Abstract

In the present investigation, a steady-state mathematical model is developed for a typical four stage Industry. Each stage of the sequence is composed of chemical additions and mixing, reaction in a reten-tion tower, and washing. Unit operation models were formulated using mass balances on liquor, fibres, kappa number, chemicals and COD based on the assumption of perfect mixing and quasi steady-state. The COD is used in this paper as an indication of the amount of effluent coming out from four bleaching stages. COD measurement of bleach plant effluent separately is not a routine mill measure-ment; so COD is calculated in the basis of correlation of COD given by Anjana . In order to validate the model, the simulated results were compared the literature data; a good agreement between the simulation results with the literature data is achieved. In the case studies, the optimization of the process variables are performed in which the effects of operating temperature, residence time, consistency, bleaching liquor flow rate and the wash water flow rates in the washers are studied.