Pulp System Design Requirements
1.The flow and concentration of pulp and white water should be kept stable. For this reason, the liquid level of pulp in the papermaking pulp tank should be relatively stable, and the pulp in the high level box and the white water in the flushing tank should be properly overflowed.
The stability of incoming pulp concentration depends on the previous process to achieve stable concentration adjustment.
2. Try to use concentrated white water to dilute the slurry. The concentrated white water contains a lot of fibers, fillers and various additives. Full reuse is conducive to reducing costs and making production operations more reasonable. Thin white water is only used to supplement the deficiency of concentrated white water.
3. The equipment configuration is reasonable, and the layout is compact, so that the connecting pipes between the equipment are the shortest.
4. The inner wall of the equipment and pipelines in contact with the slurry should be smooth and free from slurry to prevent the generation of slurry. The corners of the high-level box and the flushing tank should be designed to be streamlined as much as possible. The corners of the pipeline should have a larger bending radius to avoid eddy currents and even pressure pulsations in the slurry.
5. The falling speed of concentrated white water in the flushing tank should be less than or equal to 0.12m/s, to facilitate the rise and overflow of air bubbles. However, for high-filler paper, the falling speed of concentrated white water should not be too low, otherwise the falling speed of filler and white water will be inconsistent, resulting in concentration fluctuations.
6. The flow velocity of the slurry in the horizontal pipe should not be lower than 3m/s, otherwise the air is easy to separate and accumulate in the pipe to cause pressure pulsation.
7. The selection of slurry pump and pressure screen should fully consider the pressure pulsation, and try to choose low-pulse equipment.
8. Determine whether to use a degassing device according to the speed of the paper machine. According to the speed of the vehicle and the form of the head box, it is decided whether to use the pulsation damping device.
High level box design and piping arrangement
A correctly designed high-level box must have the following three points
Reduce flow fluctuations in thick stock conveying.
Provides constant head pressure for quantitative control valves.
The open surface of the header box removes free air.
For this reason, the design of the inlet and outlet pipelines of the high level box shall meet the following requirements:
1.The discharge slurry pipe from the high level box to the slurry pump should be installed vertically, avoid turning, and maintain a slurry flow rate of 3.5 meters per second to avoid separation of slurry and water. The quantitative valve at the outlet of the high-level tank must be installed below the liquid level of the white water bucket to ensure that the pipe behind the valve is submerged in white water.
If this is not the case, the installation position of the valve is higher than the liquid level of the white water bucket. When the valve opening is small, air will be generated behind the valve, causing flow fluctuations.
2. The flow rate of the slurry entering the high level box should be slightly greater than the flow rate of the slurry outlet pipe to maintain a certain amount of slurry backflow to prevent the vortex in the high level box from bringing air into the slurry.
3. The installation height of the high-level box should generally be guaranteed to be 3 meters higher than the liquid level of the white water bucket, so that the slurry can enter the slurry pump smoothly.
4. The pipe from the high-level box to the suction port of the slurry pump should be installed at the end and in the center of the suction pipe, so that the slurry can be sucked in smoothly and reduce fluctuations. Others such as auxiliary material pipes and return pipes should be installed at the suction port, must be 45 with the entrance angle to reduce flow fluctuations.
White sink design
A properly designed white water tank must have the following advantages: all dehydration of the net part is collected. Make sure there is enough to remove the air bubbles in the white water. Keep the inlet pressure of the flushing pump constant.
For this reason, the design of white water tank and pipeline interface should meet the following requirements:
1. The height of the white water tank should be about 800mm~1000mm higher than the thick white water tray interface of the wire section of the paper machine, to ensure that the air bubbles brought into the thick white water have enough deforming space after entering the white water tank.
2. The volume of the white water tank should be such that the descending speed of the concentrated white water in the tank is less than or equal to 0.12 m/s, to facilitate the rise and overflow of air bubbles.
3. The concentrated white water outlet of the white water tank is designed in a trumpet shape to reduce the bubbles generated by the white water pulsation and be brought into the pulp by the pulp pump.
The thick pulp from the pulp tank of the paper machine enters the tank body obliquely upward at a small angle, and is covered with a concentric, large-diameter pipe to connect the overflow pulp of the degassed.
The two pipes stop at the connecting part between the outlet of the tank body and the pump in the white water tank outside the machine. The thick slurry pipeline is closer to the outlet of the tank body, and the pipe is narrowed at the end to form local turbulent flow, which is beneficial to slurry mixing.
The design of the paper machine sizing system is a delicate design work, and the designer should follow the basic principle of "providing the paper machine with a uniformly dispersed slurry, the smaller the pressure fluctuation, the better, and the less air in the pulp, the better"principle.
According to the product variety, the specific requirements of the paper machine and head box for the sizing system, combined with the incoming pulp quality, the process flow, equipment modeling, control scheme, equipment and pipeline layout design, specific conditions and specific analysis, only in this way can we design a real Practical sizing system.
