Ash leaching and crystallization solutions

The Valmet ash treatment systems remove Chloride and Potassium from pulp mills. This lowers recovery boiler corrosion and increases production.


Chloride and Potassium enter the liquor cycle with the raw material and cause corrosion in the digester, the evaporators and the recovery boiler. The recovery boiler superheater is an especially sensitive area. Common problems are plugging and increased consumption of sootblowing steam as well as reduced efficiency in the electrostatic precipitator.

If a mill frequently needs to stop the boiler for water washing and has elevated levels of chloride and/or potassium in the black liquor, a Valmet ash treatment system will result in increased uptime and production.

Valmet has extensive references of ash treatment systems and offers three solutions that remove unwanted chemicals from the electrostatic precipitator ash. Every mill is different, and to find the optimal solution a careful analysis is always required.


Valmet Ash Leaching

The ash leaching technology from Valmet is a well-proven, uniquely simple and effective solution that removes chlorides and potassium from ESP ash. Ash leaching does not require steam and runs independently of the other chemical recovery systems.

Valmet's ash leaching systems have been providing outstanding value for pulp producers ever since the start of the first unit in 2002. Currently, there are systems up and running all around the globe at mills that produce pulp from eucalyptus, acacia, pine and other wood species. Thanks to the simplicity of the process, an leaching plant is very easy to maintain and operate. Valmet ash leaching stands for high availability and good long-term performance.

Valmet Ash Leach Duo

The Ash Leach Duo system is a two-stage ash leaching solution that provides superior leaching efficiency when treating ash with a high carbonate content. The Valmet Ash Leach Duo provides better performance than the single stage ash leaching systems with almost the same simplicity of operation.

Valmet Ash Crystallization

The Valmet Ash Crystallization technology offers the highest efficiency in treatment of recovery boiler ash. Valmet's ash crystallizers perform very close to the theoretical maximum of ash crystallization.

But the ash crystallization process differs from the leaching process in several ways. The most important difference is that ash crystallization has an evaporation step and therefore requires steam. A crystallization plant is therefore more complex than a leaching plant, but the performance is superior.

To date, Valmet has built the world's biggest ash crystallization system. This plant was designed to treat 920 tons of ESP ash per day and went into continuous operation in 2017. The startup was smooth and according to plan.


Ash crystallization at the OKI mill

At the APP OKI pulp and paper mill the recovery boiler ash is treated in an ash crystallization plant to keep potassium and chlorine at the desired low levels in the mill’s recovery cycle.