Mineral insulated heating cables with mineral insulation are used to heat molten salt in solar thermal power plants.

Published on:

2023-02-17 17:04

Since the development of solar thermal power technology in the 1980 s, various attempts have been made to use materials used as heat carriers, including water and steam, air, liquid metal, heat transfer oil, and molten salt. Molten salt has the advantages of high working temperature, high thermal stability, high specific heat capacity, high convective heat transfer coefficient, low viscosity, low thermal insulation and steam tower, low price, etc. D., and has become the most recognized means of heat transfer and storage in the field of photothermal energy. One of the environments.

Due to the features of the operation of the trough and tower-type solar thermal power plants, the main coolant (heat transfer oil and salt melt) pipelines and heat collection and storage system equipment are at risk of freezing to varying degrees. At present, electric heating is commonly used in the field of solar thermal energy production for preheating and heat maintenance in the process system.

When molten salt is mainly used as a heat transfer medium in tray and tower type solar thermal power generation projects, the safe temperature is about 270 degrees Celsius, of which the maximum operating temperature of the heat storage tray is about 390 °C. and the maximum operating temperature of the tower energy storage is about 565 °C.

The solar thermal power plant is equipped with an electric heating system, which is mainly used for preheating an empty pipe with a molten salt environment, maintaining valve temperature, pipeline concentration area, etc. D., as well as to ensure the safety of thermal insulation of equipment and normal operation of the system in extreme weather conditions and high insulation of equipment. There are two main modes of operation of salt pipelines and electric heating of solar thermal power plant equipment: (1) preheating of unloaded salt pipelines, heating to a safe working range of salt melt temperatures (290-550 °C), called the preheating function; (2) to maintain the temperature of the molten salt pipeline in a safe operating temperature range of molten salt (Approximately above 275 °C), which is called a heating function.

Products in the electric heating industry that can meet the requirements of higher service temperature and exposure temperature are mainly "mineral insulated heating cables with mineral insulation." Currently, mineral insulated mineral insulated heating cables meet the following requirements: (1) High output power: The maximum output power is 269 W/m and the maximum temperature can be maintained at 550 °C. (2) High temperature exposure: the maximum exposure temperature is 652 degrees Celsius, shell options such as alloy 825 are available. (3) Strong resistance to environmental corrosion. (4) It has high mechanical strength and can be used in explosive areas.

Of course, mineral insulated heating cables also have certain disadvantages: (1) Each electric heating circuit must be designed in advance and specially adapted; (2) The installation requirements are strict, and the cross-cutting heating cables are not allowed.

In solar thermal power plant projects, electric heating is a key auxiliary system for heat collection and storage systems. The electric heating system uses an accurate and optimized design to compensate for the thermal losses of pipelines and equipment into the environment by converting electrical energy into thermal energy, and to prevent solidification and crystallization of heat carriers such as molten salt and heat transfer oil. Piping and equipment. and freezing protection of the hydraulic environment at 0 °C to ensure the fluidity of the process system. At the same time, the electric heating system is also used for preheating process pipes and equipment during start-up-the upper stage of the unit. A well-designed, reliable product and strict installation of the electric heating system can not only make the heat collection and storage process of the photovoltaic power plant safer and more stable, but also avoid large losses caused by freezing of the working fluid.

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