PRESSURIZED FLUIDIZED-BED COMBINED CYCLE POWER GENERATION SYSTEM

Abstract: A pressurized fluidized-bed combined cycle electric power generation system intended to increase the output of the gas turbine and improve the prevention of surging, comprising a steam turbine, a pressurized fluidized-bed boiler for burning air from an air supply system and fuel from a fuel supply system to generate steam to be supplied to the steam turbine, a gas turbine driven by exhaust gas consisting of combustion gas of the pressurized fluidized-bed boiler and the air and a compressor directly coupled to the gas turbine; the system being further provided with a first bypass passage having a valve and communicating with both of the outlet side of the compressor and the exhaust side of the gas turbine, a second bypass passage having a valve and communicating with both of the outlet side of the compressor and the inlet side of the gas turbine, and a control system to which pressure values detected by a pressure sensor for detecting the outlet pressure of the compressor are inputted for controlling the valves of the first and the second bypass passages according to the relationship between a predetermined opening of a variable stator blade of the compressor inlet and surging limit pressure; wherein steam generated by the pressurized fluidized-bed boiler is partly bled and mixed into the exhaust or the air to be supplied to the gas turbine, and air from the compressor is supplied as combustion air for the pressurized fluidized-bed boiler.

Description: Background of the Invention Field of the Invention The present invention relates to a combined electricity generation system which combines two methods for generating electricity in which a steam turbine is driven by steam generated from a pressurized fluidized bed boiler and a gas turbine is driven using the exhaust gas from the boiler. Description of the Related Art Pressurized fluidized bed combined electricity generation systems are electricity generation systems which combine two methods such that electricity is generated by driving a steam turbine with steam generated from a fluidized bed boiler housed within a pressurized container, and electricity is generated by driving a gas turbine by introducing exhaust gas from the pressurized fluidized bed boiler into the gas turbine. For the combustion which occurs in the pressurized fluidized bed boiler, air for combustion is introduced into the boiler in a pressurized state from a compressor, crushed coal is added to the fluidized bed in which limestone forms the fluid medium, and combusted in a fluid state. A steam pipe is arranged within this fluidized bed, steam is generated due to the heat of combustion in the fluidized bed, the steam turbine is driven and electricity is generated. In addition, with this type of combustion, since limestone is used, it is possible to conduct desulfurization within the furnace at the same time. Further explaining the principle of the fluidized bed boiler mentioned above, an air dispersion plate is provided in the bottom of a container, and solid particles are charged into the part above the air dispersion plate. Air is blown uniformly from the bottom of the air dispersion plate, and when the amount of air is increased, solid particles move vigorously and randomly within a layer of a certain height above the air dispersion plate. The solid particle layer which is floated and fluidized by means of a fluid in this way is referred to as a fluidized bed, and the combustion in a fluid state of liquid fuel or solid fuel of a suitable size added to this fluidized bed is fluidized bed combustion. Figure 9 is a schematic diagram showing an example of the pressurized fluidized bed combined electricity generation system explained above. In Figure 9, reference 1 indicates the entire pressurized fluidized bed boiler, and it comprises a pressurized container 10 and a boiler 11 therewithin. Reference 12 is a coal/limestone supply device, and it supplies the limestone which forms the fluid medium and the coal starting materials to the boiler 11. Reference 13 is a cyclone which removes particles which are non-combustible, and the like, from the exhaust gas from the boiler 11. Reference 14 is a dust collecting device which comprises a ceramic filter, and ash and the like are filtered and removed by means of this ceramic filter. Reference 15 is a gas turbine which is directly coupled to the compressor 16, and driven by high temperature exhaust gas from the dust collecting device 14. Reference 17 is a denitrification device, 18 is a high pressure exhaust heat recovery/supply-water heater and 19 is a low pressure exhaust heat recover/supply-water heater. The high pressure exhaust heat recovery/supply-water heater 18 and the low pressure exhaust heat recover/supply-water heater 19 recover exhaust heat from the exhaust gas and preheat the water being supplied to the boiler 11 using this exhaust heat. Reference 20 is a chimney for discharging exhaust gas to the atmosphere. In addition, in Figure 9, reference 21 is a steam turbine and reference 22 is a condenser to which cold water is sent by pump 51 and in which steam from the steam turbine 21 is cooled and condensed. Reference 23 is a low pressure supply-water heater which heats the condensed water and regulates the temperature of the supply water. Reference 24 is a deaerator for removing air bubbles from the supply water. Reference 25 is a drum which supplies water to each of the pipes of boiler 11, that is, to main steam pipe system 30, reheating gas pipe system 31, and boiler circulation pipe system 32. In the pressurized fluidized bed combined electricity generation system of the above-described structure, the limestone which is the fluidized bed medium and the coal starting material from the coal/limestone supply device 12 is sent to the boiler 11 by means of the supply system 41, while air from the compressor 16 is blown into boiler 11 by means of air system pipe 42, a fluidized bed is formed by means of this limestone, and the coal is burned, thereby, fluidized bed combustion is carried out. At the same time, supply water that has been heated in advance is supplied from the drum 25 to the main steam pipe system 30. The main steam pipe system 30 is heated by the boiler 11, steam is generated and the high pressure turbine of steam turbine 21 is driven. The steam discharged therefrom is returned to the boiler 11 again, it is reheated, run back into the steam turbine 21 a second time by means of the reheating steam pipe system 31, drives the low pressure turbine, and flows to the condenser 22. In addition, the supply water in the drum 25 circulates between the boiler 11 and the drum 25 by means of the boiler circulation pipe system 32 such that it is heated. Next, large particles are removed by the cyclone 13, ash and the like are removed by means of dust collecting device 14, then the combustion exhaust gas from the boiler 11 is supplied to the gas turbine 15, the turbine is driven and electricity is generated. The exhaust gas which drives the gas turbine 15 is denitrified by means of denitrification device 17. Then the remaining heat in the exhaust gas is used to heat the supply water being supplied to the boiler 11 by each of the high pressure exhaust heat recovery/supply-water heater 18 and the low pressure exhaust heat recover/supply-water heater 19. Thereafter, the exhaust gas is discharged to the atmosphere from chimney 20. The exhaust steam which drives the steam turbine 21 is condensed and liquefied by the condenser 22, to which cold water is sent by the pump 51, this condensed water is sent to the low pressure supply-water heater 23 by the pump 52 where it is heated and its temperature adjusted. Then it is preheated by exhaust gas in the low pressure exhaust heat recover/supply-water heater 19 and then sent to the deaerator 24 and bubbles are removed. The supply water from the deaerator 24 is sent to the high pressure exhaust heat recovery/supply-water heater 18 by the pump 53, where it is preheated again and then sent to drum 25 by means of pipe 33. In the above-described pressurized fluidized bed combined electricity generation system, there is a combined cycle system which generates electricity by driving the steam turbine 21 and by the gas turbine 15 using the exhaust gas from the boiler 11, and it obtains high electricity generation efficiency. In addition, since the boiler 11 is housed inside the pressurized container 10 which is pressurized it can be made to be compact. In addition, since limestone is used as the fluid medium, desulferization can be carried out within the boiler 11, an exhaust gas desulferizer is not necessary, and it is possible to make the plant equipment area smaller compared with the past. In the above-described pressurized fluidized bed combined electricity generation system, there is a combined cycle method in which a turbine is driven by steam generated by a pressurized fluidized bed boiler 1 and the gas turbine 15 is driven by exhaust gas from the pressurized fluidized bed boiler 1, and it is possible to obtain high electricity generation efficiency and to make the apparatus compact. In this type of system, the output of the gas turbine 15 is influenced by the characteristics of the fuel used (coal), the combustion method of the pressurized fluidized bed boiler 1 (combustion temperature, layer height), and the like, however, it depends greatly on the temperature of the intake air of the compressor 16 of the gas turbine 15 and the air-fuel ratio for the combustion in the pressurized fluidized bed boiler 1. The temperature of the intake air of the compressor 16 can be varied intentionally by operation using intake of air from indoors/outdoors, but it is basically determined by natural conditions. The air-fuel ratio in the combustion in the pressurized fluidized bed boiler 1 has a certain degree of freedom due to changes in the operating conditions of the pressurized fluidized bed boiler 1, but it is impossible to exceed the upper limit of the compressor 16. Under these types of conditions, it is possible, to some extent, to take measures to increase the output of the gas turbine 15 but, even in situations where the output of the gas turbine 15 is limited for some reason, for example, the temperature of the air drawn into to the compressor 16 is higher than anticipated, there are cases (gas turbine certification output tests and the like) where it is necessary to increase the output of the gas turbine 15 beyond what is practically possible using present technology. In these types of situations, at present, it is not possible to cope with increasing output of the gas turbine 15. In addition, in coal gasification combined electricity generation systems, in the same way, in cases when there is, for some reason, a limitation to gas turbine output, there are cases (gas turbine certification output tests and the like) where it is necessary to increase the turbine output beyond what is possible using present technology, in these situations as well, increases in output beyond what can be responded to using present technology are impossible. An object of the present invention is the provision of a pressurized fluidized bed combined electricity generation system which is a combined electricity generation system (such as a pressurized fluidized bed combined electricity generation system or a coal gasification combined electricity generation system) having a gas turbine and a steam turbine as the electricity generation devices, wherein, in addition to conventional measures such as varying the temperature of the intake air for the compressor and varying the air fuel ratio for the combustion in the boiler, it is possible to increase turbine output by changing the composition of the fuel gas introduced into the existing gas turbine. In addition, the pressurized fluidized bed combined electricity generation system according to the present invention relates to improvement of surge prevention for the compressor when the load in the pressurized fluidized bed combined electricity generation system varies. In more detail, in the above-mentioned pressurized fluidized bed combined electricity generation system, unlike usual systems, the compressor 16 which is directly coupled to the gas turbine 15 has a large capacity pressurized container 10 on the outlet side, therefore, variation in the pressure ratio with respect to variation in the quantity of intake air is slow. When the load decreases, since it is necessary to reduce the quantity of air for combustion within the pressurized container 10 in response to the amount of carbon supplied, the amount of air supplied to the pressurized container 10 from the compressor 16 must be decreased. At the time of this reduction in air, at a certain limiting pressure, the compressor 16 causes surging, but the surge limiting pressure ratio of this compressor 16 is simultaneously decreased along with the decrease in the quantity of air. However, even if the air flow rate is reduced, since there is a large capacity pressurized container 10 on the outlet side of the compressor 16, the operating pressure ratio does not decrease, and the earlier high pressure condition is maintained. As a result, as the air quantity is reduced, the pressure during operation reaches a surge limiting pressure threshold, and the compressor 16 surges. Therefore, the present invention has as an object the provision of a pressurized fluidized bed combined electricity generation system plant in which, when the air quantity is reduced as described above, before the compressor begins to surge, a quantity of air from the compressor is made to bypass so that the pressure at the outlet side of the compressor does not reach the surge limiting pressure, and thereby it is possible to avoid surging of the compressor. Summary of the Invention In order to solve the above-described problem, the present invention provides a pressurized fluidized bed combined electricity generation system comprising a steam turbine; a pressurized fluidized bed boiler for combusting air from an air supply system and fuel from a fuel supply system and generating steam for supply to the above-mentioned steam turbine; and a gas turbine driven by exhaust gas comprising combustion gas from the above-mentioned pressurized fluidized bed boiler and the above-mentioned air; wherein, a part of the steam generated by the above-mentioned pressurized fluidized bed boiler is extracted and supplied to the above-mentioned gas turbine in the manner more precisely defined by the claims. JP 4 - 246 244 and WO 95/10693 both disclose combined electricity generation systems in which steam is extracted from a steam pipe system leading to the steam turbine, instead of a reheating steam pipe system issuing from that steam turbine, towards the gas turbine. According to this pressurized fluidized bed combined electricity generation system, since the flow rate at the gas turbine inlet is increased by means of mixing steam having a large specific heat (among the gas characteristics at the gas turbine inlet) into the exhaust gas going to the gas turbine, it is possible to increase the output of the gas turbine. The steam supplied to the above-mentioned gas turbine can be mixed in to the above-mentioned exhaust gas or the air supply system. Thereby, since the steam is supplied to the gas turbine after being heated in the boiler, the temperature at the gas turbine inlet does not decrease and it is possible to increase the output ofthe gas turbine more effectively. In addition, according to the pressurized fluidized bed combined electricity generation system of the present invention, it is possible, in a combined electricity generation system in which air from a compressor which is coupled directly to the above-mentioned gas turbine is supplied as fuel air for the above-mentioned pressurized fluidized bed boiler, to have a first bypass duct communicating between the outlet side of the above-mentioned compressor and the exhaust side of the above-mentioned gas turbine and having a switching valve; a second bypass duct communicating between the outlet side of the above-mentioned compressor and the inlet side of the above-mentioned gas turbine and having a switching valve; and a control device which receives measured pressure values from a pressure detector which measures the pressure at the outlet of the above-mentioned compressor, and the above-mentioned control device controls the switching valves of the above-mentioned first and second bypass ducts based on the relationship between the degree of opening of the inlet variable guide vane of the above-mentioned compressor which is determined in advance and a surge limiting pressure. Thereby, when the pressure at the outlet of the compressor measured by the pressure detector exceeds the predetermined value, the control device maintains the degree of opening of the inlet variable guide vane, opens the switching valve of the above mentioned first or second bypass duct, and allows a quantity of air flowing to the pressurized fluidized bed boiler to be bypassed in such a way as to prevent a pressure increase, thereby, it is possible to prevent surging of the compressor. Here, two surge limiting pressure values are established in the above-mentioned control device in advance, and when the pressure during operation which is measured by the above-mentioned pressure detector reaches one of the above-mentioned surge limiting pressures, this control device is capable of controlling by maintaining the degree of opening of the inlet variable guide vane and opening the switching valves of the first bypass duct and, in addition, when the above-mentioned pressure reaches the other limiting pressure, it opens the switching valve of the second bypass duct, and this is suitable for preventing surging of the compressor. Furthermore, in accordance with the temperature of the intake air for the above-mentioned compressor, it is possible for the control device to adjust the values of the above-mentioned two surge limiting pressures which are determined in advance, and adjusting the surge limiting pressure values changed according to the temperature of the intake air is even more suitable for preventing surging of the compressor. Brief Description of the Drawings Figure 1 is a schematic diagram of a combined electricity generation system according to background art. Figure 2 is a schematic diagram of a combined electricity generation system according to a first mode of an embodiment of the present invention. Figure 3 is a schematic diagram of a combined electricity generation system according to a second mode of an embodiment of the present invention. Figure 4 is a graph showing the quantity of steam necessary for extraction according to a method for increasing the output of the gas turbine according to the first and second modes of an embodiment of the present invention. Figure 5 is a graph showing the relationship between the amount of increase in the output of the gas turbine and the plant load according to the second mode of an embodiment of the present invention. Figure 6 is a schematic diagram of a combined electricity generation system according to another embodiment of the present invention. Figure 7 is a diagram showing the relationship between the degree of opening of the inlet variable guide vane of the inlet of the compressor in the combined electricity generation system according to another embodiment of the present invention. Figure 8 is a control flow chart for the control apparatus of the combined electricity generation system according to another embodiment of the present invention. Figure 9 is a schematic diagram showing an example of a pressurized fluidized bed combined electricity generation system. Best Modes for Carrying Out the Present Invention In the following, an embodiment of the present invention will be explained in detail based on the Diagrams. Figure 1 is a schematic diagram of a combined electricity generation system according to background art. As shown in Figure 1, the combined electricity generation system comprises a pressurized fluidized bed boiler 1, a dust collecting device 14, a gas turbine 15, a compressor 16, a steam turbine 21, a condenser 22, a main steam pipe system 30, and a reheating steam pipe system 31, and these structural elements have approximately the same structure as the structural elements having the same references as in the pressurized fluidized bed combined electricity generation system shown in Figure 9. As shown in Figure 1, the combined electricity generation system has the feature of having a steam extraction pipe system 2. As shown in Figure 1, steam extraction pipe system 2 is provided in a condition connected between the reheating steam pipe system 31 and the outlet side of pipe system 15A of the dust collecting device 14, and high temperature steam from the reheating steam pipe system 31 is extracted, the extracted steam is mixed in with the exhaust gas from the outlet of the pressurized fluidized bed boiler 1, and the exhaust gas mixed with the steam is supplied to the gas turbine 15. In the above-described structure, since the steam extraction pipe system 2 is feeding steam in at the outlet side of dust collecting device 14, the amount of gas passing through dust collecting device 14 does not change from conventional systems, the temperature at the inlet of the gas turbine 15 decreases to some extent, but the output response of the gas turbine 15 is fast, and the output of the gas turbine 15 increases more than when steam is not extracted. However, in the first mode of the present embodiment, it is necessary to take care that the gas turbine 15 does not momentarily enter the surging range (25% margin). In the following, a second mode of the present embodiment will be explained in greater detail based on the Figures. Figure 2 is a schematic diagram of a combined electricity generation system according to a first mode of an embodiment of the present invention. In the first mode of the present embodiment shown in Figure 2, the point of difference with the above-described first mode shown in Figure 1 is the provision of steam extraction pipe system 3 in place of steam extraction pipe system 2. This steam extraction pipe system 3 is provided in a condition connected between the reheating steam pipe system 31A on the low temperature side which returns the low temperature steam which drove the turbine by main steam pipe system 30 and the inlet side of pipe system 14A of the dust collecting device 14 between the outlet of the pressurized fluidized bed boiler 1 and the dust collecting device 14, and low temperature reheated steam is extracted from the reheating steam pipe system 31A, that steam is mixed with the exhaust gas of the outlet side of the pressurized fluidized bed boiler 1 and is supplied to the gas turbine 15. In the above-described structure, since the steam extraction pipe system 3 is feeding steam in at the inlet side of dust collecting device 14, the amount of gas passing through dust collecting device 14 is increased over conventional systems, the temperature of the gas at the inlet of the gas turbine 15 falls by the amount that the temperature of the steam which passes through the dust collecting device 14 falls, and decreases more than that for the first mode of the present embodiment described above, but the gas turbine output response is as fast as in the above-described first mode and the output of the gas turbine 15, while less than the above described first mode, does increase. In addition, in the same way as in figure 8, it is necessary to take care that gas turbine 15 does not momentarily enter the surging range (25% margin). In the following, a second mode of the present embodiment will be explained in greater detail based on the Figures. Figure 3 is a schematic diagram of a combined electricity generation system according to a second mode of the an embodiment of the present invention. In Figure 3, a point of difference with the above-described first mode shown in Figure 2 is that a steam extraction pipe system 4 is provided in place of the steam extraction pipe system 3. This steam extraction pipe system 4 is arranged between the reheating steam pipe system 31A on the low temperature side and the air supply system 16A of the pressurized fluidized bed boiler 1, low temperature reheated steam is extracted, this steam is mixed into the air supply system 16A going to the pressurized fluidized bed boiler 1, and the air mixed with the steam is supplied to the pressurized fluidized bed boiler 1. Since the steam which is mixed into the air which is supplied to the pressurized fluidized bed boiler 1 is fluidized bed combusted within the pressurized fluidized bed boiler 1, flows into the dust collecting device 14 together with the exhaust gas, and is supplied to the gas turbine 15, the amount of gas which passes through the dust collecting device 14 is increased by that amount. In addition, since the steam which has been mixed in is heated within the pressurized fluidized bed boiler 1, there is no decrease in temperature and the temperature at the gas turbine inlet does not vary from conventional systems. In addition, the output response of the gas turbine 15 is gradual since the mixing in is conducted indirectly via the pressurized fluidized bed boiler 1, and increases in output of the gas turbine 15 are larger than those for the above-described first mode and are the largest for the present embodiment. Figure 4 shows the relationship between the degree of opening of the IGV (inlet variable guide vane) and the amount of steam extracted for each of the first and second modes of the present embodiment described above. The same amount of air taken in using the compressor (the temperature of the air taken in using the same compressor is determined by the degree of opening of the IGV) is shown on the horizontal axis and the necessary amount of steam extracted from each of the pipe lines which was necessary to obtain the same amount of increase in the output of the gas turbine is shown on the vertical axis, thereby, the relationship between the two is shown. In Figure 4, the relationship between the amount of air taken in by the same compressor and the necessary amount of steam extracted is shown and (A) represents the background art shown in Figure 1, (B) represents the first mode shown in Figure 2, and (C) represents the second mode shown in Figure 3. Here, as can be understood from Figure 4, the system for which the amount of extracted steam required for the same degree of opening of the IGV was largest was the case of the second embodiment, represented by (B), in which steam was extracted from the reheating steam pipe system 31A on the low temperature side and then mixed into the boiler output gas in the inlet side of pipe system 14A on the dust collecting device 14. The second largest was the case represented by (A) in which steam was extracted from the reheating steam pipe system 31 on the high temperature side and mixed into the boiler output gas in the outlet side of pipe system 15A on the dust collecting device 14. The case in which the amount of extracted steam required was the smallest was (C) in which the steam was extracted from the reheating steam pipe system 31A on the low temperature side and fed into the air supply system 16A of the pressurized fluidized bed boiler 1. In the above-described way, the necessary amount of steam increases in the order of second mode (C), background art (A), and first mode (B). The reason for this is that, in cases (A) and (B), the gas temperature falls due to the mixing in of extracted steam between pressurized fluidized bed boiler 1 and the inlet of the gas turbine 15, accordingly the gas temperature at the inlet of the gas turbine 15 is reduced, and a phenomenon occurs in which the output increase of the gas turbine 15 declines. On the other hand, in the case of (C), since there is no reduction in gas temperature due to the mixing in of steam between the pressurized fluidized bed boiler 1 and the gas turbine 15, it is the most effective method out of all of the modes. Here, the reason for the increase in output of the gas turbine 15 due to the extraction and mixing in of steam is that water (H 2 O) has a high specific heat (among the properties of the gases at the inlet to the gas turbine), and an increase in the gas flow rate is brought about by mixing steam into the gas and, as a result, this brings about the effect of increasing the output of the gas turbine 15. As mentioned above, in the present invention, steam is mixed in to the gas and causes the moisture (H 2 O) content within the gases at the inlet of the gas turbine 15 to increase and, for the reasons mentioned above, it is possible to increase the output of the gas turbine 15. In the method of extracting and mixing in steam described above, in the case of the second embodiment, shown by (C), in which steam is extracted from the reheating steam pipe system 30A on the low temperature side and is mixed into the air supply system 16A of the pressurized fluidized bed boiler 1, with regard to rating points, it is possible to expect an increase in the output of the gas turbine of the level of about 150 kw to 200 kw by inserting steam into the air supply system of the boiler. At partial loads of the plant which occur in the pressurized fluidized bed combined electricity generation system, the temperature of the boiler output gas decreases, consequently, the output increase falls by that amount. Figure 5 is a graph showing the amount of increase in the output of the gas turbine at partial loads which occur in the case of the second mode of (C) above. When the plant load is 30%, the amount of output increase is 100 kW or less and, when the plant load is 100%, the output increase is 150 kW or greater. In addition, in the first and second modes of the present embodiment, examples of combined electricity generation system which use a pressurized fluidized bed boiler were explained, but the present invention can also be applied to methods of increasing the output of gas turbines of systems in which steam turbines and gas turbines are combined in coal gasification combined electricity generation systems, and the same results are obtained. In the following, another embodiment of the present invention is explained in detail based on the Figures. Figure 6 is a schematic diagram of the pressurized fluidized bed combined electricity generation system according to the present embodiment. As shown in Figure 6, the pressurized fluidized bed combined electricity generation system of the present embodiment comprises a pressurized fluidized bed boiler 1, a steam extraction pipe system 2, a dust collecting device 14, a gas turbine 15, a compressor 16, a steam turbine 21, a condenser 22, a main steam pipe system 30, and a reheating steam pipe system 31. These structural elements have generally the same structure as the structural elements having the same references in the pressurized fluidized bed combined electricity generation systems shown in Figure 2 and Figure 9. As shown in Figure 6, the combined electricity generation system of the present embodiment is a combined electricity generation system in which air from the compressor 16 which is connected to the gas turbine 15 is supplied as fuel air for the pressurized fluidized bed boiler 1. In addition the combined electricity generation system of the present embodiment has the feature of comprising a bypass pipe (a first bypass duct) 68 which is connected between the outlet side of the compressor 16 and the exhaust gas side of the above-mentioned gas turbine 15 and which has a surge prevention valve (switching valve) 67; a bypass pipe (a second bypass duct) 66 which is connected between the outlet side of the compressor 16 and the inlet side of the above-mentioned gas turbine 15 and which has a compressor outlet bypass valve (switching valve) 65; and a control device 70 which controls the above-mentioned surge prevention valve 67 and the compressor outlet bypass valve 65 (the switching valves of the first and second bypass duct) based on the relationship between the predetermined degree of opening of inlet variable guide vane 71 of the compressor and surge limiting pressures, and into which measured pressure values from a pressure detection device 69 which measures the pressure at the outlet of the compressor 16 is input. With regard to the above-mentioned control device 70, two surge limiting pressure values which can be adjusted according to the temperature of the intake air for the compressor 16 are determined in advance. In addition, when the pressure measured during operation by the above-mentioned pressure detection device 69 reaches one of the pressures of the above-mentioned surge limiting pressures, this control device 70 maintains the degree of opening of the inlet variable guide vane 71 and opens the surge prevention valve (the switching valve of the first bypass duct) 67. Additionally, when the other limiting pressure is reached, this control device opens the compressor outlet bypass valve (the switching valve of the second bypass passage)65. During normal operation, the combined electricity generation system of the present embodiment compresses air by means of the compressor 16 which is driven by gas turbine 15, passes it through compressor outlet valve 60, and supplies it as fuel air to the pressurized fluidized bed boiler 1 by duct 61. In addition, during start-up, since the fuel gas from the pressurized fluidized bed boiler 1 is not sufficiently supplied from duct 62, start-up gas combustor 63 is driven, air from the compressor 16 is supplied to the duct 64 side by switching the compressor outlet valve 60, and the gas turbine 15 is driven, thereby, operation is initiated. After the pressurized fluidized bed boiler 1 has been sufficiently heated, the air from duct 64 is shut off by switching the compressor outlet valve 60, and gas turbine 15 is driven by fuel gas from the pressurized fluidized bed boiler. In the furnace within the pressurized fluidized bed boiler 1, the height of the fluidized bed is varied with respect to variation in load, the heat transfer surface area of the heat transfer pipe within the fluidized bed is increased or decreased, and the amount of steam generated is adjusted. In Figure 6, the compressor outlet bypass valve 65 is provided partway along bypass pipe 66 which is arranged between the outlet side of compressor 16 and the duct 64 which is connected to the gas turbine duct on the inlet side of the gas turbine 15. The surge prevention valve 67 is provided partway along the bypass pipe 68 which is connected to the outlet side of the compressor 16 and the exhaust pipe duct of the gas turbine 15. The pressure detection device 69 measures the pressure at the outlet side of the compressor 16. The control device 70 receives signals for the pressure at the outlet side of the compressor 16 from the pressure detection device 69, and, as explained below, when a value just prior to the occurrence of surging of the compressor 16 is reached, the control device opens the surging prevention valve 67 or the compressor outlet bypass valve 65, and, thereby, controls in such a way as to prevent surging. Figure 7 is a graph showing the relationship between the compressor outlet pressure and the degree of opening of the inlet variable guide vane 71 of the compressor of the present embodiment. In Figure 7, the values of the surge line (S) are known in advance for the compressor 16, and values for pressures 25% lower than the curve of this surge line (S) are the operating limit pressures and form control line (A). Furthermore, values for pressures 20% lower than the values of surge line (S) are set as control line (B). The value data for these control lines (A) and (B) are set in advance in control device 70 and can be controlled in such a way that adjustments are made with respect to the temperature of the intake air of the compressor 16. More specifically, in Figure 7, when the temperature of the intake air increases, the surge line (S) or the control lines (A) and (B) move downward, and when the temperature of the intake air falls, they move upward, therefore, these types of adjustments can be made by the control device 70. In Figure 7, the point C is an operating point and the degree of opening of the inlet variable guide vane thereat is α2, when the present load falls and the air flow rate of the compressor 16 falls, if the degree of opening of the inlet variable guide vane 71 is reduced; in the above-described way, since the outlet side of the compressor 16 communicates with the large pressurized container 10, shown in Figure 9, of the pressurized fluidized bed boiler 1, the pressure does not fall immediately, it is maintained in that condition, and control line (A) is reached at pressure β1 for point C' at degree of opening α1. In the present embodiment, firstly, the pressure β1 at the outlet of the compressor for this point C' is measured by pressure detection device 69, and the degree of opening of the inlet variable guide vane 71 are maintained at α1, the surge prevention valve 67 shown in Figure 6 is opened, and the air at the outlet side of the compressor 16 is allowed to escape from bypass pipe 68, such that the pressure at the outlet of the compressor 16 does not rise above this point. The pressure at the above-mentioned point C' is maintained at the point of β1, and does not rise, but there are times when high temperature steam is mixed into the air, in this type of situation, additionally, the pressure at the outlet of the compressor 16 rises suddenly. In this type of situation, when the pressure rises to pressure β2 at point d, control line (B) is reached, and, in the present embodiment, pressure β2 at this point d is measured by pressure detection device 69, compressor outlet bypass valve 65 shown in Figure 6 is opened, air on the outlet side of the compressor 16 escapes into the inlet side of the gas turbine 15 from the bypass pipe 66, such that the pressure at the outlet of the compressor 16 does not rise to surge line (S). In control device 70, as shown in Figure 8, a storage device 70A is provided, and data of control lines (A) and (B) like those shown in Figure 7 are stored in advance in this storage device 70. In the pressurized fluidized bed combined electricity generation system, when the load during operation decreases and the degree of opening of inlet variable guide vane 71 is decreased in order to reduce the amount of air in the compressor 16, the pressure at the outlet of compressor 16 during operation is measured by pressure detection device 69, and if this pressure exceeds the stipulated value of control lines (A) and (B) which are set in advance, the control device 70 immediately opens the surge prevention valve 67 or the compressor outlet bypass valve 65 in addition to maintaining the degree of opening of the inlet variable guide vane 71, and prevents a rise in the pressure by allowing an amount of air flowing to the pressurized fluidized bed boiler 1 to bypass, thereby, this control device 70 prevents surging. In the following, the flow of control device 70 is explained in detail. Figure 8 is a flow chart of control within the control device 70 which carries out the control explained above. In Figure 8, as shown at Step S1, when the load of the pressurized fluidized bed boiler 1 decreases, it is also necessary to decrease the amount of air from the compressor 16, therefore, as shown in Step S2, the degree of opening of the inlet variable guide vane 71 of the compressor are decreased. At that time, as shown in Step S3, the pressure at the outlet of the compressor is measured by the pressure detection device 69, data for the control line (A) is taken in from storage device 70A, and whether or not this measured pressure value is within the specified pressure values is checked. If the measured pressure value is equal to or exceeds the value established by control line (A), as shown in Step S4, surge prevevtion valve 67 is opened, a quantity of air is allowed to bypass, and surging is prevented. If the measured outlet pressure has not reached the pressure value established by control line (A), operations are continued without change at Step 7. Next, as shown in Step 4, after the surge prevention valve 67 is opened, as shown in Step S5, data of control line (B) is taken in from storage device 70, and whether or not the pressure at the outlet of the compressor 16 during operation measured by the pressure detection device 69 has reached the pressure value established by this control line (B) is checked, if it has been reached, then the compressor outlet bypass valve 65 is opened as shown in Step S6, and the air flow is again allowed to bypass, and surging is prevented. If the pressure value established by control line (B) is not reached, operation is continued without change as shown in Step S7. At Step S7, after the processing of each of Steps S1, S3, S5, and S6, operation is continued, and as shown in Step S8, if adjustment of the degree of opening of the inlet variable guide vane is necessary, Step S2 is returned to, if this is not necessary, processing is completed. When control device 70 reduces the degree of opening of the inlet variable guide vane in this way, the pressure at the outlet of compressor 16 does not decrease and approaches surge line (S), at the time it reaches control line (A), the degree of opening of the inlet variable guide vane 71 is maintained, surge prevention valve 67 or compressor outlet bypass valve 65 is opened, and an amount of air flowing from the outlet side of compressor 16 is allowed to bypass, and surging of compressor 16 is prevented. Of course, in addition to the effects mentioned above, the same effects as for the first mode of the previous embodiment are obtained.

Claims: A pressurized fluidized bed combined electricity generation system comprising: a steam turbine (21); a pressurized fluidized bed boiler (1) for generating steam for supply to said steam turbine (21) via a main steam pipe system (30) by combusting air and fuel; a gas turbine (15) driven by exhaust gas supplied from said pressurized fluidized bed boiler (1) and air; a compressor (16) for supplying said air; and a reheating steam pipe system (31) having a high temperature side and a low temperature side, and connected between said pressurized fluidized bed boiler (1) and said steam turbine; and a steam extraction pipe system (3) for extracting a part of the steam generated by said pressurized fluidized bed boiler (1) characterized in that the pressurized fluidized bed combined electricity generation system further comprises a dust collecting device (14) connected to said pressurized fluidized bed boiler (1) and having an inlet side; said gas turbine (15) being connected to said dust collecting device (14) and driven by exhaust gas supplied through said dust collecting device (14); and said steam extraction pipe system (3) extracts a part of the steam generated by said pressurized bed boiler (1) from said low temperature side of said reheating steam pipe system (31) and supplies the steam to the inlet side of said dust collecting device (14). A pressurized fluidized bed combined electricity generation system comprising: a steam turbine (21); a pressurized fluidized bed boiler (1) for generating steam for supply to said steam turbine (21) via a main steam pipe system (30) by combusting air and fuel; a gas turbine (15) driven by exhaust gas supplied from said pressurized fluidized bed boiler (1) and air; a compressor (16) having an outlet side for supplying said air to said pressurized fluidized bed boiler (1), and a reheating steam pipe system (31) having a high temperature side and a low temperature side, and connected between said pressurized fluidized bed boiler (1) and said steam turbine (21) ; and a steam extraction pipe system (4) for extracting a part of the steam generated by said pressurized fluidized bed boiler (1) characterized in that the pressurized fluidized bed combined electricity generation system further comprises a dust collecting device (14) connected to said pressurized fluidized bed boiler (1) and having an inlet side; said gas turbine (15) being connected to said dust collecting device (14) and driven by exhaust gas supplied through said dust collecting device (14); and said steam extraction pipe system (4) extracts a part of the steam generated by said pressurized bed boiler (1) from said low temperature side of said reheating steam pipe system (31) and supplies the steam to the outlet side of said compressor (16). A pressurized bed combined electricity generation system as set forth in claim 1or 2 further comprising: a first bypass duct (68) which communicates between an outlet side of said compressor (16) and an exhaust gas side of said gas turbine (15) and which has a surge prevention valve (67) ; a second bypass duct (66) which communicates between the outlet side of said compressor (16) and an inlet side of said gas turbine (15) and which has a compressor outlet bypass valve (65); and a control device (70) which receives measured pressure values from a pressure detection device which detects the pressure at the outlet side of said compressor (16) and which controls said valves of said first and second bypass ducts (68, 66) based on a relationship between a surge limiting pressure and a predetermined degree of opening of an inlet variable guide vane (71) of said compressor (16); wherein air from said compressor (16) which is connected to said gas turbine (15) is supplied as the air for combustion in said pressurized fluidized bed boiler (1). A pressurized fluidized bed combined electricity generation system according to claim 3, wherein: said control device (70) is adapted to establish in advance two surge limiting pressure values and, to maintain the predetermined degree of opening of the inlet variable guide vane (71) and open said surge prevention valve (67) of said first bypass duct (68) when said pressure detector detects that a pressure during operation reaches a pressure of one of said surge limiting pressure values, and wherein said control device (70) is adapted to open said outlet bypass valve of said second bypass duct (66) when said pressure detector detect that said pressure during operation reaches the other surge limiting pressure value. A pressurized fluidized bed combined electricity generation system according to claim 4, wherein said control device (70) is able to adjust the values of said two surge limiting pressures established in advance depending upon a temperature of intake air of said compressor (16).

Inventors: ABE KATSUHIKO, FUJII FUMINORI, HYAKUTAKE YOSHINORI, KATO MAKOTO, MASUDA YOSHIFUMI, UCHIDA SATOSHI, ABE, KATSUHIKO, FUJII, FUMINORI, HYAKUTAKE, YOSHINORI, KATO, MAKOTO, MASUDA, YOSHIFUMI, UCHIDA, SATOSHI, ABE, Katsuhiko, Mitsubishi Heavy Industries, Ltd., FUJII, Fuminori, Mitsubishi Heavy Indust., Ltd., HYAKUTAKE, Yoshinori, Mitsubishi Heavy Indus. Ltd, KATO, Makoto, Mitsubishi Heavy Industries, Ltd., MASUDA, Yoshifumi, Mitsubishi Heavy Indust., Ltd., UCHIDA, Satoshi, Mitsubishi Heavy Indust., Ltd.
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1998
Main classification: F01K23
IPC codes: F01K23, F02C3, F01K21, F01K17, F02C6