COOLANTS AND REFRIGERANT PUMPS
In the refrigeration business, we focus on two areas of mediums used for heat transport. The coolants who are the “secondary refrigerants” like brines and glycol. You find them in low temperature applications and especially for the use in more complex piping networks. Most of the time regular centrifugal pumps are in use for this area.
For colder applications [-40°C; frozen food processing; freezing; deep temp. storage], the refrigerant fluids generally employed are ecologically harmless “primary refrigerants” such as CO2 or ammonia.
This article is about the selection of these related primary refrigerant pumps.
Because these liquids [CO2 and ammonia] are dangerous to people if leaked to atmosphere, pumps have to be sealed in a special way. One way is the use of a “canned” motor-pump, the other by using a magnetically coupled pump.
TWO MAIN TYPES OF PUMP- CANNED MOTOR
Canned motor-pumps have been very popular of recent times because of their safety and the higher cost of “mag-drive” pumps. There are also several high quality manufacturers of these pumps. The canned motor pump has a hermetically sealed casing around the motor, which is directly coupled to the pump. There is therefore no need for mechanical seals and the chances of a leak is very minimal. The only draw-back of this design is that pumped fluid needs to pass through the motor chamber to keep the motor cool, therefore using part of the motor’s energy to provide this function.
TWO MAIN TYPES OF PUMP- MAG DRIVE
Over time, the cost of magnetically coupled pumps has reduced, and German pump manufacturer, EDUR, has produced a line of refrigerant pumps using this principle.
Having a magnetic coupling means the pumps are hermetically sealed without having to use specialised motors or use the pumped media for motor cooling. This has several benefits.
Firstly, off the shelf, mass produced TEFC motors can be utilised in lieu of specialist motors used in the canned motor-pumps. And because of the spatial separation between motor and pump, heat transfer into the medium is reduced or avoided, benefiting the energy balance of the system. Finally, and most importantly, because energy is not being used to pump fluid over the motor, EDUR pumps are more energy efficient – a benefit when pumps are running 24 hours per day, 365 days per year.
Any pump used in refrigerant systems needs to have a low NPSHr (Net Positive Suction Head required) because the pumped fluid will always be close to its “boiling” point. It is also best if the selected pump is able to handle certain levels of gas content.
Both canned motor-pumps and EDUR magnetically coupled pumps have low NPSHr, but because of their “diffuser devices”, EDUR pumps handle some evaporation of refrigerants reliably.
EDUR refrigerant pumps:
The EDUR Torque-Flow (FUB) range of centrifugal pumps have vortex impellers and are capable of handling spherical solids up to 80mm in diameter. They are close-coupled and available with casings of Cast Iron, Ductile Iron or Gunmetal Bronze, impellers of Ductile Iron, Gunmetal Bronze or Stainless Steel, with Stainless Steel shafts (in 2 grades). Some models are available in all Stainless Steel construction. Abrasion-resistant protective linings of ceramic and polyurethane are also available.
- Flows to 100 l/s
- Heads to 35m
- Handle solids sizes to 80mm
- Handle temperatures from -40oC to 140oC
- Handle Viscosity to 60cSt
- Handle 15% solids
- A variety of mechanical seals available to suit specific applications
The EDUR LBU multiphase pump is a multi-stage centrifugal pump with the unique capability of being able to pump a liquid/gas mixture. The centrifugal pump is constructed of either C.I./ Bz/ SS, Nodular Cast Iron, All-Bronze, Stainless Steel, or Super-Duplex Stainless Steel construction, so may be used to handle a variety of liquids.
Air, Oxygen, Carbon Dioxide and Ozone gases can be introduced into the suction line and transported and used to mix or disperse the gases. This makes the pump ideal for DAF plants, where the multiphase pumps provide the task of air saturation without the use of compressed air (no compressor, air saturation tank or associated controls).
- Liquid flows to 16 l/s
- Gas content up to 20%
- Cast iron/Bronze/Stainless steel, Nodular cast Iron, All-Bronze, Stainless Steel, or Super-Duplex Stainless Steel construction
- Completely replace the “old” DAF system with a single pump
Designing pumps since 1927, EDUR Pumpenfabrik has developed a range of pumps for use in refrigeration systems. They have been designed to provide a maximum level of safety, reliability and efficiency. They are the safe option because they use standard TEFC motors, which don’t need to be cooled using the pumped media. They are efficient because they use magnetic couplings. By using magnetic couplings energy is not wasted by pumping fluid over the motor [as with “canned motor pumps”] and back through to the separator.
- Suitable for ammonia, C02, synthetic refrigerants and refrigerants containing hydrocarbons/li>
- No heat transfer from motor to pumped media/li>
- Low maintenance/li>
- Low NPSH values/li>
- Pulsation free operation/li>
- Long service life
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