Heat and Water Recovery From Oil Sands Waste Streams

Abstract

Methods and systems for recovering heat and water from waste streams produced during oil sands extraction to form dry, stackable tailings. A tailings stream is preheated in a heat exchanger, thereby reducing the energy required to dry the tailings. The preheated tailings are then dried, thereby reducing the tailings to dry stackable tailings or thickened tailings suitable for mine backfill. Heat and high-quality water are recovered from the drying operation and re-used in the preheat operation, or in other steps of oil sands extraction or treatment processes, thereby reducing the overall heat and water requirements.

1 . A method for treating a tailings stream produced during extraction of bitumen from oil sands, comprising:
 drying the tailings stream in a dryer using input steam in indirect thermal contact with the tailings stream to produce a dried tailings stream, whereby the input steam converts to a condensed water effluent; and   recycling steam produced from the dryer back into the dryer, wherein the input steam comprises (i) the recycled steam and make-up steam, or (ii) the recycled steam passed through a compressor, and optionally make-up steam.   
     
     
         2 . The method of  claim 1  further comprising, prior to drying the tailings stream, introducing the tailings stream into a heat exchanger to preheat the tailings stream and produce a preheated tailings stream which is then fed into the dryer. 
     
     
         3 . The method of  claim 2  wherein the preheating in the heat exchanger is by indirect contact with the condensed water effluent which is passed from the dryer. 
     
     
         4 . The method of  claim 2  wherein the heat exchanger is a self-cleaning heat exchanger. 
     
     
         5 . The method of  claim 1  wherein the input steam comprises the recycled steam and the make-up steam. 
     
     
         6 . The method of  claim 1  wherein the tailings stream comprises at least one of the following: coarse tailings, fine tailings, froth separation tailings, and tailings solvent recovery unit tailings. 
     
     
         7 . The method of  claim 6  wherein the fine tailings comprise a middling stream, flotation tailings, or mature fine tailings. 
     
     
         8 . The method of  claim 1  further comprising increasing a solid content of the tailings stream fed to the dryer by introducing a portion of the dried tailings stream into the tailings stream. 
     
     
         9 . The method of  claim 1  wherein the step of drying the tailings stream is carried out below atmospheric pressure, such that the boiling point of water is reduced, leading to a lower temperature of the dried tailings. 
     
     
         10 . The method of  claim 9  wherein the dryer pressure is controlled by an ejector, the ejector also serving to remove produced steam from the dryer, and to mix the steam produced from the dryer with make-up steam. 
     
     
         11 . The method of  claim 1  wherein the input steam comprises a combination of recycled steam and make-up steam passed through the compressor. 
     
     
         12 . The method of  claim 1  further comprising recovering at least one heavy mineral from the dried tailings stream. 
     
     
         13 . The method of  claim 12  wherein the at least one heavy mineral comprises zirconium oxide or titanium oxide. 
     
     
         14 . The method of  claim 1  further comprising mixing the dried tailings with a bypass stream of untreated tailings. 
     
     
         15 . The method of  claim 1  wherein the condensed water effluent from the dryer is processed in a separation step to recover condensed hydrocarbons. 
     
     
         16 . A system for treating a tailings stream produced during extraction of bitumen from oil sands, comprising:
 a dryer for receiving the tailings stream and input steam, drying the tailings stream using heat from the input steam, and producing a condensed water effluent; and   a steam recycling unit for recycling steam produced from the dryer back into the dryer, wherein the input steam comprises (i) the recycled steam and optionally make-up steam, or (ii) the recycled steam passed through a compressor, and optionally make-up steam.   
     
     
         17 . The system of  claim 16  further comprising a heat exchanger for receiving the tailings stream and the condensed water effluent from the dryer in indirect thermal contact with one another, and preheating the tailings stream using heat from the condensed water effluent, prior to drying. 
     
     
         18 . The system of  claim 16  further comprising an ejector for providing the input steam. 
     
     
         19 . The system of  claim 18  wherein the ejector is also for controlling a pressure environment in the dryer. 
     
     
         20 . The system of  claim 16  wherein the input steam comprises steam removed from the dryer and passed through a compressor, with make-up steam as required. 
     
     
         21 . The system of  claim 20  wherein the make-up steam is combined with the steam removed from the dryer before the compressor. 
     
     
         22 . The system of  claim 20  wherein the make-up steam is combined with the steam removed from the dryer after the compressor. 
     
     
         23 . The system of  claim 16  wherein the dryer comprises a shell for receiving the input steam and a cavity for receiving the preheated tailings stream, the shell and the cavity being distinct compartments in thermal communication with one another. 
     
     
         24 . The system of  claim 16  further comprising a mixer for adding a bypass stream of untreated tailings to dried tailings exiting the dryer. 
     
     
         25 . A method for treating a tailings stream produced during extraction of bitumen from oil sands, comprising:
 a) introducing the tailings stream and a flue gas into a first heat exchanger to preheat the tailings stream,   b) introducing the tailings stream into a second heat exchanger to preheat the tailing stream, wherein step a) is performed before step b) or step b) is performed before step a), to produce a preheated tailings stream,   c) drying the preheated tailings stream in a dryer using input steam in indirect thermal contact with the preheated tailings stream to produce a dried tailings stream, whereby the input steam converts to a condensed water effluent,   d) recycling steam produced from the dryer back into the dryer, wherein the input steam comprises (i) the recycled steam and optionally make-up steam, or (ii) the recycled steam passed through a compressor, and optionally make-up steam; and   e) passing the condensed water effluent from the dryer to the second heat exchanger to preheat the tailings stream.   
     
     
         26 . A system for treating a tailings stream produced during extraction of bitumen from oil sands, comprising:
 a first heat exchanger for receiving the tailings stream and a flue gas, and preheating the tailings stream using heat from the flue gas;   a second heat exchanger for receiving the tailings stream and a condensed water effluent and preheating the tailings stream using heat from the condensed water effluent, wherein the first or the second heat exchanger is placed upstream of the other;   a dryer for receiving the preheated tailings stream and input steam, heating the preheated tailings stream using heat from the input steam to produce a dried tailings stream, and producing the condensed water effluent used in the second heat exchanger; and   a steam recycling unit for recycling steam produced from the dryer back into the dryer, wherein the input steam comprises (i) the recycled steam and optionally make-up steam, or (ii) the recycled steam passed through a compressor, and optionally make-up steam.