Abstract:
The purpose of the present invention is to provide an exhaust purifier which suppresses unnecessary consumption of pressurization air so as to improve a removal rate of dust. An exhaust purifier for removing particulate matter adhered to a NOx catalyst by injecting pressurized air using an air injection nozzle into a housing of a catalyst reactor in which the NOx catalyst serving as a catalyst is positioned, wherein an injection valve of a soot blower supplying pressurized air into the housing of the catalyst reactor is opened and closed based on an exhaust gas flow rate so as to inject the pressurized air.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an exhaust purifier of an internal combustion engine. 
       BACKGROUND ART 
       [0002]    Conventionally, an exhaust purifier which reduces NOx to nitrogen and water with a catalyst reactor in which a selective reduction NOx catalyst (SCR catalyst) is arranged and ammonia which is a reducing agent so as to decrease NOx (nitrogen oxide) included in exhaust gas from an internal combustion engine is known. The ammonia is generated by urea water injected to exhaust gas with high temperature and contacts the NOx catalyst so as to reduce NOx to nitrogen and water. 
         [0003]    In the exhaust purifier, a material having a carrier of oxides, such as Ti including active ingredients, such as V and Cr which is formed to be a honeycomb structure in which many through holes are formed is used as the NOx catalyst of the catalyst reactor. According to the configuration, a contacting area is increased so as to promote a reduction reaction. On the other hand, when exhaust gas passes through the through holes, dust included in the exhaust gas may adhere to the NOx catalyst and close the holes so as to lower the reduction reaction. Accordingly, there is an art in which compressed air is injected to a NOx catalyst so as to remove dust adhering to the NOx catalyst and suppress adhesion of dust. For example, an art described in the Patent Literature 1 is so. 
         [0004]    In a catalyst reactor (reactor) of an exhaust purifier (exhaust denitration device) described in the Patent Literature 1, if needed, compressed air is injected from an injection nozzle toward a NOx catalyst so as to hit dust adhering to the NOx catalyst, thereby removing the dust. Generally, the exhaust purifier is configured so that compressed air is injected periodically based on operation time of an engine. Namely, in the exhaust purifier, the compressed air is injected without considering an adhesion state of dust in the NOx catalyst. Accordingly, there is a problem that in the exhaust purifier, the compressed air is vainly consumed by unnecessary injection of the compressed air. 
       PRIOR ART REFERENCE 
     Patent Literature 
       [0000]    
       
         
           
             Patent Literature 1: the Japanese Patent Laid Open Gazette H8-126817 
           
         
       
     
       DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
       [0006]    The present invention is provided for solving the problems mentioned above, and the purpose of the invention is to provide an exhaust purifier which suppresses unnecessary consumption of compressed air so as to improve a removal rate of dust. 
       Means for Solving the Problems 
       [0007]    The problems to be solved by the present invention have been described above, and subsequently, the means of solving the problems will be described below. 
         [0008]    According to the present invention, in an exhaust purifier wherein compressed air is injected into a catalyst reactor in which a catalyst is arranged so as to remove dust adhering to the catalyst, the compressed air is injected into the catalyst reactor based on an exhaust gas flow rate. 
         [0009]    According to the present invention, when the exhaust gas flow rate is not more than a reference exhaust gas flow rate, the compressed air is injected into the catalyst reactor at a predetermined condition. 
         [0010]    According to the present invention, when a pressure difference between exhaust gas upstream the catalyst and exhaust gas downstream thereof is raised higher than a pressure difference between exhaust gas upstream the catalyst and exhaust gas downstream thereof at an initial state at the same exhaust flow rate for not less than a reference pressure difference raising amount, the compressed air is injected into the catalyst reactor at a condition different from the predetermined condition regardless of the exhaust gas flow rate. 
       Effect of the Invention 
       [0011]    The present invention brings the following effects. 
         [0012]    According to the present invention, the compressed air is injected at a mode at which dust is removed efficiently based on an operation state of an internal combustion engine. Accordingly, unnecessary consumption of the compressed air can be suppressed so as to improve a removal rate of the dust. 
         [0013]    According to the present invention, the compressed air is injected only in the state in which removal of the dust by power of exhaust gas is not expected. Accordingly, the unnecessary consumption of the compressed air can be suppressed so as to improve the removal rate of the dust. 
         [0014]    According to the present invention, a condition of injection of the compressed air is changed corresponding to an adhesion amount of the dust. Accordingly, the unnecessary consumption of the compressed air can be suppressed so as to improve the removal rate of the dust. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a drawing of an entire configuration of an embodiment of an exhaust purifier according to the present invention. 
           [0016]      FIG. 2  is a drawing of a catalyst reactor of the embodiment of the exhaust purifier according to the present invention. 
           [0017]      FIG. 3  is an enlargement of an air injection nozzle provided in the catalyst reactor of the embodiment of the exhaust purifier according to the present invention. 
           [0018]      FIG. 4  is a schematic drawing of a notification means of the embodiment of the exhaust purifier according to the present invention. 
           [0019]      FIG. 5  is a graph showing temporal change of a pressure difference for every load rate of the exhaust purifier according to the present invention. 
           [0020]      FIG. 6  is a graph showing a relation between an exhaust gas flow rate and a lowering rate of the pressure difference of the exhaust purifier according to the present invention 
           [0021]      FIG. 7  is a conceptual drawing of a mode of soot blow in the catalyst reactor of the embodiment of the exhaust purifier according to the present invention. 
           [0022]      FIG. 8A  is a photo showing a state of a NOx catalyst to which dust is adhered of the embodiment in the exhaust purifier according to the present invention. 
           [0023]      FIG. 8B  is a photo showing a state of the NOx catalyst after the soot blow in the exhaust purifier according to the present invention. 
           [0024]      FIG. 9  is a photo showing a state of a NOx catalyst after the soot blow in an exhaust purifier having a conventional soot blower. 
           [0025]      FIG. 10  is a graph showing a relation between a pressure difference rising amount and a lowering rate of a denitration rate of the exhaust purifier according to the present invention. 
           [0026]      FIG. 11  is a graph showing a reference pressure difference rising amount for every initial pressure difference of the exhaust purifier according to the present invention. 
           [0027]      FIG. 12  is a flow chart showing a basic control mode of the soot blow in the catalyst reactor of the embodiment of the exhaust purifier according to the present invention. 
           [0028]      FIG. 13  is a flow chart showing a control mode of soot blow control in the catalyst reactor of the embodiment of the exhaust purifier according to the present invention. 
           [0029]      FIG. 14  is a schematic drawing of a ship on which an engine having the exhaust purifier according to the embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    Below, referring to  FIGS. 1 to 4 , an exhaust purifier  1  which is a first embodiment of an exhaust purifier according to the present invention is explained. In this embodiment, an “upstream side” means an upstream side in a flow direction of fluid, and a “downstream side” means a downstream side in the flow direction of the fluid. The exhaust purifier  1  is not limited to this embodiment and may alternatively be airless type which does not use pressurized air. 
         [0031]    As shown in  FIG. 1 , the exhaust purifier  1  purifies exhaust gas discharged from an engine  22  which is an internal combustion engine driving a generator  28 . The exhaust purifier  1  is provided in an exhaust pipe  23  of the engine  22 . The exhaust purifier  1  has a urea water injection nozzle  2 , a urea supply passage  3 , a first air supply passage  4 , a pressurized air supply pump  5  (compressor), an air tank  6 , a urea air valve  8 , a urea water supply pump  9 , a switching valve  11 , a catalyst reactor  12 , a soot blower  15 , a pressure difference sensor  20 , an exhaust gas temperature sensor  21 , a control device  26 , a notification means  27  and the like. The exhaust purifier  1  may alternatively purify exhaust gas discharged from a main engine  105  and an auxiliary engine  106  provided in a ship  100  (see  FIG. 14 ). 
         [0032]    The urea water injection nozzle  2  supplies urea water to an inside of the exhaust pipe  23 . The urea water injection nozzle  2  is configured by a pipe member, and one of ends (downstream side) thereof is inserted from an outside to an inside of the catalyst reactor  12  or the exhaust pipe  23 . The urea water injection nozzle  2  is arranged upstream a first NOx catalyst  14   a  of the catalyst reactor  12  discussed later. The urea water injection nozzle  2  is connected to the urea supply passage  3  which is a passage of urea water. The urea water injection nozzle  2  is connected to the first air supply passage  4  which is a passage of pressurized air. 
         [0033]    The pressurized air supply pump  5  supplies pressurized air. The pressurized air supply pump  5  pressurizes (compresses) air and supply it. The pressurized air supply pump  5  supplies air to the air tank  6  (reservoir tank  7 ) when a pressure of the air tank  6  (reservoir tank  7 ) is less than a predetermined pressure, and stops when the pressure of the air tank  6  (reservoir tank  7 ) reaches the predetermined pressure. In this embodiment, the pressurized air supply pump  5  is not limited and may be any member which can maintain the pressure of the air tank  6  (reservoir tank  7 ). 
         [0034]    The urea air valve  8  opens and closes the passage of pressurized air. The urea air valve  8  is provided in the first air supply passage  4 . The urea air valve  8  is configured by an electromagnetic valve, and can open and close the first air supply passage  4  by sliding a spool (not shown). Namely, when the urea air valve  8  opens the first air supply passage  4 , pressurized air is supplied to the urea water injection nozzle  2 . The urea air valve  8  is not limited to this embodiment, and may be any member which opens and closes the passage of pressurized air. 
         [0035]    The urea water supply pump  9  supplies urea water. The urea water supply pump  9  is provided in the urea supply passage  3 . The urea water supply pump  9  supplies urea water in a urea water tank  10  via the urea supply passage  3  to the urea water injection nozzle  2  at a predetermined flow rate. The urea water supply pump  9  is not limited to this embodiment, and may be any member which supplies urea water. 
         [0036]    The switching valve  11  switches the passage of urea water. The switching valve  11  is provided downstream the urea water supply pump  9  in the urea supply passage  3 . The switching valve  11  is configured by an electromagnetic valve, and can open and close the urea supply passage  3  by sliding a spool (not shown). Namely, when the switching valve  11  opens the urea supply passage  3 , urea water is supplied to the urea water injection nozzle  2 . The switching valve  11  is not limited to this embodiment, and may be any member which opens and closes the passage of urea water. 
         [0037]    The catalyst reactor  12  reduces selectively NOx ion exhaust gas by a NOx catalyst arranged therein. The catalyst reactor  12  has a housing  13  and the NOx catalyst  14 . 
         [0038]    As shown in  FIGS. 1 and 2 , one of ends of the housing  13  is connected to the exhaust pipe  23  connected to the engine  22 . The other end of the housing  13  is connected to the exhaust pipe  23  opened to the outside. Namely, the housing  13  is configured as an exhaust passage through which exhaust gas from the engine  22  flows from the one side to the other end. Inside the housing  13 , the NOx catalyst  14  is arranged. Concerning the NOx catalyst  14 , the first NOx catalyst  14   a,  a second NOx catalyst  14   b  and a third NOx catalyst  14   c  are arranged in order from the one side of the housing  13  (the upstream side of exhaust gas) at predetermined intervals. The first NOx catalyst  14   a,  the second NOx catalyst  14   b  and the third NOx catalyst  14   c  can be sealed within the housing  13  and are detachable. The number of the NOx catalyst  14  arranged inside the housing  13  is not limited to this embodiment. 
         [0039]    For example, the NOx catalyst  14  is formed by a material including metal such as alumina, zirconia, vanadia/titania and zeolite. The NOx catalyst  14  is configured by a substantially rectangular parallelepiped having a honeycomb structure in which many through holes are formed. The NOx catalyst  14  is arranged inside the housing  13  of the catalyst reactor  12  so that an axial direction of the through holes is in agreement with a flow direction of exhaust gas. Accordingly, the catalyst reactor  12  is configured so that exhaust gas supplied from the one side of the housing  13  passes through the through holes of the NOx catalyst  14  in the order of the first NOx catalyst  14   a,  the second NOx catalyst  14   b  and the third NOx catalyst  14   c  and then discharged via the other side of the housing  13 . 
         [0040]    As shown in  FIGS. 1 to 3 , the soot blower  15  removes dust adhering to the NOx catalyst by pressurized air. The soot blower  15  has an air injection nozzle  16 , an injection valve  17 , a pressure control valve  18  and a second air supply passage  19 . 
         [0041]    The air injection nozzle  16  injects pressurized air. The air injection nozzle  16  is configured by a nondirectional nozzle. The air injection nozzle  16  is attached to a wall surface of the housing  13  so as to insert an injection port into the housing  13  in an optional position of the housing  13  of the catalyst reactor  12 . In this case, the air injection nozzle  16  is arranged near the wall surface of the housing  13  while the injection port is directed to an optional direction in the housing  13 . Namely, the injection port of the air injection nozzle  16  should be arranged inside the housing  13  of the catalyst reactor  12 . Accordingly, as shown in  FIG. 3 , for detaching the air injection nozzle  16  from the housing  13 , a large space is not required in a direction separating from the housing  13  (see a thick black arrow in  FIG. 3 ). The air injection nozzle  16  is connected to the reservoir tank  7  via the second air supply passage  19  which is a passage of pressurized air. The reservoir tank  7  is connected to the air tank  6  arranged at a separated position. 
         [0042]    The injection valve  17  opens and closes the passage of pressurized air. The injection valve  17  is configured by an electromagnetic valve by pilot air. The injection valve  17  is provided in the second air supply passage  19  connected to the air injection nozzle  16 . The injection valve  17  can switches whether pressurized air is supplied from the reservoir tank  7  to the air injection nozzle  16  or not. Concretely, the injection valve  17  can open and close the second air supply passage  19  by sliding a spool (not shown). When the injection valve  17  opens the second air supply passage  19 , pressurized air is supplied to the air injection nozzle  16 . The injection valve  17  is not limited to this embodiment, and may be any member which opens and closes the passage of pressurized air. 
         [0043]    The pressure control valve  18  changes pressure of pressurized air. The pressure control valve  18  is provided in the second air supply passage  19  and upstream the injection valve  17 . The pressure control valve  18  is configured by an electromagnetic proportional valve and can change pressure of pressurized air. Accordingly, concerning the soot blower  15 , pressure of pressurized air is changed by the pressure control valve  18  corresponding to supply pressure and states of the NOx catalyst  14 . The pressure control valve  18  is not limited to this embodiment, and may be any member which changes pressure of pressurized air. In addition to the pressure control valve  18 , a flow rate may be changed by changing a sectional area of the second air supply passage  19  by a chipped circular partition plate or the like. 
         [0044]    The second air supply passage  19  supplies pressurized air. The second air supply passage  19  connects the reservoir tank  7  to the air injection nozzle  16 . As shown in  FIGS. 2 and 3 , an end of the second air supply passage  19  to which an air injection nozzle is connected is bent so as to be along the wall surface of the housing  13  of the catalyst reactor  12 . Namely, the second air supply passage  19  is arranged toward a side surface of the housing  13  different from the side surface thereof in which the air injection nozzle  16  is arranged. Accordingly, in the exhaust purifier  1 , it is not necessary to secure a space for maintenance of the air injection nozzle  16  in a direction in which the air injection nozzle  16  of the catalyst reactor  12  is provided (see the thick black arrow in  FIG. 3 ). 
         [0045]    As shown in  FIG. 1 , the pressure difference sensor  20  detects a pressure difference ΔP between an upstream exhaust pressure and a downstream exhaust pressure of the catalyst reactor  12 . The pressure difference sensor  20  is configured by an upstream pressure sensor and a downstream pressure sensor. The upstream pressure sensor is arranged upstream the catalyst reactor  12 , and the downstream pressure sensor is arranged downstream the catalyst reactor  12 . Namely, the pressure difference sensor  20  detects the pressure difference ΔP between an exhaust pressure upstream the first NOx catalyst  14   a  and an exhaust pressure downstream the third NOx catalyst  14   c.  According to the configuration, existence and degree of closing of the through holes of the NOx catalyst  14  can be detected from a value of the pressure difference ΔP. 
         [0046]    The exhaust gas temperature sensor  21  detects an exhaust temperature T. The exhaust gas temperature sensor  21  is arranged in a middle part of the exhaust pipe  23  and near an exhaust manifold. According to the configuration, the exhaust temperature T just after combustion in the engine  22  can be detected. 
         [0047]    The exhaust pipe  23  discharges exhaust gas from the engine  22  to the outside (atmosphere). In the exhaust pipe  23 , the urea water injection nozzle  2  and the catalyst reactor  12  of the exhaust purifier  1  are provided. In the exhaust pipe  23 , a branch pipe  23   a,  and a first valve  23   b  and a second valve  23   c  switching passages of exhaust gas are provided upstream the urea water injection nozzle  2 . Namely, in the exhaust pipe  23 , the first valve  23   b,  the second valve  23   c  and the urea water injection nozzle  2  are arranged in this order from the upstream side. The branch pipe  23   a  is connected to the exhaust pipe  23 . The first valve  23   b  is arranged inside the branch pipe  23   a.  The second valve  23   c  is arranged inside the exhaust pipe  23 , upstream the urea water injection nozzle  2  and downstream the branch pipe  23   a.    
         [0048]    The first valve  23   b  and the second valve  23   c  can be opened and closed interlockingly to each other. Concretely, the first valve  23   b  and the second valve  23   c  are configured so that the first valve  23   b  is closed when the second valve  23   c  is opened, and the first valve  23   b  is opened when the second valve  23   c  is closed. Accordingly, when the second valve  23   c  is opened and the first valve  23   b  is closed, in the exhaust pipe  23 , a passage supplying exhaust gas to the exhaust purifier  1  is configured (the state of  FIG. 1 ). On the other hand, when the second valve  23   c  is closed and the first valve  23   b  is opened, in the exhaust pipe  23 , a passage that exhaust gas is not purified by the exhaust purifier  1  and is discharged via the branch pipe  23   a  to the outside (atmosphere) is configured. In the exhaust pipe  23 , the urea water injection nozzle  2 , the first valve  23   b  and the second valve  23   c  may alternatively be arranged in this order from the upstream side. In this case, when urea water is injected, the first valve  23   b  is controlled to be closed. 
         [0049]    As another embodiment, the switching valve  11  which closes selectively one of the exhaust pipe  23  and the branch pipe  23   a  may alternatively be provided in a connection part of the branch pipe  23   a . When the branch pipe  23   a  is closed, the exhaust pipe  23  configures a passage through which exhaust gas is supplied to the exhaust purifier  1 . On the other hand, when the exhaust pipe  23  is closed, the exhaust pipe  23  configures a passage that exhaust gas is not purified by the exhaust purifier  1  and is discharged via the branch pipe  23   a  to the outside (atmosphere). 
         [0050]    An ECU  24  controls the engine  22 . The ECU  24  may be configured by connecting a CPU, a ROM, a RAM, a HDD and the like with a bus, or may alternatively be a one-chip LSI or the like. The ECU  24  can obtain information concerning an engine rotation speed N and a fuel injection amount F. 
         [0051]    The control device  26  controls the urea air valve  8 , the urea water supply pump  9 , the switching valve  11 , the injection valve  17 , the pressure control valve  18 , the first valve  23   b,  the second valve  23   c  and the like. In the control device  26 , various programs and data for controlling the urea air valve  8 , the urea water supply pump  9 , the switching valve  11 , the injection valve  17 , the pressure control valve  18 , the first valve  23   b,  the second valve  23   c  and the like, a restriction area map M 1  for calculating a restriction area of exhaust gas, an exhaust gas flow rate map M 2  for calculating an exhaust gas flow rate based on the engine rotation speed N, the fuel injection amount F and the exhaust temperature T, an initial pressure difference map M 3  for calculating an initial pressure difference ΔPi which is a pressure difference of the catalyst reactor  12  in the initial state at every exhaust gas flow rate, a reference pressure difference rising amount map M 4  for calculating a first reference pressure difference rising amount ΔPt 1  at which the catalyst must be exchanged because of temporal change and the like and a second reference pressure difference rising amount ΔPt 2  which is a condition different from that of the soot blow at a normal predetermined condition and at which the soot blow with higher washing effect is required at every initial pressure difference ΔPi, and the like are stored. The control device  26  may be configured by connecting a CPU, a ROM, a RAM, a HDD and the like with a bus, or may alternatively be a one-chip LSI or the like. The control device  26  may be configured integrally with the ECU  24  controlling the engine  22 . 
         [0052]    As shown in  FIG. 4 , the notification means  27  notifies a state of the exhaust purifier  1  to an operator. The notification means  27  is provided in a control panel  26   a  in which the control device  26  is housed. The notification means  27  is configured by a display screen  27   a  showing the state of the exhaust purifier  1 , a speaker  27   b  emitting alarm sound, a switch  27   c  stopping emission of an alarm, and the like. 
         [0053]    The control device  26  is connected to a solenoid of the urea air valve  8  and can control opening and closing of the urea air valve  8 . 
         [0054]    The control device  26  is connected to a driving motor of the urea water supply pump  9  and can control a driving state of the urea water supply pump  9 . Namely, by controlling the driving state of the urea water supply pump  9 , the control device  26  can change optionally an amount of urea water added to exhaust gas. 
         [0055]    The control device  26  is connected to the switching valve  11  and can control opening and closing of the switching valve  11 . 
         [0056]    The control device  26  is connected to the injection valve  17  and can control opening and closing of the injection valve  17 . 
         [0057]    The control device  26  is connected to the pressure control valve  18  and can control opening and closing of the pressure control valve  18 . 
         [0058]    The control device  26  is connected to the pressure difference sensor  20  and can obtain a signal concerning the pressure difference ΔP between the upstream exhaust pressure and the downstream exhaust pressure of the catalyst reactor  12  detected by the pressure difference sensor  20 . 
         [0059]    The control device  26  is connected to the first valve  23   b  and the second valve  23   c  and can control opening and closing of the first valve  23   b  and the second valve  23   c.    
         [0060]    The control device  26  is connected to the ECU  24  and can obtain the engine rotation speed N, the fuel injection amount F and various information concerning the engine  22  detected by the ECU  24 . The control device  26  may obtain the information concerning the engine  22  directly without the ECU  24 . 
         [0061]    The control device  26  is connected to a GPS (global positioning system) device  25  and can obtain a position detected by the GPS device  25 . The control device  26  is connected to an input device (not shown) and can obtain a signal concerning a target purification rate and a concentration of urea water inputted via the input device. Otherwise, information concerning the target purification rate and the concentration of urea water may be inputted previously. 
         [0062]    The control device  26  is connected to the notification means  27 , and can notify the state of the exhaust purifier  1  and emit an alarm showing abnormal degradation of the NOx catalyst  14 . 
         [0063]    For example, when the exhaust purifier  1  configured as the above is mounted on a ship, the control device  26  obtains an actual position of the ship detected by the GPS device  25  and judges whether the actual position is within the restriction area (restriction sea area) of exhaust gas or not with the restriction area map M 1 . When the actual position is judged to be within the restriction area of exhaust gas, the control device  26  opens the second valve  23   c  and closes the first valve  23   b.  Namely, exhaust gas is purified by the exhaust purifier  1  and then discharged to the outside. When the actual position is judged not to be within the restriction area of exhaust gas, the control device  26  closes the second valve  23   c  and opens the first valve  23   b . Namely, exhaust gas is not purified by the exhaust purifier  1  and discharged to the outside via the branch pipe  23   a . It may alternatively be configured that the control device  26  receives an opening and closing signal of the first valve  23   b  and the second valve  23   c  by manual operation and controls the first valve  23   b  and the second valve  23   c  corresponding to the opening and closing signal. 
         [0064]    Next, referring to  FIGS. 5 and 6 , temporal change of the pressure difference ΔP for every load rate Wr (exhaust gas flow rate Ve) of the engine  22  in the exhaust purifier  1  is explained.  FIG. 5  shows temporal change of a pressure difference rising amount (ΔP−ΔPi) of the catalyst reactor  12  for every load rate Wr at the predetermined engine rotation speed N. 
         [0065]    As shown in  FIG. 5 , when the engine  22  is operated at the predetermined engine rotation speed N under the load rate of 100% or 75%, the pressure difference rising amount (ΔP−ΔPi) of the catalyst reactor  12  is increased gradually following progress of operation time. On the other hand, when the engine  22  is operated at the predetermined engine rotation speed N under the load rate of 25%, the pressure difference rising amount (ΔP−ΔPi) of the catalyst reactor  12  is increased more suddenly than that of the case of the load rate of 100% or 75%. Herein, the pressure difference ΔP of the catalyst reactor  12  is raised when dust adheres to the NOx catalyst  14  and the NOx catalyst  14  is clogged. Namely, as low as the load rate Wr of the engine  22  is, as often as dust adheres to the NOx catalyst  14 . That is because the exhaust gas flow rate Ve is lowered when the load rate Wr of the engine  22  is low so that an amount of dust removed from the NOx catalyst  14  by power of exhaust gas is reduced. Accordingly, as shown in  FIG. 6 , in the exhaust purifier  1 , as low as the exhaust gas flow rate Ve is (as low as the load rate Wr is), as large as the lowering rate of the pressure difference ΔP of the catalyst reactor  12  caused by removal of dust from the NOx catalyst  14  by the soot blow is. Accordingly, in the exhaust purifier  1 , by performing the soot blow at the exhaust gas flow rate Ve which is not more than a reference exhaust gas flow rate Vt at which the lowering rate α of the pressure difference ΔP of the pressure difference ΔP of the catalyst reactor  12  by the soot blow, dust can be removed efficiently. 
         [0066]    Next, referring to  FIGS. 7 to 9 , an instantaneous pressurization method which is a method of the soot blow in the exhaust purifier  1  is explained. 
         [0067]    In the exhaust purifier  1 , pressurized air is supplied into the housing  13  of the catalyst reactor  12  whose internal pressure is a pressure P for a time t by the soot blower  15 . In this case, the pressurized air is supplied so that the pressure (P+ΔIP) in the housing  13  after the supply is not less than a predetermined value β as shown by a formula (P+ΔIP) ≧β, and a pressure increase rate per unit time ΔIP/t is not less than a predetermined value as shown by a formula ΔIP/t≧γ. Accordingly, in the housing  13 , a shock wave IW is generated by sudden pressure rising. As shown in  FIG. 7 , the shock wave IW spreads spherically from the air injection nozzle  16  of the soot blower  15  via exhaust gas in the housing  13 . Since the housing  13  is filled with the exhaust gas, the shock wave IW spreads in all the directions in the housing  13  centering on the air injection nozzle  16  regardless of a direction and a position of the air injection nozzle  16  in the housing  13 . Namely, the shock wave IW reaches the whole surface of the NOx catalyst  14  contacting the exhaust gas in the housing  13 . 
         [0068]    In a conventional exhaust purifier in which dust is removed by applying pressurized air to a NOx catalyst  14 , power of the pressurized air acts on only the dust adhering to a part of the NOx catalyst to which the pressurized air is applied. Accordingly, as a NOx catalyst shown in  FIG. 9 , the power of the pressurized air does not act on the dust adhering to a part of the NOx catalyst which is not included within an injection area of a nozzle, whereby the dust is not removed (a clogged part in  FIG. 9 ). On the other hand, in the exhaust purifier  1  according to the present invention, the power of the shock wave  1 W acts equally on the dust adhering to the surface of the NOx catalyst  14  contacting the exhaust gas in the housing  13 . Accordingly, the large percentage of the dust adhering to the surface of the NOx catalyst  14  as shown in  FIG. 8A  is removed uniformly by the power of the shock wave  1 W as shown in  FIG. 8B . 
         [0069]    Next, referring to  FIGS. 10 and 11 , a relation between a rising amount of the pressure difference ΔP of the catalyst reactor  12  for every load rate Wr (exhaust gas flow rate Ve) of the engine  22  and a lowering rate of a denitration rate is explained.  FIG. 10  shows a rising amount of the pressure difference ΔP for every load rate Wr at the predetermined engine rotation speed N and the lowering rate of the denitration rate.  FIG. 11  is the reference pressure difference rising amount map M 4  showing the first reference pressure difference rising amount ΔPt 1  and the second reference pressure difference rising amount ΔPt 2  for every initial pressure difference ΔPi. 
         [0070]    As shown in  FIG. 10 , in the exhaust purifier  1 , NOx catalyst remaining dust is accumulated by long-term operation, and a difference between the initial pressure difference ΔPi of the catalyst reactor  12  and the actual pressure difference ΔP is increased and the denitration rate is lowered regardless of the load rate of the engine  22 . Accordingly, in the exhaust purifier  1 , the lowering rate of the denitration rate is guessed from the difference between the initial pressure difference ΔPi of the catalyst reactor  12  and the actual pressure difference ΔP at the optional exhaust gas flow rate Ve. Accordingly, in the exhaust purifier  1 , in a range not less than the first reference pressure difference rising amount ΔPt 1  which is a reference value of the difference between the initial pressure difference ΔPi of the catalyst reactor  12  and the actual pressure difference ΔP at which the lowering rate of the denitration rate is not less than a predetermined value ε for every load rate Wr, lowering of the denitration rate of the NOx catalyst  14  by long-term operation can be suppressed by exchanging the catalyst because of temporal degradation and washing the catalyst manually. Similarly, in the exhaust purifier  1 , in a range not less than the second reference pressure difference rising amount ΔPt 2  which is a reference value of the difference between the initial pressure difference ΔPi of the catalyst reactor  12  and the actual pressure difference ΔP at which the lowering rate of the denitration rate is not less than a predetermined value ζ for every load rate Wr, lowering of the denitration rate of the NOx catalyst  14  by long-term operation can be suppressed by performing the soot blow with higher washing effect than the normal soot blow. In the exhaust purifier  1 , when a NOx density sensor or the like is provided, by comparing the lowering rate of the denitration rate calculated from the pressure difference rising amount and the obtained NOx density for every load rate Wr, abnormal degradation of the NOx catalyst (a part of a middle dashed line in  FIG. 10 ) can be detected. 
         [0071]    Accordingly, as shown in  FIG. 11 , based on the map reference pressure difference rising amount M 4  which determines the first reference pressure difference rising amount ΔPt 1  at which the catalyst must be exchanged because of temporal change and the like and the second reference pressure difference rising amount ΔPt 2  at which the soot blow with higher washing effect than the normal soot blow is required for every initial pressure difference ΔPi, a control mode of the soot blower  15  can be determined from the initial pressure difference ΔPi and the pressure difference rising amount (ΔP−ΔPi). 
         [0072]    Below, referring to  FIGS. 12 and 13 , the control mode of the soot blower  15  in the exhaust purifier  1  which is an embodiment of the exhaust purifier  1  according to the present invention is explained. In this embodiment, the exhaust purifier  1  is mounted on a ship  100  shown in  FIG. 14 . However, the exhaust purifier  1  is not limited thereto and may alternatively be provided in an engine for a generator arranged ashore. 
         [0073]    In the case in which the actual position of the ship  100  on which the exhaust purifier  1  is mounted is within the restriction area of exhaust gas, when a difference between the pressure difference ΔP of the catalyst reactor  12  and the calculated initial pressure difference ΔPi of the catalyst reactor  12  is less than the first reference pressure difference rising amount ΔPtl, the control device  26  starts soot blow control. On the other hand, when the difference between the pressure difference ΔP of the catalyst reactor  12  and the calculated initial pressure difference ΔPi of the catalyst reactor  12  is not less than the first reference pressure difference rising amount ΔPt 1 , the control device  26  judges as pressure difference abnormality and emits an alarm. 
         [0074]    In the soot blow control, when the difference between the pressure difference ΔP of the catalyst reactor  12  and the calculated initial pressure difference ΔPi of the catalyst reactor  12  is less than the second reference pressure difference rising amount ΔPt 2  and the calculated exhaust gas flow rate Ve is less than the reference exhaust gas flow rate Vt, the control device  26  performs the soot blow of a standard mode. On the other hand, when the difference between the pressure difference ΔP of the catalyst reactor  12  and the calculated initial pressure difference ΔPi of the catalyst reactor  12  is not less than the second reference pressure difference rising amount ΔPt 2 , the control device  26  performs the soot blow of a washing mode. When the calculated exhaust gas flow rate Ve is not less than the reference exhaust gas flow rate Vt, the soot blow is not performed. 
         [0075]    Herein, a blow pressure of the washing mode (for example, 0.8 MPa) is set higher than a blow pressure of the standard mode (for example, 0.5 MPa). A blow interval of the washing mode (for example, 30 min) is set higher than a blow interval of the standard mode (for example, 15 min). A number of blow of the washing mode (for example, 5) is set higher than a number of blow of the standard mode (for example, 3). 
         [0076]    Next, the control mode of the soot blower  15  in the exhaust purifier  1  which is the embodiment of the exhaust purifier  1  according to the present invention is explained concretely. The control device  26  controls the soot blower  15  interlockingly with start and stop of the engine  22 . 
         [0077]    As shown in  FIG. 12 , in a step S 110 , the control device  26  obtains an actual position of the ship  100  detected by the GPS device  25 , and shift to a step S 120 . 
         [0078]    In the step S 120 , the control device  26  judges whether the obtained actual position of the ship  100  is within the restriction area or not based on the restriction area map M 1 . 
         [0079]    As a result, when the obtained actual position of the ship  100  is judged to be within the restriction area, the control device  26  shift to a step S 130 . 
         [0080]    On the other hand, when the obtained actual position of the ship  100  is judged not to be within the restriction area, the control device  26  shift to a step S 230 . 
         [0081]    In the step S 130 , the control device  26  closes the first valve  23   b,  opens the second valve  23   c,  and shift to a step S 140 . 
         [0082]    In the step S 140 , the control device  26  obtains the engine rotation speed N and the fuel injection amount F from the ECU  24 , obtains the pressure difference ΔP of the catalyst reactor  12  from the pressure difference sensor  20 , obtains the exhaust temperature T from the exhaust gas temperature sensor  21 , and shift to a step S 150 . 
         [0083]     In the step S 150 , the control device  26  calculates the exhaust gas flow rate Ve from the obtained engine rotation speed N, the fuel injection amount F and the exhaust temperature T based on the exhaust gas flow rate map M 2 , and shift to a step S 160 . 
         [0084]     In the step S 160 , the control device  26  calculates the calculated initial pressure difference ΔPi of the catalyst reactor  12  at the exhaust gas flow rate Ve from the calculated exhaust gas flow rate Ve based on the initial pressure difference map M 3 , and shift to a step S 170 . 
         [0085]     In the step S 170 , the control device  26  calculates the first reference pressure difference rising amount ΔPt 1  at which the catalyst must be exchanged because of temporal change and the like and the second reference pressure difference rising amount ΔPt 2  at which the soot blow with higher washing effect than the normal soot blow is required from the calculated initial pressure difference ΔPi based on the map reference pressure difference rising amount M 4 , and shift to a step S 180 . 
         [0086]    In the step S 120 , the control device  26  judges whether the difference between the obtained pressure difference ΔP of the catalyst reactor  12  and the calculated initial pressure difference ΔPi of the catalyst reactor  12  is less than the calculated first reference pressure difference rising amount ΔPt 1  or not. 
         [0087]    As a result, when the difference between the obtained pressure difference ΔP of the catalyst reactor  12  and the calculated initial pressure difference ΔPi of the catalyst reactor  12  is judged to be less than the calculated first reference pressure difference rising amount ΔPt 1 , the control device  26  shift to a step S 300 . 
         [0088]    On the other hand, when the difference between the obtained pressure difference ΔP of the catalyst reactor  12  and the calculated initial pressure difference ΔPi of the catalyst reactor  12  is judged not to be less than the calculated first reference pressure difference rising amount ΔPt 1 , the control device  26  shift to a step S 290 . 
         [0089]    In the step S 300 , the control device  26  starts soot blow control A and shift to a step S 310  (see  FIG. 13 ). 
         [0090]    In the step S 230 , the control device  26  opens the first valve  23   b,  closes the second valve  23   c,  and shift to the step S 110 . 
         [0091]    In the step S 290 , the control device  26  emits a pressure difference abnormality alarm by the notification means  27 , and shift to the step S 110 . 
         [0092]    As shown in  FIG. 13 , in the step S 310 , the control device  26  judges whether the difference between the obtained pressure difference ΔP of the catalyst reactor  12  and the calculated initial pressure difference ΔPi of the catalyst reactor  12  is less than the calculated second reference pressure difference rising amount ΔPt 2  or not. 
         [0093]    As a result, when the difference between the obtained pressure difference ΔP of the catalyst reactor  12  and the calculated initial pressure difference ΔPi of the catalyst reactor  12  is judged to be less than the calculated second reference pressure difference rising amount ΔPt 2 , the control device  26  shift to a step S 320 . 
         [0094]    On the other hand, when the difference between the obtained pressure difference ΔP of the catalyst reactor  12  and the calculated initial pressure difference ΔPi of the catalyst reactor  12  is judged not to be less than the calculated second reference pressure difference rising amount ΔPt 2 , the control device  26  shift to a step S 340 . 
         [0095]    In the step S 320 , the control device  26  judges whether the calculated exhaust gas flow rate Ve is less than the reference exhaust gas flow rate Vt or not. 
         [0096]    As a result, when the calculated exhaust gas flow rate Ve is judged to be less than the reference exhaust gas flow rate Vt, the control device  26  shift to a step S 330 . 
         [0097]    On the other hand, when the calculated exhaust gas flow rate Ve is judged not to be less than the reference exhaust gas flow rate Vt, the control device  26  shift to the step S 110  (see  FIG. 12 ). 
         [0098]    In the step S 330 , the control device  26  performs the soot blow of the standard mode which is the normal soot blow, finishes soot blow control A, and shift to the step S 110  (see  FIG. 12 ). 
         [0099]    In the step S 340 , the control device  26  performs the soot blow of the washing mode which is a condition different from that of the soot blow at the normal predetermined condition and at which the soot blow has higher washing effect, finishes soot blow control A, and shift to the step S 110  (see  FIG. 12 ). 
         [0100]    According to the configuration, in the exhaust purifier  1 , the soot blow is performed with the mode in which dust can be removed efficiently based on an operation state of the engine  22 . Accordingly, in the exhaust purifier  1 , both improve of a removal rate of dust by the soot blow and suppression of an amount of compressed air used for the soot blow can be realized. 
         [0101]    In the exhaust purifier  1 , by transmitting the shock wave  1 W using compressed air via exhaust gas, power of the shock wave  1 W acts on the whole area of the surface of the NOx catalyst  14  contacting the exhaust gas. Namely, by change of pressure in the catalyst reactor  12 , the dust is removed equally from the NOx catalyst  14 . Accordingly, in the exhaust purifier  1 , a purification rate (denitration rate) of the NOx catalyst  14  and the pressure difference ΔP can be recovered to the initial state. 
         [0102]    In the exhaust purifier  1 , accumulation of remaining dust on the NOx catalyst  14  by temporal change is guessed by increase of the pressure difference ΔP of the catalyst reactor  12 . Accordingly, in the exhaust purifier  1 , lowering of the purification rate (denitration rate) of the NOx catalyst  14  by the temporal change can be suppressed by performing the soot blow different from the normal soot blow. 
         [0103]    In the exhaust purifier  1 , abnormality of the NOx catalyst  14  is judged based on the pressure difference rising amount (ΔP−ΔPi) and notified to an operator so as to perform suitable treatment. Furthermore, the exhaust purifier  1  may be configured that when the NOx density sensor is provided, the lowering amount of the purification rate (denitration rate) is calculated from the pressure difference rising amount of the NOx catalyst  14  and the fuel injection amount F and fuel injection timing of the engine  22  is changed so as to reduce a NOx discharge amount so as to reduce load of the NOx catalyst  14 . Accordingly, in the exhaust purifier  1 , temporal lowering of the denitration rate of the NOx catalyst  14  caused by accumulation of dust can be compensated. 
         [0104]    Referring to  FIG. 14 , the ship  100  which is a first embodiment of a ship on which the engine  22  having a supercharger according to the present invention is mounted is explained. 
         [0105]    As shown in  FIG. 14 , the ship  100  has a hull  101 , a bridge  102 , an engine room  103 , a propeller  104  and a rudder  108 . In the ship  100 , the bridge  102  having a cockpit and the like is provided above the hull  101 . In the ship  100 , the engine room  103  is provided in a rear part of the hull  101 . In the engine room  103 , the main engine  105  which is an internal combustion engine driving the propeller  104  and the auxiliary engine  106  which is an internal combustion engine driving a generator  107  are provided. In a rear end of the hull  101 , the propeller  104  and the rudder  108  are provided. In the ship  100 , power of the main engine  105  can be transmitted via a propeller shaft  104   a  to the propeller  104 . 
         [0106]    The main engine  105  and the auxiliary engine  106  are configured by the engine  22  which is a diesel engine using light oil or heavy oil as fuel. The engine  22  drives rotatively an output shaft by mixing outside air with the fuel and burning them. The engine  22  is not limited to the diesel engine. 
       INDUSTRIAL APPLICABILITY 
       [0107]    The present invention can be used for an exhaust purifier of an internal combustion engine. 
       DESCRIPTION OF NOTATIONS 
       [0000]    
       
           1  exhaust purifier 
           12  catalyst reactor 
           13  casing 
           14  NOx catalyst 
           15  soot blower 
           16  air injection nozzle 
           17  injection valve