2021 RETA Breeze May-June

LINKEDIN AND FACEBOOK VALUABLE CONNECTIONS

The other week I was working at a facility in the electrical control room. I was updating the PLC program and operator interface. About every 12 or so minutes I heard a loud noise outside the electrical room. It took a while for me to realize I was hearing the sound that is associated with a liquid hammer event.

Turns out that it was the liquid line that goes from the high pressure receiver to the recirculator package. The line is three inches in diameter and about 30 feet in length. There are only four, 90 degree elbows between the float switch controlled king valve and the liquid feed valves on the recirculator vessel. The minimum level switch on the receiver was satisfying and calling, as liquid came to the receiver from the evaporative condensers. At first glance, it seemed that there was not enough ammonia available to satisfy the recirculator and maintain the minimum level in the receiver. The recirculator would continue to call for

liquid while the king solenoid valve closed. The pressure between the receiver and the recirculator dropped to the suction pressure as the liquid evaporated from the line. Then the liquid level in the receiver reached the satisfaction, setting on the float operated switch assembly. The switch sent power to the king solenoid valve which opens suddenly. The rush of liquid down the line caused the banging I heard – the pipe shook as well. I consulted with the operator about this situation. On investigation, it was found that the recirculator package was operating at a 40 percent setting with a five percent deadband. At 40 percent set

point, there was this on-going starve and fill action setting up. The operator chose to lower the control set point from 40 percent to 30 percent. It took about an hour to see the results of this change. The 30 percent operating level was sufficient for the operation of the vessel. There was no cavitation of the ammonia pumps at this new setting. The open/close cycling of the minimum level switch on the high pressure receiver came to an end. There was no more hammering taking place. This was seen in the first hour after re-setting the working level in the recirculator. What was not expected was that the evaporators started

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