Who would think that a small lime kiln, in operation since 1955, would be capable of significantly increasing its output to debottleneck a recausticising plant, and allow the rest of the plant to achieve a new design output? Such was the case for the lime kiln, at the Carter Holt Harvey (CHH) Tasman Kraft Pulp mill, which produces burnt lime (CaO) for converting sodium carbonate into caustic.
The mill had been upgraded in 2006 with the rebuild of the No.1 pulp machine, but it was underperforming due to a white liquor (caustic) shortage from the causticising plant. Beca AMEC was engaged to prepare a study and identify bottlenecks in the plant. The mill personnel were fully engaged in the process.
Using duration curves and benchmarking techniques new to this area, the team reviewed the many interactions in this complex plant, and found that the aged lime kiln held the answer. It appeared the existing lime mud filter was undersized for the actual kiln capacity, but by upgrading the kiln with a new claridisc lime mud filter it could have a new lease of life.
Once capital was approved by the owner, Beca AMEC undertook the engineering design and handled the construction management for the installation. Success was immediate. Not only did the new filter allow an 80-100% increase in lime kiln output on commissioning but it has also improved the overall environmental performance. Furthermore, the mill has reduced purchases of imported lime from 12,000 to 2,000 tonnes per year and drastically reduced chemical make-up costs.