Patent Publication Number: US-11662093-B2

Title: System for removing particulate matter from biomass combustion exhaust gas comprising gas cyclones and baghouses

Description:
This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application Ser. No. 63/010,187 filed Apr. 15, 2020. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a system for removing particulate matter from exhaust gas generated by combustion of biomass, and more particularly to such a system comprising a plurality of particle separation stages including a cyclone separation stage and a baghouse filtration stage, which is particularly but not exclusively suited for removing substantially all potassium chloride generated by burning poultry litter or waste. 
     BACKGROUND 
     Biomass is becoming an increasingly popular form of renewable energy which can be combusted in a furnace to generate heat. 
     In particular, poultry litter or waste has been found to be an attractive biofuel that is increasingly available as it is a by-product of poultry production which continues to expand worldwide. Thus, for poultry producers, this is a convenient renewable energy source which is readily locally available for production of heat for example for heating facilities which house the poultry production. 
     Although biomass such as poultry litter is a convenient renewable energy source, combustion of same produces harmful particulate matter such as potassium chloride which is not desirable to emit into the atmosphere along with exhaust gas from the biomass combustion. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the invention there is provided a system for removing particulate matter from exhaust gas generated by combustion of biomass comprising: 
     a frame arranged for resting on a support surface, the frame extending longitudinally between first and second ends and laterally between first and second sides; 
     an inlet for receiving a flow of the exhaust gas; 
     a first particle separation stage supported on the frame and comprising a plurality of substantially vertically oriented gas cyclones each configured to form a vortex to separate from the flow of the exhaust gas the particulate matter exceeding a first prescribed threshold size; 
     the gas cyclones of the first particle separation stage being in parallel fluidic communication with the inlet, the gas cyclones being arranged one beside the other in a generally laterally extending row across the frame; 
     a second particle separation stage supported on the frame and in fluidic communication with the first particle separation stage so as to receive the flow of the exhaust gas with the particulate matter exceeding the first prescribed threshold size removed therefrom; 
     the second particle separation stage comprising a plurality of baghouses each including a housing and a plurality of bag filters suspended therein, each baghouse being arranged to separate from the flow of the exhaust gas the particulate matter exceeding a second prescribed threshold size which is smaller than the first Prescribed threshold size; 
     the baghouses of the second particle separation stage being in series fluidic communication with one another, the baghouses being arranged one beside the other in a generally longitudinally extending row across the frame; and 
     an outlet in fluidic communication with the second particle separate stage for discharging the flow of the exhaust gas with the particulate matter exceeding the second prescribed threshold size removed therefrom. 
     This arrangement which is particularly but not exclusively suited for treating exhaust gas from combustion of poultry litter provides highly efficient removal of the particulate matter from the combustion exhaust gas before discharge thereof into the atmosphere, while occupying a minimal physical footprint. 
     Preferably, the bag filters of each baghouse are arranged in a generally laterally extending row within the housing of the baghouse. 
     Preferably, the baghouses are arranged with the first particle separation stage in a generally common longitudinally extending row across the frame. 
     Preferably, each baghouse is configured to pass the flow of the exhaust gas from the housing through to insides of the bag filters to remove the particulate matter exceeding the second prescribed threshold size, and the housings of the baghouses are in series fluidic communication. 
     Preferably, each bag filter comprises a fabric membrane in the form of a bag, which is arranged to prevent passage of the particulate matter exceeding the second prescribed threshold size therethrough, that is supported on an exterior of a support cage generally in the shape of a rectangular prism. 
     In one such arrangement, the support cage of each bag filter has a length between top and bottom ends, a width between a substantially-parallel opposite pair of narrow faces, and a thickness between a substantially-parallel opposite pair of wide faces, and the width of the support cage is between 7 and 12 times greater than the thickness of the support cage. 
     In one such arrangement, a length of the support cage of each bag filter between top and bottom ends is between about 22 and about 35 inches. 
     Preferably, the support cage of each bag filter is generally sheet-like in shape so as to have a substantially-parallel opposite pair of wide faces between which a thickness of the cage is defined and a substantially-parallel opposite pair of narrow faces between which a width of the cage is defined, and a plane of the sheet-like support cage extends in the longitudinal direction of the frame and is parallel to the plane of the adjacent support cage of a common one of the baghouses. 
     In the illustrated arrangement, the system includes a fan downstream of the second particle separation stage and upstream of the outlet that is configured for generating suction for drawing the flow of the exhaust gas from the inlet to the outlet, the fan being located to one side laterally of a downstream-most one of the baghouses of the second particle separation stage. 
     In the illustrated arrangement, the fan is carried on a cantilevered platform of the frame arranged to be supported at a spaced height above the support surface. 
     Preferably, the system further includes a bypass duct which fluidically intercommunicates the first particle separation stage and the outlet so as to guide the flow of the exhaust gas, with the particulate matter exceeding the first prescribed threshold size removed therefrom, to the outlet without passing through the second particle separation stage, and a bypass valve operatively supported in the bypass duct for movement relative thereto between a closed position in which the bypass duct is substantially obstructed to prevent passage of the flow of exhaust gas therethrough and an open position in which the bypass duct is substantially unobstructed to permit passage of the flow of exhaust gas therethrough, wherein the bypass valve is configured so that movement from the closed position to the open position is responsive to detection of a pressure gradient exceeding a prescribed threshold in one of the bag houses. 
     Preferably, the first and second particle separation stages include collection hoppers arranged to gravitationally convey the removed particulate matter downwardly to bottom discharges of the collection hoppers, the bottom discharges of the collection hoppers of the first and second particle separation stages being communicated with a common conveyor arranged to transfer the removed particulate matter to a collection bin. 
     In the illustrated arrangement, the conveyor extends underneath the bottom discharges to a discharge end disposed substantially at a periphery of the frame. 
     In the illustrated arrangement, the frame is arranged to carry the bottom discharges of the collection hoppers at spaced heights above the support surface so that the collection bin can be disposed below the bottom discharges and at least partially within the periphery of the frame. 
     In the illustrated arrangement, an inlet of each baghouse is located at a height of the bag filters thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in conjunction with the accompanying drawings in which: 
         FIG.  1    is a side view of a system for removing particulate matter from biomass combustion exhaust gas according to an arrangement of the present invention; 
         FIG.  2    is a perspective view of the system of  FIG.  1   , where some components are omitted for convenience of illustration or to show parts which are otherwise hidden; 
         FIG.  3    is a cross-sectional view taken along line  3 - 3  in  FIG.  4   ; 
         FIG.  4    is an end view of the system of  FIG.  1   ; 
         FIG.  5    is a top plan view of the system of  FIG.  1   , where some components are omitted for convenience of illustration or to show parts which are otherwise hidden, and a portion of a bypass duct is shown as transparent to show an otherwise hidden bypass valve therein; and 
         FIG.  6    is a cross-sectional view along line  6 - 6  in  FIG.  1   . 
     
    
    
     In the drawings like characters of reference indicate corresponding parts in the different figures. 
     DETAILED DESCRIPTION 
     The accompanying figures show a system indicated at  10  for removing particulate matter from exhaust gas generated by combustion of biomass. In industry this system  10  may be referred to as a scrubber for treating the exhaust gas. 
     With reference to  FIG.  1   , the system  10  is arranged to be disposed in series fluidic communication with a furnace  1  (schematically shown), in which the biomass is combusted, and a chimney or flue  3  (schematically shown) arranged for discharging or expelling the exhaust gas to atmosphere, or more generally the ambient environment. More specifically, the system  10  is located intermediate the furnace  1  and the chimney  3  so that untreated exhaust gas released from the furnace  1  after being passed through a heat exchanger of the furnace can be treated to remove harmful particulates in the form of solid particles, such as potassium chloride, carried by the exhaust gas before the same is discharged to the surrounding environment. 
     The particulate removal system  10  comprises a frame  12  arranged for resting on a support surface SS defined by, for example, a concrete floor. The frame  12  extends longitudinally between first and second ends  14 ,  15  and laterally between first and second sides  17 ,  18 . The frame  12  comprises a plurality of legs  20  in spaced relation to each other defining a footprint of the frame on the support surface SS, that is a surface area on the support surface occupied by the frame  12 . The legs  20  extend vertically from bottoms  20 A arranged for engaging the support surface SS to tops  20 B thereof defining a top of the frame. Each of the legs  20  comprises a lower section  21 A defining the bottom  20 A and an upper section  21 B defining the top  20 B, which are interconnected. 
     The legs  20  are interconnected by a laterally opposite pair of longitudinally extending beams  24  arranged at the tops  20 B of the legs, an upper pair of longitudinally opposite laterally extending cross members  25  arranged at the tops  20 B of the legs and a lower pair of longitudinally opposite laterally extending cross members  26  arranged at an intermediate height between the tops and the bottoms of the legs. A pair of laterally opposite brace members  27  are provided generally at the second end  15  of the frame  12  to interconnect a respective one of the legs  20  and a respective one of the beams  24  adjacent thereto. The foregoing components also form the frame  12 . 
     On the frame there is supported a first particle separation stage  30  which comprises a plurality of gas cyclones  31  for providing a first coarse particle removal step of the treatment process performed by the system  10  on the combustion exhaust gas. Referring to  FIG.  3   , the gas cyclones  31  are of a conventional design each comprising a generally cylindrical outer housing  33  defining an inlet  34  of the cyclone and an inner generally cylindrical duct  36  defining an outlet  37  of the cyclone that is substantially coaxial with the outer housing  33 . An axis  39  of the cyclone which is encompassed by the outer housing  33  is substantially vertically oriented such that a stream of gas admitted into the housing  33  through the inlet  34  is guided in a generally horizontal direction, tangentially of the axis  39 , and the gas stream is emitted from the cyclone  31  in a generally vertical direction substantially coaxially of the cyclone. 
     The substantially conventional gas cyclones  31  are configured to form a vortex within the outer housing  33 , as represented by a path of arrow  42  showing flow of the exhaust gas in the cyclone, to separate from the exhaust gas flow particulate matter which exceeds a first prescribed threshold size. 
     Referring to  FIG.  4   , the inlets  34  of the gas cyclones  31  are fluidically communicated with a common inlet  45  of the system which in turn is in fluidic communication with the furnace  1 . Thus all of the gas cyclones  31  of the first particle separation stage  30  are in parallel fluidic communication with the inlet  45  so as to each receive a portion of an input flow of the exhaust gas received by the system  10  for substantially simultaneous treatment. 
     As such, the substantially vertically oriented gas cyclones  31  are arranged one beside the other in a generally laterally extending row across the frame  12  such that the first particle separation stage  30  occupies a minimum amount of space within the frame  12 . 
     The cyclonic separation stage  30  is suited as the first particulate removal stage in the system  10  receiving untreated exhaust gas because the gas cyclones  31  comprise non-combustible metallic components which are well suited for preventing sparks, which are emitted by the combustion of the flammable biomass and carried with the exhaust gas, from continuing to stages and components of the system  10  which are downstream of the cyclones  31  relative to the flow of exhaust gas through the system  10 . 
     To remove finer solid particles carried by the exhaust gas, the system  10  includes a second particle separation stage  50  which comprises a plurality of baghouses  51  for providing a second fine particle removal step of the treatment process performed by the system  10  on the combustion exhaust gas. The second particle separation stage  50  is supported on the frame  12  and is in fluidic communication with the first particle separation stage  30  so as to receive the flow of the exhaust gas with the particulate matter exceeding the first prescribed threshold size removed therefrom, or in other words, receiving the exhaust gas containing particulate matter which is substantially no larger than the first prescribed threshold size. More specifically, the outlets  37  of the gas cyclones  31  are in parallel fluidic communication with the second particle separation stage  50  which is downstream of the cyclones  31  via duct  52  which extends upwardly and longitudinally from the outlets  37  to an inlet  53  of the second bag filtration stage  50 . 
     The baghouses  51  of the second stage  50  are of a generally conventional design and are arranged in series fluidic communication with one another so that the exhaust gas flow received from the first particle separation stage  30  is initially admitted into an upstream-most one of the baghouses indicated at  51 A, which defines the inlet of the second stage  50 , before eventually flowing to a subsequent downstream one of the baghouses  51 B. Despite their series fluidic arrangement, the multiple baghouses  51  substantially work in parallel to treat the exhaust gas such that providing more than one baghouse acts to increase a maximum flow rate of gas which can be treated by the system  10 , similarly to providing multiple parallel gas cyclones  31 . 
     The series baghouses  51  are arranged one beside the other in a generally longitudinally extending row across the frame  12  so that the second particle separation stage  50  occupies a minimum amount of space within the frame  12 . Furthermore, the upstream-most baghouse  51  is disposed on the frame in adjacent relation to the cyclonic separation stage  30 . 
     Each conventional baghouse comprises a housing  54  and a plurality of bag filters  55  suspended therein. Each baghouse  51  is arranged to separate, from the flow of the partially treated exhaust gas, particulate matter which exceeds a second prescribed threshold size smaller than the first prescribed threshold size already removed from the exhaust gas by the first particle separation stage  30 . It will be appreciated that the housings  54  of the baghouses  51  are substantially enclosed although they are shown for example in  FIGS.  2  and  5    as open at their tops above the bag filters  55  which is for the purpose of showing internal features of the baghouses  51 , such as the bag filters  55 , which are otherwise hidden from view. 
     Each baghouse  51  is of the pulse-jet type meaning that the baghouse is configured to pass the flow of the exhaust gas from the housing  54  surrounding the bag filters  55  supported inside same, to which the gas flow is input, through to insides of the bag filters  55  to remove the particulate matter exceeding the second prescribed threshold size, leaving the same on outsides of the filters  55 . Thus, more specifically it is the housings  54  of the baghouses that are in series fluidic communication to enable passage of the exhaust gas input to the second particle separation stage  50  to each of the baghouses  51 . 
     Each bag filter  55  comprises an outer fabric membrane  58  in the form of a bag, which is arranged to prevent passage of the particulate matter exceeding the second prescribed threshold size therethrough, and an internal support cage  59  providing structural support for the bag  58  and defining a plurality of openings to enable passage from the selectively permeable fabric membrane  58  through to an interior of the individual bag filter that is delimited by the cage. The support cage  59  has a top hanger portion configured for mounting to a support portion  62  of the housing  54  defining a plurality of slots into which each of the bag filters  55  can be lowered. The support portion  62  forms a divider wall which separates the housing  54  into an input chamber  64  to which dirty gas is confined, that is the exhaust gas carrying the particulate matter including particles greater than the second threshold size, and an output chamber  65  which is fluidically communicated with the insides of the bag filters  55  to receive the exhaust gas with the foregoing particles removed therefrom. The insides of the bag filters  55  are fluidically communicated with the input chamber but the fabric membrane  58  provides selective transmission of particles smaller no larger than the second prescribed size through to the output chamber  65 . 
     Thus each baghouse  51  comprises a plurality of the bag filters  55  to increase a maximum flow rate of the exhaust gas which can be treated by the respective baghouse. The bag filters  55  of each baghouse are arranged in a generally laterally extending row within the housing  54  of the baghouse, that is in a direction cross-wise to the longitudinal arrangement of the baghouses  51 , so as to minimize a footprint of the respective baghouse. This mirrors the lateral arrangement of the constituent gas cyclones  31  of the first stage  30 . 
     To further reduce the overall footprint of the system  10  comprising only two particle separation stages  30  and  50  for the purposes of removing substantially all of the harmful particulate in the exhaust gas before discharge to the atmosphere, the baghouses  51  are arranged with the first particle separation stage  30  in a generally common longitudinally extending row across the frame  12 . 
     Returning now to the baghouses  51 , in order to increase the maximum flow rate of gas which can be treated thereby, the support cages  59  which carry the bag-like membranes  58  on their exteriors are each generally in the shape of a rectangular prism instead of the conventional circular cylindrical shape. 
     More specifically, the support cage  59  which is generally in the shape of a rectangular prism is substantially planar like a sheet so as to have a substantially-parallel opposite pair of wide faces  69  between which a thickness of the cage is defined and a substantially-parallel opposite pair of narrow faces  70  between which a width of the cage is defined. The thickness of the cage  59  is substantially smaller in size than the width of the support cage which is between 7 and 12 times greater than the thickness of the support cage, and preferably between 8 and 10 times greater than the thickness of the support cage. Also, a length of the cage  59  between top and bottom ends  73 ,  74  is between about 1.2 and about 2 times greater than the cage width, and preferably between about 1.4 and about 1.6 times greater than the cage width. Generally speaking, the length of the support cage is between about 22 and about 35 inches, and preferably between about 25 and about 30 inches. In at least one arrangement, the support cage is 28 inches long, 18 and ⅝ inches wide, and 2 inches thick. 
     A plane P of the sheet-like support cage  59 , as more clearly shown in  FIGS.  5 - 6   , which is substantially vertically oriented, extends in the longitudinal direction of the frame  12  and is parallel to the plane P of the adjacent support cage  59  of a common one of the baghouses. This further minimizes a volumetric size of the baghouse  51 . 
     The output chambers  65  of the baghouses  51  are in fluidic communication with an outlet  77  of the system for discharging the flow of the exhaust gas with the particulate matter exceeding the second prescribed threshold size removed therefrom. In the illustrated arrangement, a duct  79  is provided to fluidically intercommunicate the output chambers  65  of the series baghouses  51  such that the system outlet  77  can be directly fluidically communicated with the downstream-most baghouse  51 B. 
     It also will be appreciated that the input chambers  64  of the baghouses are fluidically communicated by duct  80  so that the partially treated exhaust gas from the first cyclonic separation stage  30  is admitted to both serially-arranged baghouses  51  for substantially simultaneous treatment by bag filters  55  before discharge from the output chambers  64  to the outlet  77 . 
     It will also be appreciated that the inlet  53  and the duct  80  which defines an inlet to the downstream baghouse  51 B are located closer to a top of the input chamber  64  than to a bottom thereof, and preferably at the top therefor at the divider wall  62  from which the bag filters  55  hang, so that the input partially-treated exhaust gas is guided across the bank of plural bag filters  55  parallel to the planes P thereof. As such the inlet of each baghouse  51  is located closer to a top of the housing  54  than to a bottom thereof so as to be located at a height of the bag filters  55  so that the exhaust gas flow is substantially horizontally directed across the housing  54 , and directed substantially normal to a direction of the flow of treated gas through the bag filters  55  to the output chamber  65 . 
     The system  10  includes a fan  82  arranged downstream of the second particle separation stage  50  and upstream of the outlet  77 , which is configured for generating suction for drawing the flow of the exhaust gas from the inlet  45  to the outlet  77  and through the serially-arranged particle separation stages  30 ,  50 . The fan  82  is mounted on the frame  12  so as to be located to one side laterally of the downstream-most baghouse  51 B that is opposite to the duct  79  disposed on the other lateral side of the baghouses  51 . 
     More specifically, the fan  82  is carried on a cantilevered platform  85  of the frame  12  which is arranged to be supported at a spaced height above the support surface SS. The cantilevered platform  85  is formed by a pair of laterally extending cross-members arranged at the tops  20 B of the legs, which extend past the side  18  of the frame as defined by the legs  20  that are located on that side  18 . One of the foregoing laterally extending cross-members is defined by one of the end cross-members  25  that is located on the end  15  of the frame, which extends beyond the side  18 , and a distinct cross-member  88  connected at an intermediary location to one of the longitudinal beams  24  that is on the side  18 . Each of the frame members  25 ,  88  defining the cantilevered platform  85  are braced by a distinct inclined support member  89 ,  90 . The frame members  25 ,  88  are interconnected at their distal ends to the frame side  18 . 
     As more clearly shown in  FIG.  6   , the system  10  further includes a set of sensors schematically shown at  93 ,  94  disposed in each of the baghouses  51  for measuring a pressure gradient between the input and output chambers  64 ,  65  of the baghouse. Generally speaking, there will exist a difference in pressure between these two chambers as the bag filters  55  act to restrict the flow of the exhaust gas from the input chamber  64  to the output chamber  65 . 
     The pressure sensors  93 ,  94  are operatively associated with a controller  96  (schematically shown) for communication therewith. For convenience of illustration, the controller  96  is shown in  FIG.  6    as communicating only with one of the sensors, specifically that indicated at  93 , although it will be appreciated that it communicates with both pressure sensors. 
     The controller  96  is configured to monitor the measured pressure gradient determined by pressure measurements obtained from the sensors  93 ,  94  to check whether the measured gradient in one of the baghouses  51  has exceeded a prescribed threshold value. 
     That is, it will be appreciated that in accordance with the generally conventional pulse-jet arrangement of the baghouses  51 , each baghouse  51  is configured to periodically inject a short burst of pressurized air into each bag filter  55  so as to dislodge the particulate which has collected on the exterior of the fabric member  58 , thereby automatically periodically cleaning the filters. 
     However, in the event that the automatic cleaning feature is not effective, the pressure gradient between the two chambers  64 ,  65  of a common baghouse  51  may increase above a safe level. In this case, the operation of the baghouse  51  would need to be interrupted for inspection or manual cleaning. 
     To enable continuous operation of the particulate removal system  10  in the event that maintenance work has to be performed on the baghouses  51  of the second particle separation stage  50 , the system  10  additionally includes a bypass duct  100  which fluidically intercommunicates the first particle separation stage  30  and the outlet  77  so as to guide the flow of the exhaust gas, with the particulate matter exceeding the first prescribed threshold size removed therefrom, to the outlet  77  without passing through the second particle separation stage  50 . More specifically, an inlet  100 A of the bypass duct is communicated with the duct  52  which is at an intermediate location between the first stage  30  and the second stage  50 , and an outlet  100 B of the bypass duct is communicated with ducting at an intermediate location between the fan  82  and the second particle separation stage  50 . Thus the system  10  can continue to operate by at least partially treating the exhaust gas by applying cyclonic separation thereto. 
     A bypass valve  102  is operatively supported in the bypass duct  100  for movement relative thereto between a closed position in which the bypass duct  100  is substantially obstructed to prevent passage of the flow of exhaust gas therethrough, for example during normal operation so that the flow of exhaust gas is forced to pass through both particle separation stages  30  and  50  to remove substantially all of the particulate therefrom, and particularly the potassium chloride, before being exhausted to atmosphere, and an open position in which the bypass duct is substantially unobstructed to permit passage of the flow of exhaust gas therethrough, such as when maintenance on the baghouses  51  needs to be performed. The bypass valve  102  is configured so that movement from the closed position to the open position is responsive to detection by controller  96  of the pressure gradient exceeding the prescribed threshold in one of the baghouses. Therefore, the bypass valve  102  is operatively associated or coupled with the controller  96  which actuates movement of the valve to the open position, and also back to the closed position once the baghouses  51  have been cleaned so as to be returned to operation. 
     In regard to removal of the particulate which has been separated from the exhaust gas passing through the system  10 , the first and second particle separation stages  30 ,  50  include bottom collection hoppers  107  arranged to gravitationally convey the removed particulate matter downwardly to bottom discharges  108  of the collection hoppers. Furthermore, each gas cyclone  31  of the first separation stage  30  has a bottom hopper portion  109  to gravitationally urge the separated particulate towards a common collection hopper  107  which is in communication with all of the gas cyclones of the first stage  30 . The bottom discharges  108  of the first and second particle separation stages  30 ,  50  are selectively communicated via an air lock  108 A (schematically shown) with a common conveyor  111  which is arranged to transfer the removed particulate matter to a collection bin  113 . The air locks  108 A enable each particle separation stage to remain suitably pressurized in order to suitably treat the exhaust gas. The air locks  108  are operatively associated with the controller  96  to actuate the same. 
     The bottom discharges  108  of the collection hoppers lie along a common longitudinally extending axis located laterally centrally of the frame so that a single conventional screw conveyor  111  can be provided to move the separated particulate to the collection bin  113 . This arrangement is made easier as the parallel gas cyclones of the first particle separation stage  30  and the baghouses  51  are all arranged in a common longitudinally extending row. 
     The screw conveyor  111  comprises a tubular housing  115 , a shaft  116  supported for driven rotation inside the housing, and a helical flight  117  connected to the rotatable shaft. The conveyor  111  extends underneath the bottom discharges  108  to a discharge end  120  of the conveyor which is disposed substantially at a periphery of the frame  12  as more clearly shown in  FIG.  3   . Each collection hopper discharge  108  is communicated with the housing  115  of the conveyor at an axially spaced position from an adjacent one of the bottom discharges  108 . An air lock  122  is provided at the conveyor discharge end  115  to selectively fluidically communicate the conveyor housing  116  and the collection bin  113 . 
     As more clearly shown in  FIGS.  1  and  3   , the frame  12  is arranged to carry the bottom discharges  108  of the collection hoppers  107  at spaced heights above the support surface SS so that the collection bin  113  can be disposed below the bottom discharges and at least partially within the periphery of the frame, as more clearly shown in  FIG.  3   , where the bin  113  is located between the legs  20  at the second end  15  of the frame. This further reduces the overall footprint of the system with the waste particulate collection system provided by the conveyor  111  and collection bin  113 . The collected particulate, for example, may be recycled as fertilizer. 
     This arrangement which is particularly but not exclusively suited for treating exhaust gas from combustion of poultry litter provides highly efficient removal of the particulate matter from the combustion exhaust gas before discharge thereof into the atmosphere, while occupying a minimal physical footprint. 
     In use, once the exhaust gas is generated by the combustion of biomass in the furnace  1 , the untreated exhaust gas is guided into the particulate removal system  10  through the inlet  45 . Upon entering the system  10 , the exhaust gas is passed through the first particle removal stage  30  where cyclonic separation is applied to the exhaust gas to separate therefrom the particles which exceed the first prescribed threshold size. 
     The partially treated exhaust gas is subsequently guided to the second particle separation stage  50  where it is serially admitted into each of the constituent baghouses  51  of the second stage  50 . 
     At the second stage  50 , mechanical filtration is applied to the exhaust gas to further remove therefrom particles which exceed the second prescribed threshold size but which are no larger than the first prescribed threshold size which were permitted to be passed to the second stage  50  by the first particle separation stage  30 . 
     The mechanically dry filtered exhaust gas is subsequently guided to the outlet  77  where it is discharged to the ambient environment. 
     During normal operation of the system to treat the exhaust gas progressively using the multiple particle separation stages  30 ,  50 , the bag filters  55  of the baghouses  51  are periodically cleaned by injecting pressurized air into the bag filters. 
     The separated particulate eventually gravitationally settles and is gravitationally conveyed to bottom discharges  108  of the collection hoppers  107  of each particle separation stage. 
     In the event that the pressure gradient in any one of the baghouses is detected as exceeding the prescribed threshold pressure gradient, the bypass valve  102  is actuated by the controller  96  to provide an auxiliary flow path directly from the output of first particle separation stage  30  to the outlet  77 . 
     In other words, the system  10  provides a two stage particle separation process to remove unwanted potassium chloride from high temperature, combustion air exhaust. 
     High temperature flue gases are pulled into the top of the first stage  30  of the system at high speed, where the gases are subjected to cyclonic, centrifugal forces that push the heavy, larger particles and sparks out of the air stream against the wall of the cyclone. The particles then fall into a collection hopper which has an air lock that opens to a screw auger which takes the particles to a collection bin. The position of the exhaust port and the cyclonic hopper within the first stage hopper provide a high recovery rate for the separated particulate. 
     The second stage  50  is a dual pass bag filter system which has pneumatic, self-cleaning filter banks for the removal of fine dust particles. The pneumatic cleaning system is on a set timer which can be adjusted as needed through a PLC controller. With a small vacuum these particles are then dropped into the collection hoppers. The airlock located on the bottom of each hopper opens to unload the particles into a screw auger which takes the particles to the collection bin. The airlock are controlled by the PLC in an electrical panel of the system  10 . 
     Together, these stages combine to form a self-contained, low vacuum, sealed system which treats the exhaust gas to remove substantially all of the particulate initially carried thereby. 
     Accordingly, one benefit of the illustrated arrangement is a system which yields valuable, resalable or reusable fertilizer product that can be safely reintroduced into the plant growing cycle. 
     The system can be retrofitted to almost any existing biomass boiler system. 
     The system can also be used in other applications where such a process is needed, that is for exhaust gas treatment to remove particle particularly potassium chloride. 
     Exhaust gas from combustion devices is hot, moist and heavily laden with potassium chloride particulate as it leaves the combustion exhaust chamber. When it enters the cooler exhaust/chimney zone, it begins to condense. 
     These operating conditions present a variety of problems for electrostatic precipitators and wet scrubbers such as clogging/plugging up and corrosive liquid byproducts. 
     A typical baghouse filter system has a very large footprint unlike our small footprint. It usually pulls air in through the bottom of the structure where larger particles drop out of the air stream and smaller particles are filtered out by the bags situated near the outlet. 
     The Environmental Protection Agency (EPA) wants to eliminate air borne contaminants, issues with dangerous land fill waste product and liquid byproducts that can find their way into local waterways that feed into major bodies of water causing toxic algae blooms. The illustrated arrangement of exhaust gas treatment system removes these contaminants when burning waste products, that is poultry litter, which acts to produce energy. 
     The scope of the claims should not be limited by the preferred embodiments set forth in the examples but should be given the broadest interpretation consistent with the specification as a whole.