METHOD FOR SEPARATING A MULTICOMPONENT FEEDSTREAM

• US 3,793,157 A
• Filed: 03/24/1971
• Issued: 02/19/1974
• Est. Priority Date: 03/24/1971
• Status: Expired due to Term

• Current Assignee: James W. Hobbs, Ricardo J. Callejas
• Original Assignee: James W. Hobbs, Ricardo J. Callejas
• Inventors: Hobbs, James W., Callejas, Ricardo J.
• Primary Examiner(s): Sofer, Jack
• Application Number:
  US05/127,542
• Time in Patent Office: 1,063 Days
• Field of Search: 203/2 196/132 159/44
• US Class Current: 203/2
• CPC Class Codes: B01D 3/425 Head-, bottom- and feed stream
• CPC Class Codes: C10G 7/12 Controlling or regulating
• CPC Class Codes: Y10S 203/19 Sidestream
• CPC Class Codes: Y10S 208/01 Automatic control

Abstract

A method for separating a multicomponent hydrocarbon feedstream in a column into an overhead vapor stream and a liquid bottomsproduct stream having a specified purity by maintaining the overhead vapor stream at about one preselected temperature, maintaining the rate of heat input into the column by the feedstream at a value greater than the heat input into said column by a lower portion heating means, and regulating the rate of heat input into the column by the feedstream for maintaining the liquid bottoms-product stream at the preselected purity.

Claims

2. Apparatus as set forth in claim 1, wherein the eighth means comprises:

eleventh means for delivering a signal LB representative of the amount of a preselected component in a volume of liquid from the lower portion of the column;

twelfth means for receiving signal LB, comparing said signal to a preselected set point (SP LB) and delivering a signal BB representative of the difference between the received signal and said set point;

thirteenth means for receiving signals BB and F and delivering a signal BS representative of the quantity (KBFR + BB)(F) where KBFR is a signal of the thirteenth means, said signal F being a signal representative of the flow rate of the feedstream; and

fourteenth means for controlling the flow of the liquid bottoms product stream from the column in response to signal BS.

3. Apparatus, as set forth in claim 1, wherein the ninth means comprises:

tenth means for receiving signals TO, F, RB, RDFG, and BS and delivering a signal TS representative of the quantity (BS(KTB-TO)) + (K2(RDFG + RB)) - (K3(RIBS)) where KTB, RIBS, K2, and K3 are setpoint signals of the fourteenth means and BS is a signal representative of the flow rate of the bottoms product stream.

4. An apparatus, as set forth in claim 3, including means for applying dead time and lag time constants to the signals BS, RB, RDFG, and F delivered to the 14th means.

5. Apparatus, as set forth in claim 3, wherein the eighth means comprises:

eleventh means for delivering a signal LB representative of the amount of a preselected component in a volume of liquid from the lower portion of the column;

twelfth means for receiving signal LB, comparing said signal to a preselected set point (SP LB) and delivering a signal BB representative of the difference between the received signal and said set point;

thirteenth means for receiving signals BB and F and delivering a signal BS representative of the quantity (KBFR + BB)(F) where KBFR is a signal of the thirteenth means; and

fourteenth means for controlling the flow of the liquid bottoms product stream from the column in response to signal BS.

6. An apparatus, as set forth in claim 5, wherein the 10th means delivers a signal representative of the amount of a preselected hydrocarbon having carbon molecules in the range of C1 to C3.

7. An apparatus, as set forth in claim 5, including means for applying dead time and lag time constants to the signal F delivered to the 12th means.

8. In a distillation process for separating a multicomponent feedstream within a column having upper, middle, and lower portions with a reflux stream entering the upper portion, an overhead vapor stream discharging from the upper portion, a feedstream entering the middle portion, and a liquid bottoms product stream discharging from the lower portion of the column with said bottoms product stream having a preselected purity, and a lower portion heating means for heating the column, the improvement comprising:

continuously maintaining the rate of heat input into the column by the feedstream at a value greater than the heat input into said column by the lower portion heating means, the ratio of the rate of heat input by the feedstream to the rate of heat input by the lower portion heating means being a value greater than about 18;

controlling the flow rate of the reflux stream into the column in response to the temperature of the overhead stream, temperature of the reflux stream, and flow rate of the feedstream;

controlling the flow rate of the bottoms product stream in response to an analysis of a liquid from the bottom portion of the column and the flow rate of the feedstream; and

controlling the temperature of the feedstream in response to the temperature of the overhead stream, flow rate of the feedstream, and the flow rate of the bottoms product stream.

9. A process, as set forth in claim 8, wherein the feedstream comprises ethane and including maintaining the temperature of the overhead vapor stream at a temperature in the range of about -50* to -55* F.

10. A process, as set forth in claim 8, wherein the feedstream comprises ethane and including maintaining the mol percent of ethane in the liquid bottoms product stream in the range of about 0.2-1.0 mol percent.

11. A process, as set forth in claim 8, including analyzing a hydrocarbon having carbon molecules in the range of C1 to C3.

12. A process, as set forth in claim 8 wherein controlling the flow rate of the reflux stream comprises:

measuring the temperature of the reflux stream and delivering a signal TR representative of that temperature;

measuring the temperature of the overhead stream and delivering a signal TO representative of that temperature;

measuring the flow rate of the feedstream and delivering a signal F representative of that temperature;

receiving the signal TO, comparing said signal to a setpoint (SP TO) and delivering a signal RB representative of the difference between said received signal and said setpoint;

receiving signals RB, TR, TO, and F and delivering a signal RDFG representative of the quantity (SP RDFG)(F) and a signal RS representative of the quantity (SP RDFG)(F) + RB/1 + K(TO-TR) where signals (SP RDFG) and (K) are preselected setpoint signals;

K CP/ eta CP specific heat of said external reflux stream eta heat of vaporization of said external reflux stream RDFG (SP RDFG)(F) SP RDFG preselected internal reflux setpoint; and

controlling the flow of the reflux stream into the column in response to signal RS.

13. A process as set forth in claim 12 wherein K is a value in the range of about 0.002-0.007 per *F.

14. A process, as set forth in claim 12, wherein controlling the temperature of the feedstream comprises:

receiving signals TO, F, RB, RDFG, and BS and delivering a signal TS to the feedstream, said signal being representative of the quantity (BS(KTB-TO)) + (K2(RDFG + RB)) - (K3(RIBS)) where KTB, RIBS, K2, and K3 are set point signals;

KTB preselected temperature of the liquid bottoms product streams;

K2 eta /CPD where eta heat of vaporization of the external reflux stream and CPD specific heat of the overhead vapor stream;

K3 eta B/CPD where eta B heat of vaporization of the bottoms product stream and CPD specific heat of the overhead vapor stream;

RIBS internal reflux in the lower portion of the column;

BS signal representative of the flow rate of the bottoms product stream.

15. A process, as set forth in claim 14, wherein KTB is a value in the range of about 85*-150*F.

16. A process, as set forth in claim 14, wherein controlling the flow rate of the bottoms product stream comprises:

delivering a signal LB representative of the amount of a preselected component in a volume of liquid from the lower portion of the column;

receiving said signal LB, comparing said signal to a preselected setpoint (SP LB), and delivering a signal BB representative of the difference between the received signal and said setpoint;

receiving signals BB and F and delivering a signal BS representative of the quantity (KBFR + BB)(F);

where KBFR preselected liquid bottoms product stream flow rate divided by preselected feed flow rate; and

controlling the flow of the liquid bottoms product stream from the column in response to signal BS.

17. A process, as set forth in claim 14, including adjusting signals BS, RB, RDFG, and F by applying a dead time and lag time constants thereto.

18. A process, as set forth in claim 8, wherein controlling the flow rate of the bottoms product stream comprises:

delivering a signal LB representative of the amount of a preselected component in a volume of liquid from the lower portion of the column;

receiving signal LB representative of the amount of a preselected component in a volume of liquid from the lower portion of the column;

receiving signal LB, comparing said signal to a preselected setpoint (SP LB), and delivering a signal BB representative of the difference between the received signal and said setpoint;

receiving signals BB and F and delivering a signal BS representative of the quantity (KBFR + BB)(F);

where KBFR preselected liquid bottoms product stream flow rate divided by preselected feed flow rate, said signal F being a signal representative of the flow rate of the feedstream; and

controlling the flow of the liquid bottoms product stream from the column in response to signal BS.

19. A process, as set forth in claim 18, wherein KBFR is a value in the range of about 0.02-0.1.

20. A process, as set forth in claim 18, including adjusting the flow signal F by applying dead time and lag time constants thereto.