Sivola Processes

The Sivola sulfite cooking and recovery process was developed in the early 1950s

to produce either dissolving or high-grade sulfite pulp at Rauma from spruce and

balsam woods [15–17]. The sodium-based, multi-stage cooking concepts of the

“Sivola” type comprise the bisulfite-neutral sulfite (soda), the acid bisulfite-neutral

sulfite (soda), and the bisulfite-acid sulfite-soda processes. The bisulfite-neutral

sulfite process is characterized by a change of the pH level from around 3.5–4.0 in

the first stage up to 7.0–8.5 (and higher) in the second stage. Differences in pulp

quality are observed if the first-stage liquor is drained before alkali is added to the

second stage. Pulps of superior burst and tear levels are obtained when the alkali

is introduced directly into the first-stage liquor. However, when the first-stage

liquor is drained before alkali is added, tearing resistances close to that of kraft pulps

are obtained, but the burst was not further improved. The effect of a two-stage bisulfite-

soda cooking process as compared to conventional acid sulfite and bisulfite pulping

methods using aspen as a raw material is detailed in Tab. 4.64 [15].

Tab. 4.64 Comparative evaluation of acid sulfite, bisulfite and

bisulfite-soda (Sivola) cooks of aspen (according to [15]).