Control of a fractional distillation process

Claim 2

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 withdrawing an overhead vapor stream, having a substantially 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; 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said accumulator; means for withdrawing condensate from said accumulator and for passing a first portion of the thus withdrawn condensate into an upper portion of said fractional distillation column as an external reflux stream therefor and for passing a second portion of the thus withdrawn condensate as an overhead product stream; means for withdrawing a bottoms product stream, having a substantially increased concentration of said second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 responsive to the concentration of said first component in said bottoms product stream; means for establishing a second signal which is responsive to the concentration of said second component in said overhead product stream; means for establishing a third signal which is responsive to the sum of said first signal and said second signal; and means for manipulating the flow rate of said external reflux stream in response to said third signal.

Claim 3

Apparatus in accordance with claim 1 wherein said means for establishing said first signal comprises: means for establishing a fourth signal representative of the actual concentration of said first component in said bottoms product stream; means for establishing a fifth signal representative of the desired concentration of said first component in said bottoms product stream; means for dividing said fourth signal by said fifth signal to establish a sixth signal; and means for multiplying said sixth signal by a weighting factor to establish said first signal.

Claim 4

Apparatus in accordance with claim 2 wherein said means for establishing said second signal comprises: means for establishing a seventh signal representative of the actual concentration of said second component in said overhead product stream; means for establishing an eighth signal representative of the desired concentration of said second component in said overhead product stream; means for dividing said seventh signal by said eighth signal to establish a ninth signal; and means for multiplying said ninth signal by 1.0 minus the magnitude of said weighting factor to establish said second signal.

Claim 5

Apparatus in accordance with claim 3 wherein said means for manipulating the flow rate of said external reflux stream in response to said third signal comprises: means for establishing a tenth signal which is representative of a prediction of the flow rate of the internal reflux in said fractional distillation column required to maintain the actual concentration of said first component in said bottoms product stream substantially equal to the desired concentration represented by said fifth signal; means for establishing an eleventh signal representative of 1.0; means for comparing said eleventh signal and said third signal and for establishing a twelfth signal which is responsive to the difference between said eleventh signal and said third signal, wherein said twelfth signal is scaled so as to be representative of any change in the flow rate of the internal reflux represented by said tenth signal required to maintain the actual concentration of said first component in said bottoms product stream substantially equal to the desired concentration represented by said fifth signal; means for summing said tenth signal and said twelfty signal to establish a thirteenth signal which is representative of the desired flow rate of the internal reflux in said fractional distillation column; means for establishing a fourteenth signal which is representative of the desired flow rate of said external reflux stream in response to said thirteenth signal; and means for manipulating the flow rate of said external reflux stream in response to said fourteenth signal.

Claim 6

Apparatus in accordance with claim 4 wherein said means for establishing said tenth signal comprises: means for establishing a fifteenth signal representative of the flow rate of said feed mixture to said fractional distillation column; and means for multiplying said fifteenth signal by a sixteenth signal, which is representative of a prediction of the ratio of the internal reflux flow rate in the fractional distillation column to the flow rate of the feed mixture required to maintain the actual concentration of said first component in said bottoms product stream substantially equal to the desired concentration represented by said fifth signal, to establish said tenth signal.

Claim 7

Apparatus in accordance with claim 4 wherein said means for establishing said fourteenth signal comprises: means for establishing a fifteenth signal representative of the actual temperature of said overhead vapor stream (T 1 ); means for establishing a sixteenth signal representative of the actual temperature of said external reflux (T 2 ); means for establishing a seventeenth signal representative of the specific heat of the said external reflux divided by the heat of vaporization for said external reflux (K); means for establishing an eighteenth signal representative of 1+K (T 1 -T 2 ) in response to said fifteenth, sixteenth and seventeenth signals; and means for dividing said thirteenth signal by said eighteenth signal to establish said fourteenth signal.

Claim 8

Apparatus in accordance with claim 1 additionally comprising: means for establishing a fourth signal which is responsive to the concentration of said first component in said bottoms product stream; means for establishing a fifth signal which is responsive to the concentration of said second component in said overhead product stream; and means for establishing a sixth signal which is responsive to the difference between said fourth signal and said fifth signal; and means for manipulating the flow rate of said bottoms product stream in response to said sixth signal.

Claim 9

Apparatus in accordance with claim 7 wherein said means for establishing said fourth signal comprises: means for establishing a seventh signal representative of the actual concentration of said first component in said bottoms product stream; means for establishing an eighth signal representative of the desired concentration of said first component in said bottoms product stream; means for dividing said seventh signal by said eighth signal to establish a ninth signal; and means for multiplying said ninth signal by a weighting factor to establish said fourth signal.

Claim 10

Apparatus in accordance with claim 8 wherein said means for establishing said fifth signal comprises: means for establishing a tenth signal representative of the actual concentration of said second component in said overhead product stream; means for establishing an eleventh signal representative of the desired concentration of said second component in said overhead product stream; and means for dividing said tenth signal by said eleventh signal to establish said fifth signal.

Claim 11

Apparatus in accordance with claim 9 wherein said means for manipulating the flow rate of said bottoms product stream in response to said sixth signal comprises: means for adding said weighting factor to said sixth signal to establish a twelfth signal. means for establishing a thirteenth signal representative of 1.0; means for comparing said twelfth signal and said thirteenth signal and for establishing a fourteenth signal which is responsive to the difference between said twelfth signal and said thirteenth signal, wherein said fourteenth signal is scaled so as to be representative of the percentage of said feed mixture which should be removed from said fractional distillation column as said bottoms product stream in order to maintain the actual concentration of said second component in said overhead product stream substantially equal to the desired concentration represented by said eleventh signal; means for establishing a fifteenth signal representative of the flow rate of said feed mixture to said fractional distillation column; means for multiplying said fourteenth signal and said fifteenth signal to establish a sixteenth signal which is representative of the desired flow rate of said bottoms product stream; and means for manipulating the flow rate of said bottoms product in response to said sixteenth signal.

Claim 12

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 withdrawing an overhead vapor stream, having a substantially 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; 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 a substantially 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 responsive to the concentration of said first component in said bottoms product stream; means for establishing a second signal which is responsive to the concentration of said second component in said overhead product stream; and means for establishing a third signal which is responsive to the difference between said first signal and said second signal; and means for manipulating the flow rate of said bottoms product stream in response to said third signal.

Claim 13

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 withdrawing an overhead vapor stream, having a substantially 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; 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 a substantially 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 responsive to the concentration of said first component in said bottoms product stream; means for establishing a second signal which is responsive to the concentration of said second component in said overhead product stream; and means for establishing a third signal which is responsive to the difference between said first signal and said second signal; and means for manipulating the flow rate of said bottoms product stream in response to said third signal.

Claim 14

Apparatus in accordance with claim 11 wherein said means for establishing said first signal comprises: means for establishing a fourth signal representative of the actual concentration of said first component in said bottoms product stream; means for establishing a fifth signal representative of the desired concentration of said first component in said bottoms product stream; means for dividing said fourth signal by said fifth signal to establish a sixth signal; and means for multiplying said sixth signal by a weighting factor to establish said fourth signal.

Claim 15

Apparatus in accordance with claim 12 wherein said means for establishing said second signal comprises: means for establishing a seventh signal representative of the actual concentration of said second component in said overhead product stream; means for establishing an eight signal representative of the desired concentration of said second component in said overhead product stream; and means for dividing said seventh signal by said eighth signal to establish said second signal.

Claim 16

Apparatus in accordance with claim 13 wherein said means for manipulating the flow rate of said bottoms product stream in response to said third signal comprises: means for adding said weighting factor to said third signal to establish a ninth signal. means for establishing a tenth signal representative of 1.0; means for comparing said ninth signal and said tenth signal and for establishing an eleventh signal which is responsive to the difference between said ninth signal and said tenth signal, wherein said fourteenth signal is scaled so as to be representative of the percentage of said feed mixture which should be removed from said fractional distillation column as said bottoms product stream in order to maintain the actual concentration of said second component in said overhead product stream substantially equal to the desired concentration represented by said eight signal; means for establishing a twelfth signal representative of the flow rate of said feed mixture to said fractional distillation column; means for multiplying said eleventh signal and said twelfth signal to establish a thirteenth signal which is representative of the desired flow rate of said bottoms product stream; and means for manipulating the flow rate of said bottoms product in response to said thirteenth signal.

Claim 19

A method in accordance with claim 15 wherein said step of establishing said first signal comprises: establishing a fourth signal representative of the actual concentration of said first component in said bottoms product stream; establishing a fifth signal representative of the desired concentration of said first component in said bottoms product stream; dividing said fourth signal by said fifth signal to establish a sixth signal; and multiplying said sixth signal by a weighting factor to establish said first signal;

Claim 20

A method accordance with claim 16 wherein said step of establishing a seventh signal representative of the actual concentration of said second component in said overhead product stream; establishing an eighth signal representative of the desired concentration of said second component in said overhead product stream; dividing said seventh signal by said eighth signal to establish a ninth signal; and multiplying said ninth signal by 1.0 minus the magnitude of said weighting factor to establish said second signal.

Claim 21

A method in accordance with claim 17 wherein said step of manipulating the flow rate of said external reflux stream in response to said third signal comprises: establishing a tenth signal which is representative of a prediction of the flow rate of the internal reflux in said fractional distillation column required to maintain the actual concentration of said first component in said bottoms product stream substantially equal to the desired concentration represented by said fifth signal; establishing an eleventh signal representative of 1.0; comparing said eleventh signal and said third signal and establishing a twelfth signal which is responsive to the difference between said eleventh signal and said third signal, wherein said twelfth signal is scaled so as to be representative of any change in the flow rate of the internal reflux represented by said tenth signal required to maintain the actual concentration of said first component in said bottoms product stream substantially equal to the desired concentration represented by said fifth signal; summing said tenth signal and said twelfth signal to establish a thirteenth signal which is representative of the desired flow rate of the internal reflux in said fractional distillation column; establishing a fourteenth signal which is representative of the desired flow rate of said external reflux stream in response to said thirteenth signal; and manipulating the flow rate of said external reflux stream in response to said fourteenth signal.

Claim 22

A method in accordance with claim 18 wherein said step of establishing said tenth signal comprises: establishing a fifteenth signal representative of the flow rate of said feed mixture to said fractional distillation column; and multiplying said fifteenth signal by a sixteenth signal, which is representative of a prediction of the ratio of the internal reflux flow rate in the fractional distillation column to the flow rate of the feed mixture required to maintain the actual concentration of said first component in said bottoms product stream substantially equal to the desired concentration represented by said fifth signal, to establish said tenth signal.

Claim 23

A method in accordance with claim 19 wherein said step of establishing said fourteenth signal comprises: establishing a fifteenth signal representative of the actual temperature of said overhead vapor stream (T 1 ); establishing a sixteenth signal representative of the actual temperature of said external reflux (T 2 ); establishing a seventeenth signal representative of the specific heat of the said external reflux divided by the heat of vaporization for said external reflux (K); establishing an eighteenth signal representative of 1+K (T 1 -T 2 ) in response to said fifteenth, sixteenth and seventeenth signals; and dividing said thirteenth signal by said eighteenth signal to establish said fourteenth signal.

Claim 24

A method in accordance with claim 15 additionally comprising the steps of: establishing a fourth signal which is responsive to the concentration of said first component in said bottoms product stream; establishing a fifth signal which is responsive to the concentration of said second component in said overhead product stream; and establishing a sixth signal which is responsive to the difference between said fourth signal and said fifth signal; and manipulating the flow rate of said bottoms product stream in response to said sixth signal.

Claim 25

A method in accordance with claim 21 wherein said step of establishing said fourth signal comprises: establishing a seventh signal representative of the actual concentration of said first component in said bottoms product stream; establishing an eighth signal representative of the desired concentration of said first component in said bottoms product stream; dividing said seventh signal by said eighth signal to establish a ninth signal; and multiplying said ninth signal by a weighting factor to establish said fourth signal.

Claim 26

A method in accordance with claim 22 wherein said step of establishing said fifth signal comprises: establishing a tenth signal representative of the actual concentration of said second component in said overhead product stream; establishing an eleventh signal representative of the desired concentration of said second component in said overhead product stream; and dividing said tenth signal by said eleventh signal to establish said fifth signal.

Claim 27

A method in accordance with claim 23 wherein said step of manipulating the flow rate of said bottoms product stream in response to said sixth signal comprises: adding said weighting factor to said sixth signal to establish a twelfth signal. establishing a thirteenth signal representative of 1.0; comparing said twelfth signal and a said thirteenth signal and establishing a fourteenth signal which is responsive to the difference between said twelfth signal and said thirteenth signal, wherein said fourteenth signal is scaled so as to be representative of the percentage of said feed mixture which should be removed from said fractional distillation column as said bottoms product stream in order to maintain the actual concentration of said second component in said overhead product stream substantially equal to the desired concentration represented by said eighth signal; establishing a fifteenth signal representative of the flow rate of said feed mixture to said fractional distillation column; multiplying said fourteenth signal and said fifteenth signal to establish a sixteenth signal which is representative of the desired flow rate of said bottoms product stream; and manipulating the flow rate of said bottoms product in response to said sixteenth signal.

Claim 30

A method in accordance with claim 25 wherein said step of establishing said second signal comprises: establishing a fourth signal representative of the actual concentration of said first component in said bottoms product stream; establishing a fifth signal representative of the desired concentration of said first component in said bottoms product stream; dividing said fourth signal by said fifth signal to establish a sixth signal; and multiplying said fourth signal by a weighting factor to establish said sixth signal.

Claim 31

A method in accordance with claim 26 wherein said step of establishing said second signal comprises: establishing a seventh signal representative of the actual concentration of said second component in said overhead product stream; establishing an eighth signal representative of the desired concentration of said second component in said overhead product steam; and dividing said seventh signal by said eighth signal to establish said second signal.

Claim 32

A method in accordance with claim 27 wherein said step of manipulating the flow rate of said bottoms product stream in response to said third signal comprises: adding said weighting factor to said third signal to establish a ninth signal. establishing a tenth signal representative of 1.0; comparing said ninth signal and said tenth signal and establishing an eleventh signal which is responsive to the difference between said ninth signal and said tenth signal, wherein said eleventh signal is scaled so as to be representative of the percentage of said feed mixture which should be removed from said fractional distillation column as said bottoms product stream in order to maintain the actual concentration of said second component in said bottoms product stream substantially equal to the desired concentration represented by said eighth signal; establishing a twelfth signal representative of the flow rate of said feed mixture to said fractional distillation column; multiplying said eleventh signal and said twelfth signal to establish a thirteenth signal which is representative of the desired flow rate of said bottoms product stream; and manipulating the flow rate of said bottoms product in response to said thirteenth signal.