Staged settling process for removing water and solids from oils and extraction froth

摘要

Diluent-diluted bitumen froth containing bitumen and diluent hydrocarbons, water, sand and fines (collectively “dilfroth”) is fed into a gravity settler (‘splitter’) and temporarily retained to produce a bottom layer of tails comprising sand and middlings, a rag layer of discrete three-dimensional structures, each comprising hydrocarbons contained in a skin of fines, and a top layer of hydrocarbons containing small droplets of water and fines (‘raw dilbit’). The flux in the splitter is less than 6 m³/h of dilfroth fed per m² of horizontal cross-sectional rag area. The in-coming dilfroth is fed directly into the splitter middlings. Demulsifier is added to the overflow stream of raw dilbit and the mixture is subjected to prolonged settling in a polisher tank, to produce polished dilbit containing less than 1.0% water and 0.3% solids. The splitter underflow tails, containing less than 15% bitumen, is mixed with diluent to raise the diluent/bitumen ratio to 4 to 10 and is gravity settled in a scrubber. Scrubber overflow, mostly diluent containing residual bitumen stripped from the tails, is recycled to the splitter. In concept, the sand is first separated from the bitumen in the stripper. The substantially sand-free bitumen can then feasibly be treated with chemical and prolonged settling in the polisher to reduce water and fines contents to low levels. Bitumen lost in the splitter tails is recovered in the scrubber using a high concentration of diluent. The scrubber overflow of bitumen and diluent is recycled to the stripper to conserve diluent.