Patent Application
20100300111
The invention relates to a method for operating a power plant comprising integrated gasification and to a power plant.
An IGCC plant of this kind is known for example from WO 03/008768. This plant comprises a gasification device in which, for example, particulate coal is converted together with oxygen and steam to form a syngas (partial oxidation). Following several processing steps the syngas is fed as a gaseous fuel to a gas turbine combustion chamber. In WO 03/008768 a cryogenic air separation plant (=LZA) is implanted in the IGCC plant for obtaining oxygen. This separates the air in a thermodynamic process into its essential components, nitrogen and oxygen. The oxygen obtained in the LZA is fed to the gasification device.
In the meantime, membrane-based units have been proposed as an alternative to cryogenic air separation plant. The oxygen ion-conveying membranes lead to an at least partial separation of oxygen from the air. Replacing the cryogenic air separation unit with a membrane is regarded as a potential option for increasing efficiency in conventional IGCC power plant. The implementation of a membrane can also be expected to compensate for the loss in efficiency in the case of CO2-free power plant designs.
An example of a membrane-based oxygen separation can be found in U.S. 2004/0011057 A1 which describes an IGCC plant in which oxygen-rich gas is produced via a membrane, oxygen transportation taking place within the membrane by way of diffusion of oxide ions and the membrane being brought and/or held at operating temperature via a heat exchanger by hot waste gases from the turbine.
U.S. Pat. No. 5,562,754 describes a method of oxygen separation in which gas (air) containing oxygen is directly heated by combusting a fuel in the gas flow, whereby a hot combustion product containing oxygen is produced that is fed to a membrane. Alternatively, the gas containing oxygen is heated by indirect heat exchange with a combustion product that is produced by combustion of the oxygen-deficient air, which remains during oxygen separation, with fuel.
However, membrane-based arrangements for oxygen separation have the drawback that the membrane unit has to be kept at a comparatively high operating temperature for it to be able to carry out the function. Heating energy therefore has to be permanently fed to the membrane reactor, so it is at the requisite process temperature for oxygen separation.
An object of the invention is to provide a method and a power plant which overcome the above-mentioned drawbacks in a membrane=based oxygen separation process.
This object is achieved by a method for operating a power plant and a power plant as claimed in the independent claims.
Further advantageous embodiments are cited in the dependent claims.
In the inventive method heating energy is fed to the membrane to maintain the required process temperature, the heating energy being obtained from the syngas and from the hot oxygen or hot oxygen-depleted air in heat exchange with the air, and the heated air is conveyed to the membrane.
The heat exchange process and its advantageous connection to the high temperature level of the syngas (crude gas) obtained in the gasification device, and the flows of oxygen and oxygen-depleted air that are produced during oxygen separation result in a particularly efficient method of heating the air to the required process temperature and then feeding the heated air to the membrane unit such that it is already at the correct temperature.
The membrane can be brought to and held at the operating temperature, typically 700° C. to 1000° C., particularly easily hereby. A portion of the heating energy brought into the air before oxygen separation is released to the following air in an indirect heat exchange following oxygen separation from oxygen and the oxygen-depleted air respectively. The following air is then completely heated to membrane operating temperature via a syngas/air heat exchange.
It is expedient in this connection to arrange the heat exchangers in a suitable manner with respect to each other. As a result of the higher temperature of the syngas, compared with the temperature of the oxygen or the oxygen-depleted air, it is advantageous to connect the oxygen/air heat exchanger or the oxygen-depleted air/air heat exchanger upstream of the syngas/air heat exchanger. In another advantageous arrangement the three heat exchangers are connected in parallel and the air flows, after heating in the heat exchangers, are conveyed together and as a whole air flow to the membrane.
To bring the membrane to operating temperature at the start of the process it is expedient to obtain the heating energy from the waste gas from a separate combustion in heat exchange with the air. The waste gas cooled after heat exchange with the air is advantageously used in a waste heat steam generator in order to generate steam.
It is also advantageous to use the syngas cooled after heat exchange with the air in a waste heat steam generator connected downstream of the syngas/air heat exchanger in order to generate steam.
It is also advantageous to further prepare the syngas after heat exchange with the air, in particular to purify it, before it is subjected to a CO shift reaction. The main components, CO2 and hydrogen, are then the main components, CO2 and hydrogen, are then advantageously separated. The hydrogen is diluted with an inert medium, preferably steam (H2O), as needed, before it is combusted in a gas turbine.
The compressed air required for oxygen separation is expediently removed as compressor exhaust air from a compressor part associated with a gas turbine, the removal of air advantageously being carried out at the compressor outlet after the end stage or optionally being carried out at a lower compressor air pressure level.
The oxygen-depleted air “remaining” after oxygen separation and cooled in heat exchange with the air coming from the compressor is advantageously fed as combustion air to the burner of the gas turbine, whereby the temperature of combustion is advantageously lowered. Unlike in cryogenically-operating air separation plant, sufficiently pure oxygen is not available as a product following oxygen separation via the membrane, which oxygen could be added to the syngas to improve the combustion characteristics. The addition of air is not an option owing to the oxygen content.
Waste gases from the gas turbine are expediently used in a waste heat steam generator connected downstream of the gas turbine in order to generate steam. The superheated steam can then advantageously be used in a steam turbine, or as a diluting medium for the fuel or to render the fuel inert, and as a carrier gas during conveying to the gasification device. If CO2 is separated from the syngas, however, it is expedient to render the fuel inert with CO2 or to use CO2 as the carrier gas and to advantageously use the generated steam in a steam turbine.
The inventive power plant comprises a gas turbine with which a combustion chamber having at least one burner is associated, a fuel treatment process system connected upstream of the combustion chamber having a gasification device with a fuel feed pipeline for fossil fuel and a gas pipeline that branches from the gasification device and ends in the combustion chamber, a membrane unit for separating oxygen from air, the membrane unit being connected by its oxygen-side removal side to the gasification device via an oxygen pipeline (the desulfurization process potentially also requires oxygen). At the primary side the gas pipeline that branches from the gasification device is connected to a first heat exchanger, so, at the secondary side, the air which can be fed to the heat exchanger may be heated to a process temperature and be fed to the membrane unit. A second heat exchanger is connected at the primary side into the oxygen pipeline and at the secondary side is connected upstream of the membrane unit, so the air that can be fed to the second heat exchanger may be heated, and/or a third heat exchanger is connected at the primary side into a waste air pipeline that branches from the membrane unit and at the secondary side is connected upstream of the membrane unit, so the air that can be fed to the third heat exchanger may be heated.
The second and/or third heat exchanger(s) can be connected to the first heat exchanger in series or in parallel.
If the syngas waste heat is not at a sufficiently high energy level, for example as the gasifier starts up, it is advantageous if a burner is connected to the gas pipeline, upstream of the first heat exchanger, and the gas pipelines can be closed upstream of the burner to bring the membrane to operating temperature by indirect heat exchange with the waste gas from a separate combustion process (with natural gas, syngas, etc.).
It is expedient if the cooled waste gases from the burner, as well as the waste gases from the gas turbine plant, can be fed to a waste heat steam generator for steam generation.
A waste heat steam generator is also advantageous for using the heat from the syngas following passage through the first heat exchanger. The inventive power plant advantageously also comprises a syngas purification device, a CO shift reactor for the CO conversion in the syngas (CO+H20−>CO2+H2) and a CO2 separating device by means of which CO2 can be separated from the syngas.
With oxygen separation plants that do not operate cryogenically and in which no sufficiently pure nitrogen accumulates during oxygen separation, improved combustion can be achieved by feeding steam to the syngas or by introducing the oxygen-depleted air into the combustion chamber.
In the case of a conventional IGCC power plant it is advantageous if superheated steam can be supplied to the fuel treatment process as a carrier gas and for inerting, as well as to the gasification device.
In the case of a ZEIGCC, i.e. IGCC with CO2 separation, it is advantageous if, during normal operation, appropriately compressed, separated CO2 can be used as an inerting medium or carrier gas. If CO2 separation does not take place, such as, for example, during start-up or in the event of an accident, it is expedient if, as in the case of a conventional power plant, superheated steam can be supplied to the fuel treatment process.
The membrane is advantageously an oxygen ion-conveying membrane.
The power plant preferably comprises a compressor part for providing compressed air for both the oxygen separation plant and the combustion chamber.
The invention will be described in more detail with reference to exemplary embodiments which are illustrated in the drawings, in which:
The power plant 1 comprises a gas turbine plant 29, having a compressor part 25, a combustion chamber 3 with at least one burner and a gas turbine 2. At the waste gas side a waste heat steam generator 22 is connected downstream of the gas turbine 2. The waste heat steam generator 22 is connected into the water-steam circuit of a steam turbine (not shown in detail), so a “combined cycle” or combined gas and steam turbine plant (GuD) is achieved. Hot waste gases 30 or burnt gases from the gas turbine 2 heat and in the process evaporate water in the waste heat steam generator 22 to form steam 23 which can be used in the steam turbine or for inerting in the fuel treatment process 37 or for fuel-conveying to the gasification device 6.
The fuel treatment process system 5 comprises a gasification device 6 which comprises a feed pipeline 7 for the fossil fuel and an oxygen pipeline 12 that ends in the gasification device 6. The fossil fuel 26 and the oxygen 19 are partially burnt in the gasification device 6, so a low-calorie combustion gas, the syngas 17, is formed which is fed via a gas pipeline 8 to the burner 4 associated with the gas turbine 2 for combustion purposes.
Oxygen 19 is separated at a process temperature from air 18 in a membrane unit 9 by means of a membrane 10, the separated oxygen 19 being fed from the oxygen-side removal side 11 of the membrane unit 9 via the oxygen line 12 to the gasification device 6 for reaction with the fossil fuel 26.
Heating energy is fed to the membrane 10 to maintain the required process temperature. The heating energy is obtained from the syngas 17 and also from the hot flows of oxygen 19 and oxygen-depleted air 20 in heat exchange with the air 18. The heated air 18 is fed to the membrane 10. In
The air 18 fed to the membrane 10 is heated in heat exchange with the oxygen 19, the oxygen-depleted air 20 and the syngas 17 to 700° C. to 1000° C., preferably 800° C. to 900° C., to ensure an adequate operating temperature of the membrane unit 9.
After heat exchange with the air 18 the oxygen-depleted air 20 can be fed via the waste air pipeline 27 as cool air to the gas turbine 2 and/or as combustion air to the burner 4.
Before it is fed to the burner 4, the syngas 17 passes through a syngas waste heat utilization device 31, a gas purification device 32 and an optional CO2 separating device 28. The separated CO2 24 can be fed for inerting purposes and as a carrier gas to the fuel treatment process 37. Superheated steam 23 at an appropriate pressure level is used for this purpose in the case of a conventional IGCC power plant (without CO2 separation).
The air 18, which is to be fed to the membrane 10, is heated by indirect heat exchange of the air 18 with the waste gas 21 from a separate combustion, for example of natural gas 38. A burner 16 is connected into the gas pipeline 8 between gasification device 6 and first heat exchanger 13 for this purpose. As long as the burner 16 is operating the gas pipeline 8 between gasification device 6 and burner 16 is closed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07016780.4 | Aug 2007 | EP | regional |
This application is the US National Stage of International Application No. PCT/EP2009/027230 filed Aug. 13, 2008, and claims the benefit thereof. The International Application claims the benefits of European Patent Application No. 07016780.4 EP filed Aug. 27, 2007. All of the applications are incorporated by reference herein in their entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP08/60616 | 8/18/2008 | WO | 00 | 2/25/2010 |
