Thermal fluid (hot oil) heating system for process heating

01

Keep the heater within the fluid's bulk and film temperature limits

Eastman's bulletin for its Therminol 58 synthetic heat transfer fluid gives a maximum bulk temperature of 300 °C, a maximum film temperature of 339 °C, a normal boiling point of 352 °C, a flash point of 195 °C (COC) and an autoignition temperature of 351 °C, and states that operation at or below the recommended maximum bulk and film temperatures can provide long service life. It also states that the fluid, despite its relatively high flash point, is not classified as fire-resistant, so protective devices may be required. [1]

The bulletin lists the minimum liquid temperature for fully developed turbulent flow (Reynolds number above 10,000) as 69 °C at 10 ft/s (3.048 m/s) and 47 °C at 20 ft/s (6.096 m/s) in a 1 in tube, and for transitional flow (above 2,000) as 26 °C and 14 °C. Where fluid in the expansion tank may be heated above 80 °C, it says the fluid should be protected from air, and Eastman recommends an inert gas blanket, or keeping the tank below 80 °C or using a cold seal trap. [1]

Fulton describes its FT-C fuel-fired vertical coil heater as passing flue gases over both sides of each coil to reduce the fluid's peak film temperature and so extend its life. [2] Editorial calculation: with Therminol 58, the film limit leaves 339 - 300 = 39 K between the hottest fluid at the heater wall and the bulk limit, so ask the heater supplier for the calculated film temperature at full firing and minimum flow.

Give the supplier the users and their heat loads, supply and return temperatures, fluid type and volume, heater type and fuel or electrical supply, flow rate and pump redundancy, expansion tank and blanketing, piping layout and elevations, controls and safety devices, hazardous-area classification and site conditions.

02

Size the heater output and the expansion the tank must take

Fulton lists its FT-C vertical coil thermal fluid heater in models from 800,000 to 14,000,000 BTU/hr output, capable of temperatures up to 750 °F (400 °C), fired on natural gas, dual fuel, propane, #2 fuel oil or bio-fuel, with a four-pass double helical coil and an integrated air-preheating economizer, and states that heaters can be combined in modular engineered systems. [2]

Eastman's property table for Therminol 58 gives a liquid density of 883 kg/m³ at 20 °C, 830 kg/m³ at 100 °C, 759 kg/m³ at 200 °C and 679 kg/m³ at 300 °C. [1] Jinan Changtong describes its thermal-oil heating and storage tank system for bitumen as using an indirect heat-transfer-oil circuit for heating, circulation and transfer, with tank quantity and capacity chosen around storage volume and operating cycle. [3]

Editorial calculation: 800,000 BTU/hr is about 800,000 × 0.000293 ≈ 234 kW and 14,000,000 BTU/hr about 4,100 kW. Between 20 °C and 300 °C, Therminol 58 expands by 883 ÷ 679 ≈ 1.30, so a loop holding 1,000 litres when cold holds about 1,300 litres when hot, and the expansion tank must accept about 300 litres of swell on top of its normal reserve. [2] [1]

03

Jinan Changtong thermal-oil heating for bitumen

Jinan Changtong lists thermal-oil heating and storage tanks for bitumen and heat-transfer-oil assisted asphalt melting equipment. Ask for heater output, fluid, expansion tank and controls.

04

Heater, fluid, pumps, expansion tank and users in one hot-oil loop

The heater has to keep the fluid below its film limit and the expansion tank has to take the fluid's growth on heating; pumps, users and controls complete the loop.

05

Heater output, bulk and film temperature limits and sheath temperature

For Therminol 58 the bulk limit is 300 °C but the film limit is 339 °C, so the heater surface or sheath temperature row matters as much as the output row.

06

Send the load, fluid and loop data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Users: [equipment; heat load; temperature]
Fluid: [type; volume; bulk and film limits]
Heater: [fired or electric; fuel; output]
Loop: [flow; pumps; piping layout; elevations]
Expansion: [tank volume; inert blanket]
Safety: [fire protection; hazardous area; interlocks]
Site: [space; utilities]

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