The forestry industry group BillerudKorsnäs is constantly evaluating various energy efficiency projects. At the Karlsborg integrated pulp and paper mill located in northern Sweden, energy consumption has recently been greatly reduced in the cleaner plant of PM2.

This has been achieved without investing in new equipment which would have required a long pay-back time. Instead, these results have been achieved by a number of small optimizations in the cleaner plant. It has been possible to perform these measures during ordinary shut-downs, in order to avoid interruptions in the mill's production.

BillerudKorsnäs has been able to recoup the investment in just a few weeks.With five cleaning stages, each requiring a pump, the cleaner plant consumes a lot of energy.

“We investigated how we could optimize the plant by minimizing the pump flow,” says Ralf Bäckvik, technical expert at GL&V Sweden.

Optimizing the process flow

There are two ways of optimizing pump capacity.

• Installation of variable speed control

• Adapting the pump wheel diameter

In Karlsborg’s case it was found that the pay-back time for installation of variable speed control would be too long, so the decision was made to scale down the pump wheel to the right size for an optimum flow.

Nils Nordling, process engineer at BillerudKorsnäs Karlsborg, found that one of the pumps was very oversized.

“Now that the pumps are modified to a smaller capacity, the energy consumption in the plant has been significantly reduced” he says.

Audit of the cleaner plant

A technical audit mapped out the system in detail and the results showed that the need to separate light rejects was less compared to when the plant was originally installed. The inlet consistency to the plant was also adjusted by blinding cleaner positions off at each stage. These adaptations optimized operation of the cleaner plant for today’s conditions and great energy savings became possible.

Empirical data shows how much the fibre consistency can be raised without deterioration of efficiency and since making these changes we have seen that our balance calculations agree very well with the measurements made in the factory,” says Ralf Bäckvik.

Nils Nordling confirms this pattern. “We have maintained the same cleaning efficiency but with reduced energy costs.”

Smooth start-up

The project has gone well, according to Ola Nilsson, process engineer at BillerudKorsnäs Karlsborg.

Robert Johansson, Customer Key Account Manager at GL&V Sweden and Ralf Bäckvik came up with three different options and decided to proceed with one of the solutions that we had all agreed upon. A process engineer at the mill then produced new pump data so that we knew how much the pump wheel could be scaled down without any negative effects on the pumps and the process.

“We have had no teething troubles at all. Nothing unusual has happened,” says Ola Nilsson.

“It has been problem free,” adds Nils Nordling.

“We hired the expertise from GL&V to remove equipment – not to install anything new. We have taken equipment out of operation in a controlled way,” Ola Nilsson points out.

“For my part, I mainly look at the energy and operability advantages of the project. We also have significantly less maintenance to do than before.”

Well-balanced plant

Many pulp and paper mills in Sweden have been built in a higher production capacity than they actually use, which means unfavourable operating conditions from an energy point of view. Nils Nordling therefore thinks it is very likely that other plants could benefit from similar conversions.

“Every mill is individual, so things must be based on their own circumstances. However, many older plants were built with spare production capacity which means that they often are operated inefficient from an energy consumption point of view.”

In conclusion, Robert Johansson believes that many more mills would have a great deal to gain from optimizing their cleaner plants so as to achieve a well-balanced plant in terms of function and operating costs.

“There are also benefits from an environmental point of view,” says Robert Johansson, who points out that it is always important for the pulp and paper industry to minimize its fibre emissions.

(Courtesy of www.pulpapernews.com)