D0-STAGE CONTROL IN ECF BLEACHING AND MID-DIGESTER KAPPA-MEASUREMENT

Chlorine-free bleaching is spreading rapidly, necessitating the develo pment of process measurements and controls: traditional control system s cannot handle these new processes. Moreover, process steps preceding the bleaching sequence are now more crucial for the end result than e ver. Different measurement combinations and D0-stage control solutions are compared using results from mill-scale trials, and the benefits, drawbacks and results of each alternative are discussed. Midpoint kapp a measurement is also presented:it allows quicker feed-forward control of the digester washing zone giving a stabilized, optimized blowoff k appa number.