Kraft ECF pulp bleaching: A review of the development and use of techno-economic models to optimize cost, performance, and justify capital expenditures

Abstract

This work evaluates the findings of various research efforts and describes the development, use, and benefits of applying techno-economic models of different types to various production and bleach plant scenarios. During the late 1980s and early 1990s, researchers determined that bleach plants were releasing potentially significant quantities of chlorinated organics into receiving waters. This led to extensive research to develop bleaching chemicals to eliminate chlorine and hypochlorite from the bleaching sequence. Over time, 100% chlorine dioxide substitution for chlorine became the industry standard (today’s elemental chlorine free [ECF] bleaching), and research efforts shifted toward chemical optimization of the ECF bleaching sequence. Several delignification stage and brightening stage models were developed and refined for use in bleach plant simulations to optimize chemical performance. Advances in computing power and the availability of packaged spreadsheet and simulation programs likewise led to the development of detailed material and energy balance models of the bleach plants. These simulations are used to minimize bleaching and pulp production costs, and to assist engineers in the development of justifications for capital expenditures. These models have been used to predict operating conditions that could lead to or reduce scale formation. They have also been extensively used to predict environmental performance of both new and modified bleach plants.