Surge control in compressors

• US 4,971,516 A
• Filed: 08/07/1989
• Issued: 11/20/1990
• Est. Priority Date: 05/04/1988
• Status: Expired due to Fees

• Current Assignee: Exxon Research and Engineering Company (Exxon Mobil Corporation)
• Original Assignee: Exxon Research and Engineering Company (Exxon Mobil Corporation)
• Inventors: Lawless, Brian S., Stickel, John E.
• Primary Examiner(s): Look, Edward K.
• Assistant Examiner(s): Nguyen, Hoang
• Application Number:
  US07/391,673
• Time in Patent Office: 470 Days
• Field of Search: 415/1, 415/11, 415/13, 415/15, 415/16, 415/17, 415/26, 415/27, 415/30, 415/36, 415/37, 415/39, 415/40, 415/43, 415/118, 417/282, 417/293, 417/294, 73/24
• US Class Current: 415/1
• CPC Class Codes: F04D 27/0207 by bleeding, bypassing or recycling fluids influencing the boundary layer by an uncontrolled bleeding of the working fluid F04D29/681
• CPC Class Codes: G01F 1/662 Constructional details

Abstract

Method and apparatus for operating compressors to avoid surges. The compressor is controlled by direct measurement of the rate of volumetric flow, Q, of gas through the compressor via the use of an acoustic flow meter, or other sonic velocity measuring device in combination with a standard flow meter and the measurement of the speed, N, of the compressor. The Q/N ratio is calculated electronically and output to a controller which, through a control circuit, operates a recycle valve in a by pass line leading from the discharge side to the suction side of the compressor. The Q/N ratio measured by the controller at compressor operating conditions is compared with a Q/N ratio at which surge will occur. When the measured Q/N ratio is less than the Q/N ratio at surge, the recycle valve will open and flow gas from the discharge side to the suction side of the compressor to avoid surge flow in the compressor.

Claims

1. In a method for controlling a compressor in which a control valve is employed in an electronic circuit to control the recycle of gas from the discharge outlet to the suction inlet to the compressor, the steps of:

measuring the sonic velocity, that is the speed of sound in the gas, and the rate of volumetric flow, Q, of gas through said operating compressor,

measuring the rate of speed, N, of said operating compressor,

establishing a Q/N ratio from the values Q and N generated by the operating compressor,

establishing a set point Q/N ratio based on a rate of gas flow above which compressor surge can occur, and

comparing the Q/N ratio of the operating compressor with the Q/N set point ratio such that a measured Q/N ratio in the direction of a lower gas flow will open the control valve and permit the flow of recycle gas from the discharge outlet of the compressor to the suction inlet of the compressor, and return of the Q/N ratio of the operating compressor to the set point Q/N ratio will close the control valve to cut off the flow of recycle gas, wherein the Q/N set point ratio is constantly redefined based on measured gas sonic velocity during operation of the compressor.

2. The method of claim 1 wherein the rate of volumetric flow Q of gas through the operating compressor is established by direct measurement of the absolute velocity of the gas.

3. The method of claim 2 wherein the value measured for the sonic velocity of the gas is directly used for control of the control valve.

4. The method of claim 1, wherein the sonic velocity is measured with an acoustic flow meter.

5. The method of claim 1, wherein the sonic measuring device is used in conjunction with a non-acoustic flow meter.

6. In apparatus for operating a compressor to avoid surges wherein is included,

a compressor through which a gas is flowed which has a suction inlet for the introduction of a gas into said compressor, for compression, and a discharge outlet for the removal of compressed gas from said compressor,

a first line for supplying a gas to the suction inlet of said compressor,

a second line for compressed gas from the discharge outlet of said compressor,

a bypass line connecting said first line and said second line through which gas flow through said compressor to said compressor discharge outlet can be recycled to said compressor suction inlet,

a control valve located in said bypass line which can be opened to recycle gas from said compressor discharge outlet to said compressor suction inlet, and closed to recycle gas from said compressor discharge outlet to said compressor suction inlet,

an electronic circuit operatively associated with said control valve of said bypass line for opening and closing said control valve in response to an electronic signal,

a controller operatively associated with said electronic circuit for regulating and control valve by opening and closing same, responsive to means for producing a signal representative of the flow rate of gas through said compressor on comparison with a set point representative of a gas rate minimum limit below which surge can occur,

the improved combination which further includes,

a flow meter located in a conduit of said compressor through which gas is passed to directly measure the absolute and sonic velocity, that is the speed of sound in the gas, and rate of flow, Q, of gas through said compressor, and input said value of Q to the controller,

a means associated with said compressor for measuring the rate of speed, N, of the compressor and inputting said value to the controller,

whereby the controller computes the Q/N ratio of the operating compressor and compares this value with a set point Q/N ratio representative of a gas flow rate minimum below which surge can occur to open the valve of the bypass line when the Q/N ratio of the operating compressor moves below the set point Q/N ratio in the direction of surge, and close the valve of the bypass line when the Q/N ratio of the operating compressor returns above the set point Q/N ratio and whereby the Q/N set point ratio is constantly redefined based on the measured sonic velocity of the gas during operation of the compressor.

7. The apparatus of claim 6, wherein said flow meter is an acoustic flow flow meter located in the inlet line which supplies gas to the suction of the compressor.

8. The apparatus of claim 6 wherein the acoustic flow meter is located in the outlet line which transports compressed gas from the discharge of the compressor.

9. The apparatus of claim 8 wherein the compressor is an axial flow compressor.

10. The apparatus of claim 8 wherein the compressor is a centrifugal flow compressor.