Retention aids for high speed newsprinters

In recent years, papermaking science and technology workers at home and abroad have conducted extensive research and exploration on the application of retention aids in the papermaking industry, demonstrating that retention aids can produce excellent retention and retention effects under conditions in which the paper web remains well formed. Widespread development and application prospects. This article briefly describes the characteristics of retention aids and their application examples on high-speed newsprinters.
1. Characteristics of retention aids The retention aids can be divided into three types: single-polymer retention aids, double-polymer retention aids and microparticle retention aids. Single polymer retention aids include polyacrylamides, polyethyleneimines, polyethylene oxides and cationic starches. The bipolymer retention aid consists of aggregating agent + polyacrylamide. Microparticle retention agent consists of high polymer + bentonite.
The characteristics of retention aids are as follows: First, they are added in the slurry; second, the retention rate of the slurry in the network can be improved, and at the same time, the dewatering performance of the pulp can be improved. Third, the retention mechanism is flocculation or agglomeration. The three steps to keep are: agglomeration, flocculation, and filtration.
Microparticle retention aid is the latest generation of retention aid. It adopts the micro-flocculation mechanism. Its advantages are: strong retention and filter efficiency; flexible and convenient control of sheet formation; effective neutralization of anionic impurities and viscous substances , Clean paper machine system; has better paper machine running performance and higher paper machine production efficiency.
2 Application Examples of Particulate Retention Agents 2.1 Reasons for using retention aids Newsprinters usually use a very short clamping area in the forming area. This requires that the same part has a very strong dewatering capacity in order to ensure that the exit section The wet web has enough dryness to enter the press section. Under strong vacuum dehydration, a large amount of fines will be lost to white water. When the white water reaches a higher concentration, the wet chemical environment of the paper machine will inevitably deteriorate, which will affect the application of other chemicals. At the same time, the degree of beating of the Internet pulp will increase, the dewatering capacity of the paper machine will decline, and the use of nets and blankets will decrease. The shortening of the cycle. In order to reduce the concentration of white water and ensure the normal operation of the paper machine, high speed paper machines are required to use retention aids.
2.2 Operation conditions of the paper machine The No. 5 paper machine of Nanping Paper Mill is a large-scale high-speed paper machine with a width of 5.5m and a running speed of 1270m/min to produce 48.8g/m2 offset newsprint paper. The ratio of slurry is: TMP43%, DIP17%, GP20%, BKP2O%.
2.3 Retention mechanism In the retention and filter aid system of the Nanhu paper mill, which is composed of bentonite and high polymer, the bentonite is used to absorb various disadvantages of the polymer floccule in the slurry. Condensation of negative electrical impurities, such as resin, adhesive and other colloidal substances. The function of the polymer is to flocculate fines, soaps and fibers that have absorbed various impurities and remain on the paper sheet, so as to achieve the purpose of retention and cleaning of the paper machine system.
2.4 Preparation of retention aid solution The solid product is dissolved as a liquid with a concentration of polymer O. 3% an O. 5%, bentonite 3% to 5%. Use a 125 mesh filtration system for filtration. After the addition of the retention aid, the secondary dilution is performed so that the concentration of the retention aid added is not more than 0. O5%.
2.5 Addition of Retention Agent The polymer was added before the slush pump. Bentonite is added before the press screen of the paper machine, which should be the best point of reaction with the polymer, and together with the polymer constitute the retention system. The retention agent solution was added using a screw metering pump. The amount to be added depends on the nature of the pulp and the requirement for retention aid filtration. It is usually a polymer of 250-300 g/t paper and a bentonite of 3-4 kg/t paper.
2.6 Retention effectiveness An important indicator of the retention effect is the concentration of white water under the net. The measurement results showed that the concentration of white water under the No. 5 paper machine net in Nanping Paper Mill was stable at 0.36%-0.44%, which was approximately 0.4O%, the volatility was 10%, and the one-way retention rate of the net department was maintained. At 51-55%, the above technical indicators are still relatively satisfactory. From the operation of the No. 5 paper machine, the author believes that the particulate retention aid has played an important role in reducing the concentration of white water, stabilizing the wet chemical conditions of the paper machine and ensuring the normal operation of the paper machine.
2.7 Adjustment of Retention Effect Although there are many factors affecting the enrichment, they will eventually be reflected in the concentration of white water. It is usually to maintain the amount of bentonite added, by adjusting the amount of polymer to control the concentration of white water. During the operation of the paper machine, the amount of polymer is adjusted in time according to the change of the white water concentration, which is the key to obtain an ideal retention rate. Therefore, the optimal retention control mode is to link the amount of polymer with the measured value of the white water concentration. When the measured value of the white water concentration is higher than the control target value, the system automatically increases the amount of polymer and controls the white water concentration in a timely manner.
2.8 Production cost Currently, the amount of polymer used is 300g per ton of paper, the amount of bentonite is 4kg per ton of paper, and the cost of retention aid is 53.4 yuan per ton of paper. Since the No. 5 paper machine is in the process of commissioning, the chemical condition of the wet end of the paper machine is not stable enough. Therefore, at this stage, we mainly ensure the paper machine's papermaking effect and stability. Optimizing the production cost will be the next step. As the operation of the paper machine is gradually normal, various process parameters will tend to be stable. After optimization, the effect of the retention agent will be further exerted, the retention rate of the network department will be increased, and the production cost will be further reduced.
3 Problem Discussion The addition of retention aids to high speed paper machines is not only a need for retention, but also a need to remove various impurities in the paper machine system. Therefore, the use of retention aids should be adhered to, but a gradual increase in the amount of use, that is, to maintain a low dosage, run for a period of time, to increase the amount after the system is clean and improve the retention of fine material. However, it is also necessary to see the adverse effects of high molecular weight polymers on the wet end of the paper machine. For example, strong agglomeration affects the quality of the paper.
In summary, retention aids have great potential for development in high-speed paper machines. We believe that with the understanding of the chemical processes of the wet end, it will become more and more obvious to apply the retention mechanism to monitor the economic benefits of the wet end of the paper machine.