Abstract:
The invention provides a filter system, a regeneration system, a combined soot-removing system and applications for the systems. The filter system may act as a purifier and a muffler for heavy and light duty diesel vehicles. The invention is a unique dual pass filter system that removes particulates and nitrogen oxides in successive passes before the gas exits the filter. The regeneration system includes an electric-powered heat source for safety and better control of the regeneration process. A motor vehicle application is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates generally to exhaust filtering and, in particular, to a filter system, regeneration system for the filter system, a combined soot removing system and applications of those systems. 
     2. Related Art 
     Filtering of exhaust is a well-known mechanism to reduce pollution. Related art devices have suffered from a number of drawbacks. For instance, most of the filters are adaptations of substrates used for automotive catalytic converters in which alternating channels are plugged to force the gas through the substrate walls. A number of other filter configurations and materials have been tried, but none have been robust enough or cost effective enough for widespread use. Also, once the particulates or other materials have been collected, they must be removed before the filter can function effectively. This is typically accomplished by igniting and burning the collected burnable particulates using a variety of techniques. Current techniques in the art of regeneration are expensive, complex, and many are outright hazardous, e.g., some use explosive, compressed gas or highly flammable (compared to diesel fuel) liquids. 
     In addition, the catalytic converter materials were designed to operate at much lower temperatures than can be reached during an uncontrolled regeneration (rapid, uncontrolled burning of the soot collected in the filter). In many cases, the filter media cracks, melts, or is otherwise damaged by either vehicle induced vibration or very high temperatures. In addition, many filters include two or more integral filter sections for filtering different pollutants. Unfortunately, these filters make regeneration difficult. Further, when one filter section is in need of repair, all of the sections must be replaced. 
     Another problem with related art devices is their inability to accommodate different applications because of their inflexible size. A new mold must be made for each different size filter unit, which dramatically increases cost or limits the ability to tailor the filter for the application. U.S. Pat. No. 5,250,094 to Chung et al. discloses a filter construction having a number filter sections 114. Unfortunately, the device is limited in application by the size of the enclosure. 
     Related art devices also do not adequately provide a regeneration system that is safe and controllable. In particular, U.S. Pat. No. 5,820,833 to Kawamura includes an electric wire net that is integral with a filter, i.e. in-filter regeneration. Since the regeneration system and filter are inseparable, the device may be subject to vibrations that may induce damage. U.S. Pat. No. 5,394,692 to Teuber-Ernst discloses a separate regeneration system that is fired by an explosive gas, which is an unsafe situation when in an environment where other fuel sources are nearby. Another problem with these regeneration systems is their inability to adequately control the rate of burn and, therefore, the temperature of the filter during regeneration. Many filters cannot withstand the repeated exposure to higher temperatures caused by some regeneration systems. Further, the potential for regeneration to proceed uncontrollably is potentially dangerous due to the extreme amount of heat that is generated by the burning soot. 
     Accordingly, there is a need in the art for a filter that includes separate filtering sections for ease of repair and regeneration. Furthermore, there is a need for a readily size-adjustable filter system. It would also be advantageous if this filter could be retrofitted to a variety of exhaust producing devices that exhaust a variety of different pollutants. Moreover, there is also a need for a safe and controllable regeneration system. A system that combines the above filter and regeneration system would also be advantageous. 
     SUMMARY OF THE INVENTION 
     The invention provides an exhaust filter system that serves as a particulate trap, a muffler, and a purifier as well as a regeneration system that is safe and controllable. The filter system design removes the structural load from the filter, while the regeneration system design eliminates most of the failure modes found in current regeneration systems. The invention provides for longer filter life; less complicated regeneration, less modification to an exhaust producing device for retrofitting, and much lower life cycle costs to the end user. In addition, the filter system can tolerate much higher temperatures than conventional filter systems thereby increasing the durability and use range of the filters. 
     In a first aspect of the invention is provided a filter system for removing soot from the exhaust of an exhaust producing device, the filter system comprising one or more self-contained, module, attachable units for varying the size of the filter system. Each unit includes: a housing; a particulate filter section positioned within the housing; and a nitrogen oxide filter section having a gas-impervious inner cylinder spaced within the particulate filter section and a nitrogen-oxide removing catalyst positioned within the inner cylinder. This aspect provides a dual pass filter system that has two separate sections. The number of units can be selected to match the type of exhaust producing device, exhaust source size, and expected operating profile. However, even an individual unit can function as a complete, dual-pass filter. In addition, the filter system may replace a muffler in many settings, which reduces costs to an end-user, and may be retrofitted without major modifications to a variety of exhaust producing devices. Further, unlike pure catalyst based filter systems, the filter system is not limited for use with a particular exhaust producing fuel, e.g., expensive low-sulfur diesel fuel. 
     A second aspect of the invention includes a regeneration system for an exhaust filter, the system comprising an electrically heated regenerator for producing heated gas to be passed through the filter to regenerate the filter. This aspect provides a safer and more easily controlled regeneration process. The system may be implemented separate from the exhaust producing device to prevent vibration induced damage or may be coupled to the device where the device is capable of moving, e.g., a motor vehicle. 
     A third aspect of the invention provides a soot removing system for an exhaust producing device comprising: a filter for removing soot from exhaust of the exhaust producing device; and a regeneration system having an electrically heated regenerator for producing heated gas to be passed through the filter to regenerate the filter. This aspect provides for a combined system having the above-described attributes of the filter and regeneration systems. 
     A fourth aspect of the invention includes a motor vehicle comprising: an engine for driving ground engaging members; an exhaust filter for removing soot from exhaust of the engine, the filter including one or more attachable units for varying the size of the filter; and an electrically heated regenerator for producing heated gas to be passed through the filter to regenerate the filter. 
     The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiments of this invention will be described in detail, with reference to the following figures, wherein like designations denote like elements, and wherein: 
     FIG. 1 is a cross-sectional view of a filter system in accordance with the invention; 
     FIG. 2 is an exploded view of a unit of the filter system; 
     FIG. 3 is a cross-sectional view of a unit of the filter system; 
     FIG. 4 is a detailed cross-sectional view of a three unit filter system; 
     FIG. 5 is a cross-sectional view of an alternative aspects of a unit of the filter system; 
     FIG. 6 is a side view of a soot removing system including a regeneration system in accordance with the invention; and 
     FIG. 7 is a motor vehicle incorporating the systems of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Although certain preferred embodiments of the present invention will be shown and described in detail, it should be understood that various changes and modifications may be made without departing from the scope of the appended claims. The scope of the present invention will in no way be limited to the number of constituting components, the materials thereof, the shapes thereof, the relative arrangement thereof, etc., which are disclosed simply as an example of the preferred embodiment. 
     For convenience, the disclosure will be broken down into the following headings for organizational purposes only: 
     I. Filter System 
     II. Regeneration System 
     III. Combined Soot Removing System 
     IV. Applications 
     I. Filter System: 
     Referring to the FIGS. 1-5, a filter system  10  for removing soot from the exhaust of an exhaust producing device  12  is shown. Filter system  10  includes one or more attachable units  14  for varying the size of filter system  10  that are preferably cylindrical in cross-section. As shown, a number of units  14 A,  14 B,  14 C, etc. may be sealingly coupled together to create a filter. In this case, a shell support  18  may be provided to secure a lower unit  20 . Alternatively, as shown in FIG. 4, a number of units  14  can be stacked into a shell  16  to produce filters of various capacities. Shell  16  may be a standard muffler shell of, for instance, a diesel engine driven truck. Shell  16  is preferably made of standard muffler steel. 
     As shown best in FIGS. 1-3, each unit  14 ,  14 A,  14 B,. etc. includes a housing  22 , a particulate filter section  24  and a nitrogen oxide (NOX) filter section  26 . Housing  22  encloses filter sections  24 ,  26  and is preferably made of a corrosion-resistant metal such as high temperature, stainless steel like AISI types  301 - 325  or  401 - 440 . Each housing  22  also includes a coupling  23  for sequentially attaching a unit  14 A to an adjacent unit  14 B. Coupling  23  may take a variety of forms known to those skilled in the art; as shown, coupling  23  includes an interference fit-type coupling such that each unit  14  has a recessed portion that fits into an expanded portion of an adjacent unit  14 . This provides structural rigidity and support for the stack. Other mechanisms of attachment such as clips may also be provided. 
     Particulate filter section  24  includes a filtering section  28  having either a set of radially oriented plates or a set of radially oriented pleats  30 , and a porous cylinder  32  for supporting an inner surface of plates or pleats  30 . Plates or pleats  30  are composed of low back pressure filter media such as woven ceramic fiber, ceramic fiber cloth, ceramic fiber paper/felt or a combination of those materials. The fibers are preferably one of the following ceramic materials: aluminum oxide, silicon dioxide, mullite (a mixture of aluminum oxide and silicon dioxide), aluminosilicate (another mixture of aluminum oxide and silicon dioxide), silicon carbide, silicon carbonitride, or silicon oxycarbide. Ceramic fiber plates or pleats  30  are preferably rigidized, protected, and rendered more durable by a thin coating of ceramic. This media is further improved and stiffened by the use of a coating of pre-ceramic polymers such as that disclosed in U.S. Pat. No. 5,153,295 to Whitmarsh et al., hereby incorporated by reference. Preferably, the pre-ceramic polymer is selected from the group comprising: silicon carbide, oxycarbide, aluminosilicate and alumina. It should be recognized that other pre-ceramic polymers may also be possible. The ceramic coating and pre-ceramic polymers are fired to form a ceramic coating on plates or pleats  30 . Filtering section  28  is then more resistant to damage than typical materials used for filters because the ceramic protects the fibers from the exhaust gas, prevents the fibers from rubbing against each other, and prevents plates or pleats  30  from flexing sufficiently to damage each other. An outer surface  31  of plates or pleats  30  has a smaller outer diameter than an inner diameter of housing  22  to create a substantially annular chamber  33  for passage of exhaust therebetween. Couplings  23  are also separated from outer surface  31  of plates or pleats  30  to provide for the continuation of annular chamber  33  between units  14 . 
     Porous cylinder  32  is preferably constructed of a corrosion-resistant metal such as high temperature, stainless steel like AISI types  301 - 325  or  401 - 440 . 
     Nitrogen oxide filter section  26  includes a gas-impervious inner cylinder  34  and a nitrogen-oxide removing catalyst  36  positioned within inner cylinder  34 . Inner cylinder  34  is spaced from an inner portion of particulate filter section  24  to create a substantially annular chamber  38  therebetween, i.e., cylinder  34  has a smaller diameter than an inner diameter of porous cylinder  32 . Inner cylinder  34  is preferably constructed of a corrosion-resistant metal such as high temperature, stainless steel like AISI types  301 - 325  or  401 - 440 , and has open ends  35 . NOX catalyst  36  is preferably composed of a non-porous ceramic material that is bonded into gas-impervious cylinder  34 . Examples of material suitable for catalyst  36  are: cordierite, mullite, silicon carbide and aluminum oxide. It should be recognized, however, that other types of ceramic catalyst support media maybe used and any nitrogen oxide catalyst material available commercially may be suited for use with the invention. 
     Each unit  14  also preferably includes a first, upper end cap  40  and a second, lower end cap  42 . End caps  40 ,  42  function to seal off the ends of plates or pleats  30  and annular chamber  38 . Additionally, each end cap  40 ,  42  includes a central aperture  46  that acts to position nitrogen oxide filter section  26  and, in particular, inner cylinder  34 , such that section  26  is substantially concentric within particular filter section  24 . 
     A special end cap  44 , referred to as a stop cap, may be provided on a lowermost unit  14 , as shown in FIGS. 1,  4  and  5 . Stop cap  44  does not include a central aperture  46  and may be formed as a solid member or may include a plug  48 , shown in FIG. 4, to close aperture  46 . As illustrated in FIG. 5, stop cap  44  may also include an exhaust directing formation  50  for directing exhaust into nitrogen oxide filter section  26 . Formation  50  may be created by, for example, stamping a solid stop cap  44  or plug  48 . Another stop cap  45 , shown in FIG. 1, may be provided to seal an uppermost unit  14  of filter system  10 . Stop cap  45  preferably seals to housing  22  of the uppermost unit  14 , as shown in FIG. 1, to prevent exhaust  52  from escaping through annular chamber  33 . Sealing is provided by the use of compressible fiber gasketing, rigidized fiber felt or a polymer slurry. Alternatively, as shown in FIG. 5, a filter system output shroud  47  may be coupled directly to housing  22  to eliminate the need for stop cap  45 . A vent port  49  may also be provided on gas impervious cylinder  34  to mate with an adjacent unit  14  and, hence, direct exhaust  52  from one NOX filter section  26  to the next (shown in FIG.  1 ), or to direct exhaust  52  through shroud  47  (shown in FIG.  5 ). 
     Each end cap  40 ,  42 ,  44 ,  45  and plug  48  are preferably made of a corrosion-resistant metal such as high temperature, stainless steel like AISI types 301-325 or 401-440. Filtering section  28  may be sealed to the appropriate caps  40 ,  42 ,  44 ,  45  by the use of compressible fiber gasketing, rigidized fiber felt or a polymer slurry. 
     Operation of filter system  10  will be described with reference to FIGS. 1,  4  and  5 . In operation, exhaust  52  from an exhaust producing device  12  is directed to filter system  10  by an adaptor  54 . Adaptor  54  is preferably made of standard muffler steel. Adaptor  54  is preferably in the form of an inverted Y with three openings  56 ,  58  and  62 . First opening  56  is shaped and sized to mate with a lowermost unit  14  of filter system  10 ; second opening  58  is shaped and sized to mate with an exhaust port  60  of exhaust producing device  12 ; and third opening  62  is shaped and sized to mate with a regeneration system  64 , as will be described below. As will be recognized by those skilled in the art, adapter  54  may also require other adapter components (not shown) for proper coupling to filter system  10 , exhaust producing device  12  and regeneration system  64 . 
     Referring to FIG. 1, during operation of filter system  10 , third opening  62  is closed by a flange or valve  66 . Exhaust  52  from exhaust producing device  12  is communicated by adapter  54  to filter system  10  where it enters annular chamber  33  between housing  22  and particulate filter section  24 . Exhaust  52  may pass from one unit  14 B to an adjacent unit  14 A within annular chamber  33 , and so on through all of the units in system  10 . As exhaust  52  is routed through chamber  33 , it radially enters particulate filter section  28 , i.e., it moves inwardly, where particulates from the exhaust  52 , such as soot, sulfates, oxides and other particulates are removed. Subsequently, exhaust  52  is routed through porous cylinder  32  and into annular chamber  38 . Because of the sealed ends of annular chamber  38 , exhaust  52  is routed into NOX filter section  26  at an open end  35  of gas impervious cylinder  34  where it passes longitudinally through section  26 . NOX catalyst  36  reacts with and removes nitrogen oxides (NOX) from exhaust  52 . Further removal of NOX is provided as exhaust  52  passes from unit, e.g.,  14 B, to another unit, e.g.,  14 A and so on through all units  14 , i.e., exhaust  52  that passes through lower units  14  is subject to repeated NOX removal as it passes through adjacent unit(s)  14 . The resulting exhaust gas, when it emerges from filter system  10  will be significantly depleted in NOX and particulates. Another advantage of filter system  10  is that it also acts to muffle noise from exhaust producing device  12 , i.e., system  10  acts as a muffler and a filter. 
     It should be recognized that any number of units  14 ,  14 A,  14 B, etc. may be stacked together to form a filter. The particular illustrations of two units (FIG.  1 ), three units (FIG. 4) and one unit (FIG. 5) are for illustration purposes only. Furthermore, as shown in FIG. 1, NOX filter section  26  may be shorter than particulate filter section  24  to promote routing of exhaust  52 . However, this is not necessary, as shown in FIG. 5, where stop cap  45  includes formation  50  to promote routing of exhaust  52  to nitrogen oxide filtering section  26 . 
     II. Regeneration System: 
     Referring to FIG. 6, a regeneration system  64  of the invention is shown in greater detail. Regeneration entails the burning out of soot from a filter, such as filter system  10 , to restore the filtration capacity of a filter. Regeneration system  64  includes an electrically powered regenerator or heat source  70  for producing heated gas  72  to be passed through a filter such as filter system  10  to regenerate the filter. Regenerator  70  preferably includes an electric powered metal wire, an electric powered ceramic element or an electric powered intermetallic element having a power rating of 1000-15,000 watts. 
     Regeneration system  64  also preferably includes: adaptor  54 ; an air pump or blower  74  for pressurizing heated gas  72 ; a source of inert gas  76 ; and a computer control system  78 . Adapter  54 , as described above, may include a second flange or valve  67  for closing off second opening  58  to exhaust producing device  12  during regeneration. As an alternative, adaptor  54  may simply be disconnected from exhaust producing device  12 . 
     Source of inert gas  76  is preferably provided to supply inert gas  80  with heated gas  72  to control the burn rate of soot within filter system  10 , i.e., the amount of inert gas  80  controls the temperature of the filter by controlling the amount of oxygen available for burning. A preferred inert gas for use in system  64  is nitrogen. 
     Computer-control system  78  operates to control the regeneration process by controlling: regenerator or heat source  70 , the temperature of filter system  10  and air pump or blower  74 . In order to control the above parameters, computer control system  78  may include: a thermocouple  84  for measuring temperature in filter system  10  during regeneration; a heat source temperature controller  90 ; and an air supply controller  92 . Thermocouple(s)  84  may be provided anywhere along filter system  10  to accurately determine temperature of filter system  10 , e.g., within each unit  14 . Heat source temperature controller  90  controls the amount of heat produced by regenerator  70 , and air supply controller  92  controls the amount of air supplied by air pump or blower  74 . Advantageously, air supply controller  92  also may control the amount of inert gas  80  supplied from source of inert gas  76 . 
     Regeneration system  64  also may include a scrubber  82  that attaches to an outlet of filter system  10 . Scrubber  82  collects pollutants generated during the regeneration process. 
     In operation, filter system  10  is regenerated once it collects enough soot to increase the back-pressure therein to a pre-determined point; a condition that may be determined by a pressure gauge (not shown) on filter system  10 . At that stage, filter system  10  would be brought to a regeneration system  64 , or vice versa, where regenerator  70  is quickly attached to filter system  10  at adaptor  54  opening  62 , e.g., by using flange or valve  66 . Second flange or valve  67  is closed to block flow of heated gas  72  and inert gas  80  to exhaust producing device  12 . The temperature inside filter system  10  is tracked by thermocouple(s)  84  that feed back information to computer control system  78  for control of regenerator  70  and air supply controller  74 . 
     As heat is applied to filter system  10  from regenerator  70 , the soot will combine with the pumped-in heated gas  72  to bum and generate its own heat. The burning will propagate through filter system  10  and from unit  14  to unit  14  until all of the burnable soot is removed. The effluent from the burning soot may be cleaned by scrubber  82 , if one is provided, and subsequently vented to the atmosphere. Thermocouple(s)  84  may be provided in each unit  14  to monitor temperature. Computer control system  78  may then prevent overheating by decreasing either the heat or the air supply or increasing the amount of inert gas to maintain a controlled burn rate. 
     After the regeneration process is complete, scrubber  82  and regenerator  70  are disconnected, flange/valve  66  closed, and flange/valve  67  opened for communication with exhaust producing device  12 . Filter system  10  may then be re-used. 
     III. Combined Soot Removing System: 
     As also shown in FIG. 6, the invention also includes a soot removing system  98  that, in general terms, is a combination of aspects of filter system  10  and regeneration system  64 . Soot removing system includes a filter, such as filter system  10 , for removing soot from exhaust  52  of an exhaust producing device  12  and a regeneration system  64  having an electrically heated regenerator  70  for producing heated gas  72  to be passed through the filter to regenerate the filter. Aspect of the above-described systems that may be part of soot removing system include: source of inert gas  76  for supplying an inert gas  80 , e.g., nitrogen, to the filter with hot gases  72 ; adaptor  54  for coupling to the filter for directing exhaust of exhaust producing device  12  or heated gas  72  from regenerator  70  through the filter. As discussed above, adaptor  54  preferably includes a first opening  56  coupled to a first end of the filter, a second opening  58  for coupling to an exhaust port  60  of exhaust producing device  12 , a third opening  62  for coupling to regenerator  70 ; and a valve  66  for closing off second opening  58  during regeneration. A scrubber  82  may be attached to an output end of the filter. 
     In a preferred embodiment, shown in FIG. 6, regenerator  70  is separate from exhaust producing device  12  and filter system  10 . Alternatively, regenerator  70  may be attached to exhaust producing device  12 , as shown in FIG.  7 . Filter system  10  includes one or more units  14  including: a housing  22 ; a particulate filter section  24 ; and a nitrogen oxide filter section  26  having a gas-impervious inner cylinder  34  having a first and second open end  35  and a nitrogen-oxide removing catalyst  36  located within inner cylinder  34 . Regenerator  70  includes a heat source chosen from the group comprising: an electric powered metal wire, an electric powered ceramic element and an electric powered intermetallic element. Regeneration system  64  includes an air pump or blower for pressurizing heated gas  72  and a computer-control system  78 . Computer-control system  78  includes: a thermocouple  84  for measuring temperature in the filter during regeneration, a heat source temperature controller  90 ; and an air supply controller  92 . 
     IV. Applications: 
     Filter system  10 , regeneration system  64  and soot removing system  98  in accordance with the invention have applications with a variety of exhaust producing devices  12 . For instance, exhaust producing device  12  may be: an engine, a paint booth, a furnace, a stove, a cement making kiln, an asphalt paving machine, etc. The types of engine the systems  10 ,  64 ,  98  may be applied to are limitless and include, for example, light and heavy duty diesel engines, one and two cylinder engines, two and four cycle engines, etc. 
     As shown in FIG. 7, another aspect of the invention is the application of the above systems to a motor vehicle  100  and, especially, a diesel powered motor vehicle. Motor vehicle  100  includes an engine  104  (i.e., an exhaust producing device) for driving ground engaging members  106 , e.g., wheels or tracks; an exhaust filter  10  for removing soot from exhaust of engine  104 , the filter including one or more attachable units  14  for varying the size of the filter; and an electrically heated regenerator  170  for producing heated gas to be passed through the filter to regenerate the filter. As illustrated, regeneration system  64  can be a part of motor vehicle  100 . As an alternative, as illustrated in FIG. 6, regeneration system  64  may be a separate system to which a motor vehicle  100  is occasionally attached to, when necessary, for regenerating filter system  10 . 
     When filter system  10  is used on a motor vehicle  100 , units  14  may be housed in a metal shell  16 , shown in FIG. 6, that is approximately the dimensions of a muffler, e.g., a diesel muffler, or can form the muffler themselves. For a typical heavy duty diesel truck, a stack of 3-4 segments would be mounted into a steel muffler shell  16  that would be mounted in place of a contemporary muffler. Alternatively, as shown in FIG. 7, units  14  may form the outermost shell of a filter/muffler themselves. 
     While a particular application of the invention has been discussed, it should be recognized that other applications are possible. For instance, the teachings of the invention may be applied to: heavy duty and light duty diesel engines such as used on trucks or trains; stationary diesel generators, mining vehicles, and power plants; smoke removal; and the collection and burning/oxidizing (rendering harmless) of Volatile Organic Compounds (VOCs) generated from for paint booths. Additional applications include smoke and hydrocarbon removal for cooking establishments; particulate removal for cement manufacturers; VOC and hydrocarbon emission prevention for asphalt paving equipment; etc. 
     While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.