Patent Publication Number: US-2023151753-A1

Title: Exhaust Gas After-Treatment System Of An Engine Designed As Gas Engine Or Dual-Fuel Engine, Engine And Method For Operating The Same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an exhaust gas after-treatment system of an engine designed as gas engine or as dual-fuel engine. Furthermore, the invention relates to an engine designed as gas engine or dual-fuel engine and to a method for operating the exhaust gas after-treatment system or the engine. 
     2. Description of the Related Art 
     Large engines, such as are employed for example as internal combustion engines on ships, are increasingly embodied as gas engines or dual-fuel engines. In gas engines, a gaseous fuel, such as for example natural gas, is combusted. In dual-fuel engines, a gaseous fuel, such as for example natural gas, can be combusted in a gas fuel operating mode and a liquid fuel, such as for example diesel fuel, in a liquid fuel operating mode. 
     The exhaust gas of such large engines has to be cleaned. For this purpose, engines are equipped with exhaust gas after-treatment systems. There is a need for an exhaust gas after-treatment system of compact design of an engine designed as gas engine or dual-fuel engine, in particular of a large engine, which is preferentially employed as propulsion unit on a ship. 
     SUMMARY OF THE INVENTION 
     Starting out from this, it is an object of the invention to create a new type of exhaust gas after-treatment system of an engine configured as a gas engine or as a dual-fuel engine having such an exhaust gas after-treatment system. 
     This object may be solved through an exhaust gas after-treatment system having a catalyst that can be flowed through by exhaust gas. 
     Further, the exhaust gas after-treatment system according to the invention comprises a control tube extending through a recess in the catalyst, which control tube is movable relative to the catalyst and which can likewise be flowed through by exhaust gas. 
     Further, the exhaust gas after-treatment system according to the invention comprises an actuator which is equipped to move the control tube relative to the catalyst, dependent on at least one operating condition of the engine and/or at least one operating condition of the exhaust gas after-treatment system, in such a manner that in a first relative position of the control tube relative to the catalyst, the catalyst can be flowed through by exhaust gas but not the control tube, and in that in a second relative position of the control tube relative to the catalyst the control tube can be flowed through by exhaust gas but not the catalyst. 
     In the exhaust gas after-treatment system according to the invention the control tube is integrated in the catalyst in such a manner that the control tube penetrates a recess in the catalyst and is movable relative to the catalyst. In the first relative position of the control tube the same makes possible an exhaust gas flow through the catalyst, in the second relative position of the control tube the same prevents the exhaust gas flow through the catalyst but allows the exhaust gas flow through itself. Such an exhaust gas after-treatment system requires little installation space. Bypass tubes, insulations, flaps, rupture discs as well as control valves for the bypass tubes can be omitted. 
     Preferentially, the catalyst is a ring catalyst which radially inside is delimited in the region of the recess receiving the control tube by a first catalyst tube which radially outside is delimited by a second catalyst tube and/or a pressure reactor, which at a first axial end comprises a flow inlet side for exhaust gas and at a second axial end a flow outlet side for exhaust gas. Such a catalyst is particularly preferred for ensuring a compact design of the exhaust gas after-treatment system. 
     Preferentially, the control tube carries on a first portion a first closure body which in the first relative position of the control tube allows the flow through the catalyst and in the second relative position of the control tube prevents the flow through the catalyst. This also provides a compact design of the exhaust gas after-treatment system. 
     Preferentially, the control tube on a second portion carries a second closure body which in the first relative position of the control tube seals a gap between the control tube and the catalyst. In this manner, the necessary installation space of the exhaust gas after-treatment system can be advantageously reduced. 
     Preferentially, the control tube on a third portion comprises recesses, which are blocked in the first relative position of the control tube and are open in the second relative position of the control tube. These also reduce the installation space of the exhaust gas after-treatment system. 
     Preferentially, the exhaust gas after-treatment system comprises a sprayer for a regeneration agent, via which in the first relative position of the control tube relative to the catalyst and in the second relative position of the control tube relative to the catalyst a regeneration agent can be introduced into the catalyst. By way of the sprayer it is possible to introduce regeneration agent into the catalyst with compact design of the exhaust gas after-treatment system. 
     Preferentially, the exhaust gas after-treatment system comprises at least one sensor and a control unit to detect the at least one operating position of the engine and/or the at least one operating condition of the exhaust gas after-treatment system, and to control the actuator independently of the at least one operating condition of the engine and/or of the at least one operating condition of the exhaust gas after-treatment system. This allows a particularly advantageous operation of the exhaust gas after-treatment system in order to either conduct exhaust gas through the catalyst or conduct the exhaust gas through the control tube past the catalyst in the sense of a bypass operation. In this manner, the exhaust gas after-treatment system can be automatically adapted dependent on the at least one operating condition of the exhaust gas after-treatment system and/or of the at least one operating condition of the engine in order to operate the same either in the catalyst mode or in the bypass mode for the catalyst. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
       Preferred further developments of the invention are obtained from the following description. Exemplary embodiments of the invention are explained in more detail by way of the drawing without being restricted to this. There it shows: 
         FIG.  1    an exhaust gas after-treatment system according to the invention in a first state; 
         FIG.  2    the exhaust gas after-treatment system of  FIG.  1    in a second state. 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
     The invention relates to an exhaust gas after-treatment system of an engine configured as a gas engine or as a dual-fuel engine and to such an engine having a fuel supply system. Further, the invention relates to an engine designed as gas engine or dual-fuel engine and to a method for operating the exhaust gas after-treatment system and the engine. 
       FIGS.  1  and  2    show, schematically, a preferred exemplary embodiment of an exhaust gas after-treatment system  1  according to the invention of a gas engine or dual-fuel engine which is not shown in more detail, which is in particular a large engine that is employed as propulsion unit on a ship. 
       FIGS.  1  and  2    show an exhaust line  2  which leads from the engine that is not shown in the direction of the exhaust gas after-treatment system  1 . 
     The exhaust gas after-treatment system  1  is equipped with a catalyst  3 . The catalyst  3  can be flowed through by exhaust gas. 
     Further, the exhaust gas after-treatment system  1  is equipped with a control tube  4 , which extends through a recess  5  in the catalyst  3 . The control tube  4  is movable relative to the catalyst  3  and likewise be flowed through by exhaust gas. The control tube  4  is guided in the recess  5  of the catalyst  3  so as to be axially movable. 
     Furthermore, the exhaust gas after-treatment system  1  is equipped with an actuator  6 . The actuator  6  is equipped to move the control tube  4  relative to the catalyst  3  dependent on at least one operating condition of the engine and/or dependent on at least one operating condition of the exhaust gas after-treatment system  1 . 
     In a first relative position I (see  FIG.  1   ) of the control tube  4  relative to the catalyst  3 , the catalyst  3  can be flowed through by exhaust gas but not the control tube  4 . 
     In a second relative position II (see  FIG.  2   ) of the control tube  4  relative to the catalyst  3 , the control tube  4  can be flowed through by exhaust gas but not the catalyst  3 . 
     The catalyst  3  is a ring catalyst. The catalyst  3  is delimited radially inside in the region of the recess  5  receiving the control tube  4  by a first catalyst tube  7 . The catalyst  3  is delimited radially outside by a second catalyst tube  8  and/or by a pressure reactor  9 . In  FIGS.  1  and  2   , a portion  9   a,    9   b  of the pressure reactor  9  follows on both axial sides of the catalyst  3  or second catalyst tube  8 . 
     The catalyst  3  has two axial ends located opposite one another. On a first axial end  10  of the catalyst  3  a flow inlet side of the catalyst  3  for exhaust gas is formed. On a second axial end  11  of the catalyst  3  located opposite, a flow outlet side for the exhaust gas is formed. 
     In particular when the control tube  4  assumes the first relative position relative to the catalyst  3  shown in  FIG.  1   , exhaust gas A, which flows via the exhaust pipe  2  to the exhaust gas after-treatment system  1 , can initially flow into portion  9   a  of the pressure reactor  9  and from there flow into the catalyst  9  by way of the flow inlet side formed at the first axial end  10 . Having flowed through the catalyst  3 , the exhaust gas A flows out of the catalyst  3  via the flow outlet side formed at the second axial end  11  located opposite, enters the portion  9   b  of the pressure reactor  9  and can from this portion  9   b  flow in the direction of a further exhaust pipe  12 , in order to be discharged from the exhaust gas after-treatment system  1 . 
     On a first portion  4   a,  the control tube  4  comprises a first closure body  13 . In the first relative position of the control tube  4  relative to the catalyst  3  (see  FIG.  1   ), this first closure body  13  allows exhaust gas A to flow through the catalyst  3 , while accordingly the first closure body  13  in this position opens the flow inlet side of the catalyst  3  formed at the first axial end  10  for the exhaust gas flow. In the second relative position (see  FIG.  2   ) of the control tube  4  by contrast, the first closure body  13  prevents exhaust gas to flow through the catalyst  3 , while in this position the first closure body  13  accordingly blocks the flow inlet side of the catalyst  3  formed at the first axial end  10  for the exhaust gas flow. The first portion  4   a  of the control tube  4 , on which the same carries the first closure body  13  radially outside projects at the first axial end  10  of the catalyst  13  relative to the catalyst  3 . The first portion  4   a  of the control tube  4  accordingly projects, at the first axial end  10  of the catalyst  3 , from the same. 
     On a second portion  4   b,  the control tube  4  comprises a second closure body  14 . In the first relative position of the control tube  4  relative to the catalyst  3 , this second closure body  14  seals a gap  15  formed between the control tube  4  and the catalyst tube  7  located radially inside. This is not required in the second relative position (see  FIG.  2   ) of the control tube  4  relative to the catalyst  3 . 
     In a third portion  4 c, the control tube  4  has recesses  16 . In the first relative position (see  FIG.  1   ) of the control tube  4  relative to the catalyst tube  3 , these recesses  16  are blocked, in particular via the inner catalyst tube  7  and the second closure body  14 . In the second relative position (see  FIG.  2   ) between control tube  4  and catalyst  3  by contrast, these recesses  16  in the third portion  4 c of the control tube  4  are open. In the state of  FIG.  2   , i.e. in particular when the control tube  4  assumes the second relative position relative to the catalyst  3 , exhaust gas A, which is fed via the exhaust pipe  2  to the portion  9   a  of the pressure reactor  9 , can flow into the control tube  4  and thus flow past the catalyst  3  in order to then enter via the recesses  16  of the control tube  4  into the second part  9   b  of the pressure reactor  9  and from their be discharged from the exhaust gas after-treatment system  1  via the exhaust pipe  12 . 
     Furthermore, the exhaust gas after-treatment system  1  is equipped with a sprayer  17  for a regeneration agent. The sprayer  17  is positioned adjacently to the flow inlet end of the catalyst  3  formed at the first axial end  10  of the same, wherein the sprayer  17  can be supplied with reaction agent emanating from a metering valve  18 . 
     The sprayer  17  is preferentially formed as a circular spray tube with the help of which the regeneration agent can be evenly applied to the flow inlet side of the catalyst  3  formed at the first axial end  10 . 
     The actuator  6  of the exhaust gas after-treatment system  1  in the shown exemplary embodiment is equipped with a piston  19  actuated by a pressure medium, which piston  19  is moveably guided in a pressure medium cylinder  20 . A piston rod  21 , which is operatively connected to the second closure body  14 , acts on the said piston  19 . 
     The pressure medium cylinder  20  can be supplied with a pressure medium, emanating from a pressure medium reservoir  22 , in order to move the pressure medium piston  19  and, via the pressure medium piston  19 , the control tube  4  in the axial direction relative to the catalyst  3 . 
     The exhaust gas after-treatment system  1  is equipped, furthermore, with at least one sensor in order to detect at least one operating condition of the engine and/or at least one operating condition of the exhaust gas after-treatment system. 
     Accordingly,  FIG.  1    shows a sensor  23  which is assigned to the exhaust pipe  2 , wherein this sensor  23  is focussed on recognising for example engine misfiring. For this purpose, the sensor  23  can be designed for example as temperature sensor which, in particular when fuel is combusted in the engine and then recognises a temperature drop, can then suggest misfiring in the engine. 
     Furthermore,  FIG.  1 ,  2    shows a temperature sensor  24  in the region of the second portion  9   b  of the pressure reactor  9  in order to detect the exhaust gas temperature of the exhaust gas flowing out of the catalyst  3 . 
     Furthermore,  FIG.  1 ,  2    shows a pressure sensor  25  which, with a first measuring point upstream of an orifice plate  26 , and with a second measuring point downstream of the orifice plate  26 , acts on the exhaust pipe  12 . 
     Further, the exhaust gas after-treatment system  1  is equipped with a control device with the help of which the actuator  6  can be controlled as a function of the at least one operating condition of the engine and/or of the at least one operating condition of the exhaust gas after-treatment system in order to move the control tube  4  either into the position shown in  FIG.  1    or into the position shown in  FIG.  2   . 
     Accordingly, the exhaust gas after-treatment system according to the invention is equipped with the catalyst  3 , which is preferentially formed as ring catalyst, the control tube  4  integrated in the catalyst  3 , which is movable in the axial direction relative to the control tube  4 , and the actuator  6 . 
     Preferentially, the exhaust gas after-treatment system  1  further includes the sprayer  17  for the regeneration agent and at least one sensor  23 ,  24 ,  25 . 
     The control tube  4  is moveably arranged in the catalyst  3 , namely within the inner catalyst tube  7 , and axially moveable via the actuator  6 . No absolute tightness of control components is needed. An effective exhaust gas after-treatment can be ensured with little installation space. 
     The catalyst  3  is designed annular in the cross-section and accordingly is equipped with the recess  5 , within which the control tube  4  is guided. Exhaust gas can be conducted past the catalyst  3  by the control tube  4 . By way of the exhaust gas conducted via the control tube  4 , the catalyst  3  can already be preheated while exhaust gas does not yet flow via the same. 
     In particular when running up the engine during an engine start, high ignitable residual gas concentrations of the gaseous fuel are present in the exhaust gas. These can then be conducted past the catalyst  3  via the control tube  4  without oxidative reaction in the catalyst  3 . 
     The control tube  4  is moved in the axial direction with the help of the actuator  6 . The movement of the control tube  4  can be for example dependent on the exhaust gas pressure and/or the exhaust gas temperature. Temperatures and pressures can be detected by measurement with the help of the sensors  24  and  25 . 
     The control tube  4  carries the closures  13 ,  14 . Depending on the relative position of the control tube  4  relative to the catalyst  3 , either the first closure body  13  or the second closure body  14  is effective. 
     Preferentially, the closure bodies  13 ,  14  have a conical contour. Because of this conical contour of the closure bodies  13 ,  14  the same can ensure an effective sealing in their respective closure position without separate seals being required. 
     The exhaust gas after-treatment system  1  can be supplied with the exhaust gas via the exhaust line  2 . Cleaned exhaust gas can be discharged via the exhaust line  12 . By way of a further line  27 , regeneration agent, in the regeneration mode of the catalyst  3 , can be discharged from the exhaust gas after-treatment system  1 . 
     For regenerating the catalyst  3 , the exhaust gas after-treatment system  1  comprises the sprayer  17  with the help of which the regeneration agent can be applied to the catalyst  3  in the region of the first axial end  10  and thus in the region of the flow inlet side. In particular, a regeneration of the catalyst  3  is conducted in particular when the catalyst  3  is not flowed through by exhaust gas. Then, an effective regeneration of the catalyst  3  can be ensured with very low quantities of regeneration agent. The regeneration can take place at low temperatures in the catalyst  3 . The regeneration can also be conducted with the engine stationary or during other operating states. 
     The catalyst  3  is preferentially a methane catalyst. Ethanol or ethane or nitrogen is then suitable as regeneration agent. 
     Furthermore, the invention relates to an engine having the exhaust gas after-treatment system  1  described above and to a method for operating the exhaust gas after-treatment system  1 . 
     In particular when the control tube  4  assumes the first relative position of  FIG.  1   , exhaust gas is cleaned in the catalyst  3 . Accordingly, the control tube  4  assumes this first position of  FIG.  1    in the catalyst mode when gaseous fuel is combusted in the engine. Then, the exhaust gas A flows through the catalyst  3  and can be discharged via the exhaust pipe  12 . With the help of the temperature sensor  24 , a permissible exhaust gas temperature for example can be detected downstream of the exhaust gas catalyst  3 . With the help of the pressure sensor  25 , an exhaust gas pressure can be detected downstream of the catalyst  3 . Dependent on this, the control tube  4  is movable from the relative position of  FIG.  1    into the relative position of  FIG.  2   , wherein the relative position of  FIG.  2    corresponds to a catalyst bypass mode, during which no exhaust gas is conducted via the catalyst  3 , but the exhaust gas is rather conducted through control tube  4  past the catalyst  3 . 
     The control tube  4  in a dual-fuel engine assumes the relative position of  FIG.  2    in particular when the same is operated with liquid fuel, i.e. when diesel fuel is combusted in the engine. Exhaust gas of diesel fuel should not be conducted via a methane catalyst. Furthermore, the exhaust gas after-treatment system, namely the control tube  4  of the same, assumes the relative position of  FIG.  2    when the engine is run up during an engine start and/or when the engine is run down during an engine stop, and/or during emergency operation and/or during an engine fault, for example in the case of misfiring, and/or in the case of an exhaust gas overheating. 
     The invention allows with minimum installation space requirement of the exhaust gas after-treatment system  1  an effective exhaust gas cleaning of the exhaust gas of a gas engine or of a dual-fuel engine operated in the gas fuel operating mode. Existing engines can be readily retrofitted with the help of the exhaust gas after-treatment system  1  according to the invention. The catalyst  3  can be subjected to an effective regeneration with minimum need for regeneration agent. 
     Thus, while there have been shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.