GB1221926A - Method of control of distillation columns - Google Patents

Abstract

1,221,926. Distillation columns; control. BRITISH PETROLEUM CO. Ltd. 25 Jan., 1968 [31 Jan., 1967], No. 4582/67. Heading BIB. [Also in Division C5] The continuous distillation of a multi-component feed mixture, such as crude petroleum, in a distillation column is automatically controlled to maintain the minimum allowable difference between the temperature of at least one liquid or vapour withdrawal stream from the column and a theoretical reference temperature (TRT), defined as the bubble point or dew point of a perfectly fractionated liquid or vapour cut, by measuring the temperature at the withdrawal point and operating the column so as to increase the amount of heat withdrawn from the column above the withdrawal point, if the temperature difference exceeds the minimum. As shown, the feed is introduced into column 1 through feedheater 13 and line 27, the flow of heating-medium being controlled by controller 11 and temperature-sensing device 12. A bottoms product is withdrawn from the column through line 28. The overhead vapour flows to condenser 2; and a portion of the condensate is withdrawn as overhead product through line 23, the remainder being refluxed to the column through line 22. A cooler (not shown) and lines 25, 26, provide a circulating reflux system below the withdrawal point 24, the flow in the circulating system is controlled by valve 19 and flow-controller, 17. The quantity of heat removed by the circulating reflux system is measured by device 18 which receives signals from temperature-sensing devices 14, 15 and a flow-measuring device 16. The temperature of the side-cut removed via line 24 is measured by device 7. The TRT is derived by a device 8 which receives information concerning the flow-rates of the feed and product streams from device 9. The difference between the withdrawal temperature and the TRT is calculated by device 10 which sends signals to either or both controller 11 and device 18. An increase in the temperature-difference increases the feed temperature and/or decreases the quantity of heat removed by the circulating reflux system. The temperature of the overhead vapour is measured by device 4 which sends a signal to the controller 5 of valve 6, so that an increase in the vapour-temperature causes the flow of top reflux supplied via line 22 to increase. In the distillation of crude petroleum, sidestreams comprising naphtha, kerosine, light gas oil, and heavy gas oil may be withdrawn from the column. The sidestreams may be steam-stripped, the stripper overheads being returned to the column; and steam-injection may be used in the main column.