TY - JOUR A1 - Wu, Dejian A1 - Schmidt, Martin A1 - Tan, X. A1 - Zhao, P. A1 - Huang, W. A1 - Qian, X. T1 - Minimum ignition temperature of carbonaceous dust clouds in air with CH4/H-2/CO below the gas lower explosion limit JF - Fuel N2 - Godbert-Greenwald furnace was used to investigate the minimum ignition temperature of dust clouds (MITC) in air with the presence of flammable gas which is lower than its lower explosion limit (LEL). Three flammable gases (CH4, H2 and CO) and three carbonaceous dusts (anthracite coal, bituminous coal and sweet potato starch) were tested. Results showed that all flammable gases have distinct effects on the MITC of the dust samples and volatile matter content of dust plays an important role during the ignition process. Specifically, the MITC of anthracite coal dust decreased from 610 °C to 560 °C, 580 °C and 570 °C with 3% CH4, 3% CO and 2.5% H2, respectively. Moreover, a heterogeneous ignition mechanism model was proposed to verify the equally global ignition characteristic between hybrid anthracite coal-CxHy mixture and bituminous coal. All three gases had an ignorable effect on the MITC of starch dust considering the experimental error. The presence of CO and H2 slightly promoted the ignition of bituminous coal dust, but the addition of CH4 showed a distinct concentration effect on the MITC of bituminous coal: the MITC decreased with 1% CH4 while increased with 2% and 3% CH4. This negative-effect of flammable gases at such low concentrations on ignition temperature of bituminous coal dusts was found for the first time. Furthermore, the presence of the 2nd flammable gas had a smaller effect on the MITC of dust samples with a higher volatile content, resulted from the competition of heterogeneous and homogeneous ignition mechanisms. KW - Dust explosions KW - Gas explosions KW - Minimum ignition temperature KW - Hybrid mixtures PY - 2020 DO - https://doi.org/10.1016/j.fuel.2019.116811 SN - 0016-2361 VL - 264 SP - 116811 PB - Elsevier Ltd. AN - OPUS4-50856 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Martin A1 - Wu, Dejian A1 - Zhao, P. A1 - Tan, X. A1 - Huang, W. A1 - Qianc, X. T1 - Minimum explosion concentrations of coal dusts with CH4/H2/CO below the gas lower explosion limit JF - Fuel N2 - A 20-L spherical explosion chamber was used to investigate the explosion characteristics of dust clouds in air with the presence of flammable gas which is lower than its lower explosion limit (LEL). including minimum explosion concentration (MEC) of dust. Explosion pressure (Pex) and explosion pressure rise (dp/dt)ex). Two dust samples (anthracite coal, bituminous coal) and were three flammable gases (CH4, H2 and CO) were tested. Experimental results showed that the explosion of hybrid mixtures occurs when both dust and gas concentrations are lower than the LEL/MEC of the single substances. Meanwhile. all flammable gases with different volume fractions have distinct effects on the MEC. Pex and (dp/dt)ex of the dust samples. With the increase of the flammable gas concentration. either the Pex and (dp/dt)ex increase or the MEC decreases for all the hybrid mixtures of both two dust samples. At the same concentration of coal dusts. the addition of CH4 promotes higher explosion risks than the other two flammable gases. The distribution of (dp/dt)ex is quite different with the restricted area defined by empirical formulas. These results improve our understanding of the explosion behaviour and the explosion risk of hybrid dust-gas mixtures in air. KW - Dust explosions KW - Gas explosions KW - Minimum explosible concentration KW - Lower explosion limit KW - Hybrid mixtures PY - 2020 DO - https://doi.org/10.1016/j.fuel.2019.116401 SN - 0032-5910 VL - 260 SP - UNSP 116401 PB - Elsevier Sci. Ltd. AN - OPUS4-49956 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wu, Dejian A1 - Tan, X. A1 - Wei, A. A1 - Duan, Q. A1 - Huang, W. A1 - Schmidt, Martin T1 - Ignition temperature and mechanism of carbonaceous dust clouds: The roles of volatile matter, CH4 addition, O2 mole fraction and diluent gas JF - Journal of hazardous materials N2 - Minimum ignition temperature of dust clouds (MITC) was studied experimentally and theoretically in different atmospheres. Three carbonaceous dusts were tested in both air and O2/CO2 atmospheres with CH4 mole fraction from 0 to 2%. Results showed that the ignition risk of the three dusts significantly increases (decrease of MITC by ~100 ℃) with increasing XO2 from 21% to 50%, but significantly decreases replacing N2 in air with CO2. The inhibition effect of CO2 on MITCs could be diminished by increasing XO2 or adding CH4. The addition of small amount of CH4 has different effects on the MITCs of different dust samples, following the opposite order of volatile matter content: anthracite>bituminous coal>starch. Two modified steady-state ignition models, considering the density of mixture gas and dust cloud, XO2 and its diffusivity, were developed to interpret the experimental observations. The analysis revealed that the global heterogeneous ignition model suits well for the hybrid mixtures of anthracite or bituminous coal dusts. In contrast, the proposed global homogeneous ignition model was found to be only valid for the pure starch dust, and the extra CH4 addition could strongly affect the ignition process of starch, particularly in O2/CO2 atmospheres with higher XO2. KW - Dust explosions KW - Gas explosions KW - Minimum ignition temperature KW - Hybrid mixtures PY - 2021 DO - https://doi.org/10.1016/j.jhazmat.2020.124189 SN - 0304-3894 SN - 1873-3336 VL - 405 SP - 1 EP - 10 PB - Elsevier CY - Amsterdam AN - OPUS4-53838 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -