(55c) Selection and Comparison of Thermic Fluids in a Fired Heater

Hot fluid properties such as density, thermal conductivity, heat capacity, vapor pressure, and viscosity of hot oils such as 100N, ULSD, Dowtherm A, Dowtherm G, and Therminol are used to estimate their thermal and hydraulic performance parameters. Thermal performance parameters include the Reynolds number, Prandtl number, Nusselt number, and heat transfer coefficient. Hydraulic performance parameters include line pressure drop, friction factor, hydraulic horse power, velocity, and flow rate. Cost benefit evaluation based on the hydraulic performance parameters was performed for different hot oil. Even though the cost of 100N and ULSD per barrel is 23 times inexpensive than Therminol and Dowtherm, these cannot be used when operating temperatures are above 600°F due to thermal degradation. Also, though Therminol-71 has higher heat transfer coefficients, Dowtherm G is the optimal hot oil due to its lower operating costs and lower vapor pressures. This study shows a systematic approach for selection of hot oil fluid. This study can be utilized in optimization and debottlenecking studies of existing or new heater projects for wide varieties of temperature range.