The white liquor clarifier rake failed in three pulp mills, two in the United States and one in Canada.
You might think that the same event would be addressed the same way by different organizations, but the truth is different. In each case, the lime kiln had been shut down to remove a large ring. With the kiln offline, lime mud inventory rose faster than planned. The clarifier overloaded, the aging rakes became buried, and the rakes bent and failed during forced re-starts. Each mill repaired the damage and returned the clarifier to service, at high cost.
All three mills were operating as profitable going concerns. In each case, management worked to preserve optimism and a can-do attitude during the crisis. Crews were told the problem was solvable and that the mill would recover. That optimism mattered. It kept people engaged, reduced panic that the mill would be abandoned, and allowed limited production to continue where possible.
What differed was how optimism was created and how far it was allowed to go. In one culture, optimism came from speed and technical confidence. In another, it came from authority and urgency. In the third, it came from careful analysis and shared responsibility. In all three cases, the equipment was repaired. The deeper risk, however, was not equally understood.
At the first plant, the response was calm and efficient. Engineers reviewed data and chose a low-cost repair path. Over eight days, the clarifier was emptied and the rake repaired while the pulp mill stayed down and the paper machines ran on baled pulp. Confidence came from keeping machines running. Months later, the rake failed again under similar conditions. The plant repeated the same response. The system recovered, but it did not learn.
At the second plant, the failure escalated immediately. Corporate leadership treated the bent rake as a threat to financial predictability. Production was halted across the site. The clarifier was dumped to wastewater, heavy equipment was used to excavate the rakes, overtime was mandated, and a central engineering team arrived. The clarifier was back online in five days. Optimism was real, but enforced, and key decisions around the kiln outage were quietly smoothed over.
At the third plant, the response was slower and more deliberate. Operations, engineering, and maintenance examined the full chain of events, including the kiln shutdown, operator workload, leadership decisions, and the effects of switching to purchased lime. The rake was reinforced, procedures were changed, and crews retrained. Restart took slightly longer, but confidence increased because the cause was understood.
Each mill believed in its approach. One ignored human judgment, one concealed it, and one confronted it. None fully treated the kiln ring and its removal as the primary technical driver of a multi-million-dollar loss. That omission and not the broken rake is why the risk remained.
About Mike Ryan
Mike Ryan is recognized for enhancing operational reliability and efficiency, combining deep technical expertise with a strong focus on training and process improvement across a wide range of industrial settings.
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