Heat Transfer Oils Thermic Fluids

Steam is one of the most common options for heating. However, a steam pressure of 10 kg/cm and more will be required for achieving 150 °C and higher temperatures. This needs specially designed and fabricated vessels (heating jackets and coils), steam pipelines, and valves, with the approval of Pressure Vessel and Steam Boiler Inspection Authorities in the country. This is not necessary when heat transfer oils are used for heating even up to 270 °C as the system can operate at atmospheric pressure. 

Obtain a sample of the HTO for testing for the thermal stability (it shall not form any thick deposits in the tanks or pipes during the high-temperature operation). Also check the vapour pressure data for HTO oils while heating the oil beyond 200 °C. 

Caution There are chances of fire due to the circulating high-temperature oil, and hence, the motors, electrical fittings, and lighting must be flameproof. The pipelines, valves, gaskets, and pumps (with mechanical shaft seals) must he selected for high-temperature and high-pressure service and shall he tested as per statutory requirements. 

Since the heat transfer coefficient is much lower with HTO as compared to that of condensing steam, the HTO fluid will have to be heated about 20-30 °C above the required temperature for proper transfer of thermal energy to the material in the vessel. 

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Use higher pressure/temperature steam or a heat transfer oil (thermic fluid) at higher temperature for heating provided the jacket and the reactor shell are able to withstand these conditions. Check suitability of high temperature for the reaction mass inside before hand. 

Temperature to be achieved in the process vessel. It may be noted that the thermic fluid will have to be at a temperature at least 20-30 °C above the required temperature for maintaining a reasonable driving force for the transfer of heat. (The heat transfer coefficient is lower than in the case of condensing steam since the heat is transferred from the liquid oil only.) Vapour pressures of thermic oils are on the higher side beyond 200 °C and this must be looked into carefiilly while heating the oil. 

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