(647d) Modelling and Optimization of Washing Plant of A Paper Mill

Paper is an essential commodity for human society and an indicator of development of a nation. This material is manufactured through a series of unit operations in a paper mill. The paper industry is capital intensive in terms of consumption of raw materials, chemicals, energy and labour with generation of huge pollutants. Modeling and simulation can help in optimizing such a host of bewildered processes and can assist in accruing resource saving. The industry consists of a number of subsystems, which are complex and intricate in nature. Interlinking the subsystems is rather difficult mathematically. In this present study a series of mathematical models are developed for optimizing a multi-stage washing plant interlinking with other operations and processes such as multi-stage bleaching, multi stage evaporation, combustion and effluent treatment. In order to achieve the above goal, an objective function, Eq.1 has been developed based on total annual cost. This in turn demands development of models of succeeding stages and subsequent optimizing each of them.

Min (CT) = (Pw + Pm)*N + PE* (CE +CA + CL) + Ps* CS + PNB* CNB + (C13 * N + C5 * (N-1) + C6 * N + C4)* Po + CLW +PEff* CEff + Csl* Psl + Ctsl* Ptsl (1)

A non-linear programming problem with constraints - conjugate gradient (Fletcher-Reeves)-the method of constrained optimization is used for optimization of multi-stage BSW. For modeling and optimization of individual operations a number of algorithms have been developed and solved through various mathematical techniques and simulated through computer program. Because all interconnecting operations are discrete individually but continuous in integrated process to maintain production of paper, the model predicted data are subjected to univariate/multivariate statistical linear or nonlinear regression models, to build up the link before two corresponding interacting operation. The decision variables are N, DF or both for representative equations in optimization program of BSW plant. From the results of constrained nonlinear optimization of washing operation base on total annual cost taking in to account all costs including BOD treatment cost, it is found that the dilution factor (DF) and number of stages (N) are of the order of 2.789 and 3.958(°Ö4 as N can not be a fraction) respectively for minimum cost of washing.