Patented technology revolutionizes pulp processing
A new patented technology for filtering green liquor raises capacity and significantly reduces energy and chemical use in the pulp industry.
The technology in question differs from the conventional green liquor filters on the market. The secret lies in an initial filtration stage followed by a microfilter layer, according to Lennart Källén, President of Cleanflow, which also gives its name to the process.
Lennart Källén compares the purification process to a kidney;
– We work with a technology in which a high flow of green liquor passes through a 1.5-meter tubular ceramic element comprising 19 channels each 6 mm in diameter. The method prevents sludge from building up in the filter, which is a problem that affects standard filters. The sludge is removed continuously as part of the process.
A pilot plant featuring the technology was commissioned at the Aspa mill in 2010. It was operated for 500 days and a total of 12,000 hours until January 2013. The trial was so successful that Aspa decided to construct a full-scale plant that has been in full operation since the spring.
The Aspa mill’s former manager Bengt Lindqvist wanted a type of booster facility, a combined clarification process involving the modernization of part of the flow process by deploying Cleanflow technology to process 25%, or 22 cubic meters per hour, of the green liquor volume. The second part of the green liquor clarification process comprised Aspa’s existing cassette filters, which handled the bulk of the volume. This arrangement relieved the hydraulic pressure on the old cassette filter, allowing it to operate more smoothly and efficiently. The Cleanflow process resulted in completely particle-free green liquor and the overall result was a reduction in the volume of sludge.
The full-size plant in Aspa is fitted with two filter brackets each containing 46 filter elements. An initial filter removes particles larger than 6 mm.
The unfiltered green liquor at the Aspa mill contains about 700 milligrams of sludge per liter, while the filtered green liquor that has passed through the Cleanflow plant has such low particle levels that it is not possible to measure, even using advanced light scattering detection methods. The unwanted, non-process elements have been significantly reduced.
Up until November, the Cleanflow plant at the Aspa mill had clarified 95,000 cubic meters of green liquor, corresponding to 27,000 tons of pulp.
The Aspa mill has achieved its capacity, availability and purification targets as expected and is now operating the plant itself. The process handles 22 cubic meters of green liquor an hour, of which one-quarter passes through the new green liquor plant, which is monitored remotely.
The project agreement was signed on July 5, 2012 and the plant was completed in January 2013. Commissioning took place on March 4, 2013 and Aspa has run the plant at full capacity since May. In this year alone, Aspa has estimated that it will have saved up to SEK 10 M as a result of installing the plant.