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minimum explosion concentration (MEC) and limiting oxygen concentration (LOC) in our recent works. This work further studies the reasonability and reliability of the alternative method experimentally and theoretically. Six different dust samples were tested via a 20-L spherical explosion chamber. The experimental results showed that the data of MEC and LOC determined by using the alternative and the standardized methods are in good agreement. The minimum flame propagation velocity (Sf) and the corresponding maximum combustion duration time (tc) were found at its MEC and LOC, suggesting that the theoretical analysis can well explain all the experimental data. It is the first time to study the theoretical basis of the explosion criterion, thus helping to improve our understandings of dust explosion characteristics, and to amend the explosion criterion in future test standards.
MIKE III apparatus tests were conducted to investigate the minimum ignition energy (MIE) of coal dusts in air and O2/CO2 atmospheres with and without small amount of CH4/H2. The O2 mole fraction (XO2) in the gas mixtures varied from 21% to 50% with the CH4/H2 mole fraction from 0 to 2%. Experimental result showed that MIE of coal dusts significantly decreases even by three orders of magnitude in mJ with increasing XO2 and the addition of CH4/H2. Compared with CH4, H2 had a relatively strong promotion effect on the spark ignition of coal dusts. The inhibiting effect of CO2 was found to be much stronger than N2, but this inhibiting effect of CO2 could be eliminated by 9% increment of XO2. The effect on MIE of coal dusts thus followed by the order: 9% increment of XO2 > CO2 replacing N2 > 2% CH4 or H2 addition. Moreover, two empirical models were used to estimate the MIE of hybrid dust-gas mixture (HMIE), and the results showed that calculated data can well reflect the promoting effect of elevated XO2 and flammable gas addition, and the inhibiting effect of inert gas
Iron dust explosion characteristics with small amount of nano-sized Fe2O3 and Fe3O4 particles
(2022)
Iron powder, as one of the most abundant metal fuels that can be used as recyclable carriers of clean energy, is a promising alternative to fossil fuels in a future low-carbon economy. It may pose a potential explosion hazard during the process of processing, storage, transport, and reduction/oxidation (redox). The explosion characteristics of iron dust in air were undertaken via a 20 L spherical explosion chamber with an emphasis on minimum explosion concentration (MEC) of iron dust. The alternative method of combustion duration time (tc) was used to determine MEC and compared with the standardized over pressure method. Two kinds of nano-sized iron oxides (Fe2O3 and Fe3O4) were used as inertants to determine the inhibition effect of different oxidation products. The iron dust explosion products with various shapes and sizes were found to be able to grow up 4–6 times of the iron dust for the first time. Adding small amount of Fe2O3 or Fe3O4 could reduce the explosion severity and sensitivity of iron dust. The MEC data determined by both methods were comparable. The addition of 5 % oxide has obvious inhibition effect under 1500 g/m3 concentration. With the increase of oxide concentration to 10 %, the inerting effect increases, and the MEC of iron dust increases more than 3 times. The increase of dust concentration will weaken the inerting effect. When the concentration increases from 500 g/m3 to 3000 g/m3, the weakening effect of 10 % Fe2O3 on the explosion pressure decreases from 38.45 % to 2.24 %, and 10 % Fe3O4 decreases from 46.21 % to 10.63 %. Unlike coal, biomass or aluminum dusts, the iron dust explosion was found to have a unique secondary acceleration of pressure rise rate for the first time. These results provide a fundamental basis to mitigate the iron dust explosion via solid inerting method without adding extra elements.