Abstract:
Provided is a power plant including a gas turbine that uses a fuel gas as a fuel; a fuel gas cooler that cools the fuel gas, which is to be pressurized in a fuel gas compressor and re-circulated, using cooling water; and a dust collection device that separates/removes impurities from the fuel gas that is to be guided to the fuel gas compressor; wherein the power plant further includes heating means that heats the fuel gas that is to be guided to the dust collection device using the fuel gas that has been used to generate an anti-thrust force acting on a rotor of the fuel gas compressor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of Japanese Application No. 2010-270615 filed in Japan on Dec. 3, 2010, the contents of which are hereby incorporated by its reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a power plant provided with a gas turbine, which uses a low-heating-value gas, such as blast furnace gas (BFG), as a fuel, and a fuel gas cooler that cools fuel gas pressurized in a fuel gas compressor and re-circulated. 
         [0004]    2. Description of Related Art 
         [0005]    Known power plants provided with a gas turbine, which uses a low-heating-value gas, such as blast furnace gas (BFG), as a fuel, and a fuel gas cooler that cools fuel gas pressurized in a fuel gas compressor and re-circulated include, for example, that disclosed in  FIG. 1  in Japanese Unexamined Patent Application, Publication No. Hei 9-79046. 
         [0006]    In the case where the power plant disclosed in  FIG. 1  of the above-mentioned Japanese Unexamined Patent Application, Publication No. Hei 9-79046 is used in a location where the temperature of the fuel gas can become 5° C. or lower, such as a cold region etc., there is a risk that ice may be formed on a dust collector (dust collection device)  5 , causing abnormal discharge of the dust collector  5 , and that the ice formed on the dust collector  5  may be scattered toward a fuel gas compressor  6  located downstream, which may damage blades of the fuel gas compressor  6 . Therefore, if the power plant disclosed in  FIG. 1  of the above-mentioned Japanese Unexamined Patent Application, Publication No. Hei 9-79046 is used in a location where the outside temperature can become 5° C. or lower, such as a cold region etc., the fuel gas that has passed through a fuel gas cooler  16  is supplied to an intermediate position in piping (fuel gas supply system) that guides the fuel gas, which has been mixed and adjusted in a mixing chamber  4  so as to have a suitable heating value, to the dust collector  5 , thereby intentionally increasing the temperature of (heating) the fuel gas flowing through the piping. 
         [0007]    However, if the gas turbine is operated at the rated output, only a small amount of fuel gas is bypassed to the fuel gas cooler  16 . Therefore, in such a case, there has been a problem in that the power generation level is limited because it is required to forcedly reduce the output of the gas turbine (i.e., the power generation level) to generate the fuel gas that is to be bypassed to the fuel gas cooler  16 , thereby increasing the temperature of (heating) the fuel gas that is passing through the piping with the fuel gas supplied from the fuel gas cooler  16 . 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The present invention has been conceived in light of the circumstances described above, and an object thereof is to provide a power plant that is capable of increasing the temperature of (heating) a fuel gas that is to be guided to a dust collection device without reducing the output of a gas turbine. 
         [0009]    In order to solve the problems described above, the present invention employs the following solutions. 
         [0010]    The power plant according to the present invention includes a gas turbine that uses a fuel gas as a fuel; a fuel gas cooler that cools the fuel gas, which is to be pressurized in a fuel gas compressor and re-circulated, using cooling water; and a dust collection device that separates/removes impurities from the fuel gas that is to be guided to the fuel gas compressor; wherein the power plant further includes heating means that heats the fuel gas that is to be guided to the dust collection device using the fuel gas used to generate an anti-thrust force acting on a rotor of the fuel gas compressor. 
         [0011]    With the power plant according to the present invention, regardless of the output of the gas turbine, the fuel gas used to generate the anti-thrust force acting on the rotor of the fuel gas compressor is used to increase the temperature of (heat) the fuel gas that is to be guided to the dust collection device. 
         [0012]    By doing so, it is possible to increase the temperature of (heat) the fuel gas that is to be guided to the dust collection device without reducing the output of the gas turbine. 
         [0013]    In addition, by increasing the temperature of (heating) the fuel gas that is to be guided to the dust collection device, it is possible to prevent ice from forming on the dust collection device, thereby preventing an abnormal discharge of the dust collection device. 
         [0014]    Further, it is possible to increase the temperature of (heat) the fuel gas that is to be guided to the dust collection device to control the temperature of the fuel gas flowing into the fuel gas compressor within the desired range (for example, within the range from 20° C. to 30° C.), and it is possible to widen the outside temperature range at which there is no reduction in the compressor efficiency of the fuel gas compressor. 
         [0015]    In the above-mentioned power plant, the heating means may be provided with a nozzle that injects the fuel gas, guided from a balancing chamber in the fuel gas compressor, into the fuel gas that is to be guided to the dust collection device. 
         [0016]    With such a power plant, the fuel gas that has been used to generate the anti-thrust force acting on the rotor of the fuel gas compressor and that has reached the balancing chamber of the fuel gas compressor is sprayed (directly) through the nozzle into the fuel gas flowing towards the dust collection device, thereby (directly) warming up the fuel gas flowing towards the dust collection device. 
         [0017]    By doing so, a heat exchange device (heat exchanger) that has a complex structure and unavoidably large contact area and flow resistance (pressure loss) does not need to be arranged at the upstream side of the dust collection device; therefore, it is possible to achieve a simple structure and to minimize the increase in the flow resistance (pressure loss). 
         [0018]    With such a power plant according to the present invention, an advantage is afforded in that it is possible to increase the temperature of (heat) the fuel gas that is to be guided to the dust collection device without reducing the output of the gas turbine by effectively using a thrust-balancing gas that is conventionally discharged to a fuel gas cooler and whose waste heat is exhausted after being used to generate the anti-thrust force. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0019]      FIG. 1  is a schematic structural diagram of a power plant according to an embodiment of the present invention. 
           [0020]      FIG. 2  is a cross-sectional diagram of the BFG compressor shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    A power plant according to an embodiment of the present invention will be described below with reference to  FIGS. 1 and 2 . 
         [0022]      FIG. 1  is a schematic structural diagram of a power plant according to this embodiment, and  FIG. 2  is a cross-sectional diagram of the BFG compressor shown in  FIG. 1 . 
         [0023]    As shown in  FIG. 1 , a power plant  10  according to this embodiment is provided with a gas turbine  11 , a BFG compressor (fuel gas compressor)  12 , a generator (not shown), a fuel gas cooler (hereinafter referred to as “gas cooler”)  13 , a BFG (blast furnace gas) supply system  14 , a COG (coke-oven gas) supply system (not shown), and an HRSG (exhaust heat recovery boiler)  15 . 
         [0024]    The gas turbine  11  is provided with an air compressor  16 , a (gas turbine) combustor  17 , and a turbine  18 . In addition, the gas turbine  11 , the BFG compressor  12 , and the generator are connected via a speed-reduction mechanism  19 , and the BFG compressor  12  and the generator are configured to rotate co-operatively with the rotation of the gas turbine  11 . 
         [0025]    The BFG supply system  14  is a fuel supply line that guides BFG (low-heating-value fuel gas) to a gas nozzle (not shown) that constitutes the combustor  17 , the COG supply system is a fuel supply line that suitably adjusts the heating value of the BFG by mixing COG (high-heating-value fuel gas) with the BFG, and the downstream end of this BFG supply system in which the COG has been mixed is connected to the combustor  17 . 
         [0026]    The BFG supply system  14  is provided with an upstream line  21  that guides the BFG generated in a blast furnace (not shown) to the BFG compressor  12 , a downstream line  22  that guides the BFG that has been compressed in the BFG compressor  12  (that has been sent out (discharged) from the BFG compressor  12 ) to the gas nozzle, and a bypass line  23  that communicates between an intermediate position in the upstream line  21  and an intermediate position in the downstream line  22  to return the BFG passing through the downstream line  22  to the upstream line  21  as required. 
         [0027]    The upstream line  21  is provided with, at intermediate positions therein, a mixing chamber  24  that mixes heating-value-adjusting gas (for example, N2 for reducing the heating value and/or COG for increasing the heating value) with the BFG that has been guided from the blast furnace such that the BFG is adjusted to have a suitable heating value, a dust collection device (for example, wet type electric dust collector (Electrostatic Precipitator))  25  that separates/removes fine particles (impurities), such as fine dust, from the BFG that is to be guided to the BFG compressor  12  from the mixing chamber  24 , and a (first) temperature detector  26  that detects the temperature of the BFG flowing into the dust collection device  25 . 
         [0028]    In addition, a shut-off valve  27  is provided at an intermediate position in the downstream line  22 . 
         [0029]    The bypass line  23  is provided with, at intermediate positions therein, a bypass valve (flow regulating valve)  28  that adjusts the amount of BFG that is returned (extracted) from an intermediate position in the downstream line  22  to an intermediate position in the upstream line  21  located between the mixing chamber  24  and the dust collection device  25 , and the gas cooler  13  that is positioned downstream of the bypass valve  28  and cools the BFG that is returned (extracted) from the intermediate position in the downstream line  22  to the intermediate position in the upstream line  21  located between the mixing chamber  24  and the dust collection device  25 . 
         [0030]    The gas cooler  13  is provided with a cooling-water supply pipe  32  that guides cooling water pooled in a cooling-water pit  31  to a spray nozzle (not shown) arranged inside the gas cooler  13 , a hopper (not shown) that collects the cooling water that falls after cooling the BFG by being sprayed from the spray nozzle, and a cooling-water return pipe  33  that guides the cooling water held in the hopper to the cooling-water pit  31 . In addition, a cooling-water pump  34  and a cooler (not shown) are provided at intermediate positions in the cooling-water-supply pipe  32 . 
         [0031]    The level of the cooling water (water level) held in the hopper is maintained (naturally) at a constant level (water level) by a U-shaped pipe (not shown) provided at the most upstream portion of the cooling-water return pipe  33 . 
         [0032]    A drain line  35  that guides the cooling water pooled in the cooling-water pit  31  to a drain pit (not shown) is connected to the cooling-water supply pipe  32  positioned downstream of a cooler  35 , and an orifice  36  and an open/close valve  37 , which is normally kept open, are provided at intermediate positions in the drain line  35 . 
         [0033]    In addition, the discharged water (waste water) pooled in the drain pit is blown out (discharged) from the system through a blow line (not shown) and a blow pump (not shown) as required. 
         [0034]    As shown in  FIG. 2 , balancing discs  41  are provided in the BFG compressor  12 , such that the thrust force (force that presses the rotor  42  to the left in  FIG. 2  along the axial direction (the left/right direction in  FIG. 2 )) that is applied to (acts on) the rotor  42  is cancelled (compensated) by an anti-thrust force (force that presses the rotor  42  to the right in  FIG. 2  along the axial direction (the left/right direction in  FIG. 2 )) that is applied to (acts on) the rotor  42 . The BFG that has leaked from a labyrinth seal  43  provided on a peripheral portion of the balancing discs  41  flows into a balancing chamber  44  provided (formed) in a casing  12   a,  and subsequently is returned (brought back) to the intermediate position of the flow path formed within the gas cooler  13  through a BFG return pipe  45  (see  FIG. 1 ). 
         [0035]    As shown in  FIG. 1 , a (first) switching valve  46  is provided at an intermediate position in the BFG return pipe  45 , and a BFG-heating line (heating means)  51  that communicates between an intermediate position in the upstream line  21  and an intermediate position in the BFG return pipe  45  and that allows, as required, the BFG passing through the BFG return pipe  45  to flow into the upstream line  21  is connected to the BFG return pipe  45  positioned upstream of the switching valve  46 . The downstream end (outlet end) of the BFG-heating line  51  is connected to the upstream line  21  at a position that is downstream of the mixing chamber  24  and is upstream of the position where the downstream end (outlet end) of the bypass line  23  is connected. In addition, a (second) switching valve  52  is provided at an intermediate position in the BFG-heating line  51 , and a nozzle (not shown) is provided on the downstream end (outlet end) of the BFG-heating line  51 . 
         [0036]    The BFG injected from the nozzle (directly) warms up the BFG that is passing (flowing) through the upstream line  21 , flows downstream in the upstream line  21  towards the dust collection device  25  together with the BFG that is flowing in the upstream line  21  from the upstream side, flows into the dust collection device  25 , and is guided into the BFG compressor  12  after fine particles (impurities), such as fine dust, are separated/removed therefrom in the dust collection device  25 . 
         [0037]    If the temperature detected by the temperature detector  26  exceeds (is higher than) 5° C., the switching valve  46  is fully opened and the switching valve  52  is fully closed. Once the temperature detected by the temperature detector  26  becomes 5° C. or lower, the switching valve  46  is fully closed and the switching valve  52  is fully opened. 
         [0038]    With the power plant  10  according to this embodiment, regardless of the output of the gas turbine  11 , the BFG used to generate the anti-thrust force acting on the rotor  42  of the BFG compressor  12  is used to increase the temperature of (heat) the BFG that is to be guided to the dust collection device  25 . 
         [0039]    By doing so, it is possible to increase the temperature of (heat) the BFG that is to be guided to the dust collection device  25  without reducing the output of the gas turbine  11 . 
         [0040]    In addition, by increasing the temperature of (heating) the BFG that is to be guided to the dust collection device  25 , it is possible to prevent ice from forming on the dust collection device  25 , thereby preventing an abnormal discharge of the dust collection device  25 . 
         [0041]    Further, it is possible to increase the temperature of (heat) the BFG that is to be guided to the dust collection device  25  to control the temperature of the BFG flowing into the BFG gas compressor  12  within the desired range (for example, within the range from 20° C. to 30° C.), and it is possible to widen the outside temperature range at which there is no reduction in the compressor efficiency of the BFG gas compressor  12 . 
         [0042]    In addition, with the power plant  10  according to this embodiment, the BFG that has been used to generate the anti-thrust force acting on the rotor  42  of the BFG compressor  12  and that has reached the balancing chamber  44  in the BFG compressor  12  is sprayed (directly) through the nozzle into the BFG flowing towards the dust collection device  25 , thereby (directly) warming up the BEG flowing towards the dust collection device  25 . 
         [0043]    By doing so, a heat exchange device (heat exchanger) that has a complex structure and unavoidably large contact area and flow resistance (pressure loss) does not need to be arranged at the upstream side of the dust collection device  25 ; therefore, it is possible to achieve a simple structure and to minimize the increase in the flow resistance (pressure loss). 
         [0044]    The present invention is not limited to the embodiment described above, and appropriate modifications and alterations are possible as required. 
         [0045]    For example, in the embodiment described above, the COG (coke-oven gas) and the BFG (blast furnace gas) are described as specific examples of the high-heating-value fuel and the low-heating-value fuel, respectively; however, the type of fuel may include those other than the COG (coke-oven gas) and the BFG (blast furnace gas). 
         [0046]    In addition, in the embodiment described above, the downstream end (outlet end) of the BFG-heating line  51  is connected to the upstream line  21  at a position that is downstream of the mixing chamber  24  and is upstream of the position where the downstream end (outlet end) of the bypass line  23  is connected; however, the downstream end (outlet end) of the BFG-heating line  51  may be connected to an intermediate position in the bypass line  23  that communicates between the gas cooler  13  and the upstream line  21 . 
         [0047]    Furthermore, by arranging, in the vicinity of the inlet (intake port) of the BFG compressor  12 , a (second) temperature detector (not shown) that detects the temperature of the BFG that flows into the BFG compressor  12 , and by connecting the downstream end (outlet end) of a branch pipe (not shown) branched from the BFG-heating line  51  to an intermediate position in the upstream line  21  that communicates between the dust collection device  25  and the BFG compressor  12 , the temperature of the BFG that flows into the BFG compressor  12  may be finely adjusted (controlled) by adjusting the degree of opening of a flow regulating valve (not shown) arranged at an intermediate position in the branch pipe while monitoring the temperature detected by the (second) temperature detector. 
         [0048]    By doing so, it is possible to control the temperature of BFG flowing into the BFG gas compressor  12  within the desired range, and to widen the outside temperature range at which there is no reduction in the compressor efficiency of BFG gas compressor  12 .