US 4,028,194 AGranted

Systematized method and control of fractionation heat balance

AssigneeUop LLC

InventorDavid M. Boyd

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Abstract

Heat balance of a fractionation column is controlled and maintained by obtaining three differential temperatures between selected temperature-sensing points along the height of the column. A signal representing one of the delta-T's is employed in regulating the quantity of reflux returned to the rectification zone. The remaining two delta-T's are conjunctively utilized to regulate the enthalpy (heat-input content) of the reboiled liquid bottoms stream being returned to the reboiler section of the column. With respect to the latter, a selected one of the two delta-T signals is multiplied by a multiplier representing the ratio of the number of trays between the temperature sensing points supplying the non-selected delta-T signal to the number of trays between the temperature sensing points supplying the selected delta-T signal. A signal representing the resulting product is correlated with the non-selected signal, and the signal representing the resulting relationship is utilized to regulate the degree to which the returned liquid bottoms material is vaporized.

Claims7

Dependent claims

In a fractionation column containing a plurality of spaced-apart trays or decks, and wherein (i) a feed stream is introduced through a locus intermediate the top and bottom thereof;

(ii) liquid bottoms material is recovered from the lower end of said column, and at least a portion thereof partially vaporized and returned to the reboiler section;
and, (iii) overhead material is recovered from the upper end of said column, condensed and at least a portion thereof returned to the rectification section as a reflux stream, the control system which comprises, in cooperative combination:
a. a first pair of vertically-spaced temperature sensors below and proximate to said feed locus, said pair separated by a first plurality of trays, and a first differential-temperature measuring device communicating with said first pair of temperature sensors;
b. a second pair of vertically-spaced temperature sensors below said feed locus and separated by a second plurality of trays which are greater than said first plurality of trays, and a second differential-temperature measuring device communicating with said second pair of temperature sensors;
c. first differential-temperature computing means communicating with a selected one of said first and second differential-temperature measuring devices to determine a first differential communicating output, said output being a function of the ratio of said second and said first plurality of trays;
d. second differential temperature computing means communicating with said first computing means and the non-selected differential temperature measuring device, and co-acting with first control means for regulating the degree of vaporization of said liquid bottoms material returned to said reboiler section;
e. a third pair of vertically-spaced temperature sensors above said feed locus;
and,
f. a third differential-temperature measuring device communicating with said third pair of temperature sensors and co-acting with second control means for regulating the quantity of reflux returned to said rectification section.

6 more elements

A method for controlling a fractionation column, wherein (i) a feed stream is introduced through a locus intermediate the top and bottom thereof;

(ii) liquid bottoms material is recovered from the lower end of said column, and at least a portion thereof is partially vaporized and returned to the reboiler section;
and, (iii) vaporous overhead material is recovered from the upper end of said column, condensed and at least a portion thereof returned to the rectification section as a reflux stream, which method comprises the steps of:
a. sensing a first temperature differential between two vertically-spaced temperature sensing points below said feed locus, separated by a first plurality of trays, measuring the resulting first differential-temperature and generating a first signal representative thereof;
b. sensing a second temperature differential between two vertically-spaced temperature sensing points below said feed locus, separated by a second plurality of trays which is greater than said first plurality of trays, measuring the resulting second differential temperatue and generating a second signal representative thereof;
c. multiplying a selected one of said first and second differential temperature signals by a multiplier representing the ratio of the number of trays between the sensors supplying the non-selected differential temperature signal to the number of trays between the sensors supplying said selected differential temperature signal, and generating a third signal representing the resulting product;
d. obtaining a computed relationship of said third signal and said non-selected signal, and generating a fourth signal representative of the resulting computed relationship;
e. regulating the degree to which said liquid bottoms material is vaporized in response to said fourth signal;
f. sensing a third temperature differential between two vertically-spaced temperature sensing points above said feed locus, measuring the resulting third differential temperature and generating a fifth signal representative thereof;
and,
g. regulating the quantity of said returned reflux stream responsive to said fifth signal.

7 more elements

Dependencies are inferred from the claim text.