US 4,350,569 AGranted

Fractional distillation column control

AssigneePhillips Petroleum Company

InventorDanny L. Furr

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Abstract

In a fractionation distillation process in which a pump around stream and an external reflux are utilized to control heat removal from an upper portion of the fractional distillation column and in which the pump around stream is utilized to preheat the feed stream flowing to the fractional distillation, the flow rate of the pump around stream is manipulated so as to substantially maximize the flow rate of the pump around stream while maintaining a desired heat removal from the fractional distillation column. Priority control of the pump around stream and external reflux result in a maximum preheating of the feed stream flowing to the fractional distillation column which improves the energy efficiency of the fractional distillation process.

Claims3

Dependent claims

A method for maintaining a desired internal reflux flow rate in an upper portion of a fractional distillation column, wherein a feed stream to said fractional distillation column is preheated by a pump around stream which is withdrawn from a first upper portion of said fractional distillation column and returned to a second upper portion of said fractional distillation column which is above said first upper portion of said fractional distillation column and wherein an overhead vapor stream is withdrawn from an upper portion of said fractional distillation column, cooled, and separated into a liquid phase and a vapor phase, with a first portion of said liquid phase being returned to a third upper portion of said fractional distillation column as an upper external reflux which is above said first upper portion and a second portion of said liquid phase being withdrawn as a product stream, said method comprising the steps of:

using computing means to calculate and establish a first signal representative of the actual flow rate of the internal reflux in an upper portion of said fractional distillation column;
using computing means to calculate and establish a second signal representative of the flow rate of the internal reflux in the upper portion of said fractional distillation column required to maintain a desired product specification for said product stream;
comparing said first signal and said second signal to thereby determine if the internal reflux flow rate in the upper portion of said fractional distillation column should be increased or decreased;
determining if the flow rate of said pump around stream can be increased;
determining if the flow rate of said upper external reflux can be decreased;
using computing means to calculate and establish a third signal representative of the flow rate of said pump around stream required to make said first signal substantially equal to said second signal;
establishing a fourth signal representative of the highest desired flow rate of said pump around stream;
using computing means to calculate and establish a fifth signal representative of the flow rate of said upper external reflux required to make said first signal substantially equal to said second signal;
establishing a sixth signal representative of the lowest desired flow rate of said upper external reflux;
manipulating the flow rate of said pump around stream in response to said third signal and manipulating the flow rate of said upper external reflux in response to said sixth signal if it is desired to increase the flow rate of said internal reflux and it is determined that the flow rate of said pump around stream can be increased or if it is desired to decrease the flow rate of said internal reflux and it is determined that the flow rate of said upper external reflux cannot be decreased;
and
manipulating the flow rate of said pump around stream in response to said fourth signal and manipulating the flow rate of said upper external reflux in response to said fifth signal if it is desired to increase the flow rate of said internal reflux and it is determined that the flow rate of said pump around stream cannot be increased, or if it is desired to decrease the flow rate of said internal reflux and it is determined that the flow rate of said upper external reflux can be decreased.

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Dependencies are inferred from the claim text.

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Abstract

using computing means to calculate and establish a first signal representative of the actual flow rate of the internal reflux in an upper portion of said fractional distillation column;
using computing means to calculate and establish a second signal representative of the flow rate of the internal reflux in the upper portion of said fractional distillation column required to maintain a desired product specification for said product stream;
comparing said first signal and said second signal to thereby determine if the internal reflux flow rate in the upper portion of said fractional distillation column should be increased or decreased;
determining if the flow rate of said pump around stream can be increased;
determining if the flow rate of said upper external reflux can be decreased;
using computing means to calculate and establish a third signal representative of the flow rate of said pump around stream required to make said first signal substantially equal to said second signal;
establishing a fourth signal representative of the highest desired flow rate of said pump around stream;
using computing means to calculate and establish a fifth signal representative of the flow rate of said upper external reflux required to make said first signal substantially equal to said second signal;
establishing a sixth signal representative of the lowest desired flow rate of said upper external reflux;
manipulating the flow rate of said pump around stream in response to said third signal and manipulating the flow rate of said upper external reflux in response to said sixth signal if it is desired to increase the flow rate of said internal reflux and it is determined that the flow rate of said pump around stream can be increased or if it is desired to decrease the flow rate of said internal reflux and it is determined that the flow rate of said upper external reflux cannot be decreased;
and
manipulating the flow rate of said pump around stream in response to said fourth signal and manipulating the flow rate of said upper external reflux in response to said fifth signal if it is desired to increase the flow rate of said internal reflux and it is determined that the flow rate of said pump around stream cannot be increased, or if it is desired to decrease the flow rate of said internal reflux and it is determined that the flow rate of said upper external reflux can be decreased.

9 more elements