Explosibility and flammability of four olive pomace dust samples

It is a fact and common knowledge that the Mediterranean Sea is a rich region and adapted to the growth of several vegetal species, as well as the production of a lot of products deriving from those. Among the typical activities in this region, there is the olive trees cultivation, from which it is possible to obtain numerous olive oil and olive qualities. The Mediterranean zone is responsible for the production of about 98% of the olive oil world-wide produced, which counts 900 million of olive trees occupying 10 million of hectares. However, the manipulation of 100 kg of olives leads to the production of 40 kg of wastes (woody parts, leaves and olive pomace), which is potentially valorisable and usable as energetic or material source. In general, in the past 20 years, bioenergy production (energy production from biomass) has increased, but along with it the number of accidents related to bioenergy production plants. In order to enlight the hazard associated to the manipulation and to the handling of olive pomace, a risk analysis assessment (RAS) was made. The literature lacks in informations about olive pomace-related hazard in industry, thus this work's aim was also to fill that absence. When pelletized or in chunks, olive pomace does not pose any greater hazard than a pile of woody material, but when pulverized, it might become dangerous. Four different sized dust samples was chosen: 425, 212, 75 and 45 μm. The development of this RAS was carried out by estimating several parameters associated to olive pomace dust explosibility and flammability: minimum ignition energy (MIE), minimum autoignition temperature (MAIT), maximum pressure rise rate ((dP/dt)max and KSt), maximum pressure reached in an explosion (Pmax) and minimum explosible concentration (MEC). Moreover, a study of chemical and physical characterization was carried out: moisture content, particle size analysis, Scanning Electronic Microscope (SEM) investigation, thermogravimetric analysis (TGA), solid-state Nuclear Magnetic Resonance (NMR), mass spectrometry, calorific value and bulk density estimation. The results from TGA and calorimetric bomb showed the samples had different thermal behaviors after only a grinding-sieving step, but according to NMR results the composition was not changing greatly. SEM images showed different morphology between the two coarsest samples and the two finest ones. As regards the MIE test, no samples seemed to be sensible to be ignited by electrical sparks (with an associated energy of 1 J), while the MAIT showed again deep differences between coarsest and finest samples: in fact, the two coarsest samples were more thermally reactive than the other two, showing MAIT about 50°C less than the 45 and 75 μm samples. Speaking of explosion tests, explosion parameters ((dP/dt)max and KSt) were influenced more by the particle size than samples energetic content, that otherwise influenced more the Pmax.