The vacuum drum washer is a pulp making machine for pulp washing and concentrating. It consists of pulp tank, drum tank, intermediate tank, washing drums, vacuum units, washing unit, and discharge unit. As an essential pulp washing equipment, the vacuum drum washer and other paper pulper machines (pulp digester, blow tank, twin roll press, single screw press, etc)affect whole paper pulp production line. For maximizing the benefits, it is necessary to figure out how to optimize vacuum drum washer? According to the applications, there are some ways to increase washing and concentrating effects, reduce energy consumption and save the cost of pulp making.
Optimization of vacuum seal
The vacuum seal is a part of the vacuum drum washer, which is made up of water leg tube, black liquor sealing groove and small tanks.
Defect: The height of water leg nozzle is equal to that of the small groove in the black liquid sealing groove, and the air easily enters the water leg before the black liquid volume is filled with the small groove. At the same time, the water leg of the washing machine communicates with the small groove in the black liquor tank at an angle of 90°, which easily causes the black liquor to flow poorly, and the air is easy to enter into the water leg. When the water leg contains air, the degree of vacuum is easily broken, which causes the pressure difference of the vacuum washer to decrease, which affects the washing effect.
Optimization: Bending the pipe diameter of the water leg pipe, increasing the discharge flow rate of the water leg pipe; changing the curvature of the water leg pipe so that the water leg pipe does not communicate with the small groove in the black liquor tank at a right angle, but in the form of an obtuse angle, reducing the resistance of the black liquor in the water leg tube; opening a skylight in the middle of the small groove in the black liquor tank, and lowering the height of the water leg tube outlet, so the outlet height of the water leg tube is lower than the bottom edge of the skylight, and the outlet of water leg tube is quickly immersed in the liquid quickly after the vacuum washer is turned on, making it difficult for air to enter.
Key technology
- Water leg pipe diameter: The pipe diameter is too large, and the liquid discharge is insufficient, which easily leads to air ingress, which destroys the vacuum and reduces the washing effect. The pipe diameter is too small, which hinders drainage and affects the generation of vacuum.
- The camber of the water leg tube: the horizontal distance and height difference of the black liquid tank and the water leg tube are fixed, and if the water leg tube has a high camber setting, and the liquid discharged from the water leg tube has a large impact on the liquid surface, which is likely to cause production fluctuation. If the water leg tube has a low camber setting, the water leg pipe will communicate with the small groove in the black liquid tank at a small angle, which will undoubtedly increase the resistance of the liquid discharge and affect the generation of the vacuum.
Innovation: A skylight is opened in the middle of the small tank, and the outlet of the water leg tube is lower than the bottom edge of the skylight. After the vacuum washer is turned on, the outlet of the water leg tube can quickly completely immerse the black liquid discharged from the water leg tube to prevent the air from entering, and at the same time, the black liquid flows out from the sky window, increasing the potential difference of the water leg tube, which is beneficial to the improvement of the vacuum degree.
Optimization of the intermediate tank
Defect: The intermediate tank of the vacuum drum washer is used for extract the last section of the washing. It consists of a casing, a pulp conveying screw and a discharge tube. The pulp conveying screw is a single screw, which can only be used for pulp transportation, not mixing. Meanwhile, the discharge tube is installed at the bottom of the casing, so that the pulp removed from the washing drum cannot be diluted in the intermediate tank, but directly discharged from the discharge tube, and the discharged pulp concentration is about 10%-12%. The concentration cannot meet the use of the next process, which require setting a pulp chest or pulping tank, and install a stirrer to dilute and mix the washed pulp. It not only needs to increase equipment investment, but also has a large area and high power consumption.
Optimization: Sealing the nozzle of the original discharge tube, changing the mouth of the discharge tube to the upper part of the casing, it must be higher than the conveying screw. Next, welding the stirring body on the conveying screw, and introducing the dilution water pipe on the side of the casing higher than the conveying screw. The pulp which is peeled off from the washing drum can be diluted by adding dilution water in the intermediate tank casing, and the pulp is stirred and mixed by the stirring body welded on the conveying screw, and then discharged from the discharging tube into the next section.
Innovation: While the water is diluted in the intermediate tank, the stirring body is welded on the conveying screw, and the stirring body is driven by the existing motor to stir and mix the pulp in the intermediate tank, thereby saving power consumption.
Install press roll on the washing drum
Defect: The vacuum washer uses vacuum to absorb the liquid in the pulp to achieve the goal of pulp washing and pulp concentrating. However, when producing a chloride pulp with a high degree of beating and a high viscosity, due to the poor drainability and slow speed of liquor drainage of the chloride pulp, the air is easy to enter the vacuum sealing device, the vacuum cannot meet the requirement, and the concentration of chloride pulp is relatively low at the outlet of vacuum drum washer, only 7.5%-8.5%, the pulp washing efficiency is affected, and the chlorinated lignin remains in the pulp layer, affecting the alkalization effect and increasing the amount of the alkalizing section.
Optimization: A water squeezing roller is added at the end of the vacuum washing zone, and the water squeezing roller is placed in the sliding hole of the slider through the shaft ends of the two ends. The spring is connected to the upper and lower sides of the slider, and the lower end of the lower spring is connected with the bottom surface of the support frame, and the upper end of the upper spring and the top surface of the support frame is connected, and the slider can move freely up and down in the support frame. The pulp layer passes between the water squeezing roller and the washing drum, and the pulp layer is pressed. Strengthen the washing effect of the vacuum washer to ensure the pulp concentration at the outlet of the washer.
Key technology
- If the squeezing roller is installed at an improper position of the drum, can’t display its function fully.
- If the natural spacing between the water squeezing roller and the washing drum is too large, the effect of squeezing water will not be achieved. If the natural spacing is too small, the drum washing operation will be affected.
- Installation of the spring on the slider. When the pulp is squeezed, the water squeezing roller does not perform a linear motion but performs an arc motion. To ensure that the squeezing roller is squeezing the pulp while its movement is hindered reasonably, there must be a strict requirement on the installation of spring on the sliders.
Innovation: Combined with the vacuum action and the extrusion action, the separation of the liquid in the pulp is increased, thereby increasing the concentration of the pulp and enhancing the washing effect.
