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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONThis application claims priority from Canadian Patent Application 2,677,479 filed 16 Sep. 2009 entitled HEAT AND WATER RECOVERY FROM OIL SANDS WASTE STREAMS, the entirety of which is incorporated by reference herein.FIELD OF THE INVENTIONThe present invention relates generally to recovery of heat and water from waste streams produced during oil sands extraction.BACKGROUND OF THE INVENTIONOil sands are deposits comprised of bitumen, clay, sand, and connate water, and make up a significant portion of North America's naturally-occurring petroleum reserves. To produce a marketable hydrocarbon product from the oil sands, the bitumen must be recovered from the oil sands matrix. Depending on geographic location, bitumen may be recovered by surface mining or in-situ thermal methods, such as steam assisted gravity drainage (SAGD), cyclic steam stimulation (CSS), vapor extraction process (VAPEX), liquid addition to steam for enhancing recovery (LASER) or ...

AI Technical Summary

Benefits of technology

It is therefore an object of the present invention to obviate or mitigate at least one disadvantage of known systems or methods.

In one aspect, there is provided methods and systems for treating tailings produced during oil sands extraction. 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 changing 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 the oil sands extraction process, thereby reducing the overall heat and water requirements.

Problems solved by technology

Because the bitumen itself is a highly viscous material, separating it from the extracted sands poses certain practical difficulties.

While effective, the extraction treatment processes require the use of significant quantities of water, and heat to raise the temperature of the water, which significantly increases the cost associated with recovery of petroleum from the bitumen-laden oil sands.

This tailings storage method is ineffective for at least three reasons: firstly, it is not very efficient, as a significant amount of time is required for most of the solid materials to settle out of the tailings by operation of gravity alone; secondly, it does not allow for the recovery of any of the large amount of energy contained within the tailings stream in the form of heat, which is significant, as tailings are initially sent to the ponds for storage at temperatures between 20 and 90° C.; thirdly, the resulting tailings ponds are voluminous, occupying a large footprint of land that cannot be used for any other purposes during the settling process.

There has been, however, a lack of success in effective water and energy recovery.

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