Increasing pulp yield in kraft cooking of softwoods by high initial effective alkali concentration (HIEAC) during impregnation leading to decreasing secondary peeling of cellulose

• Pulp yield can be improved by a more homogeneous delignification of the chips, achieved by improved impregnation prior to the cooking stage. Complete and efficient impregnation is obtained by increasing the diffusion rate by means of an impregnation liquor with a high initial effective alkali concentration (HIEAC). In the present study, the effect of HIEAC in the impregnation was evaluated and compared to a reference impregnation procedure and a prolonged impregnation. After the various impregnation scenarios, the alkali concentration was always adjusted to the same level in the beginning of the cooking stage. Impregnation with a HIEAC resulted in yield improvements by 1-1.5% units, due to a higher cellulose yield and possibly also to higher yield of glucomannan. The HIEAC with an even alkali distribution within the chips prior to the cooking stage resulted in a more uniform delignification carbohydrate degradation. Yield increase obtained by uniform delignification is due to both decreased shives content as well as less secondary peeling.

Nyckelord

chemical composition

diffusion

high initial effective alkali concentration (HIEAC)

homogeneous delignification

impregnation

kraft pulping

molecular mass distribution (MMD)

peeling

pulp yield

softwood

Cellulose

Delignification

Kraft process

Kraft pulp

Molecular mass

Softwoods

Alkali concentrations

Chemical compositions

Diffusion rate

Kraft cooking

Molecular mass distributions

Pulp yields

Yield Improvement

Yield increase

Pulp cooking

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)