Valmet Continuous Cooking

Valmet Continuous Cooking is Valmet’s system for more cost-effective pulp production. It is the first-hand choice for kraft mills pulping hardwoods (eucalyptus, acacia, birch etc.), softwoods (pine, spruce etc.) or bamboo.

The Evolution of Continuous Cooking

In 1948 Valmet received the first order for a commercial continuous digester. The development of the continuous cooking system has resulted in a number of innovative features. The new digester process builds on the strength of previous technologies and experience that has been built up over the years.

The latest steps of development make use of the most recent progress in research while also focusing on simplifying the cooking system. This lead to the Valmet Continuous Cooking concept.

Simplifying the system has significantly reduced the investment and operational cost. Increased flexibility and a process that is easier to operate are other benefits from the simplification of the system. The development aslo includes a new layout where pipe length, accessibility & maintenance has been improved.

Steaming and impregnation

Valmet ImpBin™ chip impregnation system establishes a thorough impregnation of the chips with liquor before cooking. The atmospheric Impbin combines the basic features of the traditional chip pre-steaming bin, impregnation vessel and flash system. Impregnation of chips at low temperature for a longer time has proven to be very effective generating pulps with very low reject content. Effective impregnation in combination with the benefits of Valmet’s continuous cooking process produce pulps with high yield and excellent pulp quality.

Process flexibility

Valmet’s continuous cooking process chemistry is a further development of the “four rules of Kraft cooking” originally developed at STFI and the Royal Institute of Technology. The Continuous Cooking system is a very flexible process allowing the liquor to wood ratio to be controlled in a unique way during the various parts of the cooking process.

This added process flexibility allows the alkali profile to be optimized achieving a more selective cook with less carbohydrate degradation resulting in better pulp quality and higher yield. Valmet’s continuous cooking process re-circulates black liquor to the impregnation and cooking stages. As a result the hydrogen sulphide concentration is increased during the impregnation and cooking stages. By optimizing the hydroxide and increasing the hydrogen sulphide concentration it has been possible to increase the selectivity of the Kraft process in the initial cooking phase, the bulk delignification stage, and thereby decreasing the amount of slowly reacting residual phase lignin. The above has led to an increase in the rate of delignification in the bulk phase which is utilized to decrease the cooking temperature. Decreasing the temperature minimizes carbohydrate degradation and strength losses.

Two-vessel system

The Continuous Cooking system design is based on results from the latest research on delignification chemistry. Benefits of a two-vessel system compared to a single-vessel are many. A two-vessel system has no radial temperature and alkali concentration variations, well defined impregnation zone, simple liquor to wood ratio control of the different cooking zones, recirculation of black liquor to the impregnation phase for process benefits.

Customer cases

Klabin’s massive Puma II project makes history with Eukaliner kraftliner

Dec 18, 2020

Klabin’s massive Puma II project in Brazil is making history by challenging the conventional thinking that softwood pulp is required to make high-quality kraftliner. Its new OptiConcept M kraftliner machine will produce Eukaliner – the world’s first kraftliner using 100 percent eucalyptus.

Even better pulp and yield at Smurfit Kappa Piteå

Sep 1, 2020

Pulp with higher quality, combined with increased yield from the wood raw material, is now a reality for Smurfit Kappa at its mill in Piteå, Sweden. The cooking process technology from Valmet played an important role in the successful rebuild project.

Consistent pulp quality optimizes the process

Jan 8, 2018

Cleaner pulp, higher, more consistent quality and reduced maintenance. These are some of the results since SCA’s liner mill in Obbola brought its new cooking plant into operation in 2015.

Irving leaps forward with Valmet CompactCooking

Jun 20, 2017

When Irving Pulp and Paper of Saint John, New Brunswick, on the Atlantic coast of Canada, started up its new continuous pulping operation in March, 2016, it was a milestone in the Canadian pulp and paper industry. The two-phase modernization project for the bleached kraft pulp mill represented the largest investment in the Canadian industry since 1993.