In hemisphere point temperature (Thp) measurement of continuous casting mold
flux, the evaporation of volatiles under high temperature will have a strong
impact on the results. Based on the comprehensive analysis of hemisphere
point method and its influencing factors, the corresponding
volatile-containing mold flux and non-volatile mold flux were selected to
get Thp with different heating rates. Combined with the Thp measurement and
TG-DSC results, the effect of relevant factors during measuring process were
analysed and the way to characterize and evaluate the effects were
suggested. Furthermore, an improved method of mold flux melting point test
was put forward. The results showed that for non-volatile mold flux, the
temperature hysteresis has a greater effect than heat transfer delay and
fractional melting. And for mold flux with volatile, the effect of
evaporation is greater than other factors. Traditional hemisphere-point
method is no longer suitable for the volatile mold flux. In order to get
through this problem, improved methods were proposed. One is measuring Thp
by traditional way, correcting the composition at the Thp, corresponding Thp
with the corrected composition. Another is taking the initial composition,
revising the hemispherical point temperature Thp, matching the revised Thp
with the initial composition.
The pyrolysis characteristics of Shenmu coal under an atmosphere containing H2 (40%) and another containing CH4 (40%) were studied via a thermogravimetric analysis, and the kinetic parameters of pyrolysis were calculated by using a distributed activation energy model (DAEM). The results showed that H2 promoted the cleavage of CH-like functional groups by providing reactive hydrogen groups to combine with CH groups and –OH groups in the coal. However, the H2 and CH4 atmosphere inhibits the cleavage of oxygen-containing functional groups such as carbonyl groups and C–O groups, and this is unfavorable to the production of CO2 and CO. The pyrolysis weight-loss rate of raw coal decreases with the increase of the heating rate, and the weight-loss curve shifts to the high-temperature region. At the same conversion rate and pyrolysis temperature, the activation energy of pyrolysis under the H2 and CH4 atmospheres is lower than that under the N2 atmosphere, and the activation energy does not conform to the Gaussian distribution. The activation energy of pyrolysis was distributed in a narrow range, in which the activation energy of the H2 and CH4 atmospheres was concentrated in the range of 175–215 kJ/mol and 225–230 kJ/mol, respectively, and the activation energy of the H2 atmosphere was lower than that of the CH4 atmosphere under the same conversion rate.
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