Design of electric heating of molten salt storage tank at photothermal power plant
There are usually three types of electric heating systems, namely electric heating, steam heater and hot air heater. Generally, the cost of an electric heating system is relatively low, the cost of a steam heating system is relatively high, and the cost of a hot air heating system is in the middle. The principle of electric heating system is relatively simple. The main equipment used is heating cable. The heating cable uses electricity as an energy source.
The electric heating system consists of electric heating wire, heating wire accessories, distribution box, heating control and detection system, and installation accessories.
The outer shell material of the electric heating cable is generally a stainless steel or nickel-based material, which has good corrosion resistance, can resist pitting corrosion, chloride corrosion, acid corrosion, and can be used in high temperature conditions for a long time. Time. Common electric heating outer shell materials include stainless steel 304/306/321 and 347, etc. D., as well as high quality 310S stainless steel, Inconel 600 and Inconel 825, etc. D. The quality of stainless steel mainly depends on the composition of the material itself and the improvement of the heat treatment process performance.
Generally, highly compressed oxides are used to insulate resistance wires, and the voltage can reach 600 V. A fully closed shell protects magnesium oxide from steam pollution and increases the reliability of electric heating. Faced with resistive wires of different materials and specifications, people should choose according to the output power of electric heating. The wire of the heating cable at the non-heating end is pulled outward from the high-temperature heating equipment, and the length of the cold-end wire is determined according to factors such as the insulation thickness and location of the junction box.
The electric heating system is a new type of heating device combining the preheating of the molten salt tank and the heating of molten salt in a single device. Electric heating is arranged on the bottom and wall of the tank, and the salt melt is heated by electric heating when the unit is not working. During the first salt injection preheating, the electric heating system heats the tank wall, cools the tank wall with an external storage tank circulation fan and simultaneously heats the air, and also uses heated hot air to budget the tank top. And the bottom of the tank.
The electric heating device includes an electric heating and thermocouple of the bottom and wall of the tank, a circulation fan, an air duct outside the tank, an air tank, a fixed spiral nozzle and a spiral nozzle, etc. The electric heating partitions of the bottom and the wall of the tank are arranged and controlled independently of each other, and the temperature in each partition is controlled by thermocouples. Before preheating, turn on the external circulation fan of the tank, make the tank body metal through the air intake pipe and nozzle, and control the rate of increase in the temperature of the tank wall and the temperature difference between the different parts, adjusting the air circulation rate in the pipes and the amount of electric heating. Finally, the temperature of the metal walls of the tank is heated to a calculated value. When the device is turned off to heat the molten salt, the electric heating within the appropriate height range is turned on according to the liquid level of the molten salt to maintain heat dissipation and heat the molten salt.
Electric heating cable is a heating method that uses insulation resistance or resistance heating wire to create a temperature after power supply. It can automatically adjust the output temperature and reasonably maintain the process temperature requirements to keep warm, raise the temperature and protect the heating equipment from freezing. The insulation and antifreeze effect of the container is very good.
Transport of heavy oil through the pipeline over long distances and long-term retention in the pipeline will result in a drop in temperature due to heat dissipation and increased viscosity, which will cause the pipeline to be blocked by freezing or condensation-related accidents. Electric heating is widely used as effective insulation of pipelines and anti-freeze protection.
According to the statistics of the Hydrometeorological Center, the average daily minimum temperature at the location of the CNPC tank farm is 5 ° C, and the average daily maximum temperature is 14 ° C. Since the freezing point of the PX is about 15 °C, the supply pipeline needs heat preservation and heating. The oil depot has been in operation for many years without a stable source of steam, therefore, this project is considering the use of electric heating technology.
Long-distance crude oil pipelines with a high paraffin content with freezing temperatures above 50 °C. According to the requirements of the production plan of the plant, the volume of oil transportation through the pipeline is 150 thousand rubles. Tons per year, maximum-200 thousand. Tons per year.. According to the thermodynamic analysis of the pipeline, the initial supply temperature of the pipeline is 80 ° C (TN), and the temperature of the end entering the tank is 60 ° C (Tu). Since the transportation temperature needs to be adjusted according to the time of year, it sometimes needs to be transported by heat.
In petrochemical engineering, trunk infusion pipelines are the lifeblood of the factories. The temperature in the northern region is too low in winter and the pipeline needs to be insulated to compensate for the heat loss due to the low temperature in winter to ensure the normal operation of the pipeline.
The toughness of the asphalt is greatly affected by the temperature. When the temperature decreases, the toughness of the asphalt increases, and the drop in resistance of the asphalt during pipeline transportation increases; when the temperature falls below the freezing point, the asphalt solidifies, causing the pipeline to clog and the conveyor belt to come to trouble. Therefore, electric heating and heat preservation during the transportation of asphalt are very important.
To solve many problems in the "three high levels" crude oil extraction process, the thermal energy generated by the electric heating is used to heat the crude oil in the oil pipe throughout the process to improve the fluidity of the crude oil. Effectively solve various technical problems encountered in the operation of high-condensation, high-viscosity and high-paraffin crude oil, and achieve the goal of improving the productivity and efficiency of oil wells.