Case study – Aspa Bruk Munksjö



Aspa Bruk, Sweden, was the first mill to introduce the filter into its pulping production and has had results exceeding its expectations.


The implementation of the green liquor filtration resulted in:

  • Increased pulp production through removal of bottle-neck
  • Decreased lime handling
  • Decreased cost of filter lining
  • Decreased lime purchases
  • Decreased energy consumption
  • Prolonged, smoother runtime of clarifier/cassette filter thanks to 20% hydraulic relief


CEO, 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.”

The second part of the green liquor clarification process is comprised of Aspa’s existing cassette filters, which manages the bulk of the volume. This arrangement relieves the hydraulic pressure on the old cassette filter, allowing it to operate more smoothly and efficiently.


We are very pleased with the results of the new process. That is why we now choose to buy the (CleanFlow) filter which is the first of its kind worldwide.

Michael Berggren, Chief of production at Aspa Bruk


700 mg/l of sludge removed

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 undetectably low particle levels, even when using advanced light scattering detection methods.

The unwanted, non-process elements have been significantly reduced. Up until March 2017, the CleanFlow plant at the Aspa mill had clarified 480,000 cubic meters of green liquor, corresponding to 130,000 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.


We have together with CleanFlow evaluated the new process technology since August 2010. After installing the attenuator to reduce the pressure drop on the feeding pump´s suction side the pilot has been running with high availability. The results with the new method show that particles in the green liquor are eliminated completely. We think with the good progress results obtained this is an attractive alternative to conventional green liquor filtration process.”

Bengt Lindqvist, Former Manager, Aspa Bruk, Sweden