Systematic Modeling And Comprehensive Optimization Of Pulp Quality,Bleaching Cost And AOX Emissions

Nowadays,facing the new or upgraded established papermaking advanced production lines and wastewater treatment technology,how to further reduce production cost and environmental pollution is an urgent challenge to be solved by papermaking workers in recent years.Researchers from both China and overseas,have optimized pulp quality,bleaching cost and environmental pollution by establishing empirical model,kinetic model and optimization model of bleaching stage,but the research object is not involved in the whole bleaching system and the research goal is relatively single.Therefore,how to further reduce the bleaching cost and environmental pollution of whole bleaching process under the premise of ensuring pulp quality is particularly important.In this study,a single factor experiment was designed for eucalyptus kraft pulp.Based on the experimental data,the mathematical relationship between the process conditions of each bleaching stage（chemical dosage,temperature,time,p H value）and the pulp quality（brightness,viscosity,and kappa number）,the content of adsorbable organic halides（AOX）and chemical oxygen demand（COD）were analyzed by using Spss and origin software.And the calculation model of the cost of the bleaching system was deduced.Based on the above mathematical calculation model,the influence of each bleaching process condition on bleaching cost and AOX content was analyzed.It was found that the amount of chlorine dioxide in the chemical cost had the greatest influence on the bleaching cost,followed by the amount of hydrogen peroxide and sodium hydroxide.In the energy cost,steam had the greatest influence on the bleaching cost;the amount of clean water and the discharge of bleaching wastewater have little influence on the bleaching cost.The bleaching conditions of D₀ stage（chlorine dioxide dosage,temperature,time,and p H）had the greatest influence on AOX content.Building on the established mathematical calculation models of pulp brightness,viscosity,kappa number,bleaching cost and AOX content,the system model of pulp bleaching quality-cost-AOX was founded,and the pulp-water balance calculation of the bleaching system was completed.On these bases,the pulp bleaching system was simulated though using the Simulink component of Matlab software,which the model could be used to predict pulp quality（brightness,viscosity,kappa number）,bleaching operation cost,AOX content,AOX discharge and wastewater discharge.Based on the mathematical calculation model of pulp quality,AOX content and bleaching cost,this study proposed the comprehensive optimization strategy of pulp bleaching system,established the optimization model of pulp bleaching system,and solved the model and verified by experiment.The experimental results showed that the relative error between the calculation value and the experimental value of the optimized conditions was 0.32%～6.62%,indicating that the reliability of the optimized parameters was extremely high.Compared with the quality of pulp quality before optimization,the brightness of the optimized pulp decreased by 0.33%,and the viscosity increased by 2.51%.However,the optimized AOX emissions,COD emissions,and bleaching cost decreased by 13.41%,9.76%,and 6.94%,respectively.