Effect of Consistency on Pitch Precipitation by Flotation, 1994 Pulping Conference Proceedings

A. Nadezhdin, G. Dube, G. Sherson, R. Duncan

We modified pitch measurement technique based on air flotation to study the effect of pulp consistency on the tendency to form pitch deposits. The new method discriminates between dispersed and dissolved pitch constituents and reflects interactions between them in a given system. The results were similar between naturally occurring softwood sulphite pitch and a “synthetic” pitch made by solubilizing tall oil from softwood kraft production. In both cases, pitch precipitation reached its maximum level within a relatively narrow range of pulp consistency. In the case of softwood sulphite pulp this range corresponded approximately to paper machine wet end conditions. The observed effects suggest the need to examine abrupt changes in pulp and paper stock consistency, in addition to the commonly recognized effects of temperature and pH shocks as pitch stimulating factors, when approaching the challenging problem of pitch control along the entire production process in a mill.