Determination of the minimum ignition energy of wood dust

Prašne eksplozije se pojavljajo v delovnih okoljih, kjer je v delovnih procesih prisoten gorljiv prah. Poleg prisotnosti gorljivega prahu mora biti za nastanek prašne eksplozije izpolnjenih pet dejavnikov, ki bodo natančneje predstavljeni v nadaljevanju. Na začetek in potek eksplozije pa vplivajo številne spremenljivke. V sklopu diplomskega dela so predstavljene fizikalne lastnosti in eksplozijski parametri treh vrst lesnih prahov: bukov, smrekov in macesnov. Vzorcem smo določili vsebnost vlage s termično analizo in specifično površino po BET metodi. Vzorce lesnega prahu smo presejali in tako dobili različne velikostne frakcije določene vrste lesnega prahu. Prvotnim vzorcem in izbranim velikostnim frakcijam smo določili velikosti in porazdelitev velikosti delcev. Določili smo minimalno vžigno energijo vzorcem lesnega prahu. Meritve so bile izvedene za vse tri prvotne vzorce lesnega prahu, ter za tri velikostne frakcije (80-100 μm, 100-125 μm in 125-160 μm) za bukov in smrekov lesni prah. Po končanih meritvah, smo dobili območja minimalne vžigne energije. Območje v katerem se vname macesnov prah je med 600 in 1000 mJ. Za prvotni smrekov prah je območje vžiga med 10 in 30 mJ, za bukov prah pa med 30 in 100 mJ. Za smrekov prah je območje za velikostno frakcijo 125-160 μm in 80-100 μm med 30 in 100 mJ, za velikostno frakcijo 100-125 μm pa med 100 in 300 mJ. Za bukov prah smo izvedli meritve za enake velikostne frakcije, vendar je do vžiga prišlo le pri frakciji 125-160 μm, pri ostalih dveh pa ne. Eksplozijsko območje za to frakcijo je med 300 in 600 mJ. Rezultate meritev sem primerjala z vrednostmi iz literature. Za macesnov prah v literaturi nisem našla nobenih vrednosti. Za smrekov in bukov prah je vrednost MVE iz literature nižja od naše izmerjene vrednosti. Glede na rezultate določitev območja minimalne vžigne energije lesnih prahov ugotavljam, da najmanjšo verjetnost za nastanek eksplozije predstavlja macesnov lesni prah. Najbolj nevaren pa je lesni prah smreke, saj je do vžiga prišlo pri vseh treh frakcijah in prvotnem vzorcu. Poleg tega pa ima smrekov prah tudi najnižje vrednosti energije potrebne za vžig.Dust explosions occur in work environments where combustible dust is present in work processes. In addition to the presence of combustible dust, five factors must be met for a dust explosion to occur, which will be presented below. The beginning and course of the explosion are influenced by many variables. The thesis presents the physical properties and explosion parameters of three types of wood powders: beech, spruce and larch. The moisture content of the samples was determined by thermal analysis and specific surface area by the BET method. Wood dust samples were sieved to obtain different size fractions of a certain type of wood dust. Particle sizes and particle size distributions were determined from the original samples and selected size fractions. We determined the minimum ignition energy of the wood dust samples. Measurements were performed for all three original wood dust samples, and for the three size fractions (80-100 μm, 100-125 μm and 125-160 μm) for beech and spruce wood dust. After the measurements were completed, we obtained areas of minimum ignition energy. The area in which larch dust ignites is between 600 and 1000 mJ. For the original spruce dust, the ignition range is between 10 and 30 mJ, and for beech dust between 30 and 100 mJ. For spruce dust, the range for the size fraction 125-160 μm and 80-100 μm is between 30 and 100 mJ, and for the size fraction 100-125 μm between 100 and 300 mJ. For beech powder, measurements were performed for the same size fractions, but ignition occurred only in the fraction 125-160 μm, and not in the other two. The explosion range for this fraction is between 300 and 600 mJ. I compared the results of the measurements with the values from the literature. I found no literature values for larch powder. For spruce and beech dust, the MVE value from the literature is lower than our measured values. Based on the results of determining the range of minimum ignition energy of wood powders, I find that the lowest probability of an explosion is larch wood dust. The most dangerous, however, is spruce wood dust, as ignition occurred in all three fractions and the original sample. In addition, spruce dust also has the lowest values of energy required for ignition