SINGLE SHAFT COMBINED CYCLE PLANT

Abstract: In a system configuration and operating method for a single shaft combined cycle plant comprising a gas turbine (10), an exhaust heat recovery boiler (30) for generating steam using exhaust heat discharged from the gas turbine; and a steam turbine (20) driven by steam generated from the exhaust heat recovery boiler (30), rotors of the gas turbine (10) and rotors of the steam turbine (20) being coupled, and the steam turbine comprising a high pressure turbine (21) being supplied with and driven by high pressure steam generated at a superheater of the exhaust heat recovery boiler (30) and a reheating turbine (22) supplied with and driven by steam that passes through the high pressure turbine (21) and is reheated by a reheater of the exhaust heat recovery boiler (30), the gas turbine (10) operates independantly, a regulated amount of cooling steam is supplied to the steam turbine (20) in order to prevent superheating due to windage loss of the steam turbine (20) rotating in an unventilated state, a bypass path (75) is provided in parallel with the exhaust heat recovery boiler (30) as a path through which cooling steam flows in order to further raise the cooling effect, and each turbine and a condenser (25) are made to communicate so as to make pressure within the turbines low.

Description: Technical Field The present invention relates to a combined cycle plant where a gas turbine and a steam turbine are coupled on a single shaft and the steam turbine is a reheating-type steam turbine. Background Art With reheating-type plants of related single shaft combined cycle plants, in that disclosed in, for example, Japanese Patent Laid-open Publication No. Sho. 62-101809, steam provided to a high-pressure turbine bypasses the high-pressure turbine and is supplied to the reheating turbine. The high-pressure turbine is then made to communicate with a condenser and heating accompanying windage loss of high-pressure turbines and reheating turbines at the time of activation of the steam turbine is prevented EP 0 379 930 discloses a single shaft combined cycle plant comprising a gas turbine and a reheat steam turbine. The reheat steam turbine includes a high pressure turbine section and a low pressure turbine section. A heat recovery steam generator heated by the gas turbine includes a high pressure steam generating section supplying steam to the high pressure steam turbine section through control valves, and a reheater section receiving steam exhausted from the high pressure steam turbine section. A valveless steam conduit is connected between the outlet of the steam reheater section and the inlet of the low pressure turbine section, whereby the steam in the steam reheater and in the valveless steam conduit may freely expand through the low pressure steam turbine. Disclosure of Invention There are cases where steam supplied to a high pressure turbine is superheated by a reheater of an exhaust heat recovery boiler and supplied to a reheating turbine due to the influence of activation conditions, etc. When unit capacity is increased in a single shaft combined cycle plant, output of a steam turbine also rises in accompaniment with increases in output of a gas turbine and the influence of accompanying heat generated due to windage loss occurring due to the rotor blades of the steam turbine being long is substantial. The object of the present invention is to provide a single shaft combined cycle plant and single shaft combined cycle plant activating method capable of suppressing the influence of steam superheated by the exhaust heat recovery boiler at the time of activation of a reheating type single shaft combined cycle plant and capable of providing stability while suppressing the influence of windage loss of the high pressure turbine and the reheating turbine. This object is obtained by a single shaft combined cycle plant comprising the features of claim 1. As a result, at the time of plant activation the following steps take place. A first step of activating the gas turbine and causing the rotational speed thereof to rise, a second step of supplying gas turbine exhaust gas to the exhaust heat recovery boiler and causing steam to be generated at the exhaust heat recovery boiler, a third step of discharging steam remaining within the high pressure turbine using a first discharging means, arranged upstream of a check valve provided at the second steam path, for discharging steam within the high pressure turbine to outside of the high pressure turbine, supplying steam to the reheating turbine and the low pressure turbine using separately provided steam supplying means, and discharging steam passing through the reheating turbine and flowing down the third steam path using a second discharging means, arranged at the third steam path, for discharging steam to outside of the third steam path, a fourth step of supplying steam generated by the superheater to the reheating turbine via the reheater after desired conditions for the steam generated from the exhaust heat recovery boiler are reached and a fifth step of obtaining an output from the steam turbine. Superheating due to windage loss of the high pressure turbine and reheating turbine and steam reheated by the reheater does not flow as high temperature steam into the low temperature reheating piping downstream of the reheating turbine and high pressure turbine. The present invention described above can also work in an effective manner in cases where operation is temporarily halted and then restarted again after only a brief cessation or cases where a long period of time is required between the starting up of the gas turbine and the ventilating of and the obtaining of an output from the steam turbine for some reason at the time of start up. The present invention therefore sets out to pay attention to the fact that, due to conditions at the time of start up etc., steam outputted from the high pressure steam turbine is superheated by the exhaust heat recovery boiler and cannot cool turbines superheated due to windage loss at the time of supplying steam to the reheating turbine, in such a manner that superheating due to windage loss can be suppressed in the high pressure turbine and the reheating turbine by preventing this situation. The reheating type single shaft combined cycle plant is therefore capable of suppressing the influence of superheating of steam by the exhaust heat recovery boiler due to the influence of the activation conditions etc. and providing stability while suppressing the influence of windage loss of the high pressure turbine and the reheating turbine. Brief Description of Drawings FIG. 1 is a structural view of the outline a first embodiment single shaft combined cycle plant of the present invention. FIG. 2 is an outline view of an example of conditions for applying the present invention. FIG. 3 is an outline illustration of a second embodiment of the present invention. Best Mode for Carrying Out the Invention When independent operation of a gas turbine is possible in a combined cycle plant power installation where a gas turbine and steam turbine are coupled on a single shaft, the steam turbine is made to rotate at a high speed by the operation of gas turbine. The rotor blades of the steam turbine are then heated up by so-called windage loss due to frictional heating with steam staying within the turbine as a result of the inflow of gland sealing steam and when this amount of heating due to this windage loss builds up, overheating of the turbine at high temperatures can be suppressed. In order to prevent these temperature rises in a related single shaft combined cycle plant, accumulation of heat is avoided and temperature rises within the steam turbine are prevented by only supplying cooling steam to an intermediate and low pressure turbine where temperature may rise due to windage loss with long rotor blades and having an amount of heat generated by windage loss flow away at a following stage. This is described below. The present invention is by no means limited to the embodiments described below. FIG. 1 is a structural view of the outline of a first embodiment of a reheating-type single shaft combined cycle power installation of the present invention. An outline of common portions of the present invention is described in the following. Numeral 10 indicates a gas turbine, numeral 20 indicates a steam turbine, numeral 21 indicates a high pressure turbine, numeral 22 indicates a reheating type turbine, numeral 23 indicates a low pressure turbine, numeral 25 indicates a condenser and numeral 62 indicates a generator. Further, at an exhaust heat recovery boiler 30 taking exhaust gas 91 of the gas turbine 10 as a heat source, numeral 31 indicates a low pressure drum, numeral 32 indicates an intermediate pressure drum, numeral 33 indicates a high pressure drum and numeral 34 indicates a reheater. A rotor 64 communicates with the gas turbine 10 and the steam turbine 20. Numeral 71 represents a high pressure steam pipe for connecting the high pressure drum 33 and the high pressure turbine 21. Numeral 41 represents a high pressure steam valve for controlling the amount of steam generated at the high pressure drum 33 that is supplied to the high pressure turbine 21. Numeral 72 represents a low temperature reheating steam pipe for connecting the high pressure turbine 21 and the reheater 34. Numeral 73 represents a high temperature reheating steam pipe for connecting the reheater 34 and the reheating type turbine 22. Numeral 42 is a reheated steam valve for controlling the amount of steam reheated by the reheater 34 that is supplied to the reheating type turbine 22. Numeral 74 represents a crossover pipe for connecting an outlet of the reheating type turbine 22 and an inlet of the low pressure turbine 23. Numeral 83 represents a high pressure turbine bypass pipe and numeral 47 represents a high pressure turbine bypass valve. Numeral 84 represents a reheating turbine bypass pipe and numeral 52 represents a reheating turbine bypass valve. Numeral 85 represents a high pressure turbine piping system, numeral 53 represents a high pressure regulation valve, numeral 85 represents a low pressure steam pipe and numeral 43 represents a low pressure steam valve for controlling the amount of low pressure steam generated at the low pressure drum 31 that is supplied to the low pressure turbine 23. Numeral 46 represents an intermediate pressure steam valve for controlling the amount of steam of intermediate pressure generated at the intermediate pressure drum 32 that is supplied to the reheating type turbine 22. Numeral 92 represents a water supply pipe for steam condensed by the condenser, numeral 63 represents a low pressure water supply pump, numeral 64 represents an intermediate pressure water supply pump and numeral 65 represents a high pressure water supply pump. Supplied water that has been raised in pressure at the low pressure water supply pump 63 is raised to a high pressure so as to correspond to the intermediate pressure drum 32 and the high pressure drum 33. Signal lines and control means etc. are omitted. The present invention prevents overheating of a reheating type single shaft combined cycle plant where a steam piping system connecting a high pressure turbine and a reheating turbine is divided using valves. During normal operation of the plant, exhaust gas 91 from the gas turbine 10 is supplied to the exhaust heat recovery boiler 30. The exhaust heat recovery boiler 30 performs heat exchanging using a plurality of heat exchangers taking the exhaust gas 91 as a heat source so that high pressure steam, intermediate pressure steam and low pressure steam is generated. High pressure steam generated by the high pressure drum 33 passes through the high pressure steam pipe 71 and is supplied to the high pressure turbine 21 via the high pressure steam valve 41. Steam is therefore supplied at a temperature of approximately 538 °C at a flow rate of approximately 180 t/h at a pressure of approximately 100 ata. Low temperature reheated steam flowing in the low temperature reheating steam pipe 72 after the high pressure turbine 21 has done its job becomes high temperature regenerated steam regenerated at the reheater 34. The high temperature regenerated steam flows through the high temperature reheating steam pipe 73 and is supplied to the reheating type turbine 22 via the reheated steam valve 42. For example, steam is supplied at a pressure of 25 ata at approximately the same temperature as the steam supplied to the high pressure turbine. Steam passing through the reheating type turbine 22 passes through the crossover pipe 74 and is supplied to the low pressure turbine 23. For example, steam is supplied at a temperature lower than that of supplying to the reheating turbine at a pressure of approximately 4 ata. Steam passing through the low pressure turbine 23 is then condensed at the condenser 25. This is again supplied to the exhaust heat recovery boiler 30 using the low pressure water supply pump 63 via the water supply pipe 92 and is reutilized as a steam source. As an example, the condenser attains a steam pressure of approximately 0.05 ata using a vacuum pump. Further, electricity is generated by the generator 62 connected to the intermediate pressure water supply pump 64 as a result of rotations of the rotor 64 to which the gas turbine 10 and the steam turbine 20 are coupled. Intermediate steam generated from the intermediate pressure drum 32 can then be mixed at the low temperature reheating steam pipe 72 via the intermediate pressure steam valve 46 shown in the drawings or mixed at the high temperature reheating steam pipe 73 via a further intermediate steam valve 48. Further, the low pressure steam of the low pressure drum 31 is supplied to the crossover pipe 74 via the low pressure steam valve 43 and the amount of steam going to the low pressure turbine 23 can be increased. A flow of, for example, approximately 25t/h can be achieved, although this differs depending on the scale of the plant. The intermediate pressure steam and the low pressure steam can then be individually regulated to the desired steam conditions using an intermediate pressure steam regulating valve 66 (or 67) and a low pressure steam regulating valve 68. Next, an outline at the time of start up is shown in the following with reference to FIG. 1 and FIG. 2. The single shaft combined cycle plant of the present invention first ignites the gas turbine 10 and sequentially raises the rotational speed. When the rated rotational speed is approached, outputting from the gas turbine 10 is commenced. If the exhaust heat recovery boiler 30 reaches prescribed steam conditions due to the exhaust gas 91 of the gas turbine, the steam turbine 20 is completely ventilated and the steam turbine 20 starts up. The high pressure steam valve 41, intermediate pressure steam valve 46 (or 48), the low pressure steam valve 43 and the reheated steam valve 42, for example, are closed until the ventilation to the steam turbine 20 from activation of the gas turbine 10 commences. For example, the steam generated at the high pressure drum 33 is supplied to the condenser via the high pressure regulation valve 53 and the high pressure turbine piping system 85 so that raising of the steam conditions can be awaited. Further, when a high pressure turbine bypass system is installed, improvement of the steam conditions can also be awaited by opening the high pressure turbine bypass valve 47, allowing steam to flow through the low temperature reheating steam pipe 72 via the high pressure turbine bypass pipe 83 and opening the reheating turbine bypass valve 52 so that steam flows from the high temperature reheating steam pipe 73 to the condenser via the reheating turbine bypass pipe 84. In order to obtain the output from the steam turbine 20, the high pressure regulation valve 53 is closed and the high pressure steam valve 41 is opened so that steam generated by the exhaust heat recovery boiler 30 is supplied to the high pressure turbine 21. Alternatively, for example, during a time period in which a rated A further embodiment is described in the following. A second embodiment is now described using the outline configuration view of FIG. 1 and the outline illustration of the embodiment of FIG. 3. In addition to the common configuration, the supplementary steam supplying device 61b, regulating valve 55b and check valve 56b are arranged in such a manner as to be connected by low pressure steam piping. A piping system 81 communicating with the condenser 25 is provided at the high temperature reheating steam pipe 73 on the downstream side of the reheated steam valve 42 and is provided with a reheating turbine discharge valve 51. The high pressure turbine piping system 82 communicating with the condenser 25 also communicates with the low temperature reheating steam pipe 72 and is provided with the discharge valve 57. The check valve 58 is provided downstream of the part of the low temperature reheating steam pipe 72 that communicates with the high pressure turbine piping system 82. From the time of activation of the gas turbine unit 1 there is ventilation to the steam turbine. The high pressure turbine 21, reheating type turbine 22 and low pressure turbine 23 communicate with the condenser 25. Cooling steam is supplied to the reheating type turbine 22 and the low pressure turbine 23 and heating up due to the windage loss of these turbines is prevented. Steam from the supplementary steam supplying device 61b flows to the low pressure turbine 23 and the reheating type turbine 22. The amount of steam flowing differs depending on the size of the plant but, for example, flows of 16t/h on the low pressure turbine side and 2t/h on the reheating turbine side are possible. The supplementary steam supplying device 61b supplies to the low pressure steam pipe 86 via the regulating valve 55b and check valve 56b. Steam is supplied to the reheating type turbine 22 via the low pressure steam valve 43 controlled to be open to an extent that allows the required amount of steam to flow. Steam that passes through the reheating type turbine 22 enters the high temperature reheating steam pipe 73, flows into the piping system 81 and is discharged from the high temperature reheating steam pipe 73 via the reheating turbine discharge valve 51. This is then supplied to the condenser 25. As the high pressure steam valve 41 is open, steam remaining at the high pressure turbine 21 enters the low temperature reheating steam pipe 72, flows through the high pressure turbine piping system 82 and is discharged outside the low temperature reheating steam pipe system 72 via the discharge valve 57 so as to be supplied to the condenser 25 thereafter. In addition to the amount of heat generated due to windage loss being proportional to the vane wheel diameter and the rotor blade length, the amount of heat generated due to windage loss is also proportional to the specific weight of the steam within the atmosphere to which the rotor blades are exposed within the steam turbine, i.e. the steam pressure. It is, however, possible to reduce the amount of heat generated due to windage loss by lowering the pressure within the steam turbine 20 to as great an extent as possible. As a means for achieving this, a method is employed where the flow of steam to the high pressure turbine 21 and the reheating type turbine 22 is interrupted to as great an extent as possible, each steam turbine 20 is connected to a condenser that is in a vacuum state and the pressure within the steam turbine 20 is reduced. In order to achieve low pressure conditions within the high pressure turbine 21, the high pressure steam valve 41 is closed completely, steam generated from the high pressure drum 33 is stopped and the check valve 58 is installed at the low temperature reheating steam pipe 72 at the discharge part side of the high pressure turbine 21 so as to isolate the reheater 34. Further, the high pressure turbine piping system 82 is installed so as to connect directly with the condenser 25 and the remaining steam is forcibly discharged to the condenser 25 by the flowing in of gland sealed steam within the high pressure turbine 21. Further, with the reheating type turbine 22 also, by completely closing the reheated steam valve 42 so as to interrupt the reheated steam and similarly installing the piping system 81 so as to directly connect with the condenser 25 at the inlet part of the reheating type turbine 22, steam within the reheating type turbine 22 can be forcibly discharged to the condenser 25 and a low pressure state can be attained within the reheating type turbine 22. As the rotor blades of the low pressure turbine 23 are long and generate a large amount of heat under vacuum conditions due to a condenser producing a small amount of heat in response to windage loss it is therefore preferable to supply cooling steam to carry out forcible cooling. This vacuum is a vacuum of an extent obtained by a vacuum pump connected to the condenser 25 or a vacuum of an extent obtained by coupling with the condenser, the same being applied to the following cases. As a result, supplying of reheated steam to the reheating type turbine 22, heat generation due to windage loss and remaining heat are suppressed. Further, some of the steam supplied from the low pressure steam valve 43 diverges at the crossover pipe 74 and is supplied to the low pressure turbine 23. Supplying of steam superheated by the reheater 34 to the turbines can be suppressed and rises in the temperature of each turbine can be prevented. In this embodiment, the influence of the exhaust heat recovery boiler 30 can be completely interrupted using the reheated steam valve 42 and the check valve 58 and the capacity of the supplementary steam generator can be made small. Further, by opening the high pressure steam valve 41, steam within the high pressure turbine 21 flows through the high pressure turbine piping system 82 to the condenser 25 and the inside of the high pressure turbine 21 is put under low pressure. Alternatively, when the high pressure steam valve 41 is opened to a limited extent, some of the steam from the high pressure drum 33 may be supplied to the high pressure turbine 21 as cooling steam. For example, steam that passes through the high pressure turbine 21 flows from the low temperature reheating steam pipe 72 to the high pressure turbine piping system 82 and flows into the condenser 25. Even in such a case, windage loss can be suppressed at each of the turbines without being affected by reheating due to the reheater 34. After this, if the steam from the exhaust heat recovery boiler 30 has reached the desired condition and the conditions are sufficient to obtain an output from the steam turbine, the reheated steam valve 42 is opened, the low pressure steam valve 43 is closed, the connection control valve 45 is closed, the high pressure regulation valve 53 is closed (or the reheating turbine bypass valve 52 is closed and the high pressure turbine bypass valve 47 is closed), the high pressure steam valve 41 is opened and steam generated by the exhaust heat recovery boiler 30 is supplied to the high pressure turbine, the reheating turbine and the low pressure turbine for activation. Alternatively the high pressure regulation valve 53 is closed (or the reheating turbine bypass valve 52 is closed), the reheated steam valve 42 is opened, the low pressure steam valve 43 is closed and the connection control valve 45 is closed, so that steam generated by the exhaust heat recovery boiler 30 is supplied to the reheating turbine, the reheating turbine and low pressure turbine are activated and the high pressure turbine is sequentially activated. If ventilation has commenced, the amount of steam supplied is gradually increased and an output from the steam turbine can be obtained. , After the step of supplying cooling steam at the time of activation is finished, practically all of the steam generated at the high pressure drum 33 is supplied to the reheater 34. The aforementioned determining elements and conditions can be used for the conditions etc. of steam outputted from the exhaust heat recovery boiler. FIG. 2 is an outline view of an example of a situation to which the present invention is applied, where A shows the case at the time of normal operation and B shows the case where the time for providing cooling steam is long. In the normal operation A, the gas turbine 10 is activated and as the steam turbine that is in a non-ventilated state causes overheating to occur due to windage loss while increasing it's speed, supplying of cooling steam is carried out. When the steam generating conditions of the exhaust heat recovery boiler 30 fall within a prescribed range in accompaniment with the rising of the output of the gas turbine 10, complete ventilation to the steam turbine 20 is carried out, an output from the steam turbine 20 is obtained and the cooling steam is not required. However, as shown in B, when the time for which the gas turbine 10 operates independently prior to the starting of complete ventilation of the steam turbine 20 is prolonged, such as at the time of the occurrence of activation congestion, reactivation not long after halting of operation, or when the checking of other equipment is necessary, it is possible that the exhaust heat recovery boiler 30 will rise to a high temperature. The time until complete ventilation is influenced by the metal temperature conditions etc. of the steam turbine and can be a few minutes or, as in the case of B, a few hours. In the case of B, when a system is present for supplying cooling steam via the exhaust heat recovery boiler 30 to the reheating type turbine 22, the cooling steam is superheated at the reheater 34 of the exhaust heat recovery boiler 30 and the superheated cooling steam is supplied to the reheating turbine. In this case, the present invention shown in each of the above embodiments operates effectively when steam generated by the exhaust heat recovery boiler 30 is reheated and not supplied to the reheating type turbine 22.

Claims: A single shaft combined cycle plant, comprising: a gas turbine (10); an exhaust heat recovery boiler (30) for generating steam using exhaust heat discharged from the gas turbine (10); and a steam turbine (20) driven by steam generated from the exhaust heat recovery boiler (30), rotors of the gas turbine (10) and rotors of the steam turbine (20) being coupled, the steam turbine (20) comprising a high pressure turbine (21) being driven by high pressure steam generated at a superheater (33) of the exhaust heat recovery boiler (30) supplied via a first steam path (71), and a reheating turbine (22) supplied with and driven by steam flowing through the high pressure turbine (21) and a second steam path (72), being reheated by a reheater (34) of the exhaust heat recovery boiler (30), and flowing through a third steam path (73) after reheating, characterized in that first discharging means (57) is arranged upstream of a check valve (58) provided at the second steam path (72) for discharging steam within the high pressure turbine (21) to outside of the high pressure turbine; separately provided steam supplying means (61 b) supplies steam to the reheating turbine (22); second discharging means (51) discharges steam, that flows through the third steam path (73) after being supplied from the steam supplying means via the reheating turbine, to outside of the third steam path (73), the second discharging means (51) being positioned downstream from a reheated steam valve (42) provided at the third steam path (73) for regulating the amount of steam flowing to the reheating turbine (22).

Inventors: HASHIMOTO TSUGUO, URUSHIDANI HARUO, WADA NORIHISA, HASHIMOTO, TSUGUO, URUSHIDANI, HARUO, WADA, NORIHISA
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1996
Main classification: F01K23
IPC codes: F01K23, F01K13