Method for preventing surge in a dynamic compressor using adaptive preventer control system and adaptive safety margin

Abstract

A method of preventing surge in a dynamic compressor is disclosed. The method includes providing an anti-surge valve having an adjustable opening for increasing the flow through a dynamic compressor. The next step is sensing process conditions in the dynamic control to determine a compressor load variable. A control system estimates a process disturbance model using the compressor load variable. The control system then adjusts a safety margin using a rate limited response and initiates a closed loop response using process feedback based on the process disturbance model. The control system adjusts the opening of the anti-surge valve according to the safety margin and closed loop response.

Claims

1. A method of preventing surge in a dynamic compressor, the method comprising the steps of: providing a surge valve having an adjustable opening for increasing a flow through the dynamic compressor; sensing process conditions in the dynamic compressor to determine a compressor load variable; estimating a process disturbance model using the compressor load variable using a digital derivative of the compressor load variable; adjusting a safety margin based on the process disturbance model; initiating a closed loop control response to open the surge valve based on the process disturbance model; and adjusting the opening of the surge valve according to the safety margin.

2. The method of claim 1 wherein the compressor load variable is determined based on a compressor dynamic operating point as a function of a surge limit line.

3. The method of claim 1 wherein the compressor load variable is determined based on compressor driver power.

4. The method of claim 3 wherein the compressor driver is selected from the group consisting of a motor, a steam turbine and a gas turbine.

5. The method of claim 1 wherein the compressor load variable is determined based on compressor driver rotating speed.

6. The method of claim 1 wherein the compressor load variable is determined based on a system process variable.

7. The method of claim 6 wherein the system process variable is a header pressure or flow of a process associated with the compressor.

8. The method of claim 1 wherein the compressor load variable is determined based on mathematical modeling of a system component or process.

9. The method of claim 1 wherein the compressor load variable is a flow of the compressor.

10. The method of claim 1 wherein the compressor load variable is a temperature measurement associated with the compressor.

11. The method of claim 1 wherein the compressor load variable is a pressure measurement associated with the compressor.

12. The method of claim 1 wherein the compressor load variable is a distance of a compressor operating point from a surge limit line.

13. The method of claim 1 wherein the compressor load variable is a power of the compressor driver.

14. The method of claim 1 wherein the compressor load variable is a speed of the compressor.

15. The method of claim 1 further comprising the step of differentiating a steady state response from process disturbance upsets.

16. The method of claim 1 wherein the safety margin is adjusted using a rate limited response based on the process disturbance model.

17. The method of claim 1 further comprising the step of increasing the safety margin based on an increase in response of the process disturbance model.

18. The method of claim 17 further comprising the step of resetting the safety margin based on a rate limited response to a decrease in response of the process disturbance model.

19. The method of claim 18 wherein the decrease in response of the process disturbance model corresponds to a positive rate of approach of a compressor dynamic operating point to a surge limit line.

20. The method of claim 17 wherein the increase in response of the process disturbance model corresponds to a negative rate of approach of a compressor dynamic operating point to a surge limit line.

21. The method of claim 1 wherein the surge valve is opened whenever a distance of a compressor dynamic operating point from a surge limit line is less than the safety margin.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of a dynamic compressor;

(2) FIG. 2 is a graph showing flow versus pressure ratio to determine a surge limit line;

(3) FIG. 3 is a block diagram of a surge adapter response of a control system of a dynamic compressor;

(4) FIG. 4 is a block diagram of a surge adapter response of a control system of a dynamic compressor using a dynamic rate limiter;

(5) FIG. 5 is a block diagram of a surge preventer and adaptor control system of a dynamic compressor; and

(6) FIG. 6 is a block diagram of an alternative surge preventer and adaptor control system on a dynamic compressor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(7) FIG. 1 shows a dynamic compressor 10 that includes a compressor 12 that is driven by a compressor driver 14. The compressor driver is of any type including a motor, gas turbine, steam turbine or the like. The compressor 12 has a gas inlet 16 and a gas outlet 18 wherein gas flows through the compressor 12 to be compressed. A surge or recycle valve 20 is fluidly connected between the gas inlet 16 and gas outlet 18 so that when the surge valve 20 opens a fluid flow path exists to convey gas from the gas outlet 18 to the gas inlet 16. A plurality of sensors 22 including pressure sensors, temperature sensors, flow measurement sensors and the like are placed throughout the dynamic compressor 10 in order to determine processed conditions for the components of the dynamic compressor including the compressor 12, the driver 14, the gas inlet 16, and gas outlet 18 and the surge valve 20. The plurality of sensors 22 are electrically connected to the control system 24 where the control system is in real time communication with all of the components of the dynamic compressor and controls the opening of the surge valve 20.

(8) Control system 24 utilizes the plurality of sensors 22 to determine process conditions so that a compressor load variable can be calculated. The compressor load variable can be determined based on different methods. The compressor load variable can be determined by using the compressor dynamic operating point as a function of surge limit. The compressor load variable also can be determined by calculating the power of the compressor driver 14 or the rotating speed of the compressor driver 14. The compressor load variable can also be determined by a system process variable such as header pressure or header flow of the compressor 12 connected in a compression network. A final way of determining the compressor load variable is through mathematical modeling of the compressor 12, the driver 14 or the associated process. Specifically, the compressor load variable is determined using any of these or a combination.

(9) The control system 24, after determining the compressor load variable, estimates a process disturbance model using one of several methods. The first is to take a digital derivative of the compressor load variable. The second is to take a delayed response of the compressor load variable. The third is to utilize filter response of the compressor load variable. The fourth is to utilize a surge model response of the compressor load variable. Once a process disturbance model is estimated a safety margin can be adjusted using a rate limited response of the process disturbance that is obtained and a closed loop response using process feedback can be initiated.

(10) FIG. 3 shows an adaptive set point calculation by the control system 24 utilized to determine an adaptive safety margin. The compressor load variable is inputted into a digital filtering disturbance model 30. After the process disturbance model is determined the control system 24 then utilizes a rate of change detector 32 to provide a signal 34 of a safety margin that is then presented to a model based dynamic rate limiter 36 in order to differentiate steady state response from process disturbance upsets. FIG. 4 shows an example of a dynamic rate limiter 36 that uses a steady state model 38 in combination with a disturbance model 46 to provide adaptive set points 42 and 43 in order to arrive at an adaptive safety margin.

(11) FIG. 5 shows an adaptive closed loop surge preventer response process 44 that based on the distance of compressor operating point from the surge-line provides an adaptive closed loop fast response. A process disturbance dynamic model with provisions for differentiating steady state response from process disturbance upsets adjusts the closed loop response further in response to disturbance model output. In one embodiment the distance of compressor operating point to surge line is communicated to a system function 48 to send a response signal 50 that is considered an adaptive surge preventer response signal. En another embodiment for process 44, as shown in FIG. 6, the compressor load variable is inputted into a disturbance model 46 in order to estimate a process disturbance model response. The process disturbance model output is then communicated to a system function 48 to send a response signal 50, that is considered an adaptive surge preventer response signal in another embodiment. Simultaneously the surge controller 52 sends a signal 53 to be summed with the response signal 50 at summation point 54 before the signal goes to the surge valve 20.

(12) Thus, upon crossing of a predetermined second set point such as a surge preventer control line as shown in FIG. 2 the control system 24 initiates the closed loop adaptive surge preventer response based on a compressor load feed back variable. In this manner, the method is self adaptive because a compressor feedback variable is used to determine the size of the response going forward in time.

(13) Thus, provided is a dynamic compressor 10 that utilizes a control system 24 that provides a method of adjusting a recycle valve 20 that improves upon the state of the art. Specifically, by determining an adaptive safety margin based upon a compressor load variable to provide a process disturbance model, improved control of the surge valve 20 and protection of the dynamic compressor 10 is provided. Additionally, by using an online determination of parameters based on steady state and dynamic change of compressor load variable measurements an adaptive safety margin rate is utilized thus providing an improved functioning over the prior art. Further, by utilizing the process disturbance model, process feedback is used to determine the size of the response of the control system 24 going forward instead of relying on heuristic open loop jumps as a function of time or gain Changes in proportion to control loop error. Therefore, an adaptive closed loop fast response comes from an online self compensation or self correction of the surge valve action as a result of the steady state and dynamic model of compressor load variable measurements improving upon the state of the art. Thus, at the very least all of the stated objectives have been met.

(14) It will be appreciated by those skilled in the art that other various modifications could be made to the device without departing from the spirit and scope of this invention. All such modifications and changes fall within the scope of the claims and are intended to be covered thereby.