Kerosene vapor phase drying equipment

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1. Overview
The insulation drying operation of oil immersed power transformer is a very important process in the transformer manufacturing process, which has a great impact on the final quality of the transformer. Some of them are not completely dry, and the residual moisture in the insulating material will form an electrode under high electric field, which will continuously generate free discharge, thus gradually destroying the insulating characteristics of the insulating material. At the same time, in the normal operation of the transformer, the aging process of the insulating material itself will be accelerated, and the service life of the transformer will be shortened. If the drying is excessive, the crystal water in the insulating material will escape, which will lead to the aging of the insulating material in advance and the decrease of the mechanical strength.

2. How it works
The basic principle of kerosene vapor phase is to use kerosene to heat and evaporate under vacuum to become high temperature kerosene steam. When encountering the workpiece with low temperature in the vacuum tank, it condenses and emits condensation latent heat (about 306.6kj/kg) to heat the body. The condensed kerosene is collected, transported to the evaporator through the kerosene conveying system, heated and evaporated again. The temperature of the workpiece keeps rising for many times, and the water in it also continuously evaporates into water vapor, which is pumped away by the vacuum system, finally achieving the goal of thorough drying.

① Preparation stage
Vacuum the product in the vacuum tank, and reduce the pressure to below 700pa. At the same time, the vacuum tank body is heated and insulated, and the evaporator pre heats the kerosene, so that the kerosene steam outlet temperature of the evaporator gradually rises from 98 ℃ to 130 ℃. The kerosene transforms from liquid state to steam state and diffuses in the vacuum tank, fully exchanging heat with the product.

② Heating stage:
At this time, only one maintenance pump is needed for the vacuum system, and the vacuum degree of the vacuum tank and the condensation collection tank is maintained at the vacuum degree specified in the process. Kerosene steam exchanges heat with transformer, flows to buffer tank after condensation, and then returns to evaporator to form a cycle. With the continuous rise of temperature, the pressure in the vacuum tank increases gradually due to the evaporation of kerosene steam and water vapor in the insulating material. At this time, the above mixed gas is pumped to the condensation recovery system through the maintenance pump for condensation and separation. The kerosene liquid separated by condensation is input into the evaporator, and the above process continues until the temperature of the reactor body reaches the process requirements, and then it can enter into the step-down stage.

③ Step down stage (or low vacuum stage):
Stop the delivery of kerosene to the evaporator, and continuously draw the mixed gas in the vacuum tank out of the vacuum tank, so that the kerosene remaining in the insulating material can be evaporated again, so as to condense and recover. According to the different product capacity and voltage level, the intermediate step-down stage and heating stage can be alternately carried out several times to achieve the best drying effect.

④ High vacuum stage:
Start the main vacuum system to vacuumize the vacuum tank. The final pressure is less than 10Pa. When the temperature of the body reaches the specified temperature and the water yield of the insulating material reaches to less than 10g per hour per ton of insulating material, the drying process is completed.

3. Advantages of kerosene gas drying equipment
① Dryer body temperature uniformity
As the heat released by kerosene vapor condensation is used for heating, the lower the temperature is, the more intense the condensation is, that is, the higher the heat release is, so the temperature of the body is uniform.

② High heating temperature
In the process of kerosene vapor phase drying, the insulation material aging process is very slow when the body is in vacuum. Compared with the hot air circulation vacuum drying, the heating temperature can be increased by about 30 ℃ to about 130 ℃.

③ Fast drying
The body of the device is always in a vacuum state, so the water outflow process runs through the whole drying cycle. At the same time, due to the increase of body temperature, the diffusion coefficient of moisture in the insulation material increases, which shortens the drying cycle.

④ It can clean the body
After kerosene vapor condenses into liquid, it can clean the inside and outside of the transformer body, which has unique advantages in the treatment of repair transformer. After the treatment of the transformer body, the surface is clean and free of oil dirt and stains.

4. Application
In recent years, there is no pollution in kerosene vapor phase vacuum drying process of oil immersed power transformer, and the labor intensity of workers is greatly reduced.