Coal flame speed

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... 

It is more than likely that when sulfur occurs in a crude oil or in coal (other than the pyrites), it is organically bound in one of the three forms listed in Table 3—the thiols, sulfides, or disulfides. The combustion of these compounds is very much different from that of other sulfur compounds in that a laige portion of the fuel element is a pure hydrocarbon fragment. Thus in explosion or flame studies, the branched-chain reactions that determine the overall consumption rate or flame speed would follow those chains characteristic of hydrocarbon combustion rather than the CS, SO, and S radical chains which dominate in H2S, CS2, COS, and Sg combustion. 

Gas comp. Natural gas Producer gas Water gas Coal gas Lurgi gas Landfill gas Bio gas Sewage gas Flame speed Mf (MJ/m ) combustion... 

Pulverized coal is fed directly from a variable speed auger into the high velocity primary air stream which conveys it to the injector at the top of the furnace. The coal and primary air enter the combustor through a single low-velocity axial jet. Secondary combustion air is divided into two flows which enter the combustor coaxial to the primary stream. Part of the flow is introduced through a number of tangential ports to induce swirl which is necessary for flame stabilization. The remainder enters the combustor axially. The two secondary air streams are separately preheated using electrical resistance heaters. 

High speed emission spectroscopy has been used to study free radicals and positive, negative, and multiple ions produced in explosions and flames. Many excited states would exist for many different species from coal subjected to high energy. Complex spectra would result. The combination of electronic-vibration-rotation transitions observable in emission spectroscopy... 

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In the underfeed stoker, coal is fed by a worm feeder into the bottom of a retort (Figure 14.15). The coal rises vertically in the retort and air enters through tuyeres in the sides. The fire is ignited at the top and the flame front moves downward and its speed is matched by the rising flow of coal, fulfilling the requirement of the flame front traveling in the opposite direction of the primary air. 

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