbines and fuel cells are directly driven by gasified coal.

On account of the above reason, the power generating system by gasification of coal has been expected as a high efficiency power generating system for next generations.

In accordance with coal gasification technology, a combustible gas composed of hydrogen, carbon monoxide, methane, carbon dioxide, steam, and others is generated by contacting coal with an oxidizing agent such as oxygen, steam, and the like at a high temperature.

One of the coal gasification apparatus for realizing the coal gasification is a fluidized bed type (a type of gasification in an entrained state) gasification apparatus. In accordance with the fluidized bed type coal gasification apparatus, coal is pulverized to fine particles of approximately tens microns in diameter in order to increase a contact efficiency with gases.

Because of an accelerated reaction, a temperature inside the gasifying apparatus is elevated high, and the gasification reaction is completed rapidly.

Furthermore, ashes contained in the coal can be melted, because inside the gasification furnace reaches at a high temperature (1400 1800 0 Melting the ashes is preferable in view of anti-environmental pollution, because harmful metals contained in the coal can be enclosed in the melted ashes. Accordingly, the fluidized bed type coal gasification is a preferable coal gasification apparatus superior in view of a high efficiency and anti-environmental pollution.

However, the temperature of the generated gas is high, because the coal is reacted at a high temperature (1400 1800 0 Furthermore, the generated gas contains residual unreacted carbon which is remained because the coal is not reacted completely, ashes contained in the coal, and corrosive gases such as hydrogen sulfide and ammonia. In a state at a high temperature exceeding 1500 0 C, the ashes in the coal are in a molten state (the molten ashes are called slug), and the slug adheres to various members. Therefore, any countermeasure for preventing the ashes from adhering to the various members becomes necessary. In order to supply the generated gas to gas turbines, it is necessary to cool the generated gas at a high temperature to approximately lower than 400 0 C in consideration of the material composing the present gas turbines.

In view of the above problems, various methods for cooling the generated gas at a high temperature have been proposed. The cooling types can be divided roughly in two categories, the one is cooling by removing radiation heat from heat conducting planes, and the other is heat exchange on heat conducting planes by convection of the generated gas.

In accordance with JP-A-61-228093 (1986), a heat exchanger is installed by being connected directly to a gasifying reactor (but, not in the same vessel).

However, in order to avoid adhering the slug spread from the gasifying reactor to the heat exchanger, the heat exchanger is installed in a manner so as not to disturb the flow of the generated gas, but to surround the periphery of the gas flow. That is, the heat exchanger is installed in parallel to the gas flow. And, the heat exchangers are arranged closely so as to disturb the gas flow at positions where the slug has been solidified by cooling.

In accordance with the above arrangement of the heat exchangers to surround the gas flow, the heat can be recovered without disturbing significantly the gas flow.

In particular, even if floating materials such as ashes are existing in the generated gas, disturbance by the floating materials is not significant. However, a heat conductance per unit volume of the heat exchanging part of the heat exchanger is small, because the heat exchangers are arranged so as to surround the gas flow, and a problem that the size of the heat exchanger itself becomes large is generated. The increase in size of the heat exchanger causes cost-up of the apparatus as a whole.

Furthermore, because of increasing the size of the heat exchanger itself, it becomes necessary to install plural exchanging parts. Since the temperature of connecting portions of these plural heat exchanging parts also become high, selection of the material and structure design for the connecting portion become difficult. In particular, when the gas is flowed upwards from bottom of the gasifying reactor, the generated gas flows downwards from top of heat conducting parts through the connected pipes. Then, the spread fine particles are remained at the bottom of the heat conducting parts, and a problem is caused in the apparatus.

JP-A-7-97579 (1995) discloses a method wherein convection heat conducting planes are provided in aiming that the heat is recovered by not only radiation but also conduction. In accordance with the above method, the size of the apparatus can be reduced, because a large number of conducting pipes can be used in the apparatus.

However, the slug in the gas flow is adhered onto the convection heat conducting planes, and causes such problems as choking the gas flow path, and forming local high temperature states.

Another method has been proposed; wherein the generated gas is cooled by mixing with a cooling gas. The above method does not require the heat exchanger if the cooling gas can be mixed desirably. However, mixing a large amount of the cooling gas is necessary, and accordingly, the total amount of the whole gas is increased. Therefore, the amount of the gas tobe treated in following apparatus is increased, and accordingly, the size of the following apparatus is also increased.

The following apparatus includes dust separators, desulfurizers, and others. Therefore, if the sizes of these apparatus are increased, it causes an increment of the whole size of the plant.

Another method has been proposed; wherein the heat of the generated gas is recovered by utilizing an endothermic reaction of mixing coal and the like with the generated gas. The above method is effective for improving an efficiency of the gasification, because the heat is recovered by the endothermic reaction.

However, a special apparatus for separating and recovering unreacted products is required, because the unreacted products are mixed into the generated gas.

Practically, the special apparatus are such as cyclones, filters, and the like. The separation of the unreacted products must be performed at a high temperature, and accordingly, the apparatus become complex.

In particular when power generation is a main object, a response in the separation part is slow, and a problem is caused in a gas supply following to load variation.

SUMMARY OF THE INVENTION Advantageously, the present invention provides a coal gasification apparatus and a method of coal 25 gasification, wherein the heat generated by the gasifying reaction of coal can be recovered with a low cost by Rdecreasing a load to following apparatus.

P:\OPER\A-xcf2l277() mI.d=c09) I)1 -7- The present invention advantageously also provides a coal gasification hybrid power generation system using the above coal gasification apparatus.

According to one aspect of the invention there is provided a coal gasification apparatus comprising: a gasifying reaction part for gasifying coal; a heat recovery part for recovering heat generated by gasification of coal in said gasifying reaction part, said heat recovery part being positioned at an upper part of said gasifying reaction part and including a heat conducting tube arranged so as to intersect a gas flow from said gasifying reaction part substantially at right angles, said heat recovery part and said gasifying reaction part being arranged in a vessel; an outlet positioned at an upper part of said heat recovery part for gas generated in said gasifying reaction part; an outlet positioned at a lower part of said gasifying reaction part for slag generated in said gasifying reaction part; and upper and lower burners for supplying coal and oxidizing agent to the upper and lower parts of said gasifying reaction part; wherein, in use, coal and oxidizing agent are supplied from 25 said lower burner so as to melt ash in the coal, and coal and oxidizing agent are supplied from said upper burner so as to generate char from the coal, whereby the surface of melted slag flowing towards said heat recovery part with gas generated at said lower burner is covered with the char 30 generated by said upper burner.

~According to another aspect of the invention there is provided a coal gasification apparatus comprising: a gasifying reaction part for gasifying coal; a heat recovery part for recovering heat generated by gasification of coal in said gasifying reaction part, said heat recovery part being positioned at an upper part of said P:OPERUAxdU1277(X) rsl.doc-400 II -7Agasifying reaction part and including a heat conducting tube arranged so as to intersect a gas flow from said gasifying reaction part substantially at right angles, said heat recovery part and said gasifying reaction part being arranged in a vessel; an outlet positioned at an upper part of said heat recovery part for gas generated in said gasifying reaction part; an outlet positioned at a lower part of said gasifying reaction part for slag generated in said gasifying reaction part; a lower burner to supply said gasifying reaction part with coal and oxidizing agent; an upper burner to supply only coal between said gasifying reaction part and said heat recovery part; and a char recycling nozzle arranged to supply char separated and recovered from discharge gas of the outlet into said gasifying reaction part; whereby the surface of melted slag flowing toward said heat recovery part with gas generated at said lower burner is covered with char generated by gasification at said upper ee burner.

According to a further aspect of the invention there is .provided a coal gasification apparatus comprising: 25 a gasifying reaction part for gasifying coal; a heat recovery part for recovering heat generated by gasification of coal in said gasifying reaction part, said heat recovery part being positioned at upper part of said gasifying reaction part and including a heat conducting tube arranged so as to intersect a gas flow from said gasifying reaction part substantially at right angles, said heat recovery part and said gasifying reaction part being S"arranged in a vessel; an outlet positioned at an upper part of said heat recovery part for gas generated in said gasifying reaction Spart; an outlet positioned at a lower part of said gasifying P:\OPERkAd\2J277O .doc4)9AiiOI -7Breaction part for slag generated in said gasifying reaction part; a burner to supply said gasifying reaction part with coal and oxidizing agent; a char recycling nozzle arranged at a position above said burner of said gasifying reactor part to supply char separated and recovered from the discharge gas of the outlet into said gasifying reactor part; whereby the surface of melted slag flowing toward said heat recovery part with gas generated by the gasification at said burner is covered with char supplied by said char recycle nozzle.

According to yet another aspect of the invention there is provided a coal gasification hybrid power generation system comprising: a coal gasification apparatus for gasifying coal; a scrubber for separating dust and char from gas generated by said coal gasification apparatus; a desulfurizer for removing sulpha from the gas with dust and char removed; a gas turbine for combusting and converting the gas "purified by said scrubber and said desulfurizer into electric power; a heat recovery boiler for recovering heat from the 25 discharged gas as steam; a steam turbine to convert supplied steam recovered and supplied by said heat recovery boiler into electric power; :wherein said coal gasification apparatus comprising a gasifying reaction part for gasifying coal; a heat recovery part for recovering heat generated by gasification of coal in said gasifying reaction part, said S•heat recovery part being positioned at an upper part of said S"gasifying reaction part and including a heat conducting tube being arranged so as to intersect a gas flow from said RA 5' gasifying reaction part substantially at right angles, said heat recovery part and said gasifying reaction part being P:\OPERA.d\2127700 rsl.doc-09/0101 -7Carranged in a same vessel; an outlet positioned at upper part of said heat recovery part for gas generated at said gasifying reaction part; an outlet positioned at lower part of said gasifying reaction part for slag generated at said gasifying reaction part; and upper and lower burners for supplying coal and oxidizing agent to upper and lower parts of said gasifying reaction part; wherein, in use, coal and oxidizing agent are supplied from said lower burner so as to melt ash in the coal, and coal and oxidizing agent are supplied from said upper burner so as to generate char from the coal, and whereby the surface of melted slag flowing towards said heat recovery part with gas generated at said lower burner is covered with the char generated by said upper burner.

In the first heat recovery part, the generated gas at *ooo *oo o 8 1400 0 C is cooled to approximately 900 0 C, and the gas at 900 0 C is cooled to approximately 400 0 C in the second heat recovery part.

The coal gasification apparatus further comprises a coal supplying means for regulating a ratio of carbon to ashes in the generated gas by supplying carbon, arranged at a place between the gasifying reaction part and the heat recovery part.

Furthermore, a coal gasification method using a coal gasification apparatus is provided, wherein a reaction part for gasifying the coal and a heat recovery part for recovering the heat generated in the reaction part are arranged in a vessel: wherein the heat recovery part is arranged directly at a rear stage of the gasifying reaction part; the heat recovery part comprises heat conducting tubes which exchange heat by radiation and convection; and the heat conducting tubes oooo .o are arranged so as to intersect the gas flow substantially in right angles; 20 the reaction part comprises an upper reaction zone and a lower reaction zone; the upper reaction zone is supplied oe with such an amount of oxidizing agent that the S• temperature in the zone is kept lower than the melting ooo temperature of the ashes contained in the coal; the lower 25 reaction part is supplied with an amount of oxidizing agent, wherein the amount is determined by subtracting Sthe amount of the oxidizing agent supplied to the upper reaction part from the amount of the oxidizing agent necessary for converting all the coal supplied to the upper and the lower reaction parts to carbon monoxide and hydrogen; and the heat generated by the reaction is recovered at the heat recovery part connected directly to the reaction part, wherein the heat is conducted by radiation and convection.

Furthermore, there is provided a method of coal gasification comprising the steps of; reacting coal and an oxidising agent in a gasifying reaction part, which is composed so that cross sections at the upper end and the lower end of the reaction part are reduced from the cross section at parts other than the both ends of the reaction part; discharging the ashes from the lower end of the gasifying reaction part by melting; and cooling the generated combustible gas S: taken out from the upper end of the gasifying reaction o. part by the heat recovery part arranged directly above the gasifying reaction part; wherein: an amount of the oxidizing agent, which can elevate the temperature in the gasifying reaction part higher than the melting point of the ashes contained in the supplied coal, is supplied to the lower part of the gasifying reaction part; an amount of the oxidizing agent, which can not elevate the temperature in the gasifying reaction o 25 part higher than the melting point of the ashes contained 0 in the supplied coal, is supplied to the upper part of Ile, the gasifying reaction part; and the supplying amount of carbon is regulated so that the ashes are not adhered to the heat recovery part by supplying carbon from a carbon supplying means arranged at a place between the gasifying reaction part and the heat recovery part.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration indicating a condition of the gasifying reaction in the gasification apparatus of the present invention, FIG. 2 is a graph indicating a relationship between a carbon content in the ashes and an adhesiveness of the ashes depending on temperature, FIG. 3 is a schematic longitudinal cross section of the coal gasification apparatus in embodiment 1, FIG. 4 is a set of schematic transverse cross sections of the coal gasification apparatus in embodiment 1, FIG. 5 is a flow diagram of the coal gasification hybrid power generation system using the gasification apparatus in embodiment 1, FIG. 6 is a graph indicating the operating temperatures of the coal gasification apparatus of the present embodiment, in comparison with a conventional example, FIG. 7 is a graph indicating the size of the coal gasification apparatus of the present embodiment, in comparison with conventional examples, SFIG. 8 is a schematic longitudinal cross section of the coal gasification apparatus in embodiment 2, and FIG. 9 is a schematic longitudinal cross section of the coal gasification apparatus in embodiment 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention is explained in details with preferred embodiments referring to the drawings.

Main gasifying reactions of coal can be expressed by the following chemical equations coal volatiles (CHM, CO, H 2 etc.) char(C) (1) char H 2 0 CO H 2 (2) char CO 2 -b 2CO (3) (coal, char) 02 CO CO (4) The reactions expressed by the above equations are endothermic, and the reaction of the equation (4) is exothermic.

Generally, volatile materials are generated by the reaction of the equation first. Then, the temperature in a reactor is elevated by combustion of the volatile materials with generation of char. With starting the reaction of the equation the temperature in the reactor is further elevated, and CO, CO 2 are generated by reacting the coal and oxygen.

The HO0 and CO, generated by combustion of the volatile materials are reacted with unreacted carbon (char) under a high temperature atmosphere as shown by the equations and to form combustible H, and CO.

In accordance with a fluidized bed type gasification apparatus, the temperature in the reactor is elevated high enough to melt the ashes contained in the coal during the reaction, the ashes are discharged as a liquid slug by melting the ashes, and the liquid slug is solidified in a vitreous state by cooling for enclosing harmful metals and disposal.

The coal gasification apparatus of the present invention is a fluidized bed type two stage gasification apparatus, wherein inside the gasification reactor is divided into two stages, i.e. an upper stage and a lower stage. Coal and a small amount of an oxidizing agent are supplied from the upper stage, and coal and a large amount of the oxidizing agent are supplied from the lower stage.

Accordingly, the temperature in the lower stage is elevated high enough to melt the ashes in the coal.

The adhesion of the ashes onto side walls of the reactor by the gasifying reaction can be suppressed by making the temperature in the upper stage low insufficient to melt the ashes. In accordance with the above method, increasing efficiencies of both handling the ashes and the gasification to high can be made compatible.

FIG. 1 indicates schematically a condition of the gasifying reaction in the gasification apparatus of the P:\OPERAxd2 127700 rmI.doc09/O IAI -13 present invention.

The coal supplied from a lower stage burner generates a generated gas and molten ashes (slag) by reacting with a large amount of an oxidising agent. On the other hand, the coal supplied from the upper stage burner generates fine char by the endothermic reaction.

The char generated in the upper part of the gasifying reactor is adhered as powder onto surface of the slag generated in the lower part of the gasifying reactor, and achieves an advantage to suppress the adhesion of the slag onto the wall and heat recovery part. In accordance with the coal gasification apparatus of the present invention, adhesion of the slag onto the heat recovery part can be prevented by making particularly the slag generated in the gasifying reactor less adhesive, and the gasifying reactor o and the heat recovery part (heat conducting tubes) can be ooeo arranged in the same body.

0@ FIG. 2 indicates relationships of a ratio of carbon to ashes in char, and temperature to the adhesiveness of the oo ashes. The abscissa indicates carbon content in the ashes, and the ordinate indicates temperature.

oo• "The ashes has a high adhesiveness in the region ooooo *see expressed by hatched lines. That means, in the region, wherein the temperature is high and the carbon content in 25 the ashes is low, the ashes in the generated gas are readily adhered onto the heat recovery part (heat conducting tubes) L On the contrary, when the temperature is low (under 900 9C), or the carbon content in the ashes is high (at least 10 the adhesiveness of the ashes is low. That is, the ashes are hardly adhered to the heat conducting tubes.

In accordance with the above findings, the adhesion of the ashes to the heat recovery part such as heat conducting tubes and the like can be suppressed by increasing the ratio of the carbon to the ashes in the generated gas. Accordingly, a compact coal gasification apparatus, wherein the heat recovery part for recovering the heat generated by the reactions can be arranged directly at a rear stage of the gasifying reactor in the same body, can be provided.

In accordance with the coal gasification apparatus of the present invention, supply of cooling gas is not required, or even if required, the amount of the cooling gas is small. Therefore, sizes of apparatus for following processes can be reduced, because mixing of extra gas into the generated gas is small and the total amount of the gas flowing into the following apparatus can be maintained minimum.

The heat recovery part arranged directly at a rear stage of the gasifying reaction part of the present invention preferably comprises a structure composed of a first heat recovery part, and a second heat recovery part having a surface, of which temperature is lower than the temperature of the surface of the first heat recovery part, arranged directly at a rear stage of the first heat recovery part. The first and second heat recovery parts are arranged in the gas flow so as to intersect the gas flow in right angles. In the first heat recovery part, the temperature of the generated gas, i.e. 1400 is cooled down to 900 0 C. Here, steam at a high temperature can be obtained. On the other hand, in the second heat recovery part, the temperature of the generated gas, i.e.

900 is cooled down to 400 C.

The reason to compose the heat recovery part as described above is aiming at increasing the efficiency of the heat conductance, and utilizing the space of the apparatus more effectively. The reason to make the heat recovery part have two parts having different temperature each other is aiming at recovering the heat of the generated gas most effectively.

Examples of the practical shapes of the heat recovery part are a spiral wound shaped, or a zig-zag shaped metallic heat conducting tube. A composing density of these tubes is arbitrary determined based on the capacity of the gasifying reactor of the apparatus.

Water at a high temperature (or steam at a high temperature) is flowed through the first heat recovery part, i.e. heat conducting tubes, and water (or steam) at a temperature lower than the temperature of water (or steam) to the first heat conducting tube is flowed through the second heat recovery part, i.e. heat conducting tubes for recovering the heat generated by the gasifying reaction. That means, the first heat recovery part is used as an evaporator or a superheater, and the second heat recovery part is used as an evaporator or an economizer.

Hereinafter, the present invention is explained based on more practical embodiments.

(Embodiment 1) FIG. 3 indicates a schematic longitudinal cross section of the coal gasification apparatus of the present invention. The gasification apparatus comprises a gasifying reaction part surrounded by a vessel 51 and a heat recovery part arranged directly at a rear stage of the gasifying reactor. The gasifying reaction part (hereinafter called gasifying reactor) is composed of an upper part of the reactor 28 and a lower part of the reactor 29. Upper stage nozzles 31 are arranged at the upper part of the reactor 28, and lower stage nozzles 32 are arranged at the lower part of the reactor 29.

Recycle nozzles 6 are provided at the upper end part i*e• of the gasifying reactor 25, a slag tap 26 is provided at the lower end part of the gasifying reactor 25, and 0*diameters of the gasifying reactor at the upper end and 25 the lower end are reduced. A slag water-cooling tank is arranged beneath the gasifying reactor 25. Slag 12 Ksolidified by the slag water cooling tank 30 is discharged P:\OPER\AU 12277Mo -Ldc)9OAI 16Aout of the gasifying reactor Furthermore, a high temperature heat recovery part 23 0e 9 9 90999.

9 9*9* a 9a*S .9 9 9* 99 9 a and a low temperature heat recovery part 22 are arranged directly above the gasifying reactor 25. Inner walls of the gasifying reactor 25 are protected by water-cooled walls 24 cooled by water and refractory materials placed at their inner surface.

FIG. 4 is a set of schematic transverse cross sections of the gasifying reactor. FIG. 4 (a)is a transverse cross section indicating a part where the recycle nozzles 6 for supplying recycle gas are arranged, is a transverse i0 cross section indicating a part where the upper stage nozzles 31 are arranged, and is a transverse cross section indicating a part where the lower stage nozzles 32 are arranged.

A direction of each nozzle is oriented so that the gas flow is supplied to more the central region in the order of and as shown by whirling diameters 41 43 of the gas flows. Accordingly, the reactor wall can be covered by recycle gas, the upper stage generated gas, and the lower stage generated gas in the order near the reactor wall. That means, the reactor wall 44 is protected by making the lower temperature gas flow nearer the reactor wall.

Coal 9 and oxygen 8 in a designated ratio are supplied through the upper stage nozzles 31, wherein the designated ratio is determined so as not to make the temperature in the gasifying reactor exceed the melting temperature of the ashes in the coal. Coal 9 and oxygen 8 in a designated 18 ratio are supplied through the lower stage nozzles 32, wherein the designated ratio is determined so as to make the temperature in the gasifying reactor exceed the melting temperature of the ashes in the coal.

Here, an additive agent 11 made of limestone and the like for assisting the decrease of the melting temperature of the ashes, or reactions in the reactor such as desulfuration and the like can be supplied with coal.

Furthermore, steam 10 can be supplied for regulating the temperature in the reactor and as an oxidizing agent.

Recycle char 13 recovered by the apparatus (scrubber) at the rear stage of the coal gasification apparatus is supplied from the lower part of the gasifying reactor Accordingly, a reaction zone at a temperature lower than the melting point of the ashes is formed at the upper part of the reactor 28. Furthermore, a reaction zone at a temperature higher than the melting point of the ashes is formed at the lower part of the reactor 28, and molten "2 slug is formed between this reaction zone and the reactor wall. Main components of the above recycle char is non-combustion carbon and the ashes.

Next, an example of operating conditions of the above

*SS*

coal gasification apparatus is indicated in Table 1.

2 Table 1 Coal supplying amount 1024 t/d Upper stage Oxygen supplying amount 590 t/d Ratio of oxygen/coal 0.58 Temperature 980 0C Coal supplying amount 1024 t/d Lower stage Oxygen supplying amount 1048 t/d Ratio of oxygen/coal 1.02 Temperature 1560 °C Coal supplying amount 2048 t/d Total Oxygen supplying amount 1638 t/d Ratio of oxygen/coal 0.80 Temperature 1340 °C With the above operating conditions, an equal amount of coal was supplied from the upper part 28 and the lower part 29 of the reactor, respectively. A sufficient amount of oxygen for gasifying the supplied coal is supplied.

The ratio of total oxygen/total coal under the above operating conditions is 0.8 by weight.

At the upper part 28 of the reactor, the ratio of oxygen/coal was set to be 0.58, in order to supply an amount of oxygen for making the temperature in the reactor lower than the melting point of the ashes in the coal.

I The supplying amount of oxygen to the lower part 29 of the reactor is an amount obtained by subtracting the supplying amount of oxygen to the upper part of the reactor from the total amount of oxygen. Accordingly, the ratio of oxygen/coal at the lower part of the reactor becomes 1.02 under the above operation conditions. The ratio is based on the total amount of oxygen including the oxygen supplied with the recycle char.

Under the above operating conditions, the temperature at the lower part 29 of the reactor becomes approximately 1560 0 C. This temperature is sufficient for melting the ashes in the coal.

On the other hand, char is generated at the upper part 28 of the reactor, because the temperature in this region is lower than the melting point of the ashes (900 C 1400 cC), and the char is adhered as powders onto the surface of the slag generated at the lower part of the reactor. Therefore, even if the slag reaches at the heat recovery parts 23, 22 (heat conducting tubes) arranged above the gasifying reactor 25, the slag is not adhered *0 onto the heat conducting tubes. Accordingly, an improvement to avoid lowering the heat conductance by 1*90; adhering the slag onto the surface of the heat conducting tubes can be achieved.

0 00"0" Since the above carbon powder is also useful for 25 destroying boundary layers of adhered materials, the heat conductance coefficient of the heat conducting tubes Fcan be maintained preferably.

The generated gas containing the slag, which is less adhesive because of being surrounded by the powder, is exhausted from an outlet aperture part 27 of the gasifying reactor 25, cooled first at the high temperature heat recovery part 23 cooled by high temperature water 5, and the heat is recovered as high pressure steam 4. Then, the gas is further cooled at the low temperature heat recovery part 22 cooled by low temperature water 3, and the heat is recovered as low pressure steam 2. The gas 1 cooled as above is transferred to apparatus arranged at rear stages through the outlet 21 of the gasifying apparatus.

In accordance with the present embodiment, the heat recovery parts and the gasifying reactor 25 are arranged together in a vessel 51, and the size of the gasifying apparatus itself can be made small.

Next, a composition of coal gasification hybrid power o Oo0.

generating system using the gasification apparatus in the present embodiment is indicated in FIG. The present power generating system comprises a coal gasification apparatus, a gas purifying apparatus, gas turbine-steam turbine complex power generators, and others.

0. Oxygen is supplied to the coal gasification apparatus o 25 from an oxygen producing apparatus 81. Pulverized coal is supplied from a coal hopper 80, pressurized by excess Snitrogen generated in the oxygen producing apparatus 81, and supplied to the coal gasification apparatus vessel 51 through the upper stage nozzles 31 and the lower stage nozzles 32. The supplying amount of coal through the upper stage nozzles 31 is regulated by an upper stage coal supplying amount regulating apparatus 92. The supplying amount of coal through the lower stage nozzles 32 is regulated similarly by a lower stage coal supplying amount regulating apparatus 93. The heat generated at the gasifying reactor 25 in the coal gasification apparatus vessel 51 is recovered as low pressure steam 2 by the heat recovery parts (22, 23 in FIG. which absorb the heat by convection and radiation. The heat conducting tubes are arranged so as to intersect the gas flow in right angles.

Therefore, heat exchange with the high temperature gas o:o: is performed sufficiently to cool the gas from a high o: temperature of more than 1400 0 C to 400 cC.

O V Dusts in the generated gas are removed by a scrubber 83 comprising a cyclone, high temperature bag filters, oo or high temperature electric dust precipitator.

Furthermore, sulfide such as H 2 S, COS, and the like are removed by a desulfurizing apparatus 84 such as wet type desulfurizer, which removes the sulfide with an absorbing solution, or dry type desulfurizer, which removes the sulfide with solid desulfurizing agents.

The generated gas purified by removing the dust and RAsulfide as above is supplied to a coustor of the gas sulfide as above is supplied to a combustor of the gas turbine 85, and converted to electric power by direct combustion and driving the turbines. The gas temperature at the inlet of the gas turbine must be approximately lower than 400 °C on account of reliability of valves, and the like. In the gas turbine 85, air 61 is compressed to be pressurized air, and supplied to the oxygen producing apparatus 81 or the coal gasification apparatus 82.

A part of the purified gas is pressurized by a compressor 101, and supplied to the coal gasification apparatus 82 through the recycle nozzles 6 for cooling the generated gas in the gasifying reactor 25 as shown in Fig.3.

Exhaust gas at a high temperature from the gas turbine is recovered as steam by a heat recovery boiler 86.

The recovered steam is supplied to the steam gas turbine 87, and converted to electric power.

SThe steam generated by a heat exchanger connected directly to the gasifying reactor is also supplied to the *e steam turbine, and converted to electric power.

20 As explained above, in accordance with the coal gasification apparatus of the present invention, the :ooo: supplying amount of the cooling gas can be decreased, because the generated gas is cooled effectively at the heat recovery part provided by connecting directly.

*o 25 Accordingly, the amount of gas, other than coal gas, passing through the scrubber 83 or the desulfurizing apparatus 84 is small, the sizes of these apparatus can be reduced, and the total size of the coal gasification hybrid power generation system can be decreased.

Next, FIG. 6 is a graph indicating the operating temperatures of the coal gasification apparatus of the present embodiment in comparison with a conventional example.

In accordance with the conventional gasification apparatus, the gas temperature at the outlet of the gasifying reactor is high as approximately 1500 C.

Therefore, a large amount of cooling gas is required, because the temperature of the generated gas must be decreased to lower than 900 0 C before reaching at the heat exchanger. This temperature is indicated in FIG. 2.

On the contrary, in accordance with the gasifying system of the two stage reaction of the present embodiment, the temperature of the generated gas at the outlet 27 of the gasifying reactor 25 is already as low as 400 and the adhesion of the ashes to the heat recovery part and others can be suppressed, because the ratio of carbon to the ashes in the generated gas is large. The temperature of the gas entering the heat recovery part may by approximately 1200 OC. Accordingly, even if the cooling gas is required, the amount of the cooling gas is small.

FIG. 7 is a graph indicating the size of the coal gasification apparatus of the present embodiment in comparison with conventional examples (including the heat recovery part).

The conventional example 1 is a case when one stage reaction gasifying reactor and a radiation heat recovery part are used. Because the radiation area per unit cross sectional area can not be increased, the size of the reactor must be increased.

The conventional example 2 is a case using a two stage reaction gasifying reactor. Because the temperature of the gas at the outlet of the reactor can be lowered, the size of the heat recovery part can be relatively small.

In accordance with the coal gasification apparatus of the present embodiment, wherein the heat recovery part and the gasifying reactor are formed in a vessel, a convection heat conducting part can be used in addition to the radiation heat conducting part in the heat recovery part, the size of the gasification apparatus can be decreased significantly.

(Embodiment 2) The present embodiment is explained referring to FIG.

8. Two gasifying zones, i.e. an upper stage gasifying zone and a lower stage gasifying zone, are formed, only coal is supplied to the upper stage gasifying zone, all the ashes generated in the upper stage gasifying zone is discharged to out of the reactor, unreacted char, which is caught at an external of the system, is supplied to the lower stage gasifying zone as recycle char 13. Oxygen 8 and coal 9 are supplied to the lower stage gasifying zone 29, and mainly a combustion reaction is proceeded.

Mainly a gasifying reaction is proceeded in the upper stage gasifying zone 28 formed at the upper portion of the gasifying reactor A specific advantage of the present embodiment is that the calorific value of the generated gas can be increased, because the combustible gas generated in the upper stage gasifying zone 28 can be taken out without touching with any oxidizing agent.

(Embodiment 3) The present embodiment is explained referring to FIG.

9. The present embodiment is a one stage gasifying type coal gasification apparatus. Coal 9 and oxygen 8 are supplied to the gasifying zone 33. In order to suppress the adhesion of the ashes to the heat recovery part, unreacted carbon is generated by selecting the appropriate ratio of oxygen to coal small. The unreacted carbon is recovered by a scrubber in a rear stage, and supplied again as the recycle char.

Because a supplying position of the char is set directly beneath the heat recovery part 23, adhesion of slug can be suppressed by the char.

A specific advantage of the present embodiment is that the structure of the apparatus can be simplified, because the gasifying zone 33 is made one stage, and cost of the apparatus can be decreased.

P:OPERA.xd\21277(X) rcs I.doc.-)90A) 1 -27- In accordance with the present invention, adhesion of the ash slag is suppressed by generating unburned carbon in the gasifying reactor, or supplying char into the gasifying reactor. Accordingly, the heat recovery part and the gasifying reactor can be formed in a vessel, and size of the coal gasification apparatus can be decreased.

Because supply of the cooling gas is not necessarily required, an excess amount of gas is not flowed to the following apparatus, and the whole system can be simplified.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

a oeoo

Claims

1. A coal gasification apparatus comprising: a gasifying reaction part for gasifying coal; a heat recovery part for recovering heat generated by gasification of coal in said gasifying reaction part, said heat recovery part being positioned at an upper part of said gasifying reaction part and including a heat conducting tube arranged so as to intersect a gas flow from said gasifying reaction part substantially at right angles, said heat recovery part and said gasifying reaction part being arranged in a vessel; an outlet positioned at an upper part of said heat recovery part for gas generated in said gasifying reaction part; an outlet positioned at a lower part of said gasifying reaction part for slag generated in said gasifying reaction part; and upper and lower burners for supplying coal and oxidizing agent to the upper and lower parts of said gasifying reaction part; wherein, in use, coal and oxidizing agent are supplied from said lower burner so as to melt ash in the coal, and coal and oxidizing agent are supplied from said upper burner so as to generate char from the. coal,, whereby the surface of melted slag flowing towards said heat recovery part with gas generated at said lower burner is covered with the char g generated by said upper burner. 20

2. A coal gasification apparatus according to claim 1 further comprising: a char recycling nozzle arranged at the lower part of said gasifying reactor part to supply char separated and recovered from discharge gas of the vessel.

3. A coal gasification apparatus according to claim 1 further comprising: ooooo S•a char recycling nozzle arranged at the upper part of said gasifying reactor part to 25 recycle partial gas with char separated and recovered from discharge gas of the vessel.

4. A coal gasification apparatus comprising: a gasifying reaction part for gasifying coal; a heat recovery part for recovering heat generated by gasification of coal in said *a gasifying reaction part, said heat recovery part being positioned at an upper part of said gasifying reaction part and including a heat conducting tube arranged so as to intersect a gas flow from said gasifying reaction part substantially at right angles, said heat recovery P:\OPER\Axdj21277) r .doc-09#) WlI -29- part and said gasifying reaction part being arranged in a vessel; an outlet positioned at an upper part of said heat recovery part for gas generated in said gasifying reaction part; an outlet positioned at a lower part of said gasifying reaction part for slag generated in said gasifying reaction part; a lower burner to supply said gasifying reaction part with coal and oxidizing agent; an upper burner to supply only coal between said gasifying reaction part and said heat recovery part; and a char recycling nozzle arranged to supply char separated and recovered from discharge gas of the outlet into said gasifying reaction part; whereby the surface of melted slag flowing toward said heat recovery part with gas generated at said lower burner is covered with char generated by gasification at said upper burner. A coal gasification apparatus comprising: a gasifying reaction part for gasifying coal; a heat recovery part for recovering heat generated by gasification of coal in said gasifying reaction part, said heat recovery part being positioned at upper part of said gasifying reaction part and including a heat conducting tube arranged so as to intersect a gas flow from said gasifying reaction part substantially at right angles, said heat recovery 20 part and said gasifying reaction part being arranged in a vessel; an outlet positioned at an upper part of said heat recovery part for gas generated in said gasifying reaction part; an outlet positioned at a lower part of said gasifying reaction part for slag generated in said gasifying reaction part; 25 a burner to supply said gasifying reaction part with coal and oxidizing agent; a char recycling nozzle arranged at a position above said burner of said gasifying reactor part to supply char separated and recovered from the discharge gas of the outlet into said gasifying reactor part; whereby the surface of melted slag flowing toward said heat recovery part with gas generated by the gasification at said burner is covered with char supplied by said char h recycle nozzle.

V a a a a a a a P:\OPER~A2d 127700 rsl.doc-O9i1I I

6. A coal gasification hybrid power generation system comprising: a coal gasification apparatus for gasifying coal; a scrubber for separating dust and char from gas generated by said coal gasification apparatus; a desulfurizer for removing sulpha from the gas with dust and char removed; a gas turbine for combusting and converting the gas purified by said scrubber and said desulfurizer into electric power; a heat recovery boiler for recovering heat from the discharged gas as steam; a steam turbine to convert supplied steam recovered and supplied by said heat recovery boiler into electric power; wherein said coal gasification apparatus comprising a gasifying reaction part for gasifying coal; a heat recovery part for recovering heat generated by gasification of coal in said gasifying reaction part, said heat recovery part being positioned at an upper part of said gasifying reaction part and including a heat conducting tube being arranged so as to intersect a gas flow from said gasifying reaction part substantially at right angles, said heat recovery part and said gasifying reaction part being arranged in a same vessel; an outlet positioned at upper part of said heat recovery part for gas generated at said 0*.o gasifying reaction part; 20 an outlet positioned at lower part of said gasifying reaction part for slag generated at said gasifying reaction part; and upper and lower burners for supplying coal and oxidizing agent to upper and lower S parts of said gasifying reaction part; wherein, in use, coal and oxidizing agent are supplied from said lower burner so as o: 25 to melt ash in the coal, and coal and oxidizing agent are supplied from said upper burner so as to generate char from the coal, and whereby the surface of melted slag flowing towards said heat recovery part with gas generated at said lower burner is covered with the char generated by said upper burner. 4 "o5o

7. A coal gasification hybrid power generation system according to claim 6, further comprising a char recycling nozzle arranged at the lower part of said gasifying reaction part to supply char separated and recovered from discharge gas of the vessel. part to supply char separated and recovered from discharge gas of the vessel. P:\OPER\Axd2U127700 s I .doc-12M1/A -31

8. A coal gasification hybrid power generation system according to claim 6 further comprising a char recycling nozzle arranged at the upper part of said gasifying reaction part to recycle partial gas with char separated and recovered from discharge gas of the vessel.

9. A coal gasification apparatus according to claim 1, 4 or 5 and substantially as hereinbefore described with reference to the drawings. A coal gasification hybrid power generation system according to claim 6 and substantially as hereinbefore described with reference to the drawings. DATED this 12th day of January, 2001 Hitachi, Ltd AND Babcock-Hitachi Kabushiki Kaisha By DAVIES COLLISON CAVE Patent Attorneys for the Applicants