This ammonia refrigeration process is equipped with an oil transfer pump that transfers fresh refrigeration oil from a barrel to fill up the compressor oil separators to the operating oil level. However, the oil pump has been idle for a prolonged period, with the electrical power connection incomplete.
Conversely, the associated piping system seems completed. One end of the oil distribution header is connected to the oil transfer pump discharge port. In contrast, the other end is connected to an oil recovery vessel which is always under the ammonia vapor suction pressure at 28 psi as per the pressure gauge reading.
The mechanical seal inside the oil pump is relatively dry, and lacks oil lubrication to form a proper seal. Therefore, ammonia vapor under pressure could easily escape through the tiny clearance between the stationary and rotating rings of the mechanical seal to the atmosphere into the machinery room.
March 22, 2022
1) Around 12:30 pm, the shift engineer on duty took a reading in the machinery room and noticed a mild ammonia smell.
2) The monitoring panel outside the room was flashing green, and two ammonia gas detectors were showing below 10 parts per million of ammonia concentration.
3) Shift engineer turned on the emergency exhaust fan and attempted to locate the ammonia leak with litmus paper. Without any success, the shift engineer called in a licensed refrigeration contractor for help.
4) Around 2:00 pm, a licensed refrigeration contractor showed up. The ammonia leak from the oil transfer pump shaft seal was identified.
5) The pump was isolated by shutting off the suction valve (#264) and discharge valve (#269). The pump remained mechanically depressurized.
Facts and evidence
- The customer service report recommended replacing the shaft seal for the oil pump.
- The oil pump was not isolated. It was idle for a prolonged period with the associated piping system under ammonia vapor suction pressure.
- No Safe Operating Procedures for oil pump start-up and shutdown were found.
- No written training manual for the oil pump was provided to the client’s operating engineers.
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