WO1995000747A1

WO1995000747A1 - Method of operating a cogas plant, and a cogas plant operated by this method

Info

Publication number: WO1995000747A1
Application number: PCT/DE1994/000657
Authority: WO
Inventors: Marcel Moricet; Bert Rukes
Original assignee: Siemens Aktiengesellschaft
Priority date: 1993-06-24
Filing date: 1994-06-13
Publication date: 1995-01-05
Also published as: DE4321081A1

Abstract

The invention concerns a method of operating a combined gas and steam turbine (COGAS) plant (1a, 1b) in which the heat in the exhaust gases (AM') produced by the gas turbine (2) is used to generate steam for the steam turbine (10) which is connected into a water/steam circuit (12). In order to increase the thermal efficiency, the invention calls for the fuel (BS) used to generate the hot gases (AM) which drive the gas turbine (2) to be pre-heated. The plant (1a, 1b) includes a combustion chamber (4) connected in front of the gas turbine (2), the fuel line (6) to the combustion chamber passing through a heat exchanger (62, 62') connected to the water/steam circuit (12).

Description

description

Process for operating a gas and steam turbine plant and a combined cycle gas plant

The invention relates to a method for operating a gas and steam turbine plant (CCGT plant) in which the heat contained in the relaxed working medium from the gas turbine is used to generate steam for the steam turbine connected to a water-steam circuit . It continues to focus on a combined cycle plant that uses this process.

In a gas and steam turbine system, the heat contained in the relaxed working fluid from the gas turbine is used to generate steam for the steam turbine. The heat transfer takes place in a steam generator or waste heat boiler downstream of the gas turbine, in which heating surfaces are arranged in the form of tubes or tube bundles. These in turn are switched into the water-steam cycle of the steam turbine. The water-steam cycle comprises several, for example two, pressure stages, each pressure stage having a preheating, an evaporator and a superheater heating surface. With such a combined cycle plant, known for example from European patent specification 0 148 973, a thermodynamic efficiency of about 50% to 55% is achieved, depending on the pressure conditions prevailing in the water-steam cycle of the steam turbine.

The invention is based on the object of specifying a method for operating such a gas and steam turbine installation with which an increase in the thermodynamic efficiency is achieved. In a suitable gas and steam turbine plant, this should be achieved with particularly simple means.

With regard to the method, the stated object is achieved according to the invention in that a is preheated by means of fuel used for the gas turbine.

The fuel is preheated advantageously by indirect heat exchange of the fuel with a partial flow of preheated water taken from the water-steam cycle of the steam turbine, which water is returned to the water-steam cycle after the heat has been exchanged with the fuel. The partial flow for heating the fuel is expediently taken from either a high-pressure stage or a low-pressure stage of the water-steam cycle.

According to an advantageous development, a partial flow is taken from both the high-pressure stage and the low-pressure stage and used for a two-stage fuel heating. In a first stage, the fuel is moistened and heated by direct heat exchange with preheated water. The water used for humidification is preheated by indirect heat exchange with the first partial stream taken from the low-pressure stage of the water-steam cycle. In a second stage, the heated fuel is then further heated by indirect heat exchange with the second partial stream taken from the high-pressure stage of the water-steam cycle.

If a liquid or gaseous fuel (heating oil, natural gas) is used, the fuel is preheated to a temperature of 100 ° C. to 400 ° C. In the event that the partial flow is taken from the low-pressure stage of the water-steam cycle , the fuel is advantageously preheated to a temperature of approximately 150 ° C. In the event that the partial stream is removed from the high-pressure stage of the water-steam circuit, the fuel is preheated to a temperature of approximately 280 ° C. to 320 ° C. In the case of a two-stage fuel preheating with fuel humidification, the fuel is preheated to a temperature of likewise 280 ° C to 320 ° C. With regard to the gas and steam turbine system with a combustion chamber upstream of the gas turbine, into which a fuel line opens, and with a steam-steam circuit of the steam turbine connected in at least two pressure stages, which has a condensate preheater and has a high-pressure preheater, the above object is achieved in that a heat exchanger is provided for fuel preheating, which is connected on the primary side in the water-steam cycle and on the secondary side in the fuel line.

The heat exchanger is advantageously connected in parallel with the condensate preheater on the primary side. In this case, the preheated water of the partial flow used to preheat the fuel is at low pressure. On the primary side, however, the heat exchanger can also be connected in parallel with the high-pressure preheater, so that the preheated water of the partial flow serving to preheat the fuel is at a correspondingly high pressure.

In the case of two-stage fuel preheating with fuel moistening, a further heat exchanger is expediently provided, which is arranged on the secondary side in the flow direction of the fuel upstream of the first heat exchanger. It is also connected on the primary side to the low-pressure stage of the water-steam cycle and is parallel to the condensate preheater, while the first heat exchanger is connected to the high-pressure stage of the water-steam cycle for further heating of the fuel and is parallel to the high-pressure preheater.

The preheating of the fuel in the first stage is expediently carried out by moistening the fuel by means of preheated water conducted in a water circuit. For this purpose, a fuel humidifier is connected in the fuel line, in which the fuel and the preheated water are guided in counterflow to one another. The preheating of the The water serving as fuel is humidified in the further heat exchanger connected to the low-pressure stage of the water-steam cycle.

Embodiments of the invention are explained in more detail with reference to a drawing. Show it:

Figures 1 and 2, a gas and steam turbine system with a heat exchanger connected at alternative points to a water-steam circuit of the steam turbine for preheating Bren s off, and

Figure 3 shows a gas and steam turbine system according to Figures 1 and 2 with two heat exchangers for fuel moistening and - preheating.

Corresponding parts are provided with the same reference symbols in all figures.

A gas and steam turbine plant according to FIGS. 1 to 3 comprises a gas turbine plant 1 a and a steam turbine plant 1 b. The gas turbine system 1 a comprises a gas turbine 2 with a coupled air compressor 3 and a combustion chamber 4 connected upstream of the gas turbine 2 and which is connected to a fresh air line 5 of the air compressor 3. A fuel line 6 opens into the combustion chamber 4 of the gas turbine 2. The gas turbine 2 and the air compressor 3 as well as a generator 7 sit on a common shaft 8.

The steam turbine system 1b comprises a steam turbine 10 with a coupled generator 11 and, in a water-steam circuit 12, a capacitor 13 connected downstream of the steam turbine 10 and a waste heat steam generator 14.

The steam turbine 10 consists of a high-pressure part 10a and a low-pressure part 10b, which drive the generator 11 via a common shaft 15. An exhaust pipe 17 is connected to an inlet 14a of the heat recovery steam generator 14 for supplying working medium AM ′ or flue gas relaxed in the gas turbine 2 to the heat recovery steam generator 14. The relaxed working medium AM ¹ from the gas turbine 2 leaves the heat recovery steam generator 14 via its outlet 14b in the direction of a chimney (not shown).

In a low-pressure stage of the water-steam circuit 12, the steam generator 14 comprises a condensate preheater 20 and a low-pressure evaporator 22 as well as a low-pressure superheater 24. It also comprises in a high-pressure stage of the water-steam circuit 12 a high-pressure preheater or economizer 26, a high-pressure evaporator 28 and a high-pressure superheater 30. The low-pressure superheater 24 is connected to the low-pressure part 10b of the steam turbine 10 via a steam line 32. The high-pressure superheater 30 is connected to the high-pressure part 10 a of the steam turbine 10 via a steam line 34. The low-pressure part 10b of the steam turbine 10 is connected on the output side to the condenser 13 via a steam line 36.

The water-steam circuit 12 shown in FIGS. 1 to 3 is thus made up of two pressure stages. However, it can also be constructed from three pressure stages. In this case, the waste heat steam generator 14 additionally has a medium-pressure evaporator and a medium-pressure superheater, which are connected to the water-steam circuit 12 and are connected to a medium-pressure part of the steam turbine 10.

The condenser 13 is connected to the condensate preheater 20 via a condensate line 42. A condensate pump 44 is located in the condensate line 42. The condensate preheater 20 is connected on the outlet side to a feed water tank 46. The feed water tank 46 is connected on the output side via a low pressure pump 48 to a water / steam separation vessel 50 of the low pressure stage. The low-pressure superheater 24 and - via a circulation pump 52 - the low-pressure evaporator 22 are connected to this vessel 50. The feed water tank 46 is also connected on the output side via a high-pressure pump 54 to the economizer 26, which in turn is connected on the output side to a water-steam separation vessel 56 of the high-pressure stage. The high-pressure superheater 30 and - via a circulating pump 58 - the high-pressure evaporator 28 are connected to the vessel 56. A steam line 60 connected to the steam line 32 also opens into the feed water tank 46. Furthermore, the feed water tank 46 is connected to the condensate line 42 via a circulation pump 59.

The secondary side of a heat exchanger 62 is connected into the fuel line 6 and, according to FIG. 1, is connected in parallel with the condensate preheater 20. For this purpose, the heat exchanger 62 is connected on the primary side via an inflow line 64 to the feed water tank 46 and via an outflow line 66 to the condensate line 42. A pump 68 is connected to the inflow line 64. A throttle 70 is connected in the outflow line 66.

According to FIG. 2, a heat exchanger 62 'is connected in parallel with the economizer 26 on the primary side. For this purpose, the heat exchanger 62 'is connected on the primary side via an inflow line 64' to the outlet of the economizer 26 and via an outflow line 66 'to the suction side of the high-pressure pump 54. A throttle 70 'is connected in the outflow line 66'.

When the gas and steam turbine system la, lb is in operation, the combustion chamber 4 is supplied with liquid or gaseous fuel BS, for example natural gas or heating oil, via the fuel line 6. The fuel BS is preheated in the heat exchanger 62, 62 'to a temperature T _] _ of 100 ° C. to 400 ° C. The preheated fuel BS is used to generate the Working medium AM for the gas turbine 2 in the combustion chamber 4 burns with compressed fresh air L from the air compressor 3. The hot and high-pressure working medium AM or flue gas that arises during the combustion is expanded in the gas turbine 2 and drives it and the air compressor 3 and the generator 7. The relaxed working medium AM 'emerging from the gas turbine 2 with a temperature T2 of approximately 550 ° C. is introduced into the waste heat steam generator 14 via the exhaust gas line 17 and used there to generate steam for the steam turbine 10. For this purpose, the flue gas stream and the water-steam circuit 12 are linked to one another in countercurrent.

In order to achieve particularly good heat utilization, vapors are generated at different pressure levels, the enthalpy of which is used to generate electricity in the steam turbine 10. In the low-pressure stage, steam can be generated with a pressure p _N of 6 bar and a temperature T _N of 200 ° C. In the high pressure stage steam can be generated with a pressure p _H of 80 bar and a temperature T _H of 520 ° C.

The expanded steam emerging from the low-pressure part 10b of the steam turbine 10 is fed to the condenser 13 via the steam line 36 and condenses there. The condensate is pumped into the condensate preheater 20 via the condensate pump 44 and preheated there. The preheated condensate flows into the feed water tank 46.

According to the exemplary embodiment according to FIG. 1, in order to preheat the fuel BS, a partial stream t 1 of the preheated feed water which is at low pressure is removed from the feed water tank 46 via the inflow line 64. This partial flow t _] _ is first brought to a pressure above the fuel pressure by means of the pump 68 and then fed to the heat exchanger 62. There, the heat contained in the partial flow t_ of the preheated feed water is transferred to the fuel BS by indirect heat exchange. The The partial flow t 1 of the cooled feed water which is conducted via the outflow line 66 is first throttled and then mixed with the condensate flowing via the condensate line 42. The fuel is preheated at a fuel pressure p _BS of 5 to 20 bar. In order to prevent gaseous constituents of the fuel BS from entering the condensate or feed water, the partial flow t] _ of the preheated feed water is brought to a pressure above the fuel pressure by means of the pump 68. As a result of the indirect heat exchange between the partial flow t _{] of} the preheated and low-pressure feed water and the fuel BS in the heat exchanger 62, fuel preheating to a temperature T of about 150 ° C. is achieved.

With the system circuit according to FIG. 1, an increase in efficiency compared to the efficiency mentioned at the outset is achieved by 0.3 to 0.4 percentage points.

In the exemplary embodiment according to FIG. 2, preheated feed water under high pressure is fed to the heat exchanger 62 '. For this purpose, a partial flow t ′ ι of the preheated feed water, which is under high pressure, is removed from the economizer 26 via the discharge line 64 ′. After indirect heat exchange with the fuel BS has taken place, the partial flow t'i is conducted via the discharge line 66 'and, after throttling in the throttle 70', the water-steam circuit 12 of the steam turbine 10 between the feed water tank 46 and fed to the high pressure pump 54 again. Due to the indirect heat exchange in the heat exchanger 62 * between the partial flow t'i of the preheated and high-pressure feed water from the high-pressure stage of the water-steam circuit 12 and the fuel BS, fuel preheating is reduced to one Temperature T] _ reached of about 280 ° C. With a circuit according to the exemplary embodiment according to FIG. 2, an efficiency increase of 0.5 to 0.6 percentage points is achieved.

In the exemplary embodiment according to FIG. 3, in which the gas and steam turbine system 1 a, 1 b is constructed in the same way as in the exemplary embodiments according to FIGS. 1 and 2, a two-stage fuel preheating takes place. In a first stage, the fuel BS is heated to a temperature T3 of approximately 130 ° C. to 150 ° C. The fuel is heated in a fuel humidifier 80 connected to the fuel line 6 by direct heat exchange with heated water UW flowing in a water circuit 82. The circulating water UW is heated by indirect heat exchange in a further heat exchanger 83 connected on the secondary side in the water circuit 82. The heat exchanger 83 is connected on the primary side to the water-steam circuit 12 of the steam turbine. A partial flow t ″ 1 of the preheated feed water is taken from the feed water tank 46, similarly to the exemplary embodiment according to FIG. 1, via an inflow line 64 ″ and a pump 68 ″. After indirect heat exchange with the water UW circulating in the water circuit 82, the partial flow t ″ 1 is fed back to the water-steam circuit 12 via an outflow line 66 ″ connected to the condensate preheater 22. The heat exchanger 83 is located at least in part of the condensate preheater 20 parallel.

The fuel BS fed to the fuel humidifier 80 in the manner of a countercurrent column at the sump 84 is saturated from below with the water UW trickling down from the head 86 in the countercurrent. The pressure, temperature and throughput of the circulating water UW depend on the minimally achievable degree of saturation of the fuel BS and on the minimum required sprinkling density within the fuel humidifier 80, so that only part of the water UW used evaporates. This part is fresh water FW replaced, which is fed via a fresh water line 88 to the water circuit 82, into which a pump 90 is connected. As a result of the saturation process, the fuel BS heats up from below, while the water UW cools down from above. The water UW emerging at the sump 84 of the fuel humidifier 80 is mixed with the fresh water FW and heated by indirect heat exchange with the partial flow t ″ ″ of the preheated feed water. Pressure, temperature and quantity per unit of time of the partial flow tι_ • ■ depend on the operating state of the fuel humidifier 80 and are selected such that the water temperature at the head 86 of the fuel humidifier 80 above the saturation state of the the heated fuel BS 'leaving the humidifier 80.

The on the temperature T3 of e.g. 150 ° C heated fuel BS 'is further heated in a second stage by means of a heat exchanger 62' 'to a temperature T] _ of 250 ° C to 320 ° C. The heat exchanger 62 * ', which is connected downstream of the fuel humidifier 80 in the fuel line 6, is connected on the primary side - as in the exemplary embodiment according to FIG. 2 - to the high-pressure stage of the water-steam circuit 12 of the steam turbine 10. The further heating of the fuel BS 'takes place by indirect heat exchange with a partial stream t2 of the preheated feed water which is under high pressure and which is taken from the high pressure stage. This partial flow t2 is fed to the heat exchanger 62 ″ via a feed line 64 ″ ″ connected to the high-pressure preheater 26. After the heat exchange and subsequent throttling in the throttle 70 '' 'lying in an outflow line 66' '', the partial flow t2 is fed to the condensate preheater 20.

With the circuit according to the exemplary embodiment according to FIG. 3, an increase in efficiency of 0.6 to 0.7 percentage points is achieved. In circuits with a water-steam cycle built up from three pressure levels, 80 efficiency increases of 0.4 to 0.6 percentage points are achieved without the interposition of a fuel humidifier; With 80 fuel humidifier, efficiency increases of 0.6 to 0.8 percentage points are achieved.

Claims

claims

1. A method for operating a gas and steam turbine plant in which the heat contained in the relaxed working medium (AM ') of the gas turbine (2) is used to generate steam for the steam turbine connected to a water-steam circuit (12) (10) is used, characterized in that a fuel (BS) used to generate the working medium (AM) for the gas turbine (2) is preheated.

2. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that preheating the fuel (BS) to a temperature (T ^) of 100 ° C to 400 ° C takes place.

3. The method according to claim 1 or 2, characterized in that the preheating by indirect heat exchange of the fuel (BS) with a from the water-steam circuit (12) of the steam turbine (10) withdrawn partial flow (tι_, t '^) .

4. The method according to any one of claims 1 to 3, wherein the water-steam circuit (12) of the steam turbine (10) has at least two pressure stages (20, 22, 24 and 26, 28, 30), characterized in that the Partial stream (tι_ or t'ι_) for preheating the fuel (BS) one

Low pressure stage (20, 22, 24) and / or a high pressure stage

(26, 28, 30) of the water vapor circuit (12) is removed.

5. The method according to claim 4, characterized by a two-stage heating of the fuel, in a first stage the fuel (BS) by direct heat exchange with by indirect heat exchange with one of the low-pressure stage (20, 22, 24) of the water vapor -Kreiεlaufε (12) taken first partial stream (t''ι) preheated water is heated, and in a second stage the heated Fuel (BS ¹ ) is further heated by indirect heat exchange with a second partial stream (t2) taken from the high-pressure stage (26, 28, 30) of the water-steam circuit (12).

6. The method of claim 5, d a d u r c h g e k e n n z e i c h n e t that the preheated in the first stage by indirect heat exchange with the first partial stream (t '' ι_) Wasεer (UW) in counter current to the flow direction of the fuel (BS) is performed.

7. Gas and steam turbine system (la, lb) with a combustion chamber (4) upstream of the gas turbine (2), into which a fuel line (6) opens, and with one into at least two pressure stages (20, 22, 24 and 26, 28, 30) have the water-steam circuit (12) of the steam turbine (10) switched heat recovery steam generator (14), the heat recovery steam generator (14) having a condensate preheater (20) and a high pressure preheater (26) has, characterized in that for preheating fuel by means of preheated water from the

Water-steam circuit (12) of the steam turbine (10) a heat exchanger (62, 62 ', 62 "') is provided, which is connected on the primary side to the water-steam circuit (12) and which on the secondary side Fuel line (6) is switched.

8. System according to claim 7, so that the heat exchanger (62, 62 ', 62' ') is connected in parallel on the primary side to the condensate preheater (20) or the high pressure preheater (26).

9. Plant according to claim 7 or 8, characterized by a further heat exchanger (83), which is arranged on the secondary side in the flow direction of the fuel (BS) upstream of the first heat exchanger (62 ''), and which is on the primary side parallel to the condensate preheater (20 ) lies.

10. Plant according to claim 9, characterized by a fuel humidifier (80) connected in the flow direction of the fuel (BS) upstream of the heat exchanger (62 '') into the fuel line (6), the further heat exchanger (83) on the secondary side for humidification of the fuel (BS) serving water (UW) heated.