The distribution, material balances and operational implications of a number of foreign (non-process) chemical elements have been studied with special attentionto the effects of increased systems closure. The elements and compounds discussed include Potassium (K), calcium (ca), silicon (Si), aluminum (Al) and manganese (Mn). The results are based on detailed surveys of two kraft millsof different degrees of closure, on theoretical chemical equilibrium calculations, laboratory studies and material balance modelling.
It is concluded that the chemical elements may be grouped in two classes. One class, including Ca, Mg, P and Mn, may be almost completely removed fromthe liquor system by green and white liquor clarification, i.e. in dregs, lime mud and grits. The other class, including K, Cl, Al and (with some reservations) Si, is not so removed and will tend to build-up in the liquor system with increased systems closure. Thus, these elements will call for special measures for reduced input, or specific output processes.
The effects of the non-process elements in some mill departments are discussed, mainly evaporator scalingand the effects on recovery furnace operation. Increased potassium (K) levels in the liquor system, for instance, are predicted to increase fly-ash flow and reduce sulfur emissions from the recovery furnace.
TAPPI Press, 1979. 77-83 p.
Tappi/ATCP Pulping Conference, Seattle, WA. USA