| Recent decade, recycling of waste paper has been increasingly developing as an important fiber resource for paper industry. It saves wood fibre, reduces the impact on environment, also decreases production cost. Currently, newsprint and supercalendered paper grades can be produced with 100% deinked pulp. However one of most important obstacles in ultilizing recycled fibers is sticky substances caused problems. Especially for the highly recirculated water system, the troubles caused by stickies are more severely increased. Therefore, control of the sticky contaminants is crucial for paper production with recycled fibers. In this paper, models of stickies were constructed with several components to study how they would influence the stability and deposition behaviors of sticky substances. The effect of heat-dispersing on stickies by changing temperature, disc clearance, or pulp consistency was further investigated to acquire useful information for guide the mill operation. Meanwhile, two fixing agents provided by a commercial chemicals company were applied to the deinked pulp, and their effects on control of sticky contaminants were examined.Effect of heat-dispersing on sticky substances was studied, including by varying temperature, disc clearance, or pulp consistency. Status of sticky substances was quantitatively investigated, in category of macro-, mini-, and micro-stickies. Furthermore, their removal in the subsequent post-floatation was evaluated. The results showed that by raising temperature, reducing disc clearance, or increasing pulp consistency can improve significantly the dispersion efficiency of sticky substances. Under temperature of 100°C, disc clearance of 0.3 mm, and pulp consistency of 30%, macro- and mini-stickies decreased by 92% and 83%, respectively. Due to being dispersed to a smaller size, removal of mini- and micro-stickies was enhanced in post-floatation to 25-26% and 68-70%, respectively.Effect of heat-dispersing on dissolved and colloidal substances, and suspended solids was quantitatively investigated by varying temperature, disc clearance, and inlet pulp consistency. Furthermore, their removal in the subsequent post-flotation was examined. The results showed that raising temperature, reducing disc clearance, or increasing pulp consistency improved significantly the dispersion of sticky substances, and increased amount of DCS in deinked pulp. Under temperature of 100°C, disc clearance of 0.3 mm, and pulp consistency of 30%, DCS, dissolved substances, and colloidal substances were increased by 13.6-16.8%, 5.7-5.9%, and 60.7-65.3%, respectively. DS were as a major component in DCS, although CS was showed with a higher increasing rate after dispersion. SS were increased significantly after heat-dispersing, reached to 21.7-26.0%. The post-flotation removed about 45.2-46.6% of SS, and 6.1-6.8% of CS, while only small amount of DCS were removed.Two fixing agents, Hybrid 7655 and Hybrid 8185 were examined and their effects on control of sticky contaminants were discussed. Pulps were sampled from three major points of a deinking pulping line, i.e. the post-flotation, the DIP storage tower and the PM head box. Deposition of sticky contaminants were evaluated by the aluminum foil method, and influences of applying fixing agent on the dissolve and colloidal substances, the filtrate turbidity, the cationic demand and Zeta potential of pulps were examined. The results showed that deposits can be significantly decreased, meanwhile, decreased DCS, turbidity and cationic demand accordingly. The fixing agent Hybrid 7655 was more effective for removing stickies, moreover, adding the fixing agent into the DIP storage showed a better performance. Adding fixing agents deteriorated to some extent the paper physical properties, but the negative effect depended on the addition level.The effects of temperature, pH, cationic polymers, salts and inorganic mineral filler on the physical chemistry characteristics, stability and deposition of the stickies were investigated by building sticikies models with serval components. Based on the results, it was showed that rising temperature and decreasing pH value could reduce the viscosity of stickies, consequently the deposition of stickies increased to some extent. Salts could cause precipitation of stickies, especially Al3+ with a higher valence which may have stickies destabilized at low concentrations. Ca2+ reacted with sticky substances to generate easily-deposited calcium soap, while the calcium soap deposition decreased as introduced pulp fibres. Cationic polymers showed significant effects on the stability and deposition of stickies. Polyethylene imine (PEI) could result in completely destabilization, and deposition happened at the neutral point. Cationic polyacrylamide (CPAM) can aggregate stickies at a low dosage. The sticky particles lost their stability when adding excessive PEI. Sticky substances can deposite by attaching on the fibres. Increasing CPAM does not restabilized sticky particles, but the deposition of stickies can be reduced due to attached to fibres. Inorganic mineral filler can adsorbe stickies, but they can attract stickies and deposit them to fibers even at low dosage. Decrease of stickies does not propotionly increase with increasing dosage of fillers.
|
PDF Full Text Request