Abstract:
A gasification system which ensures stable dust precipitation performance and which can achieve an increase in capacity is provided. In a coal gasification furnace having a coal gasification furnace configured to produce a gas fuel by gasification of a carbon-containing fuel, a cyclone which is provided downstream of the coal gasification furnace and which separates and removes char in the gas fuel, and a first filter and a second filter which are provided downstream of the cyclone and which precipitate char remaining in the gas fuel, the first and the second filters are disposed in parallel.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a gasification system configured to use a solid or a liquid carbon-containing fuel as a gas fuel by gasification. 
         [0003]    This application is based on Japanese Patent Application No. 2004-236546, the content of which is incorporated herein by reference. 
         [0004]    2. Description of Related Art 
         [0005]    In the gasification system as described above, as disclosed, for example, in Japanese Unexamined Patent Application Publication No. 5-222951 (sections 0016 to 0023, and FIG. 1), in order to separate char, which is an uncombusted component contained in a gas fuel produced in a gasification furnace, a dust precipitation system is provided downstream of the gasification furnace. As the dust precipitation system, a combination of a cyclone, which is a centrifugal solid-gas separator, and a filter, which has a cloth or a ceramic filtering medium for filtration, has been widely used. This system is designed so that most of the char is efficiently separated by the cyclone and the remaining char is then reliably separated by the filter. 
         [0006]    In recent years, concomitant with the increases in the sizes of gasification systems, dust precipitation systems have also been required to have larger capacities. In order to increase the capacity, a plurality of lines which are arranged in parallel and which each contain a cyclone and a filter in combination has been used in practice. 
         [0007]    In an arrangement in which a plurality of lines (such as two lines), each line having a cyclone and a filter in combination and the lines being provided in parallel, when the differential pressure is increased due to, for example, clogging of one of the filters for some reason, a gas flow rate of a gas passing through this clogged filter is decreased. Accordingly, since a gas flow rate of a gas passing through a cyclone connected to this clogged filter is also decreased, gas velocity in this cyclone is decreased, and as a result, centrifugal classification performance is degraded. When the centrifugal classification performance is degraded, char concentration in gas flowing into the filter is increased, and as a result, the clogging of the filter is further worsened. The clogging of the above filter rapidly worsens, and in the worst case, operation must inevitably be suspended to remove the clogging material. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    In consideration of the above problems, an object of the present invention is to provide a gasification system which ensures stable dust precipitation performance and which can achieve an increase in capacity. 
         [0009]    To this end, the present invention was made as described below. 
         [0010]    That is, a gasification system of the present invention includes: a gasification furnace configured to produce a gas fuel by gasification of a carbon-containing fuel, a first dust precipitator which is provided downstream of the gasification furnace and which separates and removes char contained in the gas fuel, and fine dust precipitators which are provided downstream of the first dust precipitator and which precipitate char remaining in the gas fuel. In the gasification system described above, the fine dust precipitators are disposed in parallel. 
         [0011]    According to the present invention, from the gas fuel produced from a carbon-containing fuel by the gasification furnace, most of the char is separated and removed by the first dust precipitator, and the gas fuel is then divided into streams flowing into respective fine dust preceptors, so that the remaining char is recovered by the fine dust preceptors. 
         [0012]    As the first dust precipitator, a centrifugal precipitator, such as a cyclone, is used which relatively easily achieves the increase in capacity, and 80% to 90% of the char can be efficiently separated and removed thereby. 
         [0013]    As the fine dust precipitator, in order to reliably recover the remaining char, for example, a filter is used which precipitates dust at a low velocity using a cloth or a ceramic filtering medium. 
         [0014]    As described above, according to the present invention, since the fine dust precipitators configured to precipitate dust at a low velocity are disposed in parallel downstream of the first dust precipitator, the processing capacity is increased by the fine dust precipitators. Hence, even when the size of the first dust precipitator is increased, the process can be sufficiently performed by the fine dust precipitators, and as a result, an increase in the capacity of the gasification system can be achieved. 
         [0015]    In addition, the number of the fine dust precipitators may be determined in accordance with the capacity of the first dust precipitator. 
         [0016]    When the differential pressure is increased due to, for example, clogging of one of the fine dust precipitators, the gas flow rate of the gas fuel passing through the above clogged fine dust precipitator is decreased thereby, and the flow rate of the fuel gas passing through the other fine dust precipitator is simply increased corresponding to the above decrease in flow rate, so that the flow rate of the gas fuel passing through the first dust precipitator is not influenced at all. Hence, since the dust precipitation performance of the first dust precipitator is not degraded, the concentration of the char in the gas fuel flowing into each fine dust precipitator is not increased. Accordingly, since the clogging of the fine dust precipitator does not rapidly worsen, the performance thereof can be restored by backwashing, which is performed at a predetermined timing, and as a result, stable dust precipitation performance can be ensured. 
         [0017]    In addition, the gasification system according to the present invention may further include a collector configured to collect char recovered from the fine dust precipitators; and a char recycling device configured to supply the char collected in the collector to the gasification furnace. 
         [0018]    As described above, since the gasification system further includes the collector configured to collect char recovered from the fine dust precipitators and the char recycling device configured to supply the char collected in the collector to the gasification furnace, the variation in the amount of char recovered in the fine dust precipitators can be handled by the collector. Hence, the char recycling device may be designed to have a capacity corresponding to the amount of char collected at an outlet of the first dust precipitator, and as a result, this char recycling device can be designed to be small overall compared to the case in which char recycling devices are provided for the respective dust precipitators. In addition, since piping and the like may be more easily performed, the production cost can be reduced. 
         [0019]    Furthermore, in the gasification system according to the present invention, the collector may also be configured to collect char separated by the first dust precipitator. 
         [0020]    As described above, since the collector also collects the char separated by the first dust precipitator, without considering the variation in amount of char separated in the respective dust precipitators, the char recycling device may have a capacity corresponding to the amount of char which is generated, and hence this char recycling device can be designed to be small overall compared to the case in which char recycling devices are provided for each dust precipitator. In addition, since piping and the like may be more easily performed, the production cost can be further reduced. 
         [0021]    According to the present invention, since the fine dust precipitators which collect dust at a low velocity are provided in parallel downstream of the first dust precipitator, an increase in capacity of the gasification system can be achieved and stable dust precipitation performance can be ensured. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0022]      FIG. 1  is a block diagram schematically showing a structure of a coal gasification system according to a first embodiment of the present invention. 
           [0023]      FIG. 2  is a block diagram schematically showing a structure of a coal gasification system according to a second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Hereinafter, embodiments of the present invention will be described with reference to the drawings. 
       First Embodiment 
       [0025]    Hereinafter, a coal gasification system (gasification system)  1  of a first embodiment according to the present invention will be described with reference to  FIG. 1 . 
         [0026]      FIG. 1  is a block diagram showing a schematic structure of the coal gasification system  1 . 
         [0027]    The coal gasification system  1  has a coal gasification furnace (gasification furnace)  3 , a dust removing system  5 , a desulfurization device  7 , and a gas turbine  9 . 
         [0028]    The coal gasification furnace  3 , the dust removing system  5 , the desulfurization device  7 , and the gas turbine  9  are connected to each other by a main system line  17 . 
         [0029]    Into the coal gasification furnace  3 , fine powdered coal  11 , a gasification agent  13 , and char  15  are supplied with pressure. The fine powdered powder  11  is obtained by pulverizing raw coal to a size of several micrometers to several hundreds of micrometers in a previous step (not shown) and is then supplied. As the gasification agent  13 , air or oxygen is supplied. The char  15  is an uncombusted component contained in a gas fuel produced in the coal gasification furnace  3 , as described below. 
         [0030]    In the coal gasification furnace  3 , when the fine powdered coal  11 , the gasification agent  13 , and the char  15  are combusted, carbon contained in the fine powdered coal  11  and the char  15  react with CO 2  and H 2 O in a high temperature gas, and an endothermic reaction thereby occurs in which CO and H 2  are produced. The CO and H 2  thus produced are used as a gas fuel for the gas turbine  9 . 
         [0031]    The gas fuel produced in the coal gasification furnace  3  contains char and the like, which are uncombusted solid components, and is supplied to the dust removing system  5  via the main system line  17 . 
         [0032]    The dust removing system  5  has a cyclone (first dust precipitator)  19 , a first filter (fine dust precipitator)  21 , and a second filter (fine dust precipitator)  23 , the above two filters being provided in parallel downstream of the cyclone  19 . 
         [0033]    The cyclone  19  is a centrifugal solid-gas separator and separates 80% to 90% of the char contained in the gas fuel. The char  15  thus separated is supplied to the coal gasification furnace  3  by a first char recycling device  25 . 
         [0034]    The gas fuel from which most of the char has been separated by the cyclone  19  is divided into two streams at a position A of the main system line  17 , and the two streams of the gas fuel flow are supplied into the first filter  21  and the second filter  23 . 
         [0035]    The first filter  21  and the second filter  23  each have a ceramic filtering medium and are each designed to filter char contained in the gas fuel when it passes through the filtering medium. The char thus filtered is made to fall downward by supplying a backwashing gas such as nitrogen in the direction opposite to that of the flow of the gas fuel at a predetermined timing and is then recovered. 
         [0036]    The char recovered in the first filter  21  is supplied to the coal gasification furnace  3  by a second char recycling device  27 . 
         [0037]    The char recovered in the second filter  23  is supplied to the coal gasification furnace  3  by a third char recycling device  29 . 
         [0038]    The char recovered by the first char recycling device  25 , the second char recycling device  27 , and the third char recycling device  29  is pressurized by nitrogen gas supplied from respective compressors (not shown) to have a pressure higher than that in the coal gasification furnace  3  and is then supplied therein. 
         [0039]    The gas fuel passing through the first filter  21  and the gas fuel passing through the second filter  23  combine at a position B and are supplied to the desulfurization device  7 . 
         [0040]    In the desulfurization device  7 , for example, sulfur components are removed from the gas fuel. The desulfurization device  7  is generally a wet type device and is formed, for example, of a COS converter converting COS in the gas fuel into H 2 S by a catalyst, a gas cooling tower, a gas scrubbing tower, a H 2 S absorbing tower in which a H 2 S absorbing solution is filled, and a heat exchanger in which a cooled gas fuel is heated. 
         [0041]    The gas fuel processed by desulfurization and the like in the desulfurization device  7  is supplied to the gas turbine  9  via the main system line  17 . In the gas turbine  9 , the gas fuel supplied from the desulfurization device  7  is combusted by high-pressure air supplied by an air compressor (not shown) and is converted into a rotation driving force. 
         [0042]    By this rotation driving force, electricity is obtained by rotating a power generator or the like. 
         [0043]    The operation of the above coal gasification system  1  of this embodiment will be described. 
         [0044]    In the coal gasification furnace  3 , by combusting the fine powdered coal  11 , the gasification agent  13 , and the char  15 , which are supplied with pressure, carbon contained in the fine powdered coal  11  and the char  15  react with CO 2  and H 2 O in a high-temperature gas, so that a gas fuel containing CO and H 2  is produced. 
         [0045]    The gas fuel produced in the coal gasification furnace  3  is supplied to the cyclone  19  via the main system line  17 , and approximately 80% to 90% of the char  15  mixed in the gas fuel is recovered by the cyclone  19 . The char  15  thus recovered is collected in the first char recycling device  25 , and after being pressurized by nitrogen gas supplied from a compressor (not shown), the recovered char  15  is then returned to the coal gasification furnace  3  so that recycling of the char  15  may be performed. 
         [0046]    The gas fuel from which most of the char is recovered by the cyclone  19  is divided at the position A of the main system line  17  into two streams, and the two streams of the gas fuel are supplied to the first filter  21  and the second filter  23 . 
         [0047]    When the gas fuel supplied to the first filter  21  passes through a ceramic filtering medium, the char in the gas fuel is filtered. The char thus filtered is made to fall downward by supplying a backwashing gas such as nitrogen in the direction opposite to that of the flow of the gas fuel at a predetermined timing and is then recovered. Subsequently, the char  15  thus recovered is collected in the second char recycling device  27 , and after being pressurized by nitrogen gas supplied from a compressor (not shown), the recovered char  15  is returned to the coal gasification furnace  3 , thereby performing the recycling. 
         [0048]    When the gas fuel supplied to the second filter  23  passes through a ceramic filtering medium, the char in the gas fuel is filtered. The char thus filtered is made to fall downward by backwashing performed at a predetermined timing and is then recovered. Subsequently, the char  15  thus recovered is collected in the third char recycling device  29 , and after being pressurized by nitrogen gas supplied from a compressor (not shown), the recovered char  15  is returned to the coal gasification furnace  3 , thereby performing the recycling. 
         [0049]    As described above, since the first filter  21  and the second filter  23  are provided in parallel downstream of the cyclone  19  in this embodiment, the processing capacity can be increased by the first filter  21  and the second filter  23 . Hence, when the capacity of the cyclone  19  is increased, in accordance with this increase, the process can be performed by the first filter  21  and the second filter  23 , and as a result, the increase in capacity of the gasification system can be achieved. 
         [0050]    In addition, when the capacity of the cyclone  19  is further increased, in accordance with the increase thereof, by further increasing the number of the first filter  21  and the second filter  23 , the process can be satisfactorily performed. 
         [0051]    In addition, when the differential pressure is increased due to, for example, clogging of the first filter  21 , the flow rate of the gas fuel passing through the first filter  21  is decreased thereby. In this case, when the flow rate of the fuel gas passing through the second filter  23  is simply increased corresponding to the above decrease in flow rate, the flow rate of the gas fuel passing through the cyclone  19  is not influenced at all. Hence, since the dust precipitation performance of the cyclone  19  is not degraded, the concentration of the char in the gas fuel flowing into the first filter  21  and the second filter  23  is not increased. Accordingly, since the clogging of the first filter  21  does not rapidly worsen, the performance thereof can be restored by backwashing which is performed at a predetermined timing, and as a result, stable dust precipitation performance can be ensured. 
         [0052]    The gas fuel passing thought the first filter  21  and the gas fuel passing through the second filter  23  combine at the position B and are supplied to the desulfurization device  7 , and for example, sulfur components are removed from the gas fuel. 
         [0053]    The gas fuel processed by desulfurization and the like in the desulfurization device  7  is supplied to the gas turbine  9  via the main system line  17  and is then combusted with compressed air supplied from an air compressor. 
         [0054]    Accordingly, the gas turbine  9  is driven to rotate, and for example, a power generator connected to a rotation shaft of the gas turbine  9  converts rotation driving force into electricity. 
       Second Embodiment 
       [0055]    Next, the coal gasification system  1  of a second embodiment according to the present invention will be described with reference to  FIG. 2 . 
         [0056]      FIG. 2  is a block diagram showing a schematic structure of the coal gasification system  1 . 
         [0057]    In this embodiment, the structure configured to handle the char recovered in the dust removing system  5  is different from that in the first embodiment. The other constituent elements are the same as those of the first embodiment, and hence duplicated descriptions are omitted. 
         [0058]    The same reference numerals of the first embodiment designate the same constituent elements in this embodiment. 
         [0059]    In the dust removing system  5 , a collector  31  is provided. The collector  31  is designed so as to collectively store the char separated and recovered by the cyclone  19 , the first filter  21 , and the second filter  23 . 
         [0060]    The char stored in the collector  31  is supplied to the coal gasification furnace  3  by a collective char recycling device (char recycling device)  33 . 
         [0061]    The char supplied to the collective char recycling device  33  is pressurized by nitrogen gas supplied from a compressor (not shown) to a pressure higher than that in the coal gasification furnace  3  and is then supplied therein. 
         [0062]    The operation of the above coal gasification system  1  of this embodiment will be described. 
         [0063]    In the coal gasification furnace  3 , by combusting the fine powdered coal  11 , the gasification agent  13 , and the char  15 , which are supplied with pressure, carbon contained in the fine powdered coal  11  and the char  15  react with CO 2  and H 2 O in a high-temperature gas, so that a gas fuel containing Co and H 2  is produced. 
         [0064]    The gas fuel produced in the coal gasification furnace  3  is supplied to the cyclone  19  via the main system line  17 , and approximately 80% to 90% of the char  15  contained in the gas fuel is recovered by the cyclone  19 . The char  15  thus recovered is collected in the collector  31 . 
         [0065]    The gas fuel from which most of the char is recovered by the cyclone  19  is divided at the position A of the main system line  17  into two streams, and the two streams of the gas fuel are supplied to the first filter  21  and the second filter  23 . 
         [0066]    When the gas fuel supplied to the first filter  21  passes through a ceramic filtering medium, the char in the gas fuel is filtered. The char thus filtered is made to fall downward by supplying a backwashing gas such as nitrogen in the direction opposite to that of the flow of the gas fuel at a predetermined timing and is then recovered. Subsequently, the recovered char  15  is collected in the collector  31 . 
         [0067]    When the gas fuel supplied to the second filter  23  passes through a ceramic filtering medium, the char in the gas fuel is filtered. The char thus filtered is made to fall downward by backwashing performed at a predetermined timing and is then recovered. Subsequently, the recovered char  15  is collected in the collector  31 . 
         [0068]    As described above, since the first filter  21  and the second filter  23  are provided in parallel downstream of the cyclone  19  in this embodiment, the processing capacity is increased by the first filter  21  and the second filter  23 . Hence, when the capacity of the cyclone  19  is increased, corresponding to this increase, the process can be performed by the first filter  21  and the second filter  23 , and as a result, the increase in capacity of the gasification system can be achieved. 
         [0069]    In addition, when the capacity of the cyclone  19  is further increased, corresponding to the increase thereof, by further increasing the number of the first filter  21  and the second filter  23 , the process can be satisfactorily performed. 
         [0070]    In addition, when the differential pressure is increased due to, for example, clogging of the first filter  21 , the flow rate of the gas fuel passing through the first filter  21  is decreased thereby. In this case, when the flow rate of the fuel gas passing through the second filter  23  is simply increased corresponding to the above decrease in flow rate, the flow rate of the gas fuel passing through the cyclone  19  is not influenced at all. Hence, since the dust precipitation performance of the cyclone  19  is not degraded, the concentration of the char in the gas fuel flowing into the first filter  21  and the second filter  23  is not increased. Accordingly, since the clogging of the first filter  21  does not rapidly worsen, the performance thereof can be restored by backwashing which is performed at a predetermined timing, and as a result, stable dust precipitation performance can be ensured. 
         [0071]    The char stored in the collector  31  is supplied to the collective char recycling device  33 . The char supplied to the collective char recycling device  33  is pressurized by nitrogen gas supplied from a compressor (not shown) and is then returned to the coal gasification furnace  3  for recycling. 
         [0072]    As described above, since the char recovered by the cyclone  19 , the first filter  21 , and the second filter  23  are once collected in the collector  31  and is then supplied to the coal gasification furnace  3  by the collective char recycling device  33 , the collective char recycling device  33  may have a capacity corresponding to the amount of the char which is generated. Accordingly, in the case in which char recycling devices are respectively provided for the cyclone  19 , the first filter  21 , and the second filter  23 , each char recycling device must have a capacity taking into consideration the variation in the amount of recovered char; however, according to the embodiment described above, compared to the case described above, the size of the collective char recycling device  33  can be reduced overall. In addition, since piping and the like may be more easily performed, the production cost can also be reduced. 
         [0073]    In this embodiment, although the char recovered by the cyclone  19 , the first filter  21 , and the second filter  23  is stored in the collector  31 , the present invention is not limited thereto, and for example, when the char recovered by the first filter  21  and the second filter  23  is stored in the collector  31 , and a char recycling device is independently provided for the cyclone  19 , a reduction in production cost can also be effectively achieved. 
         [0074]    The gas fuel passing thought the first filter  21  and the gas fuel passing through the second filter  23  combine at the position B and are supplied to the desulfurization device  7 , and for example, sulfur components are removed from the gas fuel. 
         [0075]    The gas fuel processed by desulfurization and the like in the desulfurization device  7  is supplied to the gas turbine  9  via the main system line  17  and is then combusted with compressed air supplied from the air compressor. 
         [0076]    Accordingly, the gas turbine  9  is driven to rotate, and for example, a power generator connected to the rotation shaft of the gas turbine  9  converts rotation driving force into electricity.