What factors affect the limit vacuum of

water ring vacuum pump?

In many processes of industrial production, such as vacuum filtration, vacuum degasification, vacuum distillation, vacuum suction, vacuum concentration, vacuum drying, vacuum smelting, water ring pump has been widely used. This paper analyzes the factors that affect the working ability of the vacuum pump, such as the selection of the water ring liquid medium, the size of the water ring liquid flow, the temperature of the water ring liquid, and the vacuum auxiliary system.

Water ring vacuum pump is used to suction air and other non-corrosive, insoluble in water, does not contain solid particles of gas pump, in order to form a vacuum in a closed container, to meet the requirements of the process.

The influencing factors of limit vacuum

The limit vacuum of the liquid ring vacuum pump is determined by the saturated vapor pressure of the working liquid, which mainly depends on the following aspects:

1. The medium selected for the liquid ring

Water as the working fluid, the ultimate pressure can only reach 2000 ~ 4000 Pa, oil as the working fluid, up to 130 Pa. Because of the high cost of oil and the pollution of the environment after direct discharge, the use of oil as a water ring liquid phase is less, generally only in the case of high vacuum demand, and need to add a gas-liquid separator, and in the gas-liquid separator circulation fluid to the vacuum pump pipeline installed heat exchanger for cooling, to ensure that the oil can be recycled and reduce costs.

Most industrial production uses tap water, industrial water, production water, circulating water, desalinated water, etc., as the working liquid, the price is relatively cheap, the cost is low, you can choose to do the water ring liquid directly into the sewage system, such as the circulating water used for material cooling in chemical plants, need to regularly discharge a part, add chemicals and use new water replacement. It is economical to make a certain amount of water ring liquid after continuous straight row.

If the water ring liquid needs to be recovered, generally use desalted water as the water ring liquid, so as not to bring in other impurity ions. In some devices will also choose to use other organic or inorganic solvents involved in production or reaction as water ring liquid, after the recovery of gas components can be directly used, both environmentally friendly and economic, but the vacuum pump design should pay attention to the pump cavity, impeller and other materials that may be in contact with the solvent part selection.

2. Working temperature of water ring liquid

The effect of the working temperature of the water ring liquid on the size of the vacuum pump is also more obvious. The temperature of the working liquid is too high, which will reduce the pumping volume of the pump. Under certain circumstances, the lower the temperature of the water ring liquid, the larger the vacuum can be formed. Generally, the maximum temperature of the working liquid can not exceed 65 ℃.

When the high temperature gas or steam above 80 ℃ is removed, the condenser should be installed in the suction line of the vacuum pump. When the working liquid is discharged directly, the water ring liquid can be maintained at a lower temperature, and the working liquid used in circulation can be cooled by cooling water on the connecting pipeline between the soda water separator and the vacuum pump because of the work and heat release of the vacuum pump.

For the device that needs to accurately control the vacuum size, the automatic control of the temperature of the water ring liquid can be used. After setting the required working temperature of the water ring liquid according to the vacuum size, the temperature of the water ring liquid can be stabilized by interlocking adjustment with the opening of the cooling water feeding valve, so as to ensure the stability of the vacuum. Another control method is to ensure that the temperature of the cooling water is in a certain range. The manual valve at the inlet and outlet of the heat exchanger is fixed at a certain opening, such as fully open, and the vacuum suction valve that automatically controls the opening size can also play a role in stabilizing the vacuum. When the accuracy of vacuum size is really high, the combination of water ring liquid temperature automatic control and vacuum automatic control can also be considered.

3. Flow rate of water ring liquid

The size of the water supply flow of the vacuum pump has an effect on the vacuum degree, pumping volume and power consumption of the pump. In the case of the same temperature of the working fluid, the larger the suction volume of the vacuum pump, the more water needs to be consumed.

If the flow rate of the water ring liquid is too low, it will cause the vacuum capacity of the vacuum pump to decrease, but if the flow rate of the water ring liquid is too large, it will also lead to the increase of the power consumption of the pump, and even the overcurrent jump. Therefore, the size of the water supply should be strictly controlled within the prescribed range.

Whether it is straight in and straight out or through the gas-liquid separator circulation, the working fluid water supply pipeline is generally designed with a flowmeter and valve, while ensuring that the pressure on the inlet pipe is stable in a certain range, and the flow rate of the water ring liquid water supply and the automatic control valve are interlocked to adjust the water supply of the vacuum pump through the valve opening size. Or the water supply of the soda separator and the water supply of the soda separator to the pump, so as to use the minimum water consumption to ensure that the pump operates under the required technical conditions, so that the power consumption is minimized and the performance index is reached. When extracting high temperature gas or 80°C steam, it is recommended to use a precondenser or to use a working fluid of 2 times the standard flow rate.

4. Vacuum auxiliary system

In some processes of industrial production, such as vacuum degasification, vacuum evaporation and concentration, in addition to the vacuum produced by the water ring vacuum pump, the suction pipe of the vacuum pump is often designed with an auxiliary spray system, condensation system, etc., its main purpose is to recover the gas out; The second is to cool the air intake of the vacuum pump, which can effectively use heat and protect the vacuum pump. The continuous spray cycle of the lower temperature liquid in these devices and the sudden contraction of the volume when the gas condensates into a liquid can produce a certain degree of negative pressure, which is equivalent to increasing the vacuum of the system, or reducing the power consumption of the vacuum pump under the condition that a certain vacuum is required to control.

Practice has proved that within a certain range, if the spray cycle flow is greater, the spray liquid temperature is lower, and the vacuum can be formed by the continuous spray cycle is greater. In some chemical designs, the vacuum pump can only be used as the initial start-up to quickly reach the required vacuum, and then the vacuum can be maintained through the spray cycle, so that the vacuum pump can be stopped and energy can be saved, and all possible toxic and harmful gases are recovered by spraying with good solubility, which is very environmentally friendly.