Patent Publication Number: US-2007095053-A1

Title: Method and apparatus for emissions trap regeneration

Description:
FIELD OF THE DISCLOSURE  
      The present disclosure relates to methods and apparatus for removal of emissions from exhaust gas.  
     BACKGROUND OF THE DISCLOSURE  
      There are emissions traps used to trap emissions in an effort to prevent discharge of the emissions into the atmosphere. From time to time, these traps need to be regenerated to remove the emissions trapped thereby for further use of the traps.  
     SUMMARY OF THE DISCLOSURE  
      According to an aspect of the present disclosure, there is provided an apparatus comprising an emissions trap and a trap regenerator. The trap regenerator is fluidly coupled to the emissions trap to advance a regenerative agent thereto to regenerate the emissions trap. The trap regenerator is configured to change a concentration of the regenerative agent advanced to the emissions trap from a first trap-regenerating level to a second trap-regenerating level different from the first trap-regenerating level. In this way, the amount of emissions discharged into the atmosphere can be reduced. An associated method is disclosed.  
      The emissions trap may be any one of a number of different types of emissions traps. For example, the emissions trap may be configured as a NOx (i.e., nitrogen oxides) trap, a sulfur trap, and/or an ammonia trap, to name just a few.  
      The above and other features of the present disclosure will become apparent from the following description and the attached drawings.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a simplified block diagram showing a trap regenerator for regenerating an emissions trap;  
       FIG. 2  is a simplified block diagram showing an exemplary embodiment of the trap regenerator; and  
       FIG. 3  is a simplified block diagram showing another exemplary embodiment of the trap regenerator. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
      While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives following within the spirit and scope of the invention as defined by the appended claims.  
      Referring to  FIG. 1 , there is shown an apparatus  10  comprising an emissions trap  12  configured to trap emissions present in an exhaust system associated with a producer of exhaust gas (“EG” in the drawings) such as an internal combustion engine  14 . From time to time, the emissions trap  12  needs to be regenerated so as to remove the trapped emissions therefrom for further use of the trap  12 . To do so, there is a trap regenerator  16  fluidly coupled to the emissions trap  12  to advance a regenerative agent thereto to regenerate the emissions trap  12 . The trap regenerator  16  is configured to change a concentration of the regenerative agent advanced to the emissions trap  12  from a first trap-regenerating level to a second trap-regenerating level different from the first trap-regenerating level. In doing so, the amount of emissions discharged into the atmosphere can be reduced as discussed in more detail below.  
      It is believed that trap regeneration may be a two-step process involving (1) release of emissions from the trap  12  (i.e., desorption), and (2) conversion of the released emissions to a more environmentally acceptable form. In some cases, the conversion rate may occur more slowly than the release rate at least for some initial period of time during trap regeneration. In such a case, this could result in undesirable spikes in the amount of unconverted emissions discharged into the atmosphere.  
      To address this issue, the trap regenerator  16  may be operated to slow the release rate during this initial period of time. In particular, the trap regenerator  16  may be operated to provide the first trap-regenerating level to the trap  12  during a first period of time and the second-trap regenerating level to the trap  12  during a second period of time subsequent to (e.g., immediately or shortly after) the first period of time, the first and second trap-regenerating levels being selected so that the release rate during the first period of time is slower than the release rate during the second period of time. Upon expiration of the first period of time, the conversion rate is able to “handle” the faster release rate of the second period of time, thereby allowing an increase in the overall speed of trap regeneration during the second period of time.  
      Illustratively, the trap regenerator  16  comprises at least one component  18  configured to provide at least a portion of the regenerative agent and an electronic controller  20  electrically coupled to the at least one component  18 . The controller comprises a processor  22  and a memory device  24  electrically coupled to the processor  22 . The memory device  24  has stored therein a plurality of instructions which, when executed by the processor  22 , cause the processor  22  to operate the at least one component  18  in a first mode establishing the first trap-regenerating level, and operate the at least one component  18  in a second mode establishing the second trap-regenerating level.  
      The emissions trap  12  may be embodied as any number of different types of emissions traps. For example, the trap  12  may be, but is not limited to, a NOx trap for trapping NOx present in exhaust gas of the engine  14 , a sulfur trap for trapping sulfur (e.g., in the form of SOx, sulfur oxides) present in the exhaust gas, and/or an ammonia trap for trapping ammonia that may have been introduced into the exhaust gas to facilitate reduction of NOx at a selective catalytic reduction device.  
      A fuel-rich environment may be created about the emissions trap  12  to regenerate the trap  12 . This is particularly useful where the emissions trap  12  includes a NOx trap, a sulfur trap, and/or an ammonia trap. As such, the regenerative agent may have an air-to-fuel ratio and the trap regenerator  16  may change the air-to-fuel ratio from the first trap-regenerating level to the second trap-regenerating level, both trap-regenerating levels being fuel-rich. To change the air-to-fuel ratio from the first trap-regenerating level to the second trap-regenerating level, the amount of exhaust gas (which contains O 2 ) and/or fuel supplied to the trap  12  can be varied in a variety of ways (discussed in more detail below). What is meant herein by the term “fuel-rich” is that the air-to-fuel ratio is less than the stoichiometric air-to-fuel ratio of the fuel (stated quantitatively, the lambda value of a fuel-rich mixture is less than 1.0).  
      Considering for a moment the particular case where the trap  12  is a NOx trap, it is believed that NOx-trap regeneration is a two-step process involving (1) release of NOx from the trap  12  (i.e., NOx desorption), and (2) chemical reduction of the released NOx to N 2  by a NOx reductant of the regenerative agent. During NOx trap regeneration, NOx is released from the surface nitrate storage sites faster than it is initially reduced to N 2  by reaction with the reductant, which, in some cases, may result in spikes in the amount of NOx discharged to the atmosphere. As such, the trap regenerator  16  may be operated so that, although both trap-regenerating levels is fuel-rich to effect NOx reduction, the first trap-regenerating level is less fuel-rich than the second trap-regenerating levels. As a result, the NOx-release rate is slower during the first period of time than during the second period of time, allowing the NOx-reduction rate time to increase to an amount to handle the increased NOx-release rate of the second period of time. In this way, the amount of NOx discharged into the atmosphere during a trap regeneration event can be reduced.  
      Referring to  FIG. 2 , the trap regenerator  16  may be embodied as the trap regenerator  116 . The regenerator  1   16  comprises the controller  20  that controls operation of one or more of the components illustrated in  FIG. 2  to change the concentration, or more particularly the air-to-fuel ratio, of the regenerative agent advanced to the trap  12  from the first trap-regenerating level to the second trap-regenerating level.  
      Illustratively, the regenerator  116  may include an air valve  26 , a fuel injector  28 , and/or a fuel reformer  30  electrically coupled to and under the control of the controller  20  to change the air-to-fuel ratio of the regenerative agent supplied to the trap  12 . The controller  20  may be electrically coupled to the air valve  26 , the fuel injector  28 , and the fuel reformer  30  via electrical lines  32 ,  34 , and  36 , respectively.  
      The air valve  26  may be, for example, the throttle valve that controls the amount of air introduced into the engine  14 . In such a case, the position of the air valve  26  may be varied to change the amount of  02  in, and thus the air-to-fuel ratio of, the exhaust gas that flows to the trap  12 .  
      The fuel injector  28  may be, for example, one or more of the fuel injectors that injects fuel into the engine  14 . In such a case, the position of the fuel injector  28  may be varied to change the amount of fuel in, and thus the air-to-fuel ratio of, the exhaust gas that flows the to the trap  12 .  
      The fuel reformer  30  may be used to dose the exhaust gas with a reformate gas comprising, for example, hydrogen (H 2 ) and/or carbon monoxide (CO) so as to change the air-to-fuel ratio provided to the trap  12 . In the case where the trap  12  is a NOx trap, such fuel acts as a NOx reductant.  
      The air valve  26 , the fuel injector  28 , the fuel reformer  30 , or any combination thereof may be included in the trap regenerator  116  to change the air-to-fuel ratio of the regenerative agent advanced to the trap  12 .  
      Referring to  FIG. 3 , the trap regenerator  16  may be embodied as the trap regenerator  216 . The regenerator  216  comprises the controller  20  which controls operation of one or more of the components illustrated in  FIG. 3  to change the concentration, or more particular the air-to-fuel ratio, of the regenerative agent advanced to the trap  12  from the first trap-regenerating level to the second trap-regenerating level.  
      Illustratively, there are two emissions traps  12   a  and  12   b  positioned in a dual-leg arrangement of the exhaust system. The first trap  12   a  is positioned in a first leg  38  and the second trap  12   b  is positioned in a parallel second leg  40 . As such, the traps  12   a,    12   b  are flow-parallel to one another.  
      An exhaust valve arrangement is used to control flow of the regenerative agent to the traps  12   a,    12   b.  The regenerative agent comprises exhaust gas from the engine  14 , or more particularly the O 2  present therein, and a reformate gas (e.g., H 2  and/or CO) generated by the fuel reformer  30 . In the case where the trap  12   a  or  12   b  is a NOx trap, the reformate gas acts as a NOx reductant. The exhaust valve arrangement is thus configured to control flow of the exhaust gas and the reformate gas to the traps  12   a,    12   b.    
      Illustratively, the exhaust valve arrangement comprises a first exhaust valve  52 , a second exhaust valve  54 , and a third exhaust valve  56 . The first exhaust valve  52  is positioned upstream from the traps  12   a,    12   b  at an upstream junction of the legs  38 ,  40  so as to be able to control flow of exhaust gas and the agent component to the traps  12   a,    12   b.  The second exhaust valve  54  is positioned in the first leg  38  downstream from the first trap  12   a.  The third exhaust valve  56  is positioned in the second leg  40  downstream from the second trap  12   b.    
      The controller  20  is electrically coupled to each valve  52 ,  54 ,  56  and the fuel reformer  30  via electrical lines  58 ,  60 ,  62 ,  36 , respectively, to control operation of these components and thus regeneration of the traps  12   a,    12   b.  Normally, both traps  12   a,    12   b  are “on-line” such that they trap emissions present in exhaust gas advanced through both traps  12   a,    12   b.  To establish this configuration, the first exhaust valve  52  is positioned to allow exhaust gas to flow to both legs  38 ,  40  and each of the second and third exhaust valves  54 ,  56  is opened the position shown in solid in  FIG. 3  to allow exhaust gas to flow freely therethrough. The fuel reformer  30  is not operated when both traps  12   a,    12   b  are on-line.  
      As alluded to above, each trap  12   a,    12   b  is regenerated in two phases, the first phase occurring during a first period of time and the second phase occurring during a second period of time subsequent to the first period of time. In the first phase (i.e., during the first period of time), the first trap-regenerating level is advanced to the trap  12   a,    12   b,  and, in the second phase (i.e., during the second period of time), the second trap-regenerating level is advanced to the trap  12   a,    12   b.    
      Each of the valves  52 ,  54 ,  56  allows a certain amount of exhaust gas to leak past it even when it is “closed.” More particularly, the first exhaust valve  52  has a higher leakage rate than each of the second and third exhaust valves  54 ,  56 . Exemplarily, the first exhaust valve  52  may allow about 3% leakage when it assumes either the solid or phantom position shown in  FIG. 3  and each of the second and third exhaust valves  54 ,  56  may allow about 1% leakage when it assumes the solid position shown in  FIG. 3 . Such a difference in leakage rates facilitates establishment of the first and second trap-regenerating levels during regeneration of the traps  12   a,    12   b.    
      To regenerate the first trap  12   a  while the second trap  12   b  remains on-line, the controller  20  signals the first exhaust valve  52  to move to the position shown in solid in  FIG. 3  and signals the fuel reformer  30  to produce the reformate gas. As such, the first exhaust valve  52  directs most of the exhaust gas away from the first leg  38  into the second leg  40 , thereby taking the first trap  12   a  “off-line” while the second trap  12   b  remains on-line. The controller  20  signals the third exhaust valve  56  to remain open in the solid position of  FIG. 3  to allow passage of reformate gas supplied thereto to the first leg  38 .  
      The controller  20  operates the second exhaust valve  54  to establish the first and second trap-regenerating levels of the first and second phases of trap regeneration. In particular, in the first phase, the controller  20  signals the second exhaust valve  54  to assume its opened position shown in solid in  FIG. 3 . In this way, the amount of leakage of exhaust gas into the first leg  38  is established by the larger leakage rate of the first exhaust valve  52 . The O 2  of the leaked exhaust gas mixes with the reformate gas from the fuel reformer  30  to provide the regenerative agent of the first phase which has an air-to-fuel ratio at the first trap-regenerating level. The trap  12   a  is thus exposed to the first trap-regenerating level so as to reduce the amount of discharged to the atmosphere during the first phase.  
      Upon expiration of the first period of time, the controller  20  signals the second exhaust valve  54  to assume its “closed” position shown in phantom in  FIG. 3  to commence the second phase. In this way, the amount of leakage of exhaust gas into the first leg  38  is established by the smaller leakage rate of the second exhaust valve  52 . As a result, less O 2  enters the first leg  38  than in the first phase so that the regenerative agent becomes more fuel-rich and the trap  12   a  is exposed to the second trap-regenerating level.  
      A process similar to what has just been discussed in connection with the regeneration of trap  12   a  may be used to regenerate trap  12   b.  In particular, the controller  20  signals the first exhaust valve to assume the position shown in phantom in  FIG. 3  so as to direct most of the exhaust gas away from the second leg  40  to the first leg  38  and to direct reformate gas supplied by the fuel reformer  30  to the second leg  40 . In the first phase, the controller  20  signals the third exhaust valve to assume its open position shown in solid in  FIG. 3  so that the exhaust gas leakage rate into the second leg  40  is established by the larger leakage rate of the first exhaust valve  52  to expose the second trap  12   b  to the first trap-regenerating level. Upon expiration of the first period of time, the controller  20  signals the third exhaust valve  56  to assume its “closed” position shown in phantom in  FIG. 3  so that the exhaust gas leakage rate into the second leg  40  is established by the smaller leakage rate of the second exhaust valve  56  to expose the trap  12   b  to the second trap-regenerating level.  
      In some embodiments, the second and third valves  54 ,  56  may be eliminated. In such a case, the first exhaust valve  52  may be variable in the sense that its position can be varied in small amounts by the controller  20  so as to change the leakage rate of exhaust gas into a leg  38 ,  40  from the higher leakage rate (e.g., 3%) establishing the first trap-regenerating level to the lower leakage rate (e.g., 1%) establishing the second trap-regenerating level. The first exhaust valve  52  may be, for example, a proportional valve. In other examples, a stepper motor or other valve actuator may be used to vary the position of the valve  52  in this way.  
      In other embodiments where the second and third valves  54 ,  56  have been eliminated, the controller  20  may vary operation of the fuel reformer  30  while the first exhaust valve  52  remains stationary. In other words, the amount of reformate gas may be varied while the leakage rate of exhaust gas past the valve  52  is generally fixed. In such a case, the fuel reformer  30  may be operated to produce more reformate gas during the second phase than during the first phase to establish the first trap-regenerating level during the first phase and the more fuel-rich second trap-regenerating level during the second phase. It is within the scope of this disclosure to control the fuel-richness of the regenerative agent by a combination of varying the leakage rate of exhaust gas into the respective leg  38 ,  40  and varying the amount of reformate gas supplied by the fuel reformer  30 .  
      In still other embodiments, the second NOx trap  12   b  and the third exhaust valve  56  may be eliminated from the apparatus. In such a case, the second leg  40  may act simply as a bypass of the first leg  38 .  
      The fuel reformer  30  may be configured in a variety of ways. For example, it may include a catalytic reformer and/or a plasma fuel reformer. A catalytic reformer may be embodied as any of a steam reformer catalyst, a partial oxidation catalyst, and/or a water-shifting catalyst, to name just a few. A plasma fuel reformer generates an electrical arc (i.e., a plasma) to initiate partial oxidation of a fuel (e.g., diesel, gasoline) into reformate gas including, for example, H 2  and/or CO. In some cases, the fuel reformer  30  may include a combination of a plasma fuel reformer and a catalyst.  
      It is to be understood that the fuel reformer  30  may be replaced by a fuel source in any of the regenerators  16 ,  116 ,  216 . As such, the fuel source may supply fuel (rather than reformate gas) such as diesel fuel, gasoline, etc. for use in regeneration of the traps.  
      The duration of the first period of time and the second period of time may depend on a number of factors (e.g., trap composition, final air-to-fuel ratio of interest). Exemplarily, each of the first and second periods of time may be on the order of 1 to 5 seconds.  
      While the concepts of the present disclosure have been illustrated and described in detail in the drawings and foregoing description, such illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected.  
      There are a plurality of advantages of the concepts of the present disclosure arising from the various features of the systems described herein. It will be noted that alternative embodiments of each of the systems of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of a system that incorporate one or more of the features of the present disclosure and fall within the spirit and scope of the invention as defined by the appended claims.