Optimizing Feed Mixer Performance In A Paraffinic Froth Treatment Process (Exxonmobil Upstream Research Company)

CATEGORY: BITUMEN
PATENT
Optimizing Feed Mixer Performance In A Paraffinic Froth Treatment Process (Exxonmobil Upstream Research Company)
Publication number
US20120279824 A1
Application number
13/554,792
Publication date
Nov 8, 2012
Inventors
Michael F. Raterman
Arun K. Sharma
Original Assignee
Exxonmobil Upstream Research Company
US 20120279824 A1
Abstract
The invention relates to improved bitumen recovery processes and systems. One process provides for operation of a bitumen froth treatment plant at optimum shear rates in the feed pipe carrying the bitumen froth to the froth settling unit. Another process provides for optimizing the design of a bitumen froth treatment plant by optimizing the diameter of the feed pipe to impart an optimum shear rate to the bitumen froth mixture and further optimizing the volume of the feed pipe to impart an optimum residence time for the bitumen froth stream in the feed pipe. An optimal plant design is also disclosed, the plant including optimal diameter and volume of the feed pipe.
FIELD OF THE INVENTION
The present invention relates generally to producing hydrocarbons. More specifically, the invention relates to methods and systems for optimizing the performance of feed mixing devices in a solvent based froth treatment process.
BACKGROUND OF THE INVENTION
The economic recovery and utilization of heavy hydrocarbons, including bitumen, is one of the world's toughest energy challenges. The demand for heavy crudes such as those extracted from oil sands has increased significantly in order to replace the dwindling reserves of conventional crude. These heavy hydrocarbons, however, are typically located in geographical regions far removed from existing refineries. Consequently, the heavy hydrocarbons are often transported via pipelines to the refineries. In order to transport the heavy crudes in pipelines they must meet pipeline quality specifications.
The extraction of bitumen from mined oil sands involves the liberation and separation of bitumen from the associated sands in a form that is suitable for further processing to produce a marketable product. Among several processes for bitumen extraction, the Clark Hot Water Extraction (CHWE) process represents an exemplary well-developed commercial recovery technique. In the CHWE process, mined oil sands are mixed with hot water to create slurry suitable for extraction as bitumen froth.
The addition of paraffinic solvent to bitumen froth and the resulting benefits are described in Canadian Patents Nos. 2,149,737 and 2,217,300. According to Canadian Patent No. 2,149,737, the contaminant settling rate and extent of removal of contaminants present in the bitumen froth generally increases as (i) the carbon number or molecular weight of the paraffinic solvent decreases, (ii) the solvent to froth ratio increases, and (iii) the amount of aromatic and napthene impurities in the paraffinic solvent decreases. Further, a temperature above about 30 degrees Celsius (° C.) during settling is preferred.
One reason for processing the heavy hydrocarbon product in such a process is to eliminate enough of the solids to meet pipeline transport specifications and the specifications of the refining equipment. For example, the sediment specification of the bitumen product as measured by the filterable solids test (ASTM-D4807) may be used to determine if the product is acceptable. As such, a higher settling rate of solid particles including mineral solids and asphaltenes from the froth-treated bitumen is desirable.
One of the first steps in a bitumen froth treatment process is to introduce the bitumen froth to a settling tank, where a portion of the asphaltenes and mineral solids settle out of the froth. Stirred tanks and static mixers have been used in such settling tanks These are very low shear devices. They were used because it was thought that high shear in settling tanks was detrimental to settling and that low shear only impacted quantity of material precipitated, not the precipitation rate.
Methods to improve the settling rate of the minerals can significantly impact the efficiency of heavy hydrocarbon (e.g. bitumen) recovery processes. There exists a need in the art for a low cost method to produce bitumen which meets various sediment specifications.
SUMMARY OF THE INVENTION
In one aspect of the invention, a method of recovering hydrocarbons is provided. The method includes providing a bitumen froth emulsion containing solids, a feed pipe, and a settling unit; determining an optimum average shear rate for the bitumen froth emulsion; and imparting the optimum shear rate to the bitumen froth emulsion in the feed pipe before the bitumen froth emulsion enters the settling unit. The step of determining the optimum average shear may include measuring a solids concentration of the bitumen froth emulsion in the settling unit at a first average shear rate; adjusting the first average shear rate to an adjusted average shear rate; and repeating the measuring and adjusting steps until the solids concentration is at least below a design target for the bitumen froth emulsion.
In another aspect of the invention, a method of optimizing a bitumen treatment process is provided. The method includes determining an optimum average shear rate for a bitumen froth emulsion provided to a settling unit through a feed pipe; determining an optimum residence time in the feed pipe for the bitumen froth emulsion; calculating an optimum diameter of the feed pipe to impart the optimum shear rate to the bitumen froth emulsion; and calculating an optimum volume of the feed pipe to impart the optimum residence time to the bitumen froth emulsion. The step of determining an optimum shear rate may include measuring a solids concentration of the bitumen froth emulsion in the settling unit at a first average shear rate; adjusting the first average shear rate to an adjusted average shear rate; and repeating the measuring and adjusting steps until the solids concentration is at least below a design target for the bitumen froth emulsion.
In another aspect of the invention, a system for recovering hydrocarbons is provided. The system includes a bitumen stream having solids; a solvent stream; a mixing unit configured to mix the bitumen stream and the solvent stream to form a bitumen froth stream; and a feed pipe to receive the bitumen froth stream and provide the bitumen froth stream to a settling unit through a feed pipe inlet, the feed pipe having a diameter and a volume, wherein the diameter of the feed pipe is configured to induce an optimized shear rate to the bitumen froth stream to promote precipitation of solids.
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