Softwood bark in an abundant resource produced as side-stream in sawmills and pulp mills. Bark is not fully utilized, most of it is currently used as energy source. The aim of this study was to create a process concept combining hot water flow-through extraction (HWE), slow pyrolysis and anaerobic digestion (AD) to fully utilize bark.<br/>Recent studies show that hot water extraction can be used to extract tannins and stilbenes from bark, which will be utilized as binders, preservatives or even as food ingredients. The solid residue from HWE will be pyrolysed to produce biochar, which can be used as soil amendment or further processed as bio-based activated carbons. Pyrolysis liquids formed as a side product from pyrolysis will be added to AD process in small doses to increase methane production. Finally, solid residue from AD process can be used as soil amendment, which returns nutrients and carbon back to soil.<br/>HWE for spruce and pine bark were performed at 75 °C using 3-liter flow-through extraction system to extract tannins from bark. HW extracted 8.2 – 8.8 % of spruce and 6.2 – 6.5 % of pine bark. Bark was dried after HWE and pyrolysed at 443 °C. Slow pyrolysis produced 37-38 % char, 40 – 42 % of pyrolysis oil and 20 – 21 % gas. HW extracted bark was treated also in AD process as well as original bark without HWE as a comparison. Especially when pine bark was used, HWE treatment increased the methane production of bark.<br/>Results of these experiments showed that HWE, slow pyrolysis and AD can be combined in a meaningful way. The process can utilize spruce and pine bark and valorize it to streams that could be used for more than only energy production. Optimization of process parameters seems to be a fascinating topic for further research.

Cascade processing of softwood bark with hot water extraction, pyrolysis and anaerobic digestion

2019 Spring National Meeting

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