Means for controlling a solvent refining unit

A control system for a solvent refining unit which treats charge oil with a solvent in a refining tower to yield raffinate and extract-mix, strippers separate the solvent from the raffinate and extract-mix to provide refined waxy oil and extract oil, respectively, the solvent is returned to the tower and the refined waxy oil is subsequently dewaxed to provide refined oil, comprising temperature sensing means for sensing the temperature of the extract-mix in the refining tower and providing a signal T.sub.P corresponding thereto;

• charge oil sensing means for sensing the flow rate of the charge oil and providing a corresponding signal CHG.sub.p ;
• extract oil sensing means for sensing the flow rate of the extract oil and providing a signal EO.sub.P representative thereof;
• solvent sensing means for sensing the flow rate of the solvent and providing a signal S.sub.P corresponding thereto;
• signal means connected to all the sensing means for providing signals T.sub.D, CHG.sub.D and S.sub.D corresponding to a desired temperature for the extract mix in the refining tower, to a desired flow rate for the charge oil and to a desired flow rate for the solvent in accordance with signals CHG.sub.P and T.sub.P and EO.sub.P so as to operate the refining unit to achieve either a maximum allowable flow rate for the solvent, or a maximum allowable flow rate for the extract oil or a maximum allowable refined oil flow rate or a reduced charge oil flow rate for a fixed refined oil flow rate;
• and control means connected to the signal means for controlling the charge oil flow rate, the refining tower extract mix temperature and the solvent flow rate in accordance with signals CHG.sub.D, S.sub.D and T.sub.D.