9 requirements you need to know when designing an electric heating thermal oil furnace

Nine Requirements You Need to Know When Designing an Electric Heating Thermal Oil Boiler

1. Design Heat Load. A certain margin should be left between the heat load and the effective heat load of the thermal oil boiler; this margin is generally 10-15 percent.

2. Design Temperature. The design temperature of the thermal oil boiler is determined by its operating temperature and should be designed in accordance with the relevant provisions of GB9222, "Strength Calculation of Water-Tube Boiler Components."

3. Design Pressure. The design pressure of the thermal oil should be slightly higher than the operating pressure and should not be less than the opening pressure of the safety valve. The design pressure of a gas-phase furnace should be 1.2 to 1.5 times the operating pressure; the design pressure of a liquid-phase furnace should be 1.05 to 1.2 times the operating pressure. The pressure difference between the inlet and outlet of the thermal oil in a liquid-phase furnace should be greater than 0.15 MPa (1.5 kgf/cm²).

4. Thermal Oil Inlet and Outlet Temperatures. The design should be economical and safe, ensuring an appropriate temperature differential within the system for the thermal oil. This temperature differential should be less than 30°C.

5. Flow rate of the thermal oil within the pipe. A certain flow rate should be designed to prevent localized overheating and coking. Generally, a flow rate of 2-4 m/s is used for radiant sections, and 1.5-2.5 m/s is used for convection sections. When determining this parameter, the resistance of the thermal oil within the pipe and the need to maintain turbulent flow should also be considered. Larger pipe diameters result in higher flow rates; smaller pipe diameters require lower flow rates.

6. Average thermal strength of the furnace tubes. The design requires that the average thermal strength of the furnace tubes be within a certain range to prevent overheating of the thermal oil and fully utilize the heat transfer area of the furnace tubes. The average heat intensity of a typical radiant section furnace tube is 0.084-0.167 GJ/(m²/h), and for a six-section furnace tube, it is 0.033-0.047 GJ/(m²/h).

7. Exhaust gas temperature. Based on the operating temperature of the thermal oil, the difference between the exhaust gas temperature and the thermal oil temperature should be controlled between 80-120°C, with the exhaust gas temperature preferably between 350-400°C to minimize the convective heating surface. To fully utilize the thermal energy, waste heat recovery equipment should be installed to recycle the higher exhaust gas temperatures removed by the thermal oil furnace. This is particularly important for larger thermal oil furnaces.

8. All pipes and accessories that come into contact with the thermal oil must not be made of non-ferrous metals or cast iron. Flanges and valves must be cast steel valves with a nominal pressure of 2.5 MPa (approximately 25 kgf/cm²) or higher. Seals must be made of high-temperature and oil-resistant materials. Use biphenyl mixture-based heat transfer oil and use tongue-and-groove or convex-and-concave flange connections.

9. The heat transfer oil boiler requires a low-level drain valve that can completely drain the material, ensuring no residual liquid remains.