Bark: a mill by-product replacing fossil fuels

Project Description

Starting in the spring of 2015, substantial investments were made to replace fossil fuels with bark. This was achieved by installing a feeding system allowing tight control of the weight and the feed rate. Since 2012, the mill has been taking systematic steps to reduce the use of fossil fuels. In 2014, around 20% of the energy for the lime kiln came from fuel oil. Södra Cell Mönsterås has long used a unique process to fuel the kiln with bark, but this is problematic because the material is very abrasive, has a high risk of self-ignition and makes it difficult to maintain an even flow rate (like many other solid materials). Since the supply of good quality bark was a bottleneck in production, a new lifters section was installed in order to increase the heat transfer from the flue gas to the lime mud. The concept of using bark, a mill by-product, is very appealing. In this way, Södra is contributing to the circular economy and reducing the carbon footprint from production in several ways. Firstly through the substitution itself, and secondly by the savings on production and transport of the fuel.

Project Purpose

The project consisted of two parts: to enable a high amount of bark to be fired in the lime kiln, and to lower the energy demand of the lime kiln by increasing heat transfer. The overall goal was to increase the use of internal fuels thereby eliminating fossil fuels.

Project Evaluation

The project has had several very positive effects. Bark usage increased from 50% in 2014 and early 2015 to more than 60% in 2015 and 2016 (Figure 1). Fuel oil consumption in the lime kiln was reduced from 6,000 cubic metres in 2014 to 2,800 cubic metres in 2015. Until the maintenance shutdown in September 2016, only 1,000 cubic metres of fuel oil were used (compared with 4,500 in the corresponding period of 2014). The project also utilised side streams from the pulp mill and turned a low-value by-product into a valuable substitution for costly fuel oil. This increased the use of internal fuels and produced an economic benefit of around €1 million per year.

Henric Dernegård

Responsible for strategic energy issues at Södra

“Before beginning this project, we had known for a long time that the lime kiln was the largest consumer of oil in the mill. We noticed that there were large variations in the bark feed rate and that those variations posed an obstacle to reducing the use of oil in the lime kiln. The project aimed at stabilising the process of supplying solid biofuel (bark) to the burner. This model shows that, as in many other cases, the key to continuous improvement is through stabilising a process.

Södra has made significant efforts towards decarbonising in the past and has set a very ambitious goal of using zero fossil fuels by 2020.”

Main Features:

CO2 reduction:

18,000 tonnes of CO2 during 2015 and 2016 (9,000 tCO2/ year)


€2 million

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