Abstract:
An apparatus for rotary dumping of rail cars, including a backside airflow diverter, a backside hood for removing contaminated air from the back side of the pit and at least two baffles on a rotational frame, the baffles each presenting a leading edge that contacts the backside airflow diverter during at least a portion of rotational motion. At least one air intake is positioned to pass through the upper surface of the backside diverter into the backside hood at a location where pressure in the backside hood is maintained at a substantially neutral or negative level even when pressure in the material receiving pit is increased by a down rush of air caused by the exit of the load from the railcar.

Description:
RELATED APPLICATION 
     This application is a continuation of application Ser. No. 12/332,826 filed Dec. 11, 2008, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to rotary-dumping of material from rail cars, and more particularly, to a method and apparatus for controlling environmental contamination produced by rotary-dumping material from rail cars. 
     BACKGROUND OF THE INVENTION 
     Rail cars have been used for many years to efficiently haul large quantities of bulk materials over land. Items commonly shipped include grain, iron ore and coal. Shipping such items via rail car is very efficient due to the ability to transport extremely large loads of these materials in one shipment. For example, one single rail car may hold up to 110 tons of coal and an entire train made up of such cars may be over 130 cars in length, extending 6000 feet in total length. 
     Once at the destination, it is necessary to unload the cargo. For bulk material such as grain, ore, or coal, bottom-dumping and rotary-dumping are commonly used. Bottom-dumping involves staging a particular car over a receiving pit and opening hatches located in the bottom of the car. The cargo exits the car though the bottom hatches or doors and proceeds into the pit below. U.S. Pat. No. 5,302,071, assigned to Svedala Industries, Inc., discloses one example of a bottom-dumping rail car. 
     Bottom-dumping requires the use of rail cars that are specifically designed for bottom-dumping. This is due to the need to direct the car contents to a centrally located chute on the bottom of the car. The sides of the car must be at least partially sloped to urge the contents towards the chute, or else there would be a partial retention of the material being carried. This configuration decreases the ratio of the car&#39;s size vs. cargo capacity. Additionally, the bottom-dump configured rail cars are not easily interchangeable with standard cars at a dumpsite because the dump apparatus for standard cars must be uniquely configured to accommodate bottom-dump cars. The bottom-dump rail cars are also environmentally disadvantageous, as will be described more fully below. 
     Rotary-dumping is the other commonly used method of unloading a rail car. In rotary-dumping, a standard rectangular rail car is staged or indexed in a rotary-dump apparatus. The apparatus then rotates approximately one-half turn, thereby dumping the contents of the car into a receiving pit. Typically, the cars of the train remain connected during the dumping process through the use of rotary couplings between each car. Such couplings permit the cars to be rotated while still connected though an axis center at the coupling. U.S. Pat. Nos. 4,479,749 and 4,609,321, both assigned to Dravo Corporation, disclose conventional rotary-dump apparatuses. In some applications, such as the dumping of coal at major power plants, cars may be rotated and emptied at the rate of one car every four minutes. 
     Environmental pollution is an important concern to the design of a material dumping facility. When the car&#39;s load is dumped, a large quantity of material exits the car in a very short time. The turbulence generated by the quick unloading causes fine dust particles to billow up from the receiving pit and pollute the air surrounding the dump facility. The resulting dust, such as from grain or coal, is very explosive when in sufficient density. It is also an environmental pollutant. Therefore, there is a need to provide an apparatus and method for minimizing the polluting effect of dust. 
     Bottom-dump apparatuses have two critical drawbacks. First, they require special cars equipped with the bottom chutes as discussed previously. Second, the dust cloud produced by bottom-dumping is recognized by those skilled in the art to be larger, more aggressive and less controllable than the cloud produced by the rotary-dump method. 
     Rotary-dump systems control the dust cloud by using fans with large motors to exhaust the dust-filled air surrounding the car though conduits and into filtering devices. This process requires a very high flow of air and correspondingly very large motors to drive such high capacity system. These motors are commonly several hundred horsepower. Multiple motors of this size may be required at any given installation. 
     The dust cloud is typically large enough and aggressive enough to overpower any reasonably sized removal system. Therefore, the airflow around the car and in the pit is controllably designed to keep the dust cloud suppressed long enough to allow the dust collection system to suck the dust from the surrounding area. The better the airflow is managed, the less horsepower is needed to drive the system. This results in greatly improved efficiency. 
     Prior art patents disclose a method of enclosing a rail car within a fixed enclosure. This design has several drawbacks. First, it restricts the operator&#39;s ability to observe the load as it is being dumped to ensure that the system does not malfunction and that no impurities or foreign objects are introduced into the pit. Next, the fixed enclosure requires multiple large motors to drive the plurality of air handling units. The filtering portions of the air handling units are within the dumping facility, which makes cleaning and maintenance more difficult. Finally the efficiency of the system is low due to the large motors required to produce sufficient air removal capacity because the control of the airflow around the car does not have good dust cloud retention time. 
     There are two different types of rotary car dumpers in common use. Those skilled in the art refer to the two types of dumpers as rings out dumpers and rings in dumpers. The rings referred to are the structural ends of a car dumper which support the entire car dumper barrel and the railcar itself Depending upon the design of a rotary car dumper it may have the rings located at the far ends of the dumper barrel, a rings out design, or it may have the rings located approximately one quarter of the length of the barrel in from the ends, the rings in design. 
     When a railroad car is dumped more air is displaced by the rush of product exiting the railcar than can be evacuated by a blower system in a period of time during the dump. Thus, there is a tendency for the moving dust laden air to escape from the car dumper pit by any exit path that may be available. 
     Prior art car dumper dust control systems have made great improvements in dust control. However, dust still escapes from car dumpers in sufficient quantity to create significant air pollution and deposition of dust onto horizontal surfaces in the vicinity of car dumpers. 
     Often, attempts have been made to control the remaining escaping dust by wet suppression techniques. That is water is sprayed into the area to dampen the dust particles. This causes them to fall to the ground or other horizontal surface. Wet suppression is generally effective in removing dust from the air. Unfortunately, wet dust adheres to everything it comes into contact with in the area and is difficult to clean up. 
     Prior dust control systems are described in U.S. Pat. Nos. 6,960,054 and 7,322,785 which are assigned to the assignee of the present application. 
     Therefore, there is a continuing need to provide a rotary-dumper dust collection apparatus and system that overcomes the drawbacks of the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the disadvantages in the prior art and the need to provide an environmentally friendly and efficient way to unload rail cars by providing a method and apparatus for controlling dust generated by the rotary dumping of rail cars. One or more flexible baffles are provided to the back-side of a rotary dump frame to seal a portion of the material receiving pit during at least a portion of the rotary motion. The dust cloud generated by this dumping is retained in the pit for an increased time due to tumbling of the cloud induced by the baffles and other features of the facility. A plurality of intake ducts removes the dust cloud from the pit for transfer to a remote filtering facility. 
     The present invention provides for additional air intakes be placed at a location where they can assist in extracting dust laden air from between the baffles. 
     Car dumpers that have been adapted for dust control still release some dust into the environment. As will be discussed below, there is a tendency for dust to be trapped between the baffles which hang down and seal between the car dumper carriage and the ski jump or backside diverter during at least part of the dumping process. Dust trapped between the baffles tends to be released in a puff of dust when the leading baffle clears the upper outer edge of the ski jump and is no longer in contact with ski jump. 
     A rotary car dumping facility with relation to the present invention generally includes an interior and an exterior. Within the interior is located a material receiving pit. The pit has a dump side and a back side. A rotational frame is located at least partially in the pit and is adapted to receive a loaded rail car and to dump the load from the rail car during rotational motion of the rotational frame and the rail car. The rail car starts in an upright position where the entire load is in the rail car and is rotated by the rotational frame to a dumping position where the load exits the rail car. Inside the pit is located a backside airflow diverter, also known as a ski jump. The backside airflow diverter is located adjacent the backside of the pit and includes a curved upper surface which, because of its shape leads to being referred to as the ski jump. 
     The backside hood for removing contaminated air from the backside of the pit is also located on the backside of the pit generally beneath the backside diverter. The rotational frame supports one or more baffles that hang downward from the rotational frame and make contact with the upper surface of the backside airflow diverter during at least a portion of the rotational motion. The present invention is particularly useful in the context of a car dumper that has at least two baffles disposed on the rotational frame. 
     The baffles located on the rotational frame are separated by some distance so that as one baffle leaves the top of the backside airflow diverter, a second baffle is still in contact with the top of the backside airflow diverter and a third baffle may be making contact with the lower edge of the backside airflow diverter. Thus, there is a space located between each pair of the baffles. A first space located between the first and second baffle and a second space located between the second and third baffle. 
     Dust laden air often occupies the spaces between the first and second baffle and the second and third baffle. The present invention allows for the removable of the dust laden air from the space between the baffles to a filtering facility where dust and particulate matter in the dust laden air can be removed before the air is released into the surrounding environment. For the purposes of this discussion, a car dumping facility with three curtain baffles secured to the rotational dumping frame will be discussed. However, this should not be considered to be limiting. A larger or smaller number of curtain baffles may be utilized in accordance with the present invention. 
     As the rotational frame begins its rotation, from an upright position, none of the curtain baffles are in contact with the upper surface of the backside airflow diverter. As the rotation continues, the first curtain baffle makes contact with the backside airflow diverter and forms a seal between the rotational frame and the backside airflow diverter. During this time period, dust laden air from the dumping process can enter the space behind the first baffle. As the rotational frame continues its rotation, the second baffle makes contact with the lower edge of the backside airflow diverter. When this contact is made, dust laden air that is in the space behind the first baffle but in front of the second baffle, is trapped in the space bounded by the rotational frame, the first baffle, the second baffle and the upper surface of the backside airflow diverter. As rotation continues, the first baffle clears the top edge of the backside airflow diverter, at this time there tends to be a puff of dust laden air that escapes from the space between the first and second baffle. In the prior art, this dust laden air is released into the environment and contributes to environmental pollution in the area surrounding a car dumper. As rotation of the car dumper continues, the second baffle remains in contact with the upper surface of the backside airflow diverter and the third baffle makes contact with the lower edge of the backside airflow diverter and continues up to the top of the backside airflow diverter. At this time dust laden air can be captured in the space bounded by the second baffle, the third baffle, the rotational frame and the upper surface of the backside airflow diverter. As rotation continues to the final dumping position, the second baffle clears the upper edge of the backside airflow diverter and a second puff of dust laden air may be released into the environment surrounding the car dumping facility. After the car is completely dumped, the rotational frame reverses its rotational direction and returns to an upright position. The present invention removes dust laden air from the space between the first and second baffle and the space between the second and third baffle prior to that dust laden air being released into the ambient environment as a puff of dust laden air. 
     The present invention includes at least one additional air intake that passes through upper surface of the backside airflow diverter at a location so that dust laden air can be drawn into the backside hood and removed from the space between the first and second baffle and the space between the second and third baffle before these spaces are opened to the ambient atmosphere and allow release of the dust laden air into the surrounding environment. 
     The additional air intakes in accordance with the present invention are located at a position relative to the backside hood where the backside hood narrows as it approached attached ductwork, thus creating a higher speed flow of air to the filter system that is utilized with the car dumper of the present invention. The additional air intake is also located so that the edge of the first baffle passes the additional air intake after the edge of the second baffle has made contact with the lower edge of the upper surface of the backside airflow diverter. This prevents the additional air intakes from drawing additional dust laden air from the pit into the space between the baffles. 
     Thus, dust laden air is withdrawn from the space between the first baffle and the second baffle while the rotational frame is rotating. In accordance with the present invention, the location of the additional air intake is also such that the second baffle passes the location of the additional air intake shortly after the third baffle makes contact with the lower edge of the backside airflow diverter. 
     In accordance with the present invention, the additional air intake is sized to allow for essentially complete evacuation of dust laden air from between the first baffle and the second baffle or the space between the second baffle and the third baffle prior to the leading baffle breaking contact with the upper edge of backside airflow diverter. 
     Additional air intakes in accordance with an example embodiment of the present invention, may take the form of generally horizontally oriented slits passing through the upper surface of the backside airflow diverter and into the backside hood. The additional air intakes are located aligned with at least one of the air intake ducts that are positioned beneath the backside airflow diverter. The additional air intakes may also be formed in other shapes including circular or square. 
     In some example embodiments of the present invention it is beneficial if the edges of the additional air intake are chamfered or rounded. Chamfering or rounding may minimize wear on the edges of the baffles as they pass over the additional air intakes. 
     During operation of a car dumper prior to dumping of a rail car while the exhaust fans are operating, pressure inside of the backside hood is negative relative to the inside of the pit because of the operation of the exhaust fans. When a railway car is being dumped, the solid granular material being dumped from the rail car rushes downward into the pit and carries along with it a great deal of air. This down rushing air increases pressure inside the car dumper pit for a period of time and briefly causes there to be positive pressure within at least the lower portion of the interior of the backside hood. This positive pressure reaches some distance up the backside hood toward the air intake duct work. As the backside hood narrowers and transitions to the ductwork the velocity of air flow increases as a result of the fans withdrawing air thus transitioning from positive pressure to negative pressure. 
     Described another way, the pit is subject to spike increases in pressure initiated by the load exiting the rail car and entering the pit. The spike increases in pressure travel into the backside hood an attenuating distance from a primary hood intake before being attenuated. The attenuating distance is that distance from the primary hood intake at which the pressure within the backside hood is less than or equal to the pressure in the interbaffle space. 
     In an example embodiment of the invention at least one secondary air intake is positioned to pass through the upper surface of the backside diverter into the backside hood at a location at least the attenuating distance from the primary intake. 
     In accordance with an example embodiment of the present invention, the additional air intakes are positioned in a zone of the backside hood where there is always neutral or negative pressure relative to the inside of the pit. This positioning overcomes a tendency for dust laden air passing into the backside exhaust hood under pressure from the pit to puff out of the additional air intakes into the space between the baffles and then into the environment. Thus, in accordance with the present invention, the additional air intakes may be positioned at a location toward the upper end of the backside hood where pressure in the backside hood remains neutral or negative even when downwardly rushing material dumped from the rail car into the pit and air that accompanies it transiently increase pressure in the lower portion of the backside hood. In an example embodiment the location of the additional air intakes is near the location of the transition from the top end of the backside hood to the exhaust duct that draws air from the backside hood. 
     In another example embodiment, the invention includes a method of reducing release of dust generated during rotary dumping of rail cars in a dumping facility. The facility includes a material receiving pit that has a dumpside and a backside. A rotational frame is disposed at least partially in the pit and is configured to dump a load from a rail car during rotational motion of the rotational frame between an upright position wherein the load is in the rail car and a dumping position wherein the load can clear the rail car supports baffles. A backside airflow diverter is within the pit adjacent the back side of the pit. A backside hood is located generally beneath the backside diverter. The baffles each present a leading edge that is configured to contact the backside airflow diverter during at least a portion of the rotational motion. The pit is subject to spike increases in pressure initiated by the load clearing the rail car and entering the pit. The spike increases in pressure travel into the backside hood an attenuating distance from a primary hood intake before being attenuated. The attenuating distance is that distance from the primary hood intake at which the pressure within the backside hood is less than or equal to the pressure in the interbaffle space. The method includes locating at least one secondary air intake positioned to pass through the upper surface of the backside diverter into the backside hood at a location at least the attenuating distance from the primary hood intake. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary end elevational view of a rail car dumper in accordance with an embodiment of the invention; 
         FIG. 2  is a top plan view of the car dumper of  FIG. 1  taken along section line  2 - 2 ; 
         FIG. 3  is a detailed view of the area encircled at  3  in  FIG. 2 ; 
         FIG. 4  is a detailed view of the area encircled at  4  in  FIG. 1 ; 
         FIG. 5  is an end view of the car dumper of  FIG. 1  with a dumping frame beginning to rotate; 
         FIG. 5A  is a detailed view of area  5 A in  FIG. 5 ; 
         FIG. 6  is a detailed view of area  6  in  FIGS. 5 and 5A ; 
         FIG. 7  is an end view of the car dumper of  FIG. 1  with the dumping frame about midway in its rotation; 
         FIG. 7A  is a detailed view of area  7 A in  FIG. 7 ; 
         FIG. 8  is an end view of the car dumper of  FIG. 1  with the dumping frame near the end of its rotation; and 
         FIG. 8A  is a detailed view of area  8 A in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     Car dumper facility  10  of the present invention generally includes upper portion  12  and lower portion  14 . Rotational frame  16  is disposed within car dumper facility  10 , generally overlapping upper portion  12  and lower portion  14 . 
     Car dumper facility  10  also includes dust removal apparatus  18 . Curved arrows in  FIGS. 5 ,  5 A,  6 ,  7 ,  7 A,  8  and  8 A demonstrate the general direction of airflow in accordance with the invention. 
     Lower portion  14 , in an example embodiment, generally includes pit  20 , grizzly  22 , backside diverter  24 , dumpside diverter  26  and dumpside baffle  28 . 
     Pit  20  is covered by grizzly  22 . Grizzly  22  is a grate having apertures of a size appropriate to receive the coal or other granular material dumped while not large enough to pass foreign matter that they be mixed with the dumped material. Backside diverter  24  is located in pit  20  on the backside and has a generally curved upper surface. Backside diverter  24  is also sometimes known as the ski jump because of its shape. Dumpside diverter  26  is located on the dumpside of pit  20  and is generally sloped toward grizzly  22  and extends upwardly away toward the exterior of pit  20 . Dumpside baffle  28  is located on the dumpside of pit  20  and is generally stationary and secured to structure in or above pit  20 . 
     Rotational frame  16  is rotationally disposed above pit  20  and is adapted to support rail car  30 . Rotational frame  16  generally includes rail car support  32  positioned so that rotational axis  34  coincides with rotational coupler (not shown) of rail car  30 . Rotational frame  16  generally includes counter weight  36  and baffle support  38 . Baffle support  38 , in an example embodiment, supports first baffle  40 , second baffle  42  and third baffle  44 . First baffle  40 , second baffle  42  and third baffle  44  are flexible and/or are hingedly supported by baffle support  38 . First baffle  40 , second baffle  42  and third baffle  44  may be partially or completely formed of flexible material. For example, first baffle  40 , second baffle  42  and third baffle  44  may be formed of a heavy weight flexible rubber or polymer material. Further, they may be formed of a ridged or semi-ridged structural material and have a flexible seal (not shown) at the lowest edge thereof. 
     Dust removal apparatus  18  generally includes dumpside hood  46 , dump side ductwork  48 , backside hood  50  and backside duct work  52 . Dumpside hood  46  is generally located on the dumpside of car dumper facility  10 . Dumpside hood  46 , in an example embodiment, is positioned in upper portion  12  of car dumper facility  10 . Dumpside hood  46  is in fluid communication with dump side ductwork  48 . Dumpside ductwork  48  leads to an exhaust fan (not shown) which is coupled to a filtering facility (not shown) located in or near car dumper facility  10 . Dumpside hood  46  includes dumpside intake  54 . Dumpside intake  54  is located near and generally above dumpside diverter  26 . Dumpside baffle  28  is located, in an example embodiment, adjacent to dumpside intake  54 . 
     In an example embodiment, backside hood  50  is located generally beneath backside diverter  24 . Backside hood  50  is in fluid communication with backside ductwork  52 . Backside ductwork  52  is in fluid communication with exhaust fan (not shown) and filtering facility (not shown). As can be seen in  FIGS. 1 and 2 , backside hood  50 , in an example embodiment, is located generally beneath backside diverter  24 . Backside hood  50  includes backside intake  56 . Backside intake  56  is located generally at the bottom of backside hood  50 . In the example embodiment depicted in  FIG. 1 , backside intake  56  extends over a portion of grizzly  22 . 
     Referring particular to  FIG. 2 , backside hood  50  may include a number of backside sub-hoods  58 . In an example embodiment depicted in  FIG. 2 , six backside sub-hoods  58  are included. In  FIG. 2 , backside sub-hoods  58  are each located in bays  60 . Generally, each backside sub-hood  58  includes straight portion  62 , tapered portion  64 , transition portion  66  and attached exhaust duct  68 . In an example embodiment, straight portion  62  has generally parallel sides when viewed from above, tapered portion  64  tapers from straight portion  62  to transition portion  66 . Both straight portion  62  and tapered portion  64  may tapered somewhat when viewed from the side. Transition portion  66  transitions in shape from a generally rectangular cross section of straight potion  62  and tapered portion  64  to the generally circular cross section of exhaust duct  68 . 
     Each backside sub-hood  58  may include secondary intake  70 . Secondary intake  70  comprises a fluid communication that passes through backside diverter  24  and into backside sub-hood  58 . As depicted in  FIG. 2 , in an example embodiment, secondary intake  70  may be located approximately at the juncture between tapered portion  64  and transition portion  66 , however, this should not be considered limiting. 
     Referring particularly to  FIGS. 3 ,  4  and  6 , secondary intake  70  allows fluid communication of backside sub-hood  58  with the space above, backside diverter  24 . Secondary intake  70  may be generally slit shaped as depicted herein. However, this should not be considered limiting as secondary intake  70  may include other shapes including circular, square or rectangular. The secondary intake  70 , in an example embodiment may, include a generally horizontal oriented rectangular slit. Secondary intake  70  may include chamfered edges  72 . 
     Referring to  FIGS. 5 and 5   a,  rotational frame  16  is depicted rotated approximately 90°, first baffle  40  and second baffle  42  are in contact with backside diverter  24 . As depicted in  FIGS. 5 and 5   a,  this contact creates first interbaffle space  74 . First inter baffle space  74  is bounded by first baffle  40 , second baffle  42 , backside diverter  24  and baffle support  38 . Secondary intake  70  is located so that first interbaffle space  74  is in fluid communication with backside hood  50 , via backside sub-hood  58 , when first baffle  40  and second baffle  42  are in contact with backside diverter  24 . 
     Referring to  FIGS. 7 and 7   a,  rotational frame  16  is pictured having rotated approximately 125°. At this stage in the rotation, first baffle  40  has cleared the upper edge of backside diverter  24 . Second baffle  42  and third baffle  44  are in contact with backside diverter  24 . Second interbaffle space  76  is thus bounded by second baffle  42 , third baffle  44 , dumpside diverter  26  and baffle support  38 . Second interbaffle space  76 , as depicted, is in fluid communication with backside hood  50  via secondary intake  70 . 
     Referring to  FIGS. 8 and 8   a,  rotational frame  16  is depicted having rotated approximately 155°. In this orientation, both first baffle  40  and second baffle  42  have cleared the upper edge of backside diverter  24 . Third baffle  44  remains in contact with backside diverter  24 . At this point of the rotation second interbaffle space  76  is opened to the air near upper portion  12  of car dumping facility  10 . 
     In an example embodiment of the invention, secondary intake  70  is located relative to backside hood  50  at a location where pressure within backside hood  50  remains neutral or negative relative to the pressure within pit  20  when a load of granular material is being dumped from rail car  30  into pit  20 . The dumping of granular material from rail car  30  brings along with it a rush of air that is carried along by the granular material as it departs rail car  30  and is carried by gravity into pit  20 . This rush of air creates increased pressure in pit  20 . Negative pressure is generally maintained within backside hood  50  and backside ductwork  52  because of the action of exhaust fans (not shown) in the filtering facility (not shown). As the rush of air that accompanies the granular material being dumped enters pit  20 , pressure within pit  20  rises and pressure within the lower portion of backside hood  50  rises as well. There is a location within backside hood  50  and/or backside ductwork  52  at which pressure remains neutral or negative because of the action of exhaust fans (not shown). 
     In an example embodiment of the invention, secondary intakes  70  are located such that they are adjacent to the portion of backside hood  50  at which air pressure remains neutral or negative relative to the elevated pressure in pit  20  caused by the dumping of granular material. Additionally, secondary intake  70  being located at this location allows secondary intake  70  to facilitate the evacuation of dust laden air from first interbaffle space  74  when secondary intake  70  is in fluid communication with first interbaffle space  74  and from secondary interbaffle space  76  when secondary intake  70  is in fluid communication with second interbaffle space  76 . 
     Referring to  FIGS. 5 ,  5   a ,  7 ,  7   a  and  8 - 8   a , in operation, rail car  30  is indexed within rotational frame  16  as depicted in  FIG. 1 . Rail car  30  is secured to rotational frame  16  and rotational frame  16  begins rotating as depicted in  FIG. 5 . As rotational frame  16  and rail car  30  rotate, granular material (not shown) within rail car  30  begins dump into pit  20 . As rotational frame  16  continues to rotate as depicted in  FIGS. 5 ,  5   a ,  7 ,  7   a , and  8 ,  8   a , granular material (not shown) continues to pour from rail car  30  into pit  20 . 
     As granular material (not shown) pours from rail car  30  into pit  20 , the pressure within pit  20  rises because of the on rush of air carried along with the granular material (not shown). Referring to  FIGS. 5 and 5   a,  when rotational frame  16  reaches a certain point in rotation, fluid communication is established between secondary intake  70  and first interbaffle space  74 . At this point, first interbaffle space  74  may be filled with dust laden air from the dumping of granular material from rail car  30  in the pit  20 . Dust laden air is then withdrawn from interbaffle space  74  into backside hood  50  because of the relatively lower pressure in backside hood  50 . 
     As rotation of rotational frame  16  continues, as depicted in  FIGS. 7 and 7   a,  second interbaffle space  76  establishes fluid communication with secondary intake  70 . Because secondary intake  70  is located relative to backside hood  50 , where internal pressure in backside hood  50  remains neutral or negative relative to pit  20  as second interbaffle space  76 , dust laden air is withdrawn from second interbaffle space  76 . Because dust laden air has been withdrawn from first interbaffle space  74 , no puff of dust laden air is released from first interbaffle space  74  when it reaches the position depicted in  FIGS. 7 and 7   a . Further no puff of dust laden air escapes from second interbaffle space  76  when it reaches the position depicted in  FIGS. 8 and 8   a . Thus, the present invention prevents or reduces the release of environmental contaminants from pit  20  in car dumper facility  10 . 
     Rotational frame  16  carrying empty rail car  30  then can be returned to the upright position as depicted in  FIG. 1  and removed from the car dumper facility  10  so that another rail car  30  that is loaded may be indexed for dumping. 
     The invention may be embodied in other specific forms without departing from the spirit of the essential attributes thereof, therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the forgoing description to indicate the scope of the invention.