Safe handling of renewable fuels and fuel mixtures
The overall objective of this research project, was to create new data on safety-technical characteristics of renewable fuels, wastes, low-rank coals and mixtures of these. The safety aspects of fuel storage, handling and feeding are an important issue in the development of new energy production technologies like pressurised IGCC and PFBC power production systems. Knowledge of basic handling and safety-technical characteristics of fuels and fuel mixtures is of crucial significance for the design of handling and feeding equipment, and safety systems, and for the assessment of explosion and fire hazards. The results are the outcome of a two-year study (1996 - 1997) on the spontaneous ignition behaviour and the volatility of twelve selected fuels samples. Four woody and four herbaceous biomasses were selected together with two low-grade lignites and two biomass/lignite mixtures for this study. Thermo-gravimetrical analyses at ambient and elevated pressure were performed to classify the fuels according to their propensity for spontaneous heating. Several safety-technical properties of the selected fuels were determined with respect to their behaviour on hot surfaces and as dust clouds. Self-ignition tests at pressures of 1 and 25 bar were carried out with several sample sizes, which facilitate the extrapolation of the self-ignition behaviour of a particular fuel to real size storage bins. Dust explosion testing was performed at initial pressures of up to 15 bar and temperatures of 150 degrees Celsius to simulate pressurised drying and handling of the biomass fuels. Inert tests with nitrogen and flue gases were carried out to determine the requirements of non-explosive conditions. Suppression test were also performed to assess the usability of this explosion protection method for biomass fuels in elevated conditions. The results show that elevated pressure increases the tendency for spontaneous ignition of biofuels. The required safe oxygen level is much lower than the level of preventing dust explosions. Very high explosion pressures and rates of pressure rise are measured at elevated initial pressures. The required level of inertisation of dust explosions is dependent on the initial pressure and temperature. These parameters also affect the suppression of the dust explosions, making a successful suppression more demanding. The use of partly inert atmosphere led to an increasing efficiency of the explosion suppression system.