公开(公告)号：US3905873A

公开(公告)日：1975-09-16

申请号：US40000073

申请日：1973-09-24

Applicant: STANDARD OIL CO OHIO

Inventor： WRIGHT ROBERT M ,  JOHNCOCK ALLAN W

IPC: B01D3/42 ,  C07D233/62 ,  C10G7/12

CPC classification number: B01D3/425 ,  Y10S203/08

Abstract: Our novel control apparatus optimizes the operation of a fractionation tower. A feed varying in composition flows into the tower at an uncontrolled, varying rate. This feed is distilled so that a portion of the feed is withdrawn from the tower as distillate and another portion is withdrawn from the tower as bottoms. A part of the distillate is returned to the top of the tower as reflux. The control apparatus includes a reflux controller for automatically controlling the rate at which reflux is returned to the tower, a pressure controller for automatically controlling the pressure within the tower, a distillate controller for automatically controlling the rate at which distillate is withdrawn from the tower, and a bottoms controller for automatically controlling the rate at which bottoms are withdrawn from the tower. As the feed flow rate and feed composition change, distillate and bottoms flow rates are changed in proportion to these changes in feed. A divider circuit, responding to the feed flow rate and feed composition changes, controls the distillate and bottoms flow controllers so that the distillate and bottoms flow rates and the ratio between these flow rates are such that product specifications are maintained despite variations in the feed flow rate and feed composition. An override circuit, responding to fluctuations in the liquid level in the tower, controls the material balance within the tower. When the liquid level is in danger of exceeding predetermined level limits, the override circuit terminates control of the bottoms controller by the divider circuit and controls the bottoms controller as a function of the liquid level until the liquid level is no longer in danger of exceeding the predetermined level limits. The control apparatus includes means calibrated to maintain the bottoms flow rate such that the liquid level is within the level limits, and calibration means which calibrate said calibrated means whenever the override circuit terminates the divider circuit''s control of the bottoms controller. The pressure controller maintains the tower pressure essentially constant, and it includes means for controlling the rate at which heat flows into the tower so that said heat flow rate is changed in response to any incipient pressure changes to maintain tower pressure essentially constant. The reflux controller includes means responsive to the reflux temperature for modifying the reflux flow rate as the reflux temperature deviates from a standard temperature. This reflux controller also includes means for establishing a maximum and minimum reflux flow rate. Preferably, the control apparatus also includes means for manually adjusting the ratio between the distillate and bottoms flow rates and for manually controlling the distillate and bottoms reflux and heat flow rates.