The key to getting the best heat transfer coefficients in industrial ammonia-based refrigeration systems is the cleanliness of the refrigerant. In purifying the ammonia refrigerant, the primary focus has been in purging noncondensables and removing excess moisture. Unless this is done routinely, temperatures begin to rise above design limits, resulting in higher electricity consumption. Purger systems typically are used to remove noncondensables, and distiller systems separate water from ammonia through an evaporation-separation process.
Oils and particles that migrate to unwanted areas also can create maintenance problems and lower heat transfer coefficients. Particles enter the systems primarily during installation as byproducts of the welding and installation processes. Because of the high cost of cleaning ammonia systems prior to startup, it is seldom done. The result is that damaging particles of various sizes are left in the system, degrading performance.
Compressors and valves have strainers and bags that capture larger-size particles. However, there have been no large-tonnage ammonia refrigeration systems with filtration capability to remove contaminants below submicron level beginning at startup.
The prototype ammonia filtration system installed in a North American ice-making plant was a collaborative effort between two of Parker Hannifin Corp.'s operating groups: Filtration, and Climate and Industrial Controls, both headquartered in Cleveland. It was designed to remove particles to submicron (0.5 micron) size and handle up to 250 gal/min of liquid ammonia with a pleated single cartridge and a 300 psig carbon steel vessel. The pressure drop across the vessel was initially recorded at 3 psig.
“After three months of operation, the pressure drop across the vessel has increased from 3 to 5 psig, and the bagged ice production per hour is greater,” said Ivan Villalba, market development manager, Mexico, for Parker Hannifin. “Particle removal has proven to be the key factor in increasing system capacity and reliability.”
With the large surface volume of the pleated cartridge, serviceability has eased maintenance. Due to the caking factor, the filtration ability increases with time until the scheduled replacement of the cartridge. The removal of particles from the system has proven to be a key issue in boosting its capacity and reducing total kilowatt-hour consumption.
In an industrial refrigeration system, the cleanliness of its coolant is as important as the quality of blood in the human anatomy. Just as dialysis can be a human life saver, investments in filtration systems will mean healthier ammonia refrigeration system operation for years to come.