(218d) Effluent Reduction in Pulp and Paper Manufacturing: Paper Machine White Water Recycle in Bleaching Section

The pulp and paper industry is one of the largest consumers of water in the US industrial sector. Of the different process areas in a typical integrated bleached Kraft mill, the paper machine and pulp production account for around 75% of the total mill freshwater consumption. Therefore, the most significant freshwater reduction potential exists in these process areas. The overall objective of this study is to develop innovative strategies for water reuse from the paper-making process in the pulping process for reducing overall freshwater consumption.

In previous work, we applied Windows General Energy and Material Balance Systems (WinGEMS) to develop a process simulation model for the bleaching and paper machine sections capturing the material, water, energy, and the Non-Process Elements (NPEs) flows. Steady-state equations for the Elemental Chlorine Free (ECF) bleaching sequence D₀EopD₁EpD₂ are included in the simulation. The simulation model captures the effects of carry-over from brown stock washers (BSW) and extraction stage washer on the pulp brightness. It provides a tool to predict changes in the kappa number, brightness, and effluent Chemical Oxygen Demand (COD) values with changes in the operating parameters. We validated the EFC bleaching simulation model outputs using industrial data. Difference between industry operation data and simulation results in terms of key pulp properties such as brightness and kappa number were in the range of 1.8 to 5.5%, respectively.

This presentation focuses on the results of laboratory bleaching experiments for further validating the ECF simulation model results and incorporating Visual-MINTEQ software with the WinGEMS simulation model to determine the distribution of Ca²⁺ ions in the paper machine white water. The design of experiments for the laboratory bleaching study is constructed to replicate industry bleaching operation conditions. The preliminary experimental results revealed that the difference was in the range of 2.9 to 7.9% when comparing the laboratory bleaching work for the first two delignification stages, D₀Eop, with the simulation values for the pulp brightness and the kappa number, respectively. Current experimental work focuses on bleaching experiments for validating the final pulp brightness and the effluent COD values coming out of the bleaching sequence with the simulation values. For determining the distribution of Ca²⁺ ions in the paper machine white water, we will integrate the Visual-MINTEQ software with bleaching and the paper machine section simulations. This comprehensive model will capture the pulp parameters of kappa number and brightness in the bleaching sequence along with the white water Ca²⁺ ions distribution. The WinGEMS and Visual-MINTEQ integrated model will enable us to investigate the scope of white water recycle into the bleaching section. The results of this investigation will be discussed in the presentation.