Pressurized fluidized bed combustion combined cycle power plant and method of operating the same

Abstract: A pressurized fluidized bed combustion combined cycle power plant has a gas turbine unit of single spindle type in which a turbine (2) driven by combustion gas from burning of coal in a pressurized fluidized bed combustion boiler (4) drives an electrical generator (3) at constant speed and drives a compressor (1) supplying compressed combustion air to the boiler (4). To permit partial load running, control means are provided to effect, in dependence on an operating load of the boiler, control of at least one of (a) the flow rate of said combustion air into said boiler, and (b) the operating pressure in said combustion chamber of said boiler. The control means may be for example a valve (19) controlling a by-pass flow of the combustion air and/or inlet guide vanes (20) of the compressor (1).

Description: The present invention relates to a pressurized fluidized bed combustion combined cycle power plant, more particularly a combined cycle power plant comprising a pressurized fluidized bed combustion boiler for burning coal and producing steam, a gas turbine, a compressor and a generator. The steam may be used to drive a steam turbine. The invention is concerned with maintaining a stable fluidization in the pressurized fluidized bed combustion boiler even at partial load. In the prior art, there is known a combined plant which is constructed mainly of a gas turbine, a steam turbine and a waste heat recovery boiler so that the steam turbine may be driven with the steam produced in the waste heat recovery boiler by the exhaust gases from the gas turbine. Such a combined plant using a pressurized fluidized bed combustion boiler as a combustor for the gas turbine is called the "pressurized fluidized bed combustion combined cycle power plant". Most known pressurized fluidized bed combustion combined cycle power plants are constructed by adopting a double-spindle type gas turbine unit as shown in Fig. 2 of the present drawings, described below. At full-load run of this plant, the combustion air boosted by the gas turbine compressor is wholly introduced into the pressurized fluidized bed combustion boiler, in which a fuel or coal is poured and burned to operate the gas turbine. On the other hand, the steam is produced by recovering the heat in the pressurized fluidized bed combustion boiler and the waste heat recovery boiler of the gas turbine and is led into the steam turbine to operate the latter. At partial load, on the other hand, the combustion air flow rate and the pressure in the pressurized fluidized bed combustion boiler are varied for the partial load run of the plant by changing the speed of the gas turbine compressor. If, however, a single-spindle gas turbine unit is adopted, the speeds of both the compressor and the turbine are always the same, because the generator driven by the same spindle must rotate at constant speed. As a result, full-load run is performed as with the double-spindle gas turbine. For a partial load run, however, the discharge air flow rate of the gas turbine compressor is not changed from that in the full-load run, nor is the pressure in the pressurized fluidized bed combustion boiler changed, so that in principle partial load run of the pressurized fluidized bed combustion combined cycle power plant is impossible. The present invention overcomes this problem, as described below. JP-A-55-164732 shows a power plant having a double-spindle gas turbine. In order to limit the temperature of the combustion gas reaching the turbine, there is a bypass line controlled by a valve, between the compressor outlet line and the turbine inlet line. Other prior art documents showing a control element or division in the compressor outlet line include JP-A-63-75406 where the line divides, to provide two, controlled air flows to the pressurized fluidized bed combustor, in order to improve combustion efficiency by increasing the temperature at the top of the combustor. Similarly in JP-A-57-212309 the compressed air line divides, in order to supply air to a second burner arranged in the combustion gas line to the gas turbine. In US-A-4838209, there are shown valves in the compressed air line, the gas turbine inlet line and a bypass line connecting these two lines. These two lines are used for emergency shut-down. US-A-4852345 shows a branch line from the main compressed air line; the branch has a valve and supplies air to a distributor for cooling fluidized bed material in an ash chamber. After cooling the bed material, this air is used in the combustion. A general review of the development of pressurized fluidized bed combustion and its application in combined cycle power plants is given by Pillai in pages 555-593 of "Electricity: efficient end-use and new generation technologies and their planning implications", published by Lund University Press, Sweden and Chartwell-Bratt, England. The prior art thus far described is disadvantageous for the design of the pressurized fluidized bed combustion combined cycle power plant in that the type of gas turbine used is restricted. In order to reduce this restriction, therefore, it is very effective, for the pressurized fluidized bed combustion combined cycle power plant using the single-spindle gas turbine unit, if the partial load run is possible as in a pressurized fluidized bed combustion combined cycle power plant using a double-spindle gas turbine unit. It is mentioned also that DE-A-3801886 illustrates pressurized fluidized bed combustion combined cycle power plants having a single spindle gas turbine unit. In one form of the apparatus described there is a booster compressor for the supply of air to the fluidized bed boiler and also a by-pass valve for control of air flow from the compressor of the gas turbine unit to the boiler. In another form of apparatus shown there is the booster compressor and also two valves controlling flow rate from respective heat exchanger regions in the boiler to the turbine of the gas turbine unit, these two valves being provided in order to adjust the distribution of the flue gas-fly ash stream between the two heat exchanger regions. DE-A-3123391 is similarly mentioned as showing a similar combined cycle power plant in which there is a by-pass valve for control of air flow from the compressor of the gas turbine unit to the boiler and also a valve controlling flow through an expansion turbine operated by compressed air from the compressor of the gas turbine unit. An object of the present invention is thus to enable the pressurized fluidized bed combustion combined cycle power plant to perform at partial load even when a single-spindle gas turbine unit is used. In one aspect therefore, the invention provides, a pressurized fluidized bed combustion combustion cycle power plant as set out in claim 1. The invention further provides a method of operating such a plant as set out in claim 8. A gas turbine unit of single spindle type used in this invention has a compressor and a turbine on a common spindle, the turbine having, at least at full load of the plant, an inlet pressure which is essentially equal to the operating pressure of the boiler and an outlet pressure which is essentially equal to the combustion gas exhaust pressure of the plant. Small pressure loss may be caused by for example dust separators upstream of the turbine, but in principle the full pressure drop is across the turbine. This is in contrast with the double-spindle type where two turbines, on different spindles, are in series. By the invention control of the combustion air flow rate and/or the operating pressure so as to maintain support of the combustion of the coal over a load range of the boiler from full load to less than 80% of full load, even more advantageously from full load to less than 60% of full load. The control is achieved by adjustment of at least two adjusting means, each adapted to adjust at least one of the combustion air flow rate and the operating pressure. In the attached drawings, various combinations of such adjusting means are illustrated. Such adjusting means may include two or more of (i) a throttle valve controlling air pressure at the compressor inlet, (ii) vanes controlling air flow rate at the compressor inlet, (iii) a bypass valve controlling air flow rate from the compressor to the boiler, (iv) drive means of a booster compressor controlling pressure of air supplied from the compressor to the boiler, (v) a valve controlling flow through an expansion turbine operated by compressed air from the compressor, (vi) a valve controlling combustion gas flow rate from the boiler to the single spindle turbine, and (vii) a valve controlling combustion gas flow from the boiler to a second gas turbine which is not mounted on the spindle of the gas turbine unit, excluding certain combinations as set out in claim 1. In one preferred form of the invention, a power plant has adjustable vanes for controlling air flow rate into the compressor, a conduit extending from the compressor to the boiler for the pressurized combustion air, a conduit extending from the boiler to the turbine for said combustion gas, a by-pass connecting the first conduit to the second conduit, and flow control means for controlling the air flow rate in said by-pass. The control is effected by control of at least one of the vanes and the flow control means of said bypass. In this embodiment, preferably the method comprises adjusting the vanes in order to control the plant operation over a first range of operating load of the plant, and adjusting the flow control means of the bypass in order to control the plant operation over a second range of operating load of the plant, the first range being closer to the full operating load of the plant than the second range. It is furthermore preferred to control at least one of the combustion air flow rate and the operating pressure in order to control the temperature of the inlet gas to said gas turbine in dependence on the operating load of the plant. The outlet temperature of the combustion gas from the boiler is preferably controlled in order to control the outlet temperature of the gas turbine, thereby to improve the plant efficiency. In another embodiment, the plant has a conduit extending from the compressor to the boiler for the pressurized combustion air, a branch conduit from said conduit, an air expansion turbine connected to the branch conduit and flow control means for controlling flow in the branch conduit to the air expansion turbine, the flow control means being controlled to effect the control of at least one of the combustion air flow rate to the boiler and the operating pressure in the boiler. Suitably, the plant has a sensor for at least one of temperature and pressure of the combustion gas at entry to the gas turbine, and the flow control means for the air expansion turbine is adjusted in dependence on an output of the sensor, in order to maintain the combustion air flow rate and the operating pressure within a predetermined relationship to each other. Embodiments of the invention are described below by way of non-limitative example with reference to the accompanying diagrammatic drawings, in which:- Fig. 1 shows diagrammatically a pressurized fluidized bed combustion combined cycle power plant system incorporating a single-spindle type gas turbine to which the present invention is applied. Fig. 2 shows diagrammatically an example of a conventional pressurized fluidized bed combustion combined cycle power plant system in which a double-spindle type gas turbine is applied. Fig. 3 is a graph showing characteristics between air flow rate and combustion gas amount and their pressures supplied to a pressurized fluidized bed combustion (P-FBC) boiler (under a condition where fluidized velocity is constant). Figs. 4 and 5, Figs. 6 and 7, Figs. 8 and 9, Figs. 10 and 11 and Figs. 12 and 13 are in each case a diagram of a pressurized fluidized bed combustion combined cycle power plant embodying the invention and a graph illustrating its partial load characteristics. Figs. 14 and 15 show a further embodiment of a power plant system of the present invention and its partial load characteristic (with combined control of a compressor inlet guide vane structure and a bypass valve). Figs. 16 and 17 show another embodiment of a power plant system of the present invention and its partial load characteristic (with combined control of a throttle valve and a bypass valve). Figs. 18 and 19 show for interest another power plant system and its partial load characteristic (with combined control of an expansion turbine and a bypass valve). However this system is excluded from the claims of this specification. Figs. 20 and 21 also show for interest another power plant system and its partial load characteristic (with combined control of a booster compressor and a bypass valve). However this system too is excluded from the claims of this specification. Figs. 22 and 23 show another embodiment of a power plant system of the present invention and its partial load characteristic (with combined control of a throttle valve and a compressor inlet guide vane structure). Figs. 24 and 25 show a further embodiment of a power plant system of the present invention and its partial load characteristic (with combined control of a compressor inlet guide vane structure and an expansion turbine). Figs. 26 and 27 show another embodiment of a power plant system of the present invention and its partial load characteristic (with combined control of a compressor inlet guide vane structure and a booster compressor). Figs. 28 and 29 show yet another embodiment of a power plant system of the present inventin and its partial load characteristic (with combined control of a throttle valve and an expansion turbine). Figs. 30 and 31 show another embodiment of a power plant system of the present invention and its partial load characteristic (with combined control of a throttle valve and a booster compressor). Figs. 32 and 33 show another embodiment of a power plant system of the present invention and its partial load characteristic (with combined control of a booster compressor and an expansion turbine). Figs. 34 and 35 show another embodiment of a power plant system of the present invention and its partial load characteristic (with combined control of a throttle valve, a compressor inlet guide vane structure, a bypass valve and a boosting compressor). Fig. 36 shows yet another embodiment of a power plant system of the present invention (with combined control of a throttle valve, a compressor inlet guide vane, a bypass valve structure and a booster compressor). Fig. 37 shows another embodiment of a power plant system of the present invention (with combined control of a throttle valve, a compressor inlet guide vane structure, a bypass valve, a booster compressor and an expansion turbine). Fig. 38 shows another embodiment of a power plant system of the present invention (with control of inlet flow rate to the main expansion turbine). Fig. 39 is a further embodiment of a power plant system of the present invention, similar to that of Fig. 10, but having in addition a temperature feedback control. Fig. 40 is a graph illustrating the use of the temperature feedback control of Fig. 39. In the following description and drawings, the same reference numerals are used for corresponding parts of the plant. For brevity such parts are not described repeatedly. Referring to Fig. 1, there is exemplified the case of a schematic system of a pressurized fluidized bed combustion combined cycle power plant which is constructed of a pressurized fluidized bed combustion boiler apparatus, a single spindle gas turbine apparatus, a steam turbine apparatus and a power plant apparatus. The air 21 introduced into a gas turbine compressor 1 is pressurized to form high-pressure air 22 and is used to burn pulverized coal in a pressurized fluidized bed combustion boiler 4 so that the resultant high-temperature and high-pressure gases 23 expand to do work in the gas turbine 2. The gas turbine 2 rotates a generator 3 to generate electric power. After this, the gas turbine exhaust gases 24 exchange heat with supply water 36 in a feed water heater 10 and then are released at a low temperature to the atmosphere as gas turbine exhaust. Due to requirements, e.g. of electricity generation, the rotors of the compressor 1, the turbine 2 and the generator 3 are all rotated at the same constant speed, being mounted on a single spindle. On the other hand, the hot feed water 37 fed to the boiler 4 is heated by the combustion in the boiler 4 and fed as high-temperature and high-pressure steam 31 to rotationally drive a high-pressure steam turbine 5. Then, the expanded low-temperature and low-pressure steam 32 is reheated by the boiler 4. The resultant high-temperature and high-pressure steam 33 is fed to rotate a reheated steam turbine 6 so that electric power is generated by a steam turbine generator 7. The steam thus having worked in the steam turbine 6 is turned into low-temperature and low-pressure steam 34 and undergoes heat exchange with brine 35 in a steam condenser 8 so that it is condensed into water and collected in the steam condenser 8. This condensed water is boosted by a high-pressure water supply pump 9, which is disposed at the exit of the steam condenser 8, to be supplied to the feed water heater 10. In the pressurized fluidized bed combustion combined cycle power plant thus constructed, the single-spindle gas turbine plant is adopted so that the full-load run is driven by the method thus far described. However, during a partial load run the discharge air flow rate of the gas turbine compressor 1 is unchanged from that during the full load run, since the spindle still rotates at the same speed. Thus, the pressure in the boiler 4 during a partial load run is not changed so that in theory a partial load run of the power plant cannot be performed. On the other hand, in the combined cycle power plant having a boiling water type pressurized fluidized bed combustion boiler, to enable a partial load run while maintaining the air/fuel ratio within a predetermined control range, the absolute amounts of air and fuel have to be changed. To achieve the combustion reaction while maintaining the fluidization in a stable state, the ratios of the air flow rate for combustion use, the combustion gas flow rate in the boiler or the combustion gas flow rate at the outlet of the boiler to the pressures at these respective positions have to be controlled to substantially the same ratio as at the full rated load over a predetermined control range, and the fluidization velocity in the reactor has to be kept constant. On the other hand, in the plant of Fig. 2, respresenting the prior art proposal using a double-spindle compressor/gas-turbine, there are a first compressor 1 and turbine 2 on a first spindle together with a generator 3, and a second compressor 11 and second, low-pressure turbine 12 on a second spindle. An intermediate cooler 13 is provided between the compressors 11 and 1. The compressed air flow 22 to the boiler 4 can be varied by controlling the speed of the compressor 11 and turbine 12. Fig. 3 shows an ideal control condition of the coal-burning pressurized fluidized bed combustion (P-FBC) boiler 4 of Fig. 1, in which a control range is established on both sides of a target control line which represents a constant ratio of air flow rate/pressure or combustion gas flow rate/pressure over a range from full load to low load of the power plant. In this control range, stable performance of the P-FBC boiler is achieved. Figs. 4 to 39 show various ways in which control within the desired control range is achieved, over a load range. In the characteristics diagrams, e.g. Fig. 5, the actual control achievable is compared with the desired control range. Fig. 4 shows a system diagram in which a bypass valve 19 for adjusting air flow rate is disposed between the combustion air flow 22 and the combustion gas flow 23, and Fig. 5 shows the control characteristic thereof. As is apparent from the drawing, the bypass air flow rate adjustment control shows a characteristic of (pressure/flow rate) ≧ 1. Control within the desired control range is possible over a relatively small partial load control range. Fig. 6 shows a system diagram in which a compressor inlet guide vane structure 20 is provided and opening control of the vane structure 20 is performed to control air flow rate, and Fig. 7 shows the control characteristic thereof. The gas turbine inlet guide vane opening control shows a characteristic of (pressure/flow rate) < 1. Again the partial load control range is small. Fig. 8 shows a system diagram in which a controlled throttle valve (throttle damper) 17 is disposed in the inlet air flow 21 to the compressor 1, and Fig. 9 shows the control characteristic thereof. Control by the throttle valve shows a characteristic of (pressure/flow rate) < 1. Fig. 10 shows a system diagram in which control of air flow rate is performed by an expansion turbine 27 branching from the air flow 22, the flow rate being controlled by a valve 27a. Fig. 11 shows the control characteristic thereof. Control by means of the expansion turbine 27 shows a characteristic of (pressure/flow rate) about 1. Fig. 12 shows a system diagram in which control of air flow rate to the boiler 4 is achieved by a booster compressor 14 driven by an adjustable motor M and Fig. 13 shows the control characteristic thereof. Control by the booster compressor 14 shows a characteristic of (pressure/flow rate) < 1, in the upper partial load region. In the present invention it is preferred by combining two or more types of control elements (e.g. a control element associated with the relationship of pressure/flow rate ≧ 1, and a control element associated with the relationship of pressure/flow rate ≦ 1) to achieve a better control over a larger partial load range. In the next embodiments combinations of the control elements are explained. Fig. 14 shows a system diagram of a boiling water type pressurized fluidized bed combustion combined cycle power plant in which both a gas turbine compressor inlet guide vane structure 20 controlling the air flow rate at the inlet of the compressor 1 and an adjustable bypass valve 19 controlling the air flow rate supplied from the outlet of the compressor to the boiler are provided. Fig. 15 shows the partial load characteristic of the air flow rate supplied to the boiler 4 (or combustion gas flow rate) and the air pressure charged to the boiler 4 (or combustion gas pressure), when the gas turbine compressor inlet guide vane opening control and the bypass air flow rate control are combined. As will be seen from the drawing, by this control method control achieving stable fluidization in the boiler 4 within a predetermined ratio of pressure/flow rate is enabled over a wide partial load range. The control method may be selected from the following methods (1) - (4):- (1) a control method performed within a predetermined control range in which a control unit having a relationship of (pressure/flow rate) ≧ 1 precedes; in this case a control unit (air flow rate control with the bypass valve 19) having a relationship of (pressure/flow rate) ≧ 1 is operated precedingly, and subsequently a control unit having a relationship of (pressure/flow rate) ≦ 1 is operated. (2) a control method performed within a predetermined control range in which a control unit having a relationship of (pressure/flow rate) ≦ 1 precedes; in this case a control unit (air flow rate control with the compressor inlet guide vane structure 20) having a relationship of (pressure/flow rate) ≦ 1 is operated precedingly, and subsequently a control unit having a relationship of (pressure/flow rate) ≧ 1 is operated. (3) a simultaneous control method performed within a predetermined control range in which a control unit having a relationship of (pressure/flow rate) ≧ 1 and a control unit having a relationship of (pressure/flow rate) ≦ 1 are controlled together. (4) a control method performed within a predetermined control range in which the variation bands of the pressure and flow rate in a control unit having a relationship of (pressure/flow rate) ≧ 1 and a control unit having a relationship of (pressure/flow rate) ≦ 1 are varied and the control unit having the relationship of (pressure/flow rate) ≧ 1 and the control unit having the relationship of (pressure/flow rate) ≦ 1 are effected alternatively and repeatedly. Fig. 14 also shows a schematic control system for the plant. The steam turbine generator 7 end output A and gas turbine generator 3 end output B are integrated in an adder, and the difference between the total and a plant target load required at a central operation room is measured by a comparator. In a proportional integrator, load adjustment required to cause the difference measured at the comparator to be zero is effected, and a fuel control signal is sent to a fuel controller and a fluidized bed layer height controller. In the fuel controller, supply of coal is controlled in response to the load demand. In the layer height controller, layer height is controlled according to the load. Further, therein, in order to control the air flow rate for combustion to the pressurized fluidized bed combustion boiler, control signals are sent to controllers of each of the compressor IGV (inlet guide vane structure 20) and the compressor outlet air flow rate bypass valve 19. The IGV 20 and the bypass valve 19 send feedback signals to the IGV and the bypass valve controllers through the layer height controller so as to achieve an appropriate layer height. On the other hand, with layer height determined according to load and in order to maintain stable combustion, fluidization velocity must be kept constant, so that change of pressure detected by a sensor Px in the combustion gas of the pressurized fluidized bed combustion boiler is detected under a condition of a constant layer temperature measured by a sensor Tx, and the detected pressure change is sent to the layer height controller, wherein flow rate and pressure are controlled so that fluidized velocity is constant. Fig. 16 shows a power plant in which a throttle valve 17 (or throttle damper or throttle vane) for controlling the compressor inlet air pressure and a bypass valve 19 for controlling air flow rate supplied from the compressor outlet to the boiler are both provided. Fig. 17 shows the corresponding partial load characteristic of the air flow rate and the air pressure in the boiler when pressure control by the throttle valve 17 (or throttle damper or throttle vane) and flow rate control by the bypass valve 19 are combined. As in the case of Figs. 14 and 15, the control method can be selected from methods corresponding to the methods (1) - (4) outlined above. Control over a wide partial load range is obtainable. The bypass valve 19 is a control unit of relationship (pressure/flow rate) ≧ 1, and the throttle valve a control unit of relationship (pressure/flow rate) ≦ 1. Fig. 18 shows a system diagram of a power plant which is provided with both an expansion turbine 27 disposed in a conduit line extracting the air flow from the outlet of the compressor 1 to a line other than the boiler supply line, and a bypass valve 19 controlling the supply air flow rate to the boiler from the outlet of the compressor. Flow control to the turbine 27 is effected by a valve 27a. Fig. 19 shows the corresponding partial load characteristic of the air flow rate and the air pressure when flow rate control by the expansion turbine 27 and flow rate control by the bypass valve 19 are combined. As in the cases of Figs. 14 and 16, the control method can be selected to achieve a stable fluidization in the boiler 4, over a wide load range, using methods corresponding to methods (1) - (4) set out above. Air flow rate control with the bypass valve 19 has a relationship (pressure/flow rate) ≧ 1 and air flow rate control with the turbine 27 has a relationship (pressure/flow rate) ≦ 1. Fig. 20 shows a system diagram of a power plant which is provided with a booster compressor 14 controlling the air pressure charged to the boiler 4 from the outlet of the compressor 1 and the bypass valve 19 controlling the air flow rate supplied to the boiler 4 from the outlet of the compressor 1. The motor M of the booster compressor 14 is controlled. Fig. 21 shows the corresponding partial load characteristic of the air flow rate and the air pressure when pressure control by the booster compressor 14 and flow rate control by the bypass valve 19 are combined. As in the cases of Figs. 14, 16 and 18, control achieving stable fluidization in the boiler 4 within a predetermined range of ratio of pressure/flow rate is enabled over a wide range, and the control method can be selected from methods corresponding to the methods (1) - (4) set out above. The air flow rate control with the bypass valve 19 has a relationship of (pressure/flow rate) ≧ 1, while the pressure control by the booster compressor 14 has a relationship of (pressure/flow rate) ≦ 1. Fig. 22 shows a system diagram of a power plant which is provided with a gas turbine compressor inlet guide vane structure 20 controlling the air flow rate to the inlet of compressor 1 and a throttle valve 17 (or throttle damper, or throttle vane) controlling the air pressure at the compressor inlet. Fig. 23 shows the resulting partial load characteristic of the air flow rate supplied to the boiler 4 and the air pressure charged to the boiler 4, when flow rate control by the inlet guide vane structure 20 and pressure control by the throttle valve 17 (or throttle damper, or throttle vane) are combined. As in Figs. 14 to 21, control achieving stable fluidization in the boiler 4 is enabled over a range from the rated load (100% air quantity) to a partial load level. In this case, the control method may be selected from: (5) a control method performed within a predetermined control range in which a control unit having a relationship of (pressure/flow rate) ≦ 1 precedes, e.g. flow rate control by the gas turbine compressor inlet guide vane opening or pressure control by the throttle vane (or throttle damper or throttle vane) having a relationship of (pressure/flow rate) ≦ 1 is effected precedingly and subsequently, a control unit having a relationship of (pressure/flow rate) ≧ 1 is effected. (6) a control method performed within a predetermined control range in which the variation bands of the pressure and flow rate in a first control unit having a relationship of (pressure/flow rate) ≦ 1 is varied and a second control unit having the relationship of (pressure/flow rate) ≦ 1 is effected alternatively and repeatedly. Fig. 24 shows a system diagram of a power plant which is provided with a gas turbine compressor inlet guide vane structure 20 controlling the air flow rate at the inlet of compressor 1 and an expansion turbine 27 with control valve 27a disposed in a conduit line extracting the air flow from the compressor outlet to a line other than the line 22 supplying the boiler 4. Fig. 25 shows the characteristic of the air flow rate supplied to the boiler 4 and the air pressure charged to the boiler 4 when air flow rate control by the inlet guide vane structure 20 and air flow rate control by the expansion turbine 27 are combined. Fig. 25 shows, that, as for Figs. 14 to 23, by this control method, stable fluidization in the boiler 4 is obtainable over a partial load range from the rated load. The control method may be selected from methods corresponding to methods (1) to (4) set out above. Air flow rate control by the expansion turbine 27 has the relationship of (pressure/flow rate) ≧ 1 and air flow rate control by the inlet guide vane structure 20 has the relationship of (pressure/flow rate) ≦ 1. Fig. 26 shows a system diagram of a power plant which is provided with a gas turbine compressor inlet guide vane structure 20 controlling the air flow rate at the outlet of compressor 1 and the booster compressor 14 with motor M controlling the air pressure charged to the boiler 4 from the compressor outlet. Fig. 27 shows the characteristic of the air flow rate supplied to the boiler 4 and the air pressure charged to the boiler 4 when air flow rate control by the inlet guide vane opening control and pressure control by the booster compressor 14 are combined. In this case, stable fluidization in the boiler within a predetermined ratio of pressure/flow rate is enabled over a relatively small range. The control method can be selected from methods corresponding to methods (5) and (6) set out above. Both air flow rate control by the gas turbine inlet guide vane opening, and pressure control by the booster compressor have a relationship of (pressure/flow rate) ≦ 1. Fig. 28 shows a system diagram of a power plant which is provided with a throttle valve 17 (or throttle damper, or throttle vane) controlling the air pressure at the inlet of compressor 1 and an expansion turbine 27 with valve 27a disposed at a conduit line through which the air flow from the compressor outlet is extracted to a line other the boiler supply line. Fig. 29 shows the characteristic of air flow rate supplied to the boiler 4 and air pressure charged to the boiler 4 when pressure control by the throttle valve 17 (or throttle damper, or throttle vane) and the flow rate control by the expansion turbine 27 are combined. Stable fluidization in the boiler within a predetermined ratio of pressure/flow rate is enabled over a range of partial load. The control method can be selected from methods corresponding to methods (1) to (4) set out above. Flow rate control by the expansion turbine 14 has a relationship of (pressure/flow rate) ≧ 1, and pressure control by the throttle valve 17 (or throttle damper, or throttle vane) has a relationship of (pressure/flow rate) ≦ 1. Fig. 30 shows a system diagram of a power plant which is provided with a throttle valve 17 (or throttle damper, or throttle vane) controlling the air pressure at the inlet of the compressor 1 and a booster compressor 14 driven by motor M controlling air pressure charged to the boiler 4 from the compressor outlet. Fig. 31 shows the characteristic of air flow rate supplied to the boiler 4 and air pressure charged to the boiler 4, when pressure control by the throttle valve 17 (or throttle damper, or throttle vane) and pressure control by the booster compressor 14 are combined. Stable fluidization in the boiler 4 is obtained within a predetermined ratio of pressure/flow rate over a relatively small partial load range. The control method may be selected from methods corresponding to methods corresponding to methods (5) and (6) set out above. Both the pressure control by the throttle valve 17 and the pressure control by the booster compressor 14 have a relationship of (pressure/flow rate) ≦ 1. Fig. 32 shows a system diagram of a power plant which is provided with a booster compressor 14 driven by motor M controlling the air pressure charged to the boiler 4 from the outlet of compressor 1 and an expansion turbine 18 in a line connecting combustion gas in the boiler 4 to exhaust and by-passing the main turbine 2. The flow rate of combustion gas to the turbine 18 is controlled by valve 18a. The turbine 18 drives the booster compressor 14. Fig. 33 shows the characteristic of pressures and flow rates of the air supplied to the boiler 4 and the combustion gas in the boiler 4 when pressure control by the booster compressor 14 and flow rate control by expansion turbine control are combined. Fig. 33 shows that stable fluidization in the boiler 4 within a predetermined ratio of pressure/flow rate is enabled over a substantial partial load range. Over at least part of this range, the control method may be selected from methods corresponding to methods (1) to (4) set out above. Flow rate control by the expansion turbine 18 has a relationship of (pressure/flow rate) ≧ 1 and pressure control by the booster compressor 14 has a relationship of (pressure/flow rate) ≦ 1. Fig. 34 shows a system diagram of a power plant which is provided with a throttle valve 17 (or throttle damper, or throttle vane) controlling the air pressure at the outlet of compressor 1, a gas turbine compressor inlet guide vane structure 20 controlling the air flow rate at the outlet of compressor 1 and an adjustable bypass valve 19 controlling the air flow rate supplied to the boiler 4 from the compressor outlet. Fig. 35 shows the characteristic of flow rate and pressure of the air supplied to the reactor when pressure control by the throttle valve 17 (or throttle damper or throttle vane), flow rate control by the guide vane 20 opening control and flow rate control by the bypass valve 19 are combined. Stable fluidization in the boiler 4 within a predetermined ratio of pressure/flow rate is enabled over a wide partial load range. The control method may be selected from methods corresponding to methods (1) to (4) set out above. Flow rate control with the bypass valve 19 has a relationship of (pressure/flow rate) ≧ 1, while pressure control by the throttle valve 17 (or throttle damper, or throttle vane) and flow rate control by inlet guide vane structure 20 have a relationship of (pressure/flow rate) ≦ 1. Fig. 36 shows a system diagram of a power plant which is provided with a throttle valve 17 (or throttle damper, or throttle vane) controlling the air pressure at the inlet of compressor 1, a gas turbine compressor inlet guide vane structure 20 controlling the air flow rate at the compressor inlet, a bypass valve 19 controlling the air flow rate supplied to the boiler 4 from the compressor outlet, and a booster compressor 14 driven by a motor M controlling the air pressure charged to the boiler 4. Fig. 35 mentioned above shows also the load characteristic of flow rate and pressure of the air supplied to the reactor when pressure control by the throttle valve 17 (throttle damper, or throttle vane), flow rate control by the guide vane 20 opening control, flow rate control by the bypass valve 19 and pressure control by the booster compressor 14 are combined. The control method can be selected from methods corresponding to methods (1) to (4) set out above. Fig. 37 shows a system diagram of a power plant which is provided with a throttle valve 17 (or throttle damper, or throttle vane) controlling the air pressure at the inlet of compressor 1, a gas turbine compressor inlet guide vane structure 20 controlling the air flow rate at the inlet of compressor 1, an adjustable bypass valve 19 controlling the air flow rate supplied to the boiler 4 from the compressor outlet, a booster compressor 14 driven by a motor M controlling the air pressure charged to the boiler 4, and an expansion turbine 28 disposed in a conduit line through which exhaust gas from the boiler outlet is extracted, by passing the main expansion turbine 2 connected to a compressor 1 for air supply for the boiler. The flow rate to the turbine 28 is controlled by an adjustable valve, not shown. Fig. 35 shows also the characteristic of flow rate and pressure of the air and combustion gas of the boiler 4 when pressure control by means of the throttle valve 17 (or throttle damper, or throttle vane), flow rate control by means of the inlet guide vane 20 opening control, flow rate control by means of the bypass valve 19, pressure control by means of the booster compressor 14, and flow rate control by means of the expansion turbine 28 are combined. The control method can be selected from the methods corresponding to the methods (1) to (4) above. Fig. 38 shows another embodiment of a power plant of the invention, in which control of pressure and/or flow rate in the boiler 4 is achieved by control of the passage resistance at the entrance of the main turbine 2. An adjustable valve 16 controls the rate of flow 23 of the combustion gases from the boiler 4 to the turbine 2, thereby achieving adjustment of pressure and/or flow rate in the boiler 4. Fig. 39 shows a modified version of the plant of Fig. 10, in which the temperature Tx and the pressure Px in the combustion gas flow 23 are measured by sensors 29 and 30 and the resultant signals are fed to a controller 52 for the adjustable valve 27a which controls the flow rate of air through the auxiliary air-driven turbine 27, in order to adjust the air flow rate to the boiler 4. The flow rate Fx to the turbine 27 is measured by sensor 51 and also fed to the controller 52, so that the desired flow rate to the boiler 4 can be set by adjustment of the valve 27a. This embodiment enables the temperature control of the combustion gas input to the turbine 2. This is an important advantage, because the power output of the gas turbine 2 varies in dependence upon the gas turbine compressor pressure ratio. It is desirable to operate the gas turbine so as to achieve maximum power output, i.e. to select the appropriate gas turbine compressor pressure ratio for maximum power output. Fig. 40 illustrates this, and shows that, at different gas turbine entrance temperatures the appropriate gas turbine compressor pressure ratio (i.e. the pressure ratio at the peak of the curve) is different. The chain-dot curve in Fig. 40 is the optimum curve for the ratio of the gas turbine output to the gas turbine compressor pressure ratio. Thus the gas turbine compressor pressure ratio should be selected, for the given gas turbine entrance temperature, to achieve the maximum gas turbine output. The arrangement of Fig. 39 permits this. In Fig. 40, the gas turbine output and the gas turbine compressor pressure ratio are expressed in percentages, relative to the value (100%) at the reference gas turbine entrance temperature T 1 .

Claims: A pressurized fluidized bed combustion combined cycle power plant comprising: a pressurized fluidized bed combustion boiler (4) for burning coal and producing steam by the combustion heat, having a combustion chamber in which said coal is burned, and a gas turbine unit (1,2,3) of single spindle type, having (a) a turbine (2) driven by combustion gas from said burning of coal in said boiler, (b) a spindle which is rotated at constant speed by said turbine, (c) an electrical generator (3) driven at constant speed by said spindle, (d) a compressor (1) on said spindle, arranged to supply compressed air to said boiler (4), as combustion air for said burning of coal, wherein there are provided control means (14,16,17,18a,19,20,27a,28) comprising a combination of at least two adjusting means selected from (i) a throttle valve (17) controlling air pressure at said compressor inlet, (ii) vanes (20) controlling air flow rate at said compressor inlet, (iii) a bypass valve (19) controlling air flow rate from said compressor to said boiler, (iv) drive means (M) of a booster compressor (14) controlling pressure of air supplied from said compressor to said boiler, (v) a valve (27a) controlling flow through an expansion turbine (27) operated by compressed air from said compressor, (vi) a valve (16) controlling flow rate of combustion gas from said boiler (4) to said turbine (2), and (vii) a valve controlling combustion gas flow from said boiler to a second gas turbine (28) which is not mounted on said spindle, but excluding (a) the combination of items (iii) and (iv) above (b) the combination of items (iii) and (v) above and (c) the combination of items (iv) and (vi) above, said control means being adapted and arranged to effect, in dependence on an operating load of said boiler (4), control of both of (a) the flow rate of said combustion air into said boiler (4), and (b) the operating pressure in said combustion chamber of said boiler (4), by adjustment of said two adjusting means. A power plant according to claim 1 wherein said control means is adapted and arranged to effect control of said combustion air flow rate and said operating pressure in a manner so as to maintain support of said combustion of coal in said boiler over a load range of said boiler from full load to less than 80% of full load. A power plant according to claim 1 or claim 2, having a conduit (22) extending from-said compressor (1) to said boiler (4) for said combustion air, a booster compressor (14) for boosting pressure of said combustion air in said conduit (22) and drive means (M) for said booster compressor, said control means controlling said drive means (M) so as to effect control of said combustion air flow rate and said operating pressure. A power plant according to any one of claims 1 to 3 having a conduit (21) for supplying air to said compressor to be compressed therein and adjustable flow resistance means (17) in said conduit, said control means controlling said flow resistance means so as to effect control of said operating pressure. A power plant according to any one of claims 1 to 4 having a conduit (22) extending from said compressor (1) to said boiler (4) for said pressurized combustion air, a branch conduit from said conduit, an air expansion turbine (27) connected to said conduit by said branch conduit and flow control means (27a) for controlling flow in said branch conduit to said air expansion turbine, wherein said control means control said flow control means (27a) to effect said control of said combustion air flow rate and said operating pressure. A power plant according to claim 5 having a sensor (Tx,Px) for at least one of temperature and pressure of said combustion gas at entry to said gas turbine and wherein said control means effects adjustment of said flow control means (27a) for said air expansion turbine (27) in dependence on an output of said sensor, in order to maintain said combustion air flow rate and said operating pressure within a predetermined relationship to each other. A power plant according to any one of claims 1 to 4 having adjustable vanes (20) for controlling air flow rate into said compressor (1), a conduit (22) extending from said compressor to said boiler (4) for said pressurized combustion air, a conduit (23) extending from said boiler (4) to said turbine (2) for said combustion gas and a by-pass connecting said first conduit (22) to said conduit (23), and flow control -means (19) for controlling the air flow rate in said by-pass, wherein said control means effects control of at least one of said vanes (20) and said flow control means (19) of said bypass, in order to control said combustion air flow rate and said operating pressure. A power plant according to claim 1 wherein said control means comprises three said adjusting means in the form of (i) said throttle valve (17) controlling air pressure at said compressor inlet, (ii) said vanes (20) controlling air flow rate at said compressor inlet, and (iii) said bypass valve (19) controlling air flow rate from said compressor to said boiler, said control means being arranged to effect adjustment of said three adjusting means. A method of operating a pressurized fluidized bed combustion combined cycle power plant, said plant comprising: a pressurized fluidized bed combustion boiler (4) for burning coal and producing steam by the combustion heat, having a combustion chamber in which said coal is burned, and a gas turbine unit (1,2,3) of single spindle type having (a) a turbine (2) driven by combustion gas from said burning of coal in said boiler, (b) a spindle which is rotated at constant speed by said turbine, (c) an electrical generator (3) driven at constant speed by said spindle, (d) a compressor (1) on said spindle, arranged to supply compressed air to said boiler, as combustion air for said burning of coal, said method comprising the step of, during operation of said plant, controlling of both of (a) the flow rate of said combustion air into said boiler (4), (b) the operating pressure in said combustion chamber of said boiler (4), in dependence on the operating load of said boiler by operation of a combination of at least two of (i) a throttle valve (17) controlling air pressure at said compressor inlet, (ii) vanes (20) controlling air flow rate at said compressor inlet, (iii) a bypass valve (19) controlling air flow rate from said compressor to said boiler, (iv) drive means (M) of a booster compressor (14) controlling pressure of air supplied from said compressor to said boiler, (v) a valve (27a) controlling flow through an expansion turbine (27) operated by compressed air from said compressor, (vi) a valve (16) controlling flow rate of combustion gas from said boiler (4) to said turbine (2), and (vii) a valve controlling combustion gas flow from said boiler to a second gas turbine (28) which is not mounted on said spindle, but excluding (a) the combination of the items (iii) and (iv) above, (b) the combination of the items (iii) and (v) above and (c) the combination of the items (iv) and (vi) above. A method according to claim 9 comprising controlling said combustion air flow rate and said operating pressure in a manner so as to maintain support of said combustion of coal in said boiler (4) over a load range of said boiler from full load to less than 80% of full load. A method according to claim 9 or claim 10, wherein said plant has adjustable vanes (20) for controlling air flow rate into said compressor (1), a conduit (22) extending from said compressor (1) to said boiler (4) for said pressurized combustion air, a conduit (23) extending from said boiler (4) to said turbine (2) for said combustion gas a by-pass connecting said first conduit to said second conduit, and flow control means (19) for controlling the air flow rate in said by-pass, said method comprising controlling of at least one of said vanes (20) and said flow control means (19) of said bypass, in order to control said combustion air flow rate and said operating pressure. Method according to claim 11 including adjusting said vanes (20) in order to control the plant operation over a first range of operating load of the plant, and adjusting said flow control means (19) of said bypass in order to control the plant operation over a second range of operating load of the plant, said first range being closer to the full operating load of the plant than said second range. A method according to any one of claims 9 to 12 wherein the step of controlling the flow rate of combustion air and the operating pressure in the combustion chamber is performed so as to maintain the ratio of said operating pressure to said flow rate in a predetermined range sufficient to maintain stable fluidization in said chamber over a load range from a partial load to full load.

Inventors: ASAO TAKASHI, HOIZUMI SHINICHI, KOIZUMI NAOTO, NOGUCHI YOSHIKI, SASAKI TOSHIHIKO, ASAO, TAKASHI, HOIZUMI, SHINICHI, KOIZUMI, NAOTO, NOGUCHI, YOSHIKI, SASAKI, TOSHIHIKO
Applicants: HITACHI ENG CO LTD, HITACHI LTD, HITACHI ENGINEERING CO., LTD., HITACHI, LTD.
Application year: 1991
Main classification: F01K23
IPC codes: F01K23, F02C3