The main function of the condenser is to condense the steam part of the mixed gas above 100 ℃ from the vacuum tank into the liquid below 25 ℃ at one time, so the cooling capacity should be particularly strong, and the condensation effect should be particularly good. Generally, the condensation power shall be more than 3 / 4 of the rated power (i.e. evaporator power) of VPD equipment.
The structure of the condenser is a shell and tube heat exchanger. There are many baffles in the shell side of the air flow to ensure that the air flow is fully condensed. The total water inlet and outlet pipes are divided into several branches in the condenser to form enough condensation area. Due to the large amount of cooling water, VPD equipment needs to have a special cooling water station or chiller to supply circulating cooling water.
The temperature of cooling water has a great influence on the performance of condenser. The lower the water temperature is, the stronger the water catching capacity is, and the lower the partial pressure of water vapor in the residual gas after condensation is. Generally, the maximum partial pressure of water vapor that the leakage pump can bear is about 3kpa, and the corresponding saturation temperature of water vapor is 24 ℃. That is to say, the temperature of the oil water gas mixture at the outlet of the condenser should not exceed 24 ℃, otherwise, too much water vapor will enter into the leakage pump, affecting its normal work; and the temperature of the cooling water needs to be lower, which is difficult to guarantee in many areas of China in summer. In recent years, in order to effectively enhance the condensation effect, the main condenser of the existing VPD equipment is cooled by a water chiller, or a small condenser with cooling water provided by the water chiller is connected in series between the collection tank and the leakage pump to further reduce the partial pressure of water vapor and kerosene vapor in the residual gas.
The working pressure of the condensing system is also very important. It is obvious that if the total pressure in the condenser and the collecting tank is lower than the saturated vapor pressure of water at that time, the water vapor is impossible to condense at all and will be pumped out by the drain pump. In order to fully condense the water vapor, the condensing pressure must be higher than the saturated vapor pressure. However, the pressure of the condensing system should not be too high. Because the pressure of the condensing system is too high, the gas pressure in the vacuum tank is required to be higher. Otherwise, the mixed gas cannot flow into the condenser naturally under the effect of the pressure difference, and the high pressure in the vacuum tank will directly affect the outward diffusion of water vapor in the insulating material. In consideration of the above two factors and the presence of permanent gas components in the residual gas, the working pressure in the condenser is selected as 4.5kpa, which can not only ensure the sufficient condensation of water swallow gas, but also make the pressure in the vacuum tank as low as possible.
In the VPD equipment, there is also an auxiliary condenser in the condensation system, which is specially used to receive the high-temperature kerosene vapor discharged in the later stage of the kerosene purification process in the distillation chamber. The structure of the auxiliary condenser is the same as that of the main condenser. The power of the condenser corresponds to the power of the distillation chamber, and the condensed kerosene liquid is also discharged to the collection tank.
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