Vacuum drum washer is common pulp washing equipment, suitable for various types of pulp such as wood pulp and straw pulp. It is the key technical equipment for the paper and pulp industry to solve wastewater pollution and implement alkali recovery project.
There are many kinds of pulp washing equipment in the world. After decades of development and application, the pulp washing equipment that has been successfully used in chemical pulp mills mainly includes drum vacuum washers and drum type washers (referred to as DD washers) ) and twin roll press. After long-term research and development, the vacuum drum washer has become the most cost-effective pulp washing equipment for non-wood chemical pulp and small chemical wood pulp projects and has been widely used in paper pulp mills.
Since the early 90s of the last century, CNBM has developed and promoted the vacuum drum washer, keeping up with the operation of the product market, constantly summing up the production experience and actively learning from foreign advanced technology. After more than 20 years of continuous innovation, the equipment structure has been carried out. Many major improvements have made the product performance reach the international advanced level, completely replacing the similar equipment abroad, widely used in China, and sold to the international market.
Main parameters of the vacuum drum washer
- Feeding concentration: 0.8~1.5% for wood pulp and 1.0~3.5% for straw pulp,
- Pulping concentration: 10~15%,
- Vacuum washers mainly rely on water legs to create a vacuum, sometimes supplemented by a vacuum pump.
Structure of vacuum drum washer
The vacuum drum washer has a single or multiple series structures depending on the position of use. The vacuum washer of a single structure mainly consists of a drum, a tank, a distribution valve, a washing device, a stripping device, a transmission device, and a screw conveyor and a hood, etc. The vacuum washer in series structures has the same main structure as that of a single device, but a dilution agitation tank is connected between the two devices, and a device such as a nip roller and a stirring roller is equipped in the tank.
principle of unit
Working principle of the vacuum drum washer
The vacuum drum washer is installed in a high position to generate a vacuum by continuously draining the water leg tube. 1%~3% of the low-concentration pulp enters into the vacuum washer. When the liquid level reaches a certain height, it overflows into the drum tank through the raft and is gravity-filtered and dehydrated. The filtrate flows into the water leg tube along the liquid passage. Uses a water leg tube to discharge a vacuum, and the filtrate is continuously permeated through the pulp layer and flows into the filtrate tank along the water leg tube under the suction of the vacuum negative pressure.
During the dehydration process, the fibers in the pulp are adsorbed on the surface of the drum to form a continuous pulp layer of uniform thickness, and the washing water is replaced and washed in the rotating process of the drum. After being transferred to the stripping zone, the pulp is peeled off to the crushing spiral by the stripping device. The conveyor is transported to the next process.
The flow rate and resistance of the filtrate have a great influence on productivity and efficiency. To obtain the necessary vacuum, the water leg tube needs to meet the following points:
- The washing machine needs to be installed at a high position. Generally, the installation height should be about 12m, so that the effective length of the water leg tube is above 9m.
- The filtrate should have sufficient flow rate in the tube. After the flow in the tube reaches a certain speed, the gas can be sucked in. The gas is withdrawn in the form of a rapid flow of the gas-liquid mixture. It is recommended that the flow rate of the filtrate in the water leg tube is 1~3m/s, the straw pulp can be lower, the wood pulp and the bleaching pulp can be higher;
- The water leg tube should be installed as vertical as possible, avoiding the horizontal section and reducing the number of elbows and the resistance.
The vacuum washer of CNBM has been developed to the fifth generation of products, and the performance and appearance quality of the equipment has been significantly improved. The series of products with diameters of φ2600 mm, φ3000 mm, φ3500 mm, φ4000 mm, φ4500 mm and filtration area of 10~120 m2 have been formed. It can be selected according to the type of pulp and production scale.
The unit production capacity of the vacuum drum washer in the project of bamboo pulp black liquor extraction has reached 6~7 t·m-2·d-1 (air-dried pulp), and the softwood lignin segment in the project of the softwood/hardwood chemical pulp unit. The area production capacity is 10~15 t·m-2·d-1 (air-dried pulp). According to the structural characteristics of the equipment and the operating experience of bamboo and wood chemical pulp, as well as the comprehensive production capacity, washing efficiency, and investment, the expected production capacity of washing different chemical fiber pulps is shown in Table 1.
| Softwood Pulp | Hardwood Pulp | Bamboo pulp | Sugarcane bagasse pulp/ reed pulp | Wheat straw pulp | |
| Unbleached pulp | 10-11 | 7-8 | 6-7 | 3.5-4.5 | 1.5-2 |
| Bleached pulp | 11-12 | 8-9 | 7-8 | 4-5 | 2-3 |
Note: t·m-2·d-1 (air-dried pulp)
To ensure that the equipment achieves the best operation and is more conducive to black liquor extraction and waste gas recovery, systematic research and continuous improvement are required for the relevant aspects of the system:
- improve the auxiliary displacement washing device for vacuum washer. Mainly refers to improve the structure of the spray pipe and nozzle, choose the appropriate spray pressure, make the spray more uniform and reduce the replacement of the washing dead zone, to maximize the replacement washing effect and improve the washing efficiency.
- Improve the air discharge measures and defoaming system in the black liquor of the vacuum drum washer. Summarize the calculation of the amount of air brought into the washing process by the vacuum washer in different working conditions, select the air that escapes from the liquid by the fan with reasonable air volume and wind pressure, and arrange a reasonable volume of the defoaming tank and defoaming device to effectively eliminate the foam. The black liquor tank is always in the working state of normal pressure or micro-negative pressure, and the vacuum degree and the optimal working state of the vacuum washer are ensured to reduce engineering investment, increase production efficiency and reduce black liquor loss.
- Accumulate relevant data to optimize system operation. The production, washing degree, and dilution of black liquor of the vacuum drum washer are contradictory unified bodies. To make overall planning and balance, it is necessary to continuously accumulate the thickness of the pulp layer, the rotating drum speed and the pulp level in different production practices. The basic data and correlation of the optimal combination of production capacity and washing efficiency, according to the characteristics of the pulp and the degree of washing, the operation control or the level of automation control is ensured to ensure efficient and stable production.
- Optimize the hood venting system of the vacuum drum washer. Use appropriate methods to calculate or determine the moisture venting capacity of the hood, improve the structural type of the hood or improve the sealing of the hood, try to choose an economical and reasonable drainage air volume, and improve the efficiency of drainage under the premise of ensuring the normal operating environment. Reduce humidity investment and power consumption. With the development of clean, environmentally friendly, energy-saving and consumption-reducing, especially due to the modern intelligent new technology revolution, higher reliability has been proposed for product reliability, system stability, clean environmental performance and automation of operation.
As a well-known supplier of washing and bleaching filtration technology and equipment, CNBM must grasp the development trend of the industry, continue to increase investment, and carry out more in-depth research on products from design to manufacturing, do more research on operation, automation, system support and clean production technology and other links to ensure the reliability of the equipment and the efficiency of the system operation, to create greater value for customers.
