Ash leaching

The ash leaching process

The ash leaching process begins with mixing the ESP ash with water. Non-process elements dissolve in the water, while the useful chemicals mostly remain as solid particles.

The solids are separated with a centrifuge and returned to the mill. The solution is rich in Chloride and Potassium and is sent to wastewater treatment.

Several strategies

Valmet’s ash leaching can be operated towards maximum removal or maximum recovery, or an optimum in between.

When more water is added, more ash dissolves and more Chloride and Potassium is removed. When less water is added, more cooking chemicals are recovered.

Valmet’s ash leaching is built for easy operation and gives operators good control of Chloride and Potassium levels in the mill.

Carbonates

Ash from modern recovery boilers contains high levels of carbonates, and this can lower the performance of an ash leaching process.

Valmet’s well-designed solutions remove the carbonates with sulfuric acid. And Valmet’s two-stage ash leaching process – AshLeach Duo – also offers good performance with high-carbonate ash.

Start and stop

Valmet’s ash leaching is separated from other mill processes and easily started and stopped. This gives the operators the option to run it only when needed. Many mills use this feature to optimize their treatment of ESP ash, so levels of Chloride and Potassium can be kept low and safe.

Valmet AshLeach is a single-stage ash leaching unit made for solid performance in a wide range of operating situations. The image above shows the the ash mixing tank (left) and the AshLeach plant (right). The ash mixing tank is sometimes placed close to the recovery boiler.

Valmet AshLeach Duo is an innovative two-stage ash leaching system that offers higher performance than single-stage leaching. The Duo also performs better on high-carbonate ash and keeps the simple operation features from Valmet's AshLeach, giving operators lots of room for control of Chloride and Potassium. The image above shows the two centrifuges, one for each stage of the ash treatment in Valmet AshLeach Duo.