Open access publications in the SLU publication database

Abstract

Uncertain long-term availability of fossil fuels and the negative environmental impact of using it have created an urgent need for reliable renewable energy sources. Wood fuel, particularly forest residues is one of these sources which are in high demand in Sweden today. Stumps can be used as a complement to these, since they contain high concentrations of energy-rich lignin and extractives. However, stump removal can have negative environmental effects such as reduction of biodiversity and disturbance of nutrient balance in the soil. As to the fuel quality of stump biomass, there are some concerns connected with the utilisation of stumps since presence of excessive contaminants leads to high ash contents which reduce its value as fuel and causes operating problems. To ensure the supply of fuel of acceptable quality, an optimal system for harvesting, handling, and storage must be devised for stump procurement. The main aim of this work was to evaluate various stump harvesting techniques, storage methods (windrow or heaps), and different storage durations at two geographical locations and examine their effect on the fuel quality of Norway spruce stump biomass. Fuel quality parameters moisture content, ash content and calorific value were evaluated on five occasions during May 2008 - September 2009. Stump harvesting techniques that split the stumps allowed better drying during 13 months of storage. Storage method had no clear effect on these stumps. The ash content decreased considerably, particularly when transport and crushing took place at temperatures exceeding 0°C. In general, fuel quality was improved in all treatments after storage. However, as the storage time progressed, the net energy increment became continuously smaller due to the increased substance losses.