Roots Vacuum Pump in Power Plant Condenser

Roots vacuum pump is a variable-volume vacuum pump with two blade-shaped rotors rotating synchronously in opposite directions. There is a small gap between the rotors, the rotors and the inner wall of the pump housing, but there is no contact with each other.

The water ring vacuum pump is equipped with an eccentric rotor with fixed blades, which throws water (liquid) to the stator wall. The water (liquid) forms a liquid ring concentric with the stator. The liquid ring and the rotor blade together constitute a variable volume rotary variable volume vacuum pump.

Water ring vacuum pump has the advantages of simple structure, low manufacturing accuracy, easy processing, compact structure and high speed. It can be directly connected with the motor without any deceleration device. Therefore, with small structure size, we can get large exhaust volume, small area, uniform suction, stable and reliable operation, simple operation and convenient maintenance, but the disadvantage is low efficiency, generally about 30%, better up to 50%, low vacuum.

At present, most condenser vacuum pumping equipment used in power plants are “water-ring vacuum pump” and water-jet vacuum pump. The disadvantages of water-ring vacuum pump are: high power of motor, large power consumption caused by uninterrupted operation, and the equipment is prone to cavitation during operation, which endangers the safe operation of equipment.

At present, the working water temperature of water ring vacuum pump in power plant is on the high side, which seriously affects the efficiency of vacuum pump and the vacuum of condenser. This phenomenon is particularly serious in summer. The original design of the water ring vacuum pump has a larger power, while the flow rate of air pumped by the condenser during normal operation is small, which further reduces the efficiency of the high-power equipment and increases the invalid power. This part of the useless work in the vacuum pump drives the friction between the rotor and the working fluid to generate heat. The suction capacity of the vacuum pump decreases, and the condenser is true. Air worsening affects economy.

At present, the power of water-ring vacuum pump is on the high side, the efficiency of normal operation is low, which is not conducive to energy saving and consumption reduction. The exhaust steam from low-pressure cylinder of steam turbine condenses to form a high vacuum, which is an isothermal physical process. However, the condenser is not absolutely tight, and the outside air will leak into the condenser, and the role of vacuum pump is that. Draw out this part of the leakage of air and a part of the invalid steam volume flow, this part of the invalid steam volume flow also increases the additional loss of the vacuum pump, resulting in waste.

Roots vacuum pump is used in condenser of power plant to improve energy saving effect. The device is composed of low-power air-cooled Roots vacuum pump group and water ring vacuum pump in series. Roots vacuum pump is used as the main pump in the work. The non-condensable water vapor and air from the condenser are compressed through Roots vacuum pump at the first stage and then enter the heat exchanger (with open water as the heat transfer medium). Then they are further compressed into the raw water ring vacuum pump and then into the steam-water separator.

Roots vacuum pump is characterized by fast start-up, low power consumption, low operation and maintenance costs, high pumping speed and efficiency, insensitive to a small amount of water vapor and dust contained in the pumped gas, large pumping rate in the pressure range of 100-1Pa, and rapid elimination of sudden gas release. This pressure range is just between the oil-sealed mechanical vacuum pump and the diffusion pump. Therefore, it is often connected in series between the diffusion pump and the oil-sealed mechanical vacuum pump to increase the pumping capacity in the middle pressure range. At this time it is also called mechanical booster pump.

Roots vacuum pump device improves the limit vacuum value, increases the suction flow, and ensures the condenser vacuum. Increasing the cooler reduces the volume flow rate and the latent heat energy of vaporization, which reduces the power of the next stage water ring vacuum pump. Through Roots vacuum pump, the inlet pressure of water ring vacuum pump is increased, and the cavitation of water ring vacuum pump is effectively avoided.