US 4,230,534 AGranted

Control of a fractional distillation column

AssigneePhillips Petroleum Company

InventorWilliam S. Stewart

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Abstract

A control system is provided for a fractional distillation column where at least a portion of the overhead vapor stream from the fractional distillation column is utilized in a refrigeration and heating system for a process with which the fractional distillation column is associated. The liquid level is an overhead accumulator associated with the fractional distillation column is maintained at a level sufficient to insure that a sufficient supply of the overhead vapor stream from the fractional distillation column is available to supply the refrigeration and heating needs of the process with which the fractional distillation column is associated. Feedforward control based on the flow rate of the feed stream to the fractional distillation column and an analysis of the feed stream flowing to the fractional distillation column is utilized to maintain the desired liquid level in the overhead accumulator associated with the fractional distillation column even where fluctuations occur in the flow rate of the feed stream being provided to the fractional distillation column.

Claims32

Dependent claims

Apparatus comprising:

a fractional distillation column means;
first conduit means for passing a feed mixture into said fractional distillation column means;
second conduit means for passing a heating fluid into said fractional distillation column means to thereby supply at least a portion of the heat required to effect the separation of said feed mixture;
third conduit means for withdrawing said heating fluid from said fractional distillation column means;
fourth conduit means for withdrawing an overhead vapor stream from an upper portion of said fractional distillation column means;
means for condensing at least a portion of said overhead vapor stream;
accumulator means;
means for passing the resulting at least partially condensed overhead stream into said accumulator means;
fifth conduit means for withdrawing condensate from said accumulator means and for passing a first portion of the thus withdrawn condensate into an upper portion of said fractional distillation column means as an external reflux stream therefor and for passing a second portion of the thus withdrawn condensate as an overhead product stream;
means for establishing a first signal representative of the predicted flow rate of said overhead vapor stream at a time T.sub.1 ;
means for establishing a second signal representative of the percentage of said overhead vapor stream which can be removed from said accumulator means as said overhead product stream while still maintaining a desired liquid level in said accumulator means;
means for combining said first signal and said second signal to produce a third signal representative of the desired flow rate of said overhead product stream;
means for establishing a fourth signal representative of the highest allowable flow rate of said overhead product stream;
a low select means having at least first and second inputs and at least one output;
means for providing said third signal to the first input of said low select means;
means for providing said fourth signal to the second input of said low select means, the one of said third and fourth signals representative of the lowest flow rate of said overhead product stream being supplied as a fifth signal from the at least one output of said low select means;
and
means for manipulating the flow rate of said overhead product stream in response to said fifth signal.

15 more elements

A method for controlling a fractional distillation column comprising the steps of:

passing a feed mixture to be separated into said fractional distillation column;
passing a heating fluid into said fractional distillation column to thereby supply at least a portion of the heat required to effect the separation of said feed mixture;
withdrawing said heating fluid from said fractional distillation column;
withdrawing an overhead vapor stream from an upper portion of said fractional distillation column;
condensing at least a portion of said overhead vapor stream;
passing the resulting at least partially condensed overhead stream into an accumulator;
withdrawing condensate from said accumulator and passing a first portion of the thus withdrawn condensate into an upper portion of said fractional distillation column as an external reflux stream therefor and passing a second portion of the thus withdrawn condensate as an overhead product stream;
establishing a first signal representative of the predicted flow rate of said overhead vapor stream at a time T.sub.1 ;
establishing a second signal representative of the percentage of said overhead vapor stream which can be removed from said accumulator as said overhead product stream while still maintaining a desired liquid level in said accumulator;
combining said first signal and said second signal to produce a third signal representative of the desired flow rate of said overhead product stream;
establishing a fourth signal representative of the highest allowable flow rate of said overhead product stream;
providing the one of said third and fourth signals representative of the lowest flow rate of said overhead product stream as a fifth signal to a means for manipulating the flow rate of said overhead product stream to thereby control the flow rate of said overhead product stream in response to said fifth signal.

9 more elements

Dependencies are inferred from the claim text.