Abstract:
It is an object to solve a bypass line corrosion problem effectively, enable prompt supply of a fuel gas into a bypass line in the event of an emergency, and provide an inexpensive coal gasification plant. An integrated coal gasification combined cycle power generation plant includes a coal gasification furnace, a dust remover, a gas refiner, a gas turbine and the like, a main system line connecting therebetween, and a bypass line connecting between the outlet side of the coal gasification furnace in the main system line and a flare stack, wherein a dust remover bypass valve which is disposed in an upstream portion of the bypass line and which opens and closes the bypass line, a treatment gas control valve which is disposed in a downstream portion of the bypass line and which controls the flow rate, and a first inert gas input line which is disposed downstream from the dust remover bypass valve and which supplies the inert gas to the bypass line are provided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a coal gasification plant, in which coal is gasified and used as a fuel for a gas turbine and the like, and a method for operating the same. 
         [0003]    2. Description of Related Art 
         [0004]    Heretofore, coal gasification plants have been noted as plants for effectively utilizing the coal with abundant reserves. Such coal gasification plants are provided with bypass lines for discharging fuel gases in the plants in order to discharge fuel gases, which cannot be utilized in downstream sides on startup, to the outside of the systems and to decompress the inside of the plants on normal shutdown or emergency shutdown. Since the fuel gases passing through the bypass lines are corrosive, corrosion protection of the bypass lines has been required. 
         [0005]    A coal gasification plant disclosed in, for example, Japanese Unexamined Patent Application, Publication No. 10-298563 has been proposed as a plant provided with the above-described corrosion protection. 
         [0006]    In this plant, a heater for heating a line is disposed upstream from a bypass valve, which is disposed in the bypass line and which opens and closes the bypass line, so as to heat the line upstream from the bypass valve and prevent the fuel gas from condensing. In addition to this, a gas having a small water content is injected into the line upstream from the bypass valve, so that the fuel gas is prevented from flowing into the bypass line. 
         [0007]    The description in Japanese Unexamined Patent Application, Publication No. 10-298563 is intended for treatments on startup, and is insufficient as the corrosion protection including the corrosion protection during operation. 
         [0008]    When a problem occurs in the coal gasification plant during operation, it is necessary that a fuel gas is allowed to flow into the bypass line, the inside of the plant is decompressed and, thereafter the plant is shut down. At this time, for the purpose of a prompt operation, the pressure in the bypass line must be kept nearly at the same level as the pressure in the plant, or else when the fuel gas is allowed to flow at about 3 MPa into the bypass line under atmospheric pressure, the inlet velocity becomes up to the velocity of sound, and the bypass valve and the bypass line are abraded rapidly, so that damage will result. Consequently, in previous cases, it is necessary that the bypass valve is opened during normal operation, and the fuel gas is allowed to flow into the bypass line and stay therein so as to balance the pressures. In order to prevent the corrosion of the bypass line, heating has been performed to prevent condensation of the fuel gas or the bypass line has been formed from an expensive corrosion-resistant material. 
         [0009]    In many cases, it is difficult to place gas treatment units close to the plants. Therefore, the lengths of bypass lines are increased and the production costs are increased. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    The present invention has been made in consideration of the above-described circumstances. Accordingly, it is an object of the present invention to solve the bypass line corrosion problem effectively, enable prompt supply of a fuel gas into a bypass line in the event of an emergency, and provide an inexpensive coal gasification plant. 
         [0011]    In order to solve the above-described problems, the following means are adopted in the present invention. 
         [0012]    A first aspect of the present invention provides a coal gasification plant including a coal gasification furnace for gasifying coal to produce a fuel gas; a dust remover for removing solids in the above-described fuel gas; a gas refiner for removing sulfides and the like in the above-described fuel gas and supplying the resulting gas serving as a fuel to a gas turbine; a main system line connecting between the above-described coal gasification furnace, the above-described dust remover, the above-described gas refiner, the above-described gas turbine, and the like; and a bypass line connecting between the outlet side of the above-described coal gasification furnace in the above-described main system line and a gas treatment unit, wherein a bypass valve which is disposed in an upstream portion of the above-described bypass line and which opens and closes the above-described bypass line, a treatment gas control valve which is disposed in a downstream portion of the above-described bypass line and which controls the flow rate, and a first inert gas input line which is disposed downstream from the above-described bypass valve and which supplies the inert gas to the above-described bypass line are included. 
         [0013]    In the startup of the coal gasification furnace, the fuel gas produced in the coal gasification furnace is unsatisfactory for a fuel because of, for example, low calorie. Therefore, the fuel gas is allowed to flow into the bypass line rather than the main system line, and is treated in a gas treatment apparatus, so as to be discharged to the outside of the system. 
         [0014]    With respect to the coal gasification plant according to the present aspect, after an increase in temperature and an increase in pressure of the coal gasification furnace are completed and the bypass valve is closed, the inert gas is supplied from the first inert gas input line to the side downstream from the bypass valve, and the fuel gas remaining in the bypass line is discharged to the gas treatment unit. After the remaining fuel gas is discharged, the inert gas is still supplied from the first inert gas input line, so that a fuel gas leaking from the bypass valve is discharged to the gas treatment unit. In addition, the pressure of the bypass line is controlled nearly at the same level as the pressure of the main system line by the treatment gas control valve. 
         [0015]    In this manner, the fuel gas allowed to flow into the bypass line on startup and the fuel gas leaking from the bypass valve during normal operation are discharged to the gas treatment unit by the inert gas supplied from the first inert gas input line. Therefore, the fuel gas do not stay in the bypass line. 
         [0016]    Consequently, since corrosive substances, e.g., sulfuric acid, due to cooling and condensation of the fuel gas are not generated, an occurrence of corrosion in the bypass line can be prevented effectively. 
         [0017]    Since a means, in which the bypass line is heated to avoid condensation or the bypass line is formed from an expensive corrosion-resistant material, for serving as the corrosion protection of the bypass line becomes unnecessary, the coal gasification plant can be produced inexpensively. 
         [0018]    Since the pressure in the bypass line is maintained nearly at the same level as the pressure in the main system line during normal operation, even when the bypass valve is opened, the fuel gas containing dust, e.g., unburnt char, does not issue in a jet into the bypass line at a very high speed, e.g., the velocity of sound. Consequently, the bypass valve can be opened during operation without consideration of damage to the bypass line and, therefore, the bypass valve can be opened promptly in the event of an emergency or shutdown, and the apparatuses in the main system line can be decompressed. 
         [0019]    A nitrogen gas is favorable as the inert gas from the viewpoint of ease of availability, cost, and the like. 
         [0020]    In the above-described aspect, a first branch line connecting some midpoint between the above-described dust remover and the above-described gas refiner in the above-described main system line and the above-described bypass line, a first branch bypass valve disposed in the first branch line, and a second inert gas input line disposed downstream from the first branch bypass valve may be included. 
         [0021]    In the case where the dust remover is started after the coal gasification furnace is started, the bypass valve is closed, and the first branch bypass valve is opened. Consequently, unburnt char and the like in the fuel gas produced in the coal gasification furnace are separated in the dust remover. The resulting fuel gas is allowed to flow into the bypass line through the first branch line, and is treated in a gas treatment apparatus, so as to be discharged to the outside of the system. 
         [0022]    In this coal gasification plant, after the startup treatment of the dust remover is completed and the first branch bypass valve is closed, an inert gas is supplied from the second inert gas input line to the side downstream from the first branch bypass valve, and the fuel gas remaining in the first branch line is discharged to the gas treatment unit. After the remaining fuel gas is discharged, the inert gas is still supplied from the second inert gas input line, so that a fuel gas leaking from the first branch bypass valve is discharged to the gas treatment unit. In addition, the pressure of the bypass line is controlled nearly at the same level as the pressure of the main system line by the treatment gas control valve. 
         [0023]    In this manner, the fuel gas allowed to flow into the first bypass line on startup and the fuel gas leaking from the first branch bypass valve during normal operation are discharged to the gas treatment unit by the inert gas supplied from the second inert gas input line. Therefore, together with the inert gas from the first inert gas input line, the fuel gas do not stay in the first branch line and the bypass line. 
         [0024]    Consequently, since corrosive substances, e.g., sulfuric acid, due to cooling and condensation of the fuel gas are not generated, an occurrence of corrosion in the first branch line and the bypass line can be prevented effectively. 
         [0025]    Since a means, in which the first branch line and the bypass line are heated to avoid condensation or the first branch line and the bypass line are formed from an expensive corrosion-resistant material, for serving as the corrosion protection of the first branch line and the bypass line becomes unnecessary, the coal gasification plant can be produced inexpensively. 
         [0026]    Since the pressures in the bypass line and the first branch line are maintained nearly at the same level as the pressure in the main system line during normal operation, even when the bypass valve or the first branch bypass valve is opened, the fuel gas does not issue in a jet into the bypass line or the first branch line at a very high speed, e.g., the velocity of sound. Consequently, the bypass valve can be opened during operation without consideration of damage to the bypass line and the like. Therefore, the bypass valve can be opened promptly in the event of an emergency or shutdown, and the apparatuses in the main system line can be decompressed. 
         [0027]    In the above-described aspect, a second branch line connecting between the outlet portion of the above-described gas refiner in the above-described main system line and the above-described bypass line, a second branch bypass valve disposed in the second branch line, and a third inert gas input line disposed downstream from the second branch bypass valve may be included. 
         [0028]    For example, in the case where the gas refiner is started after the coal gasification furnace and the dust remover are started, the bypass valve and the first branch bypass valve are closed, and the second branch bypass valve is opened. Consequently, the fuel gas produced in the coal gasification furnace is passed through the dust remover and the gas refiner, and is allowed to flow into the bypass line through the second branch line. The fuel gas is treated in the gas treatment apparatus, and is discharged. 
         [0029]    In this coal gasification plant, after the startup treatment of the gas refiner is completed and the second branch bypass valve is closed, an inert gas is supplied from the third inert gas input line to the side downstream from the second branch bypass valve, and the fuel gas remaining in the second branch line is discharged to the gas treatment unit. After the remaining fuel gas is discharged, the inert gas is still supplied from the third inert gas input line, so that a fuel gas leaking from the second branch bypass valve is discharged to the gas treatment unit. In addition, the pressure of the bypass line is controlled nearly at the same level as the pressure of the main system line by the treatment gas control valve. 
         [0030]    In this manner, the fuel gas allowed to flow into the second branch line on startup and the fuel gas leaking from the second branch bypass valve during normal operation are discharged to the gas treatment unit by the inert gas supplied from the third inert gas input line. Therefore, together with the inert gas from the first inert gas input line and the second inert gas input line, the fuel gas do not stay in the first branch line, the second branch line, and the bypass line. 
         [0031]    Consequently, since corrosive substances, e.g., sulfuric acid, due to cooling and condensation of the fuel gas are not generated, an occurrence of corrosion in the first branch line, the second branch line, and the bypass line can be prevented effectively. 
         [0032]    Since a means, in which the second branch line and the bypass line are heated to avoid condensation or the second branch line and the bypass line are formed from an expensive corrosion-resistant material, for serving as the corrosion protection of the second branch line and the bypass line becomes unnecessary, the coal gasification plant can be produced inexpensively. 
         [0033]    In the case where the fuel gas remaining in the portion located downstream from the first branch bypass valve in the first branch line can be discharged by the inert gas supplied from the first inert gas input line, the second inert gas input line can be omitted. 
         [0034]    A second aspect of the present invention provides a method for operating a coal gasification plant in which a fuel gas is produced from coal in a coal gasification furnace, solids are removed from the fuel gas in a dust remover, and desulfurization and the like are performed in a gas refiner so as to supply the fuel gas serving as a fuel to a gas turbine, the method including the steps of: 
         [0035]    discharging the above-described fuel gas, which is allowed to flow into a bypass line branched from an outlet portion of the above-described coal gasification furnace and connected to a gas treatment unit, from the above-described bypass line by an inert gas supplied to the side downstream from the bypass valve disposed in the above-described bypass line after the bypass valve is closed, on startup, and maintaining the pressure in the above-described bypass line nearly at the same level as the pressure of the above-described fuel gas by the above-described inert gas supplied continuously during normal operation. 
         [0036]    With respect to the method for operating a coal gasification plant according to the present aspect, the fuel gas allowed to flow into the bypass line is discharged to the gas treatment unit by the inert gas supplied to the side downstream from the bypass valve, on startup. Since the inert gas is supplied continuously during normal operation, the fuel gas leaking from the bypass valve is discharged to the gas treatment unit by the inert gas. In this case, the gas which passes through the bypass line is almost inert gas. 
         [0037]    Consequently, since the fuel gas do not stay in the bypass line, corrosive substances, e.g., sulfuric acid, due to cooling and condensation of the fuel gas are not generated. Therefore, an occurrence of corrosion in the bypass line can be prevented effectively. 
         [0038]    Since a means, in which the bypass line is heated to avoid condensation or the bypass line is formed from an expensive corrosion-resistant material, for serving as the corrosion protection of the bypass line becomes unnecessary, the coal gasification plant can be produced inexpensively. 
         [0039]    The pressure in the bypass line is maintained nearly at the same level as the pressure in the fuel gas during normal operation. Consequently, in the event of an emergency, the fuel gas is allowed to flow into the bypass line promptly without consideration of damage to the bypass line and, therefore, the plant can be decompressed. 
         [0040]    In the above-described aspect, the above-described fuel gas, which is allowed to flow into a first branch line branched from an outlet portion of the above-described dust remover and connected to the above-described bypass line, may be discharged from the above-described first branch line and the above-described bypass line by an inert gas supplied to the side downstream from a first branch valve disposed in the above-described first branch line after the above-described first branch valve is closed, on startup. The pressure in the above-described first branch line and the above-described bypass line may be maintained nearly at the same level as the pressure of the above-described fuel gas by the inert gas supplied continuously during normal operation. 
         [0041]    With respect to this method for operating the coal gasification plant, the fuel gas allowed to flow into the first branch line is discharged to the gas treatment unit by the inert gas supplied downstream from the first branch valve, on startup. Since the inert gas is supplied continuously during normal operation, the fuel gas leaking from the first branch valve is discharged to the gas treatment unit by the inert gas. In this case, the gas which passes through the bypass line is almost inert gas. 
         [0042]    Consequently, since the fuel gas do not stay in the first branch line and the bypass line, corrosive substances, e.g., sulfuric acid, due to cooling and condensation of the fuel gas are not generated. Therefore, an occurrence of corrosion in the first branch line and the bypass line can be prevented effectively. 
         [0043]    Since a means, in which the bypass line and the like are heated to avoid condensation or the bypass line and the like are formed from an expensive corrosion-resistant material, for serving as the corrosion protection of the bypass line and the like becomes unnecessary, the coal gasification plant can be produced inexpensively. 
         [0044]    The pressures in the first branch line and the bypass line are maintained nearly at the same level as the pressure of the fuel gas during normal operation. Consequently, in the event of an emergency, the fuel gas is allowed to flow into the first branch line and the bypass line promptly without consideration of damage to the first branch line and the bypass line and, therefore, the plant can be decompressed. 
         [0045]    In the above-described aspect, the above-described fuel gas, which is allowed to flow into a second branch line branched from an outlet portion of the above-described gas refiner and connected to the above-described bypass line, may be discharged from the above-described second branch line and the above-described bypass line by an inert gas supplied to the side downstream from a second branch valve disposed in the above-described second branch line after the above-described second branch valve is closed, on startup. The pressure in the above-described second branch line and the above-described bypass line may be maintained at nearly the same level as the pressure of the above-described fuel gas by the above-described inert gas during normal operation. 
         [0046]    With respect to this method for operating the coal gasification plant, the fuel gas allowed to flow into the second branch line is discharged to the gas treatment unit by the inert gas supplied downstream from the second branch valve, on startup. Since the inert gas is supplied continuously during normal operation, the fuel gas leaking from the second branch valve is discharged to the gas treatment unit by the inert gas. In this case, the gas which passes through the bypass line is almost inert gas. 
         [0047]    Consequently, since the fuel gas does not stay in the second branch line and the bypass line, corrosive substances, e.g., sulfuric acid, due to cooling and condensation of the fuel gas are not generated. Therefore, an occurrence of corrosion in the second branch line and the bypass line can be prevented effectively. 
         [0048]    Since a means, in which the bypass line and the like are heated to avoid condensation or the bypass line and the like are formed from an expensive corrosion-resistant material, for serving as the corrosion protection of the bypass line and the like becomes unnecessary, the coal gasification plant can be produced inexpensively. 
         [0049]    The pressure in at least the second branch line and the bypass line is maintained nearly at the same level as the pressure of the fuel gas during normal operation. Consequently, in the event of an emergency, the fuel gas is allowed to flow into the second branch line and the bypass line promptly without consideration of damage to the second branch line and the bypass line and, therefore, the plant can be decompressed. 
         [0050]    With respect to the coal gasification plant according to the first aspect of the present invention, the fuel gas allowed to flow into the bypass line and the like on startup and the fuel gas leaking from the bypass valve and the like during normal operation are discharged to the gas treatment unit by the inert gas supplied to the side downstream from the bypass valve and the like. Therefore, an occurrence of corrosion in the bypass and the like can be prevented effectively. 
         [0051]    Since a means, in which the bypass line is heated to avoid condensation or the bypass line is formed from an expensive corrosion-resistant material, for serving as the corrosion protection of the bypass line becomes unnecessary, the coal gasification plant can be produced inexpensively. 
         [0052]    Since the pressure in the bypass line is maintained nearly at the same level as the pressure in the main system line during normal operation, the bypass valve can be opened promptly in the event of an emergency or shutdown, and the apparatuses in the main system line can be decompressed. 
         [0053]    With respect to the method for operating a coal gasification plant according to the second aspect of the present invention, the fuel gas allowed to flow into the bypass line and the like on startup and the fuel gas leaking from the bypass valve and the like during normal operation are discharged to the gas treatment unit by the inert gas supplied to the side downstream from the bypass valve and the like. Therefore, an occurrence of corrosion in the bypass line and the like can be prevented effectively. 
         [0054]    Since a means, in which the bypass line and the like are heated to avoid condensation or the bypass line and the like are formed from an expensive corrosion-resistant material, for serving as the corrosion protection of the bypass line and the like becomes unnecessary, the coal gasification plant can be produced inexpensively. 
         [0055]    The pressure in the bypass line is maintained nearly at the same level as the pressure of the fuel gas during normal operation. Consequently, in the event of an emergency, the fuel gas is allowed to flow into the bypass line and the like promptly without consideration of damage to the bypass line and the like and, therefore, the plant can be decompressed. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0056]      FIG. 1  is a block diagram showing the schematic configuration of an integrated coal gasification combined cycle power generation plant according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0057]    The integrated coal gasification combined cycle power generation plant (a coal gasification plant)  1  according to an embodiment of the present invention will be described below with reference to  FIG. 1 . 
         [0058]      FIG. 1  is a block diagram showing the schematic configuration of the integrated coal gasification combined cycle power generation plant  1 . 
         [0059]    The integrated coal gasification combined cycle power generation plant  1  is provided with a coal gasification furnace  3 , a dust remover  5 , a gas refiner  7 , a gas turbine combustor  9 , a gas turbine  11 , and a waste heat recovery boiler  13 . 
         [0060]    These individual apparatuses are connected by a main system line  15 . 
         [0061]    The coal gasification furnace  3  is supplied with pulverized coal  17 , a gasifying agent  19 , and char  21  under pressure. With respect to the pulverized coal  17 , in an upstream step not shown in the drawing, raw material coal is pulverized into pulverized coal of a few micrometers to a few hundred micrometers and the resulting pulverized coal is supplied. For the gasifying agent  19 , air or oxygen is supplied. The char  21  is an unburnt component contained in a fuel gas produced in the coal gasification furnace  3  as described later. 
         [0062]    In the coal gasification furnace  3 , the pulverized coal  17 , the gasifying agent  19 , and the char  21  are combusted and, thereby, an endothermic reaction occurs, in which carbon in the pulverized coal  17  and the char  21  is reacted with CO 2  and H 2 O in a high temperature gas so as to generate CO and H 2 . The resulting CO and H 2  serve as a fuel gas for the gas turbine. 
         [0063]    The fuel gas produced in the coal gasification furnace  3  contains char and the like, which are unburnt solids, and is led to the dust remover  5  through the main system line  15 . The dust remover  5  is provided with a porous filter, and the char  21  contained in the fuel gas is trapped and recovered by passing the fuel gas through the porous filter. The thus recovered char  21  is recycled by being returned to the coal gasification furnace  3 . 
         [0064]    A dust remover inlet valve  23  is disposed upstream from the dust remover  5  in the main system line  15 . 
         [0065]    The fuel gas passed through the dust remover  5  is fed to the gas refiner  7 . 
         [0066]    In the gas refiner  7 , for example, sulfides are removed from the fuel gas. In general, the gas refiner  7  is of wet type, and is composed of a COS converter for converting COS in the fuel gas to H 2 S by using a catalyst, a gas cooling tower, a gas scrubbing tower, a H 2 S absorption tower filled with a H 2 S absorbing solution, a heat exchanger for raising the temperature of the cooled fuel gas, and the like. 
         [0067]    The fuel gas subjected to desulfurization and the like in the gas refiner  7  is led to the gas turbine combustor  9  through the main system line  15 . 
         [0068]    A flow rate control valve  25  is disposed upstream from the gas turbine combustor  9  in the main system line  15 . 
         [0069]    The gas turbine  11  is connected to an air compressor  27  with a common rotating shaft. 
         [0070]    The air compressor  27  is configured to feed compressed air to the gas turbine combustor  9 . In the gas turbine combustor  9 , the fuel gas fed from the gas refiner  7  is mixed with high pressure air from the air compressor  27 , and is combusted. The resulting combustion gas is supplied to the gas turbine  11 . 
         [0071]    A generator  29  connected to a rotating shaft driven by the gas turbine  11  is disposed opposite to the air compressor  27  with the gas turbine  11  therebetween. 
         [0072]    A combustion exhaust gas from the gas turbine  11  is led to the waste heat recovery boiler  13 . The waste heat recovery boiler  13  generates steam by using the combustion exhaust gas from the gas turbine  11 , and the gas passed through the waste heat recovery boiler  13  is released into the atmosphere from a stack  31 . 
         [0073]    The waste heat recovery boiler  13  is configured in such a way as to, for example, drive a steam turbine (not shown in the drawing) connected to the generator  29  by using the steam generated. A generator different from the generator  29  may be driven by the steam turbine. 
         [0074]    A bypass line  33  is connected to a location A between the coal gasification furnace  3  and the dust remover inlet valve  23  (an outlet side of the coal gasification furnace  3 ) in the main system line  15 . The other end of the bypass line  33  is connected to a flare stack (gas treatment unit)  39 . 
         [0075]    In the gas treatment unit, usually, the gas is subjected to an incineration treatment. The gas treatment unit may be a ground flare, in which a cover is constructed on the ground and incineration is performed therein, besides the flare stack, in which incineration is performed at un upper portion of the stack, as in the embodiment. 
         [0076]    In many cases, the flare stack  39  is disposed at some distance from (for example, a few hundred meters away from) a main unit in consideration of safety and layout because the incineration treatment is performed. 
         [0077]    A dust remover bypass valve (a bypass valve)  35  for opening and closing the bypass line  33  is disposed at an upstream portion (a position close to the main system line  15 ) in the bypass line  33 . 
         [0078]    A first nitrogen input line (a first inert gas input line)  37  for supplying a nitrogen gas is connected to immediately downstream from the dust remover bypass valve  35  in the bypass line  33 . 
         [0079]    A treatment gas control valve  41  for controlling the flow rate of the gas passing through the bypass line  33  is disposed at the downstream portion (a position close to the flare stack  39 ) in the bypass line  33 . 
         [0080]    A pressure sensor  43  for measuring the pressure in the bypass line  33  is disposed upstream from the treatment gas control valve  41  in the bypass line  33 . The treatment gas control valve  41  is controlled in such a way that the valve opening is adjusted in accordance with the value measured by the pressure sensor  43 . 
         [0081]    A first branch line  45  connecting a position B between the dust remover  5  and the gas refiner  7  in the main system line  15  to the bypass line  33  is disposed. In the first branch line  45 , a gas refining bypass valve (a first branch valve)  47  for opening and closing the first branch line  45  is disposed. 
         [0082]    A second nitrogen input line (a second inert gas input line)  49  for supplying a nitrogen gas is connected to immediately downstream from the gas refining bypass valve  47  in the first branch line  45 . 
         [0083]    A second branch line  51  connecting a position C between the gas refiner  7  and the flow rate control valve  25  in the main system line  15  to the bypass line  33  is disposed. In the second branch line  51 , a gas turbine bypass valve (a second branch valve)  53  for opening and closing the second branch line  51  is disposed. 
         [0084]    A third nitrogen input line (a third inert gas input line)  55  for supplying a nitrogen gas is connected to immediately downstream from the gas turbine bypass valve  53  in the second branch line  51 . 
         [0085]    In the present embodiment, a nitrogen gas is used as the inert gas from the viewpoint of ease of availability, cost, and the like. However, it is essential only that this is a noncombustible gas, e.g., carbon dioxide, argon, helium, and a combustion exhaust gas. 
         [0086]    It is favorable that the inert gas to be supplied has a low water content. 
         [0087]    The operation of the integrated coal gasification combined cycle power generation plant  1  according to the above-described embodiment will be described. 
         [0088]    The startup procedure of the integrated coal gasification combined cycle power generation plant  1  will be described. 
         [0089]    In the present embodiment, the gas is sequentially passed through the coal gasification furnace  3 , the dust remover, the gas refiner  7 , the gas turbine  11  and the remainder in the integrated coal gasification combined cycle power generation plant  1 . 
         [0090]    When the coal gasification furnace  3  is started up, the dust remover inlet valve  23  in the main system line  15  is closed in order that the fuel gas produced in the coal gasification furnace  3  is not fed to the dust remover  5 . The dust remover bypass valve  35  in the bypass line  33  is opened in order that the fuel gas produced in the coal gasification furnace  3  is discharged to the flare stack  39  through the bypass line  33 . 
         [0091]    In this state, the coal gasification furnace  3  is started. The fuel gas produced in the coal gasification furnace  3  on startup is fed to the flare stack  39  through the dust remover bypass valve  35  and the bypass line  33 . The fuel gas is subjected to a combustion treatment in the flare stack  39 , and is released into the atmosphere. 
         [0092]    When the temperature and the pressure of the coal gasification furnace  3  are raised sufficiently, the dust remover inlet valve  23  is opened, and the fuel gas produced in the coal gasification furnace  3  is fed to the dust remover  5 . At the same time, the dust remover bypass valve  35  is closed, and the supply of the fuel gas from the coal gasification furnace  3  to the bypass line  33  is stopped. 
         [0093]    In this state, a nitrogen gas is supplied from the first nitrogen input line  37  to the bypass line  33 . The fuel gas remaining in the bypass line  33  is led to the flare stack  39 , and is subjected to an incineration treatment so as to be discharged. 
         [0094]    The startup operation of the dust remover  5  is started and, in addition, the gas refining bypass valve  47  is opened. The fuel gas from the dust remover  5  is fed to the flare stack  39  through the first branch line  45  and the bypass line  33 . The fuel gas is subjected to a combustion treatment in the flare stack  39 , and is released into the atmosphere. 
         [0095]    When the startup operation of the dust remover  5  is completed, the gas refining bypass valve  47  is closed, and the fuel gas is fed to the gas refiner  7 . At the same time, the dust remover bypass valve  35  is closed, and the supply of the fuel gas from the coal gasification furnace  3  to the bypass line  33  is stopped. 
         [0096]    In this state, a nitrogen gas is supplied from the second nitrogen input line  49  to the first branch line  45 . The fuel gas remaining downstream from the gas refining bypass valve  47  in the first branch line  45  is led to the flare stack  39 , and is subjected to an incineration treatment so as to be discharged. 
         [0097]    When the position of the gas refining bypass valve  47  is brought close to the bypass line  33 , the length of the first branch line  45  on the side downstream from the gas refining bypass valve  47  is decreased. Therefore, the combustion gas remaining in this portion can be discharged by the nitrogen gas supplied from the first nitrogen input line  37 . 
         [0098]    In this case, the second nitrogen gas input line  49  can be omitted. 
         [0099]    The startup operation of the gas refiner  7  is started while the control valve  25  is closed and, in addition, the gas turbine bypass valve  53  is opened. The fuel gas from the gas refiner  7  is fed to the flare stack  39  through the second branch line  51  and the bypass line  33 . The fuel gas is subjected to a combustion treatment in the flare stack  39 , and is released into the atmosphere. 
         [0100]    When the startup operation of the gas refiner  7  is completed, the control valve  25  is opened, and the fuel gas is fed to the turbine combustor  9 . At the same time, the gas turbine bypass valve  53  is closed, and the supply of the fuel gas to the second branch line  51  and the bypass line  33  is stopped. 
         [0101]    In this state, a nitrogen gas is supplied from the third nitrogen input line  55  to the second branch line  51 . The gas refining bypass valve  47  is closed, the fuel gas remaining downstream from the gas turbine bypass valve  53  in the second branch line  51  is led to the flare stack  39 , and is subjected to an incineration treatment so as to be discharged. 
         [0102]    In this manner, the fuel gas allowed to flow into the bypass line  33  and the like from the main system line  15  and remain therein, on startup, is fed to the flare stack  39  by the nitrogen gas supplied from the first nitrogen input line  37 , the second nitrogen input line  49 , or the third nitrogen input line  55 , and is subjected to a combustion treatment. Therefore, the fuel gas do not stay in the bypass line. 
         [0103]    The thus started integrated coal gasification combined cycle power generation plant  1  is brought into a normal operation. 
         [0104]    In the coal gasification furnace  3 , the pulverized coal  17 , the gasifying agent  19 , and char  21  supplied under pressure are combusted and, thereby, carbon in the pulverized coal  17  and the char  21  is reacted with CO 2  and H 2 O in a high temperature gas so as to generate a fuel gas containing CO and H 2  as components. 
         [0105]    The fuel gas produced in the coal gasification furnace  3  is led to the dust remover  5  through the main system line  15 , and the contained char  21  is recovered in the dust remover  5 . The recovered char  21  is recycled by being returned to the coal gasification furnace  3 . 
         [0106]    The fuel gas passed through the dust remover  5  is fed to the gas refiner  7 , and, for example, sulfides are removed from the fuel gas. 
         [0107]    The fuel gas subjected to desulfurization and the like in the gas refiner  7  is led to the gas turbine combustor  9  through the main system line  15 , and is combusted together with the compressed air fed from the air compressor  27 . In the gas turbine combustor  9 , the fuel gas fed from the gas refiner  7  is combusted by using the high pressure air from the air compressor  27 , and the resulting combustion gas is supplied to the gas turbine  11 . 
         [0108]    The gas turbine  11  is driven to rotate by the combustion gas, and the generator  29  connected to the rotating shaft thereof converts the torque to an electric power. 
         [0109]    A combustion exhaust gas passed through the gas turbine  11  is led to the waste heat recovery boiler  13 , and steam is generated by using the sensible heat of the combustion exhaust gas. The steam generated in the waste heat recovery boiler  13  is used for a purpose of, for example, power generation through driving of a steam turbine not shown in the drawing. 
         [0110]    The combustion exhaust gas passed through the waste heat recovery boiler  13  is led to the stack  31 , and is released into the atmosphere from the stack  31 . 
         [0111]    At this time, the dust remover bypass valve  35 , the gas refining bypass valve  47 , and the gas turbine bypass valve  53  are closed and, therefore, the fuel gas is not led from the main system line  15  to the bypass line  33 . 
         [0112]    On the other hand, the nitrogen gas is still supplied continuously from the first nitrogen input line  37 , the second nitrogen input line  49 , and the third nitrogen input line  55 . The treatment gas control valve  41  is closed, and the pressure in the bypass line  33  is increased up to about 3 MPa that is the pressure in the main system line  15 . Thereafter, the amount of opening of the treatment gas control valve  41  is controlled by the pressure sensor  43  which measures the pressure in the bypass line  33 , in such a way that the pressure becomes nearly at the same level as the pressure in the main system line  15 . That is, the nitrogen gas flows almost continuously from the treatment gas control valve  41  to the flare stack  39 . 
         [0113]    As described above, although the dust remover bypass valve  35 , the gas refining bypass valve  47 , and the gas turbine bypass valve  53  are closed, the fuel leaks necessarily from the main system line  15 . The leaked fuel gas is fed to the flare stack  39  through the bypass line  33  by the nitrogen gas supplied continuously from the first nitrogen input line  37 , the second nitrogen input line  49 , and the third nitrogen input line  55 , and is subjected to an incineration treatment, so as to be released into the atmosphere. 
         [0114]    As described above, the fuel gas allowed to flow into the bypass line  33  and the like from the main system line  15  side, on startup, and the fuel gas leaking from the main system line  15  side during normal operation are fed to the flare stack  39  by the nitrogen gas supplied from the first nitrogen input line  37 , the second nitrogen input line  49 , or the third nitrogen input line  55 , and are subjected to the combustion treatment. Therefore, the fuel gas do not stay in the bypass line. 
         [0115]    Consequently, since corrosive substances, e.g., sulfuric acid, due to cooling and condensation of the fuel gas are not generated, an occurrence of corrosion in the bypass line  33 , the first branch line  45 , and the second branch line  51  on the sides downstream from the dust remover bypass valve  35 , the gas refining bypass valve  47 , and the gas turbine bypass valve  53  can be prevented effectively. 
         [0116]    Since a means, in which the significantly long bypass line  33 , the first branch line  45 , and the second branch line  51  located downstream from the dust remover bypass valve  35 , the gas refining bypass valve  47 , and the gas turbine bypass valve  53  are heated to avoid condensation or these are formed from an expensive corrosion-resistant material, for serving as the corrosion protection thereof becomes unnecessary, the integrated coal gasification combined cycle power generation plant  1  can be produced inexpensively. 
         [0117]    In the case where the integrated coal gasification combined cycle power generation plant  1  is stopped, the gas turbine bypass valve  53  is opened. Even in such a case, since the pressure in the main system line  15  and the pressure in the bypass line  33  are in balance, the fuel gas does not issue in a jet into the bypass line  33  explosively. Subsequently, the treatment gas control valve  41  is opened. In this manner, the nitrogen gas in the bypass line  33  is released from the flare stack  39 , and the pressure in the bypass line  33  is decreased. Accompanying that, the combustion gas in the main system line  15  is allowed to flow into the bypass line  33  through the second branch line  51 , and is subjected to an incineration treatment in the flare stack  39 , so as to be released into the atmosphere. 
         [0118]    Consequently, the main system line  15  is decompressed and, therefore, each apparatus can be stopped. 
         [0119]    Here, merely the gas turbine bypass valve  53  is opened. However, the dust remover bypass valve  35  or the gas refining bypass valve  47  may be opened, or at least two thereof may be opened at the same time. 
         [0120]    In the event of an emergency, for example, when leakage of the gas has occurred in the coal gasification furnace  3 , the dust remover inlet valve  23  is closed and the dust remover bypass valve  35  is opened. Even in such a case, since the pressure in the main system line  15  and the pressure in the bypass line  33  are in balance, the fuel gas does not issue in a jet into the bypass line  33  explosively. Therefore, the treatment gas control valve  41  is opened at the same time. In this manner, the nitrogen gas in the bypass line  33  is released from the flare stack  39 , and the pressure in the bypass line  33  is decreased. Accompanying that, the combustion gas from the coal gasification furnace  3  is allowed to flow into the bypass line  33  through the dust remover bypass valve  35 , and is subjected to an incineration treatment in the flare stack  39 , so as to be released into the atmosphere. 
         [0121]    Consequently, the coal gasification furnace  3  is decompressed and, therefore, the coal gasification furnace  3  can be stopped and inspected. 
         [0122]    It is favorable that an optimum valve is opened depending on a place at which the abnormality has occurred. For example, in the case where an abnormality has occurred in the dust remover  5 , the gas refining bypass valve  47  is opened, and the dust remover  5  is decompressed. In the case where an abnormality has occurred in the gas refiner  7 , the gas turbine bypass valve  53  is opened. 
         [0123]    As described above, during normal operation, the nitrogen gas is supplied continuously from the first nitrogen input line  37 , the second nitrogen input line  49 , and the third nitrogen input line  55 , and the pressures in the bypass line  33 , the first branch line  45 , and the second branch line  51  are maintained nearly at the same level as the pressure in the main system line  15  by the treatment gas control valve  41 . Therefore, even when any one of the dust remover bypass valve  35 , the gas refining bypass valve  47 , and the gas turbine bypass valve  53  is opened, the fuel gas does not issue in a jet from the main system line  15  into the bypass line  33  side explosively, for example, at a very high speed, e.g., the velocity of sound. 
         [0124]    Consequently, the dust remover bypass valve  35 , the gas refining bypass valve  47 , and the gas turbine bypass valve  53  can be opened during normal operation without consideration of damage to the bypass line  33 , the first branch line  45 , and the second branch line  51 . 
         [0125]    Therefore, the dust remover bypass valve  35 , the gas refining bypass valve  47 , and the gas turbine bypass valve  53  can be opened promptly in the event of an emergency or shutdown, and the apparatuses in the main system line can be decompressed.