Coal experiments, actual reaction

It is interesting to note that stratified combustible gas mixtures can exist in tunnel-like conditions. The condition in a coal mine tunnel is an excellent example. The marsh gas (methane) is lighter than air and accumulates at the ceiling. Thus a stratified air-methane mixture exists. Experiments have shown that under the conditions described the flame propagation rate is very much faster than the stoichiometric laminar flame speed. In laboratory experiments simulating the mine-like conditions the actual rates were found to be affected by the laboratory simulated tunnel length and depth. In effect, the expansion of the reaction products of these type laboratory experiments drives the flame front developed. The overall effect is similar in context to the soap bubble type flame experiments discussed in Section C5c. In the soap bubble flame experiment measurements, the ambient condition is about 300 K and the stoichiometric flame temperature of the flame products for most hydrocarbon fuels... 

However, actual high-temperature gasification reaction rates are not known, and the residence time at a given reactor temperature is usually determined empirically based on small-scale gasifier experiments. It is also generally accepted that reaction rates vary with coal type. 

However, the diversity of the oxidants renders the oxidation of coal very complex because the experimental parameters can vary widely (Speight, 1987). The diversity in the structural types in coal (which vary not only with rank but also within the same rank) causes many problems associated with studies of the oxidative degradation of coal. For example, optimal conditions of time, temperature, and ratio of oxidant to coal can only be determined when several experiments are performed for each oxidant. Furthermore, the presence of the mineral matter must also be considered to be an integral part of coal oxidation since mineral constituents may change the chemistry of the oxidation. If coal is pretreated with hydrochloric acid to remove mineral matter prior to oxidation, the actual oxidation reaction may be more facile. 

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