Closing the circle at the pulp mills

How to convert lime sludge into top-quality lime.

There are those who regard it as waste, but residual lime sludge can actually be converted into top-quality lime. “The recovered lime is ideally suited for the cellulose industry and demand is greater than ever before”, says Patrik Hjärpe, who is the sales director at SMA Mineral.
Lime sludge is a waste product from paper pulp manufacture that can also be converted into lime. Using SMA Mineral’s so-called Sandarne concept, the lime sludge is washed to remove contaminants before being burnt in a kiln. The resultant product is a caustic lime that is ready for re-use in the pulp mills – a smart way of protecting the environment and an excellent example of recycling.

SMA Mineral steps in
The pulp mills have their own kilns that they use to recycle the lime sludge to produce caustic lime. Unfortunately however the mills sometimes suffer from breakdowns, and that is when SMA Mineral steps in. Thanks to a high storage capacity and efficient transport, SMA Mineral can take in the lime sludge left untreated as a result of breakdown – sludge which, in the worst case, would be sent for dumping.
“We drive there, collect the lime sludge, burn it in our kilns and return top-quality caustic lime”, explains Patrik Hjärpe.

Just like the customer’s own product
The requirements for caustic lime used in pulp mills are high, and Kraftlime sludge, as the re-burnt lime sludge is called, is very highly regarded. It reacts more slowly than bought-in lime, which makes it ideal for the pulp mills’ systems and processes.
“It becomes a product that is just like the customer’s own. The use of only bought-in lime involves a risk of over-reactivity. The re-burnt lime sludge, by itself or as part of a mixture, results in smoother running”, explains Kalle Nordgren, who is the site manager at Sandarne limeworks, SMA Mineral.
And now demand for this re-burnt lime sludge has increased.
“This is due to its excellent runnability. We could supply even more”, says Patrik Hjärpe.

Increasing production
And in future SMA Mineral will be able to supply even more.
“We are in the process of doubling our filter capacity, and we will be able to produce even more Kraftlime sludge going ahead”, reports Kalle Nordgren. The increased production at Sandarne has now resulted in expanded operations at our terminal at Otterbäcken on Lake Vänern.
“As a result, we will also be able to supply Kraftkalk C from Otterbäcken. In purely geographical terms, we will be operating closer to many of our customers”, explains Patrik Hjärpe.

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