Patent Publication Number: US-2005134102-A1

Title: Mine site oil sands processing

Description:
FIELD OF THE INVENTION  
      The present invention relates to a system, located at a mine site, for mining oil sand, slurrying it and desanding the slurry to produce a pipelineable stream of bitumen, fines and water.  
     BACKGROUND OF THE INVENTION  
      Oil sand from the Fort McMurray region of Alberta has now been commercially surface mined and processed for about 40 years, to extract and recover the contained bitumen.  
      The initial technique used can broadly be described as follows: 
          excavating oil sand;     crushing the as-mined oil sand, which contains large lumps and rocks, in stages, to a size which can be slurried and pumped;     mixing the crushed oil sand with heated water and, optionally, caustic or other process aids, to produce a slurry. In the course of mixing and subsequent pipelining, lumps are ablated, bitumen is liberated from the oil sand and is dispersed into the water phase, air bubbles are entrained and bitumen droplets coalesce and are aerated (the sum of these results is referred to as ‘conditioning’);     temporarily retaining the conditioned slurry under quiescent conditions in a large gravity separation vessel (referred to as the ‘PSV’)—during this separation or flotation step, the sand settles and is removed as an underflow, together with some bitumen and water, and the aerated bitumen, contaminated with water and solids, including fines, rises and is recovered as a froth;     optionally, withdrawing watery middlings from the PSV and treating the middlings in induced air flotation cells to recover contained bitumen as a contaminated froth while rejecting water and solids as an underflow;     processing the PSV underflow to recover contained bitumen as froth while rejecting water and solids (together with small amounts of contained residual bitumen) as an underflow;     discarding the various water and solids underflows as tailings into retention areas; and     combining and cleaning the froth streams in means such as centrifuges to remove residual water and solids and produce relatively clean bitumen ready for upgrading.        

      In selecting and developing the detailed steps, conditions and equipment units that embody this broadly described system, it needs to be appreciated that many factors have an influence in arriving at the final implementation. Some of these factors are: 
          The oil sand is erosive and tacky and the throughput of oil sand is large. A typical circuit or process line, involving process steps and equipment units, might process 8000 tonnes of oil sand per hour. So the equipment used needs to facilitate processing this scale of throughput of erosive, tacky material;     The oil sand contains clays that affect processing detrimentally and the composition of the oil sand varies on an on-going basis, particularly with respect to bitumen and clay contents. It is therefore desirable to provide a system that is amenable to oil sands blending;     The system involves a line of sequential equipment units and steps. Therefore, periodic upsets along the processing line can create problems both upstream and downstream. It follows that surge capabilities and inventory supply along the line are therefore desirable, together with the feasibility of bypassing units if required;     The mining operations can be remote from the gravity separation and cleaning process operations and this separation usually increases steadily as mining proceeds. So a system adapted to cope with on-going variation in separation is desirable;     The bitumen constitutes only a small fraction of the oil sand. The main component is sand. The sand is, of course, without value and thus there is incentive to separate it out of the slurry at the first opportunity and deposit it as fill in the mine pit. So a system which is amenable to this end is desirable; and     Of course it is desirable that the recovery of bitumen be maximized and the loss of bitumen with the tailings minimized.        

      In the early embodiments of these facilities, the as-mined oil sand was transported on belt conveyors from the mine sites to central processing plants. However, the conveyors, often stretching for miles, were expensive and difficult to operate. Later it was found feasible to crush and mix the oil sand with heated water at the mine site and then pump the resulting slurry through a pipeline directly to a remote PSV. Today, this type of operation is being implemented as new mining areas are developed. At the applicants&#39; facility, this scheme more specifically involves: 
          advancing a mobile shovel along the mine face to excavate oil sand and load it into large trucks which haul the as-mined oil sand some distance to a double roll crusher;     dumping the as-mined oil sand into a hopper feeding the double roll crusher, which crushes the oil sand to conveyable size (i.e. −24 inches);     delivering the crushed ore to a surge pile using a belt conveyor;     gravity feeding oil sand from the surge pile to another belt conveyor and delivering it to the top end of a mixer tower. The mixer tower incorporates a downwardly descending arrangement of a slurry mixer, a slurry screen and a pump box. In the course of moving down through the tower elements, the oil sand is mixed with heated water in the mixer to form the slurry and the slurry is then screened to remove oversize. The screened slurry is received in the pump box and the oversize is dumped on the ground for removal or is transferred to a secondary tower where similar operations are repeated on the oversize; and     then pumping the slurry in the pump box through a pipeline to a PSV located at a processing plant remote from the mine site.        

      However, the trucks constitute a significant portion of material handling cost and the distance they must travel becomes greater as the mine face moves away from the mixer tower.  
      Thus there exists a need for a different combination of processing steps and equipment units, which eliminates or reduces reliance on trucks and which can better cope with the gradual advance of the mine face.  
     SUMMARY OF THE INVENTION  
      The phrase “mine site”, as used herein, means an area of land presently undergoing strip mining to excavate oil sand and which has one or more mine faces and one or more tailings retention facilities, which may be dike-enclosed areas or mined-out pits.  
      The adjective ‘mobile’, as used herein, is intended to indicate that equipment is mounted on driven tracks or the like for on-going advancement over terrain.  
      The adjective ‘relocatable’, as used herein, is intended to indicate that equipment is of a transportable size and on skids or the like, or can be readily disassembled into transportable sections, whereby it is stationary when operating but it is feasible to periodically move it from location to location, perhaps every few months.  
      The term “unit”, as used herein, is intended to mean a single piece of equipment or an assembly of pieces of equipment, which functions to perform one or more defined steps such as crushing and/or mixing.  
      In accordance with one embodiment of the invention, a process line comprising a combination of operatively connected mobile and relocatable equipment units is provided at a mine site. The process line functions to excavate oil sand and produce a stream of pumpable, aerated, aqueous oil sand slurry. More particularly, the process line comprises: 
          a mobile excavating means for advancing along a mine face and excavating oil sand;     a mobile sizing means for advancing along behind the excavating means, receiving the oil sand and comminuting it to conveyable size;     a relocatable first conveyor means, preferably extending along the mine face, for receiving the once comminuted oil sand from the sizing means and conveying it to a slurry preparation location;     a relocatable slurry preparation means, at said location, for mixing the oil sand with heated water and producing a pumpable, aerated, aqueous oil sand slurry; and     a first pipeline means for receiving the slurry and pumping and transporting it while simultaneously conditioning it, whereby said means produces a stream of slurry amenable for desanding and delivers it to a desanding location.        

      In one preferred feature of this embodiment of the process line, a lengthy first conveyor means, extending along the mine face, permits the slurry preparation means to remain stationary for a period of time, while coupling it for oil sand supply with the mobile and advancing excavating and sizing means.  
      In another feature of this embodiment, the slurry is moved through a pipeline, while on the mine site, to condition it in preparation for desanding.  
      In another aspect of the described embodiment, a process is provided comprising the steps of: 
          excavating oil sand progressively along a mine face;     comminuting the oil sand to conveyable size;     conveying the comminuted oil sand along the mine face to a slurry preparation location on the mine site;     mixing the oil sand with heated water at the slurry preparation location and producing a pumpable, aerated, aqueous oil sand slurry; and     transporting the slurry through a pipeline from the slurry preparation location to a desanding location.        

      In an optional extension of the previously described process and process line, a relocatable desanding means is connected with the first pipeline means at the desanding location. The desanding means functions to receive the slurry and separate liquid and sand components of the slurry. It produces a desanded product, mainly consisting of bitumen, fines and water, and tailings, which mainly consists of sand, fines and water.  
      The desanding means preferably comprises a circuit of separators, arranged in series and operating countercurrently, wherein the underflow (or heavy fraction output) of one separator is fed to the next separator, the underflow of the last separator is tailings and the overflow (or lighter fraction output) of the first separator goes to a product pipeline, which transports it from the mine site, while the overflow of each following separator is recycled to the preceding separator.  
      It is a feature of the desanding circuit that subjecting separator underflow to secondary separation improves the probability of recovering contained bitumen.  
      The underflow of the last separator may be discarded into a dike-enclosed retention area or mined-out pit or otherwise processed as described below.  
      In a preferred embodiment, a plurality of such process lines are employed at the same mine site. As a consequence it is possible to transfer oil sand ore or slurry between process lines to cope with upsets or equipment repairs. 
    
    
     DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic showing the process line for excavating, conveying and preparing a pipelineable slurry;  
       FIG. 2  is a schematic showing the process line at a mine site having mineable oil sand and employing the steps of: excavating oil sand; conveying it; mixing it with water to form a slurry; transporting and conditioning the slurry; and desanding it to produce desanded product and tailings;  
       FIG. 3  is a schematic similar to  FIG. 2  but showing an inclined settler substituted for a cycloseparator in the desanding circuit;  
       FIG. 4  is a schematic showing a plurality of process lines at a mine site, wherein in one process line a bucket wheel excavator is substituted for a shovel, and further showing a tailings retention facility and a thickener for concentrating fine solids from the tailings;  
       FIG. 5  is a perspective view of a rotary digester, which may be used in the process line to form the slurry;  
       FIG. 6  is a view similar to  FIG. 5 , showing part of the drum wall broken away to display internal lifters;  
       FIG. 7  is a side view of a cycloseparator, which may be used in the desanding circuit showing the internal section of the vortex finder in dotted lines; and  
       FIG. 8  is a sectional side view showing an inclined settler. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      A process line  1  in accordance with the invention comprises a series of operatively connected processing units located at a mine site  2 . The mine site  2  is positioned on a body of mineable oil sand  3 , such as exists in the Fort McMurray region of Alberta. The mine site  2  has one or more mine faces  4 , a slurry preparation location  5 , a desanding location  6  and a tailings retention facility  7 . As the mine faces  4  advance, one or both of the locations  5 ,  6  will periodically advance as well. As shown in  FIG. 4 , a plurality of process lines  1  may be in use on the mine site  2 .  
      In the preferred embodiment (as shown in  FIGS. 1 and 2 ), each process line  1  comprises: 
          A mobile mining shovel  10 , which is mounted on driven tracks  11 . The shovel  10  is positioned at the mine face  4  for excavating the oil sand  3 . It is operative to advance along the mine face  4 . Otherwise stated, the shovel  10  provides mobile excavating means for advancing along the mine face  4  and excavating oil sand  3 ;     A mobile sizing unit  12  which comprises a surge bin  13 , an apron feeder  16 , a double roll crusher  14 , and a conveyor and belt wagon  15 . The sizing unit  12  is mounted on one or more platforms  17 , each supported on drive tracks  18 . 
            In operation the shovel  10  dumps oil sand  3  into the surge bin  13 . The apron feeder  16  feeds oil sand  3  from the bin  13  to the crusher  14 . The crusher  14  comminutes the excavated oil sand  3  to a size that is conveyable on a belt conveyor, for example to −24 inch. The feed conveyor  19  deposits the oil sand  3  onto the conveyor and belt wagon  15  which feeds the adjacent mine face conveyor belt  20 .     In summary, the sizing unit  12  provides mobile sizing means for advancing along behind the excavating means, receiving excavated oil sand and comminuting it to conveyable size;    
            An elongate, relocatable conveyor belt  20  which extends along the mine face  4 . The conveyor belt  20  receives the oil sand  3  from the feed conveyor  19  and conveys it to a surge pile  21  located at the slurry preparation location  5 . 
            In summary, a relocatable first conveyor means receives the oil sand  3  from the sizing means, conveys it to the slurry preparation location  5  and delivers it thereto;    
            A relocatable slurry preparation unit  25  positioned at the slurry preparation location  5 . The unit  25  comprises the surge pile  21 , a feed conveyor  26 , a hopper  27 , a feed conveyor  29 , a double roll crusher  30 , a feed conveyor  31 , a hopper  32 , a jet pump  33  and a source  34  of heated water. 
            In operation, oil sand  3  is fed from the surge pile  21  by the feed conveyor  26  into the hopper  27  and fed by the conveyor  29  to the crusher  30 . The sum of these actions is referred to collectively as utilizing the oil sand. The crusher  30  comminutes the oil sand to pumpable size, typically 4 inches. A conveyor  31  feeds the crushed oil sand  3  into the gravity feed hopper  32  of the jet pump  33 . The hopper  32  dispenses the oil sand  3  into the jet pump  33 , where it is entrained into a jet of motive heated water. A source  34  supplies the water to the jet pump  33 . The jet pump  33  mixes the oil sand  3  and water, while entraining air, to produce a pumpable, aerated, aqueous oil sand slurry  35 .     In summary, there is provided relocatable slurry preparation means, at the slurry preparation location  5 , for utilizing the oil sand  3  delivered thereto, further comminuting it to pumpable size and mixing it with heated water to produce a pumpable, aerated, aqueous oil sand slurry  35 ;    
            A slurry pipeline  40  which is connected with the outlet of the jet pump  33  and extends to the desanding location  41 . The pipeline  40  may include one or more slurry pumps  42 . 
            In the course of being pumped through the pipeline  40 , the slurry stream  35  is mixed and conditioned.     In summary, there is provided a first pipeline means, connected with the slurry preparation means, for receiving the slurry  35 , transporting it while simultaneously conditioning it, and delivering it to the desanding location  6  for desanding;    
            A relocatable desanding circuit  43 , which is positioned at the desanding location  6  and is connected with the downstream end of the slurry pipeline  40 . 
            The desanding circuit  43  comprises a series of countercurrently operating separators. More particularly, the separators used are centrifugal cycloseparators  44 ,  45 ,  46 , one of which is shown in  FIG. 7 . The cycloseparators  44 ,  45 ,  46  are, respectively, generally cylindrical, hollow vessels  47 , 48 ,  49  having internal chambers  50 ,  51 ,  52 , tangential inlets  53 ,  54 ,  55  at the upstream end and central vortex finder outlets  56 ,  57 ,  58  and peripheral outlets  59 ,  60 ,  61  at the downstream ends.     The slurry stream  35  is pumped from the pipeline  40  into the tangential inlet  53  of the first cycloseparator  44  (shown in  FIG. 2 ). The slurry spins as it advances longitudinally through the vessel chamber  50 . The heavier fraction (mainly sand, fines and some water and bitumen) concentrates outwardly and leaves the vessel chamber  50  as an underflow stream  62  through the peripheral outlet  59 . The lighter fraction (mainly bitumen, fines and water) concentrates inwardly and leaves the vessel chamber  50  as a central overflow stream  63  through the vortex finder outlet  56 . The first separator overflow stream  63  is fed as desanded product to a product pipeline  65  which transports it from the mine site  2  to a remote processing plant (not shown). The first separator underflow stream  62  is fed through outlet  59  and line  66  to the inlet  54  of the second separator  45 . The same type of centrifugal separation occurs in the second separator chamber  51 . The overflow stream  67  from the second separator chamber  51  is recycled through line  68  to the inlet  53  of the first cycloseparator  44 . The underflow stream  69  from the second cycloseparator  45  is fed through the line  70  to the inlet  55  of the third cycloseparator  46 . Water may also be added as required through line  71  to the inlet  55  of the third cycloseparator  46 , as the underflow stream,  69  may need dilution. The overflow stream  72  from the third cycloseparator  46  is recycled through line  73  to the inlet  54  of the second cycloseparator  45 . The underflow stream  74  from the third cycloseparator  46  is removed through the line  75  as tailings.     In summary, there is provided relocatable desanding means, at the desanding location and connected with the first pipeline means, for receiving the slurry and separating liquid and sand components of the slurry to produce separate streams of desanded product and tailings;    
            Means are provided for depositing the tailings at the retention facility  7  (see  FIG. 4 ). In the preferred embodiment, a mobile boom  80 , carrying a cyclone  81  at its upper end, is positioned alongside the retention facility. The line  74  feeds the stream  74  of tailings to the cyclone  81 , which separates the tailings components to produce an underflow stream  82 , mainly comprising sand and some water, and an overflow stream  83 , mainly comprising water and fine solids (clay). The underflow stream  82  is deposited on the beach  84  of the retention facility  7 . The overflow stream  83  is conveyed through a line  85  to a thickener  86 . The thickener  86  separates the cyclone overflow components to produce a paste-like underflow stream  87 , which is deposited in the mined out pit, and a water stream  88  which may be recycled to the desanding circuit  43 . 
 
 Variants 
       

      It is to be understood that applicants contemplate that a person skilled in the art may substitute units without significantly affecting the way in which the process line  1  works.  
      For example: 
          A bucketwheel excavator  90 , shown in  FIG. 4 , may be substituted for the shovel  10 ;     A rotary digester  91 , shown in  FIGS. 5, 6 , may be substituted for the jet pump  33 . The digester  91  is capable of processing larger lumps of oil sand and thus may not require a secondary crusher  30 . 
            The digester  91  is a rotatable drum  92  having internal lifters  93 , drive means  94  and a trommel screen  95 . The oil sand and water are fed into a feed box  96  and are tumbled within the drum  92  to mix them and condition the produced slurry. The screen  95  removes oversize and the screened slurry is pumped through pipeline  40  by pump  97 ; and    
            an inclined plate separator  100 , shown in  FIG. 8 , may be substituted for a cycloseparator.        

      The slurry is fed into the bottom inlet  99  of the separator  100  from pipeline  40 . The sand separates and drops along the internal plates  101  and is withdrawn through the outlet  102 . The water, some bitumen and fine solids leave through the top outlet  103 .  
      The scope of the invention is defined by the claims now following.