In Part 3, I began demonstrating how the features of a pump-out system can be put to use via a case history at a representative frozen food plant located somewhere in the United States. As a reminder, for illustration purposes, assume the 30-year-old plant has approximately 1,500 employees and contains a large ammonia refrigeration system (~225,000 lb ammonia) to cool and freeze the food products and cool the production areas at the facility. In this plant, a complete pump-out system was installed as part of the initial installation of the ammonia refrigeration system. It consists of a bank of pump-out valves, an oil regenerator, and a 50 hp pump-out compressor.
Pump-Out System UsesIn a typical frozen food plant, the pump-out system may be operated on a daily basis for range of uses.
Intercoolers, Suction Accumulators and High-Pressure Receivers. The pump-out system can be used to remove the liquid ammonia from the intercoolers, the low-pressure suction accumulators, and high-pressure receivers, to install new lines or pumps, or to remove vessels from service. The pump-out system initially transfers liquid from the bottom of the vessel to a low-pressure suction accumulator. After the liquid is removed, the vessel is pulled into a vacuum to remove ammonia vapors. The actual pump-out operations for a large vessel typically take eight to nine hours, though a facility may choose to allow the system to remain under a vacuum overnight. Without pump-out system, the pump-out operations involving these vessels could take several days.
Pilot Receiver. This type of work probably would not be attempted without a pump-out system because some pilot receivers receive all of the liquid ammonia from the evaporative condensers. It takes approximately two or three hours to remove the liquid from the pilot receiver using a pump-out system. Within 10 hours from the start of the pump-out operations, the facility would be able to safely begin system tie-ins. If these jobs were performed without a pump-out system, it would take approximately two days to complete the task.
Compressors. Using a pump-out system, approximately 10 to 30 minutes are needed to pump-out an ammonia compressor for overhaul service. (The actual time needed depends on compressor size.) To avoid the possibility of removing oil from the compressor, facility operators should proceed slowly during the pump-out operations and use a pump-out line attached to the top of the compressor oil separator.
Strainers. All strainers should have pump-out connections. To clean a strainer facility, operators close two valves to isolate the strainer and open up the valve to the pump-out manifold. After 10 to 15 minutes, the strainer typically can be removed and cleaned.
Freezers. Oil can be regularly drained during production from plate freezers and spiral freezers located in the production area using the pump-out system. Without a pump-out system (in other words, if standard oil pots were used), the oil draining would probably have to be performed during nonproduction periods.
Other Uses. A pump-out compressor can be used to remove residual air from the system before equipment is placed back online following maintenance operations. A pump-out system also can be used to quickly shift liquid from one vessel to another, without the use of temporary hoses, during upsets.
ConclusionPerhaps the best argument for installing a pump-out system is the work and headaches it saves. It can save time, money, and minimize the potential for ammonia releases. Yet, like all pieces of ammonia refrigeration equipment, it must be designed and operated properly. Proper training and administrative controls must be in place. In addition, a pump-out system may not be cost-effective for every refrigeration system. If your facility can afford to shut down for the long periods required for maintenance work and system modifications, there may be no time savings (and therefore cost savings) associated with the pump-out system.
If your refrigeration system does not currently contain a pump-out system, think small. Add tie-in points to existing suction headers and slowly expand the system as time and money permits. A complete pump-out system may take years to install, but the effort required will provide numerous payback opportunities.