The liquid ring vacuum pump constitutes the vacuum pump system. Our basic requirement for the liquid ring vacuum pump is to ensure the normal operation of the vacuum system. Now let’s see what problems exist in the liquid ring vacuum pump system, so that we can solve them in a timely manner without affecting the operation.
Problems with liquid ring vacuum pump system
As the extension of liquid ring vacuum pump working time, due to the power consumption of vacuum pump and water vapor release of latent heat of vaporization can create working liquid temperature rising, and working fluid temperatures make the vacuum pump suction ability to drop, and thus reduce the condenser vacuum, affect the economy of the unit, serious when still can cause the vacuum pump cavitation, affect the safe operation of the unit. The design temperature of the working fluid is 15℃, but the actual operating temperature is higher than this. At present, the working fluid of vacuum pump is usually cooled with circulating water, but the temperature of circulating cooling water is affected by the outdoor temperature, especially in summer when the circulating water temperature rises, the working fluid temperature of vacuum pump will be far higher than the design value.
Rising temperature of working fluid will cause the following consequences:
(1) destroy the vacuum and reduce the unit economy.
As the temperature of the working fluid increases, the corresponding saturation pressure keeps rising. For example, the vaporization pressure of water at 30℃ is 4.241kPa, and that of water at 40℃ is 7.350kPa. When the suction pressure of the liquid ring vacuum pump is less than or equal to the saturation pressure corresponding to the temperature of the working fluid, part of the working fluid will be vaporized, and the vacuum pump due to the pumping of the gas produced by the vaporization of its working medium causes the vacuum pump power is seriously insufficient. Non-condensable gas will lead to heat transfer deterioration and accumulate in the condenser, damaging the vacuum of the condenser. Air with 1% mass fraction in water vapor can reduce surface heat transfer coefficient by 60%, thus reducing unit economy.
(2) cavitation of liquid ring vacuum pump.
In the operation of the vacuum pump, if the absolute pressure of the working fluid in the local area drops to the working fluid vaporization pressure under the temperature at the time, the working fluid will begin to vaporize and produce a large number of steam bubbles. These fine bubbles are extremely easy to break, the process of breaking will produce a strong impact on the impeller, over time impeller perforation, ultimately unable to repair and forced to replace the impeller, seriously affecting the safety and efficient operation of the equipment. When the flow rate of working fluid is too high, sharp noise will be generated.
In order to prevent cavitation of the liquid ring vacuum pump, the suction pressure of the vacuum pump is usually required to be at least 0.85kpa higher than the saturation pressure corresponding to the working fluid temperature during operation. If the working fluid temperature is 30℃, corresponding to the saturation pressure of 4.241kPa, the vacuum pump suction pressure shall not be lower than 5.091kPa; However, if the working fluid temperature is 20℃, the vacuum pump suction pressure can be reduced to 3.188kPa.
At present, circulating water is used for cooling liquid ring vacuum pump, but the circulating water temperature may reach more than 30 ℃ in summer, coupled with a certain heat transfer temperature difference, the temperature of working fluid may reach more than 40℃, seriously affecting the economic and safe operation of the unit, so it is necessary to consider reducing the working fluid temperature of liquid ring vacuum pump.