Valmet's ash treatment systems remove Chloride and Potassium from the recovery boiler ESP ash. High levels of these substances can lead to superheater corrosion and plugging of the recovery boiler.
Valmet has built ash treatment systems in pulp mills all over the world. Several have been upgraded as the mills have increased production.
Chloride and Potassium enter the liquor cycle with the raw material and can increase the rate of corrosion in the mill.
The chemicals change the properties of the recovery boiler ash. This can lead to buildup of ash and high rates of corrosion. In some cases, the buildup is so fast that the recovery boiler has to be stopped for water washing several times per year.
If the recovery boiler frequently needs to be stopped for water washing, or if the superheaters corrode, an ash treatment system from Valmet will result in increased uptime and production.
Valmet has extensive references and offers three different solutions that each have their pros and cons. Since every mill has different requirements, a careful analysis is needed in order to find the best solution.
Treatment of electrostatic precipitator (ESP) ash uses water to separate the unwatned chemicals.
When ESP ash is mixed with water, Chloride and Potassium generally dissolve into the water, while the pulping chemicals remain as solids. The solids can be separated from the liquid and returned to the mill. The liquid, with the unwanted chemicals, can be led to wastewater treatment.
This is the basic mechanism of the two main technologies on the market today, ash leaching and ash crystallization.
The Valmet ash treatment systems perfom very close to the theoretical maximum limits that can be achieved. The ash crystallizers, for example, offer up to 96% removal of Chloride from the incoming ash. Since the cooking chemicals are valuable, having a high rate of recovery of them is also an important measurement of an ash treatment system.
Rates of removal and recovery will differ depending on the content of the mill's ESP ash. And these levels can also vary over time.
A good ash treatment system has to be able to handle the actual situation in the mill.
Valmet can provide both leaching and crystallization technologies.
Finding the best solution for the mill requires a good analysis.