The TARCO process: For the surface extraction of tar sands

Of the various types of tar sand extraction processes under development, solvent extraction offers many significant advantages; e.g., the technology already exists, simplicity, less dependence on grade and source of ore, etc. The TARCO solvent extraction plant, located in Homer, Kentucky, is probably the largest such operation in the U.S. The plant was originally designed to use hexane as the extracting solvent, however, in the last year, it has switched to methylene chloride with minimal conversion cost. The TARCO process is very simple, utilizing screw conveyors through a series of tanks against a countercurrent flow of solvent. Extraction of the bitumen from the sands is rapid and complete. Sand drying studies indicate that solvent levels of 5-10 ppm can be obtained with a commercial oil seed desolventizer system at temperatures of 85°C. Bitumen recovery is carried out in a commercial vegetable oil flash distillation and stripper column. Residual solvent levels of 25 ppm can be achieved at temperatures of 260°F with steam stripping. The bitumen product is of low API gravity and extremely viscous. Its properties are very similar to the Athabasca bitumen of Canada, except it has a significantly lower sulfur content. Preliminary economics determined from the intermittent pilot plant runs carried out over the last two years, and based on a relatively low-grade feed (-5% bitumen), suggest a cost of approximately $20 per barrel. Optimization of the present process and use of a higher-grade ore, which is available, is expected to significantly reduce these costs.