Two-stage reciprocating compressor optimization control system

1. A method comprising:

operating a reciprocating compressor with a control system having a dual-mode model having a measurement mode and a tuning mode, wherein operating comprises:

receiving one or more inputs into the dual-mode model measured from the reciprocating compressor during operation thereof; and

in response to receipt of the one or more inputs, executing the dual-mode model in at least one of the measurement mode and the tuning mode, wherein:

in the measurement mode, execution of the dual-mode model further comprises calculating an actual flow rate of gas in the reciprocating compressor based on the one or more inputs; in the tuning mode, execution of the dual-mode model further comprises calculating one of an unloader setting and a speed set point of a physical element of the reciprocating compressor for a desired flow rate of gas, wherein the reciprocating compressor is a two-stage reciprocating compressor, including a first stage for lower pressure and a second stage for higher pressure;

setting a flow rate of gas and a minimum unloader setting for each of the first stage and the second stage;

calculating a shaft speed set point via application of the tuning mode of the dual-mode model for the set flow rate;

determining if the speed set point is greater than a minimum speed and less than a maximum speed;

increasing the minimum unloader setting associated with the first stage when the minimum speed is greater than the speed set point;

decreasing the set flow rate of gas when the speed set point is greater than the maximum speed; and

increasing the minimum unloader setting associated with the second stage when an inter-stage pressure is lower than an optimum value.

2. The method of claim 1 , further comprising:

in the tuning mode, one of receiving the unloader setting to calculate the speed of the physical element, wherein the physical element is a shaft, and receiving the speed of a shaft to calculate the unloader setting.

3. The method of claim 1 , further comprising:

calculating a mechanical power used by each cylinder in the reciprocating compressor.

4. The method of claim 1 , further comprising:

setting one of the unloader setting and the speed of a shaft based on the calculation in the tuning mode, wherein the setting is performed one of manually or automatically.

5. The method of claim 1 , wherein, in the tuning mode, execution of the dual mode comprises calculating the speed set point and the unloader setting for each of the first and second stages to adjust the inter-stage pressure between the first stage and the second stage.

6. The method of claim 1 , wherein the one or more inputs comprise a suction pressure, a suction temperature, and a discharge pressure.

7. A non-transitory, computer-readable medium storing instructions that, when executed by a computer processor, cause the computer processor to perform a method comprising:

operating a reciprocating compressor with a control system having a dual-mode model having a measurement mode and a tuning mode, wherein operating comprises:

receiving one or more inputs into the dual-mode model measured from the reciprocating compressor during operation thereof; and

in response to receipt of the one or more inputs, executing, via the control system, the dual-mode model in at least one of the measurement mode and the tuning mode, wherein:

in the measurement mode, execution of the dual-mode model further comprises calculating an actual flow rate of gas in the reciprocating compressor based on the one or more inputs and via valve pressure loss estimation based on a valve area and spring load, wherein the actual flow rate of gas is calculated by using a thermodynamic model applying thermodynamic equations for compressibility-corrected ideal gas isentropic compression to describe the pressure-temperature-volume state; and

in the tuning mode, execution of the dual-mode model further comprises calculating one of an unloader setting and a speed set point of a physical element of the reciprocating compressor for a desired flow rate of gas.

8. The medium of claim 7 , wherein, in the measurement mode, execution of the dual-mode model comprises calculating the actual flow rate of gas based on the one or more inputs comprising temperature and pressure measurements of the gas flow through the reciprocating compressor.

9. The medium of claim 7 , wherein, in the tuning mode, execution of the dual-mode model comprises calculating both the unloader setting and the speed set point of the physical element of the reciprocating compressor for the desired flow rate of gas.

10. The medium of claim 7 , wherein, in the tuning mode, execution of the dual-mode model comprises calculating the unloader setting for first and second stages of the reciprocating compressor for the desired flow rate of gas.

11. The medium of claim 10 , wherein, in the tuning mode, execution of the dual-mode model comprises calculating the unloader setting for the first and second stages to adjust an inter-stage pressure between the first and second stages of the reciprocating compressor.

12. The medium of claim 10 , wherein, in the tuning mode, execution of the dual-mode model comprises calculating the unloader setting for the first stage prior to calculating the unloader setting for the second stage.

13. The medium of claim 10 , wherein the unloader setting is different for the first and second stages of the reciprocating compressor for the desired flow rate of gas.

14. The medium of claim 10 , wherein the control system is configured to repeatedly execute the measurement mode and the tuning mode until the actual flow rate is substantially the same as the desired flow rate of gas.