Analysis and modelling of the initial self-heating in woodchip piles

Project Number 406

Degradation processes caused by metabolic activity of microorganisms may lead to temperature increase in woodchip piles. Self-heating is influenced by the environmental conditions (temperature, humidity, etc.) and the biomass properties (particle size, composition, moisture content). Self-heating at moderate temperatures (T<80°C) is mainly caused by microbiological activities. With rising temperature (T>80°C) exothermic chemical reactions (autooxidation, slow pyrolysis) gain in importance. Composition of the main wood components hemicellulose, cellulose and lignin as well as the composition of the wood extractives vary between the different types of wood leading to a different resistance against fungi and microorganisms. Self-heating during storage influences the woodchip quality significantly by reducing the higher heating value of the wood, which leads to economic losses. Furthermore, the risk of self-ignition exists, which may lead to significant economic losses.

Due to the complex (biological, chemical and physical interactions) and the sometimes very different types of storage, the actually known research (neglect of biological and wood-chemical interactions) provides only an incomplete data base for the analysis and description of the self-heating process.
The project „Analysis and modelling of the initial self-heating in woodchip piles“ approaches self-heating by a chain of experiments stretching over different scales (from lab scale to field trials in wood piles). Experimental investigations will be accompanied by detailed microbiological and chemical analysis. Within the project numerical models will be developed and validated by the experimental results. At the end of the project a predictive tool shall be provided which allows quantifying the ongoing processes during self-heating in wood piles in dependence of environmental conditions and the type of wood.

The research project is funded by the German Federal Ministry of Economics via the AiF (funding no. 18972 BG). From January 2017 to December 2019 it is jointly carried out at the following institutes:

• Ruhr University of Bochum, Faculty of Mechanical Engineering, Department of Energy Plant Technology,
• University of Hohenheim, Institute of Agricultural Engineering, Agricultural Engineering in the Tropics and Subtropics,
• Technische Universität Dresden, Institute of Plant and Wood Chemistry.

The VGB technically supports the investigations via the Technical Group Biomass and the Technical Committee Use of Renewables and Distributed Generation.