US4526657A — Control of a fractional distillation process

Claim 1

Independent Claim 557 words

Apparatus comprising: a fractional distillation column; means for passing a feed mixture containing at least first and second components into said fractional distillation column; means for passing a heating fluid to said fractional distillation column; means for withdrawing an overhead vapor stream, having an increased concentration of said first component with respect to the concentration of said first component in said feed mixture, 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said accumulator; means for withdrawing condensate from said accumulator and for passing a first portion of the thus withdrawn condensate into an upper portion of said fractional distillation column as an external reflux stream therefor and for passing a second portion of the thus withdrawn condensate as an overhead product stream; means for withdrawing a bottoms product stream, having an increased concentration of said second component with respect to the concentration of said second component in said feed mixture, from a lower portion of said fractional distillation column; means for establishing a first signal which is representative of the concentration of said first component in said bottoms product stream; means for establishing a second signal representative of the concentration of said second component in said overhead product stream; means for establishing a first control signal representative of the desired flow rate of said external reflux stream, wherein said first control signal is periodically increased or decreased by a fixed increment or left unchanged depending upon the relationship between the actual concentration of said first component in said bottoms product stream as represented by said first signal and a high limit and low limit for the actual concentration of said first component in said bottoms product stream and depending upon the relationship between the actual concentration of said second component in said overhead product stream as represented by said second signal and high and low limits for the actual concentration of said second component in said overhead product stream; means for manipulating the flow rate of said external reflux in response to said first control signal so as to maintain the actual external reflux flow rate substantially equal to the desired external reflux flow rate as represented by said first control signal; means for establishing a second control signal representative of the desired temperature at a selected point in said fractional distillation column, wherein said second control signal is periodically increased or decreased by a fixed increment or is left unchanged depending upon the relationship between the actual concentration of said first component in said bottoms product stream as represented by said first signal and said high and low limits for the actual concentration of said first component in said bottoms product stream and depending upon the relationship between the actual concentration of said second component in said overhead product stream as represented by said second signal and said high and low limits for the actual concentration of said second component in said overhead product stream; and means for manipulating the flow rate of heat to said fractional distillation column in response to said second control signal so as to maintain the actual temperature at said selected point substantially equal to the desired temperature represented by said second control signal.

Claim 2

Dependent Claim 557 words

Apparatus comprising: a fractional distillation column; means for passing a feed mixture containing at least first and second components into said fractional distillation column; means for passing a heating fluid to said fractional distillation column; means for withdrawing an overhead vapor stream, having an increased concentration of said first component with respect to the concentration of said first component in said feed mixture, 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 and for 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 for passing a second portion of the thus withdrawn condensate as an overhead product stream; means for withdrawing a bottoms product stream, having an increased concentration of said second component with respect to the concentration of said second component in said feed mixture, from a lower portion of said fractional distillation column; means for establishing a first signal which is representative of the concentration of said first component in said bottoms product stream; means for establishing a second signal representative of the concentration of said second component in said overhead product stream; means for establishing a first control signal representative of the desired flow rate of said external reflux stream, wherein said first control signal is periodically increased or decreased by a fixed increment or left unchanged depending upon the relationship between the actual concentration of said first component in said bottoms product stream as represented by said first signal and a high limit and low limit for the actual concentration of said first component in said bottoms product stream and depending upon the relationship between the actual concentration of said second component in said overhead product stream as represented by said second signal and high and low limits for the actual concentration of said second component in said overhead product stream; means for manipulating the flow rate of said external reflux in response to said first control signal so as to maintain the actual external reflux flow rate substantially equal to the desired external reflux flow rate as represented by said first control signal; means for establishing a second control signal representative of the desired temperature at a selected point in said fractional distillation column, wherein said second control signal is periodically increased or decreased by a fixed increment or is left unchanged depending upon the relationship between the actual concentration of said first component in said bottoms product stream as represented by said first signal and said high and low limits for the actual concentration of said first component in said bottoms product stream and depending upon the relationship between the actual concentration of said second component in said overhead product stream as represented by said second signal and said high and low limits for the actual concentration of said second component in said overhead product stream; and means for manipulating the flow rate of heat to said fractional distillation column in response to said second control signal so as to maintain the actual temperature at said selected point substantially equal to the desired temperature represented by said second control signal.

Claim 3

Dependent Claim 187 words

Apparatus in accordance with claim 1 wherein said first control signal and said second control signal are changed based on the relationship of said first signal (ACB) to the high (HL1) and low (LL1) limits for the actual concentration of said first component in said bottoms product stream and the relationship of said second signal (ACO) to the high (HL2) and low (LL2) limits for the actual concentration of said second component in said overhead product stream as follows: ______________________________________ Relationship Control Signals First Signal Second Signal First Second ______________________________________ ACB < LL1 ACO < LL2 no de- change crease ACB < LL1 LL2 ≦ ACO ≦ HL2 decrease de- crease ACB < LL1 ACO > HL2 decrease no change LL1 ≦ ACB ≦ HL1 ACO < LL2 increase de- crease LL1 ≦ ACB ≦ HL1 LL2 ≦ ACO ≦ HL2 no no change change LL1 ≦ ACB ≦ HL1 ACO > HL2 decrease in- crease ACB > HL1 ACO < LL2 increase no change ACB > HL1 LL2 ≦ ACO ≦ HL2 increase in- crease ACB > HL1 ACO > HL2 no in- change crease ______________________________________

Claim 4

Dependent Claim 144 words

Apparatus in accordance with claim 1 wherein said means for manipulating the flow rate of said external reflux in response to said first control signal comprises: means for establishing a third signal representative of the actual flow rate of said external reflux; means for comparing said third signal and said first control signal and for establishing a fourth signal which is responsive to the difference between said third signal and said first control signal, wherein said fourth signal is scaled so as to be representative of the position of a first control valve, operably located so as to control the flow rate of said external reflux, required to maintain the actual flow rate of said external reflux substantially equal to the desired flow rate represented by said first control signal; and means for manipulating said first control valve in response to said fourth signal.

Claim 5

Dependent Claim 288 words

Apparatus in accordance with claim 1 wherein said selected point in said fractional distillation column is a selected tray in said fractional distillation column and wherein said means for manipulating the flow rate of heat to said fractional distillation column in response to said second control signal comprises: means for establishing a third signal representative of the actual temperature of said selected tray; means for comparing said third signal and said second control signal and for establishing a fourth signal which is responsive to the difference between said third signal and said second control signal, wherein said fourth signal is scaled so as to be representative of the flow rate of heating fluid to said fractional distillation column required to maintain the actual temperature of said selected tray substantially equal to the desired temperature represented by said second control signal; means for establishing a fifth signal representative of the actual flow rate of said heating fluid; means for comparing said fourth signal and said fifth signal and for establishing a sixth signal which is responsive to the difference between said fourth signal and said fifth signal, wherein said sixth signal is scaled so as to be representative of the position of a second control valve, operably located so as to control the flow rate of said heating fluid to said fractional distillation column, required to maintain the actual flow rate of said heating fluid substantially equal to the desired flow rate represented by said fourth signal; and means for manipulating said second control valve in response to said sixth signal to thereby maintain the actual flow rate of said heating fluid to said fractional distillation column substantially equal to the desired flow rate represented by said fourth signal.

Claim 6

Dependent Claim 148 words

Apparatus in accordance with claim 1 additionally comprising: means for establishing a third signal representative of the actual flow rate of said feed mixture to said fractional distillation column; a lag means; means for passing said third signal through said lag means to establish a fourth signal; a delay means; means for passing said fourth signal through said delay means to establish a fifth signal; means for subtracting said fifth signal from said fourth signal to establish a sixth signal; means for establishing a seventh signal representative of a bias term; means for multiplying said sixth signal and said seventh signal to establish an eighth signal; and means for adding said eighth signal to said first control signal to thereby apply a feedforward compensation for changes in the flow rate of said feed mixture to said fractional distillation column to the desired flow rate of said external reflux.

Claim 7

Independent Claim 493 words

A method for controlling a fractional distillation process utilized to separate first and second components contained in a feed stream flowing to a fractional distillation column, wherein a heating fluid is introduced into said fractional distillation column to effect said separation, wherein said first component is principally removed from said fractional distillation column as an overhead vapor stream, 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 stream and a second portion of said condensate being removed from said fractional distillation process as an overhead proudct, and wherein said second component is principally removed from said fractional distillation column as a bottoms product, said method comprising the steps of: establishing a first signal which is representative of the concentration of said first component in said bottoms product stream; establishing a second signal which is representative of the concentration of said second component in said overhead product stream; establishing a first control signal representative of the desired flow rate of said external reflux stream, wherein said first control signal is periodically increased or decreased by a fixed increment or left unchanged depending upon the relationship between the actual concentration of said first component in said bottoms product stream as represented by said first signal and a high limit and low limit for the actual concentration of said first component in said bottoms product stream and depending upon the relationship between the actual concentration of said second component in said overhead product stream as represented by said second signal and high and low limits for the actual concentration of said second component in said overhead product stream; manipulating the flow rate of said external reflux in response to said first control signal so as to maintain the actual external reflux flow rate substantially equal to the desired external reflux flow rate as represented by said first control signal; establishing a second control signal representative of the desired temperature at a selected point in said fractional distillation column, wherein said second control signal is periodically increased or decreased by a fixed increment or is left unchanged depending upon the relationship between the actual concentration of said first component in said bottoms product stream as represented by said first signal and said high and low limits for the actual concentration of said first component in said bottoms product stream and depending upon the relationship between the actual concentration of said second component in said overhead product stream as represented by said second signal and said high and low limits for the actual concentration of said second component in said overhead product stream; and manipulating the flow rate of heat to said fractional distillation column in response to said second control signal so as to maintain the actual temperature at said selected point substantially equal to the desired temperature represented by said second control signal.

Claim 8

Independent Claim 493 words

A method for controlling a fractional distillation process utilized to separate first and second components contained in a feed stream flowing to a fractional distillation column, wherein a heating fluid is introduced into said fractional distillation column to effect said separation, wherein said first component is principally removed from said fractional distillation column as an overhead vapor stream, 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 stream and a second portion of said condensate being removed from said fractional distillation process as an overhead proudct, and wherein said second component is principally removed from said fractional distillation column as a bottoms product, said method comprising the steps of: establishing a first signal which is representative of the concentration of said first component in said bottoms product stream; establishing a second signal which is representative of the concentration of said second component in said overhead product stream; establishing a first control signal representative of the desired flow rate of said external reflux stream, wherein said first control signal is periodically increased or decreased by a fixed increment or left unchanged depending upon the relationship between the actual concentration of said first component in said bottoms product stream as represented by said first signal and a high limit and low limit for the actual concentration of said first component in said bottoms product stream and depending upon the relationship between the actual concentration of said second component in said overhead product stream as represented by said second signal and high and low limits for the actual concentration of said second component in said overhead product stream; manipulating the flow rate of said external reflux in response to said first control signal so as to maintain the actual external reflux flow rate substantially equal to the desired external reflux flow rate as represented by said first control signal; establishing a second control signal representative of the desired temperature at a selected point in said fractional distillation column, wherein said second control signal is periodically increased or decreased by a fixed increment or is left unchanged depending upon the relationship between the actual concentration of said first component in said bottoms product stream as represented by said first signal and said high and low limits for the actual concentration of said first component in said bottoms product stream and depending upon the relationship between the actual concentration of said second component in said overhead product stream as represented by said second signal and said high and low limits for the actual concentration of said second component in said overhead product stream; and manipulating the flow rate of heat to said fractional distillation column in response to said second control signal so as to maintain the actual temperature at said selected point substantially equal to the desired temperature represented by said second control signal.

Claim 9

Dependent Claim 187 words

A method in accordance with claim 6 wherein said first control signal and said second control signal are changed based on the relationship of said first signal(ACB) to the high (HL1) and low (LL1) limits for the actual concentration of said first component in said bottoms product stream and the relationship of said second signal (ACO) to the high (HL2) and low (LL2) limits for the actual concentration of said second component in said overhead product stream as follows: ______________________________________ Relationship Control Signals First Signal Second Signal First Second ______________________________________ ACB < LL1 ACO < LL2 no de- change crease ACB < LL1 LL2 ≦ ACO ≦ HL2 decrease de- crease ACB < LL1 ACO > HL2 decrease no change LL1 ≦ ACB ≦ HL1 ACO < LL2 increase de- crease LL1 ≦ ACB ≦ HL1 LL2 ≦ ACO ≦ HL2 no no change change LL1 ≦ ACB ≦ HL1 ACO > HL2 decrease in- crease ACB > HL1 ACO < LL2 increase no change ACB > HL1 LL2 ≦ ACO ≦ HL2 increase in- crease ACB > HL1 ACO > HL2 no in- change crease ______________________________________

Claim 10

Dependent Claim 138 words

A method in accordance with claim 6 wherein said step of manipulating the flow rate of said external reflux in response to said first control signal comprises: establishing a third signal representative of the actual flow rate of said external reflux; comparing said third signal and said first control signal and establishing a fourth signal which is responsive to the difference between said third signal and said first control signal, wherein said fourth signal is scaled so as to be representative of the position of a first control valve, operably located so as to control the flow rate of said external reflux, required to maintain the actual flow rate of said external reflux substantially equal to the desired flow rate represented by said first control signal; and manipulating said first control valve in response to said fourth signal.

Claim 11

Dependent Claim 277 words

A method in accordance with claim 6 wherein said selected point in said fractional distillation column is a selected tray in said fractional distillation column and wherein said step of manipulating the flow rate of heat to said fractional distillation column in response to said second control signal comprises: establishing a third signal representative of the actual temperature of said selected tray; comparing said third signal and said second control signal and establishing a fourth signal which is responsive to the difference between said third signal and said second control signal, wherein said fourth signal is scaled so as to be representative of the flow rate of heating fluid to said fractional distillation column required to maintain the actual temperature of said selected tray substantially equal to the desired temperature represented by said second control signal; establishing a fifth signal representative of the actual flow rate of said heating fluid; comparing said fourth signal and said fifth signal and establishing a sixth signal which is responsive to the difference between said fourth signal and said fifth signal, wherein said sixth signal is scaled so as to be representative of the position of a second control valve, operably located so as to control the flow rate of said heating fluid to said fractional distillation column, required to maintain the actual flow rate of said heating fluid substantially equal to the desired flow rate represented by said fourth signal; and manipulating said second control valve in response to said sixth signal to thereby maintain the actual flow rate of said heating fluid to said fractional distillation column substantially equal to the desired flow rate represented by said fourth signal.

Claim 12

Dependent Claim 124 words

A method in accordance with claim 6 additionally comprising the steps of: establishing a third signal representative of the actual flow rate of said feed mixture to said fractional distillation column; lagging said third signal to establish a fourth signal; delaying said fourth signal to establish a fifth signal; subtracting said fifth signal from said fourth signal to establish a sixth signal; establishing a seventh signal representative of a bias term; multiplying said sixth signal and said seventh signal to establish an eighth signal; and adding said eighth signal to said first control signal to thereby apply a feedforward compensation for changes in the flow rate of said feed mixture to said fractional distillation column to the desired flow rate of said external reflux.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1988-07-01	1988-12-31	1989-07-02	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1992-07-01	1992-12-31	1993-07-02	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1996-07-01	1996-12-31	1997-07-02	$7700.00	Window Closed / Lapsed

Control of a fractional distillation process

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