Cooling Technology

Centrifugal Pumps in Cooling Technology

Cooling technology deals with methods and procedures to remove heat. The cooling processes required here are based on various physical effects dealing with the cyclical phase shift of a refrigerant in the refrigerating machine.

Application of EDUR-Pumps in Cooling Technology

Industrial refrigeration comprises a wide spectrum of different applications in cooling technology. As a rule, systems with a higher performance from about 200 m³/h compressor suction volume are required. Typical fields of application of pumps in cooling technology can be found in food processing, slaughterhouses, dairy technology, beverage industry, breweries, pharmaceutical industry, deep-freeze warehouses as well as in the chemical industry.

Centrifugal pumps in refrigerating plants are classified according to the type of conveyed fluid. Depending on the design and size of the plant, there are coolant pumps and refrigerant pumps.

EDUR-pumps for coolants stand out due to their compact pump design, axial thrust-free, open or closed and load-relieved impellers as well as diffuser elements in the ring housing, which take up a large portion of the radial forces. This overall construction has a positive influence on the lifetime of the mechanical seal as well as on the anti-friction bearings in the drive motor. In order to prevent the mechanical seal from being damaged by freezing condensation water, EDUR-pumps are executed with antifreeze protection in case of very low temperatures of the conveyed fluid.

Refrigerant pumps are often magnetically coupled pumps, which hermetically seal the refrigerant from the atmosphere. The advantage over canned motor pumps lies in the spatial separation of the drive motor from the pump, which prevents a heat intake into the conveyed fluid i.e. the refrigerant. Consequently, the separation has a positive effect on the energy balance of the whole refrigerating plant.

Furthermore, EDUR-refrigerant pumps are characterized by very low NPSH values, which have a positive effect on the refrigerant at its boiling point. Compared to volute housing pumps, EDUR-centrifugal pumps are able to transport certain gas proportions in conveyed fluid through the diffuser element. The advantage here being that the minimal amount of refrigerant evaporation is safely handled.

Refrigeration Plants in the Chemical Industry

Refrigeration plants that are used in the chemical industry are mainly used for cooling down products, cooling rooms and condensing gases. When cooling down products, either solid products are cooled down by recirculating the ambient air or liquids are cooled in heat exchangers. When cooling rooms, it is merely a matter of reducing the room temperature below the ambient temperature. Condensing gases takes place in special heat exchangers. The condensation heat is absorbed at low temperature by the evaporating refrigerant.

Refrigeration plants consist of:

• Compressor
• Condenser
• Expansion valves
• Evaporator

and a multitude of different auxiliary units, such as single stage and multistage centrifugal pumps in horizontal or vertical design made of materials such as grey cast iron, spheroidal graphite iron or stainless steel.

The constructional design of centrifugal pumps in refrigerant plants is based on the type of conveyed fluid, which is divided into coolants and refrigerants. Coolants are liquids, which are still flowable at low temperatures and transport coldness to the desired place. Here, centrifugal pumps with single-acting mechanical seals such as so-called brine pumps are mainly used, because the conveyed fluids are normally not dangerous to people or the environment. For reasons of climate protection, natural refrigerants such as ammonia (NH3) or carbon dioxide (CO2) are increasingly used. Even if these refrigerants have proved to be very environmentally compatible, they are harmful to humans. That is why hermetically sealed centrifugal pumps such as magnetically coupled pumps are used for the transport of refrigerants, which hermetically seal the pump interior from the atmosphere.

Refrigeration Plants in Deep-Freeze Warehouses

In deep-freeze warehouses a temperature is artificially obtained, which is usually below the ambient temperature. The usual temperature range in storage rooms lies between -18 and -30°C. The refrigerating plant of a deep-freeze warehouse requires a lot of space and accounts for approx. 20% of the total investment of a refrigerated warehouse. Compressor cooling plants operated with ammonia (NH3) are used starting at 200 kW of installed refrigerating capacity mainly due to the good energy balance and the positive environmental properties. The pump technology here ranges from single stage or multistage centrifugal pumps with single-acting mechanical seal and antifreeze protection (brine pumps or coolant pumps) to magnetically coupled pumps (refrigerant pumps) for ammonia (NH3) or carbon dioxide (CO2).

Energy-Savings through Absorption Refrigerators

With an absorption refrigerator, the refrigerant is re-liquefied after evaporation through temperature differences. This procedure is also referred to as thermal compression, as opposed to compression refrigeration, whereby liquefaction occurs via a compressor.

For the supply of refrigerant-solvent mixture solution pumps are used, which are executed as magnetically coupled pumps conveying the refrigerant ammonia. Brine pumps are used for the coolant circuit. For reasons of corrosion protection, these brines are not salt solutions, but a mixture of ethylene or propylene glycol and water. Depending on the temperature level, also freezer pumps with antifreeze protection are used.

Refrigerating Plants for Earth Freezing Systems

In order to manage groundwater ingress and static stability with underground building projects, earth freezing systems freeze the building sites for the duration of construction works. By introducing steel and concrete, the earthwork is stabilised after thawing and the groundwater prevented from ingress. The cooling concept of such a system consists of refrigerating plant that is arranged above ground combined with freezing lances, which are introduced into the earthwork within the construction site area. Depending on the temperature level, various coolants are supplied through these lances, which freeze the soil around the freezing lances down to a temperature of -50°C. The EDUR-centrifugal pumps used can safely supply the viscous coolant at these extreme temperatures and are additionally executed with a reliable antifreeze protection.

At such cooling powers, the refrigerating machine itself is normally operated using the refrigerant ammonia (NH3). Even though this natural refrigerant is climate-neutral, it is still a toxic fluid which may be supplied exclusively with hermetic pumps. Here, magnetically-coupled refrigerant pumps are used to prevent the conveyed fluid from escaping into the atmosphere.