METHOD AND APPARATUS FOR OPERATING A GAS TURBINE USING WET COMBUSTION

Abstract

The aim of the invention is to significantly increase the electrical efficiency or the proportion of the effective work of gas turbines, even in small gas turbines or microsize gas turbines having a simple design. According to the invention, the drawbacks of the prior art are overcome using wet combustion with oxygen, the oxygen being supplied via mixed-conducting ceramic membranes. The driving force needed for the oxygen to penetrate is created by lowering the partial pressure of the oxygen on the permeate side of the membrane module (5), and the energy required therefor is taken from the process energy produced in the gas turbine process.

Claims

1.-7. (canceled)

8. A method for operating a gas turbine using wet combustion of a fuel with oxygen or oxygen-enriched air, wherein the oxygen needed for combustion is provided by a mixed-conducting ceramic MIEC (Mixed Ionic Electronic Conductor) membrane, by lowering an oxygen partial pressure on a permeate side of the MIEC membrane and all components involved in an operation of the gas turbine forming an overall system, the oxygen partial pressure on the permeate side of the MIEC membrane being lowered by process energy of the gas turbine to thereby increase an electrical efficiency of the overall system by at least 4 percentage points compared to a normal operation of the gas turbine with air.

9. The method of claim 8, wherein waste heat from the gas turbine is used for aspiration of the oxygen from the membrane.

10. The method of claim 8, wherein a compressor of the gas turbine is configured as a vacuum compressor which aspirates the oxygen from a membrane module at pressures below 160 mbar (absolute) and compresses the oxygen to an operating pressure of the gas turbine.

11. The method of claim 8, wherein an over-pressurized, i.e. compressed, partial gas flow of CO.sub.2, steam, or a mixture thereof is used as a sweep gas at low oxygen partial pressure on the mixed-conducting membrane to thereby obviate any mechanical gas compression using electrical energy or mechanical work.

12. An apparatus for operating a gas turbine using wet combustion, wherein the apparatus comprises an oxygen generator arranged upstream of the gas turbine and a steam generator arranged downstream of the gas turbine, the oxygen generator comprising an MIEC membrane module having a heat exchanger and a blower arranged upstream thereof, and the steam generator comprising a superheater, an evaporator, a condensate collector and an air-cooled exhaust gas cooler, and wherein the gas turbine comprises a compressor, a combustion chamber, and a power-generating turbine, the compressor is connected to the membrane module via a liquid ring pump, the superheater has a connection with the combustion chamber for introducing steam into the combustion chamber in a controlled manner so as to maintain a usual operating temperature, and the membrane module is heated to compensate for thermal losses.

13. The apparatus of claim 12, wherein a steam motor driving the liquid ring pump is arranged between the superheater and the combustion chamber.

14. An apparatus for operating a gas turbine using wet combustion, wherein an oxygen generator comprising an MIEC membrane module having a heat exchanger and a blower arranged upstream thereof is arranged upstream of the gas turbine, and a steam generator comprising a superheater, an evaporator, a condensate collector and an air-cooled exhaust gas cooler is arranged downstream of the gas turbine, and wherein the gas turbine comprises a compressor, a combustion chamber, a power-generating turbine, a first start-up valve, a second start-up valve and a hot gas fan, the first start-up valve being arranged upstream of the combustion chamber to allow air to flow into the combustion chamber, the second start-up valve being arranged between the power-generating turbine and the combustion chamber, and the hot gas fan being driven by the power-generating turbine so that part of an exhaust gas from the combustion chamber can be fed as a hot gas flow of steam and CO.sub.2 at a low oxygen partial pressure to the membrane module to act as a sweep gas.

Description

[0022] The invention will be explained in more detail below with reference to exemplary embodiments. In the Figures:

[0023] FIG. 1 is a process diagram showing the operation of a gas turbine using wet combustion, wherein the kinetic energy of the gas turbine is used for oxygen aspiration and compression;

[0024] FIG. 2 is a process diagram showing the operation of a gas turbine using wet combustion, wherein the driving force is generated from the waste heat of the gas turbine;

[0025] FIG. 3 is a process diagram showing the operation of a gas turbine using wet combustion in the oxygen/steam mixture and using oxygen generation by MIEC membranes, which are aspirated by an adapted compressor of the gas turbine, and

[0026] FIG. 4 is a process diagram showing the operation of a gas turbine using wet combustion by controlled circulation of a gas mixture of CO.sub.2 and steam.

[0027] In a first exemplary embodiment, the principle of the method according to the invention will be explained with reference to FIG. 1. A conventional Capstone C50 micro gas turbine is used, which is schematically shown in FIG. 1 as a gas turbine 1 and has an electric efficiency of 28% when operated with air and a fuel consumption of 18 Nm.sup.3 of natural gas/h. The turbine is coupled with an oxygen generator 2 and a steam generator 3. The oxygen generator 2 is configured for an output of 36 Nm.sup.3 O.sub.2/h. Fresh air is passed through the heat exchanger 8 and the adjacent membrane module 5 through a simple blower 7. Extraction of the oxygen is performed by a liquid ring pump 4 which removes the oxygen from the membrane module 5 and feeds it to the compressor 6 of the gas turbine 1. The compressor 6 of the gas turbine 1 compresses the oxygen exiting from the liquid ring pump 4 to approx. 5 bara (aabsolute) and pushes it into the combustion chamber 10 of the gas turbine 1. By varying the amount of steam entering the combustion chamber 10, the temperature in the latter is limited to the usual operating temperatures. The heating of the membrane module 5 required to compensate for thermal losses is effected by combustion of approx. 1 Nm.sup.3 of natural gas/h with the O.sub.2-depleted air in the membrane module 5. The exhaust gas from the turbine 11 is used to generate steam by being supplied first to a superheater 12 and then to the evaporator 13. Thus, only a small part of the kinetic energy of the gas turbine 1 is used to generate the driving force for O.sub.2 separation.

[0028] The exhaust gas flow is passed through the condensate collector 14 to the air-cooled exhaust gas cooler 15, which removes excess water by condensation and returns it to the cycle.

[0029] Wet combustion using oxygen increases the gross electrical efficiency of the conventional Capstone C50 micro gas turbine to 34%. The additional consumption of approx. 1 Nm.sup.3 of natural gas/h for heating the membrane module 5 and the resulting increase in overall gas consumption to approx. 19 Nm.sup.3 of natural gas/h result in a net electrical efficiency of 32% for the overall system. In addition to this increase in electrical efficiency from 28% to 32%, an exhaust gas flow of almost pure CO.sub.2 is available, moreover, for recycling, and the waste heat can be used as before.

[0030] The basic design of the second exemplary embodiment corresponds to that of the first exemplary embodiment in its essential components. Again, a conventional Capstone 50 micro gas turbine is used as the gas turbine 1 and is coupled, according to FIG. 2, with an oxygen generator 2 and a steam generator 3. The oxygen generator 2 is configured for an output of 36 Nm.sup.3 O.sub.2/h. Aspiration of the oxygen is again performed using a liquid ring pump 4 which removes the oxygen from the membrane module 5 and feeds it to the compressor 6 of the gas turbine 1. Fresh air is passed through the heat exchanger 8 and the membrane module 5 by a simple blower 7. The compressor 6 of the gas turbine 1 compresses the oxygen to approx. 5 bara (aabsolute). By varying the amount of steam, the temperature in the combustion chamber 10 is limited to the usual operating temperatures. The heating of the membrane module 5 required to compensate for thermal losses is effected by combustion of approx. 1 Nm.sup.3 of natural gas/h with the O.sub.2-depleted air in the membrane module 5. The exhaust gas from the turbine 11 is used to generate steam by being supplied first to a superheater 12 and then to the evaporator 13. The resulting steam is used to operate the steam motor 9, which in turn drives the liquid ring pump 4. Thus, only the waste heat from the gas turbine 1 is used to generate the driving force for O.sub.2 separation. The exhaust gas flow is passed through the condensate collector 14 to the air-cooled exhaust gas cooler 15, which removes excess water by condensation and returns it to the cycle.

[0031] Wet combustion using oxygen increases the gross electrical efficiency of the conventional Capstone C50 micro gas turbine to 41%. The additional consumption of approx. 1 Nm.sup.3 of natural gas/h for heating the membrane module 5 and the resulting increase in overall gas consumption to approx. 19 Nm.sup.3 of natural gas/h result in a net electrical efficiency of 39% for the overall system. In addition to this increase in electrical efficiency from 28% to 39%, an exhaust gas flow of nearly pure CO.sub.2 is available, moreover, for recycling, and the waste heat can be used as before.

[0032] In the third exemplary embodiment, the gas turbine 1 used is a conventional Capstone C65 micro gas turbine whose compressor 6 has been re-fitted to compress oxygen from 0.09 bara (aabsolute) to 5 bara. In accordance with FIG. 3, fresh air is passed through the heat exchanger 8 and the membrane module 5 by a simple blower 7.

[0033] The compressor 6 of the gas turbine 1 compresses the oxygen entering at approx. 0.09 bara to approx. 5 bara. The entire exhaust gas flow from the turbine 11 with an exhaust heat of 126 kW is used to generate steam in the superheater 12 and in the evaporator 13. A steam pressure of >5 bara is achieved so that the steam can be introduced directly into the combustion chamber 10, where it is used to regulate the exhaust gas temperature. The heating of the membrane module 5 required to compensate for thermal losses is effected by combustion of approx. 1.4 Nm.sup.3 of natural gas/h with the O.sub.2-depleted air in the membrane module 5. The exhaust gas flow is passed through the condensate collector 14 to the air-cooled exhaust gas cooler 15, which removes excess water by condensation and returns it to the cycle.

[0034] In combustion with air, the mass flow to be compressed, which flows through the gas turbine 1, is approx. 7 times greater than the mass flow of the pure oxygen from the oxygen generator 2. Accordingly, the compression work required in oxygen operation decreases to approximately 1/7. The mass flow through the turbine 11 also decreases, but is in turn increased by the additional steam mass flow through the combustion chamber 10. For this purpose, use is made only of the waste heat of the exhaust gas flow. In total, wet combustion with oxygen increases the gross electrical efficiency of the modified Capstone C65 micro gas turbine to 50%. The additional consumption of approx. 1.4 Nm.sup.3 of natural gas/h for heating the membrane module 5 and the resulting increase in overall gas consumption to approx. 24 Nm.sup.3 of natural gas/h result in a net electrical efficiency of 47% for the overall system. In addition to this increase in electrical efficiency from 29% to 47%, an exhaust gas flow of almost pure CO.sub.2 is available, moreover, for recycling, and the waste heat can be used as before.

[0035] In the fourth exemplary embodiment, only the turbine part of a conventional Capstone C30 micro gas turbine is used as the gas turbine 1, because the compressor 6 has been removed, see FIG. 4. The turbine 11 drives a hot gas fan 16, which introduces part of the exhaust gas from the combustion chamber 10 as a hot gas stream of steam and CO.sub.2 at a low oxygen partial pressure into the membrane module 5 as a sweep gas. The hot gas fan 16 requires substantially less energy than a compressor 6, which is usually part of a gas turbine 1, because the circulating gases need not be compressed. The gas turbine 1 is started up with an open first start-up valve 17 and an open second start-up valve 18, by initially operating the combustion chamber 10 with air as the oxidizing agent, until the membrane module 5 and the combustion chamber 10 have reached normal operating temperature. Next, the first start-up valve 17 and the second start-up valve 18 are closed. Since the continuous further addition of combustion gas keeps the oxygen partial pressure in the circulating partial exhaust gas flow low, oxygen in the membrane module 5 passes from the air into the exhaust gas flow, thereby oxidizing the added combustion gas. This results in a gradual pressure increase up to the operating pressure of 5 bara. Upon reaching this pressure, the exhaust gas is conducted onto the turbine 11 and expanded via the latter. The entire exhaust gas flow from the turbine 11 with an exhaust heat of 68 kW is used to generate steam in the superheater 12 and in the evaporator 13. A steam pressure of >5 bara is achieved so that the steam can be introduced directly, without subsequent compression, into the combustion chamber 10, where it is used to regulate the temperature. Compensation of thermal losses of the membrane module 5 is effected via the circulating partial exhaust gas flow. The exhaust gas flow is passed through the condensate collector 14 to the air-cooled exhaust gas cooler 15, which removes excess water by condensation and returns it to the cycle.

[0036] After start-up, the gas turbine 1 in this fourth exemplary embodiment requires no energy, during normal operation, for air or oxygen compression, because the oxygen automatically enters the circulating partial exhaust gas flow. Therefore, compared to the previous exemplary embodiments, there is a further overall increase in efficiency, i.e. in the part of the effective work obtainable from the system, to 65%. Again, an exhaust gas flow of nearly pure CO.sub.2 is available for recycling.

LIST OF REFERENCE NUMERALS

[0037] 1 gas turbine

[0038] 2 oxygen generator

[0039] 3 steam generator

[0040] 4 liquid ring pump

[0041] 5 membrane module

[0042] 6 compressor (of the gas turbine 1)

[0043] 7 blower

[0044] 8 heat exchanger

[0045] 9 steam motor

[0046] 10 combustion chamber

[0047] 11 turbine

[0048] 12 superheater

[0049] 13 evaporator

[0050] 14 condensate collector

[0051] 15 exhaust gas cooler

[0052] 16 hot gas fan

[0053] 17 first start-up valve

[0054] 18 second start-up valve