Patent Publication Number: US-8535485-B2

Title: Apparatus and process for wet crushing oil sand

Description:
This application is a Continuation-in-Part of U.S. patent application Ser. No. 12/196,538, filed Aug. 22, 2008, which is a Continuation of U.S. patent application Ser. No. 10/932,019, filed Sep. 2, 2004 and now U.S. Pat. No. 7,431,830, issued Oct. 7, 2008, and this application further claims priority to U.S. Provisional Patent Application No. 61/112,619, filed Nov. 7, 2008. 
     The present invention relates to an apparatus and process for wet crushing oil sand to form a pumpable and pipelinable oil sand slurry without screening. 
    
    
     BACKGROUND OF THE INVENTION 
     Oil sand containing bitumen mined from the ground is generally slurried with a solvent such as water as part of an initial process for eventually removing the bitumen from the oil sand. Oil sand is a type of bitumen deposit typically containing sand, water and very viscous oil (the bitumen). When the oil sand deposit is located relatively close below the ground surface, the oil sand is often extracted from the deposit by mining. The oil sand is mined by excavating down through the ground surface to where the oil sand deposit occurs and removing oil sand from the deposit with heavy machinery. 
     Typically, this removal of the oil sand from the deposit is done with some of the largest power shovels and dump trucks in the world, with the power shovels removing shovel-loads of oil sand from the deposit and loading the collected oil sand onto conveyors to be carried away for further processing. 
     The viscous bitumen tends to hold the sand and water together causing the mined oil sand to contain lumps and chunks, some of which can be quite large. Because of the size of some of these pieces of mined oil sand, the mined oil sand is typically “pre-crushed” by running it through a preliminary crusher to crush the pieces of oil sand to a suitable size for transport on a conveyor (i.e. conveyable size). 
     The pre-crushed oil sand is then transported by conveyor to a slurry preparation unit as known in the art where the pre-crushed oil sand is further processed to form an oil sand and water slurry. 
     The slurry preparation unit has to ensure that the pieces of oil sand in the oil sand and water slurry are of pumpable size before the slurry is directed to a pump box and pump to be pumped to the next step in its processing, for example, hydrotransporting the slurry in a pipeline for further conditioning. Therefore, oversize pieces of oil sand or other materials have to be prevented from being directed to the pump in order to obtain a pumpable, pipelinable oil sand slurry. There are at least two forms of slurry preparation units that have been used to form the oil sand and water slurry; slurry preparation units that use screening and more recent screen-less slurry preparation units. 
     Slurry preparation units that use screening typically comprise a vertically stacked series of components. The pre-crushed oil sand is initially fed into a mixing box where water is mixed with the oil sand to form the slurry. From the mixing box, the oil sand and water slurry is passed through some sort of screening device to remove oversize from the oil sand and water slurry. The slurry that passes through the screening device passes into a pump box where it is pumped to the next stage of the process. The rejected oversize that does not pass through the screening device is rerouted to a crusher to be comminuted and then added to a secondary mix box and again mixed with water to form a slurry before this slurry is passed through another screening device. The portion of the slurry that passes through this other screening device is then returned to the main slurry components. The oversize rejects that do not pass through the second screening device are treated as rejects and removed from the system. The removed rejects are typically eventually hauled away by trucks and dumped in a discard area. 
     Screening devices commonly used in the industry include fixed screen devices; vibrating screen devices; and rotating screen devices. Fixed screen devices are simply one or more fixed screens that the slurry is pored through. They have the advantage of having a relatively high reliability because they do not have as many moving components as other screening device; however, they have lower efficiencies and tend to have higher rejects rates. Vibrating screens typically have a lower reject rate because the movement of the screens allows more material to pass through, however, because of their motion they tend to have lower reliability. Rotating screens can potentially have higher reliability and efficiency than vibrating screens, however, they are very complex requiring an extensive structure and typically have a lower throughput than vibrating screens. 
     Slurry preparation units that use screens have a disadvantage in that a portion of the oil sand passing through the slurry preparation units is rejected by the system. This rejection of a portion of the oil sand means that the bitumen in this rejected oil sand is lost, as it is not extracted at later process stages like the rest of the system. In some screening processes, the rejection rate can be as high as 8%. This rejection rate can add up to a significant amount of bitumen that is simply being thrown away. More recently, screen-less slurry preparation towers have been used such as the screen-less system described in U.S. Pat. No. 7,431,830. 
     Screen-less slurry preparation towers form all of the oil sand and other materials entering the slurry preparation tower into a slurry and as such avoid rejects. In particular, essentially all of the oil sand that enters the tower is typically comminuted in one or more stages to a pumpable size while water is being added to it to form a slurry. This allows bitumen to be extracted from essentially all of the oil sand delivered to the slurry preparation tower, thereby essentially eliminating rejects. 
     Occasionally, however, there may be instances where tramp metal inclusions in mined oil sand may pose a problem for these screen-less slurry preparation towers. Tramp metal is often a piece of metal from machinery used earlier in the process, such as a piece of shovel tooth from the power shovel or a piece of crusher tooth from the primary crusher. If this piece of tramp metal is large enough, when it is fed into the slurry preparation tower along with a portion of oil sand, the tramp metal may damage or even jam one of the roll crushers used in the slurry preparation tower. This may result in the entire process being stopped while the crusher rolls are either repaired or the jam is located and the tramp metal removed. This may lead to lengthy outages to remove the object from the crusher rolls and affect repairs if any damage has occurred. 
     The prior art screening processes will typically remove the tramp metal through the screening apparatus, However, with screen-less slurry preparation processes, it may be desirable to remove the tramp metal prior to crushing in the slurry preparation tower to avoid such outages. 
     SUMMARY OF THE INVENTION 
     In an aspect, a system for forming an oil sand slurry from mined oil sand is provided, comprising a slurry preparation tower comprising in series an intake opening through which oil sand enters the slurry preparation tower; a first sizer device operative to comminute oil sand passing through the first sizer to a first upper size threshold; a second sizer device operative to comminute oil sand passing through the second sizer to a second upper size threshold, wherein the second upper size threshold is less than the first upper size threshold; and a pump box for receiving oil sand that has passed through the second sizer and feeding it to a pump; at least one conveyor, having a discharge end, for transporting mined oil sand to the slurry preparation tower; a metal detector for detecting a piece of metal in the mined oil sand and transmitting a signal; and a metal rejection device operative to, in response to the signal from the metal detector, reject a portion of oil sand containing the piece of metal before the portion of oil sand enters the slurry preparation tower. 
     In another aspect, a method of forming a pumpable oil sand slurry is provided comprising the steps of providing at least one conveyor for delivering the mined oil sand to a slurry preparation tower, the slurry preparation tower having a first sizer and a second sizer; monitoring the mined oil sand being delivered by the at least one conveyor for a piece of metal and in response to locating the piece of metal, automatically removing a part of the oil sand containing the piece of metal prior to delivery to the slurry preparation tower; comminuting the oil sand in the first sizer to a first upper size threshold; comminuting the oil sand that has passed through the first sizer in the second sizer to a second upper size threshold that is less than the first upper size threshold; adding a solvent to the oil sand as it passes through the slurry processing tower; and pumping formed oil sand slurry out of the slurry preparation tower; whereby substantially all of the oil sand entering the slurry preparation tower exists the slurry preparation tower as oil sand slurry. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings wherein like reference numerals indicate similar parts throughout the several views, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the figures, wherein: 
         FIG. 1  is a schematic illustration of a process for forming a pumpable oils and water slurry; 
         FIG. 2  is a schematic illustration of the internal stages is a slurry preparation tower to form an oil sand and water slurry; 
         FIG. 3  is a schematic illustration of a variation of a slurry preparation tower using a mixing box; 
         FIG. 4  is a schematic illustration of a system, in a first aspect, for detecting a piece of metal in particulate oil sand being carried along a conveyor and rejecting a portion of the particulate oil sand containing the piece of metal; 
         FIG. 5  is a schematic illustration of a data processing system for use as a controller in one aspect; 
         FIG. 6  is a flowchart illustrating a method followed by the controller of  FIG. 5  to activate a metal rejection device in response to a signal that metal has been detected; 
         FIG. 7  is a schematic illustration of a process for forming a pumpable oil sand and water slurry wherein a surge bin is not used; 
         FIG. 8  is a schematic illustration of a system, in a further aspect, for detecting a piece of metal in particulate oil sand carried along a conveyor and rejecting a portion of the particulate oil sand containing the piece of metal, using a baffle wall; and 
         FIG. 9  is a schematic illustration of a data processing system for use as a controller in one aspect. 
     
    
    
     DESCRIPTION OF VARIOUS EMBODIMENTS 
     The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventors. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details. 
       FIG. 1  illustrates a process wherein oil sand is mined then processed to form an oil sand slurry ready for hydrotransport (pumpable oil sand slurry). Oil sand mined from an oil sand deposit  2  by a power shovel  4  is fed into a hopper  6  of a preliminary conveyor  8 . The preliminary conveyor  8  deposits a flow of the mined oil sand into a preliminary (or primary) crusher  10  that reduces the size of the mined oil sand to pieces of conveyable size (pre-crushed oil sand). From the preliminary crusher  10  the pre-crushed oil sand is fed to a transport conveyor  310 , using a loading conveyor  12 , where the particulate oil sand is transported along the transport conveyor  310  to a discharge end  312  of the transport conveyor  310 . At the discharge end  312  of the transport conveyor  310 , the pre-crushed oil sand is discharged through an intake opening  25  of a surge bin  20 , where it is eventually carried up a conveyor  110  and discharged into an intake opening  55  of the slurry preparation tower  50 . The slurry preparation tower  50  takes the flow of particulate oil sand discharging from a discharge end  112  of the conveyor  110  and processes the flow of particulate oil sand to form a pumpable oil sand slurry. 
       FIG. 2  is a schematic illustration of the internal components of the slurry preparation tower  50  used to form the oil sand into an oil sand and water slurry where the oil sand in the oil sand and water slurry is of pumpable size. 
     An apron feeder  40  is positioned below the discharge end  112  of the conveyor  110  with a first end  42  of the apron feeder  40  positioned over an intake opening  55  in the slurry preparation tower  50 . 
     The slurry preparation tower  50  has two comminuting stages implement with a first sizer  52  and a second sizer  54 . 
     The first sizer  52  is positioned below the first end  42  of the apron feeder  40  so that oil sand discharging off the first end  42  of the apron feeder  40  can drop directly downwards onto the first sizer  52 . The first sizer  52  comminutes the oil sand passing through the first sizer  52  to a first upper threshold size so that substantially all the pieces of oil sand that have passed through the first sizer  52  are no greater in size than the first upper threshold size. In one aspect, this first upper threshold size is approximately eight (8) inches so that substantially all of the pieces of oil sand that have passed through the secondary sizer  52  are eight (8) inches in size or less. 
     In one aspect, the first sizer  52  can include four (4) rotatable elements in the form of crusher rolls  81  having a generally cylindrical shape and positioned side-by-side, however, it is understood that any type of mineral sizer that is known in the art could be used for the first sizer  52 . Each of the crusher rolls  81  have a plurality of crusher teeth  82  to aid in comminuting large pieces of oil sand. The crusher rolls  81  are spaced a set horizontal distance apart to form gaps between adjacent crusher rolls  81 . The size of the gaps determines the first upper size threshold the secondary sizer  52  will size oil sand passing through the first sizer  52  to. 
     The second sizer  54  comminutes the oil sand passing through the second sizer  54  to a second upper threshold size. The second upper threshold size is smaller than the first upper threshold size. In this manner, the second sizer  54  reduces the size of the larger pieces of oil sand even more than the first sizer  52 . In one aspect, this second upper threshold size is approximately four (4) inches so that substantially all of the pieces of oil sand that have passed through the second sizer  52  are four (4) inches in size or less. 
     In one aspect, the second sizer  54  can include four (4) rotatable elements in the form of crusher rolls  91  positioned side-by-side, however, as previously mentioned, any type of mineral sizer known in the art could be used for the second sizer  54 . Each of the crusher rolls  91  have a plurality of crusher teeth  92  to aid in comminuting large pieces of oil sand. However, the gaps between adjacent crusher rolls  91  are smaller than the gaps between adjacent crusher rolls  81  of the first sizer  52 , so that the second sizer  54  comminutes material to a smaller size than the first sizer  54 . Additionally, the crusher teeth  92  on the crusher rolls  91  may be smaller and there may be more crusher teeth  92  on a crusher roll  91  than the number of crusher teeth  82  on the crusher rolls  81  of the first sizer  52 . 
     The second sizer  54  can be positioned directly below the first sizer  52  so that substantially all of the oil sand passing through the first sizer  52  drops unimpeded onto the second sizer  54 . 
     A first liquid outlet  62  is provided above the first sizer  52  so that a solvent, such as water, can be added to the oil sand as it falls onto the first sizer  52 . A second liquid outlet  64  is provided above the second sizer  54  but below the first sizer  52  so that a solvent, such as water, can be added to the oil sand passing out of the first sizer  52  as it drops to the second sizer  54 . In one aspect, each outlet can comprise one or more nozzles. 
     A pump box  70  is provided below the second sizer  54  so that oil sand that has passed through the second sizer  54  drops into the pump box  70 , where it can be pumped by one or more pumps  72  to the next stage in the process. 
     In operation, oil sand is discharged from the discharge end  112  of the conveyor  110  and onto the apron feeder  40 . In normal operation, the apron feeder  40  discharges the oil sand from the first end  42  of the apron feeder  40  through the intake opening  55  and drops it downwards towards the first sizer  52 . As the oil sand falls towards the first sizer  52 , a solvent, such as water, can be sprayed onto the falling oils sand using the first liquid outlet  62 , wetting the falling oil sand that contacts the first sizer  52 . 
     When the oil sand reaches the first sizer  52 , the oil sand is comminuted as it passes through the first sizer  52  to a size equal to or smaller than the first upper size threshold before the oil sand exits the first sizer  52  and drops towards the second sizer  54 . 
     Oil sand that has passed through the first sizer  52  falls downwards towards the second sizer  54 . As the oil sand falls towards the second sizer  54 , a solvent, such as water, can be sprayed onto the falling oils sand using the second liquid outlet  64 , wetting the falling oil sand that contacts the second sizer  54 . 
     The second sizer  54  comminutes the oil sand to a size equal to or smaller than the second upper size threshold before allowing the oil sand to pass through the second sizer  54 . 
     Oils sand that has passed through the second sizer  54  drops into the pump box  70  positioned below the second sizer  54  where the oil sand and water slurry will be pumped by the one or more pumps  72  to the next stage of the bitumen extraction process for further processing. 
     In this manner, substantially all of the oil sand that is introduced into the slurry preparation tower  50  through the intake opening  55 , exits the slurry preparation tower in an oil sand and water slurry to be transported to the next stage in its processing. All of the oil sand in the slurry has been reduced to a pumpable size and none of the oil sand is rejected from the slurry preparation tower to be hauled away and discarded. 
       FIG. 3  is a schematic illustration of a further aspect of the internal components of the slurry preparation tower  50  where a mixing box  75  is provided. A number of overlapping, downwardly inclined, descending shelves  76  are provided in the mixing box  76  to mix the oil sand and water slurry as it passes through the mixing box  75  before entering the pump box  70 . 
     In the slurry preparation tower  50  shown in  FIG. 2  and  FIG. 3 , substantially all of the oil sand that is introduced into the slurry preparation tower  50  through the intake opening  55 , is formed into a slurry and exits the slurry preparation tower as this slurry to be pumped to the next stage in its processing. All of the oil sand in the slurry has been reduced to a pumpable size and none of the oil sand is rejected from the slurry preparation tower to be hauled away and discarded. 
     Because all of the oil sand and any other materials that enter the slurry preparation tower pass through the first sizer device  52  and second sizer device  54 , it may at times be beneficial to detect pieces of metal in the oil sand that is being transported to the slurry preparation tower  50  and remove the detected pieces of metal before the pieces or metal are delivered to the slurry preparation tower  50 . 
       FIG. 4  is a schematic illustration of a system  100  in a first aspect. The system  100  supplies a flow of particulate oil sand to the slurry preparation tower  50 , where the oil sand will be further crushed and slurried with water to form a pumpable oil sand slurry for further processing. The system  100  comprises: a first conveyor  110 ; a redirecting device  105  including the apron feeder  40 ; a metal detector  140 ; and a control device  150 . 
     The first conveyor  110  transports a flow of particulate oil sand along a length of the first conveyor  110  towards a discharge end  112  of the first conveyor  110 . The discharge end  112  is provided generally above an intake opening  55  of the slurry preparation tower  50 . 
     The redirection device  105  includes the apron feeder  40 . The apron feeder  40  is provided below the discharge end  112  so that a flow of particulate oil sand being discharged from the discharge end  112  of the first conveyor  110  lands on the apron feeder  40 . The apron feeder  40  is bi-directional so that the second conveyor  120  can be driven to carry material along the apron feeder  40  either in a first direction, A, or a second direction, B. The apron feeder  40  is positioned so that particulate oil sand moved by the apron feeder  40  in the first direction, A, and discharged from a first end  42  of the apron feeder  40  will drop into the intake opening  55  of the slurry preparation tower  50 . A second end  44  of the apron feeder  40  is positioned so that particulate oil sand moved by the apron feeder  40  in the second direction, B, and discharged from the second end  44  of the second conveyor  120  will not fall into the intake opening  55  of the slurry preparation tower  50 . In an aspect, the second end  44  of the apron feeder  40  is positioned so that oil sand discharged off of the second end  44  of the apron feeder  40  falls to a ground surface,  41 , beside the slurry preparation tower  50 . 
     The metal detector  140  is positioned along the first conveyor  110  a travel distance, TD, from the discharge end  112  of the first conveyor  110 . The metal detector  140  can detect a piece of metal in the flow of particulate oil sand traveling along the first conveyor  110  past the metal detector  140 . 
     The controller  150  is operatively connected to the metal detector  140  and the apron feeder  40 . The controller  150  could be a computer, a programmable logic controller (PLC), etc. operative to receive and transmit signals to control the operation of the system  100 , such as the data processing device  800  shown in  FIG. 5 . The data processing device  800  includes a processor  810 , system buses  820 , memory  830  containing program instructions  840  and an I/O interface  850 . The processor  810  is a central processing unit that is typically microprocessor based to implement the program instructions  840  and control the operation of the data processing device  800 . The system buses  820  allow the transmissions of digital signals between the various components of the data processing device  800 . The memory  830  stores the operating system, data needed for the operation of the data processing device and the program instructions  840 . Typically, the memory  830  will contain RAM for data and an EPROM or Rom for storing the operating system and program instructions  840 . The I/O interface  850  allows for the connection to remote components to receive signals from remote components and transmit signals to the remote components. A person skilled in the art will appreciate that the data processing system  800  will also include components, such as a power supply, in addition to those illustrated in  FIG. 5 . 
     Referring again to  FIG. 4 , the controller  150  is operatively connected to the metal detector  140  so that the controller  150  can receive a metal detected signal from the metal detector  140  when the metal detector  140  detects a piece of metal in the flow of particulate oil sand traveling along the first conveyor  110 . The controller  150  is operatively connected to the apron feeder  40  so that the controller  150  can control the direction of the apron feeder  40 . In an aspect, the controller  150  is operatively connected to a speed sensing device  160 , such as a pulley mounted speed encoder, to obtain a speed of the first conveyor  110 . 
       FIG. 6  is a flowchart illustrating a method  200  used by the controller  150 , in  FIG. 2 , to control the system  100 . The method  200  comprises the steps of: determining a travel time  220 ; running a first timer  230 ; generating a reject signal  240 ; running a second timer  250 ; and triggering a resume signal  260 . 
     Referring to  FIGS. 4 and 6 , method  200  is started at step  210  when the controller  150  receives a metal detected signal from the metal detector  140 , indicating that a piece of metal has been detected in the flow of particulate oil sand traveling along the first conveyor  110 . 
     At step  220 , a travel time for the piece of metal detected by the metal detector  140  to reach the discharge end  112  is determined. The travel time is determined based on the travel distance, TD, of the metal detector  140  from the discharge end  112  of the first conveyor  110  and the operating speed of the first conveyor  110 . The travel distance, TD, provides the distance the piece of metal will have to travel after it has passed the metal detector  140  before it reaches the discharge end  112  of the first conveyor  110 . The operating speed of the first conveyor  110  indicates the speed at which the metal object and the oil sand are being carried along the first conveyor  110 . The operating speed of the first conveyor  110  could be obtained by the controller  150  by having the first conveyor  110  maintain a constant operating speed, however, because the travel distance, TD, can be quite long and the travel time relatively long (more than a minute) it might be desirable to obtain the operating speed of the conveyor belt  110  directly from the speed sensing device,  160 , or from a device controlling the speed of the first conveyor belt  110 . 
     At step  230 , the method  200  runs a first timer for a period of time equal to the travel time minus a buffer time. 
     At step  240 , after the first timer has been run, a reject signal is generated from the controller  150  to the apron feeder  40 . Step  240  is performed by the controller  150  after the first timer is run. The first timer runs for a period of time equal to the travel time determined at step  220 , for the piece of metal to reach the discharge end  112  of the first conveyor  110  less a buffer time. The buffer time is a short period of time used so that a reject signal is generated by the controller  150 , at step  240 , before the piece of metal is discharged from the discharge end  112  of the first conveyor  110 . The buffer time can allow enough time for the direction of operation of the apron feeder  40  to be reversed before the particulate oil sand containing the piece of metal falls onto the apron feeder  40 , so that the apron feeder  40  is already operating in the second direction, B, by the time the piece of metal lands on the apron feeder  40 . The buffer time can also be used to account for inaccuracies in the travel time determined at step  220  and delays in the transmission of the reject signal by increasing the buffer timer to have the reject signal transmitted earlier. 
     The travel time is use to determine when the piece of metal detected by the metal detector  140  has traveled along the first conveyor  110  to the discharge end  112  of the first conveyor  110 . Before the piece of metal is discharged off the discharge end  112  of the first conveyor  110 , the controller  150  transmits the reject signal to the apron feeder  40 . 
     When the apron feeder  40  receives the reject signal from the controller  150 , the apron feeder  40  reverses its direction of travel, moving material on the apron feeder  40  in the direction, B, carrying particulate oil sand discharged onto the apron feeder  40 , from the first conveyor  110 , off the second end  44  of the apron feeder  40  so that the oil sand does not fall into the intake opening  55  of the slurry preparation tower  50  and into the number of crusher rolls (not shown) contained in the slurry preparation tower  50 . 
     At step  250 , a second timer is run for a discharge time. The discharge time will be based on the length of the apron feeder  40  and the time required for particulate material landing on the apron feeder  40  from the first conveyor  110  to be carried off the second end  44  of the apron feeder  40  and how quickly the direction of operation of the apron feeder  40  can be reversed. Typically, this time is less than one (1) minute with times of ten (10) seconds or less being possible to reduce the time the flow of particulate oil sand is stopped. 
     After the second timer has run for the discharge time, the method  200  proceeds to step  260  and a resume signal is transmitted. The controller  150  generates a resume signal and transmits it to the apron feeder  40  causing the apron feeder  40  to once again change the direction and resume normal operation. The apron feeder  40  reverses the direction of travel from the second direction, B, back to the first direction, A, causing particulate oil sand discharged from the first conveyor  110  onto apron feeder  40  to once again be discharged off the first end  42  of the apron feeder  40  and into the intake opening  55  of the slurry preparation tower  50 . 
     With step  260  completed, the system  100  is once again operating under normal conditions delivering a flow of particulate oil sand to the slurry preparation tower  50  and the method  200  ends. 
     The method  200  will be invoked again if the metal detector  140  determines that there is another piece of metal in the particulate oil sand traveling along the first conveyor  110 . 
     In this manner, when the system  100  detects a piece of metal in the oil sand traveling along the first conveyor  110 , the system  100  approximates when the piece of metal will reach the discharge end  112  of the first conveyor  110  and be discharged from the first conveyor  110 . Shortly before the piece of metal is discharged off the first conveyor  110 , the direction of travel of the apron feeder  40  is reversed so that particulate oil sand on the apron feeder  40  is rejected from the system  100  by the apron feeder  40 . The reversal of direction of the apron feeder  40  discharges a portion of particulate oil sand off the second end  44  of the apron feeder  40 , preventing the portion of particulate oil sand from entering the slurry preparation tower  50 . During this time, the piece of metal is discharged off the discharge end  112  of the first conveyor  110 , onto the second conveyor  120 , where it is rejected from the system. After a relatively short period of time, sufficient for the portion of particulate oil sand containing the piece of metal to be discharged off the apron feeder  40 , the direction of the apron feeder  40  is once again reversed and oil sand discharged from the first conveyor  110  to the apron feeder  40  is once again fed into the intake opening  55  of the slurry preparation tower  50 . 
     Although a portion of the oil sand is rejected along with the piece of metal, the amount of time the flow of oil sand entering the slurry preparation tower  50  is halted is relatively short, only the short period of time for the piece of metal to be discharged off the end of the first conveyor  110  onto the apron feeder  40 , and then discharged off the second end  44  of the apron feeder  40 . This short period of time is based on the length of the apron feeder  40 . The shorter the apron feeder  40  and the faster the apron feeder  40  can change its direction of operation, the shorter the short period of time can be. 
     Because only the operation of the apron feeder  40  is affected, the first conveyor  110  can be operated at a constant speed of operation throughout the operation of the method  200 . Stopping the first conveyor  110  or even altering the speed of first conveyor  110  requires significantly more force and time than stopping or altering the direction of motion of the apron feeder  40  because of the greater inertia of the moving much larger conveyor belt of the first conveyor  110 . Once the first conveyor  110  is stopped, significant force is also required to get the first conveyor  110  back up to operating speed. This can significantly impact the slurrying of the oil sand, because the slurry preparation is a continuous process. This continuous process is affected by the slowing down of the first conveyor  110  because this alters the flow rate of particulate oil sand entering the slurry preparation tower  50 , which can result in variations in density of the resulting oil sand slurry. The process is also interrupted for the duration of the time the first conveyor  110  is stopped because there is no particulate oil sand entering the slurry preparation tower  50  while the first conveyor  110  has stopped operating. Finally, starting the first conveyor  110  up again, after the interruption, requires the first conveyor  110  to be accelerated back up to operating speed, which again requires some time, resulting in an uneven flow rate of particulate oil sand entering the slurry preparation tower  50  during this period, until the first conveyor  110  once again achieves operating speed. 
     Because the apron feeder  40  is significantly shorter than the first conveyor  110 , altering the speed of the apron feeder  40  is much easier, requiring much less force and time than the first conveyor  110  to bring the apron feeder  40  up to operating speed. Because the first conveyor  110  can be operated at a constant operating speed while the direction of the apron feeder  40  is reversed, the flow rate of particulate oil sand being discharged from the first conveyor  110  onto the apron feeder  40  remains constant, resulting in a more constant flow rate of particulate oil sand being delivered to the slurry preparation tower  50 . 
     In some aspects, the surge bin  20  may not be used.  FIG. 7  is a schematic illustration of a variation of a process for taking mined oil sand and forming an oil sand slurry from the mined oil sand. This process is similar to the process shown in  FIG. 1 , with the exception that the surge bin  20  and the conveyor  110  are not used. Instead, the transport conveyor  310  discharges directly into the intake opening  55  of the slurry preparation tower  50 . The system  100  shown in  FIG. 7  can be used with the transport conveyor  310 , when the transport conveyor  310  is discharging directly into the slurry preparation tower  50 . The metal detector  140  can be placed at a point along the length of the transport conveyor  310 . 
     With the transport conveyor  310  discharging directly into the slurry preparation tower  50 , the difference in size between the transport conveyor  310  and the second conveyor  120  is even greater. The transport conveyor  310  may be quite long in aspects where it has to carry particulate oil sand from a preliminary crushing stage to the slurry preparation tower  50 , while the second conveyor  120  is much shorter than the transport conveyor  310 . In some instances, the transport conveyor  310  can be five hundred (500) meters long or more, requiring more than a kilometer of conveyor belt. Because of this, the forces required to slow down and stop the transport conveyor  310  are much greater than those required to alter the direction of motion of the second conveyor  120 . Additionally, to once again get the transport conveyor  310  up to a desired operating speed after the transport conveyor  310  is stopped, significant force and time is required to accelerate the transport conveyor  310  back to the desired operating speed. These variations in speed and stopping time can significantly affect the slurrying process. 
     Referring again to  FIG. 1 , even when the surge bin  20  and the conveyor  110  are used, in some cases it may be desirable to reject a piece of metal from the transport conveyor  310 , rather than the conveyor  110 .  FIGS. 8 and 9  are schematic illustrations of a system  300  in a further aspect. Because the conveyor  310  does not discharge directly into the slurry preparation tower  50 , but rather into the surge bin  20 , system  300  has to be modified from system  100 , shown in  FIG. 4  to take into account this difference. The system  300  comprises: a first conveyor  310 ; a redirection device  305 , including a second conveyor  320  and a baffle wall  370 ; a chute  375 ; a metal detector  340 ; and a controller  150 . 
     The first conveyor  310  has a discharge end  312 . Particulate oil sand traveling along the first conveyor  310  is discharged from the first conveyor  310  at the discharge end  312  of the first conveyor  310 . 
     The redirection device  305  is provided at the discharge end  312  of the conveyor  310 . The second conveyor  320  is positioned below the discharge end  312  of the first conveyor  310 . The second conveyor  320  is bi-directional so that it can be operated in a first direction, A, or a second direction, B. A first end  322  of the second conveyor  320  is positioned so that material discharged from the first end  322  of the second conveyor  320 , when the second conveyor  320  is operating in the first direction, A, falls into the intake opening  25  of the surge bin  20 . The second end  324  of the second conveyor  320  is positioned so that material discharged from the second end  324  of the second conveyor  320  is discharged to the chute  375  and the chute  375  directs the material away from the intake opening  25  of the surge bin  20 . 
     The baffle wall  370  is positioned relative to the discharge end  312  and can be moved between a first position and a second position. In the first position, as shown in  FIG. 8 , the baffle wall  370  allows particulate oil sand being discharged from the discharge end  312  of the first conveyor  310  to fall into the intake opening  25  of the surge bin  20 , with any of the particulate oil sand falling on the second conveyor  320  being carried in the first direction, A, by the second conveyor  320 , until the particulate oil sand is discharged off the first end  322  of the second conveyor  320  into the intake opening  25  of the surge bin  20 . With the baffle wall  370  placed in the second position, as shown in  FIG. 9 , the baffle wall  370  deflects all of the particulate oil sand discharging from the discharge end  312  of the first conveyor  310  towards the second conveyor  320 . 
     Typically, a hydraulic cylinder  372  is used to move the baffle wall  370  between the first position and the second position. 
     The metal detector  340  is positioned a travel distance, TD, upstream from the discharge end  312  of the first conveyor  310 . The metal detector  340  can detect a piece of metal passing by the metal detector on the first conveyor  310 . 
     The controller  150  is operatively connected to the metal detector  340 , the baffle wall  370  (specifically the hydraulic cylinder  372 ), the second conveyor  320  and optionally a speed determining device  360 . 
     The controller  150  could be a computer, programmable logic controller, etc. operative to control the operation of the system  300 . The controller  150  is operatively connected to the metal detector  340  to receive metal detected signals from the metal detector  340  when the metal detector  340  detects a piece of metal passing the metal detector  340  on the first conveyor  310 . The controller  150  is operatively connected to the hydraulic cylinder  372  and the second conveyor  320  so that the controller  150  can transmit reject signals and resume signals to the hydraulic cylinder  372  and the second conveyor  320 . 
     In response to receiving a reject signal from the controller  150 , the second conveyor  320  reverses its direction of operation from the first direction, A, with the second conveyor  320  discharging into the intake opening  25  of the surge bin  20 , to the second direction, B and the hydraulic cylinder  372  moves the baffle wall  370  from the first position (shown in  FIG. 8 ) to the second position (shown in  FIG. 9 ). In this manner, particulate oil sand discharging from the first conveyor  310  is directed away from the intake opening  25  of the surge bin  20 , so that a portion of the particulate oil sand is prevented from entering the surge bin  20  and continuing through the process. 
     In response to receive a resume signal, the second conveyor  320  reverses its direction of operation back to the first direction, A, and the hydraulic cylinder  372  moves the baffle wall  370  back to the first position (shown in  FIG. 8 ) and the system  300  resumes normal operation, continuing to transport a flow of particulate oil sand to the slurry preparation tower  50 . 
     Referring to  FIGS. 6 ,  8  and  9 , the controller  150  uses the method  200  illustrated in  FIG. 3  to control the operation of the system  300  when a piece of metal is detected by the metal detector  340 . 
     Method  200  begins at step  210  when controller  150  receives a metal detected signal from the metal detector  340 . At step  220 , the controller  150  determines a travel time for the piece of metal to travel the travel distance, TD, along the first conveyor  310  from the metal detector  340  to the discharge end  312 . 
     Using the travel time determined at step  220 , the controller  150  runs a first timer for a timer period equal to the travel time minus a buffer time. When the first timer ends, a reject signal is generated and transmitted to the hydraulic cylinder  372  and the second conveyor  320  at step  240 . 
     Upon receiving the reject signal from the controller  150 , the hydraulic cylinder  372  is activated, moving the baffle wall  370  from the first position (as shown in  FIG. 8 ) to the second position (as shown in  FIG. 9 ). With the baffle wall  370  moved to the second position, particulate oil sand discharging from the discharge end  312  of the first conveyor  310  is deflected to the second conveyor  320 . When the second conveyor  320  receives the reject signal transmitted by the controller  150 , the direction of operation of the second conveyor  320  is reversed from the first direction, A, to the second direction, B, causing particulate matter landing on the second conveyor  320  to be moved in the second direction, B, and off the second end  324  of the second conveyor  320  into the chute  375 . 
     After step  240 , any particulate oil sand discharged from the discharge end  312  of the first conveyor  310  is deflected by the baffle wall  370  to the second conveyor  320 . Once on the second conveyor  320 , the oil sand is carried to the second end  324  of the second conveyor  320  where the chute  375  directs the particulate oil sand away from the intake opening  25  of the surge bin  20 . In this manner, the system  300  temporarily directs a portion of the particulate oil sand flow being discharged from the discharge end  312  of the first conveyor  310  away from the intake opening  25  of the surge bin  20 , removing this portion of oil sand containing a piece of metal from the process of creating an oil sand slurry and preventing the piece of metal contained within the portion of particulate oil sand flow from carrying on through later steps in the process. 
     At step  240 , the controller  150  runs a second timer for a discharge time and after the second timer has run for the discharge time, step  250  is performed and a resume signal transmitted by the controller  150  to the hydraulic cylinder  372  and the second conveyor  320 . Upon receiving the resume signal, the hydraulic cylinder  372  moves the baffle wall  370  from the second position (as show in  FIG. 9 ), where the baffle wall  370  is deflecting the particulate matter discharging from the discharge end  312  of the first conveyor  310  towards the second conveyor  320 , back to the first position (as shown in  FIG. 8 . The resume signal also causes the direction of operation of the second conveyor  320  to be once again reversed so that the direction of operation of the second conveyor  320  is once again in the first direction, A. With the baffle wall  370  back in the first position and the second conveyor  320  moving in the first direction, A, the system  300  is back operating in a normal fashion and oil sand discharged from the first conveyor  310  is eventually moved through the process to be contained in an oil sand slurry. After step  260 , method  200  ends. 
     In this manner, system  300  allows a portion of oil sand containing a piece of metal to be rejected from the system  300  preventing the metal from damaging components in the slurry processing tower  50 . 
     The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.