Refrigerant Purity — Refrigerant contaminants can consist of several components:
. Lubricating oil tends to accumulate in the chiller. Lube oil contamination is reduced by controlling the amount of compressor cylinder lubrication, using synthetic lubricants, providing a good compressor discharge vapor separator to eliminate free oil, and providing a good reclaimer to remove oil accumulation.
· Lighter constituents in the refrigerant charge, such as ethane for a propane system, tend to accumulate in the refrigerant receiver, causing higher condensing pressure. Light component contamination is controlled by the type of refrigerant which is purchased. It can be further reduced by purging the receiver vapors. If the process plant inlet pressure is sufficiently low, the accumulator can be purged into the plant inlet for re-recovery of the hydrocarbons.
· Butane and heavier constituents in a propane refrigeration system tend to accumulate in the chiller. Heavy component contamination is normally not a severe problem, and it is best controlled by draining from the bottom of the lowest temperature chiller.
· Process fluid constituents may leak into the refrigerant in the chiller.
· Air can be introduced through the compressor packing if cylinder pressures are below atmospheric.
· Moisture, if present, will form ice and plug up the system either at the control valves or in the chiller. Moisture normally enters the system with the purchased refrigerant charge; it can be the source of considerable operating problems until it is removed. Some refrigeration systems employ a continuous dryer, some only a moisture indicator. The problem can usually be eliminated by injecting methanol in the system and draining it from the chiller. Moisture must also be removed prior to the start-up of a new system, normally by evacuating the system, purging the system with nitrogen or dry gas, injecting methanol, or a combination of these.
· Lighter constituents in the refrigerant charge, such as ethane for a propane system, tend to accumulate in the refrigerant receiver, causing higher condensing pressure. Light component contamination is controlled by the type of refrigerant which is purchased. It can be further reduced by purging the receiver vapors. If the process plant inlet pressure is sufficiently low, the accumulator can be purged into the plant inlet for re-recovery of the hydrocarbons.
· Butane and heavier constituents in a propane refrigeration system tend to accumulate in the chiller. Heavy component contamination is normally not a severe problem, and it is best controlled by draining from the bottom of the lowest temperature chiller.
· Process fluid constituents may leak into the refrigerant in the chiller.
· Air can be introduced through the compressor packing if cylinder pressures are below atmospheric.
· Moisture, if present, will form ice and plug up the system either at the control valves or in the chiller. Moisture normally enters the system with the purchased refrigerant charge; it can be the source of considerable operating problems until it is removed. Some refrigeration systems employ a continuous dryer, some only a moisture indicator. The problem can usually be eliminated by injecting methanol in the system and draining it from the chiller. Moisture must also be removed prior to the start-up of a new system, normally by evacuating the system, purging the system with nitrogen or dry gas, injecting methanol, or a combination of these.