Control system for an N-methyl-2-pyrrolidone refining unit receiving light sour charge oil

A refining unit treats light sour charge oil with N-methyl-2-pyrrolidone solvent, hereafter referred to as MP, in a refining extractor to yield raffinate and extract mix. The MP is recovered from the raffinate and from the extract mix and returned to the refining extractor. A system controlling the refining unit includes a gravity analyzer, a sulfur analyzer and viscosity analyzers; all sampling the light sour charge oil and providing corresponding signals. Sensors sense the flow rates of the charge oil and the MP flowing into the extractor and the temperature of the extract mix and provide corresponding signals. One of the flow rates of its light sour charge oil and the MP flow rates is controlled in accordance with the signals from all the analyzers and all the sensors, while the other flow rate of the light sour charge oil and the MP flow rates is constant.