The concept of safety has traditionally been focusing on equipment and especially human safety. In the modern, sustainable pulp industry, the concept of safety needs to be enhanced with environmental and cyber security perspectives.

Improve the safety of the recovery boiler plant

The recovery boiler has operational details that highlight the importance of a complete safety perspective. The possibility of a smelt-water explosion, dangerous daily tasks like spout cleaning, and considerable environmental safety aspects set the recovery boiler into the spotlight.  

The approach to safety should always be layered and structured 

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1. Safety starts from the drawing board because the mill's safety is strongly dictated by the whole mill's design. Before the actual engineering starts, functional description and identification of hazards set the ground for engineering.

2. Basic controls ensure that the plant operates in a reasonable & safe way in all basic scenarios. For abnormal situations alarms, interlocking, and operator intervention ensure controlled behavior for scenarios that are outside of the design specification of the recovery boiler and basic controls. 

3-4. In modern recovery boilers, a separate safety-related system (SRS) engineered according to local legislation and applied standards is an absolute standard. SRS is the outermost layer of the automation system and steps in when basic controls with abnormal situation handling fail to keep the plant safe. 

 
5. Physical protection of property, humans, and the environment. The worst-case scenario here is a water-smelt explosion. If too many protection layers fail in the recovery boiler, the mill's emergency response steps in. This includes all internal mill actions that are triggered by imminent risk at the mill. It includes topics like evacuation routes, assembly points, mill emergency services, and the mill's warning systems for danger. 

6. The final layer of community response activates when all internal layers have not been able to protect the safety of humans, equipment, properties, or the environment. Communities like cities, states, and governments will activate their resources like first response in fire departments, healthcare, and environmental agencies to prevent the hazard or treat affected parties.

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Health and Safety Executive UK has published a study Out of Control that classified the root causes for control systems when incidents occurred. Close to 60% of cases were related to the design and implementation of the system.  

The heaviest reason for incidents was related to the specification and description of the system, which accounts for 44% of the cases. It clearly highlights the importance of specifying the system well and assessing risks related to that specification to the very last detail, to ensure a safe and efficient system.  

Another critical point is any changes made to the system after commissioning. It is important to specify changes again well enough and do a proper risk evaluation for the system after the planned changes. The operation and maintenance of the system were responsible for only 15% of the incidents. It is important to do the required maintenance and operate the plant according to specification, but the biggest focus is needed on risk identification.