The influence of basic density and pulp-yield on the cost of eucalypt kraft pulping: a theoretical model for tree breeding

Abstract

The impacts of genetic improvement of density and pulp yield on the cost of converting roundwood to unbleached kraft pulp are modelled for a greenfield mill. Operating and capital costs are described as functions of density and pulp yield for each stage of the pulp mill including the chemical recovery process. The cost of converting green roundwood to unbleached pulp, per oven dry tonne of unbleached pulp produced, will decrease with increasing density and pulp yield. Pulp yield has the greatest effect on pulping cost, but the degree of influence depends upon the value of energy produced by the recovery boiler : a high energy value reduces the influence of pulp yield on pulping cost. Density has a major influence on the cost of digestion and a minor influence on the cost of evaporation, so a high relative digestion cost increases the influence of density on pulping cost. This paper does not, however, conclude pulp yield to be a more important trait than density for breeding for kraft pulp.