DE10155508C2 - Method and device for generating electrical energy - Google Patents

Description

The invention relates to a method and an apparatus for Generation of electrical energy with the help of a Relaxation turbine, a steam turbine and a gas turbine with the features of the preamble of claims 1, 9 and 10.

The increasing consumption of electrical energy in the Industrialized countries are increasingly covered by natural gas. Over great Networks make natural gas individual industrial Encouraged consumers, the line pressure through Compressor stations is kept constant at around 80 bar. For the industrial natural gas-fired combined Gas / steam turbine plants must have the natural gas on top of the existing one Pressure level in the gas turbine combustion chamber can be reduced. Contains the system's waste heat boiler from process-related If an additional firing is required, the corresponding one must be used Pressure of the natural gas mass flow can be reduced to about 2 bar.

By reducing the pressure with a possible previous electrical heating of the natural gas, the required admission pressures of the consumers can be achieved without icing of the pipeline fittings. This type of pressure reduction is associated with high losses and represents an energy destruction in the sense of public discussions about CO ₂ reduction potentials.

By expanding the natural gas in a relaxation turbine (Expander) can the high pressure potential of the natural gas in mechanical energy can be converted. It is problematic the sharp drop in temperature after relaxation, causing it to that downstream of the expansion turbine Pipe fittings are light due to the Joule-Thomson effect icing can occur.  

By heating the natural gas accordingly high before Relaxation can both minimize the risk of icing, as well achieved a higher electrical output during expansion become. From DE-PS 44 16 359 a high temperature Natural gas relaxation plant known in which the temperature increase of the high pressure natural gas in heat exchange with the Turbine exhaust gas from an upstream gas turbine system takes place. The natural gas can be in a gas / gas heat exchanger or via an intermediate circuit operated with thermal oil Waste heat boiler to be heated. A disadvantage of the gas / gas Heat exchanger is that if there are any leaks on the Natural gas side a fire risk due to the high temperature and high oxygen content of the turbine exhaust gas. In the DE PS 44 16 359 is based on a possible integration of natural gas Relaxation turbine in a combined, gas turbine and a gas / steam turbine process comprising heat recovery steam generator not received.

From US-PS 46 93 072 is a combined gas-steam Power plant known, which is under high inlet pressure Natural gas is operated. In this plant, the natural gas is passed through Extraction steam or steam from the steam turbine is heated. So that will the efficiency of the combined gas / steam turbine process reduced. If the steam turbine is operated at partial load, sink however, at the point of withdrawal the vapor pressures, which causes the natural gas is warmed up less and the risk of icing behind the expansion turbine is created. Furthermore, there is none Possibility to regulate the temperature of the natural gas.

The invention is based, which Expansion turbine so in a gas / steam turbine process incorporate that electricity generation of the actual Gas / steam turbine process is not affected.  

The task is in a generic method according to the invention by the characterizing features of Claim 1 solved. A device for carrying out the The procedure is the subject of claims 9 and 10, respectively. Advantageous embodiments of the invention are in the Subclaims specified.

In the method according to the invention, a Heat extraction via a partial flow of the in the heating surfaces of the Waste heat boiler heated water-steam cycle as Intermediate medium for heating high-pressure natural gas. To serves the feed water of the high pressure circuit or in the Low pressure part of a two-pressure steam generation system generated Lower steam. By integrating this intermediate circuit for heating the natural gas at the cold end of the waste heat boiler the electricity generation of the actual gas / steam turbine Process is not affected. Due to the high ratio of Turbine exhaust gas quantity to natural gas quantity (of about 45: 1 e.g. with 400 MW blocks with a gas turbine output of 250 MW and one Steam turbine output of 150 MW) is even at the highest Natural gas preheating the thermodynamic influence on the whole Waste heat system extremely low. In addition, through the use of the waste heat potential at the cold end of the waste heat boiler Natural gas depending on the thermal circuit of the waste heat boiler the highest possible temperatures are warmed up. Which after the Relaxing temperature of the natural gas depends on Height represents a gas turbine efficiency increase, as a result Part of the waste heat is returned to the combustion chamber of the gas turbine becomes.

The natural gas is heated by the low-pressure steam of the two-pressure steam generation system, this is Low pressure part operated in fixed pressure mode. This allows everyone  Desired natural gas temperature regardless of the steam turbine load be regulated.

Several embodiments of the invention are in the drawing are shown and are explained in more detail below. Show it:

Fig. 1 shows the diagram of a gas / steam turbine process with an expansion turbine,

Fig. 2 shows the diagram of a gas / steam turbine process with an expansion turbine according to another embodiment

Fig. 3 is a circuit diagram and

FIGS. 4 and 5 each show a schematic of a gas / steam turbine process with an expansion turbine according to another embodiment.

A gas turbine system consists of a gas turbine 1 , a compressor 2 for compressing combustion air, a combustion chamber 3 for generating a hot gas and a generator 4 for generating electricity. The gas turbine 1 , the generator 4 and the compressor 2 can be arranged on a common shaft or on several shafts.

The gas outlet of the gas turbine 1 is connected to a waste heat boiler 5 for generating steam. In the waste heat boiler 5 Fig. 1, the heating surfaces of a superheater 6, an evaporator 7 and a feedwater preheater 8 are arranged according to a high-pressure system in the direction of flow of the turbine exhaust gases in a row. A steam line 9 , which leads to a steam turbine 10 , is connected to the superheater 6 . The steam turbine 10 is coupled to the generator 4 .

The output of the steam turbine 10 is connected to an exhaust steam line 11 , which is led to a condenser 12 . In the condenser 12 , the exhaust steam is condensed by a cooling circuit which is passed through a cooling tower 13 . The condensate is conveyed to a degasser 16 via a condensate line 14 , in which a feed pump 15 is arranged. The degasser 16 is operated with bleed steam, which is removed from the steam turbine 10 via a bleed line 17 . From this tap line 17 , a line 19 can be branched off which can be shut off by a shut-off valve 18 and which leads to a heat consumer 20 .

A feed water line 21 is connected to the degasser 16 and is connected to the feed water preheater 8 arranged in the waste heat boiler 5 . A feed water pump 22 which increases the pressure of the feed water is arranged in the feed water line 21 . The feed water line 21 is connected to a condensate preheater 23 arranged in the condensate line 14 , in which a heat exchange takes place between the condensate and the feed water. The condensate is heated up to a few Kelvin below the temperature of the feed water, with the feed water temperature being lowered at the cold end of the waste heat boiler 5 when it enters the feed water preheater 8 . This is important for the heating of the natural gas supplied to the combustion chamber 3 in the gas / water heat exchanger 33 described later. On the one hand, the steam output of the combined gas / steam turbine process is retained, and on the other hand, the usable temperature difference in the gas / water heat exchanger 33 is increased.

Two branch lines 24 , 25 are connected to the outlet end of the feed water preheater 8 . The first branch line 24 opens into the water space of a steam drum 26 which serves for water / steam separation and which is connected to the evaporator 7 and the superheater 6 .

The combustion chamber 3 of the gas turbine 1 is heated with natural gas, which is supplied via a supply line 27 and is under a high inlet pressure of approximately 80 bar. The supply line 27 is connected via a high-pressure gas line 28 to the inlet of an expansion turbine 29 , the outlet of which is connected to the combustion chamber 3 via a low-pressure gas line 30 . Shut-off valves 18 are arranged in the high-pressure gas line 28 and in the low-pressure gas line 30 . The expansion turbine 29 is coupled to a further generator 31 for generating electricity. In the expansion turbine 29 , the high inlet pressure of the natural gas is reduced down to the pressure of the combustion chamber 3, producing electrical energy. A line 32, which can be shut off by a shut-off valve 18 and leads to an additional natural gas consumer, can be branched off from the low-pressure line 30 .

A gas / water heat exchanger 33 designed as a pressure vessel is arranged in the high-pressure gas line 28 , in which the natural gas is heated in order to avoid possible icing of the valves in the low-pressure gas line 30 . The preheated feed water in the feed water preheater 8 of the waste heat boiler 5 serves as heat transfer medium. For this purpose, the second branch line 25 branching off from the outlet of the feed water preheater 8 is connected to the gas / water heat exchanger 33 . In this gas / water heat exchanger 33 , the preheated feed water is cooled to a temperature below that of the degasser 16 while the natural gas is being heated. A return line 34 is connected to the outlet of the gas / water heat exchanger 33 on the feed water side, in which a pressure reducing valve 35 is arranged. The return line 34 is returned to the degasser 16 .

The throughput of the feed water through the feed water preheater 8 and the gas / water heat exchanger 33 is greater than the steam output of the combined gas / steam turbine process. Due to this higher feed water throughput, the exhaust gas temperature at the outlet of the waste heat boiler 5 can be significantly reduced, depending on the amount of natural gas to be preheated, with the same feed water heating.

Before entering the expansion turbine 29 , a bypass line 36 bypassing the expansion turbine 29 branches off from the high-pressure gas line 28 . The bypass line 36 , in which a shut-off valve 18 and a pressure reducing valve 35 are arranged, opens into the low-pressure gas line 30 .

A start-up line 37 , which can be shut off by a shut-off valve 18 , branches off from the supply line 27 parallel to the expansion turbine 29 . An electrical heater 38 for heating the pressurized natural gas and a start-up expander 39 for expanding the natural gas are arranged in the start-up line 37 . The start-up expander 39 is coupled to the compressor 2 of the gas turbine system. The start-up line 37 is also connected to the low-pressure gas line 30 via a line 40 provided with a pressure reducing valve 35 .

As shown in FIG. 2, the waste heat boiler 5 can also be equipped with a two-pressure system, each subsystem (high-pressure system and low-pressure system) having its own evaporator 7 , 7 'and its own superheater 6 , 6 '. A two-part feed water preheater 8 , 8 'is provided only on the high pressure side. The superheater 6 'of the low pressure system is connected to the low pressure part of the steam turbine 10 . The gas / water heat exchanger 33 for heating the natural gas is connected to the feed water preheater 8 of the high pressure system.

The waste heat boiler 5 can also be provided with an additional firing 41 which is fired with natural gas at a lower pressure. This natural gas flow is expanded in a second expansion turbine 42 , which is connected downstream of the first expansion turbine 29 and is connected to the further generator 31 via couplings. The outlet of the second expansion turbine 42 is connected to the auxiliary firing 41 via a gas line 43 which can be shut off by a shut-off valve 18 .

In the event of a gas turbine short-circuit, the combined gas / steam turbine block is operated in fresh air mode. In a so-called simulated waste heat mode, the same exhaust gas parameters as in the additional fire mode are achieved via a fresh air blower 47 and the existing additional firing 41 . The firing capacity of the additional firing 41 is in the order of magnitude of the natural gas used for the gas turbine 1 . In this case, natural gas heating can be guaranteed without interruption in this event.

The regulation of the feed water quantities to the feed water preheater 8 and the gas / water heat exchanger 33 takes place via the 3-component regulation shown in FIG. 3. A valve arrangement 44 is provided in the first branch line 24 leading from the feed water preheater 8 to the steam drum 26 . This valve arrangement 44 regulates the feed water quantity flowing into the waste heat boiler 5 in accordance with the load requirement of the waste heat boiler 5 . A pressure vessel 45 , which is provided with a water level control 46 , is inserted into the second branch line 25 leading to the gas / water heat exchanger 33 . This water level control 46 keeps the feed water quantity flowing through the gas / water heat exchanger 33 at a constant value.

Two operating cases are decisive for the accident analysis: the failure of the expansion turbine 29 and the failure of the gas / water heat exchanger 33 . In the event of a fault of the expansion turbine 29 the heated gas is passed via the bypass line 36 to the expansion turbine 29 and supplied via the pressure reducing valves 35 (throttling) the consumer network or the combustion chamber 3 of the gas turbine. 1 The return of the proportionate waste heat leads to a higher gas turbine efficiency. The coupling of heat into the circuit for heating the natural gas remains in effect. In the event of a fault in the gas / water heat exchanger 33 , the natural gas is taken directly from the supply line 27 . The temperature drop occurring during the throttling in the pressure reducing valve 35 is compensated via the electric heater 38 in such a way that there is no risk of icing on the downstream fittings. Due to the lack of heat extraction for the natural gas circuit, the exhaust gas temperature at the outlet of the waste heat boiler 5 increases by approximately 100 K.

The situation is somewhat different for natural gas storage facilities, because the quantities of natural gas to be expanded are considerably larger than the turbine exhaust gas quantities. Here in times of least Consumption stored in so-called caverns natural gas, and if the demand for natural gas is high, the storage tank is discharged. The loading and unloading takes place in cycles of the same length (each about 4000 h / a).

For the loading of the storage are often electric motor operated compressors used, which the necessary obtain electrical drive energy from the public grid. In addition, for protection (failure of the public network) in parallel a combination system with the same electrical output Installed. The amount of gas turbine power is thereby largely by the amount of exhaust gas generated because of  Natural gas heating determined, with gas turbines with low specific power (high exhaust gas quantity with the same electrical Performance).

When the natural gas storage unit is discharged via the supply line 27 , more natural gas is expanded in the expansion turbine 29 than is burned in the combustion chamber 3 of the gas turbine 1 . The excess relaxed natural gas is fed via line 32 to a natural gas consumer. The circuit shown in FIG. 4 is used to heat this larger amount of natural gas. A third branch line 48 branches off from the feed water line 21 leading from the degasser 16 to the feed water preheater 8 before it enters the feed water preheater 8 . This third branch line 48 is connected to the first branch line 24 , which connects the outlet of the feed water preheater 8 to the steam drum 26 . A control valve 49 , 50 is arranged in the first branch line 24 and in the third branch line 48 in front of the junction of the two branch lines 24 , 48 . Furthermore, a control valve 51 is provided in the first branch line 24 before it enters the steam drum. Depending on the position of the control valves 49 , 50 , 51 , the feed water preheater 8 can be charged with feed water such that the preheated feed water, as in the circuits according to FIGS. 1 and 2, both the evaporator 8 via the steam drum 26 and for heating the bottom increased pressure standing natural gas are supplied to the gas / water heat exchanger 33 . The control valve 49 in the first branch line 24 is open and the control valve 50 in the third branch line 48 is closed. In addition, it becomes possible to use the feed water preheated in the feed water preheater 8 only for heating the natural gas. In this case, the steam drum 26 is fed with the control valve 49 closed and the control valve 50 and 51 open via the third branch line 48 with non-preheated feed water. If the power of the gas turbine 1 and the waste heat boiler 5 is then insufficient for the necessary total electrical power, the power of the steam turbine 10 will be increased via the additional firing 41 .

According to FIG. 4, a heat exchanger 52 for generating district heating is provided behind the feed water preheater in the flow direction of the turbine exhaust gas.

If the operating pressures are around 120 to 140 bar when the natural gas storage facility is unloaded, the natural gas must be heated up in a different way for apparatus reasons. Advantageously, the heating surface tubes of the heat exchanger 33 can form the pressure body for absorbing the very high natural gas pressure. Due to the high heat transfer coefficients in the condensation of low-pressure steam, on the one hand the heating surface would be considerably less and on the other hand the pressure vessel would be easier to design. Because of the increased natural gas parameters, such as pressure, quantity and possibly temperature, the expansion turbines 29 , 42 are to be designed in an axial manner. The construction principle of steam turbines is then advantageously used for natural gas expansion.

In two-pressure combination systems, the low-pressure steam generated can be used to preheat the natural gas. Such a system is shown in FIG. 5. This system largely corresponds to the system according to FIG. 2. It is only the branch line 25 leading to the heat exchanger 33 that is no longer connected to the outlet of the feed water preheater 8 but as a connecting line to a low-pressure steam line 56 , which connects to the superheater 6 'of the low-pressure part of the Waste heat boiler 5 is connected. The necessary amount of low-pressure steam is supplied to the heat exchanger 33 via this low-pressure steam line 56 and the connecting line 25 . In the heat exchanger 33 , the required natural gas heating is regulated by a water level control. The remaining low-pressure steam is used for the thermal degassing of the feed water in the degasser 16 .

If the amount of low-pressure steam generated from the low-pressure part of the waste heat boiler 5 is not sufficient to cover the heat requirement (e.g. for the additional heating of buildings in the natural gas storage power plants), the steam can be withdrawn at the same pressure level via an extraction line 53 Steam turbine 10 and the connecting line 54 to meet the steam needs of the heat consumer 20 . The reduced steam turbine output can be compensated for by the additional firing 41 installed in the waste heat boiler 5 .

Claims (17)

1. A method for generating electrical energy with the aid of an expansion turbine ( 29 ), steam turbine ( 10 ) and a gas turbine ( 1 ) which is connected upstream of a combustion chamber ( 3 ) and a waste heat boiler ( 5 ) which is connected to a water vapor -Flowing circulation and heating surfaces designed as feed water preheaters ( 8 ), evaporators ( 7 ) and superheaters ( 6 ), natural gas under high inlet pressure being heated and then expanded to the combustion chamber pressure in the expansion turbine ( 29 ) and in the combustion chamber ( 3 ) is burned, characterized in that a partial flow is branched off from the water-steam circuit heated in the heating surfaces of the waste heat boiler ( 5 ) and that the natural gas, which is under the high inlet pressure, is heated with this partial flow. 2. The method according to claim 1, characterized in that the preheated in the feed water preheater ( 8 ) feed water is divided into a first and a second partial flow, that the first partial flow is supplied to the evaporator ( 7 ) of the waste heat boiler ( 5 ) and that with the second partial flow, the natural gas, which is under the high inlet pressure, is heated. 3. The method according to claim 1 or 2, characterized in that the natural gas is expanded in two stages and that the expanded natural gas in the second stage of an additional firing ( 41 ) of the waste heat boiler ( 5 ) is supplied. 4. The method according to any one of claims 1 to 3, characterized in that the feed water in a gas / water heat exchanger ( 33 ) cooled by the heating of the natural gas under the high inlet pressure to a temperature below the temperature inside the degasser ( 16 ) becomes. 5. The method according to any one of claims 1 to 4, characterized in that the waste heat boiler (5) supplied quantity of feed water in accordance with the load demand of the waste heat boiler (5) is controlled and that the amount of feed water for heating the natural gas via a water level control ( 46 ) is kept at a constant value in a separate pressure vessel ( 44 ). 6. The method according to any one of claims 1 to 5, characterized in that a larger amount of natural gas is expanded in the expansion turbine ( 29 ) than is burned in the combustion chamber ( 3 ) of the gas turbine ( 1 ) that the excess expanded natural gas unites Natural gas consumer ( 32 ) is supplied, that the natural gas is heated by a larger amount of preheated feed water and that a proportionate amount of non-preheated feed water is fed to the evaporator ( 7 ). 7. Ver drive according to claim 6, characterized in that the power of the steam turbine ( 10 ) is increased by an additional firing ( 41 ) when the steam output of the waste heat boiler ( 5 ) is insufficient to cover the electrical requirement. 8. The method according to claim 1, characterized in that at one a low pressure part and a high pressure part showing water-steam cycle that under the high Natural gas input pressure through a partial flow of the the low pressure part generated steam is heated. 9. Device for generating electrical energy with the aid of an expansion turbine ( 29 ), steam turbine ( 10 ) and a gas turbine ( 1 ), which is connected upstream of a combustion chamber ( 3 ) and a waste heat boiler ( 5 ), which is also used as a feed water preheater ( 8 ) , Evaporator ( 7 ) and superheater ( 6 ) is provided with heating surfaces, the inlet of the expansion turbine ( 29 ) having a supply line ( 27 ) for a natural gas under high inlet pressure via a heat exchanger ( 33 ) for heating this natural gas and the outlet of the Expansion turbine ( 29 ) is connected to the combustion chamber ( 3 ) of the gas turbine ( 1 ), for carrying out the method according to one of claims 1 to 7, characterized in that the output of the feed water preheater ( 13 ) is connected to two branch lines ( 24 , 25 ) is that the first branch line ( 24 ) connects to the heating surfaces of the waste heat boiler ( 5 ) connected downstream of the feed water preheater ( 8 ) is and that the second branch line ( 25 ) to the heat exchanger ( 33 ) and then to the feed water degasser ( 16 ) is returned. 10. Device for generating electrical energy with the aid of an expansion turbine ( 29 ), steam turbine ( 10 ) and a gas turbine ( 1 ), which is connected upstream of a combustion chamber ( 3 ) and a waste heat boiler ( 5 ), which is also used as a feed water preheater ( 8 ) , Evaporator ( 7 ) and superheater ( 6 ) is provided with heating surfaces, the inlet of the expansion turbine ( 29 ) having a supply line ( 27 ) for a natural gas under high inlet pressure via a heat exchanger ( 33 ) for heating this natural gas and the outlet of the Expansion turbine ( 29 ) is connected to the combustion chamber ( 3 ) of the gas turbine ( 1 ) for carrying out the method according to one of claims 1 or 2 or 7 or 8, characterized in that the waste heat boiler ( 5 ) in a low-pressure part with an evaporator ( 7 ') and a superheater ( 6 ') and a high pressure part with the feed water preheater ( 8 ), an evaporator ( 7 ) and a superheater ( 6 ) is divided and that the superheater ( 6 ') of the low pressure part is connected to the heat exchanger ( 33 ) for heating the natural gas. 11. The device according to claim 9 or 10, characterized in that the expansion turbine ( 29 ) is followed by a second expansion turbine ( 42 ), the output of which is connected to an additional combustion ( 41 ) arranged in the waste heat boiler ( 5 ). 12. Device according to any one of claims 9 to 11, characterized in that the output of the heat exchanger (33) is connected via a the expansion turbine (29) immediate bypass line (36) with the combustion chamber (3) and that in the bypass line (36 ) a pressure reducing valve ( 35 ) is arranged. 13. Device according to one of claims 9 to 12, characterized in that the supply line ( 27 ) via an electrical heater ( 38 ) and a pressure reducing valve ( 35 ) is connected to the combustion chamber ( 3 ). 14. Device according to one of claims 9 to 13, characterized in that a third branch line ( 48 ) is branched off from the feed water line ( 21 ) before it enters the feed water preheater ( 8 ), which with the first the output of the feed water preheater ( 8 ) is connected to the steam drum ( 26 ) connecting branch line ( 24 ) and that a control valve ( 49 , 50 ) is arranged in the first branch line ( 24 ) and in the third branch line ( 48 ) in front of the junction of these branch lines ( 24 , 48 ) , 15. The apparatus according to claim 14, characterized in that the waste heat boiler ( 5 ) is provided with an additional firing ( 41 ). 16. Device according to one of claims 9 to 15, characterized in that due to the high natural gas parameters, such as pressure, temperature and amount, the expansion turbines ( 29 , 42 ) are designed in an axial construction. 17. Device according to one of claims 9 to 16, characterized in that a fresh air operation of the combined gas / steam turbine block is provided so that the relaxation circuit for the natural gas remains in operation in the event of a failure of the gas turbine ( 1 ).