Modeling the dynamics of heptads' effect evaporator system in the kraft recovery processes

Abstract

The performance of the multi-stage evaporator (MSE) system used in the pulp and paper industry for the Kraft recovery process may vary significantly during the transient time of start-up, shutdown, load changes and rejections, troubleshooting, etc. This makes it quite imperative for a process engineer to know the transient behavior of the system under operation. Although, the steady-state models for the MSE system have been analyzed quite exhaustively by the researchers in the past but the dynamic model has not been extensively investigated. The purpose of the paper is to develop and present a detailed dynamic model for the study of transient behavior of the evaporator unit with varying process designs. A heptads' effect evaporator system with the backward feed flow configuration has been considered for the dynamic modeling in the present work. Some important and pertinent energy saving operating strategies such as live steam split, liquor feed split, feed pre-heating and their hybrids, have been incorporated in the process design. The systematically evaluated material and heat balance equations evolve into different transient models with a set of nonlinear first order differential equations. The finally derived model equations may be conveniently simulated so that the performance of process control strategies could be compared and an optimized operating strategy be screened for use by industry under different operating conditions without disturbing the paper mill production and without imperiling the equipment. © International Science Press.