Method for extracting bitumen from an oil sand stream (Shell)

CATEGORY: BITUMEN 
Method for extracting bitumen from an oil sand stream (Shell)

Type	Patent
Inventor	Ingmar Hubertus Josephina Ploemen
Inventor	Gerhardus Willem Colenbrander
Inventor	Anjana Kalpesh BHALODI
URL	Free Full Text Source:  http://www.google.com/patents/US20140083332
Assignee	Shell Canada Energy,
Patent Number	US20140083332 A1
Issue Date	Mar 27, 2014
Abstract	The present invention provides a method for extracting bitumen from an oil sand stream, the method comprising at least the steps of, a) providing an oil sand stream; b) contacting the oil sand stream with a liquid comprising a solvent to obtain a solvent-diluted oil sand slurry; c) separating the oil sand slurry to obtain a first solids-depleted stream and a first solids-enriched stream; d) filtering the first solids-enriched stream obtained in step c) to obtain bitumen-depleted sand and at least a first filtrate; e) separating at least a part of the first filtrate to obtain a second solids-depleted stream and a second solids-enriched stream; and f) contacting at least a part of the second solids-enriched stream from step e) with solvent to obtain a solvent-diluted second solids-enriched stream; and g) separating the solvent-diluted second solids-enriched stream to obtain a third solids-enriched stream and a third solids-depleted stream. BACKGROUND The present invention relates to a method for extracting bitumen from an oil sand. Various methods have been proposed in the past for the recovery of bitumen (sometimes referred to as “tar” or “bituminous material”) from oil sands as found in various locations throughout the world and in particular in Canada such as in the Athabasca district in Alberta and in the United States such as in the Utah oil sands. Typically, oil sand (also known as “bituminous sand” or “tar sand”) comprises a mixture of bitumen (in this context also known as “crude bitumen”, a semi-solid form of crude oil; also known as “extremely heavy crude oil”), sand, clay minerals and water. Usually, oil sand contains about 5 to 25 wt. % bitumen (as meant according to the present invention), about 1 to 13 wt. % water, the remainder being sand and clay minerals. As an example, it has been proposed and practiced at commercial scale to recover the bitumen content from the oil sand by mixing the oil sand with water and separating the bitumen froth from the aqueous slurry formed. Disadvantages of such aqueous extraction processes are the need for extremely large quantities of process water (typically drawn from natural sources) and issues with removing the bitumen from the aqueous phase (whilst emulsions are being formed) and removing water from the bitumen-depleted sand (and clay). Other methods have proposed non-aqueous extraction processes to reduce the need for large quantities of process water. Example of such a non-aqueous extraction process are disclosed in e.g. U.S. Pat. No. 3,475,318, US 2009/0301937 and WO 2011/021092, the teaching of which is hereby incorporated by reference. There is a continuous desire to improve the process efficiency in methods for extracting bitumen from an oil sand stream. It is an object of the present invention to meet this desire and to provide a more efficient method for extracting bitumen from an oil sand stream. It is a further object of the present invention to provide an alternative non-aqueous solvent based extraction process for extracting bitumen from an oil sand. One or more of the above or other objects may be achieved according to the present invention by providing a method for extracting bitumen from an oil sand stream, the method comprising at least the steps of: (a) providing an oil sand stream; (b) contacting the oil sand stream with a liquid comprising a solvent thereby obtaining a solvent-diluted oil sand slurry; (c) separating the solvent-diluted oil sand slurry, thereby obtaining a first solids-depleted stream and a first solids-enriched stream; (d) filtering the first solids-enriched stream obtained in step (c), thereby obtaining bitumen-depleted sand and at least a first filtrate; (e) separating at least a part of the first filtrate thereby obtaining a second solids-depleted stream and a second solids-enriched stream; and (f) contacting at least a part of the second solids-enriched stream as obtained in step (e) with solvent thereby obtaining a solvent-diluted second solids-enriched stream; and (g) separating the solvent-diluted second solids-enriched stream thereby obtaining a third solids-enriched stream and a third solids-depleted stream. It has now surprisingly been found according to the present invention that bitumen can be extracted from an oil sand stream in a surprisingly efficient and simple manner. A further advantage of the present invention is that no tailings ponds are required because no water needs to be used in the bitumen extraction process. Also, by further processing the second solids-enriched stream as obtained in step (e), more bitumen is recovered thereby increasing the overall bitumen recovery of the extraction process. According to the present invention, the providing of the oil sand in step (a) can be done in various ways. Typically, before contacting the dry oil sand (which may contain some water being present in the oil sand) with the solvent the oil sand lumps are reduced in size, e.g. by crushing, breaking and/or grinding, to below a desired size upper limit. Experience in large scale operations shows that the achievable size upper limit for such size reduction is currently about 8 inch. The contacting in step (b) of the oil sand with the liquid comprising a solvent thereby obtaining a solvent-diluted oil sand slurry is not limited in any way either. As an example, the liquid may be added before, during or after the size-reducing step (if available) of the oil sand. Further size reduction in the presence of the liquid (comprising the solvent) may be performed; part of the size reduction may take place by dissolution of bitumen present in the oil sand (bitumen acts as a bonding agent for the oil sand lumps), but further size reduction e.g. by using screens and/or again crushers, breaker or grinders may be performed, if desired. Typically, the solvent forms the major part of the liquid and is preferably present in an amount of from 40 wt. % up to 100 wt. %, preferably above 60 wt. %, more preferably above 70 wt. %, even more preferably above 80 or even above 90 wt. %, based on the amount of the liquid. The liquid may contain some solids, for example if the liquid is recycled from a downstream part of the process. The solvent as used in the method of the present invention may be selected from a wide variety of solvents, including aromatic hydrocarbon solvents and saturated or unsaturated aliphatic (i.e. non-aromatic) hydrocarbon solvents; aliphatic hydrocarbon solvents may include linear, branched or cyclic alkanes and alkenes and mixtures thereof. Preferably, the solvent in step (b) is a non-aqueous solvent and preferably comprises an aliphatic hydrocarbon having from 3 to 9 carbon atoms per molecule, more preferably from 4 to 7 carbons per molecule, or a combination thereof. Especially suitable solvents are saturated aliphatic hydrocarbons such as propane, butane, pentane, hexane, heptane, octane and nonane (including isomers thereof), in particular butane, pentane, hexane and heptane. It is preferred that the solvent in step (b) comprises at least 90 wt. % of the aliphatic hydrocarbon having from 3 to 9 carbon atoms per molecule, preferably at least 95 wt. %. Also, it is preferred that in step (b) substantially no aromatic solvent (such as toluene or benzene) is present, i.e. less than 5 wt. %, preferably less than 1 wt. %. Further it is preferred that a single solvent is used as this avoids the need for a distillation unit or the like to separate solvents. Also it is preferred that no water is added during the contacting in step (b). However, the oil sand may intrinsically contain some water; preferably the solvent-diluted slurry comprises less than 15 wt. % water, preferably less than 10 wt. %.