Control of a fractional distillation column

A method for preventing flooding of a first and second fractional distillation column means, wherein the feed stream to said second fractional distillation column means is provided from said first fractional distillation column means, and for maintaining the liquid level in at least one separator means, from which the feed to said first fractional distillation column means is supplied, within desired limits comprising the steps of:

• supplying a first feed stream to said at least one separator means;
• supplying a second feed stream from said at least one separator means to said first fractional distillation column means;
• supplying a third feed stream from said first fractional distillation column means to said second fractional distillation column means;
• establishing a first signal representative of the predicted desired flow rate of said second feed stream required to prevent flooding of said first fractional distillation column means and said second fractional distillation column means;
• establishing a second signal representative of the actual flow rate of said second feed stream;
• using computing means to compare said first signal and said second signal and establish a third signal responsive to the difference between said first signal and said second signal;
• manipulating the flow rate of said second feed stream in response to said third signal;
• establishing a fourth signal representative of the predicted desired flow rate of said first feed stream required to prevent flooding of said first fractional distillation column means and said second fractional distillation column means;
• establishing a fifth signal representative of a correction factor utilized to maintain the liquid level in said at least one separator within desired limits;
• using computing means to compare said fourth signal and said fifth signal to establish a sixth signal representative of a modified predicted desired flow rate of said first feed stream required to both prevent flooding of said first fractional distillation column means and said second fractional distillation column means and required to maintain the liquid level in said at least one separator means within desired limits;
• establishing a seventh signal representative of the actual flow rate of said first feed stream;
• using computing means to compare said sixth signal and said seventh signal and establish an eighth signal responsive to the difference between said sixth signal and said seventh signal;
• and
• manipulating the flow rate of said first feed stream in response to said eighth signal.

A method for preventing flooding of a fractional distillation column means and for maintaining the liquid level in first and second separator means, from which the feed to said fractional distillation column means is supplied, within desired limits comprising the steps of:

• supplying a first feed stream to said first separator means;
• supplying the vapor portion of said first feed stream from said first separator means to said second separator means;
• supplying the liquid portion of said first feed stream as a second feed stream from said first separator means to said fractional distillation column means;
• supplying the liquid in said second separator means as a third feed stream to said fractional distillation column means;
• establishing a first signal representative of the predicted desired total feed flow to said fractional distillational column means required to prevent flooding of said fractional distillation column means;
• establishing a second signal representative of the flow rate of said second feed stream;
• establishing a third signal representative of the flow rate of said third feed stream;
• using computing means to sum said second signal and said third signal to establish a fourth signal representative of the actual total feed flow rate to said fractional distillation column means;
• using computing means to compare said first signal and said fourth signal and establish a fifth signal responsive to the difference between said first signal and said fourth signal;
• manipulating the flow rate of said second feed stream in response to said fifth signal;
• establishing a sixth signal representative of the actual liquid level in said first separator means;
• establishing a seventh signal representative of the actual liquid level in said second separator means;
• using computing means to compare said sixth signal and said seventh signal and establish an eighth signal responsive to the difference between said sixth signal and said seventh signal;
• using computing means to combine said fifth signal and said eighth signal to establish a ninth signal;
• manipulating the flow rate of said third feed stream in response to said ninth signal;
• establishing a tenth signal representative of the predicted desired flow rate of said first feed stream required to prevent flooding of said fractional distillational column means;
• establishing an eleventh signal representative of a correction factor utilized to maintain the liquid level in said first and second separators within desired limits;
• using computing means to combine said tenth signal and said eleventh signal to establish a twelfth signal representative of a modified predicted desired flow rate of said first feed stream required to both prevent flooding of said fractional distillation column means and maintain the liquid level in said first separator means and said second separator means within desired limits;
• establishing a thirteenth signal representative of the actual flow rate of said first feed stream;
• using computing means to compare said twelfth signal and said thirteenth signal and establish a fourteenth signal responsive to the difference between said twelfth signal and said thirteenth signal;
• and
• manipulating the flow rate of said first feed stream in response to said fourteenth signal.