Flow control system and control method for parallel flow process equipment

• US 4,197,868 A
• Filed: 08/21/1978
• Issued: 04/15/1980
• Est. Priority Date: 08/21/1978
• Status: Expired due to Term

• Current Assignee: UOP Des Plaines IL A NY General Partnership
• Original Assignee: UOP Llc (Honeywell International Inc.)
• Inventors: Carson, Don B.
• Primary Examiner(s): Nilson, Robert G.
• Application Number:
  US05/935,398
• Time in Patent Office: 603 Days
• Field of Search: 137/7, 137/8, 137/9, 137/10, 137/101, 137/110, 165/34, 165/38
• US Class Current: 137/7
• CPC Class Codes: G01M 3/26 by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors
• CPC Class Codes: G05D 11/132 by controlling the flow of the individual components G05D11/133 takes precedence
• CPC Class Codes: Y10T 137/0352 Controlled by pressure
• CPC Class Codes: Y10T 137/0357 For producing uniform flow
• CPC Class Codes: Y10T 137/2524 Flow dividers [e.g., reversely acting controls]
• CPC Class Codes: Y10T 137/2562 Dividing and recombining

Abstract

A control system and a method for regulating the division of a single feed stream between two or more pieces of processing equipment operated in parallel. The feed stream enters a three-way valve and is then equally divided into two smaller streams which flow through separate pieces of process equipment and then through separate check valves. The pressure of each of the smaller streams is monitored to detect leakage in either piece of the equipment. The flow normally passing through the leaking piece of equipment is diverted to the intact piece of equipment when the leakage causes a predetermined pressure difference.

Claims

1. A flow control systrem for regulating the flow of a process stream through two heat exchangers operated in parallel which comprises:

(a) a three-way valve means having an inlet port and a first and a second outlet ports;

(b) an inlet conduit which carries the entire process stream operatively connected to the inlet port of the three-way valve means;

(c) a first and a second heat exchanger, with each heat exchanger having an inlet and an outlet;

(d) a first process flow conduit which operatively extends between the first outlet port of the three-way valve means and the inlet of the first heat exchanger;

(e) a second process flow conduit which operatively extends between the second outlet port of the three-way valve means and the inlet of the second heat exchanger;

(f) a third and a fourth process flow conduit, with the third process flow conduit having a first end attached to the outlet of the first heat exchanger and with the fourth process flow conduit having a first end attached to the outlet of the second heat exchanger, the third and the fourth process flow conduits each also having a second end;

(g) an outlet conduit which carries the entire process flow stream operatively connected to the second end of both the third and the fourth process flow conduits;

(h) a first check valve located in the third process flow conduit and a second check valve located in the fourth process flow conduit;

with both the first and the second check valves oriented to prevent fluid flow toward the three-way valve means;

(i) a flow rate measurement and control means comprising operatively connected flow rate sensors located in the first and the second process flow conduits and a flow rate controller and which monitors and compares the fluid flow rates in the first and the second process flow conduits, the flow rate measurement and control means generating a first signal which is transmitted to the three-way valve means and which regulates the operation of the three-way valve means;

(j) a pressure differential measurement and monitoring means comprising operatively connected pressure sensors located in the first and to the second process flow conduits and a pressure differential control unit and which generates a second signal when the pressure difference between the first and the second process flow conduits exceeds a predetermined limit; and

,

(k) a first signal-carrying means which interconnects the flow rate measurement and control means and the three-way valve means for transmitting the first signal, and a second signal-carrying means which interconnects the pressure differential monitoring means and the flow rate measurement and control means for transmitting the second signal.

2. A method of regulating the flow of a process stream through two heat exchangers operated in parallel-flow which comprises:

(a) passing the feed stream into a three-way valve means operated in response to signals generated in a process control means, and dividing the feed stream into a first process stream having a first flow rate and a second process stream having a second flow rate;

(b) monitoring and comparing the flow rates of the first and the second process streams and generating a first signal in the process control means, the first signal being representative of the adjustment in the operation of the three-way valve means necessary to equalize the flow rates of the first and the second process streams;

(c) passing the first process stream through a first heat exchanger and passing the second process stream through a second heat exchanger;

(d) passing the first process stream through a first check valve and passing the second process stream through a second check valve; and

,

(e) comparing the pressure of the first process stream at a point upstream of the first check valve to the pressure of the second process stream at a corresponding point upstream of the second check valve, and replacing the first signal of step (b) by a second signal generated in the process control means if the pressure differential between the first and the second process streams exceeds a predetermined limit, with the second signal effecting the adjustment in the operation of the three-way valve means necessary to terminate the flow of the process stream having the lower pressure.

3. The method of claim 2 further characterized in that the predetermined limit of the pressure differential exceeds 0.5 atm.

4. The method of claim 3 further characterized in that the predetermined limit of the pressure differential exceeds 1.0 atm.