Abstract:
A fabric filter (barrier filter) with an inlet design for high particle load that allows for individual compartments in a row to be isolated by closure of a sloped inlet damper by which the sloped design allows particulate during damper closure to flow to the opposing compartment hopper preventing damper failure from the accumulated weight of the particulate load.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present invention provides a filtration plant for removing particulate material from high volume gas flow streams and particularly for removing smoke and ash from gas effluent from a coal fired boiler. 
         [0003]    2. Background Art 
         [0004]    Fabric filters (also referred to as barrier filtration) have been used for the collection of dust from industrial applications and particulate (smoke) from coal fired boiler applications for the last fifty years. A typical filter plant employing fabric filters for a 150 Megawatt coal fired boiler would utilize eight individual filtration units with 600 filter tubes in each filtration unit. Filter plants usually are of either a high particle load design or a low particle load design. Filter plants for low particle loads are suitable for use with particle flows in the typical range of 1 grain/actual cubic foot to 35 grains/actual cubic foot. High particle load filter plants are suitable for use with particle loads well above 35 grains/actual cubic foot. 
         [0005]      FIGS. 1 and 2  show a prior art low particle load filter plant  10  where filter compartments  12  are arranged in two rows  14   a,b  with four filter compartments in each row such that each of the four compartments ( 12   a   1 - 12   a   4 ) in row  14   a  is respectively in alignment with one of the four compartments ( 12   b   1 - 12   b   4 ) in row  14   b . A common inlet manifold  16  positioned between the rows  14   a,b  conveys a particulate laden gas flow  17  from a boiler from an inlet  19  to all of the filter compartments. Each compartment is supplied a portion of the gas flow through transversely directed and dedicated stubs  18  which are in fluid communication with the inlet manifold. Each stub  18  bears the alpha-numeric designation of the compartment it feeds ( 18   a   1 - 4 ,  18   b   1 - 4 ). The gas flow to each stub can be controlled by a damper such that each compartment  12   a   1 - a   4 ,  12   b   1 - b   4  can be individually isolated for maintenance. 
         [0006]      FIGS. 3 and 4  show a prior art high particle load filter plant  20  having four filter compartments  22   a,d  each fed by a dedicated manifold  24   a,d . In this embodiment, dirty gas flow is directed from a boiler (not shown) through ductwork to an optional fluid bed scrubber  26  and to a gas splitter that divides the gas flow into dedicated flow streams  28   a,d . An isolation damper  30   a,d  is provided at an inlet  32   a,d  to each manifold  24   a,d .  FIG. 4  shows gas from the manifold  24  flows vertically downward from the isolation damper location, which is elevated with respect to the base of the filter compartments. An inlet  32  ( FIG. 4 ) at the base of each filter compartment  22   a,d  remains open with a direct vertical path to a collection hopper  34  to separate a portion of the entrained particles from the dirty gas flow by gravity prior to the full particulate load reaching filter tubes which extend vertically within the filter compartments as shown in  FIG. 5 . Thus, to remove an individual filtration compartment  22   a , for example, isolation damper  30   a  must be closed thereby removing one fourth of the filtration capacity of the entire filtration plant  20 . 
         [0007]    These and other aspects and attributes of the present invention will be discussed with reference to the following drawings and accompanying specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic view of a prior art low particulate load filtration plant; 
           [0009]      FIG. 2  is an elevation view taken along line A-A of  FIG. 1 ; 
           [0010]      FIG. 3  is a schematic view of a prior art high particulate load filtration plant; 
           [0011]      FIG. 4  is an elevation view taken along line A-A of  FIG. 3 ; 
           [0012]      FIG. 5  is a perspective view partially disassembled of a low particle load filtration plant; 
           [0013]      FIG. 6  is a side view of a cleaning mechanism for the filter tubes; 
           [0014]      FIG. 7  is a top plan view of the gas filtration plant of  FIG. 5 ; 
           [0015]      FIG. 8  is a side view taken along line A-A of  FIG. 7 ; 
           [0016]      FIG. 9  is an end view taken along line B-B of  FIG. 7 ; 
           [0017]      FIG. 10  is a side view of a gas filtration plant with a circulating bed scrubber; and 
           [0018]      FIG. 11  is an end view partially cut away of a gas filtration plant. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    While this invention is susceptible of embodiment in many different forms, there is shown in the drawings, and will be described herein in detail, specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated. 
         [0020]    The present invention provides a gas filtration unit  100  for collection of dust from industrial applications and particulate (smoke) from coal fired boiler applications. The gas filtration unit  100  is capable of processing high gas flow rates in excess of 30,000 actual cubic feet of gas per minute. The filter units are capable of removing sufficient particulate material, smoke, dust and optionally sulfur dioxide to be discharged into the environment within the legal limits set by the Environmental Protection Agency and other federal and state laws governing such matters. 
         [0021]      FIG. 5  shows the gas filtration plant  100  having a gas inlet manifold  112 , a gas outlet manifold  114  and four gas filter assemblies  116  in fluid communication with the gas inlet and outlet manifolds  112 ,  114 . Four gas filter assemblies  116  are shown but it should be understood that a fewer or a greater number could be provided such as from two to twenty without departing from the invention. The term “plurality” used herein is meant to refer to a number greater or equal to two. 
         [0022]    Each gas filter assembly  116  has an outer wall  120  defining a vertically extending tube having a generally square or rectangular shape in horizontal cross section and a top wall  122  closing a top of the tube. It should be understood the outer wall  120  could have other cross-sectional shapes such as circular, oval, polygonal or irregular without departing from the scope of the present invention. The outer wall  120  has a plurality of support bands  124  extending about the periphery of the wall and vertically spaced from one another. The top wall has a plurality of support bands  126  extending along a top surface and lateral sides of the top wall and horizontally spaced from one another. The outer wall  120  and top wall  122  define a chamber  123  therein. The support bands  124  support the outer wall from damage, such as imploding or exploding, from severe pressure changes that occur within the chamber  123  during operation of the filter unit as compared to the ambient conditions outside the chamber  123 . 
         [0023]    The outer wall  120  has four generally triangular-shaped surfaces that taper  128  axially inwardly and downwardly to define a generally downwardly extending pyramidal-shaped bottom end section  129 . The end section terminates in an opening  130  sealed by a closure member  131 . The bottom end section  129  defines a particulate collection hopper  132  therein in fluid communication with the chamber  123 . The closure member  131  is moveable from a closed position to an open position where cumulated particulate material can be withdrawn from the hopper  132 . The filter assemblies  116  are supported and elevated by surface engaging legs  134  attached to the filter assemblies  116  to provide an area underneath the hopper  132  for personnel and equipment necessary to collect and remove the particulate from the filter units. 
         [0024]    A filter unit is positioned within the chamber  123  to remove particulate material from the gas flow. In one preferred form of the invention, the filter unit has a plurality of vertically extending, elongate filters  140  and more preferably the filters  140  are in the form of tubes tubes  141  having an inner conduit through which pressurized air flows and having a first end  142  in fluid communication with the inlet manifold  112  and the second end  144  is in fluid communication with the outlet manifold  114 . The filter tubes  141  are preferably arranged in an array having a first plurality of columns of tubes and a second plurality of rows of tubes. The first plurality and the second plurality can be equal numbers or can be different numbers and preferably the first plurality and the second plurality are within a range of from 2 to 50, more preferably 4 to 25 and most preferably 6 to 15. In a most preferred form of the invention there are fifteen rows and fifteen columns of filter tubes. 
         [0025]    The filter tubes are suspended from a horizontally extending cell plate  150  seal welded to the inner wall of the compartment  120 . The filter tubes are held in an open position by internal wire cages not shown. The filter tubes  141  are effective in removing particulate material from a particulate laden flow of gas that is delivered under pressure through the inlet manifold  112  and having a first quantity of particulate material to the first end  142  of the filter tubes, the particulate laden flow of gas flows through the tube and exits the tube through the second end with a second quantity of particulate material. The second quantity of particulate is substantially reduced from the first quantity and by an amount of 95%, more preferably 98% and most preferably 99% or greater. 
         [0026]    In a preferred form of the invention the filter material is a fabric material, and more preferably a woven or felted material. Suitable woven material includes any fibrous material and even more preferably a fibrous material containing fibers of a long-chain polysulfide containing material. One suitable type of long-chain polysulfide fiber is polyphenylene sulfide (PPS) formed by the reaction of sulfur with dichlorbenzene followed by extrusion by melt spinning to form fibers or filaments. Woven fiberglass is an example of another acceptable woven material. Suitable felted materials include polytetrafluoroethylene (TEFLON®) felted material, polyimide felt, polyester felt, acrylic felt or other suitable woven or felted material well known to those skilled in the art. 
         [0027]    During operation of the filter unit particulate material collects on the filter tubes. Excess particulate material must be removed from the tubes to maintain an acceptable gas pressure and flow rate through the tubes. Accordingly, a cleaning mechanism  153  is associated with each filter unit and the cleaning mechanism is preferably positioned proximate the second end of the filter tubes  144  and even more preferably connected to the frame  150 . (See  FIGS. 5 and 6 ) In one preferred form of the invention the cleaning mechanism includes a valve  155  for controlling the flow of pressurized air through a blow tube  157 . One valve  155  and blow tube  157  assembly will be associated with either each row or each column of the filter tube array. The valve  155  is connected to a source of pressurized air and is moveable from a closed position where no air flows into the blow tube  157  to an open position where air is supplied under pressure through the blow tube  157 . 
         [0028]    The blow tube  157  has a plurality of exit holes  158  axially spaced along a length of the tube and having one of each hole associated with either each column or row of the array. In a preferred form of the invention the blow tube  157  is tuned which means that the diameter of the holes  158  are smaller at a proximal end nearest the valve  155  and increase in diameter with increasing distance from the valve  155  to ensure that an approximate equal velocity of air is delivered from each hole regardless of its axial distance from the valve. The exit holes  158  of the blow tube  157  are positioned above the second end  144  of each of the filter tubes and when the valve  157  is opened pressurized air flows downward through the filter tubes  141  and is effective in moving the filter tubes in a manner that shakes excess particulate from the filter tubes. The particulate material falls downward into the hopper  142  where it cumulates. The cleaning mechanism can be operated in various manners including opening and closing each valve one at a time, or by opening more than one valve at a time. In a most preferred form of the invention one valve is opened and closed at a time before opening and closing a second valve and this process is repeated until all of the valves have been opened and closed and then the process starts over again. 
         [0029]    Thus, the dirty, particulate laden gas flows from the inlet manifold  112 , into the first end of the filter tubes  142 , upward through the filter tubes where particulate is removed by the filter tubes and clean air exits from the top of the filter tubes. The clean air is removed from the chamber by the outlet manifold  114  where it can be vented to the environment or used for other purposes. 
         [0030]      FIGS. 7-9  show the inlet manifold and outlet manifold  112 ,  114  extending in a first direction between two opposed lines of horizontally spaced filter units. Branches  160  from the inlet manifold extend in a second direction transverse to the first direction and individually supply a gas inlet  162  of each filter unit. Similarly, branches  164  from the outlet manifold extend in a third direction transverse to the first direction and individually remove clean gas effluent from each filter unit  116  and direct it to the outlet manifold. 
         [0031]    As shown in  FIGS. 11 and 13 , the inlet manifold  112  has opposed first and second vertically extending sidewalls  180 ,  182  and a generally horizontally extending segmented bottom wall  184 . The segmented bottom wall  184  has three segments, a bottom-most first segment  184   a , a second segment  184   b  connecting a first lateral edge of the first segment to a bottom portion of the first sidewall  180 , and a third segment  184   c  connecting a second lateral edge of the first segment  184   a  to a bottom portion of the second sidewall  182 . The second segment  184   b  forms a first acute angle  185   a  with a planar surface  186  of the first sidewall  180  and the third segment  184   c  forms a second acute angle  185   b  with a planar surface  188  of the second sidewall  182 . The first acute angle and the second acute angle can be of equal value or of different values and the magnitude of the angles do not take into account whether the angle is a positive angle or a negative angle. Each of the first acute angle and the second acute angle should be from about 15 degrees to 85 degrees and more preferably from 35 degrees to 65 degrees and most preferably 55 degrees. In a most preferred form of the invention the first acute angle  185   a  and the second acute angle  185   b  are of relatively equal magnitude. 
         [0032]      FIGS. 11 and 13  also show a closure members  200   a,b  positioned over an openings  202   a,b  in the second and third segments  184   b,c  of the bottom wall. The openings  202   a,b  define a fluid inlet into their respective filter unit. Each filter unit has a corresponding inlet and a corresponding closure member. Each closure member can be independently operated so that one filter unit can be removed from service at a time unlike prior art systems, such as shown in  FIGS. 3 and 4  which requires that an entire series of filter units associated with a single inlet manifold be taken out of operation simultaneously. The present invention provides an independently operable closure member for each filter unit, and, therefore, filter units can be taken out of service one at a time and independently of one another. 
         [0033]    The closure members  200   a,b  are capable of being moved from an opened position ( FIG. 13  shows closure member  202   a  open and  202   b  closed) where dirty gas can flow into the filter unit and up through the filter tubes and to a closed position where the closure members  200   a,b  block the flow of dirty air into their respective filter units. The closure member must be capable of blocking the flow of pressurized air when in a closed position and allowing the flow of air in an open position and in one form of the invention the closure member is a louvered-type closure member having numerous generally rectangular shaped, and spaced slats that when in the closed position the lateral edges of each slat are in contact with a lateral edge of an adjacent slat to form a air tight, generally flat outer surface. To move the closure member to an open position the slats are rotated about their axes to form open channels between adjacent slats to allow dirty air to flow through the closure member and into the filter units. The closure member can take on other forms such as a hinged door or can be a valve such as a butterfly valve, a gate valve, a sliding gate valve, rotating plate valve, check valve or similar valve. 
         [0034]    When the closure member  200   a  is in a closed position as shown in  FIG. 11  to allow for servicing of a filter unit, an outlet closure valve  210  is also moved to a closed position to stop the flow of air from the top of the filter tubes into the outlet manifold to equalize the pressure across the filter tubes. The outlet closure valve  210  is, in a preferred form of the invention, a poppet valve. However, other valves could be used without departing from the scope of the present invention. As shown in  FIG. 13  when the second closure member  202   b  is in the closed position particulate material  250  ( FIG. 13 ) that drops from the dirty air cumulates on the bottom wall. Since the closure member is placed on the third segment of the bottom wall the cumulating particulate material is directed toward the opposed open closure member  200   a , and, therefore, the cumulating particulate material is not allowed to place an undue burden on the closure member  200   b  which can lead to premature failure of the closure member  200   b  which in turn can require repair of the closure member. 
         [0035]    When the closure member  200   b  is in the open position as shown in  FIG. 11 , dirty air is allowed to flow downwardly in the direction of the arrow  201  into the hopper and then upwardly through the filter tubes. The dirty air flow is required to change directions thereby substantially decreasing the flow rate of particulate when compared to the flow rate through the inlet manifold. The flow rate of dirty gas entering the filter tubes is reduced from is flow rate of from around 3200-3600 ft/min rate through the inlet manifold to about 500 ft/min or less rate as the dirty gas flow enters the hopper. Consequently, much of the particulate material that is entrained in the dirty gas flow drops out and cumulates in the hopper instead of traveling up through the filter tubes. Thus, the filter tubes can be kept in operation over a longer period of time, and the filter tubes do not have to be cleaned as frequently as they would have to be if the dirty gas flow rate was not reduced. 
         [0036]      FIGS. 10 ,  12  and  13  show a filter plant  100  of the present invention with a configuration of filter units similar to the low particle design of  FIG. 1  but having an optional circulating fluid bed scrubber (CFB)  220  which is used to reduce the quantity of sulfur dioxide contained in the dirty gas flow. Otherwise, like numerals will be used to refer to like parts of  FIG. 1 . The CFB has an inlet  222  for receiving the dirty gas flow and a venturi section  224  for increasing the velocity of the dirty gas flow to keep the particulate material entrained in the dirty gas flow. Upstream of the venturi section  224  the dirty gas enters a chamber where it is subjected to a pressurized stream of hydrated lime, pressurized water spray, re-circulated ash and lime from the hoppers provided through a recirculation line  230  that is in fluid contact with each of the hoppers. The lime or calcium hydroxide reacts with sulfur dioxide to form calcium sulfite and calcium sulfate. The pressurized water spray drives this reaction forward by cooling the gas through evaporation of the water. Due to the use of particulate material such as ash and lime, the dirty gas experiences a substantial increase in the quantity of particulate material entrained in the dirty gas flow. The quantity of particulate material can reach as high as 500 grains mass/ft 3 . Accordingly, the reduction in the dirty gas flow rate to cause the substantial particulate drop out into the hopper discussed above is significant and important particularly when using the optional CFB. 
         [0037]    From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims