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Unidentified risks in recovery boiler reports

Recovery boiler health is one of the most closely monitored processes in a pulp mill. Yet, some of the most critical risks are often unreported. In most mills, recovery boiler reporting primarily focuses on what happens inside the boiler itself.

“Serious issues can remain undetected because recovery boiler risks often originate outside the boiler,” explains Juho Saastamoinen, Product Manager for chloride and potassium removal plant service at ANDRITZ.

Keep an eye on the chloride and potassium removal plant

The chloride and potassium removal plant is one of the most influential side processes affecting recovery boiler performance. However, it is often left out of systematic monitoring and process-level maintenance.

“The purpose of the chloride and potassium removal plant is to maintain optimal chemical balance for the recovery boiler, prevent corrosion and fouling caused by chemical deposits, and maximize chemical recovery.”

Juho Saastamoinen

Early warning signs of potential issues in the chloride and potassium removal plant can be seen in recovery boiler reports if you know where to look.

“If unexplained changes are observed, for example in chloride, potassium, or sodium behavior, or in corrosion patterns, it is definitely time to assess the condition of the chloride removal plant as well as the ways in which it is operated.”

Juho Saastamoinen

Recovery boiler reporting primarily focuses on what happens inside the boiler itself. ©stock.adobe/aramyan

These issues typically develop gradually. They are often interpreted as the normal aging of the recovery boiler. However, that is not necessarily the case. If the root cause of an unstable chemical balance stays unrecognized, the consequences can escalate. In such cases, even a recovery boiler shutdown is not an exaggeration.

Systematic maintenance and reporting are essential

Mechanical maintenance alone is typically not enough to maintain optimal conditions in the chloride and potassium removal plant or to fully protect the recovery boiler.

“A deeper, process-level viewpoint is required to keep the plant running optimally. For example, this means understanding and optimizing the process parameters, debottlenecking, and training for operators. Regular assessments pay off in the form of stable production and consistent end-product quality.”

Casimir Svensson

Global Product Group Manager, Evaporation Service at ANDRITZ

The performance of the chloride and potassium removal plant has a direct impact on overall mill performance. The differences are not marginal.

“The gap between a well-performing and poorly performing chloride and potassium removal plant is significant. It directly translates into chemical losses, waste treatment costs, and recovery boiler lifetime.”

Casimir Svensson

Maintaining the chloride removal plant systematically at a process level, not just mechanically, is key to managing recovery boiler risk, a longer cleanability period, and securing stable mill performance.
If the chloride or potassium levels are too high, the situation starts to affect recovery boiler performance.

Fouling in the recovery boiler ©ANDRITZ

Early warning signs in recovery boiler reports

These indicators in recovery boiler reports can signal that it is time to assess the condition of the chloride removal plant:

Fouling in the recovery boiler superheater and boiler bank occurs in temperature ranges where high chloride or potassium levels can trigger rapid corrosion.
Unexplained changes or increased variability in chloride and potassium levels.
Corrosion rates that fluctuate without a clear operational cause.
Deposits are becoming stickier and more aggressive.
Loss of the protective layer on the heat surface.
Unstable recovery boiler char bed and furnace operation.