In the process of pulp and paper making, it is a common method to use the vacuum pumping capacity of liquid ring vacuum pump.
The general technological process of papermaking is as follows: raw material – slicing – Cooking – washing – Screening – bleaching – beating – vacuum dehydration (using water ring vacuum pump) – press dehydration – drying – forming – leaving the factory.
The pipeline system closely related to the normal operation of the vacuum pump includes the gas pipeline and its accessories as well as the liquid pipeline supplying the working fluid.
According to the direction of gas flow, the whole gas pipeline from the interface of the vacuum element of the paper machine to the exhaust port of the vacuum system and its components are: front pipeline of the pre separator, front gas water separator, rear pipeline of the pre separator, rear gas water separator or drainage ditch.
1. Front and rear pipelines of pre separator.
When the pipeline layout in the workshop is long, the gas flow rate in front of the pre separator can be selected at the speed of 18m / s, so as to determine the diameter of the pipeline in front of the pre separator.
The gas flow rate of the pipeline behind the pre separator can be selected according to the speed of 28m / s, and then the diameter of the pipeline can be calculated. When the size of the inlet and exhaust flange of the pre separator is inconsistent, the reducer with large and small head shall be used for connection.
When the pipeline layout is short, the diameter of the connecting pipeline can be directly determined by the inlet and exhaust flange of the pre separator. The layout of gas pipeline shall be conducive to drainage and minimize the setting of elbows. According to the direction of gas flow, the pipeline shall be inclined downward gradually, and the inclination angle shall be greater than 1 degree.
Occasionally, in order to facilitate the installation, some paper mills will install the pipeline directly on the ground, and the pipeline water collection will increase the pipeline loss, and cause the vacuum fluctuation to affect the paper quality.
If the collecting water enters the vacuum pump with the gas, it will also cause the sudden increase of the motor current of the vacuum pump, and sometimes even damage the pump blades.
2. Pre gas water separator.
The pre gas water separator is used to separate the water removed from the vacuum dehydration element, block the water and its contained papermaking chemical additives from entering the vacuum pump, so as to avoid the impact on the pump gas volume and shaft power and the damage to the vacuum pump.
When the water content of the gas-water mixture reaches 50% of the working water content of the vacuum pump, a pre separator is required.
The gas flow rate in the separator shall be controlled below 5m / s, so as to ensure a better separation effect.
3. Rear gas water separator or drainage ditch.
The post gas water separator or drainage ditch is the recovery equipment of the working liquid of vacuum pump. The well-designed post gas water separator or drainage ditch can also play a good role in reducing the noise.
The poor design of the post gas water separator or drainage ditch will cause the power of the vacuum pump shaft to rise, the motor to exceed the power, and even the motor to trip.
4. Water supply pipe of vacuum pump.
From the perspective of trend, the working fluid of vacuum pump is supplied by circulating water supply mode, and the water from the storage tank under the cooling tower is supplied to vacuum pump as working fluid.
The cone vacuum pump often needs a certain pressure head for water supply, so it needs to be pressurized by a series centrifugal pump on the water supply pipeline. Because the pressure required by the flat vacuum pump at the water supply interface of the pump is close to the atmospheric pressure, it does not need to be connected with a series centrifugal pump, but only needs to be raised more than 3 meters from the water storage tank.
In the design of the water supply pipeline, it should be noted that the flow rate should be controlled at about 1.5 ~ 2m/s. If the flow rate is too fast, the so-called water grab phenomenon will occur, which will cause the air volume of the vacuum pump to drop or the work is unstable.
Generally speaking, a paper production line with a fixed annual output requires a certain amount of air extraction. For paper mills, in order to reduce energy consumption, save energy, and reduce the cost of paper production, it is very important and critical for liquid ring vacuum pump to reasonably configure the vacuum pump pipeline system.