Mineral insulated heating cables with mineral insulation are used for preheating and heating pipes with molten salt.

Published on:

2023-02-18 10:22

Currently, most solar thermal power plants use molten salt medium to store heat Molten salt is a binary molten salt that becomes viscous when the temperature drops at 240 °C, the crystals precipitate at 238 °C and solidify at 220 °C. Therefore, the anti-condensation of the molten salt pipeline is very important for the normal operation of the solar thermal power plant.

For solar thermal power plants that use molten salt as a heat carrier, electric heating is commonly used as a measure to prevent the formation of condensate in molten salt pipelines. The main methods of heating include steam heating, oil heating, hot water heating, and electric heating. However, due to the high temperature of at least 290 °C required to heat molten salt in solar thermal power plants, there are disadvantages such as high operating pressure, a complex system, and easy leakage for both steam heating and hot water heating. ■ The salt pipeline uses heating means to prevent the formation of condensate to heat the cables.

Mineral insulated heating cable (called MI) is a solid alloy cable heating system (alloy 825, a type of nickel-chromium alloy recommended for high-temperature section) as shell and magnesium oxide as insulation. The maximum temperature maintained can reach 500 °C. This is a relatively common type of electric heating of high-temperature molten salt piping that is currently used in photothermal power plants. The main equipment of this heating system includes: junction box, power cable, heating cable, terminal, etc.

Heating cable with MI requires high precision installation, it is easy to get uneven distribution of heat flow when not installed correctly. And because the thermal conductivity to the pipe is limited by the energy density of the heating cable system, the thermal response is slow. However, the MI electric heating also has the advantages of 600 ℃ high temperature resistance, high mechanical strength, strong chemical anti-corrosion ability, prefabricated circuit, and convenient on-site installation and maintenance.

There are two main functions of electric heating of salt melt piping in solar thermal power plants: 1. Preheating of salt melt piping without load, heating of the safe operating temperature range of salt melt (290 °C or 550 °C), called preheating process 2. To maintain the temperature of the molten salt pipeline in the safe operating temperature range of the molten salt (approximately above 275 °C), Which is called the heating function.

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