Pumping refrigerants at extreme temperatures
When a manufacturing process involves challenging liquids handling applications, the need for pumps to operate 24 hours a day, 7 days per week, without the need for any unscheduled servicing or repair, is often an essential requirement. Pumping refrigerants at extreme temperatures is one example of a particularly challenging application, where pumps and their key components are put under significant pressure.
A good example of exceptional pump performance in these types of situations is at a freeze-drying plant provided by Star Refrigeration at a major food manufacturer where Nikkiso Non Seal canned motor centrifugal pumps have been operating as part of the process of manufacturing instant coffee.
In June 2000, MICHAEL SMITH ENGINEERS supplied six Nikkiso canned motor pumps to Star Refrigeration, with the pumps being commissioned in June 2001. Since then half of the pumps have operated almost continuously 24 hours a day, 7 days a week without any servicing, repair or breakdown. All six pumps are pumping liquid carbon dioxide, which is non-lubricating and has a viscosity of around 0.1 cP, at a temperature of -54 0 C. Four of the pumps are pumping 50 m3/hr at 25 metres differential head while two of them are pumping 44 m3/hr at 35 metres differential head. All the pumps are operating with a hydraulic efficiency of around 60%.
Michael Smith Engineers recommended the Nikkiso BQ Reverse Circulation design for these duties, a pump which is designed to be mounted vertically with the motor over the pump ensuring quick and efficient venting of any vapour / gas in the rotor chamber. This design uses the process fluid to lubricate the sleeve bearings.
Angus Gillies, Technical Director of Star Refrigeration, commented “These are the most reliable refrigerant pumps we have ever used. Carbon dioxide often causes refrigerant pump problems due to bearing wear but the Nikkiso design has operated very well from commissioning. This is our first choice of pump for this challenging application.”