Abstract:
In one aspect, the invention is directed an exhaust gas treatment apparatus that can be used to treat exhaust gas streams from vehicles having gasoline engines or diesel engines, from manufacturing plants, from incineration facilities, from coal fired stations, natural gas turbines or from virtually any exhaust gas stream. In one embodiment, the invention includes a particulate matter remover, a heat exchanger, a first reactor, a second reactor and a reagent protection device for preventing communication of reagent in the second reactor with ambient air.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to systems and methods for the treatment of exhaust from sources such as gasoline burning, diesel burning, natural gas burning, coal burning and wood burning devices, and plant stacks. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is generally acknowledged that it would be advantageous to reduce mankind&#39;s impact on the environment. To that end, many technologies have been proposed in an effort to reduce emissions from some sources such as gasoline burning, diesel burning, natural gas burning, coal burning and wood burning devices, and plant stacks. However, emissions continue to be a concern from both vehicular sources and plant sources alike. As a result, there is a continuing need to further reduce emissions from such sources. 
       SUMMARY OF THE INVENTION 
       [0003]    In a first aspect, the invention is directed to an exhaust gas treatment apparatus that can be used to treat exhaust gas streams from vehicles having gasoline engines or diesel engines, from manufacturing plants, from incineration facilities, from coal fired stations, natural gas turbines or from virtually any exhaust gas stream. In one embodiment, the invention includes a particulate matter remover, a heat exchanger, a first reactor, a second reactor and a reagent protection device. 
         [0004]    In a second aspect, the invention is directed to an exhaust gas treatment apparatus for treating an exhaust gas stream, comprising at least one reactor configured to receive the exhaust gas stream, wherein the at least one reactor includes a reagent solution holding section for holding a quantity of reagent solution, wherein the at least one reactor is configured to react the exhaust gas stream with the reagent solution, and a reagent solution protection device downstream from the at least one reactor and being configured for substantially preventing ambient air from being in fluid communication with the reagent solution holding section. 
         [0005]    In a third aspect, the invention is directed to a heat exchanger including a plurality of tubes for transporting a first fluid and a shell for holding the plurality of tubes and for passing a second fluid around the plurality of tubes, wherein each tube has a tube wall that defines a tube interior, wherein the tube has a helical baffle in the tube interior that is configured to urge a fluid flowing therethrough towards the tube wall. 
         [0006]    In a fourth aspect, the invention is directed to a reactor, comprising a reagent solution holding section for holding a quantity of reagent solution, and a reagent holding space adjacent the reagent solution holding section, wherein the reagent holding space is configured for receiving and loosely holding a solid block of reagent, wherein the reagent holding space has a bottom and has a passage at the bottom that is in fluid communication with the reagent solution holding section, so that, during use, solid reagent in the reagent holding space is exposed to reagent solution, thereby drawing solid reagent into solution. 
         [0007]    In a fifth aspect, the invention is directed to a reactor, comprising an exhaust gas treatment apparatus for treating an exhaust gas stream. The apparatus includes a particulate matter remover configured to remove particulate matter from the exhaust gas stream. The apparatus further includes a heat exchanger downstream from the particulate matter remover and configured to condense at least some water vapour in the exhaust gas stream to produce condensate such that at least some gaseous contaminants in the exhaust gas stream dissolve in the condensate. The apparatus further includes a reactor downstream from the heat exchanger. During use, the reactor contains a reagent solution selected to reduce the concentration of at least some contaminants in the exhaust gas stream. The reactor has an exhaust gas stream inlet and an exhaust gas stream outlet. During use, gas pressure in the reactor is higher than ambient air pressure so as to substantially prevent ambient air from communicating with the reagent solution during use. The apparatus further includes a reagent protection device configured to prevent ambient air from communicating with the reagent solution when the gas pressure in the reactor is not higher than ambient air pressure. 
         [0008]    In a sixth aspect, the invention is directed to a method of operating an exhaust gas treatment apparatus, comprising: 
         [0009]    a. introducing an exhaust gas stream; 
         [0010]    b. removing particulate matter from the exhaust gas stream; 
         [0011]    c. cooling the exhaust gas stream to condense out at least some water vapour from the exhaust gas stream to form condensate, wherein the condensate dissolves at least some gaseous contaminants from the exhaust gas stream after step b; 
         [0012]    d. exposing the exhaust gas stream to a reagent solution and neutralizing at least some contaminants in the exhaust gas stream thereby after step c; 
         [0013]    e. discharging the exhaust gas stream to atmosphere after step d; 
         [0014]    f. stopping the exhaust gas stream; and 
         [0015]    g. preventing exposure of the reagent solution to ambient air after step f. 
         [0016]    In a seventh aspect, the invention is directed to an exhaust gas treatment apparatus for treating an exhaust gas stream. The apparatus includes a particulate matter remover configured to remove particulate matter from the exhaust gas stream. The apparatus further includes a heat exchanger downstream from the particulate matter remover and configured to condense at least some water vapour in the exhaust gas stream to produce condensate such that at least some gaseous contaminants in the exhaust gas stream dissolve in the condensate. The apparatus further includes an upstream reactor that is downstream from the heat exchanger. The upstream reactor contains an upstream reagent solution selected to reduce the concentration of at least one contaminant selected from the group consisting of: chlorides, fluorides, nitrates, nitrites and sulfates. The apparatus further includes a downstream reactor downstream from the upstream reactor. The downstream reactor contains a downstream reagent solution selected to reduce the concentration of at least one contaminant selected from the group consisting of NOx and CO2, wherein the downstream reactor has an exhaust gas stream inlet and an exhaust gas stream outlet. During use, gas pressure in the downstream reactor is higher than ambient air pressure so as to substantially prevent ambient air from communicating with the downstream reagent solution during use. The apparatus further includes a reagent protection device configured to prevent ambient air from communicating with the downstream reagent solution when the gas pressure in the downstream reactor is not higher than ambient air pressure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The present invention will now be described by way of example only with reference to the attached drawings, in which: 
           [0018]      FIG. 1  is a plan view of an exhaust gas stream treatment apparatus in accordance with an embodiment of the present invention; 
           [0019]      FIG. 2  is a magnified sectional view of particulate matter remover that is part of the apparatus shown in  FIG. 1 ; 
           [0020]      FIG. 3  is a further magnified perspective view of an air deflector that is shown in  FIG. 2 ; 
           [0021]      FIG. 4  is perspective view of mesh packing element shown in  FIG. 2 ; 
           [0022]      FIG. 5  is a further magnified sectional elevation view of an injector shown in  FIG. 2 ; 
           [0023]      FIG. 6  is a magnified sectional elevation view of a heat exchanger shown in  FIG. 1 ; 
           [0024]      FIG. 7  is another magnified sectional view of the heat exchanger shown in  FIG. 1 ; 
           [0025]      FIG. 8  is an magnified elevation view of components that support the heat exchanger shown in  FIG. 1 ; 
           [0026]      FIG. 9  is a magnified sectional elevation view of first and second reactors shown in  FIG. 1 ; 
           [0027]      FIG. 10  is a perspective view of solid block of first reagent shown in  FIG. 9 ; 
           [0028]      FIG. 11  is a perspective view of solid block of second reagent shown in  FIG. 9 ; 
           [0029]      FIG. 12  is a magnified elevation view of a damper shown in  FIG. 1 ; 
           [0030]      FIG. 13  is a magnified sectional view of the damper shown in  FIG. 1 ; 
           [0031]      FIG. 14  is another magnified sectional view of the damper shown in  FIG. 1 ; 
           [0032]      FIG. 15  is a sectional plan view of an optional cooling room for use as part of the apparatus shown in  FIG. 1 ; 
           [0033]      FIG. 16  is a magnified elevation view of a bank of catalysts shown in  FIG. 15 ; 
           [0034]      FIG. 17  is an elevation view of a turbine that is optionally provided as part of the apparatus shown in  FIG. 1 ; 
           [0035]      FIG. 18  is a perspective view of an optional feature on the reactors shown in  FIG. 8 ; and 
           [0036]      FIG. 19  is a sectional elevation view of one of the reactors shown in  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    Reference is made to  FIG. 1 , which shows an exhaust gas treatment apparatus  200  in accordance with an embodiment of the present invention. The exhaust gas treatment apparatus  200  includes a particulate matter remover  1 , a heat exchanger  2 , a first, or upstream, reactor  3 , a second, or downstream, reactor  4  and a reagent isolation device  23 . The exhaust gas treatment apparatus  200  has an inlet  202  for receiving an exhaust gas stream  204  (which may be referred to simply as the gas stream  204 ) from a source (not shown) such as a gasoline burning, diesel burning, natural gas burning, coal burning or wood burning device, or a plant stack. The exhaust gas treatment apparatus  200  treats the exhaust gas stream  204  to reduce the level of numerous contaminants that may be contained in the exhaust gas stream  204 , such as NOx, SOx, CO, CO2, particulate matter, soot and other harmful and/or undesirable contaminants, and discharges the cleaned exhaust gas stream from an outlet  206 . 
         [0038]    Reference is made to  FIG. 2 , which shows the particulate matter remover  1  in more detail. The particulate matter remover  1  removes particulate matter shown at  208 , from the exhaust gas stream  204 . The particulate matter remover  1  includes a housing  26 . Within the housing there is, in series, a first catalytic converter element  33   a,  a mesh packing section  210 , and a second catalytic converter element  33   b.  The first catalytic converter element  33   a  pre-treats the exhaust gas stream  204  to reduce the level of hydrocarbons, NOx and CO (by conversion to CO2) in the gas stream  204 . 
         [0039]    The mesh packing section  210  includes a helical flow conduit  212 , which may be defined by any suitable means, such as, for example, an auger  31 . One or more mesh packing members  30  may be positioned in the helical flow conduit  212 . In the exemplary embodiment shown in  FIG. 2 , two packing members  30  are provided in series. A mixture  213  of water  222  and a water soluble oil  214  is provided in the packing members  30 . The mixture  213  may be, for example, Super Filter Coat spray by Research Products Corporation in Madison, Wis., USA. The mixture  213  is sprayed onto the mesh packing elements  30  from an injector  29 . Oil  214  from the mixture  213  is caught by and dwells in the mesh packing elements  30  for some period of time. When the gas stream  204  encounters the mesh packing elements  30 , the oil  214  entraps particulate matter  208  that may be entrained in the gas stream  204  and retains the particulate matter  208 . 
         [0040]    Beneath the helical flow conduit  212  there is a particulate separation chamber  216  having an upper chamber portion  218  and a lower chamber portion  37  and having a separator member  38  therebetween. The separator member  38  has apertures  220  therethrough permitting fluid communication between the upper and lower chamber portions  218  and  37 . The apertures  220  may be of any suitable size or diameter (for circular holes), such as, for example, ⅛ inch. The separator member  38  may be made by any suitable means, such as, from a perforated plate or from a mesh screen material. A perforated plate is preferable. 
         [0041]    In use, some of the oil  214  that is present in the mesh packing members  30  leaves them and, along with some of the gas stream  204  enters into the particulate separation chamber  216 . At least some of the oil  214  and the particulate matter  208  entrapped therein pass through the apertures  220  and into the lower chamber portion  37 , which itself is a particulate collection chamber. The gas stream  204  can pass relatively easily from the lower chamber portion  37  back up into the upper chamber portion  218 , however, any oil  214  and particulate matter  208  are inhibited from returning to the upper chamber portion  218  due at least in part to gravity and lack of flow velocity in the gas stream  204  leaving the lower chamber portion  237  thereby inhibiting entrainment of the oil  214  and particulate matter  208 . 
         [0042]    A drain  35  is provided for the lower chamber portion  37  so as to permit the draining of collected oil  214  and particulate matter  208  on a suitable periodic basis. Additionally, a flange joint  36  may be provided at the interface between the upper and lower chamber portions  218  and  37  to provide access to the mesh packing members  30 , to facilitate cleaning of the separator member  38  and the upper and lower chamber portions  218  and  37  generally if necessary. 
         [0043]    A set of one or more gas deflectors  34  may be provided in the particulate separation chamber  216  so as to deflect a portion of the gas stream  204  therein upwards. It has been found that deflecting upwards some of the downwards-traveling gas stream  204  improves the performance of the mesh packing section  210  at removing particulate matter  208 . The gas deflectors  34  may be configured as strips that extends downwards at a selected angle, and that have end portions  224  that are curled generally upwards so that exhaust gas  204  that is traveling downwards along the gas deflectors  34  is redirected upwards. This reduces the speed of the gas stream  204  in the particulate separating chamber  216 , thereby facilitating separation of the oil  214  and particulate matter  208  from the gas stream  204 . The end portions of the gas deflectors  34  may be provided with apertures  65  therethrough to permit oil  214  and particulate matter  208  to fall through thereby inhibiting the buildup of collected matter thereon. 
         [0044]    The gas stream  204  entering the exhaust gas treatment apparatus  200  ( FIG. 1 ) may be at an elevated temperature and may not be saturated in terms of its water vapour content. As a result, some, and possibly all, of the water  222  that is injected into the gas stream  204  may vaporize. 
         [0045]    The injector  29  may receive the mixture  213  of the oil  214  and water  222  from any suitable source, such as from a reservoir  7 . The concentration of water  222  in the mixture  213  may be less than  10 % by weight in order to reduce the likelihood of the mixture  213  freezing in cold weather. The concentration of water  222  in the mixture  213  may be higher than  10 % (by weight) in warm climates. The presence of the water  222  controls the viscosity of the mixture  213  to facilitate pumping the mixture and spraying of the mixture  213  by the injector  29 . A pump  27  may be provided for the delivery of the mixture  213  to the injector  29 . A controller  8  may be provided to determine when to activate the injector  29  and pump  27  via electrical lines  39 . 
         [0046]    Downstream from the mesh packing section  210  is the second catalytic converter element  33   b.  The second catalytic converter element  33   b  further removes contaminants from the gas stream  204 , and removes hydrocarbons that are present in the gas stream  204  as a result of the injection of the oil  214 . 
         [0047]    The particulate matter remover  1  may substantially be made from a suitable stainless steel, aside from the catalytic converter elements  33   a  and  33   b.    
         [0048]    When the gas stream  204  leaves the particulate matter remover  1 , the levels of some gaseous contaminants, such as CO, will have been reduced, and the level of particulate matter has been reduced. CO will have largely been converted to CO2. 
         [0049]    Downstream from the particulate matter remover  1  is a heat exchanger  2 . The heat exchanger  2  cools the gas stream  204  enough to condense out some of the water vapour  224 . The condensing of the water vapour  224  causes other contaminants to drop out from the gas stream  204 . For example, nitrates may become trapped in the condensed water as nitric acid. 
         [0050]    A condensate, shown at  226 , collects at the bottom of the heat exchanger  2 . The condensate  226  may be drained from the heat exchanger  2  through a heat exchanger drain conduit  228 . A manual valve  15   a  may be provided in the drain conduit  228  for providing manual closure of the drain conduit  228  in the event that, for whatever reason, the heat exchanger  2  requires removal but still contains some condensate. Additionally, an automatic valve  16   a  may be provided to automatically control the draining of condensate  226 . The condensate  226 , which contains water and such dissolved contaminants as NOx, SOx and CO2, may be acidic, and may be used for purposes described further below in relation to the second reactor  4 . 
         [0051]    Condensing out water vapour  224  may also assist in removing at least a portion of any remaining particulate matter  208  that is entrained in the gas stream  204 . 
         [0052]    The heat exchanger  2  may have any suitable configuration. For example, the heat exchanger  2  may be generally of a shell-and-tube configuration, having an upstream header  230 , a shell and tube section  232 , and a downstream header  49 . 
         [0053]    One or more baffles  44  may be provided in the upstream header  230  to disperse the gas stream  204  entering therein, thereby urging the gas stream to be more evenly distributed amongst the tubes, shown at  45 , in the shell and tube section  232 . 
         [0054]    The shell and tube section  232  includes a shell portion  236  and the tubes  45 . Coolant  47  is circulated through the shell portion  236  to cool the gas stream  204  passing through the tubes  45 . The coolant  47  may be any suitable coolant, such as a liquid coolant. 
         [0055]    The coolant  47  may be transported into and out of the shell portion  236  by a system of coolant transport conduits  42 . A pump  12  is provided to drive the circulation of the coolant  47 . A compressor  10  is provided to cool the coolant  47 . A radiator  11  may also be provided to cool the coolant  47  where the coolant does not require the compressor  10 , in order to use less energy when it is possible. 
         [0056]    A controller  13  may be provided to control the operation of the compressor  10  and pump  12  via electrical lines  41 . A temperature sensor  14  may be provided for reading the temperature of the gas stream  204  as it leaves the heat exchanger  2 , and connected to the controller  13  to provide the temperature information thereto. The controller  13  could be any suitable type of controller, such as a microprocessor based controller, or such as a simple temperature control switch. 
         [0057]    Each tube  45  may optionally be provided with an internal helical baffle  46  along its length. The helical baffle  46  provides a helical flow path to the gas stream  204  passing through the tube  45 . The helical flow path causes the gas stream  204  to be urged towards the tube wall shown at  240  as a result of centrifugal force. By urging the gas stream  204  against the tube wall  240 , more effective heat transfer can take place between the gas stream  240  and the coolant  47  in the shell portion  236  the gas stream  204  is more effectively cooled when passing through the tube  45 . Additionally, the helical baffle  46  increases the friction on the gas stream  204  passing through the tube  45  and thus slows the gas stream  204  down, thereby increasing the amount of time the gas resides in the tube  45  to be cooled. 
         [0058]    In the downstream header  49 , some of the condensate  226  that forms in the gas stream  204  drops out of the gas stream  204  and collects. A baffle  43  is provided in the floor of the downstream header  49  to hold a portion of the condensate  226  and guide it towards the drain conduit  228 , and to inhibit the condensate  226  from leaving the heat exchanger  2  through the gas stream outlet conduit, shown at  242 . 
         [0059]    A baffle  48  is provided in the downstream header  49 . The baffle  48  directs the gas stream  204  upwards away from the gas stream outlet conduit  242  so that the gas stream  204  gains further cooling from the walls of the downstream header  49 , which are in contact with the coolant  47 . After the further cooling takes place, the gas stream  204  and much of the condensate  226  entrained therein leaves the heat exchanger  2  through the gas stream outlet conduit  242 . The baffle  48  may also serve to inhibit the gas stream  204  from leaving the heat exchanger  2  before having a chance to drop out entrained condensate  226 . 
         [0060]    The gas stream  204  leaving the heat exchanger  2  includes some entrained water droplets with dissolved contaminants such as NOx, SOx and CO2 from having been cooled in the heat exchanger  2 . 
         [0061]    The heat exchanger  2  may be made from a suitable stainless steel. 
         [0062]    A tray  64  and associated drain  68  may be provided under the heat exchanger  2  to collect condensate that may form thereon from the external environment, for embodiments wherein the heat exchanger  2  is mounted in an area of a vehicle such as the trunk. 
         [0063]    Referring to  FIG. 1 , downstream from the heat exchanger  2 , and upstream from the second reactor  4  is the first, or upstream, reactor  3 , which may reduce the levels of one or more of such contaminants as chlorides, fluorides, nitrates, nitrites, sulfates and particulate matter. The first reactor  3  is shown in more detail in  FIG. 9 . The first reactor  3  has a reagent solution holding section  244  and a separation area  246 . An inlet conduit  248  transports the gas stream  204  with entrained contaminants into the reagent solution holding section  244 . The inlet conduit  248  may have a flared end  53  to assist in dispersing the gas stream  204  into a first reagent solution  250  held in the reagent solution holding section  244 . 
         [0064]    The first reagent solution  250  may be, for example, an aqueous solution of soda ash (ie. Sodium Carbonate) or some other suitable solution. The soda ash may be fed into the solution in any suitable way. For example, a solid block of soda ash, shown at  51   a,  may be provided in the reagent solution holding section  244 . Additionally or alternatively, a generally C-shaped solid block, shown at  51   b  (see  FIG. 10 ), may be provided around the outside of the reagent solution holding section  244 . An opening  252  at the bottom of the wall  254  that defines the reagent solution holding section  244  exposes the C-shaped solid block  51   b  to the solution, thereby keeping the solution fed with solid reagent. 
         [0065]    The C-shaped solid block  51   b  is loosely held in a reagent holding space  256 , which may be a hollow cylindrical space  256  that surrounds the reagent solution holding section  244 , and that is defined by the wall  254  and an outer wall  258 . 
         [0066]    As the bottommost portion of the C-shaped solid block  51   b  is consumed, it preferably slides downward to present more solid reagent at the opening  252  for feeding into solution. 
         [0067]    The C-shaped solid block  51   b  has a longitudinal channel  260  ( FIG. 10 ). The channel  260  permits the solid block  51   b  to clear components  19   a  and  66  ( FIG. 9 ) that are mounted to the wall  254 . 
         [0068]    A flange joint  20   a  may be provided to permit the first reactor  3  to be opened, for any maintenance purposes, and for replacement of the solid blocks  51   a  and  51   b  as necessary. 
         [0069]    A drain conduit  66   a  is provided so that some first reagent solution  250  is continuously drained off. New reagent is introduced, as described above, via the solid blocks  51   a  and  51   b.  This permits the first reagent solution  250  to be maintained in a state where it can react as needed with the incoming gas stream  204 . A water intake port shown at  19   a  is provided for replenishing the first reactor  3  with water as necessary. For example, water may need to be fed periodically into the first reactor  3  to make up for water lost from drainage through drain line  66   a.  Water may additionally be fed to the water intake port  19   a  during the addition of one or both blocks of soda ash  51   a  and  51   b.  During operation, however, a significant amount of water may come in the form of entrained droplets in the gas stream  204  itself. 
         [0070]    The flow of first reagent solution  250  through drain conduit  66   a  may be controlled by an automatic valve  16   b,  which may be controlled by any suitable means. The drain conduit  66   a  extends down to an effluent collection tank  5 , where effluent is held. Periodically the effluent collection tank  5  may be drained or otherwise emptied. The draining or emptying may be done manually or by automatic means. For example, a quick disconnect coupling (not shown) may be provided on the tank  5 , that can periodically receive a hose (not shown) for draining the tank  5 . The effluent that may be formed in the effluent collection tank  5  may itself have some use. For example, the effluent may be treated to separate out its water content, during which some chemicals may be separated off. For example, it is contemplated that chemicals that are useful as a fertilizer may be separated off. 
         [0071]    The first reactor  3  may further include a manual drain valve  22   a  for manually draining the first reactor  3  of any liquid prior to opening the flange joint  20   a.    
         [0072]    As the gas stream  204  reacts with the first reagent solution  250  bubbles  261  form. When the gas stream  204  leaves the first reagent solution  250 , it brings with it bubbles  261 . The gas stream  204  and bubbles  261  pass upwards through the separation section  246 , where the gas encounters a plurality of apertured members  262  which break the bubbles  261  thereby separating the liquid from the gas stream  204 . 
         [0073]    The apertured members  262  have apertures  264  and may be, for example, apertured plates, or screens. Some of the apertured members  262  may have the same size apertures  264 . A first apertured member, shown at  262   a  may have apertures  264  that are about 3/32 inch. The first apertured member  262   a  is oriented generally horizontally. In the embodiment shown in  FIG. 9 , above the first apertured member  262   a  are ten other apertured members  262 . The apertures  264  on the second, third and fourth members, identified as  262   b  may be about ⅛ inch. The apertures  264  on the fifth, sixth and seventh members, identified as  262   c,  may be about 3/16 inch. The apertures  264  on the eighth, ninth and tenth members, identified as  262   d  may be about ⅜ inch. The apertures  264  on the eleventh member, identified as  262   e  may be about 3/32 inch. At least some of the apertured members  262  may be arranged in a series wherein at least some alternate between horizontal and angled orientations. The non parallel arrangement inhibits the gas stream  204  from flowing in a purely linear path up through the separation section  246 , and increases the degree of contact that takes place between the apertured members  262  and the gas stream  204  and bubbles  261 . 
         [0074]    Baffles  54   a  and  50   a  are provided above the separation section  246  to control the gas stream  204  to prevent portions of the gas stream  204  from being preferentially exhausted through the outlet  266 , and to inhibit the presence of any dead zones of reduced flow. 
         [0075]    Quick release couplings  17  are provided at the inlet, shown at  270 , and the outlet  266  of the first reactor  3 , to facilitate removal of the reactor  3  from the conduit shown at  272  leading from the heat exchanger  2  ( FIG. 1 ), and from the transfer conduit  266 , for maintenance purposes. A suitable quick disconnect coupling (not shown) may also be provided on the drain conduit  66   a  for this purpose. The quick release couplings  17  permit the first reactor  3  to be replaced quickly with a fresh first reactor  3 , thereby permitting a vehicle to be returned to operation quickly. Whatever cleaning or other maintenance needs to be carried out on the removed first reactor  3  can then be carried out without causing delay in returning the vehicle to operation. 
         [0076]    The first reactor  3  may be made from a suitable polymeric material or a suitable metal such as steel, though the apertured members  262   a - k  may be made from a suitable polymeric material or a suitable metal, such as a suitable steel. 
         [0077]    The gas stream  204  leaves the first reactor  3  through the outlet  266  and into a transfer conduit  268  that leads to an inlet  274  to the second reactor  4 . The second reactor  4  includes a reagent solution holding section  276  and a separation section  278 . An inlet conduit  280  that extends downwards into the second reactor  4  ends at an outlet section  58  in the reagent solution holding section  276 . The outlet section  58  is apertured, with apertures that are sized to promote the release of gas from the gas stream  204  in the form of suitably sized bubbles  282  into a second reagent solution  57 , which may be a solution that is 50% by weight potassium hydroxide (KOH) and 50% water, or some other suitable solution. The outlet section  58  may be, for example, a micro-screen. The outlet section  58  preferably has at least about two times the surface area as the cross-sectional surface area of the inlet conduit  280  to reduce any backpressure that is created at the exhaust source (eg. the engine). The bubbles  282  react with the second reagent solution  57  in an exothermic reaction, which removes some contaminants, such as at least some NOx and CO2 from the gas stream  204 . 
         [0078]    The effectiveness of the second reactor  4  at removing NOx and CO2 in particular is significantly improved by the presence of the first reactor  3 , which removes contaminants, such as chlorides, fluorides, nitrites and sulfates, among others, at least some of which would significantly reduce the effectiveness of the second reactor  4  if they weren&#39;t removed or reduced in concentration in the first reactor  3 . 
         [0079]    The bubbles  282  rise and grasp the contaminants and the gas stream  204  leaves the second reagent solution  57  and enters the separation section  278  where the gas stream  204  passes through a series of apertured members  284 . In the embodiment shown in  FIG. 9 , there may be  11  apertured members  284  in total. The apertured members  284  may be similar to the apertured members  262 . The bubbles  282  break down on the apertured members  284  thereby separating the gas stream  204  from the bubbles  282 . The lowermost apertured member, shown as  284   a,  may be positioned about ½ inch to ¾ inch above the highest point of the outlet section  58 . 
         [0080]    The apertured members  284  may be arranged so that at least some of them are at an angle relative to another that is immediately above or immediately below, so as to inhibit the gas stream  204  from flowing in a purely linear path up through the separation section  278 , which in turn increases the degree of contact that takes place between the apertured members  284  and the gas stream  204  and bubbles  282 . 
         [0081]    Baffles  54   b  and  50   b  are provided above the separation section  278  to control the gas stream  204  to prevent portions of the gas stream  204  from being preferentially exhausted through the outlet, shown at  287 , and to inhibit the presence of any dead zones of reduced flow. 
         [0082]    Quick release couplings  17  are provided at the inlet, shown at  288 , and the outlet  287  of the second reactor  4 , to facilitate removal of the reactor  4  from the transfer conduit shown at  266  leading from the first reactor  3 , and from the outlet conduit  289 , for maintenance purposes. A suitable quick disconnect coupling (not shown) may also be provided on the drain conduit  66   a  for this purpose. The quick release couplings  17  permit the second reactor  4  to be replaced quickly with a fresh second reactor  4 , thereby permitting a vehicle to be returned to operation quickly. Whatever cleaning or other maintenance needs to be carried out on the removed second reactor  4  can then be carried out without causing delay in returning the vehicle to operation. 
         [0083]    The potassium hydroxide may be provided in the form of a C-shaped solid block, shown at  56  (see  FIG. 11 ). The C-shaped solid block  56  may be similar to the C-shaped solid block of soda ash  51  in  FIG. 10  and may thus have a longitudinal channel  290  that permits the block  56  of potassium hydroxide to clear a water intake port  19   b  and a drain conduit  66   b  that are mounted on the second reactor  4 . 
         [0084]    An opening  291  at the bottom of the wall  292  that defines the reagent solution holding section  276  exposes the C-shaped solid block  56  to the solution, thereby keeping the solution fed with solid reagent. 
         [0085]    The C-shaped solid block  56  is loosely held in a reagent holding space  294 , which may be a hollow cylindrical space  294  that surrounds the reagent solution holding section  276 , and that is defined by the wall  292  and an outer wall  296 . 
         [0086]    As the bottommost portion of the C-shaped solid block  56  is consumed, it preferably slides downward to present more solid reagent at the opening  291  for feeding into solution. 
         [0087]    A flange joint  20   b  may be provided to permit the second reactor  4  to be opened, for any maintenance purposes, and for replacement of the solid block  56  as necessary. 
         [0088]    The drain conduit  66   b  is provided so that some second reagent solution  257  is continuously drained off. New reagent is introduced, as described above, via the solid block  56 . This permits the second reagent solution  57  to be maintained in a state where it can react as needed with the incoming gas stream  204 . The water intake port shown at  19   b  is provided for replenishing the second reactor  4  with water as necessary. For example, water may need to be fed periodically into the first reactor  3  to make up for water lost from drainage through drain line  66   a.    
         [0089]    The flow of second reagent solution  57  through drain conduit  66   b  may be controlled by a third automatic valve  16   c,  which may be controlled by any suitable means. 
         [0090]    The drain conduit  66   b  extends to a mixing tank  21 . Additionally, the drain conduit  228  ( FIG. 1 ) extends from the heat exchanger  2  to the mixing tank  21 , so that drained reagent solution  57  and drained condensate  226  ( FIG. 6 ) can mix. Because the condensate  226  ( FIG. 6 ) is acidic and the reagent solution  57  is basic, mixing of the two will serve to neutralize both at least to some degree. A mixing tank drain conduit  298  connects the mixing tank  21  to the effluent collection tank  5 . 
         [0091]    The effluent that is collected in the effluent collection tank  5  may have a relatively high solids content, and may essentially be in solid form (in the form of particles). 
         [0092]    The second reactor  4  may further include a manual drain valve  22   b  for manually draining the second reactor  4  of any liquid prior to opening the flange joint  20   b.    
         [0093]    The second reactor  4  may be made from a suitable polymeric material or a suitable metal, such as steel, though the apertured members  284   a - k  may be made from a suitable polymeric material or a suitable metal, such as a suitable steel. 
         [0094]    Referring to  FIG. 9 , a one way intake valve  18  may be provided on the transfer conduit  268  between the first and second reactors  3  and  4 . The one way intake valve  18  permits ambient air to enter the transfer conduit  266  in the event that there is a sufficiently high pressure differential between the two reactors  3  and  4 . In the event of a sufficiently high pressure differential between the two reactors  3  and  4 , such as might occur during sufficiently hard acceleration, braking or cornering, there is an increased risk that reagent solution from one of the reactors  3  or  4  (the one at relatively higher pressure) could spill over into the other of the reactors  3  or  4 . By permitting ambient air to enter the transfer conduit  268 , any pressure differential is at least reduced thereby reducing the risk of spill. 
         [0095]    During use, gas pressure in the second reactor  4  is higher than ambient air pressure, thereby substantially preventing ambient air from communicating with the second reagent solution  57 . If ambient air were permitted to be in fluid communication with the second reagent solution  57  then the reagent would quickly neutralize through reaction with gaseous components of the ambient air. When the exhaust gas treatment apparatus  200  is not in use, however, the gas pressure in the second reactor  4  may possibly not be higher than ambient air pressure. Referring to  FIG. 1 , a reagent protection device  300  is provided downstream from the second reactor  4 , which substantially prevents ambient air from entering the outlet  206  and reacting with the second reagent solution  57  when the apparatus  200  is not operating. 
         [0096]    The reagent protection device  300  may be any suitable device, such as, for example, a motor-driven damper  23  ( FIG. 14 ). The damper  23  includes a damper blade  61 , a seal  59 , mounting brackets for the damper blade  61 , a motor mount  60  and a motor  302 . When the exhaust gas treatment apparatus  200  is not in operation, the damper  23  is moved to a closed position wherein it seals against the seal  59  so that ambient air is substantially prevented from being in fluid communication with the second reagent solution  57 . When an exhaust gas stream  204  is being generated, (eg. when a vehicle ignition key is inserted into the ignition keyhole on the vehicle dashboard or on the vehicle&#39;s steering column in embodiments wherein the apparatus  200  is vehicle mounted) the damper  23  opens automatically (ie. moves to an open position) permitting the gas stream  204  to pass therethrough from the second reactor  4  and out to atmosphere. It will be noted that by linking the damper  23  to the vehicle key, the damper  23  functions as a theft deterrent, since the vehicle&#39;s operation would be prevented if the exhaust were sealed off. 
         [0097]    The damper  23  could alternatively be any other suitable device for protecting the second reagent solution. For example, the damper  23  could be replaced by some suitable type of valve. 
         [0098]    With reference to  FIG. 1 , in an exemplary embodiment for vehicular use, selected dimensions for the system  10  are provided as follows: For a vehicular exhaust pipe that is 1¼ inch in diameter, the particulate matter remover  1  may employ a 2 inch diameter auger  31  with a 2 inch flight pitch. A 2 inch diameter conduit would lead from the particulate matter remover  1  to the heat exchanger  2 . The heat exchanger  2  may have a diameter of 6 inches and a length of about 10 inches. A 2 inch diameter conduit may carry the gas stream  204  from the heat exchanger  2  to the first reactor  3 . It will be noted that the backpressure created by this aforementioned selection of dimensions is not so great as to significantly hamper the function of the vehicle&#39;s engine, but is not so low that the gas stream  204  passes through the system  10  too quickly without a usefully significant removal of contaminants. 
         [0099]    Reference is made to  FIG. 15  which shows an optionally provided cooling room  70  that may be used in embodiments wherein the gas stream  204  is coming from a source such as a production plant, an incineration facility or a generating station such as a coal-fired generating station. In such situations, the gas stream  204  may be relatively hot. The cooling room  70  houses a conduit  77  that has a gas inlet  74 . The gas stream  204  passes from the inlet  74  to a series of baffles  76 . The gas stream  204  may be directed through a generally serpentine flow path by the baffles  76 . Suitable deflectors  72  may be provided to assist the flow of the gas stream  204 . The conduit  77 , baffles  76  and deflectors  72  may be made from any suitable material, such as a temperature resistant steel. The room  70  may include a roof and may be steel-encased. 
         [0100]    At the gas outlet  73  of the cooling room  70  there is positioned a bank  75  of catalysts  78  ( FIG. 16 ) which receive the cooled gas stream  204  and remove contaminants therefrom. After the gas stream  204  ( FIG. 15 ) leaves the bank  75  of catalysts  78  ( FIG. 16 ), the gas stream  204  may pass through a turbine  79  ( FIG. 17 ) for the purpose of rotating the turbine  79 . The rotational energy in the turbine  79  may be used for any suitable purpose, such as for the generation of electricity by providing a generator (not shown) that is connected to the output shaft  80  of the turbine  79 . 
         [0101]    Reference is made to  FIG. 18 , which shows an optional feature provided at the top of one or both of the first and second reactors  3  for facilitating the loading of a C-shaped solid block of reagent  51   b  or  56  into the reactor  3  or  4 . A C-shaped cover plate  81  is provided, and is mounted to cover and seal a C-shaped aperture  304  on an annular shoulder  604  above the hollow cylindrical space  256  or  294  in the reactor  3  or  4  to substantially prevent the influx of ambient air into the reactor  3  or  4 . In the hollow cylindrical space  256  or  294 , spaced below the C-shaped aperture  304 , a pair of overlapping flexible seal members  82   a  and  82   b  are provided. When the cover plate  81  is opened, the seal members  82   a  and  82   b  seal the reactor  3  or  4  off, inhibiting ambient air from being in fluid communication with the reagent solution  244  or  57 . As the C-shaped solid block of reagent  51   b  or  56  is lowered down, the seal members  82   a  and  82   b  seal against it to inhibit ambient air from entering the reactor  3  or  4 . Once the C-shaped solid block  51   b  or  56  is in place, the seal members  82   a  and  82   b  close and the cover plate  81  may be reinstalled. 
         [0102]    Reference is made to  FIG. 1 . The components shown in  FIG. 1  are exemplary components that permit one to carry out a method of operating an exhaust gas treatment apparatus, such as for example, the exhaust gas treatment apparatus  200 . In a first step an exhaust gas stream may be introduced. In another step particulate matter may be removed from the exhaust gas stream. The particular matter may be removed by any suitable device (eg. the particulate matter remover  1 ), and may be removed by more than one device (eg. the particulate matter remover  1  and the heat exchanger  2 ). In another step, the exhaust gas stream may be cooled to condense out at least some water vapour from the exhaust gas stream to form condensate. The condensate dissolves at least some gaseous contaminants from the exhaust gas stream. In another step, the exhaust gas stream is exposed to a reagent solution to reduce the concentration of at least some contaminants in the exhaust gas stream thereby after the aforementioned cooling step. In another step, the exhaust gas stream is discharged to atmosphere after being exposed to the reagent solution. In another step, the exhaust gas stream is stopped. Another step entails preventing exposure of the reagent solution to ambient air so as to protect the reagent solution. 
         [0103]    Several optional steps may be included in the aforementioned method. For example, the reagent solution may be a downstream reagent solution, and wherein the method may further comprise exposing the exhaust gas stream to an upstream reagent solution prior to exposure to the downstream reagent solution. The upstream reagent solution is selected to reduce the concentration in the exhaust gas stream of at least one contaminant selected from the group consisting of: chlorides, fluorides, nitrates, nitrites and sulfates. The downstream reagent solution is selected to reduce the concentration in the exhaust gas stream of at least one contaminant selected from the group consisting of NOx and CO2. 
         [0104]    In the step wherein the exhaust gas stream is exposed to the reagent solution the method may further include causing bubbling of the exhaust gas stream in the reagent solution. 
         [0105]    In the step wherein the exhaust gas stream is cooled, the method may further include capturing at least portion of the condensate, and the method may further include mixing a selected amount of the captured condensate with a selected amount of the reagent solution. The condensate is acidic and the reagent solution is basic. 
         [0106]    In this disclosure, the term ‘ambient air pressure’ means air pressure of air outside the apparatus  200 . The term ‘atmosphere’ refers to the air outside the apparatus  200 . 
         [0107]    While two reactors (ie. reactors  3  and  4 ) have been disclosed as being part of the apparatus  200 , it is optionally possible to have fewer (eg. reactor  3  only, or reactor  4  only) as part of the apparatus  200 . It is also optionally possible to have three or more reactors. For example, it is optionally possible to add one or more reactors at some suitable position, (eg. downstream from the second reactor  4 ), that remove methanol and formaldehyde from the exhaust gas stream  204 . Such reactors may have any suitable structure, and may be similar to the reactors  3  and  4 . 
         [0108]    While the above description constitutes a plurality of embodiments of the present invention, it will be appreciated that the present invention is susceptible to further modification and change without departing from the fair meaning of the accompanying claims.