Towards the valorization of spent coffee grounds: Experimental evaluation of flammability and explosion hazards

The global production of coffee is constantly increasing, and it is inevitably associated with the generation of a huge amount of waste, commonly discharged. Environmental awareness is leading towards the valorization of this material through the recovery of high-added value compounds. In recent times, industries are focusing their attention on the treatment of biomasses like spent coffee grounds, whose load, handling, and storage could introduce novel unforeseen hazardous scenarios. Indeed, hazards related to biomass dust still remain underestimated and partially unknown, leading to possible accidents like fires, explosions, and carbon monoxide emissions. This work deals with the investigation of the flammability and explosion properties of spent coffee grounds (SCG), monitoring the evolution of such properties as a function of the unit operations of the analyzed process, as a novelty in the field. SCG after treatments showed slightly higher flammability and explosiveness results, reporting minimum ignition temperatures for dust clouds between 420°C and 440 °C and maximum explosion pressure and deflagration index of 7.5 bar and 35.1 bar m/s, respectively. Indeed, their chemical composition comprised higher volatiles, cellulose, and lignin contents, leading to an enhanced sensitivity to ignition, although not further compromising SCG safe handling and storage. All tested samples did not present significant hazards when exposed to an electrical discharge of up to 3000 mJ. In view of practical application for plant design, experimental findings allowed allocating them in the explosion class St1 , corresponding to low explosion hazard. • Evolution of flammability and explosion properties of SCG over the plant was studied. • SCG after treatments showed slightly higher flammability and explosiveness only. • Minimum ignition temperatures for dust clouds were between 420°C and 440 °C. • Maximum explosion pressure and deflagration index were of 7.5 bar and 35.1 bar m/s.