Bark provides efficiency bite for Sodra: a Swedish mill finds that a modest woodyard investment deliver environmental gains and a productivity bonus.

Wood handling may not be the sexiest part of the pulp and paper industry, but as one Nordic mill is demonstrating, it can play an important part in the never-ending search for productivity gains. At SEK 50 million (US$ 6 million), the latest investment at Sodra Cell's Monsteras pulp mill on Sweden's southeast coast serves to illustrate the scale of improvements possible at relatively modest cost.

The mill is the largest of Sodra Cell's five plants, with an annual capacity of 750,000 metric tons. Monsteras produces both hardwood and softwood pulp and consumes more than 3.5 million cubic meters of raw materials each year in the form of logs and sawmill chips. Bark residue is used to generate bio-energy, which powers the mill and produces excess electrical energy sold to external users via the national power grid.

In its battle to reduce emissions, fine pulp producer has installed a range of new equipment designed to improve bark preparation quality as the material is processed for burning in the steam boiler. While this is the primary focus of the project, the new lines will also help the company deliver extra production efficiencies.

As project leader at Monsteras, Bertil Johansson explained, "Improved bark handling, drying and, burning means better performance in the early part of the process and that will help us improve productivity and quality consistency. Furthermore, as the steam boiler will be able to fire more dry bark, oil consumption will drop by 5000 cubic meters per annum, and emissions of NOx will fall by 22,000 kg/year."

That should provide major savings for the company, which gets hit with an eco-tax of SEK 40 for every kilogram of NOx released into the atmosphere from the bark boiler. "This fee is a big incentive for us to get the NOx emissions down," said Johansson. "In the winter, when the bark and sludge can get quite wet from the snow and ice, we use oil to get the material to burn. But if we can make it drier before it gets to the boiler, we can reduce the amount of oil we use and produce much less NOx. As a result, we'll save about SEK 10 million per year in oil costs and emissions taxes."

GREEN GAINS

The upgrade itself covers several separate areas of the wood handling process. New equipment transports the bark to the presses and on to the silo near the steam holler, which is also used to recover energy from sludge generated by the mill's waste treatment plant. BMH Wood Technology is supplying most of the new process machinery for installation in a new building in the woodyard. As part of the scheme, two new bark presses from BMH subcontractor, Saalasti, increase the dryness of the bark. A new water screening system supplied by Cellwa treats water generated by the presses. The system takes water from the presses and purifies it through a series of filters and cyclones before it is fed back into the mill process and eventually into the evaporation plant.

Running the new equipment does require extra energy use, so the annual 5000 [m.sup.3] reduction in oil consumption has to be balanced by an increase in electricity power consumption within the plant of approximately 5000 MWh/year, according to the mill's engineers. But considering the scale of the NOx emissions reduction and the additional operating efficiencies to be captured further down the pulp line as a result of the wood handling improvements, Sodra Cell believes that this project's four-year payback period provides an excellent investment. Not only that, but the environmental benefits will be much appreciated by the neighbors.

About the author: Jim Kenny is contributing editor/Europe, for Solutions! magazine, and is based in Brussels, Belgium. He is the former vice president of editorial for Paperloop and today heads his own company, DSI. Contact him by phone at [phone], or by email at [e-mail]