Water and steam are typically used as heat carriers in heating systems. But at high temperatures, water and steam requires a corresponding high operating pressure. In industrial heating systems, a high temperature level is often a great advantage and establishing this with water and steam can be very controversial and expensive.
In thermal oil heaters a special oil are used instead as the heat carrier, operating at atmospheric pressure up to 300°C. Comparing to water and steam, it would require a pressure of 85 bar to obtain this temperature. There are several advantages by using thermal oil compare to e.g. steam systems.
Thermal oil heaters are a real good and innovative solution for heat production in those industrial processes where high process temperatures are required. There are circumstances in which the use of a thermal fluid heater rather than a steam boiler is more suitable for heat production, usually to lower costs.
Applying basic radiation concepts to process-type heater design, Lobo & Evans developed a generally applicable rating method, that is followed with various modifications, by many heater designers. Reference Lobo & Evans, Heat Transfer in the Radiant Section of Petroleum Heaters, AICHE, Vol. 35, 1939.
Coil is commonly used where the duties are small. Selecting the heater tube material and size to use in a heater design is really a matter of experience. As designers work with different fired heaters for different services, designers develop a knowledge of what fit before in a similar design, so designer know where to start with a new design. But a few general rules can be used to start the selection.
In a thermal fluid heater, a gas or oil fired burner is mounted at one end of the heater and projects into the inner chamber. The hot gases radiate heat, which is absorbed by thermal fluid circulating through the coils. The hot fluid then circulates to one or several users before returning to the thermal fluid heater for reheating.
Process heat load requirement must be determined and remember to add at least 15 percent as a safety factor to make certain heater is not undersized.
Designers must choose the correct thermal fluid for specific operating conditions. The thermal fluid should be checked regularly to verify that it has retained its heat transfer properties.
A properly designed and installed thermal fluid heating system should give between 20 to 30 years of reliable service, but periodic maintenance is still necessary for safe and effective operation.
Keywords: Design; Oil heater; Coil; Temperature; Heat transfer
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