TOWARDS CLOSED-CYCLE KRAFT - ECF VERSUS TCF CASE-STUDIES

Chemical balances for the soluble elements sodium, sulphur, potassium and chloride are standard calculations in the design of kraft mills us ing either ECF or TCF bleaching sequences. For reduced water use mills , and for closed-cycle mills, these standard balances are enhanced by including non-process-elements in the analysis. Alternative water use reduction schemes must be evaluated in order that the most desirable p rogram may be implemented. This requires some knowledge of che fundame ntals of closed-cycle design. Closed-cycle design considerations are i llustrated using a series of seven Case Studies following a design app roach which considers: effluent volume reduction and heat balance issu es; chemical balance and recovery cycle issues; and finally the dynami c balance, control behavior and economic optimization.