Abstract:
Horizontal, negative pressure centrifugal separator apparatus ( 48, 248, 348, 448, 548 ) is provided for separating particulate material from an air stream that exhausts from the outlet of a horizontal, industrial size, rotary drum dryer ( 32 ). The centrifugal separator is especially adapted to be connected to the negative pressure inlet of a primary fan ( 42 ) which pulls large volumes of air through the rotary drum dryer. The separator apparatus includes wall structure which defines two aligned primary spiral separation plenum chambers (e.g.  78, 80 ) joined to an intermediate spiral discharge plenum chamber (e.g.  82 ), all of which intercommunicate. A pair of oppositely facing plenum chamber divider members each having a central aperture therein are mounted in the plenum chambers on opposite sides of the discharge plenum chamber and function as pressure regain stacks. Air streams containing particulate materials which are introduced into the air inlets of the primary separation plenum chambers each follow a serpentine path in a respective primary chamber before flowing through a corresponding plenum chamber divider member spiral velocity regain stack into the spiral chamber of the discharge plenum chamber. Discharge openings are provided in the primary spiral plenum chambers in positions permitting particulate material separated from the air stream as a result of centrifugal force thereon, to gravitate to a collection point therebelow. The centrifugal separator apparatus will handle an approximately 40% greater air flow than a comparable, conventional cylindrical stack member with essentially the same pressure drop.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to centrifugal separator apparatus for separating particulate material from an air stream, and especially to high efficiency, horizontal, twin-flow, two stage separator apparatus with minimum air pressure drop. The centrifugal separator apparatus is particularly useful for removing particulates from the gaseous discharge from drying equipment such as large capacity, multi-stage, horizontal rotary dryers before return of the dryer exhaust gases to the atmosphere.  
           [0003]    2. Description of the Prior Art  
           [0004]    It has long been the practice to remove the moisture from various agricultural, industrial and by-product materials by passing the moist material through a rotary drum dryer, either of the multiple stage, multiple pass or multiple stage single pass type. Burner gases at an elevated temperature are directed through the dryer to vaporize a substantial part of the product water content and to also serve as a conveying medium for the product along the length of the dryer. Often times, a certain proportion of the dried material is recycled back to the drum dryer in order to decrease the overall moisture content of the product input to the dryer, thus enhancing the dryer&#39;s efficiency.  
           [0005]    The gaseous discharge from the rotary dryer must be treated before being returned to the atmosphere in order to lower the amount of particulates entrained in the air stream to meet regulatory standards. In recent years, governmental agencies have imposed increasingly stringent regulations on the amount of particulates that may be discharged into the surrounding atmosphere from large scale drying equipment. Particulate removal has been accomplished for the most part by directing the particulate bearing exhaust gases from large scale, industrial sized rotary dryers into one or more upright cyclones. Although cyclones are functionally capable of substantially reducing the particulate content of a gas stream containing entrained particulate materials before return of the gas stream to the atmosphere, upright cyclones of requisite efficiency are relatively expensive, require a significant footprint area in the vicinity of the horizontal dryer, and work most effectively when two substantially identical cyclones are employed in side-by-side serial air flow relationship.  
           [0006]    An exemplary dryer and associated cyclone separator is shown and described in my U.S. Pat. No. 4,193,208 of Mar. 18, 1980. As illustrated in FIG. 1 of the ′849 patent, a burner assembly is provided that burns natural gas or a similar fuel feed stock to produce hot products of combustion which are directed into the inlet end of an elongated, generally horizontal, hollow drum heat exchanger rotatable about its longitudinal axis. The negative pressure inlet of a centrifugal discharge and fan unit is connected to the outlet end of the drum dryer for inducing flow of relatively high volumes of air through the dryer in association with the hot products of combustion from the burner assembly. The positive pressure outlet end of the fan unit is connected to the inlet of an upright cyclone collector which discharges the substantially particulate-free air back into the atmosphere.  
           [0007]    A conveyor at the discharge end of the dryer receives dried product and directs that product to a point of use or for further drying. Similarly, product removed from the air stream directed into the cyclone gravitates from the lower end of the cyclone vessel and may, if desired, be combined with the product output from the dryer.  
           [0008]    Another exemplary horizontal rotary dryer, fan unit and cyclone separator is described and shown in my U.S. Pat. No. 5,157,849 issued Oct. 27, 1992.  
         SUMMARY OF THE INVENTION  
         [0009]    This invention concerns a horizontal, negative pressure centrifugal separator for removing particulate material from an air stream that exhausts from the outlet end of a horizontal industrial size, rotary dryer. The centrifugal separator is adapted to be connected to the negative pressure inlet of a fan assembly which functions to pull large volumes of air through the dryer drum.  
           [0010]    The centrifugal separator preferably comprises an essentially horizontal drum having wall structure presenting two side-by-side primary material separation plenum chambers of generally spiral configuration. The primary plenum chambers mutually communicate with a central plenum chamber therebetween which is also of spiral configuration.  
           [0011]    In one form of the centrifugal separator, frusto-conical, opened-ended, pressure regain divider stacks are positioned between each of the separation plenum chambers and the central plenum chamber. In this embodiment of the centrifugal separator, each of the separation plenum chambers has an air inlet and the central plenum has an air discharge outlet. The divider stacks each have a generally conical section which is joined to an annular stack component presenting a central aperture. The divider stacks extend into the central plenum chamber with the apertures thereof in horizontal, generally axially aligned, facing relationship.  
           [0012]    Air containing entrained particulate material entering the air inlets of the separation plenum chambers follows a generally serpentine path within respective separation plenum chambers and then exits the plenum chambers into the central plenum chamber via the apertures in corresponding divider stacks. The conical configuration of the divider stacks, along with the annular stack component coaxial with the axis of a respective stack, which causes each of the stacks to have pressure regain properties, serves to minimize the pressure drop in the air flow therefore preventing significant air pressure loss during operation of the separator. The air flow through the centrifugal separator of this invention is approximately 40% greater with substantially equal pressure drop as compared with conventional cylindrical stack separators.  
           [0013]    Material removal plenums of generally spiral configuration are also provided at opposite ends of the separator drum and communicate with corresponding separation plenum chambers. Each of the material removal plenums is provided with a material discharge opening, preferably located at the lower portion of a respective material removal plenum. The centrifugal force exerted on the air streams during flow along respective spiral paths causes particulate material in the air streams to migrate toward the spiral inner surface of the separation plenum chambers. Particulate materials separated from the two air streams directed simultaneously into the separation plenum chambers collects in the outer material removal plenums and eventually is discharged from the outer material removal plenums through the material discharge openings in lower portions of respective material removal plenums.  
           [0014]    In another form of the separator, the central spiral plenum chamber has either one or two air inlets while the spiral separation plenum chambers on opposite sides thereof each have an air discharge outlet. In this form of the separator, the divider stacks are oriented such that they extend away from each other and into corresponding separation plenums. An air stream containing particulate material that must be removed from the air before discharge of the air back into the atmosphere is directed into the air inlet of the central plenum chamber, commences flow in a generally spiral direction within the central plenum chamber, passes through the central aperture in respective divider stacks, flows along spiral paths within the separator plenums, and is discharged through the air outlet openings of the two separation plenum chambers. In this embodiment, particulate material displaced from the air streams by centrifugal force is received in the spiral material removal plenums and gravitates therefrom through the discharge openings of the material removal plenums.  
           [0015]    The horizontal separator having side-by-side, simultaneously operable separation plenums which communicate with a central plenum provide a separator which is substantially as effective in removing particulate material from an air stream as a conventional upright cyclone, without occupying as much space as that cyclone and at an advantageous capital cost. In addition, the horizontal disposition of the separator permits air having particulate material entrained therein to be introduced into the separator at any one of a number of different circumferential locations, and to allow for discharge of cleaned air at any point around the circumference of the separator drum. This permits the separator to be connected between the outlet of the dryer and the primary fan at an optimal position, with a minimum overall footprint.  
           [0016]    A horizontal separator in accordance with this invention, having side-by-side dual stage separator plenums with associated pressure regain stacks is capable of removing as much as 96% or more of particulate material in a stream of products of combustion and air discharged from a horizontal industrial size product dryer. Thus, by positioning the separator between the primary fan and the dryer, and connecting the fan to one or more conventional cyclones, the level of particulates ultimately discharged into the atmosphere may be maintained at a very low level and one that meets regulatory standards therefor. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is an overall elevational view of material drying equipment incorporating horizontal, dual stage separator apparatus in accordance with this invention;  
         [0018]    [0018]FIG. 2 is a perspective view of an embodiment of a separator apparatus having dual air inlets and a single air outlet;  
         [0019]    [0019]FIG. 3 is an exploded view of the separator apparatus as shown in FIG. 2;  
         [0020]    [0020]FIG. 4 is a front elevational view of the separator apparatus of FIG. 2;  
         [0021]    [0021]FIG. 5 is a horizontal sectional view taken substantially along the line  5 - 5  of FIG. 4 and looking downwardly in the direction of the arrows;  
         [0022]    [0022]FIGS. 6, 7 and  8  are vertical cross-sectional views taken along the lines  6 - 6 ,  7 - 7  and  8 - 8 , respectively, of FIG. 4 and looking in the direction of the arrows in FIG. 4;  
         [0023]    [0023]FIG. 9 is a schematic front elevational view of a second embodiment of the separator apparatus of this invention having dual air inlets and a single air outlet;  
         [0024]    [0024]FIG. 10 is a schematic end elevational view of the separator apparatus as shown in FIG. 9;  
         [0025]    [0025]FIG. 11 is a perspective view of one of the two spaced, open-ended, frusto-conical pressure regain divider members housed within the separator apparatus as shown schematically in FIG. 9;  
         [0026]    [0026]FIG. 12 is a schematic front elevational view of a third embodiment of the separator apparatus of this invention having dual air inlets and dual air outlets of essentially equal area;  
         [0027]    [0027]FIG. 13 is a vertical cross-sectional view taken along the line  13 - 13  of FIG. 12 and looking in the direction of arrows;  
         [0028]    [0028]FIG. 14 is a schematic front elevational view of a fourth embodiment of the separator apparatus of the invention having dual air inlets and dual air outlets in which each of the outlets is of a different areas;  
         [0029]    [0029]FIG. 15 is a schematic end elevational view of the separator apparatus as shown in FIG. 14;  
         [0030]    [0030]FIG. 16 is a schematic fragmentary plan view of the dryer equipment illustrating separator apparatus having a single central air inlet and dual air outlets outboard thereof, with the separator apparatus being shown in an operative position with the air outlets leading to primary fans connected to respective dual vessel cyclone separators;  
         [0031]    [0031]FIG. 17 is a schematic fragmentary side elevational view of the dryer equipment ad depicted in FIG. 16;  
         [0032]    [0032]FIG. 18 is a schematic plan view of the separator apparatus as shown in FIG. 17 having a single central air inlet and dual air outlets with single sloped conical pressure regain divider member;  
         [0033]    [0033]FIG. 19 is a schematic end elevational view of the separator apparatus as shown in FIG. 18; and  
         [0034]    [0034]FIG. 20 is a perspective view of one of the two spaced, open-ended, frusto-conical pressure regain divider members housed within the separator apparatus as shown schematically in FIG. 18. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0035]    The material drying equipment  30  illustrated in FIG. 1 incorporates improved horizontal, dual stage, negative pressure separator apparatus in accordance with this invention. Equipment  30  includes a rotary drum dryer  32  adapted to receive and dry a particulate material, such as distillers grain by-products, alfalfa, wood by-products, poultry by-products, fish by-products, and other agricultural and industrial particulate materials having a relatively high water content requiring drying to decrease the moisture levels thereof.  
         [0036]    A furnace  34  and blending chamber  36  are provided at the inlet end of the rotary drum dryer  32 , while a rotary cooling drum  38  is located at the outlet end of the drum for receiving and cooling dried material. The equipment  30  further includes an air-handling unit  40 , including a primary fan  42 , upright recycle cyclone separator  44 , upright discharge cyclone separator  46 , horizontal, dual inlet, single outlet, dual stage centrifugal separator apparatus  48  in accordance with one embodiment of this invention, and ducting  50  interconnecting the cyclone separators  44 ,  46  and fan  42 . An optional return air conduit  52  extending from the top of upright recycle cyclone separator  44  to the inlet of furnace  34  has an intermediate blending air conduit  54  leading to chamber  36 . A pair of tandem-mounted material recycle screw conveyors  56 ,  58  which receive particulate material output from the lower ends of cyclone separators  44 ,  46  extend along the length of drum  32  from the outlet end thereof to a horizontal material input conveyor  60  at the inlet end of the dryer  32 . Similarly, a dried material screw conveyor  62  extends from the outlet end of the dryer  32  to rotary cooling drum  38 . The furnace  34  is equipped with a gas-fired burner  64  as well as a gas recycle conduit  66  connected between burner  64  and blending chamber  36 . Alternatively, a boiler gas recycle duct  68  maybe provided for directing waste heat gases to the blending chamber  36 . Air discharge from the equipment  30  is accomplished via discharge duct  70  projecting from the upper end of cyclone separator  46 .  
         [0037]    During use of the equipment  30 , the dryer  32  is rotated (typically at a speed of from about 3-12 rpm) by means of drum drive unit  72  associated with tracks trunnion drum support  74 . A track and trunnion drum support  76  rotatably carries the opposite end of the dryer drum  32 . Heated air is delivered to the input end of the drum by means of furnace  34 , blending chamber  36  and air handling unit  40 . A new charge of moist particulate material to be dried is introduced into the return conveyer  56 . In addition, a predetermined proportion of partially dried material is returned by conveyors  56 ,  58  from the outlet end of the dryer back to conveyor  56  for recycling through the dryer. The air-handling unit  40  serves to move air throughout the equipment  30 , with exhaust gases being returned to the atmosphere through duct  70 . Similarly, particulate material collected in the separators  44 ,  46  is directed into conveyors  56 ,  58 , respectively, for return to the input conveyor  60 .  
         [0038]    The drum dryer  32  preferably comprises a dryer of the type that is illustrated and described in my co-pending application Ser. No. 09/858,013, filed May 11, 2001, which is fully incorporated herein by specific reference thereto.  
         [0039]    The drum separator apparatus  48  as shown in FIG. 1 is illustrated in detail in FIGS.  2 - 8  inclusive. Referring to FIG. 2, the separator apparatus  48  includes two primary spiral separation plenum chambers  78 ,  80  joined to an intermediate spiral discharge plenum chamber  82 . As best shown in exploded view of FIG. 3, each of the plenum chambers  78 ,  80  has wall structure presenting a straight inlet duct portion  84  of square or rectangular cross-section and integral with a curvilinear scroll portion  86  that is tangential to a respective duct portion  84 . Each of the scroll portions  86  has a circular wall segment  88  connected to opposed upright wall sections  90 ,  92  which progressively decrease in width around the perimeter of a respective scroll portion  86 . The wall sections  90 ,  92  thereby each define arcuate openings  94 ,  96 . The inlet duct portions  84  each have a square or rectangular inlet opening  98  (FIG. 7). It is therefore to be seen from the cross-sectional views of FIGS.  6 - 8  that the curvilinear inner surface  100  of wall segment  88  of each of the plenum chambers  78 ,  80  causes the initially straight air stream designated by the arrows  102  containing entrained particulate materials which enters inlets  98  of inlet duct portions  84  of plenum chambers  78 ,  80  to follow a spiral path designated by the arrows  104  within each of the plenum chambers  78 ,  80 .  
         [0040]    The air discharge plenum chamber  82  has a straight, air discharge duct portion  106  which is square or rectangular in cross-section. Chamber  82  has a curvilinear scroll portion  108  that is tangential to duct portion  106 . Scroll portion  108  has a circular wall segment  110  connected to opposed upright wall sections  112 ,  114  which progressively decrease in width around the perimeter of the scroll portion  108 . Wall sections  112 ,  114  thus define arcuate openings  114 ,  116 . Discharge duct portion  106  has a square or rectangular discharge opening  118  (FIG. 8). It is to be understood that openings  94 ,  96  of plenum chamber  78 , the openings  114 ,  116  of plenum chamber  82  and the openings  94 ,  96  of plenum chamber  80  are all of equal diameter and that chambers  78 ,  82  and  80  are in side-by-side interconnected relationship as shown in FIGS. 2 and 4. It is noteworthy in this respect though that the wall segment  110  of scroll portion  108  of discharge plenum chamber  82  is of arcuate configuration defining part of a circle that has a diameter less than the diameter of the curvilinear, partial circle defining wall segments  88  of plenum chamber  78 ,  80 .  
         [0041]    Vertically oriented, drum chamber divider members  122 ,  124  are provided within each of the plenum chambers  78 ,  80  on opposite sides of the discharge plenum chamber  82 . Viewing FIGS. 3 and 5, each of the drum divider members  122 ,  124  comprises a frusto-conical open-ended pressure regain stack facing in opposite directions. Thus, each velocity recovery stack member  122 ,  124  has flared conical segment  126  integrally joined to a cylindrical segment  128 . The pressure regain stack member  122  is housed within plenum chamber  78  while pressure regain stack member  124  is housed within plenum chamber  80 . From FIG. 5, it can further be seen that the cylindrical segments  128 ,  138  of each of the pressure regain stack members  122 ,  124  is of lesser diameter than the inner surfaces  100  of plenum chamber  78 ,  80  so that a space  134  is presented between each of the members  122 ,  124 , and surfaces  100 . The outermost circular edge  130  of the velocity recovery stack member  122  is joined to scroll portion  86  of plenum chamber  78  within opening  96  thereof and to scroll portion  108  of plenum chamber  82  within opening  114 . Similarly, the outermost circular edge  132  of the velocity recovery stack member  124  is joined to scroll portion  86  of plenum chamber  80  within opening  94  thereof and to scroll portion  108  of plenum chamber  82  within opening  116 . Divider members  122 ,  124 , which project away from the discharge plenum chamber  82  in opposite direction, define apertures  136 ,  138  respectively that are of the same diameter and are axially aligned horizontally of the drum structure.  
         [0042]    Spiral path defining particulate material air discharge plenum chambers  140 ,  142  are provided outboard of plenum chambers  78 ,  80 , respectively. Each of the plenum chambers  140 ,  142  has a closed end cylindrical housing section  144  as well as a particulate material delivery duct  146  depending therefrom for removal of collected product from chambers  140 ,  142  which communicate directly with respective plenum chambers  78 ,  80 . It can be seen from FIG. 6, for example, that each of the ducts  146  has an inclined wall  148  which is tangential with a respective outer cylindrical wall  150  of each of the plenum chambers  140 ,  142 . In the normal operating orientation of separator apparatus  48 , the air inlet ducts  84  are upright at an angle of about 0° (18°) while the discharge ducts are horizontally offset from the inlet duct portions  84  of plenum chamber  78 ,  80  as shown in FIGS.  5 - 8 . In this manner, the foot print of separator apparatus  48  is minimized in that a particulate bearing air stream may be directed vertically into the plenum chambers  78 ,  80  while a cross conveyor  152  (FIG. 1) may be positioned in underlying relationship to the material delivery ducts  146  of plenum chambers  140 ,  142  and air lock  153  (FIG. 1) allows material discharge from negative pressure separator apparatus  48 .  
         [0043]    Separator apparatus  48  is especially adapted to be utilized in drying equipment as depicted for example in FIG. 1. The inlet ducts  84  of plenum chambers  78 ,  80  are both connected to a common gravity separator duct  154 . The discharge duct  106  of discharge plenum chamber  82  is joined to a duct  156  connected to the negative pressure side of the primary fan  42 . The outlet duct  158  from fan  42  leads to the cyclone separators  44 ,  46 . The combination air and dried particulate material output from dryer  32  is directed into gravity separator  154 . The heavy particles in the air stream gravitate downwardly in the separator and are collected in the cross conveyor  160  for delivery to the cooling drum  38 .  
         [0044]    The air stream pulled upwardly in separator  154  by the negative pressure of fan  42  contains particulate material fines. The particulate material bearing air stream entering separator apparatus  48  via twin inlet ducts  84  follows respective serpentine path of travel as indicated by the arrows of FIGS. 5 and 7. The separate air streams also flow around the circumference of cylindrical segment  128  of each of the dividers  122 ,  124 . The spiral path of the particulate bearing air streams flowing around corresponding drum dividers  122 ,  124  causes the particles to be separated from the air stream by centrifugal action. The separated particles which tend to collect on the inner surface  100  of each of the wall segments  88  of plenum chambers  78  and  80  gravitate toward the discharge ducts  146  of discharge plenum chambers  140 ,  142  for delivery into the cross conveyor  152  and air lock  153  that connects to duct work  162  also leading to conveyor  62  feeding the cooling drum  38 .  
         [0045]    The air flowing around the divider members  122 ,  124  within plenum chambers  78 ,  80  enters the apertures  136 ,  138  of members  122 ,  124  and passes into the discharge plenum chamber  82 . The divider members  122 ,  124  function as pressure regain stacks so that the air passing out of separator apparatus  48  through discharge duct portion  106  of discharge plenum chamber  82  regains a substantial fraction of the pressure loss that would otherwise occur in the air entering twin inlet ducts  84  of plenum chambers  78 ,  80 . Pressure regain is accomplished by acceleration of the air streams to the radius of the outlets of stacks  136 ,  138 .  
         [0046]    A second embodiment of the separator apparatus and which is designated  248  is illustrated in FIGS.  9 - 11 . Separator apparatus  248  also has dual air inlets and a single air outlet but in this instance the outlet is in the upper part of the separator drum, and the pressure regain divider members within the separator are of a different configuration than drum divider members  122 ,  124  of separator apparatus  38 . The spiral defining inlet plenum chambers  278 ,  280 , of separator apparatus  248  are of construction similar to plenum chambers  78 ,  80  and discharge plenum chambers  240 ,  242  are similar to discharge plenum chambers  140 ,  142 . The discharge plenum chamber  282  differs from plenum chamber  82  of separator apparatus  248  in the disposition of the air stream discharge duct portion  250 . It is to be seen though that the inlet duct portions  284  of plenum chambers  278 ,  280  defining separate inlets  286  duct portion  250  defining outlet  288  are at 90° angles with respect to duct portion  250  and thereby outlet  288 . Thus, separator apparatus  248  is adapted to be connected to gravity separator  154  and a primary fan such as fan  42  in a manner similar to the connection of separator apparatus  48  to these components. Utilization of separator apparatus  248  instead of separator apparatus  48  will thus be dictated by the elevation of the duct  156  of a particular drying equipment installation.  
         [0047]    The open ended pressure regain divider stacks or members  222 ,  224  utilized in separator apparatus  248  differ from divider members  114 ,  116  in that the members  222 ,  224  are of overall general conical configuration having a frusto-conical inner segment  226  joined to a smaller diameter frusto-conical segment  228 . Viewing FIG. 9, it is to be observed that the pressure regain divider members  222 ,  224  are positioned within respective plenum chambers  278 ,  280 , are aligned horizontally and located with the smaller ends thereof facing away from one another. Removal of particulate material from the air stream is accomplished in separator apparatus  248  with an even greater fraction of the consequent pressure loss being regained as described with respect to separator apparatus  48 , with particulate material being discharged from separator apparatus  248  via discharge duct  290  having an outlet  292 .  
         [0048]    The third embodiment of the separator apparatus as shown in FIGS. 12 and 13 and broadly designated  348  is of the same construction as separator apparatus  248  but in this instance has dual air inlets  384 ,  386  leading to plenum chambers  378 ,  380  respectively. The dual air stream outlets  306 ,  308 , are each of the same cross sectional area. Open ended velocity recovery divider members  322 ,  324  within plenum chambers  378 ,  380  are of the same construction and orientation as divider members  122 ,  124  of separator apparatus  48 . Separator apparatus  348  also has discharge plenum chambers  340 ,  342  outboard of plenum chambers  378 ,  380  for removal of particulate material separated from the air streams entering separator apparatus  348  through dual air inlets  384 ,  386 . The dual air outlets  306 ,  308  of apparatus  348  are oriented at an angle of 90° and 270° with respect to dual air inlets  384 ,  386 .  
         [0049]    [0049]FIG. 14 illustrates a fourth embodiment of the separator apparatus and which is designated  448  has dual rectangular air inlets  484 ,  486  of substantially equal cross sectional area, as well as dual air outlets  406 ,  408 . In this embodiment, outlet  406  is of approximately twice the cross sectional area of air outlet  408 . The pressure regain divider members  422 ,  424  within plenum chambers  478 ,  480  are of the same construction as open ended, generally conical pressure regain divider members  222 ,  224  of separator apparatus  248 . It is to be seen from FIG. 15 that the air outlets  406 ,  408  discharge horizontally in opposite, generally parallel directions.  
         [0050]    A fifth embodiment of the separator apparatus and which is designated  548  in FIGS. 16 and 17 has a single central air inlet  584  and dual outboard discharge air outlets  506 ,  508 . Outlet  506  is connected to the negative pressure side of a first primary fan  542  by duct work  550  while discharge opening  508  is connected to the negative pressure side of a second primary fan  544  by duct work  552 . The pressure regain divider members  522 ,  524  are of the same construction as divider members  222 ,  224 . Thus, separator apparatus  548  is especially adapted for use in drying equipment having dual cyclone separator units  554 ,  556 . Duct  558  returns stack gas from cyclone separator unit  556  to the rotary drum dryer  560  while stack  562  connected to cyclone separator units  554  discharges to the atmosphere.  
         [0051]    The sixth embodiment of the separator apparatus and which is designated  648  in FIGS. 19 and 20 has a single central air inlet and dual air outlets. The single central plenum separation chamber  278  extending across a majority of the width of the separator apparatus  648  has wall structure  280  presenting a substantial spiral defining wall surface as illustrated in FIG. 19 connected to inlet duct  684  presenting an inlet opening  686  which extends the full horizontal width of chamber  278 . Discharge plenum chambers  688 ,  690  are provided on opposite sides of central plenum chamber  678  and are in direct communication with the latter. Each of the discharge plenum chambers  688 ,  690  has a discharge duct portion  692  presenting an outlet opening  694 . Particulate material collected in separator apparatus  648  is discharged from plenum chamber  678  through discharge duct  696  extending substantially the full width of plenum chamber  678  and presenting a downwardly directed discharge opening  698 . It can be seen from FIG. 19, that air inlet opening  686  and air outlet opening  694  are located at substantially 90° angles with respect to one another. The facing, inwardly directed, directly opposed, open ended, frusto-conical, pressure regain divider stack members  622 ,  624  located within plenum chamber  678  are in horizontal axial alignment. The divider member  622  of FIG. 20, which is illustrative of both of the divider members  622 ,  624 , has a main open ended conical body  626  and an annular reinforcement flange  628  on the smallest diameter opening of the cone  626 .  
         [0052]    The horizontally oriented, dual separation chamber apparatus of this invention is advantageous not only from the standpoint of a minimum foot print, but also provides an efficient transition with an economy of duct work from the discharge of the horizontal drum dryer to the primary fan or fans leading to cyclone separator units. In addition, the dual separation chamber apparatus readily accommodates a gravity separator directly connected to the output of the drum dryer and which feeds material into a conveyor coupled to a typical rotary cooler. The separators of FIGS. 9, 14 and  18  will allow approximately 20% to 25% greater flow than the separators of FIGS. 5 and 12.  
         [0053]    When the dual separation chamber apparatus of this invention is properly sized in relationship to the design cubic feet per minute air flow through the horizontal drum dryer of drying equipment as shown in the drawings, and is located between a gravity separator such as separator  154  and the negative pressure side of a primary fan, at least about 96% of the fines in the air outflow from the gravity separator  154  may be removed from the air stream. In view of the fact that cyclone separator units such as units  44 ,  46  can be at least 97% efficient, the level of particulates discharged into the atmosphere from the drying equipment may be maintained very low. The apertures in the pressure regain stack divider units are sized to minimize the air pressure drop through the dual chamber separator apparatus of this invention. Decreasing the diameter of the divider units increases the separating efficiency of the apparatus, which must be then balanced against the pressure drop. Use of conical divider members which function as pressure regain stacks permits recovery of a significant part of the air pressure that would otherwise be lost.  
         [0054]    Horizontal dual separation chamber apparatus  48  ( 248 ,  348 ,  448 ,  548 ,  648 ) that typically may be for example  11 ′ in diameter and only  19 ′ long can handle the same air flow as two conventional vertical cyclone separators each of which is  11 ′ in diameter and  45 ′ high.  
         [0055]    In a typical drying equipment installation of the type illustrated in FIG. 1, assuming 50 tons per hour of dried particulate material is introduced into the gravity separator  154  from drum dryer  32 , 96% or 48 tons per hour of particulate material typically gravitates to the lower end of separator  154  for collection in horizontal cross conveyor  160  and delivery into the rotary cooler  38 . Two tons per hour of particulate fines are therefor contained in the air stream(s) entering the separator apparatus  48  ( 248 ,  348 ,  448 ,  548 ,  648 ). Ninety-six percent (96%) of the fines are removed from the air stream in the horizontal dual chamber separator apparatus, resulting in only 0.8 tons per hour of particulates being directed to the inlet of the primary fan(s). When 97% efficient vertical cyclone separator units are used, only 4.8 pounds per hour of particulates are introduced into the atmosphere though the exhaust stack  70 . If 99% efficient vertical cyclone separators that are presently commercially available are employed, then the discharge emissions to the atmosphere are no more than about 1.6 pounds per hour.