Sometimes, un-comprehensive review of process optimization, fails to recognize the effect of changing set point around compressor. Below are examples how this problem happens. One of problem in refrigeration system was, how to ensure that there is no liquid carry over to gas phase after condensed liquid is collected and separated at Low Temperature Separator (LTS). The simple solution, is increasing operating pressure in order to reduce actual gas velocity across vessel.

Kiriman dari : Cahyo Hardo

Centrifugal Compressor – Part 4

Sometimes, un-comprehensive review of process optimization, fails to recognize the effect of changing set point around compressor. Below are examples how this problem happens.

One of problem in refrigeration system was, how to ensure that there is no liquid carry over to gas phase after condensed liquid is collected and separated at Low Temperature Separator (LTS). The simple solution, is increasing operating pressure in order to reduce actual gas velocity across vessel.

How high is high? Well, this is not a simple question. Because increasing pressure in surface facilities means increasing barrier for gas flowing from subsurface. However, too low in setting pressure at separator has a significant impact in liquid carry over, especially if the system has foaming tendency.

Let we try to increase the suction pressure. How to do it? Please refer to the Process Flow Diagram (PFD) attached.

The control of compressor can be simplified below.

The basic control philosophy is “suction pressure control with high discharge pressure override”. If the compressor suction pressure goes below the set point, the turbine speed decreases in order to build up the suction pressure. If the suction pressure goes above the set point, the turbine speed increases in order to take in more gas and there by, reduce the suction pressure. However, during this increase in suction pressure, if the discharge pressure goes above its set point, there will not be any further increase in the turbine speed and this would result in the anti-surge or recycle valve opening.

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