Study On Wet End Characteristics Of Closed Whitewater System In Offset Paper Mill

For both economic and environmental reasons, considerable efforts have been made to minimize the water consumption and the discharge of polluting substances in modern pulping and papermaking industry. In paper-making workshop this has been done mainly by closing up the white water systems. But the closing of the white water system leads to a buildup of detrimental substances in water system, and will give rise to many troubles, for example reducing the performance of wet end additives. So it is necessary to study the wet end characteristics of the closed white water system.This dissertation focuses on the characteristics of offset paper production system when its white water system is closed. It consists of four parts.At first, the properties of pulp fibers of making offset paper were analyzed, including physical properties, the content of COOH, zeta potential, specific surface area, colloidal titration ratio (CTR) and so on. The influencing factors of zeta potential and the relationship of zeta potential with retention and drainage were discussed in detail.Then we have researched the wet end characteristics of white water, including pH, conductivity, CTR, cationic demand, total dissolved substance, fiber fine distribution etc. The inorganic salts in white water were investigated in detail.Thirdly, we have simulated the white water closure using dynamic drainage jar (DDJ) in lab. Fluctuation in wet end parameter was observed when closing the white water. The results showed that the conductivity, cationic demand, pH, chemical oxygen demand of white water increased with closed white water number increased. The wet end system deteriorated after white water closed, and expressed decrease of first pass retention and higher cationic demand.At last, we have done research on the effects of closed white water on retention system. Three retention systems, including a single CPAM, a dual cationic polymer system of CPAM and polyamine (PAE) and a microparticle system of PAE, CPAM and silica, were investigated. It was shown that the microparticle system was better than the single and dual retention system at high system closure. The effects of the closed white water on paper strength and optical properties have been also studies in this part. It is concluded that breaking length decreased as the number of white water recycled increased, while white water closure has a negligible effect on optical properties.