US 4,377,443 AGranted

Control of a fractional distillation process

AssigneePhillips Petroleum Company

InventorsLee Tuck, Frank W. Skraba

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Abstract

In a fractional distillation process in which a heating fluid and waste heat stream are utilized to supply heat to a fractional distillation column and in which the heat supplied from the waste heat stream is not controllable, control of the liquid level in the fractional distillation column is accomplished by manipulating the flow rate of the heating fluid so as to maintain a desired liquid level until such time as the flow rate of the heating fluid becomes zero at which time the flow rate of the external reflux to the fractional distillation column is manipulated to maintain a desired liquid level in the fractional distillation column. A switching of control of the liquid level provides a means by which an uncontrollable heat input may be provided to the fractional distillation column without losing control of the liquid level in the fractional distillation column.

Claims10

Dependent claims

Apparatus comprising:

a fractional distillation column;
means for passing a feed stream into said fractional distillation column;
means for withdrawing an overhead vapor stream from an upper portion of said fractional distillation column;
means for condensing at least a portion of said overhead vapor stream;
an accumulator;
means for passing the resulting at least partially condensed overhead stream into said accumulator;
means for withdrawing condensate from said accumulator, for passing a first portion of the thus withdrawn condensate into an upper portion of said fractional distillation column as an external reflux therefor and for passing a second portion of the thus withdrawn condensate as an overhead product stream;
means for withdrawing a bottoms product stream from a lower portion of said fractional distillation column;
means for supplying heat from a heating fluid stream to said fractional distillation column, wherein the heat supplied from said heating fluid stream is controllable;
means for supplying heat from a waste heat stream to said fractional distillation column, wherein the heat supplied from said waste heat stream is not controllable;
means for establishing a first signal which is responsive to the liquid level in the bottom of said fractional distillation column;
means for manipulating the heat supplied by said heating fluid stream in response to said first signal, if the amount of heat supplied by said waste heat stream to said fractional distillation column is not sufficient to supply all heat needed by said fractional distillation column, to thereby maintain a desired liquid level in the bottom of said fractional distillation column;
and
means for manipulating the flow rate of said external reflux in response to said first signal only if no heat is being supplied to said fractional distillation column by said heating fluid stream to thereby maintain a desired liquid level in the bottom of said fractional distillation column.

11 more elements

A method for controlling a fractional distillation process wherein an overhead vapor stream is removed from an upper portion of a fractional distillation column used in said fractional distillation process, wherein said overhead vapor stream is at least partially condensed with a first portion of the condensate being returned to an upper portion of said fractional distillation column as an external reflux and a second portion of said condensate being removed from said fractional distillation as an overhead product, wherein a bottoms product stream is withdrawn from a lower portion of said fractional distillation column, wherein heat is supplied from a heating fluid stream to said fractional distillation column, wherein the heat supplied from said heating fluid stream is controllable, wherein heat is supplied from a waste heat stream to said fractional distillation column and wherein the heat supplied from said waste heat stream is not controllable, said method comprising the steps of:

establishing a first signal which is responsive to the liquid level in the bottom of said fractional distillation column;
manipulating the heat supplied by said heating fluid stream in response to said first signal, if the amount of heat supplied by said waste heat stream to said fractional distillation column is not sufficient to supply all heat needed by said fractional distillation column, to thereby maintain a desired liquid level in the bottom of said fractional distillation column;
and
manipulating the flow rate of said external reflux in response to said first signal only if no heat is being supplied to said fractional distillation column by said heating fluid stream to thereby maintain a desired liquid level in the bottom of said fractional distillation column.

1 more element

Dependencies are inferred from the claim text.