Method for power generation with gas turbine using gasified fuel of inferior quality

Abstract: Power generation with a gas turbine using a gasified fuel of inferior quality is accomplished with high efficiency by a method which comprises bleeding part of highly compressed air emanating from an air emanating from an air compressor driven by a gas turbine and introducing the part of highly compressed air into an oxygen adsorbing tower containing an oxygen adsorbent thereby causing the oxygen from the highly compressed air to be adsorbed by the oxygen adsorbent and, at the same time, allowing the nitrogen gas from the highly compressed air to flow in a highly compressed state through the oxygen absorbing tower, desorbing the adsorbed oxygen from the oxygen adsorbent under a vacuum, compressing the oxygen gas resulting from the desorption and gasifying a fuel of inferior quality with the compressed oxygen gas as an oxidizing agent, effecting combustion of the gasified fuel of inferior quality with the remainder of the compressed air produced in the air compressor, mixing the gas arising from the combustion with the highly compressed nitrogen gas having flowed through the adsorbing tower, and introducing the resultant mixture into the gas turbine thereby driving the gas turbine and inducing power generation.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates to a method for power generation with a gas turbine using the gas resulting from gasification of a fuel of inferior quality such as coal, tar, or less volatile oil as defined in the preamble of claim 1 by the use of a pressure swing method for the production of oxygen. DESCRIPTION OF THE PRIOR ART The coal gasification composite power generation system can be expected to offer highly efficient and clean power generation because it utilizes the gas turbine which is most efficient in all the heat engines using fossile fuels and because it uses as the fuel for the gas turbine the gasified fuel which has been produced by a gasifying furnace and scrubbed to expel dust and desulfurized. For the gasification of such fuels of inferior quality as coal, tar, and less volatile oil, methods using air and methods which use oxygen respectively as an oxidizing agent have been proposed. The use of air in this gasification is disadvantageous from the standpoint of motive power because the gasifying furnace for the gasification of such a fuel of inferior quality is operated under a pressure higher than the pressure of the gas turbine and, as a result, the nitrogen which accompanies oxygen in the air is inevitably destined to grow in pressure. Further, since the gasified fuel obtained by this gasification falls short of 1,000 Kcal/Nm³ in calorific value, the combustion of this gasified fuel calls for skill. Further, since the gasifying furnace itself and the cleanup system for removal of dust and desulfurization depend largely on the amount of a gas to be treated, the method which uses air entrained by the nitrogen originating in the air incurs an unduly large cost of equipment. For the reason given above, the methods using oxygen meet expectations. In reality, however, the method of deep cooling separation which is widely used for the production of oxygen in a large volume has not overcome the drawback inherent in the use of air because it entails a heavy power consumption for the production of oxygen and incurs a high cost of equipment. Moreover, the deep cooling method encounters unusual difficulties in coping with the practices of load change, weekend interruption, and daily interruption which have found acceptance in the power generation systems in recent years. Fig. 2 is a flow sheet of an oxygen blowing coal gasifying composite power generation system possessing such merits and demerits as described above. The air which has been compressed to a pressure of about 607950 Pa (6 atm.) by an air compressor 01 is separated in a total low-pressure type deep cooling separation and production device 02 into oxygen gas 03 of a pressure in the range of 101325 Pa (1 atm.) to 121590 Pa (1.2 atm.) and into nitrogen gas 04 of a pressure in the range of 101325 Pa (1 atm.) to 121590 Pa (1.2 atm.). The oxygen obtained in the total low-pressure type deep cooling separation and production device 02 has a very high concentration falling in the range of 90 to 99.6 vol%. The power during the production of oxygen is approximately 0.36 kwh/Nm³-O₂ in the case of an oxygen purity of 90 vol% and 0.4 kwh/Nm³-O₂ in the case of an oxygen purity of 99.6 vol%. The power generation system does not require the oxygen to be in a very high concentration and, therefore, effects gasification of coal by producing oxygen gas in a purity of 90 vol%, compressing the oxygen gas to a pressure of 3039750 Pa (30 atms.) by an oxygen compressing device 05, mixing the compressed oxygen gas with steam 06, and supplying the resultant mixture as accompanied by coal 08 to a coal gasifying furnace 07. The resultant gasified coal having an average calorific value of 5,000 Kcal/Nm³ is scrubbed to expel dust by a high-temperature dust removing device 09, desulfurized by a dry type desulfurizing device 010 to be cleaned enough to be used in the gas turbine cycle, and then supplied via a flow path 011 to a combustion device 012. In the meantime, the greater part of the air which has been compressed by a compressor 013 is supplied to the combustion device 012, consumed therein for effecting combustion of the aforementioned gasified coal in a compressed state, and introduced in the form of a hot compressed fluid via a flow path 015 into an inflation type gas turbine 016. On the existing technical level, the highest allowable working temperature of the material of the gas turbine is about 1,380°C. Since the temperature of combustion in the combustion device 012 exceeds this temperature, part of the aforementioned compressed air is supplied via a flow path 017 to the flow path 015 and used for cooling the combustion device 012. The compressor 013 and the gas turbine 016 are connected with a common shaft 018 to a power generator 019 so that the rotation of the gas turbine 016 produces electric power. Since the exhaust gas which emanates at a lower temperature under a lower pressure from the gas turbine 016 after performing its work therein has a temperature of about 500°C, it is treated in a waste heat recovery boiler and steam turbine system 020 for collection of electric energy. The power generation system which uses oxygen in the place of air as an oxidizing agent in the gasification of such a fuel of inferior quality as coal as described above operates by the use of a relatively small amount of oxygen separated from nitrogen and, therefore, enjoys many prominent advantages such as; (1) Generous reduction in the power required for increasing the pressure of the oxidizing agent in the gasifying furnace and economization of the cost of the pressure increasing device. (2) Reduction in the cost of equipment due to a decrease in the cross-sectional area of the coal gasifying furnace. (3) Reduction in the equipment cost and variable cost of the dust removing device and the desulfurizing device, which both depend largely on the amount of a gas subjected to the treatment, due to a decrease in the volume of the gasified coal. (4) Improvement of the operating capacity of the combustion device due to an increase in the calorific value of the gasified coal. (5) Simultaneity of process between the power generation and the gasification for production of chemical raw material. The fact that the equipment cost and the variable cost for the method of deep cooling separation which is widely employed as means for production of oxygen in a large volume are such as to offset substantially the aforementioned advantages derived from using oxygen as the oxidizing agent for gasification and the fact that such operations as load change, weekend interruption, and daily interruption, which constitute indispensable requirements for a power generation system, are extremely difficult to effect, are causes for reluctance shown in the adoption of this method. A prior art method and apparatus as defined in the preamble of claim 1 for power generation with a gas turbine using a gasified fuel of inferior quality is known from FR-A-2 331 680. This document, however, only discloses the general apparatus for power generation by means of separation of O₂ and N₂ from compressed air and the independent use of the O₂ for the fuel-gasifying step and of N₂ for the power generation. US-A-4 015 956 describes the general concept of an adsorbing-desorbing method and and apparatus comprising interconnected adsorption towers for performing such method for obtaining gaseous mixtures having one component enriched. The adsorbent used is a type made from an O₂-selective activated carbon while zeolite filled adsorbers are generally discussed in the document for having multiple disadvantages. SUMMARY OF THE INVENTION This invention, conceived in the urge to eliminate the drawbacks of the prior art described above, aims to provide a method for power generation with a gas turbine, which method comprises gassifying a fuel of inferior quality with the aid of the pressure swing method for the production of oxygen and using the resultant gasified fuel for the operation of the gas turbine. To be specific, this invention is directed to a method for power generation with a gas turbine using a gasified fuel of inferior quality, which method is defined by the features of claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a flow diagram illustrating one embodiment of this invention and Fig. 2 is a flow diagram illustrating a conventional coal gasification composite power generation plant using oxygen. DESCRIPTION OF THE PREFERRED EMBODIMENT In this invention, part of the highly compressed air produced by an air compressor which is driven by a gas turbine is bled and introduced into an oxygen adsorbing tower, wherein the oxygen in the air is adsorbed on an oxygen adsorbent and the remaining nitrogen gas is allowed to flow therethrough in a highly compressed state. Since the adsorption of oxygen in this oxygen adsorption tower is effected under a highly compressed state, it proceeds with high efficiency on oxygen of an amount of about 20% by volume, based on the amount of air. Thus, the use of the oxygen adsorbent in a small amount suffices to effect the adsorption and the use of the oxygen adsorption tower of a proportionately small capacity suffices for the purpose of the adsorption. The oxygen adsorbed on the oxygen adsorbent is desorbed in the form of oxygen gas under a vacuum. This oxygen gas is compressed and then used as an oxidizing agent for the gasification of coal or other fuel of inferior quality. The gasified fuel which issues from the gasification of the fuel of inferior quality assumes a volume exclusive of the volume which would be occupied by the nitrogen gas when air was used as an oxidizing agent in the gasification, with the result that the calorific value of the gasified fuel is proportionately high and the volume of the gasifying device such as the gasifying furnace is small accordingly. The gasified fuel is burnt and converted into a hot highly compressed combustion gas by the remainder of the highly compressed air produced by the aforementioned air compressor. This combustion gas is mixed with the highly compressed nitrogen gas which has flowed through the oxygen adsorption tower. The resultant mixture is introduced into the gas turbine and used therein for driving the gas turbine and consequently inducing power generation. The mixed fluid of the combustion gas with the nitrogen gas which is introduced into the gas turbine has a temperature lower than the highest allowable working temperature of the material of the gas turbine owing to the incorporation therein of the nitrogen gas. This mixed fluid further allows the energy owned by the highly compressed nitrogen gas and the energy of the combustion gas to be jointly converted into motive force by the gas turbine. Now, this invention will be described more specifically below with reference to Fig. 1. An air compressor 1, an inflation type gas turbine 23, and a generator 24 are connected to a common shaft. A flow path 2 originating from the outlet of the air compressor 1 is connected to the inlet side of a combustion device 20 adapted to supply the gas turbine 23 with the combustion gas. Oxygen absorption towers 5a, 5b are parallelly disposed. Flow paths 30a, 30b connected to the bottom parts of the absorption towers 5a, 5b are connected respectively via valves 4a, 4b to a bleeding flow path 3 branched from the flow path 2 mentioned above. Inside the oxygen adsorption towers 5a, 5b, dehumidifiers of activated alumina 6a, 6b, cold accumulating agents 8a, 8b, an air heat-exchange device 7 and a Freon heat-exchange device 9 both piercing the two towers, and oxygen adsorbents of Na-A type zeolite 10a, 10b are sequentially disposed upwardly in the order mentioned. To the top parts of the oxygen adsorption towers 5a, 5b are respectively connected flow paths 31a, 31b provided with valves 11a, 11b. The flow paths 31a, 31b are connected to a flow path 22 laid between the outlet side of the combustion device 20 and the gas turbine 23. The air heat-exchange device 7 mentioned above is connected to a heat-exchange device 7' which is inserted in a flow parth 12. Flow paths 32a, 32b provided respectively with valves 13a, 13b branch from between the valves 4a, 4b of the aforementioned flow paths 30a, 30b of the oxygen adsorption towers 5a, 5b and the adsorption towers 5a, 5b. The flow paths 32a, 32b are joined to each other and connected to the inlet side of a compressor 14. The outlet side of the compressor 14 is joined to a steam supply path 15 and connected to the bottom part of a gasifying furnace 16. The bottom part of the gasifying furnace 16 is connected to a coal supply path 15'. A flow path 17 which is connected to the top part of the gasifying furnace 16 is connected to a dust removing device 18. The dust removing device 18 is connected to a desulfurizing device 19 and this desulfurizing device 19 is connected to the inlet side of the aforementioned combustion device 20. By 25 is denoted a recovery boiler steam turbine system to which the exhaust gas from the gas turbine 23 is supplied. In the present embodiment, the air compressed to a pressure of about 1519875 Pa (15 atms) in the air compressor 1 driven by the gas turbine 23 is partly bled through the flow path 2 and advanced into the flow path 3. When the valves 4a, 11a of the tower 5a, i.e. one of the parallelly disposed oxygen adsorption towers 5a, 5b, are opened, the valve 13a is closed and the valves 4b, 11b of the tower 5b are closed and, at the same time, the valve 13b is opened. Through the opened valve 4a, the compressed air enters the oxygen adsorption tower 5a. The compressed air is dehumidified with the dehumidifier 6a, cooled with the cold accumulating agent 8a and by the air heat-exchange device 7, further cooled to a temperature of about -70°C by the Freon heat-exchange device 9, and passed through the oxygen adsorbent 10a, with the result that the oxygen in the compressed air is adsorbed on the absorbent 10a. In the meantime, the nitrogen is passed in a highly compressed state through the adsorption tower 5a. The nitrogen which has passed through the absorption tower 5a possesses a pressure of 1519875 - (10132.5 ∼ 50662.5) Pa (15 - (0.1 ∼ 0.5) atms.), wherein the value 10132.5 to 50662.5 Pa (0.1 to 0.5 atm.) represents the pressure loss suffered by the nitrogen during its flow through the adsorption tower 5a. This compressed nitrogen flows through the valve 11a and the heat-exchange device 7' to the flow path 12. Since the compressed air is supplied to the oxygen adsorption tower 5a and the oxygen in a highly compressed state is adsorbed on the oxygen adsorbent 10a as described above, enhancement of the efficiency of adsorption, reduction in the amount of the oxygen adsorbent to be required, and compaction of the oxygen adsorption tower 5a are all materialized. Through the medium of the flow path 30b and the flow path 32b incorporating the opened valve 13b, the other oxygen adsorption tower 5b is connected to the inlet side of the compressor 14 and consequently caused to assume a vacuumized state. The oxygen which has been adsorbed in the oxygen adsorption tower 5b is desorbed in the form of oxygen gas from the adsorption tower 5b, introduced into the compressor 14, compressed thereby, and mixed with the steam from the steam supply path 15. The resultant mixed fluid and the coal from the coal supply path 15' are jointly supplied to the gasifying furnace 16. After the adsorption of oxygen in the oxygen adsorption tower 5a and the desorption of oxygen in the oxygen adsorption tower 5b have been completed, the valves of the adsorption towers are switched and the compressed air is introduced into the oxygen adsorption tower 5b to induce the adsorption of oxygen and then the desorption of the adsorbed oxygen from the oxygen adsorption tower 5a. The oxygen gas resulting from the desorption is introduced into the compressor 14. Thus, in the oxygen adsorption towers 5a, 5b, the adsorption and desorption of oxygen are continuously carried out by sequentially switching the adsorption of oxygen on one hand and the desorption of oxygen on the other hand. The adsorption and desorption in the oxygen adsorption towers 5a, 5b are generally each in a duration of about 75 seconds. The oxygen which has been adsorbed on the oxygen adsorbents 10a, 10b in the oxygen adsorption towers 5a, 5b is desorbed in the form of oxygen gas from the oxygen adsorbents 10a, 10b on exposure to a vacuum generated by the compressor 14. This desorption leaves the oxygen adsorbents in a regenerated state. The oxygen gas is passed through the cold accumulating agents 8a, 8b thereby deprived of the cold of -70°C and elevated substantially to normal room temperature. It is then passed through the dehumidifiers 6a, 6b saturated in advance with water and consequently dehumidified. This dehumidification leaves the dehumidifiers in a regenerated state. The oxygen gas to be supplied to the gasifying furnace 16 is compressed to a pressure of about 3039750 Pa (30 atms.) by the compressor 14 en route to the gasifying furnace 16. While the deep cooling method employed in the conventional method as already described requires oxygen of the atmospheric pressure to be compressed to about 3039750 Pa (30 atms.), the method of the present embodiment allows the oxygen gas to be compressed by a compression ratio of 3 from the level of about 1013250 Pa (10 atms.) to about 3039750 Pa (30 atms.) at the time that the desorption of the oxygen gas from the oxygen adsorbent is started. By the desorption of oxygen which proceeds over the subsequent period of about 75 seconds, the inner pressure of the adsorption towers is gradually decompressed eventually to the level of about 101325 Pa (1 atm.). In the final stage, the oxygen gas is compressed from 101325 Pa (1 atm.) to 3039750 Pa (30 atms.) by the compressor 14. In the desorption of oxygen during the period of about 75 seconds, therefore, the inner pressure becomes substantially equal to the average increase of pressure from 405300 Pa (4 atms.) to 3039750 Pa (30 atms.). The method of the present embodiment, therefore, allows an economization of about 50% in the power consumption as compared with the conventional deep cooling method. In the gasifying furnace 16, the gasification of coal is effected with the oxygen gas and the steam supplied to the furnace 16 as described above. The resultant gasified coal enters the flow path 17. Since the gasified coal thus produced, unlike that obtained by the use of air, does not entrain nitrogen, the amount of the gasified fuel is about 50% of that obtained by the use of air. As a result, the gasifying furnace 16 operates satisfactorily with a small capacity and the gasified coal possesses a calorific value exceeding 3,000 Kcal/Nm³. The gasified coal of such a small volume as mentioned above is advanced via the flow path 17, passed through the dust removing device 18 and the desulfurizing device 19 and consequently cleaned up through removal of dust and desulfurization, then introduced into the combustion device 20, burnt with the compressed air delivered from the air compressor 1 via the flow path 21, and forwarded via the flow path 22 to the gas turbine 23. In the present embodiment, the nitrogen gas which has passed in a highly compressed state through the oxygen adsorption towers 5a, 5b is mixed with the aforementioned combustion gas and introduced via the flow paths 12, 22 into the gas turbine 23. Owing to the incorporation of the nitrogen gas, the mixed fluid entering the gas turbine 23 possesses a temperature not exceeding the highest allowable working temperature of the material of the gas turbine 23 and the energy owned by the highly compressed nitrogen gas and the energy of the combustion gas are jointly recovered as converted into motive force by the gas turbine 23 and consumed in causing the generator 24 to effect power generation. The gas emanating from the gas turbine 23 is treated for recovery of its energy in the form of electric power by the recovery boiler steam turbine system 25 installed on the downstream side of the gas turbine 23. The preceding embodiment has been depicted as using two parallelly disposed oxygen adsorption towers. Optionally, it may be adapted to use three or more parallelly disposed oxygen adsorption towers. It is alternatively permissible to use a plurality of mutually independent oxygen adsorption towers and attain continuous production of oxygen by performing the adsorption and desorption of oxygen successively in each of the oxygen adsorption towers. This invention manifests the following effects. (1) The adsorption of oxygen can be carried out with high efficiency by bleeding the compressed air emanating from the air compressor of the gas turbine, introducing the compressed gas into the oxygen adsorption tower, and causing the oxygen of the compressed air to be adsorbed therein on the oxygen adsorbent under an increased pressure. Moreover, the oxygen adsorption towers effect adsorption of oxygen in an amount of about 20% by volume, based on the amount of the air. This fact coupled with the aforementioned highly efficient adsorption under a highly increased pressure allows the oxygen adsorption towers to operate satisfactorily with a small size and the oxygen adsorbent to function sufficiently in a small amount. (2) Since the gasification of a fuel of inferior quality is effected with the oxygen gas desorbed from the oxygen adsorbent, the amount of the gas to be handled and the amount of the gasified fuel to be produced are small and the gasifying furnace and the devices used for desulfurization and dust removal of the gasified fuel are proportionately small as compared with those involved in the gasification using the air. At the same time, the gasified fuel possesses a high calorific value and manifests high combustibility. (3) The highly compressed nitrogen gas which has flowed through the oxygen adsorption towers can be introduced into the gas turbine and treated therein for recovery of its energy. Further owing to the incorporation of the nitrogen gas, the hot highly compressed mixed fluid entering the gas turbine possesses a temperature not exceeding the highest allowable working temperature of the material of the gas turbine and ensure safe operation of the gas turbine. (4) The component steps of the method of this invention including the adsorption and desorption of oxygen in the oxygen adsorption towers can be quickly started, stopped, and controlled. Thus, the method of this invention can cope with load change and frequent start and stop of power generation.

Claims: A method for power generation with a gas turbine (23) using a gasified fuel of inferior quality, comprising the steps of: bleeding part of highly compressed air emanating from an air compressor (1) driven by said gas turbine (23); gasifying a fuel of inferior quality with oxygen gas as an oxidizing agent, effecting combustion of the gasified fuel of inferior quality with the remainder of said compressed air produced in said air compressor (1), mixing the gas arising from said combustion with highly compressed nitrogen gas, and introducing the resultant mixture into said gas turbine (23) thereby driving said gas turbine (23) and inducing power generation, characterized by the steps of: introducing said part of highly compressed air emanating from the air compressor (1) into an oxygen adsorbing tower (5a, 5b) containing a Na-A type zeolite as an oxygen adsorbent (10a, 10b), cooling said part of highly compressed air and then passing it through said oxygen adsorbent (10a, 10b), thereby causing the oxygen from said highly compressed air to be adsorbed by said oxygen adsorbent (10a, 10b) and, at the same time, allowing a nitrogen gas from said highly compressed air to flow in a highly compressed state through said oxygen absorbing tower (5a, 5b), desorbing the adsorbed oxygen from said oxygen adsorbent under a vacuum, compressing the oxygen gas resulting from said desorption before gasifying the fuel, and utilizing for said highly compressed nitrogen gas the nitrogen gas having flowed through said adsorbing tower (5a, 5b). The method according to claim 1, characterized in that the air compressed to a pressure of about 1519875 Pa (15 atmospheres) in said air compressor (1) is introduced into said oxygen adsorbing tower (5a, 5b) and the oxygen desorbed from the adsorbent (10a, 10b) in said oxygen adsorbing tower (5a, 5b) is compressed to a pressure of about 3039750 Pa (30 atmospheres) and used as an oxydizing agent for said gasified fuel of inferior quality. The method according to claim 1, characterized in that said part of highly compressed air introduced into said oxygen adsorbing tower (5a, 5b) is cooled to a temperature of about -70° C before it is passed through said oxygen adsorbent(10a, 10b).

Inventors: FUNAYAMA YASUO THE TOKYO ELEC, IZUMI JUN NAGASAKI TECH INST O, KANEKO SHOZO NAGASAKI SHIPYARD, OSHIMA KAZUAKI NAGASAKI SHIPYA, FUNAYAMA, YASUO THE TOKYO ELEC.POWER CO.,INC., IZUMI, JUN, NAGASAKI TECH.INST. OF MITSUBISHI, KANEKO, SHOZO, NAGASAKI SHIPYARD & ENG.WORKS OF, OSHIMA, KAZUAKI, NAGASAKI SHIPYARD & ENG.WORKS OF, Kaneko, Shozo, Nagasaki Shipyard &amp; Eng.Works of, Oshima, Kazuaki, Nagasaki Shipyard &amp; Eng.Works of
Applicants: MITSUBISHI HEAVY IND LTD, TOKYO ELECTRIC POWER CO, MITSUBISHI JUKOGYO KABUSHIKI KAISHA, THE TOKYO ELECTRIC POWER CO., INC.
Application year: 1991
Main classification: F02C3
IPC codes: B01D53, F02C3, C10J3