Abstract:
The invention relates to a method for producing hot working gases for a gas turbine system. In a burner, combustion that generates hot combustion waste gas takes place. A portion of the combustion waste gas branches off and feeds into an oxygen separation device. A heat exchanger produces a heated oxygen-containing gas from oxygen-containing gas. The heated oxygen-containing gas feeds to the oxygen separation device. The oxygen separation device includes an oxygen separation means that removes oxygen from the heated oxygen-containing gas and feeds it to the branched-off waste gas. Oxygen-reduced hot gas then leaves the oxygen separation device. Oxygen-enriched branched-off waste gas as well as fuel feed to the burner and form a combustion mixture that bums in the burner while forming the hot combustion waste gases. In order to improve the efficiency of the device, the oxygen-enriched branched-off waste gas heats the oxygen-containing gas.

Description:
This application claims the benefit of provisional application No. 60/239,887, filed Oct. 13, 2000. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a method and a device for producing hot working gases, in particular for a gas turbine system, with the characteristics of the preamble of claim  1  or, respectively, claim  4 . 
     BACKGROUND OF THE INVENTION 
     EP 0 882 486 A1 discloses a method and a device of the above-mentioned type. The known device has a burner that is supplied on an inlet side with fuel and oxygen-containing gas. In the burner, a combustion mixture of the oxygen-containing gas and the fuel is burned, whereby hot combustion waste gas is formed. A waste gas line, through which the hot combustion gas exits the burner and can be used at least in part as hot working gas in a following process, is connected to an outlet side of the burner. The known device also has an oxygen separation device that is supplied at a first inlet with combustion waste gas that is branched off from the waste gas line. At a second inlet, this oxygen separation device is supplied with heated, oxygen-containing gas. The oxygen separation device is provided with oxygen separation means that transport oxygen from the heated, oxygen-containing gas to the branched-off combustion waste gas. Oxygen-enriched combustion waste gas that is used as the oxygen-containing gas for supplying the inlet side of the burner then exits at a first outlet of the oxygen separation device. At a second outlet of the oxygen separation device, hot gas with reduced oxygen content and which can be used in a subsequent process as a hot working gas exits. In the known device, the hot gas with reduced oxygen content is used to heat the oxygen-containing gas fed to the oxygen separation device in a heat exchanger. 
     In principle, it is also possible, however, to use the hot working gases produced in this way, for example, in a gas turbine system for generating electric energy. By using such a device or such a method, it is possible to significantly reduce the noxious emissions during energy generation, especially CO 2  emissions, created during the combustion of fossil fuels. 
     The core idea of this method and these devices is that pure oxygen is used as an oxidant for the combustion, since this significantly simplifies the waste gas after treatment. The reason for this is that a combustion process with molecular oxygen results in a waste gas that essentially consists only of CO 2  and H 2 O. Since oxygen, which is produced in refrigerated plants, is very expensive, new technologies have been developed for producing oxygen. In this context, oxygen separation devices that are provided with a membrane that conducts oxygen ions and electrons, so-called MCM membranes (mixed conducting membranes play an important role. Such an MCM membrane is provided with a retention side, on which the oxygen-containing gas is located, and a pass-through side, on which the gas to be enriched is located. The MCM membrane transports oxygen ions from the retention side to the pass-through side and causes an electron transport from the pass-through side to the retention side. This causes oxygen to be removed from the gas on the retention side and to be fed to the gas on the pass-through side. In order to increase the efficiency of such an MCM membrane, it is advantageous to set a relatively high flow speed on the pass-through side in order to keep the oxygen concentration on the pass-through side as low as possible. It is advantageous for a long useful life of the MCM membrane to perform the following process steps independently from each other in separate units: heating of the oxygen-containing gas, transport of the oxygen from the oxygen-containing gas to the branched-off combustion waste gas, and combustion of the oxygen-enriched combustion waste gas with fuel. The functional separation of these procedures makes it possible to optimize the individual process steps separately, whereby, in particular, the useful life of the MCM membrane can be increased. In other known devices, described below, the previously mentioned processes are able to take place more or less simultaneously in a so-called membrane reactor that essentially corresponds to an oxygen separation device with MCM membrane, but is operated at substantially higher temperatures. 
     U.S. Pat. No. 5,976,223 discloses a device for producing carbon dioxide and oxygen that works with two oxygen separation devices that each are equipped with an MCM membrane. The first oxygen separation device, which fictions as a membrane reactor, is supplied with oxygen-containing gas that has been compressed and heated on the retention side. On the retention side, a gaseous fuel is supplied that reacts with the supplied oxygen and forms water and carbon dioxide. The oxygen-containing gas with reduced oxygen content is heated by the exothermic reaction that takes place during this process. The oxygen-containing gas heated in this manner is then fed to the second oxygen separation device on its retention side. The desired oxygen then accumulates on the pass-through side of this second oxygen separation device. 
     WO 98/55394 describes a method in which an oxygen separation device working with an MCM membrane is used as a membrane reactor for producing hot combustion waste gases for a gas turbine system. Ambient air is hereby compressed, heated, and fed to the retention side of the membrane reactor. A mixture of recycled waste gas and fuel is fed to the pass-through side. In the membrane reactor, oxygen is then deleted from the supplied air and is fed into the mixture. The fuel then reacts on the pass-through side with the oxygen on the membrane surface that is coated with an oxidation catalyst. The hot waste gases formed in this manner are then fed into a turbine. 
     WO 98/55208 discloses another method for producing hot combustion waste gases for operating a turbine, in which compressed fresh air is heated in a first burner and is fed to the retention side of an oxygen separation device working with an MCM membrane. Recycled waste gas is fed together with fuel into a second burner that may be constructed as a catalyzer. The combustion waste gases produced there are then fed to the pass-through side of the oxygen separation device, where they are enriched with oxygen. The oxygen-enriched waste gases are then fed to a third burner and burned there with fuel in order to produce hot combustion waste gases that drive a turbine. 
     SUMMARY OF THE INVENTION 
     The invention at hand relates to the objective of disclosing an embodiment for a method and a device of the initially mentioned type with improved efficiency. 
     In accordance with one embodiment of the present invention, the invention uses the general idea of using the oxygen-enriched, hot combustion waste gases after their exit from the oxygen separation device in order to heat the oxygen-containing gases before these are fed to the oxygen separation device. This measure makes it possible to significantly increase the inlet temperature of the oxygen-containing gases without having to introduce energy from the outside to the system. At the same time, the mass flow for the cooled, oxygen-enriched combustion waste gas can be increased. It is also possible to use standard, mechanically operating compressors or pumps for driving the oxygen-enriched combustion waste gases fed to the burner. By using the energy that is present in any case for heating the oxygen-containing gas, the efficiency of the process can be increased yet further. 
     In another embodiment of the present invention, the invention uses a heat exchanger, through which oxygen-containing gas to be heated and an oxygen-enriched combustion waste gas exiting from the oxygen separation device are flowing in order to heat the oxygen-containing gases. The desired temperature increase of the oxygen-containing gas is then associated with a useful temperature drop of the oxygen-enriched combustion waste gas. As explained above, this makes it possible to improve the efficiency in producing hot working gases. 
     In an especially advantageous further development, the oxygen separation device may be provided with a first chamber and a second chamber, whereby the oxygen separation means have a membrane that divides the two chambers from each other and transports oxygen from one chamber into the other chamber, whereby the flow in both chambers has the same direction and flows parallel to the membrane. Correspondingly, the branched-off combustion waste gas and the heated, oxygen-containing gas flow through the oxygen separation device according to the co-current principle. With this construction and this type of operation, a flat temperature profile results in the membrane, both in the flow direction and transversely to it. These characteristics reduce the resulting thermal loads in the membrane, increasing its useful life span. 
     Other important characteristics and advantages of the invention are found in the secondary claims, drawings, and related descriptions of the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are disclosed in the following description and illustrated in the accompanying drawings, in which: 
     FIG. 1 is a schematic view of a device according to the invention; and 
     FIG. 2 is a schematic view of a gas turbine system according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to FIG. 1, a device  1 , here symbolized by a box, is provided with a burner  2 , a heat exchanger  3 , a compressor  4 , and an oxygen separation device  5 . This oxygen separation device  5  has as an oxygen separation mean an MCM membrane  6  that is symbolized here by a dotted line. This MCM membrane  6  divides a first chamber  7  from a second chamber  8  in the oxygen separation device  5 , whereby a pass-through side  9  is associated with the first chamber  7 , and a retention side  10  of the membrane  6  is associated with the second chamber  8 . 
     In the burner  2  combustion takes place that produces the hot combustion waste gases  11  that, at an outlet side  12  of the burner  2 , enter a waste gas line  13  connected to it. At  14  the desired hot combustion waste gases  11  are discharged from the device  1 . These hot combustion waste gases  11  can be used as hot working gases in a subsequent process. 
     A return line  15  connected to a first inlet  16  of the oxygen separation device  5  branches off from the waste gas line  13 . Through this first inlet  16 , branched-off waste gas  17  is able to reach the first chamber  7 , i.e. the pass-through side  9  of the membrane  6 . 
     At  18 , oxygen-containing gas  19 , for example air, enters the device  1  and is fed there to a first inlet  21  of the heat exchangers  3 . In the heat exchanger  3 , the oxygen-containing gas  19  is heated, so that heated, oxygen-containing gas  20  exits from a first outlet  22  of the heat exchanger  3 . The first outlet  22  of the heat exchanger  3  is connected to a second inlet  23  of the oxygen separation device  5 , so that the heated, oxygen-containing gas  20  enters the second chamber  8 , i.e. on the retention side  10  of the membrane  6 . The MCM membrane  6  now brings about a transport of oxygen from the retention side  10  to the pass-through side  9 . In the process, oxygen is removed from the supplied oxygen-containing gas  20  so that its oxygen content is reduced. At the same time, oxygen is fed into the branched-off waste gas  17 , thus enriching it with oxygen. At a first outlet  24  of the oxygen separation device  5 , waste gas  25  enriched accordingly with oxygen exits from the first chamber  7  and is fed via a line  26  to a second inlet  27  of the heat exchanger  3 . The oxygen-enriched, recycled waste gas  25  is cooled in the heat exchanger  3 . Waste gas  29  cooled and oxygen-enriched in this way exits from a second outlet  28  of the heat exchanger  3 . The compressor  4  drives the flow of the branched-off waste gas  17 ,  25 ,  29 . Since the gas fed into the compressor  4  has a relatively low temperature of, for example, less than 800° C., the compressor  4  can be constructed as a mechanical compressor or a compressor or pump or fan. 
     The cooled, enriched waste gas  29  is fed via a supply line  60 , in which the compressor  4  is located, to an inlet side  30  of the burner  2 . In addition, fuel or a fuel/steam mixture  31  that enters the device  1  at  32  is fed to the inlet side  30  of the burner  2 . A combustion mixture of the oxygen-enriched recycled waste gases  29  and the supplied fuel  31  then forms in the burner  2 . This combustion mixture burns in the burner  2 , producing the desired hot combustion waste gases  11 . 
     Oxygen-containing gas  34  that now has a reduced oxygen content exits from a second outlet  33  of the oxygen separation device  5 . 
     The temperature of the heated, oxygen-containing gases  20  is not sufficient to ensure a proper oxygen transport through the membrane  6 . A suitable heating of the membrane  6  is achieved in that the recycled or branched-off waste gases  17  are again fed to the oxygen separation device  5  relatively uncooled. When flowing through chambers  7  and  8 , the membrane  6  also functions as a heat transfer means that causes a cooling of the gases in the first chamber  7  and a heating of the gases in the second chamber  8 . Accordingly, the oxygen-containing gas  34  exiting from the device  1  at  35  is relatively hot. This hot, oxygen-containing gas  34  therefore also can be used as a working gas. 
     It is hereby of special significance that the flow through the two chambers  7  and  8  flows in the same direction, so that temperature loads in the membrane  6  are as low as possible. At the inlet side of the oxygen separation device  5 , the temperature of the membrane  6  lies between the higher temperature of the recycled waste gases  17  and the lower temperature of the heated, oxygen-containing gases  20 . The temperatures of membrane  6 , waste gas  17 , and gas  20  adapt to each other until the exit from the oxygen separation device  5 . 
     In the device  1  according to the invention, it is especially important that the oxygen-containing gas  19  is heated with the help of the recycled or branched-off waste gases  25 , since this makes it possible to advantageously use the heat energy inherent in the process. The device  1  hereby forms a unit, symbolized by the frame, into which oxygen-containing air  19  or fuel  31  enters at the inlet points  18  and  32 , and from which hot working gases, i.e. hot combustion waste gases  11  and hot, oxygen-containing gases  34 , exit at outlet points  14  and  35 . The individual functions within this device  1 , such as, for example, the heating of the oxygen-containing gas  19  in the heat exchanger  3 , the transport of the oxygen in the oxygen separation device  5 , as well as the combustion of the combustion mixture in the burner  2 , hereby can be optimized independently from each other in order to increase the overall efficiency of the device  1 . With the exception at the inlet points  18  and  32  and at the outlet points  14  and  35 , the device  1  in no way interacts with any preceding or following processes. Accordingly, the optimization of the processes taking place in the device  1  can be performed independently from the preceding or following processes, thereby greatly simplifying the optimization of the device  1 . 
     As shown with reference to FIG. 2, the device  1  according to the invention can be integrated in a gas turbine  36  that is used to generate electricity. FIG. 2 shows how the inlet points  18  and  32  as well as the outlet points  14  and  35  quasi form interfaces integrating the device  1  into the gas turbine system  36 . 
     A compressor  37  compresses ambient air  38 , whereby the latter is simultaneously heated. The compressed and heated ambient air forms the oxygen-containing gas  19  that is fed at  18  to the device  1 . In the device  1 , the oxygen content of the supplied air  19  is reduced, which, in the case of air, also corresponds to an increase in its nitrogen content. The heated, oxygen-poor air  34  exits the device  1  at  35  and is fed to a turbine  39  that is connected to the compressor  37  and a generator  40  for generating electricity. The gas  34  fed to the turbine  39  is expanded in the turbine  39  and forms an expanded flow  41  whose heat is at least partially recovered in a steam generator  42 . Then, cooled, oxygen-poor gas  43  that then can be treated further exits from the steam generator  42 . 
     Fuel or fuel/steam mixture  31  is added to the device  1  at  32 , whereby this fuel  31  bums inside the device  1 —as described above—together with the oxygen of the oxygen-containing gas  19 . The resulting combustion essentially produces only CO 2  and H 2 O and forms the desired hot combustion waste gases  11  that exit the device  1  at  14 . The hot combustion waste gases  11  are expanded in a turbine  44  that drives another generator  45  for electricity generation. In the process, expanded combustion waste gases  46  that are also fed to the steam generator  42  form. The steam generator  42  hereby comprises separate chambers  47  and  48  for the expanded, oxygen-poor gases  41  and for the expanded combustion waste gases  46 . Then cooled combustion waste gas  49  exits the steam generator  42  and can be fed to a cooler  50  in which the water steam is condensed. The resulting water  51  is again fed to the steam generator  42 . The remaining CO 2    52  leaves the cooler  50  and can be compressed and, as the case may be, liquefied, in a compressor  53 . The compressed and/or CO 2    54  then can be processed further. The compressor  53  is, for example, driven by a motor  55 . A coupling with the turbine  44  is also conceivable. 
     The steam  56  generated by the steam generator  42  can be expanded in a turbine  57  that drives another generator  58  for electricity generation. The expanded steam then can be condensed in a condenser  59 ; the resulting water then can be fed into the steam generator  42 . It would also be possible to use the steam  56  as process steam for other purposes; for example, the steam  56  can be mixed with the fuel  31  to form a fuel/steam mixture. 
     In the gas turbine system  36  shown in FIG. 2, energy therefore can be generated by burning fossil fuels without emitting noxious substances, such as CO 2 , CO, NOx into the atmosphere. This is made possible by the device  1  that provides hot working gases  11  and  34  that either do not contain any noxious substances or have a composition that enables an especially easy removal of noxious substances.