US 4,096,574 AGranted

Fractionation control

AssigneePhillips Petroleum Company

InventorDavid A. Christie

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Abstract

Control of a fractionation column is accomplished by manipulating the flow rate of the external reflux in response to a calculation of the internal reflux flow rate to maintain the actual flow rate of the internal reflux at a substantially constant, desired value. An improved method for calculating the internal reflux flow rate when the heats of vaporization of the external and internal reflux are different utilizes a constant, representative of the heat of vaporization of the external reflux divided by the heat of vaporization of the internal reflux, to obtain an accurate calculation of the internal reflux flow rate. Greater accuracy in the calculation yields improved control of the fractionation column. Alternatively, the constant, representative of the heat of vaporization of the external reflux divided by the heat of vaporization of the internal reflux, may be utilized to calculate the required flow rate of the external reflux necessary to maintain some desired internal reflux flow rate. Again, use of the described constant provides greater accuracy in the calculation and yields improved control of the fractionation column.

Claims24

Dependent claims

Apparatus comprising:

a fractionation column means;
conduit means for passing a feed mixture to be separated into said fractionation column means;
conduit means for withdrawing a bottom product from a lower portion of said fractionation column means;
conduit means for withdrawing a vapor stream from an upper portion of said fractionation column means;
condensing means for partially condensing said vapor stream;
accumulator means for phase-separating the thus partially condensed vapor stream;
conduit means for withdrawing uncondensed vapor from said accumulator means as an accumulator overhead product;
conduit means for withdrawing condensate from said accumulator means and for passing at least a portion thereof into an upper portion of said fractionation column means as external reflux therefor;
means for establishing a first signal T.sub.0 representative of the temperature of the said vapor stream at the top portion of said fractionation column means;
means for establishing a second signal T.sub.R representative of the temperature of the said external reflux;
means for establishing a third signal R representative of the flow rate of said external reflux;
means for establishing a fourth signal K representative of the value of the specific heat of said external reflux divided by the heat of vaporization of said external reflux;
means for establishing a fifth signal H.sub.R /H.sub.Ri representative of the value of the heat of vaporization of the said external reflux divided by the heat of vaporization of the internal reflux, said internal reflux being the reflux liquid flowing inside said fractionation column means;
means for establishing a sixth signal R.sub.id representative of the desired flow rate of said internal reflux;
and
means for establishing a seventh signal representative of the value +1;
means for producing, in response to said first, second, third, fourth, fifth, sixth and seventh signals, an eighth signal and for utilizing said eighth signal to manipulate the flow rate of said external reflux.

14 more elements

A method of controlling a fractionation zone, said method comprising:

passing a feed mixture to be separated into a fractionation zone;
withdrawing a bottom product from a lower portion of said zone;
withdrawing a vapor stream from an upper portion of said fractionation zone;
partially condensing said fractionation vapor stream;
phase-separating the thus partially condensed vapor in an accumulation zone;
withdrawing uncondensed vapor from said accumulation zone as a vaporous overhead product;
withdrawing condensate from said accumulation zone and passing at least a portion thereof into an upper portion of said fractionation zone as external reflux therefor;
establishing a first signal T.sub.0 representative of the temperature of said vapor leaving the top of said fractionation zone;
establishing second signal T.sub.R representative of the temperature of said external reflux entering said fractionation zone;
establishing a third signal R representative of the flow rate of said external reflux;
establishing a fourth signal K representative of the specific heat of said external reflux divided by the heat of vaporization of said external reflux;
establishing a fifth signal H.sub.R /H.sub.Ri representative of the value of the heat of vaporization of said external reflux divided by the heat of vaporization of the internal reflux;
establishing a sixth signal representative of the desired flow rate of the internal reflux;
establishing a seventh signal representative of the quantity +1;
and
establishing an eighth signal in response to said first, second, third, fourth, fifth, sixth, and seventh signals and controlling the flow rate of said external reflux in response to said eighth signal.

13 more elements

Dependencies are inferred from the claim text.