Thermal analysis and dust explosion characteristics of spent coffee grounds and jatropha

The relationships of fatty oil content in spent coffee grounds (SCG) and jatropha kernels (JK) with minimum explosible concentration (MEC), minimum ignition energy (MIE), cohesion, dispersibility and thermal analysis were investigated. Both SCG and JK are carbon-rich [> 50% by weight (wt.%)] with higher total calorific values than cellulose. The MEC values for absolutely dry 75-105 μm particles of oil-retaining and oil-extracted SCG were 35 g m−3 (high explosion hazard) and 120 g m−3 (low explosion hazard), respectively. The low MEC value of oil-retaining SCG was despite a high cohesion result, suggesting that the oil content increased the likelihood of a dust explosion. Conversely, the MIE values for all SCG and JK were sufficiently high to consider them a low-level risk. Behavior analysis showed that decomposition temperature of SCG did not differ to that for its oil-extracted form. However, exothermic peak temperature of JK was 76 °C higher than for its oil-extracted form. The SCG (20 wt% oil) was little affected by oil content; however, jatropha (60 wt% oil) was greatly affected. Thermogravimetric results for all samples showed that the decomposition temperature increased with the heating rate, although the overall behavior of decomposition was not affected by heating rate.