Combustion Properties of Birch ( Betula pendula ) Black Liquors From Sulfur-Free Pulping

This article describes the combustion properties of the black liquors produced from silver birch ( Betula pendula ) sawdust using three different cooking processes: two sulfur-free cooks (soda-anthraquinone and oxygen-alkali), and one reference kraft cook. It also considers the corresponding black liquors from an integrated forest biorefinery, in which a hot-water pretreatment of feedstock was performed prior to pulping.

With the same cooking time, the total burning times for the sulfur-free black liquors were higher (15–55%) than those for the conventional kraft black liquors. However, no significant differences were noted between the total burning times for black liquors from pretreated feedstock and those from untreated feedstock. Especially in the case of untreated feedstock, the results showed that the kraft black liquors typically swelled more (25–45%) than the sulfur-free black liquors.