Safe handling of renewable fuels and fuel mixtures

The overall objective of this research project is to create new data on the safety-technical characteristics of renewable fuels, wastes, low-rank coals and mixtures of these. Knowledge of basic handling and safety-technical chracteristics is of crucial significance for the design of handling equipment and safety systems, and for the assessment of explosion and fire hazards. Ten biomass and lignite fuel samples and two fuel mixtures were included in the work programme. Extensive physical and chemical characterisation was performed for all samples. The reactivity of the combustible dusts was characterised by thermal analysis (DTA-TGA). Based on the thermal runaway temperatures of the dusts the samples are listed by order of reactivity. Self-ignition properties of the fuels were studied at normal and elevated pressure (1 - 25 bar). The results of the self-ignition tests for the fuel samples are mainly in line with the reactivity tests carried out on DTA-TGA. The elevated pressure had a significant effect on the self-ignition temperature of all fuel samples. Partial inerting increased the self-ignition temperature, but to a rather low degree. Dust explosion tests were performed in 1 m3 vessels and 20 litre spheres. Dust explosion parameters were determined both in normal conditions and at elevated temperature and pressure. A linear correlation was found between the maximum explosion pressure Pmax and the initial pressure. The values measured for the rate of pressure rise, the KSt-value, were considerably more scattered. Most differences can probably be associated with diverse turbulence conditions inside the explosion vessel. In most cases, the lower oxygen concentration LOC slightly increased with increasing initial pressure. LOC decreases with increasing initial temperature, around 1 - 3 vol% per 100 °C temperature rise. Suppression systems are frequently used in industry as a measure of explosion protection. The suppression tests were conducted in a heatable the 1 m3 vessel. Increasing the temperature makes the suppression of the dust explosion more demanding. Use of partly inert atmosphere led to an increased efficiency of the explosion suppression system.