Pumps are the heart of heat-transfer plants

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Courtesy of ALLWEILER GmbH

Manufacturers in a variety of industries depend on heat-transfer plants to heat or cool their machines and apparatus. German firm heat11 GmbH & Co. KG specializes in heat-transfer plants of virtually all types. The chemical industry uses their installations for controlling the temperature of reactors and during the production of color pigments and liquid crystals. In the plastics industry, heat-transfer plants are essential for producing polyethylene terephthalate (PET) and in the production of CDs and DVDs. But recently, according to heat11’s Managing Director Dietmar Hunold, heat recovery has become an increasingly important application.

Oil or water?
Operators considering the use of a heat-transfer plant must answer a fundamental question: water or oil as the heat-transfer liquid? If the answer is oil, then they must choose between petroleum-based and synthetic varieties. Since oil can be used up to 350 °C without pressurization, it is commonly used in applications over 200 °C in order to avoid the high pressures associated with water vapor. As a result, the entire system can be constructed with thinner walls. Oil also does not have the corrosive properties of water. By contrast, at 200 °C water exhibits a pressure of 16 bar; at 250 °C, the pressure reaches 40 bar. For applications that require temperatures of between 350 and 400 °C (such as ground preparation or manufacturing of semiconductors and printed circuits), synthetic oil is the only choice.

Pump requirements
Pumps are of central importance in every heat-transfer system, since they convey the boiler-heated liquid to the places it is needed. However, the high temperature of the liquid places special requirements on the pumps’ sealing systems. “I’ve been in this business a long time and it is my experience that pumps from Allweiler AG have proven their value in these applications,” according to Mr. Hunold. So it should come as no surprise that most of his company’s systems contain heat-transfer centrifugal pumps from Allweiler AG of southern Germany. Colfax Fluid Handling’s Allweiler brand has provided heat transfer pumps to global customers for more than 40 years. High-temperature pumps, designed specifically for synthetic heat-transfer oils, have been available for approximately 10 years.

Standard versions of these pumps are available in pressure ratings PN16 and PN25. Versions up to PN40 are available upon request for use with liquids that operate at high pressures. Special materials like nodular cast iron GGG 40.3 are used if the medium will be cooled to below -10 °C. If very high capacities are required (like in PET plants), the 'Allheat 1000” is selected. This pump is capable of moving up to 1,450 m3 /h with a delivery head of 100 m.

Similar to the choice between oil or water, operators must make a fundamental decision here as well: mechanical seal or magnetic coupling.

Due to their design characteristics, mechanical seals will always wear, necessitating regular maintenance. Pumps equipped with a magnetic coupling, on the other hand, are significantly more expensive to procure and exhibit lower overall efficiency than mechanical-seal pumps. For these two reasons, approximately 80% of pumps used by heat11 GmbH are equipped with mechanical seals, according to Mr. Hunold. In any case, synthetic heat-carrier oils do place special demands on pumps. Compared to petroleum-based oils, their lubricity is lower.

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