Vacuum Drum Washer and Twin Roll Press

Vacuum drum washer and twin roll press are two essential machines used in the pulp washing process of paper pulp manufacturing.

Vacuum Drum Washer Introduction

The vacuum washer we use is a drum type of vacuum washer, so it is also named vacuum drum washer. The vacuum drum washer provided by CNBM (AM) is the washing equipment that is to take the pumping force produced by vacuum negative pressure as the driving force to make waste liquid separated through the filtration of the pulp layer.

According to different functions of each part, as the drum is rotating, it can be divided into several zones, that is, gravity molding zone, vacuum molding zone, diffusion zone, leaching and displacement zone, and pulp stripping zone. The main parts include: rotating drum, filtering screen, curved tank, scraper, screen washing pipe, leaching pipe, pulp stripping fan, repulping propeller, etc. The rotating speed can be properly adjusted according to the required pulp yield. The general speed is 0-4 rpm, and the inlet pulp concentration is about 1-1.5%, the outlet concentration about 10%.

The main structure is shown below:

Pulp Washing Machine Production Process:

Single washing machine:

Pulp inlet→Filtering→Washing→Stripping→Conveying

Multi tandem washing machine set:

(Here takes 4 tandem washing machine set as an example)
a. Washing machine-1
Pulp inlet→Filtering→Washing→Stripping→Dilution and Agitation
b. Washing machine-2
Pulp inlet→Filtering→Washing→Stripping→Dilution and Agitation
c. Washing machine-3
Pulp inlet→Filtering→Washing→Stripping→Dilution and Agitation
d. Washing machine-4
Pulp inlet→Filtering→Washing→Stripping→Conveying

The starting procedures of the washing machine are as follows:

repulping propeller→pulp stripping fan→screen washing water pump→diluting water pump of washing machine→rotating drum→pulp inlet

Key Operations of Vacuum Drum Washer:

  • Start rotating drum (the head tank must have liquid into the curve tank).
  • Check whether each part is in normal operation, such as agitation device, outlet propeller, fan and so on.
  • Open the inlet valve and make pulp into the machine, and keep 1.5 -2.5% of pulp concentration.
  • When the pulp layer and the vacuum degree reaches normal, gradually open the washing valve. The spray volume reaches normal value in the way of gradual increase.
  • The supply and concentration of pulp should be stable.

Safety operation requirements:

Here are general operations of multi tandem washing machine set for reference. The preparation work before the start:

  1. Check whether there is sewage and other sundries at the bottom of each tank or not.
  2. Check whether all the sewage lines are closed or not.
  3. All the hoses, short pipes and flanges should be tightly connected with no leakage. The distribution valve and sealing flanges and other sealing filings have been rightly adjusted.
  4. All lubrication points are lubricated
  5. The fit clearance of the spool and seat (rotating drum) of distribution valve has been adjusted to prevent compression.
  6. The other mechanical conditions are normal.


Twin Roll Press Introduction

Twin roll press is mainly composed of a pair of squeezing roller, pulp tank, screw conveyor, scraper and oil pressure system.

Twin roller is horizontally arranged in the pulp tank. Through the relative operation of two rollers, relying on the line pressure between two rollers, the pulp will be squeezed and dewatered. The filtrate will enter the rollers through the screen and discharged from the axial outlet of liquid. The squeezed pulp is lifted passing two rollers. At the side of the rollers, it will be scraped down by the scraper and conveyed out by the repulping propeller. The concentration of inlet pulp is 3-5%, and the concentration of outlet pulp is about 30%. Twin roll press is equipped with a special hydraulic system driven by hydraulic motor, including compression, rotation, and drop.  (Seen the structure from the figure)

Working principles of Twin Roll Press

In the twin roll press, each roller in the working conditions can be divided into: dehydration zone, displacement zone, squeezing zone.

Its processes: Pulp inlet →squeezing →being discharged by repulping propeller→ screw conveying

Preparatory work before the start:

  1. Check the internal and surface of the squeezing machine and the rollers to ensure there is no accumulation of dirt and other hard sundries.
  2. Make a comprehensive inspection of the hydraulic system to check whether there are no leaks on the hydraulic pipes.
  3. All lubrication points must be lubricated. The gear box and speed reducer must reach the required oil levels.
  4. Check the sealing performances of the rollers and their ends.

Starting sequences

Screw conveying outside the machine→repulping propeller→high pressure of washing screen water→high pressure pump→main pump→ rotational speed control, →pulp inlet

Stopping sequence

  1. Turn off pulp conveying pump, close the pulp inlet valve, and stop pulp supply.
  2. Open flushing valve to make the inlet place and internal tank clean enough.
  3. The pulp from the is gradually reduced to zero. After complete stop, adjust the ratio solenoid valve of main hydraulic pump to 0%, and stop the rollers and crushing screw conveyor of repulping propeller.
  4. Close spray water. As the time is more than 3 hours, the tanks and pipes must be washed so that there is no residual left in each part.
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