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Industrial Applications

Thermal-oil pumps

for synthetic heat-transfer liquids

Posted on May 30, 2012 - ( views)

by Constanze Schmitz

Thermal-oil pumps are specifically adapted to the properties of synthetic oils used in heat-transfer systems. Traditional pump designs are not suitable for the lower lubricity and, in many cases, lower viscosity.

As soon as the temperature in a heat-transfer system becomes too high for water, a plant operator must choose between petroleum-based or synthetic oils as the heat-transfer liquid. When modern petroleum oils are used, systems with feed temperatures up to about 300°C can stay in service for their entire service life with one filling and with virtually no maintenance. Once feed temperatures rise above 300°C, only high-quality synthetic oils will be appropriate. Under these conditions, even minor temperature increases will have a decisive effect on the service life of the oils. An additional 10°C commonly doubles the product's specific rate of decomposition. When compared to petroleum-based heat-transfer oils, the amount of maintenance associated with synthetic oils is significantly lower.

The quality of the oil also directly influences pump performance. If a large number of low-boiling compounds form, pockets of gas and flow breakaways will be the result. This puts greater stress on the pumps and reduces their capacity. Low-boiling compounds reduce pump capacity, which elevates the film temperature in the heater, accelerating decomposition of the heat-transfer fluid, and ultimately forming more low boilers. Irrespective of this, synthetic heat-transfer oils place special demands on pumps. Compared to petroleum-based oils, their lubricity is lower.

That is why Colfax Fluid Handling’s Allweiler brand has developed thermal-oil pumps that are specifically adapted to the properties of synthetic oils. Two factors are critical: lower lubricity and, in many cases, lower viscosity. Traditional pump designs are not suitable for handing these conditions. Just starting the pumps is difficult. Normal operation is accompanied by high wear and consequently higher maintenance costs as well.

Thermal oil heaters manufactured by INTEC Engineering GmbH of southern Germany provide a good example of how these pumps are used. This company’s thermal oil heaters supply process heat to industrial plants around the world. INTEC focuses on the requirements of the wood, textile, palm oil, chemical, shipbuilding, and food industries. Standard heaters cover an output range of 100 to 20,000kW; custom designs can deliver even higher output.

Operators of these systems must make a fundamental choice based on their own specific requirements: water or oil as the heat-transfer liquid? If oil is chosen, a second decision arises: petroleum-based or synthetic oil? When temperatures reach approximately 180 to 200°C, the high pressures in the system almost always necessitate the use of heat-transfer oil, which can operate up to 320 °C with virtually no pressure. As a result, the entire system can be constructed with much thinner walls. Oil also does not have the corrosive properties of water. By contrast, when water is used as a heat-transfer liquid, it generates a system pressure of 80 bar at just 300 °C. For applications that require temperatures of between 350 and 400 °C, such as ground preparation (decontamination), manufacturing of semiconductors and printed circuits, or solar thermal power stations, synthetic oil is the only choice. Overall, heat-transfer oils have proven to be the best choice in most industrial processes. Solar power stations and solar field engineering are major users of synthetic oils like Therminol VP1 and Dowtherm A with feed temperatures of approximately 400 °C.

Pumps are the core elements in every heat-transfer system, since they convey the heated liquid to the places it is needed. However, the high temperature of the liquid places special requirements on the pumps’ sealing systems, especially during initial filling and the first time it is brought into service. Pumps from Colfax Fluid Handling’s Allweiler brand are proven to handle these situations. According to Edwin Karrer, Managing Director of INTEC: “We have been using pumps all the Allheat series since 1995. In fact, for a long time Allweiler AG was the only place you could get pumps for synthetic oils. Their experience in this area has benefited us tremendously.”

In addition to design-related benefits, INTEC has four additional reasons for choosing Allweiler pump/motor assemblies: the global service network; competent, rapid and on-site consultation by experienced Allweiler sales engineers; short delivery times in most cases; and strong support during warranty claims. “Like the pumps, our systems are very reliable. When problems do arise, it is very important to work with a cooperative partner who responds quickly,” according to Mr. Karrer. It is also important that each customer’s system contains pumps from only one manufacturer, since this is the only way to keep expenses associated with spare parts and maintenance low. That is why INTEC uses not only Allheat pumps, but also three-screw pumps of the Allfuel series as burner and lubrication pumps. When serving customers in the chemical industry who require ATEX safety, INTEC uses magnetically-coupled pumps of the Allmag series.

Pumps of the CTWH series pump both low-viscosity, synthetic heat-transfer oils up to 400 °C as well as hot water up to 207 °C with the identical material configuration. These pump units employ a flexible modular system. Depending on the specific application, they are available in base-plate, block, and inline versions.


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