Abstract:
In a multi-silo distribution and storage system, the regions between the stationary and transport batchers, and between transport batcher and storage bin are isolated during asphalt discharge with a bellows automatically deployed when clamshell gates of the stationary and transport batchers are opened. The storage bin is provided with a sealing door that lifts vertically for unsealing and slides horizontally to permit access to the bin interior for receiving asphalt discharged from the transport batcher. After registry above the top bin opening, the sealing door is forced downwardly to create a tight seal. For prolonged storage, a fluid seal isolates the lower discharge gate of the storage bin. Steam is delivered to the stored asphalt and bin interior to displace atmospheric oxygen vented through a valve in the bin top. An oxygen sensor linked to a process controller monitors the oxygen level within the storage bin.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     None 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     None 
     BACKGROUND OF THE INVENTION 
     This invention relates to equipment for distributing and storing large quantities of asphaltic mixtures in a multiple silo or bin system. More specifically, this invention relates to a multi-silo distribution and storage system to effectively control emissions during normal plant operations and to minimize degradation of asphaltic mixtures through oxidation during periods of prolonged storage. 
     Several techniques and numerous equipment arrangements for the preparation of asphaltic compositions are known from the prior art. Continuous production of asphalt compositions can be achieved, for example, with a drum mixer asphalt plant. Typically, water-laden virgin aggregates are dried and heated within a rotating, open-ended drum mixer through radiant, convective and conductive heat transfer from a stream of hot gases produced by a burner flame. As the heated virgin aggregate flows through the drum mixer, it is combined with liquid asphalt and mineral binder to produce various asphaltic mixtures as the desired end-product. Optionally, prior to mixing the virgin aggregate and liquid asphalt, reclaimed or recycled asphalt pavement (RAP) may be added once it is has been crushed or ground to a suitable size. The RAP is typically mixed with the heated virgin aggregate in the drum mixer at a point prior to adding the liquid asphalt and mineral fines. 
     In earlier times in this industry, one of the bottlenecks in paving construction had been trucking the asphalt mixtures from the production plant to the job site. In order to decrease the trucking expenses and also the waiting time of a truck at the production plant, temporary storage and loading facilities for asphalt plants were developed. Initially, such facilities included an elevating conveyor, such as the drag slat conveyor disclosed in Rheinfrank, Jr. U.S. Pat. No. 3,647,047, to receive asphalt mix from the production plant and to deliver it to the top of a large cylindrical silo supported above a truck load-out area. This type of temporary storage operation successfully reduced truck waiting time since a full truck load of asphalt mix was available when a truck arrived from the job site. In addition, by smoothing out loading times and enabling the orderly delivery of asphalt mix from the plant to the job site, fewer trucks were required for paving construction. 
     It was found, however, that the asphalt mixtures trickling into the large storage bin from the elevating conveyor caused separation of the aggregate within the mix which tended to roll to the outside of the cone of material within the bin. This problem was solved in the early 1970&#39;s with the development of the batcher as disclosed in Rheinfrank, Jr. U.S. Pat. No. 3,777,909. The batcher sat atop the storage silo and collected the asphalt mix from the elevating conveyor. When the batcher filled, its contents were then discharged to the larger storage silo. Segregation of the aggregate rock in the mix was avoided by dumping the larger volume of material into the storage silo at one time. Today, a batcher is found on most all asphalt storage silos specifically for the purpose of preventing segregation of the aggregate. 
     Over time, as asphalt production techniques and efficiencies improved, greater storage capacities were needed both for storing larger quantities of material and for storing asphalt mixes of differing compositions for various job applications. Storage facilities with multiple bin systems resulted and a variety of distribution schemes have been proposed. These include a separate batcher for each storage bin, multiple conveyors to deliver material to the many bins, and moving conveyors. One such example is taught in Harris U.S. Pat. No. 3,182,859. 
     A recent and simplified solution to the problem of multiple bin distribution and storage utilizes a stationary batcher to receive asphalt mix from the production plant and a transport batcher to receive mix from the stationary batcher and to then travel on an indexing rail system to deliver its load to a preselected one of several storage bins. It is this particular type of multi-silo distribution and storage system to which this invention specifically relates. 
     The asphalt industry has traditionally faced many environmental challenges. The asphalt production plant characteristically generates, as by-products, gaseous hydrocarbon emissions (known as blue-smoke), various nitrogen oxides (NO x ) and sticky dust particles covered with asphalt. Health and safety hazards resulted from the substantial air pollution control problems due to the blue-smoke produced when hydrocarbon constituents in the asphalt are driven off and released into the atmosphere. Within the asphalt production plant, exhaust gases are typically fed to air pollution control equipment such as a baghouse to filter particular matter from the exhaust gases. Thus, significant investments and efforts have previously been made by the industry in attempting to control emissions attributed to volatile hydrocarbon gases and particulates from the asphalt production plant itself. 
     Since the asphalt mix is typically delivered to the storage facilities as a hot or warm mixture, control of blue-smoke emissions from transferring equipment and from the storage bins themselves continue to be problematic. The asphaltic mixtures are exposed to atmospheric conditions when transferring mix from the stationary batcher to the transport batcher, and again when transferring mix from the transport batcher to the storage bin. The escape of volatile hydrocarbon emissions during these operational steps is inevitable. 
     Emissions also occur from the storage bin itself due to inadequate sealing of the upper access door of the bin and leakage around the lower discharge gate. During periods of prolonged storage of asphalt mixes, emissions from the storage bin continue as a result of the need for maintaining the storage material at elevated temperatures through various heating and/or insulation techniques. Volatiles from the mixes are therefore present and can escape around the lower discharge gate and upper access door of the storage bin. 
     Dillman U.S. Pat. No. 4,249,679 has proposed a seal for the lower discharge gate having a sliding door and a dispensing system to pump grease around the door and the discharge mouth of the storage bin. This was a cumbersome solution and was never widely accepted in the asphalt industry. Heretofore no solutions have been found to effectively and positively seal the upper access door of the bin. 
     In addition to the concerns over emissions during prolonged storage of asphalt mixes, degradation of the asphalt through oxidation has long been a problem. Clements et al U.S. Pat. No. 3,999,688 proposed an inerting system using tanks of carbon dioxide gas with a self-sealing top access door. However, the access door lacked any means to forcibly seal the upper opening and the inerting system was never widely adopted in the industry as a result of the maintenance issues associated with the need for an inventory of carbon dioxide tanks and frequent change out of the tanks in service. 
     A need remains in the asphalt industry for an improved multi-silo distribution and asphalt storage system to effectively control blue-smoke emissions, to provide positive seals for the upper access door and the discharge gate of a storage bin, and to provide a useful inerting system to minimize degradation of asphaltic mixtures through oxidation during periods of prolonged storage. The primary objective of this invention is to meet these needs. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the invention is to provide multi-silo distribution and storage facilities to effectively control blue-smoke emissions by isolating from the environment the discharges of both the stationary and transport batchers. 
     Another object of the invention is to provide multi-silo distribution and storage facilities of the character described where the region between the stationary batcher and the transport batcher and the region between the transport batcher and the storage bin are effectively isolated by a flexible bellows to contain blue-smoke emissions during discharge of asphalt mix from the stationary and transport batchers. 
     A further object of the invention is to provide multi-silo distribution and storage facilities of the character described where the flexible bellows associated with the stationary and transport batchers are automatically deployed to contain blue-smoke emissions whenever the clamshell gates of the stationary and transport batchers are opened. 
     Another object of the invention is to provide multi-silo distribution and storage facilities with a self-sealing top access door on the storage bin. 
     Yet another object of the invention is to provide multi-silo distribution and storage facilities with a self-sealing top access door to be forced downwardly to create a tight, positive seal and to be movable upwardly and then slid horizontally to provide access to the interior of the storage bin. 
     A further object of the invention is to provide multi-silo distribution and storage facilities with a fluid seal on the discharge gate of the storage bin to prevent emissions leakage therefrom and to isolate the bin contents from atmospheric oxygen. 
     An additional object of the invention is to provide multi-silo distribution and storage facilities of the character described having an effective seal to the top access door and an effective seal to the lower discharge gate, and further equipped with an inerting system to minimize oxidation of the asphaltic mixtures during prolonged periods of storage. 
     Yet another object of the invention is to provide multi-silo distribution and storage facilities equipped with an inerting system of the character described which is economical in operation and includes an oxygen sensor to monitor oxygen levels within the storage bin and a process controller to deliver steam to the interior of the storage bin when an excessive level of atmospheric oxygen is sensed. 
     Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the detailed description of the drawings. 
     In summary, a multi-silo distribution and storage system where the region between the stationary batcher and transport batcher and the region between the transport batcher and the storage bin are isolated during the discharge of asphalt mix with a bellows that is automatically deployed when the clamshell gates of the stationary and transport batchers are opened. Access to the interior of the storage bin is provided by a sealing door that lifts vertically for unsealing and then slides horizontally to the side to permit access to the bin for receiving asphaltic mixtures discharged from the transport batcher. After moving to registry above the top opening of the bin, the sealing door is forced downwardly to create a tight, positive seal. For prolonged periods of storage, in addition to a positive seal for the upper access of the storage bin, a fluid seal isolates the lower discharge gate of the storage bin. Thereafter, a steam generator delivers steam to the stored asphaltic mix and to the interior of the storage bin to displace atmospheric oxygen vented through a vent valve in the top of the bin. An oxygen sensor linked to a process controller monitors the oxygen level within the storage bin for operation of the steam generator. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       In the following description of the drawings, in which like reference numerals are employed to indicate like parts in the various views: 
         FIG. 1  is a top plan view of a multi-silo asphalt storage and distribution system showing six storage silos, portions of a drag slat conveyor, a stationary batcher, and a transport batcher; 
         FIG. 2  is an end elevational view of a multi-silo asphalt storage and distribution system showing the transport batcher positioned beneath the stationary batcher, 
         FIG. 2   a  is an enlarged, top plan view of the transport batcher with the movable central doors shown in the open position to access the interior of the batcher; 
         FIG. 3  is a side elevational view of a multi-silo asphalt storage and distribution system showing the transport batcher moved from the stationary batcher and positioned above the access door of a storage silo; 
         FIG. 4  is a side elevational view of the transport batcher positioned above the access door of a storage silo prior to discharge of the asphalt contents of the transport batcher to the storage silo; 
         FIG. 4   a  is an enlarged, sectional fragmentary view of the bellows as shown in  FIG. 4 ; 
         FIG. 5  is a bottom plan view of the transport batcher shown in  FIG. 4  (with cylinders and brackets removed for clarity) positioned above the access door of a storage silo prior to discharge of the asphalt contents of the transport batcher to the storage silo; 
         FIG. 6  is a side elevational view of the transport batcher positioned above the access door of a storage silo similar to  FIG. 4  but showing the access door of the storage silo open and the batcher discharge gates open with a bellows seal engaged against the housing of the access door of the storage silo when asphalt contents of the transport batcher are delivered to the storage silo; 
         FIG. 7  is a bottom plan view of the transport batcher similar to  FIG. 5  positioned above the access door of a storage silo but showing the batcher discharge gates open to discharge of the asphalt contents of the transport batcher to the storage silo; 
         FIG. 8  is a top plan view of the access door housing of a storage silo; 
         FIG. 9  is a side elevational view of the access door housing of a storage silo shown in  FIG. 8 ; 
         FIG. 10  is a top plan view similar to  FIG. 8  but with the top panel of the access door housing removed to illustrate the access door itself shown in an open position; 
         FIG. 11  is a side elevational view similar to  FIG. 9  but with the top and end panels of the access door housing removed to illustrate the access door itself; 
         FIG. 12  is a top plan view of the access door of a storage silo shown in the closed and sealed position; 
         FIG. 13  is a side elevational view of the access door as shown in  FIG. 12  in the closed and sealed position; 
         FIG. 14  is an enlarged, side elevational view of the portion of the access door as shown in  FIG. 13  in the closed and sealed position; 
         FIG. 15  is an end view, partially sectional, of the access door as shown in  FIG. 14  in the closed and sealed position; 
         FIG. 16  is a top plan view similar to  FIG. 12  but showing the access door in a position raised above the sealed position; 
         FIG. 17  is a side elevational view similar to  FIG. 13  but showing the access door in a position raised above the sealed position; 
         FIG. 18  is an enlarged view similar to  FIG. 14  but showing the access door in a position raised above the sealed position; 
         FIG. 19  is an end view, partially sectional, of the access door as shown in  FIG. 15  but showing the access door in a position raised above the sealed position; 
         FIG. 20  is a top plan view similar to  FIG. 16  but showing the access door in a raised and retracted position to exposed access to the storage silo mouth; 
         FIG. 21  is a side elevational view similar to  FIG. 17  but showing the access door in a raised and retracted position to exposed access to the storage silo mouth; 
         FIG. 22  is a side elevational, schematic view of an inerting system for an asphalt storage silo illustrating conditions of normal, daily operation; 
         FIG. 23  is a side elevational, schematic view of an inerting system for an asphalt storage silo illustrating conditions of a sealed top access door and sealed lower discharge gate; 
         FIG. 24  is a side elevational, schematic view of an inerting system for an asphalt storage silo illustrating conditions introducing an inert fluid into the storage silo; and 
         FIG. 25  is a side elevational, schematic view of an inerting system for an asphalt storage silo illustrating conditions of prolonged inert storage operation. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings in greater detail, attention is first directed  FIGS. 1-3  illustrating a multi-silo distribution and storage system specific to this invention. Illustrated in  FIG. 1  is a plurality of storage bins  30 . Although six such bins  30  are shown, this number can be expanded or contracted to any convenient number. Each storage bin  30  has a large, cylindrical upper portion  30   a  joined to a lower frusto-conical portion  30   b  with a central discharge mouth  30   c  with a discharge gate  30   d  for holding asphaltic mixtures  32  within the storage bin  30 . The storage bins  30  are vertically oriented and supported on legs above a truck load-out area (not shown). Such support is well known in the art and a representative example thereof is shown in Rheinfrank, Jr. U.S. Pat. No. 3,777,909 which is incorporated by reference. 
     Asphaltic mixtures from a production plant (not shown) are characteristically delivered to storage facilities by means of a drag slat conveyor  34  of which the upper portion thereof is illustrated in the drawings. Further details of a typical drag slat conveyor useful for transferring asphaltic mixtures from a production plant to storage facilities is shown in Rheinfrank, Jr. U.S. Pat. No. 3,647,047 which is incorporated by reference. 
     Also known in the art and mounted atop the storage bins  30  is an indexing mechanism which includes spaced apart, parallel rails  36  attached to the bins  30  along the lengths of opposed rows of bins  30 . Supported on each rail  36  is a power operated wheeled carriage  38  for coordinated movement along the rail  36 . Attached to the carriages  38  are spaced apart, parallel rails  40  oriented substantially perpendicular to the rails  36 . Supported on each rail  40  is a power operated wheeled carriage  42  for coordinated movement along the rail  40 . Attached to the carriages  42  is a transport batcher  44 , the details of which will be discussed shortly. Thus constructed, the indexing mechanism is adapted to move the transport batcher  44  back and forth over the bins  30  (in the “x-direction” relative to  FIG. 1 ) on the rails  36  by operation of the carriages  38 , and is adapted to move the transport batcher  44  back and forth over the bins  30  (in the “y-direction” relative to  FIG. 1 ) on the rails  40  by operation of the carriages  42 . Therefore, the transport batcher  44  can be caused to selectively register over each of the bins  30  in the storage facilities. 
     As shown in  FIGS. 1 &amp; 2 , beneath the discharge of the drag slat conveyor  34  is mounted a stationary batcher  46  to receive asphaltic mixtures from the conveyor  34  and then to discharge the asphaltic mixtures to the transport conveyor  44  when the transport conveyor  44  registers over the first bin  30  and under the stationary batcher  46 . The essential details of construction of the transport batcher  44  are illustrated in  FIGS. 4-7 . The stationary batcher  46  has the same construction as the transport batcher  44  and, therefore, is not separately illustrated. 
     The transport batcher  44  includes a cylindrical upper portion  44   a  having a diameter much smaller than that of the storage bin  30  and a lower frusto-conical portion  44   b  terminating in a circular discharge mouth  44   c . As best shown in  FIG. 2   a , the top of the batcher  44  includes a cover plate  44   d  having a central opening  44   e  fitted with an inlet cone  44   f . Beneath the cover plate  44   d , central opening  44   e  and the inlet cone  44   f  are a pair of movable central doors  44   g  equipped with extendable and retractable cylinders  44   h  to provide access to the interior of the batcher  44 . 
     At diametrically opposed locations on the exterior surface of the frusto-conical portion  44   b  are affixed gate brackets  48  which carry pivot pins  50  to support clamshell gates  52  that normally close the discharge mouth  44   c  as shown in  FIG. 4 . 
     Also attached to the exterior surface of the frusto-conical portion  44   b , at diametrically opposed locations that are substantially perpendicular to the diameter on with the gate brackets  48  are attached, are cylinder brackets  54 . Extendable and retractable cylinders  56  are pivotally pinned between the brackets  54  and the clamshell gates  52 . When extended, the cylinders  56 , which can be hydraulically or pneumatically operated, cause the clamshell gates  52  to close the batcher mouth  44   c  as shown in  FIG. 4 . When retracted, however, the cylinders  56  pivot the clamshell gates  52  to open the batcher mouth  44   c  as shown in  FIGS. 6 &amp; 7 . 
     The foregoing details of batcher construction are well known to those skilled in the art of asphalt storage. The transport batcher  44  and stationary batcher  46  of this invention, however, further include a cylindrical shroud  58  attached to the upper cylindrical portion  44   a  and substantially enclosing the frusto-conical portion  44   b  and portions of the clamshell gates  52 . 
     Attached to the lower end of the shroud  58  is a cylindrical bellows  60 . As best viewed in  FIG. 4   a , the bellows  60  is constructed with a flexible accordion material  62  with a cuff  64  formed in the lower end of the accordion material  62 . Within the cuff  64  is carried a weighted hoop  66 . Attached to the lowermost surface of the cuff  64  is a compressible seal strip  68 . Four brackets  70  are connected to the cuff  64  and weighted hoop  66  at spaced locations around the lower end of the bellows  60  as shown in  FIG. 5 . Secured to each bracket  70  is a flexible cable  72  which extends over a pulley  74  mounted within the shroud  58  and is secured to a connector  76  attached to the clamshell gates  52 . The length of each such cable  72  is adjusted during installation thereof such that when the clamshell gates  52  close ( FIG. 4 ), the cable  72  pulls the bellows  60  upwardly so the accordion material  62  folds against the shroud  58 . When the clamshell gates  52  open, however, the weighted hoop  66  within the cuff  64  causes the accordion material  62  to unfold by gravity downwardly. In the case of the transport batcher  44 , this action causes the sealing strip  68  at the lower edge of the bellows  60  to seal against the top closure surface of the storage bin  30 . In the case of the stationary batcher  46 , this same action causes the sealing strip  68  at the lower edge of the bellows  60  to seal against the cover plate  44   d  of the transport batcher  44 . 
     The upper end of each storage bin  30  is closed by a circular closure top  30   e  secured to the cylindrical portion  30   a . Positioned in the circular top  30   e  is a central opening  30   f  through which access is provided to the interior of the storage bin  30 . Mounted atop each of the storage bins  30  is a self-sealing closure door assembly referenced generally by the numeral  78  in  FIGS. 1-3 . Attention is next directed to  FIGS. 8-11  of the drawings for additional general details of the closure door assembly  78 . 
     As shown in  FIGS. 8 &amp; 9 , each door assembly  78  includes a housing formed from a short side wall  80  secured to the closure top  30   e  of the storage bin  30  on which is attached a top plate  82 . The top plate  82  includes a circular opening  84  fitted with a funnel  86  to register with the central opening  30   f  of the storage bin (see  FIGS. 4 &amp; 6 ). 
     Alternatively, for ease of fabrication and separate shipment as in the case of a retrofit for a storage bin, each door assembly  78  can include a bottom plate to which the short side wall  80  is attached, and then the bottom plate itself can be secured to the closure top  30   e  of the storage bin  30 . In such alternative construction, the bottom plate of the door assembly  78  includes a circular opening to register with the central opening  30   f  of the storage bin  30 . 
     Beneath the top plate  82  is housed a movable door assembly  88  carried on a pair of parallel tracks  90  mounted on the closure top  30   e  on opposite sides of the central opening  30   f  of the storage bin  30  as generally illustrated in  FIGS. 10 &amp; 11  with the top plate  82  removed.  FIG. 10  shows a top plan view with the movable door assembly  88  removed from the central opening  30   f  of the storage bin  30  while  FIG. 11  shows a side elevational view with the movable door assembly  88  sealed against the central opening  30   f.    
     Details of the construction and operation of the movable door assembly  88  are illustrated in  FIGS. 12-21 . A sealing door panel  92  is positioned between the tracks  90 . Attached to the upper surface of the door panel  92  on opposite sides thereof are a pair of spaced apart first and second pivot pins  94  &amp;  96  which extend outwardly from the door panel  92  toward but terminate short of the tracks  90 . Between each pair of pivot pins  94  &amp;  96  is a cylinder bracket  98  secured to the upper surface of the door panel  92 . One end of an extendable and retractable cylinder  100  is pivotally pinned to the cylinder bracket  98 . The opposite end of the cylinder  100  is pivotally pinned to one end of a first cam arm  102 . The opposite end of the first cam arm  102  is connected to a shaft  104  which extends over one of the tracks  90  and carries a rotatable v-groove wheel  106 . Intermediate the ends of the first cam arm  102 , between the pinned connection with the cylinder  100  and the connection with the shaft  104 , the first cam arm  102  pivotally receives the pivot pin  94  extending from the door panel  92 . 
     Also pivotally coupled to the connection between the cylinder  100  and the first cam arm  102  is one end of a linkage bar  108 . The opposite end of the linkage bar  108  is pivotally pinned to one end of a second cam arm  110  having the same configuration as the first cam arm  102 . The opposite end of the second cam arm  110  is connected to a shaft  112  which extends over one of the tracks  90  like shaft  104  and carries a rotatable v-groove wheel  114 . Intermediate the ends of the second cam arm  110 , between the pinned connection with the linkage bar  108  and the connection with the shaft  112 , the second cam arm  110  pivotally receives the pivot pin  96  extending from the door panel  92 . 
     Positioned alongside the tracks  90  are a pair of elongate, extendable and retractable cylinders  116 . One end of the cylinder  116  is pivotally pinned to a mounting bracket  118  secured to the short side wall  80  of the closure door assembly  78 . The opposite end of the cylinder is pivotally pinned to a bracket  120  attached to the sealing door panel  92  on the leading edge thereof. 
     Thus constructed, the cylinders  100  are adapted to move the sealing door panel  92  vertically up and down and the elongate cylinders  116  are adapted to move the door panel  92  horizontally on tracks  90  when the door panel  92  is elevated. 
     As shown in  FIGS. 15 &amp; 19 , the undersurface of the sealing door panel  92  is equipped with a compressible sealing gasket  122  around the perimeter of the door panel  92 . An upstanding lip  30   g  frames the central opening  30   f  of the storage bin  30  and is fitted with a u-shaped cushion strip  124  to mate with the sealing gasket  122 . The undersurface of the door panel  92  may also include an insulation layer  126 . 
     The sealed position is illustrated in  FIGS. 12-15 . With the elongate cylinders  116  fully extended, the door panel  92  is positioned above the central opening  30   f  of the storage bin  30  and registers with the frame of the upstanding lip  30   g . The cylinders  100  are fully retracted in the sealed position. Retraction of the cylinders  100  forces the first cam arm  102 , and also the second cam arm  110  through linkage bar  108 , in the direction of the leading edge of the door panel  92 . That is to say, both the first and second cam arms  102  &amp;  110  are forced to the left as viewed in  FIGS. 12-14 . This action causes both sets of pivot pins  94  &amp;  96  connected to the first and second cam arms  102  &amp;  110  to move downwardly to bias the sealing gasket  122  to engagement with the cushion strip  124  on the upstanding lip  30   g  to tightly seal the central opening  30   f  of the storage bin  30 . 
     Elevating the door panel  92  above its sealed position is illustrated in  FIGS. 16-19 . The cylinders  100  are actuated to fully extend. Extending the cylinders  100  forces the first cam arm  102 , and also the second cam arm  110  through linkage bar  108 , in a direction away from the leading edge of the door panel  92 . That is to say that both the first and second cam arms  102  &amp;  110  are forced to the right as viewed in  FIGS. 16-18 . This action causes both sets of pivot pins  94  &amp;  96  connected to the first and second cam arms  102  &amp;  110  to move upwardly and elevate the door panel  92  away from a position sealing the central opening  30   f  of the storage bin  30 . The elongate cylinders  116  pivot up slightly as the door panel is elevated which can be understood by comparing  FIGS. 13 &amp; 17 . 
     The retracted position is illustrated in  FIGS. 20-21 . With the door panel  92  elevated as shown in  FIGS. 16-19 , the elongate cylinders  116  are actuated to retract. This action pulls the door panel  92  away from registry with the central opening  30   f  of the storage bin  30  as the door panel  92  is carried by the v-groove wheels  106  &amp;  114  on the tracks  90  moving from left to right as viewed in  FIGS. 20-21 . 
     From the retracted position to the sealed position is simply the foregoing steps in reverse. The elongate cylinders  116  extend to push the door panel  92  carried by the v-groove wheels  106  &amp;  114  along the tracks  90  until the leading edge of the door panel  92  engages stop members  128  secured to the top closure  30   e . At this position, the door panel  92  registers with the upstanding lip  30   g  frame surrounding the central opening  30   f  of the storage bin  30 . After operation of the elongate cylinders  116 , then the cylinders  100  are retracted to lower the door panel  92  until the sealing gasket  122  is forcibly biased against the cushion strip  124  of the upstanding lip  30   g  to create a positive and effective closure seal of the central opening  30   f  of the storage bin  30 . 
     With a positive top seal to the storage bin  30 , an effective inerting system as schematically illustrated in  FIGS. 22-25  can be provided. In addition to the self-sealing closure door assembly  78  as previously described, the closure top  30   e  is equipped with a vent valve  130  and an oxygen sensor  132  to monitor the level of oxygen present in the interior of the storage bin  30  above the asphaltic mixtures  32  stored therein. A steam generator  134  is connected by a conduit  136  to the lower end of the frusto-conical portion  30   b  of the storage bin  30  for the delivery of steam thereto. A water supply  138  includes a conduit  140  for the delivery of water to the discharge gate  30   d  of the storage bin  30 . An electronic process controller  142  is connected to the oxygen sensor  132 , the steam generator  134  and optionally to the water supply  138 . The process controller  142  functions to operate initial deliver of steam from the steam generator  134  to the storage bin  30  through conduit  136 , to receive signals from the oxygen sensor  132  and to deliver steam from the steam generator  134  to the storage bin  30  if the oxygen level rises above a preselected level, and to initiate deliver of water  144  from the water supply  138  to the discharge gate  30   d  of the storage bin  30 . 
     During normally daily operations at an asphalt plant equipped with the asphalt distribution and storage system as previously described, the storage bin  30  as shown in  FIG. 22  can function with the opening and closing of the closure door assembly  78  to intermittently accept asphaltic mixtures  32  from the transport batcher  44  and to seal the top of the storage bin  30  to prevent emissions such as blue-smoke. Discharge gate  30   d  may be opened to dispense asphaltic mixtures  32  to trucks in the load-out area. 
     When prolonged periods of storage of the asphaltic mixtures  32  are contemplated, the first critical step is to activate the closure door assembly  78  to affect a positive seal over the central opening  30   f  of the storage bin  30 . Next, the process controller  142  causes the water supply  138  to deliver water  144  through conduit  140  to the discharge gate  30   d  in order to create a water seal around the central discharge mouth  30   c  of the storage bin  30 . This condition is illustrated in  FIG. 23  and effectively isolates the interior of the storage bin  30  from its outside environment. 
     Next, the process controller  142  causes the steam generator  134  to deliver steam through conduit  136  to the lower end of the storage bin. The vent valve  130  is opened. As the steam percolates up through the asphaltic mixtures  32 , the ambient atmosphere containing oxygen within the asphalt mixtures  32  and the interior volume of the storage bin  30  above the level of asphaltic mixtures  32  is displaced and vented through the vent valve  130 . This condition is illustrated in  FIG. 24 . 
     Thereafter, when the oxygen sensor  132  signals that the oxygen level within the storage bin  30  is below a preselected level, the vent valve  130  is closed and the storage bin  30  is secured for a prolonged period where oxidation of the asphaltic mixtures  32  is minimized. During such prolonged storage, the process controller  142  may continue to monitor the oxygen level sensed by the oxygen sensor  132  and may periodically cause the steam generator  134  to deliver additional steam to the interior of the storage bin  30  and to vent interior gases through vent valve  130  until inert conditions are restored within the storage bin  30 . 
     In operation, the multi-silo distribution and storage system receives asphaltic mixtures  32  from the production plant via the drag slat conveyor  34 . The asphalt mixtures  32  are first accumulated in the stationary batcher  46 . When the transport batcher  44  is aligned under the stationary batcher  46 , the clamshell gates of the stationary batcher  46  may be opened to discharge a load of asphaltic mixtures  32  to the transport batcher  44 . Opening of the clamshell gates  52  of the stationary batcher  46  automatically causes the bellows  60  mounted thereon to seal against the cover plate  44   d  of the transport batcher  44  to control blue-smoke emissions. 
     Once loaded and with its movable central doors  44   g  sealed, the transport batcher  44  can either remain in position at the first storage bin  30  over which the conveyor  34  is positioned, or travel on the rails  36  &amp;  40  to any preselected storage bin  30  in the bank of bins  30 . When positioned above a preselected bin  30 , the movable door assembly  88  associated with that bin  30  is operated to first elevated the sealing door panel  92  and to then horizontally move the door panel  92  away from the central opening  30   f  of the storage bin  30 . As the clamshell gates  52  of the transport batcher  44  open, the bellows  60  automatically deploys downwardly to seal against the top plate  82  of the closure door assembly  78  to control blue-smoke emissions. Once the load is transferred from the transport batcher  44  to the storage bin  30 , the movable door assembly  88  is again operated to first move the door panel  92  over the central opening  30   f  of the storage bin  30  and to then vertically move the door panel  92  downwardly to create a positive and continuous seal over the central opening  30   f . The transport batcher  44  can then be directed to return to the stationary batcher  46  on rails  36  &amp;  40  for another load. 
     It will be understood that during normal plant operations, trucks may drive into the load-out area beneath the bank of storage bins  30 . Once a truck is positioned under a bin  30 , its discharge gate  30   d  may be opened to deliver asphaltic mixtures  32  from the bin  30  to the truck. Such loading activities may go on continuously or sporadically throughout a normal work day. 
     When a prolonged period of storage is anticipated, such as overnight for example, the inverting system previously described can be implemented in order to control environmental emissions and to also protect the stored asphaltic mixtures  32  from oxidation. The storage bin  30  is effectively isolated with the fluid seal at the discharge mouth  30   c  and with the movable door assembly  88  sealing the top of the bin. 
     From the foregoing it will be seen that this invention is one well adapted to attain all the ends and objects hereinabove set forth, together with the other advantages which are obvious and which are inherent to the invention. 
     It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. 
     Since many possible embodiments may be made of the invention without departing from the scope thereof, it is understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.