IL126800A

IL126800A - Hybrid power plant

Info

Publication number: IL126800A
Application number: IL12680098A
Authority: IL
Original assignee: Abb Alstom Power Ch Ag
Priority date: 1997-11-05
Filing date: 1998-10-29
Publication date: 2002-03-10
Also published as: DE59709579D1; IL126800A0; EP0915233B1; EP0915233A1

Abstract

A hybrid power plant (10), comprising a steam turbine (21), which drives a first generator (28) and can be operated alternatively with steam from a steam generator (11) operated with fuel and/or with steam from a heat-recovery steam generator (11) and a gas turbine (50), which drives a second generator (55) and at the outlet of which the heat-recovery steam generator through which the hot combustion gases of the gas turbine flow, is arranged, and also a feedwater tank, into which the condensate formed in a condenser (34) from the exhaust steam of the steam turbine is returned and from which feedwater for the steam generation is delivered to the steam generator or the heat-recovery steam generator, the condensate being preheated before being returned into the feedwater tank and the feedwater being preheated before being delivered to the steam generator, wherein only the hot exhaust gases of the gas turbine are used for the preheating of the condensate and the feedwater. 440 כ" ו באדר התשס" ב - March 10, 2002

Description

126800/2 Hybrid power plant ABB Alstom Power (Switzerland) Ltd.

C. 113692 TITLE OF THE INVENTION Hybrid power plant BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to the field of power plant technology. It relates to a hybrid power plant, comprising a steam turbine, which drives a first generator and can be operated alternatively with steam from a steam generator operated with fuel and/or with steam from a heat-recovery steam generator, and a gas turbine, which drives a second generator and at the outlet of which the heat -recovery steam generator, through which the hot combustion gases of the gas turbine flow, is arranged, and also a feedwater tank, into which the condensate formed in a condenser from the exhaust steam of the steam turbine is returned and from which feedwater for steam generation is delivered to the steam generator or the heat-recovery steam generator, the condensate being preheated before being returned into the feedwater tank, and the feedwater being preheated before being delivered to the steam generator.

Such a hybrid power plant has been disclosed, for example, by DE-A1-195 42 917.

Discussion of Background In the case of power plants for generating electrical energy, a distinction can be made between various power plant types, which are presented, for example, in . a publication of the applicant, R. -Bachmann, M. Fetescu, H. Nielsen, More than 60 % i Efficiency by Combining Advanced Gas Turbines and Conventional Steam Power Plants, ABB Technical Paper No. PGT 2163 96 E (1996) : (1) The conventional steam power plant (CSPP; see Fig. 1 of the ABB publication) , in which the steam is generated solely in a conventional steam generator (boiler) fired with coal and is directed to one (or more) steam turbine (s) and utilized for the generation of electricity. (2) The combined-cycle power plant (CCPP; see Fig. 2 of the ABB publication) , in which the steam for one (or more) steam turbine (s) is generated solely in a heat-recovery steam generator (HRSG) , through which the hot exhaust gases from one (or more) gas turbine (s) flow. Both the steam turbine (s) and the gas turbine (s) are coupled to a generator for the generation of electricity. (3) The hybrid power plant, in which, in addition to the combination of steam and gas turbines, a combination of (externally fired) steam generator and heat-recovery steam generator (arranged downstream of the gas turbine) is also used for providing the live steam for the steam turbine (see Fig. 3 of the ABB publication or the publication DE-A1-195 42 917 mentioned at the beginning) . In this case, the gas turbine with the heat-recovery steam generator is additionally installed and integrated in a conventional steam power plant (CSPP) . This results in three different types of operation (hybrid, conventional and as combined-cycle power plant) . In particular, by changing over between the types of operation, the gas turbine and the steam generator, which have a higher failure rate compared with the jointly used steam turbine, can be serviced separately without the operation of the plant having to be completely interrupted.

The power plant types (1) and (2) described have various disadvantages : in the separate CSPP or CCPP type there is no flexibility as regards the fuel, since either coal (CSPP) or gas (CCPP) has to be used; high investment costs of 1000-1200 $/kW are required, especially in the case of the CSPP type; the efficiency, especially in the case of the CSPP type, is relatively low, and the fuel costs are high; the costs for the generation of electricity are high; the flexibility of the operation is low (CSPP type) ; an improvement in the efficiency in the case of the CSPP type by higher pressures and temperatures of the live steam, double reheating, higher feedwater temperatures, lower condenser pressures, etc . , can only be achieved by high capital investment and technological risks, namely by new materials and manufacturing processes.

In the case of the hybrid power plant type (3) , in which the gas turbine and the heat -recovery steam generator are subsequently added to a conventional steam circuit, the following situation, as can be seen from the schematic representation in Fig. 1, results: in the hybrid power plant 10, the conventional steam circuit comprises a steam turbine 24 having a plurality of stages 25...27 and a generator 28 coupled via the turbine shaft 29, a steam generator 11, a feedwater tank 35, and a condenser 34. The feedwater is fed from the feedwater tank 35 by means of a feedwater pump 36 via the feedwater feed line 38 to the steam generator 11, which is normally fired with coal, oil or gas, which passes via a fuel feed 13 into a burner 12 and is burned there, the flue gases which are produced being drawn off through a flue-gas outlet.

In the steam generator 11, the feedwater, when passing through a plurality of heat exchangers 15...17 which are at different temperature levels, is heated and converted into steam, which is fed as live steam ■ . via a live-steam line 20 to a high-pressure stage 25 of the steam turbine 24 and expanded there in a first step while performing work. From the outlet of the high-pressure stage 25, the steam either passes directly to the inlet of a following intermediate-pressure stage 26 via the bypass line 23 when valve 22 is open, or is first of all fed through a further heat exchanger 18 and reheated there when valves 19 and 21 are open. After further expansion in the intermediate-pressure stage 26, the steam is finally expanded to its final pressure in a following low-pressure stage 27 and is converted into condensate in a condenser 3 . The condensate is delivered back into the feedwater tank 35 by a condensate pump 37 via a condensate line 41.

For the preheating of the feedwater, at least one regenerative heat exchanger is provided as high-pressure preheater 39 downstream of the feedwater pump 36 in the feedwater feed line 38, and steam which is bled from the high-pressure stage 25 of the steam turbine 24 via a bleed-steam line 31 flows through this high-pressure preheater 39. For the preheating (in stages) of the condensate, at least two regenerative heat exchangers are provided _as low-pressure preheaters 42, 43 downstream of the condensate pump 37 in the condensate line, and steam which is bled from the intermediate-pressure stage 26 and the low-pressure stage 27 via bleed-steam lines 32 and 33 respectively flows through these low-pressure' preheaters 42, 43.

During the subsequent conversion into a hybrid power plant, a gas turbine 50 having a generator 55 coupled to the turbine shaft 56 and a heat -recovery steam generator 44, through which the hot combustion gases of the gas turbine 50 flow, are added to the conventional steam circuit. In the heat-recovery steam generator 44, feedwater, which is branched off between the feedwater pump 36 and the preheater 39 by means of a feedwater feed line 4,0 and is fed to the heat-recovery steam generator 44, is heated and converted into steam in a plurality of heat exchangers 45...47, and this steam, in addition to or as an alternative to the live steam from the steam generator 11, passes as live steam via the live-steam line 30 to the high- pressure stage 25 of the . steam turbine 2 . A further heat exchanger 48 in which condensate- is preheated which is branched off between the preheaters 42 and 43 by means of a condensate line 41a is arranged on the low-temperature side of the heat-recovery steam generator 4 .

The gas turbine 50 itself comprises a turbine 51 and a compressor 54, which sit on the common shaft 56. The compressor 54 draws in and compresses combustion air for a following burner 52, where the combustion of the fuel introduced via the fuel feed 53 is effected. The hot combustion gases perform work in the turbine and pass to the outside in an exhaust-gas line 49 after passing through the heat-recovery steam generator 4v The / power plant is that the preheatsrs 39, 42 and 43 .for the condensate and the__ feedwater arj2_pj?j^rat^ steam which is bled from the steam ^turbine 24. On account of the steam bleed and the preheaters, this requires a specific construction in the case of the steam turbine 24 as well as complicated line routing with corresponding controlling equipment. In addition, the bled steam is not available for the generation of electricity, as a result of which the efficiency is reduced .

SUMMARY OF THE INVENTION Accordingly, one object of the invention is to provide a novel __hybrid power .plant ..... wh_ich_ is distinguished by a very flexible mode of operation and reduced plant costs with at the same time improved efficiency.

This object is achieved in a hybrid power plant of the type mentioned at the beginning in that only the hot exhaust gases of the gas turbine are used for the preheating of the condensate and the feedwater. The devices (lines, fittings, etc.) at the steam turbine for the bleeding of the steam for the (regenerative) preheaters are thereby dispensed with. The steam turbine can be mounted on the floor, since the preheaters, which are normally arranged below the steam turbine, need not be taken into account. The steam which is not bled can be utilized in the steam turbine at a high efficiency for the generation of electricity.

A preferred embodiment of the hybrid power plant according to the invention is distinguished by the fact that a heat exchanger for the preheating of all the feedwater and a heat exchanger for the preheating of all the condensate are provided in the heat-recovery steam generator, that the condensate and the feedwater for the preheating are directed through the corresponding heat exchanger, that the heat exchanger for the preheating of the condensate is arranged on the low-temperature side of the heat-recovery steam generator, and that further heat exchangers for the generation of steam from the preheated feedwater are connected downstream toward the high temperature side of the heat exchanger for the preheating of the feedwater in the heat-recovery steam generator. In this way, the heat can be recovered in the heat-recovery steam generator at a low energy level compared with the steam bleed. The (large) preheaters in the heat-recovery steam generator work with a small temperature difference and - compared with the conventional steam-operated regenerative preheaters -lead to a smaller loss of exergy.

Further embodiments follow from the dependent claims .

BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the invention and many of the attendant advantages thereof will . be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: Fig shows the schematic construction of a hybrid power plant which has resulted from retrofitting a conventional steam power pla~ht; and Fig shows the comparable construction of a hybrid power plant in a preferred exemplary embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, a preferred 15 exemplary embodiment for a hybrid power plant is ' schematically shown in Fig. 2. An essential difference between the plant scheme shown in Fig. 2 and the plant scheme from Fig. 1 consists in the .fact that the regenerative preheaters 39, 42 and 43 operated with 20 bleed steam from the """steam turbine 24 have been completely- omitted in Fig. 2, and that the preheating of both the feedwater and' the condensate is carried out directly in the heat-recovery steam generator 44'. To this^ end, the heat-recovery steam generator 44'- is 25 designed, in such a way that it can provide preheating of all the feedwater and all the condensate. To this end, the associated low-temperature heat exchangers 47 and 48' in the heat-recovery steam generator 44' are designed to be larger compared with the heat exchangers 30 47 and 48. from Fig. 1. The feedwater feed line 40 directs all the feedwater from the feedwater pump 36 to the inlet of the heat exchanger 47'. From the outlet of _ the heat exchanger 47', the preheated feedwater alternatively passes directly into the following heat 35 exchangers 45, 46, which are at a higher temperature, \ and is converted there into live steam or passes via the feedwater feed line 38 to the steam generator 11.

The condensate is directed via the condensate line 41a entirely to the inlet of the heat exchanger 48', is ) preheated in the heat exchanger 48', and is then directed into the feedwater tank 35. Since the 1 preheating in the heat exchangers 47' , 48' utilizes the waste heat of the gas turbine 50, and no steam needs to be bled from the steam turbine 24 for preheating purposes, the corresponding connections at the steam turbine, the bleed-steam lines and the associated fittings can be dispensed with.

During normal operation of the plant from Fig. 2, all the waste heat of the gas turbine 50 is used to carry out the full preheating of all the feedwater and ; condensate and to generate live steam which corresponds to the live-steam conditions of the steam generator 11 and forms a second live-steam source in addition to the steam generator 11.

The advantages of the hybrid power plant adcording to the invention may be described as follows: The efficiency of the plant is increased by a combination of CSPP and CCPP modes of operation. jrhe heat recovered in the heat exchangers 47' and 48' at the low-energy level of the heat-recovery steam generator 4 ' replaces the steam which is bled from the steam turbine for the regenerative preheaters 39, 42 and 43 in a conventional steam circuit (Fig. 1) . The steam which is thus additionally available in the steam turbine 24 is expanded and converted into electricity. This ultimately means that the heat recovered from the waste heat of the gas turbine 50 at a low-energy level is converted into electricity. In this case, the preheaters may be reproduced by a multi- pressure heat -recovery steam generator - in accordance with the varying steam-bleed levels.

With regard to the exergy, the large heat exchangers _47' and _48 ' in the heat-recovery steam generator 44 ■ work with small temperature differences and are therefore distinguished by a loss of exergy which is smaller than in the case of the regenerative preheaters 39, 42 and 43 in Fig. 1. In contrast, the regenerative preheaters 39, 42, 43 work as desuperheater condensers with relatively high temperature differences and accordingly with high exergy losses .

The plant cost and thus the investment costs are markedly lower compared with power plants of CSPP or CCPP type or of the retrofitted hybrid type with regenerative preheaters.

Neither the regenerative preheaters nor the associated bleed-steam devices at the steam turbine are required; this means fewer lines and valves as well as less controlling equipment and reduced complexity of the plant overall.

The steam turbine can be set up directly on the floor, since there are no bleed devices and preheaters (the main reason for a platform assembly is to provide space below the steam turbine for the preheaters) . In this case, the outlet of the steam turbine may be arranged axially or at the side.

There is only one__ steam turbine for CSPP and CCPP operation, ' with only one generator,' one transformer, one switchgear panel, etc^ The one steam turbine is cheaper to set up.

The heat-recovery steam' generator can be greatly simplified (single pass with only one pressure level, no reheating, no drums, simplified control) .

On the whole, the invention results in a simplification and consequently a cost reduction in the plant with at the same time high flexibility in the plant planning, high efficiency even during part-load operation, low electricity-generating costs, and the possibility of optimizing the fuel costs and the costs for servicing and operation during the operation.

The plant according to Fig. 2 can be run in three different operating modes: Operating mode 1 : In operating mode 1 only the conventional steam circuit is used. The gas turbine 50 is not in operation. Accordingly, preheating of the feedwater and the condensate in the heat-recovery steam generator 4 ' does not take place either. This operating mode is comparable with the operation of a CSPP in which the , regenerative preheaters and the steam bleed are closed. The efficiency is accordingly lower. This operating mode is not the normal operating mode and is only used if there is a planned or forced outage of the gas turbine (s) .

To improve the situation, preheating of the condensate can be carried out in the deaerator of the feedwater tank 35. The preheating of the feedwater can be carried out in a special preheater in the steam generator 11, to which preheater some of the flue gases are fed instead of to the heat exchanger 18 for the reheating. A disadvantage is the associated increased complexity of the steam generator 11.

Operating mode 2: In operating mode 2 the plant is run by the intended hybrid operation, during which live steam for the steam turbine 24 is provided Joy both the steam generator 11 and the heat-recovery steam generator 44'. Operating mode 3: In operating mode 3 the plant is run as a pure combined-cycle plant (CCPP) , i.e. the live steam is generated solely in the heat-recovery steam generator 44'. Here, moisture may occur in the outlet of the steam turbine 24. This can be avoided by the steam being additionally heated between the intermediate- pressure stage 26 and the low-pressure stage 27 of the steam turbine 24 by a heat exchanger or by injection of hot steam into the steam line, or by steam being bled at the inlet of the low-pressure stage 27 and being added before the last section of the low-pressure stage 27.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

LIST OF DESIGNATIONS 10 Hybrid power plant 11 Steam generator (boiler) 5 12 Burner 13 Fuel feed 14 Flue-gas outlet 15....18 Heat exchanger 19, 21, 22 Valve 10 20 Live-steam line (steam generator) ~ 23 Bypass line 24 Steam turbine 25 High-pressure stage (steam turbine) 26 Intermediate-pressure stage (steam 15 turbine) 27 Low-pressure stage (steam turbine) 28 Generator 29 Shaft (steam turbine) 30 Live-steam line (heat-recovery steam 20 generator) 31...33 Bleed-steam line 34 Condenser 35 Feedwater tank 36 Feedwater pump 25 37 Condensate pump 38 Feedwater feed line; (steam generator) 39... High-pressure preheater 40 Feedwater feed line (heat-recovery steam generator) • "30 41, 41a... Condensate line 42, 43' Low-pressure preheater 44, 44' . Heat-recovery steam generator 45... 8 Heat exchanger (heat-recovery steam generator) 35 47', 48" Heat exchanger (heat-recovery steam generator) 49 Exhaust-gas line (gas turbine) 50 Gas turbine 51 Turbine Burner Fuel feed Compressor Generator Shaft

Claims

1. WHAT IS CLAIMED AS NEW AND DESIRED TO BE SECURED BY LETTERS PATENT OF THE UNITED STATES IS: 5 10 15 20 preheating of the condensate and the feedwater.

2. The hybrid power plant as claimed in claim 1, 25 wherein a heat exchanger f^) for the preheating of all the feedwater and a heat exchanger for the preheating of all the condensate are provided in the heat-recovery steam generator ^ Ό , and wherein the condensate and the feedwater for the preheating are " 30 directed, through the corresponding heat exchanger tEr*-' ^e~^¥^ res rr.

3. The hybrid power plant as claimed in claim 2, wherein the heat exchanger j^&^T' for the preheating of the condensate is arranged on the low-temperature side 35 of the heat-recovery steam generator

4. The hybrid power plant as claimed in either of claims 2 or 3, wherein further heat exchangers - -5" ¾~5 " for the generation of steam from the preheated feedwater are connected downstream toward the high- temperature side of the heat exchanger for the preheating of the feedwater in the heat -recovery steam generator {JJk^.

5. The hybrid power plant as claimed in claim ^ wherein a feedwater pump is arranged at the outlet of the feedwater tank wherein the outlet of the feedwater pump is connected to the inlet of the heat exchanger for the preheating of the feedwater, and wherein the outlet of the heat exchanger J^T is connected to the feedwater feed line (3-8 of the steam generator For the Applicants RE1NH0LD COHN AMD