Vol 60, No 5 (2017)

The oxidation of coal is generally explained by the radical-chain hypothesis. Detection of active centers and free radicals is possible by methods available today, and the formation of methyl, methylene, phenol, carbonyl, and carboxyl groups and their interaction with oxygen and water molecules may be described. Oxidation results in heating and self-combustion of coal on open storage. For each coal, there is a critical temperature (~60°C) beyond which the heating rate sharply rises and self-ignition becomes possible. The activation energy of coal oxidation in the range 0–140°C is found to be 13.4–53.6 kJ/mol. The activation energy is greatest for bituminous Zh coal.

Preliminary drying of coking batch by means of secondary energy resources generated at coke plants is considered.

The emissions of benzo[a]pyrene at different temperatures and its concentration in the exhaust gases are measured in laboratory experiments on the carbonization (at temperatures up to 850°C) of coalpitch and petroleum-pitch binders and their mixtures with roasted petroleum and pitch coke. These pitch–coke mixtures are similar in composition to the anode mass used in aluminum production. The experiments confirm that the total benzo[a]pyrene emissions are much greater in the carbonization of petroleum pitch produced by cracking (T_so = 100°C) than for electrode pitch (T_so = 89°C) and other coal pitch. In most experiments, the benzo[a]pyrene emissions in the carbonization of pitch–coke mixtures is markedly less than for individual binder pitches. It is found that the benzo[a]pyrene emissions in the carbonization of a mixture based on pitch coke are much less than for a mixture based on petroleum coke in the high-temperature region that presents the greatest environmental hazard.

The composition of narrow fractions of shale gasoline extracted from LTC (low-temperature carbonization) tar is determined by rectification and gas chromatography–mass spectrometry. The LTC tar is derived from high-sulfur Mishor Rotem shale. The fractions considered are <77°C, 77–85°C, 85–105°C, 105–115°C, 115–130°C, and 130–150°C. The selective extractants N,N-dimethylformamide and N-methylpyrrolidone are used in extractive rectification of the gasoline, toluene, and xylene fractions of the LTC shale tar. The material balances are determined, and the composition of the distillates and bottoms obtained are determined. The results show that it is possible, in principle, to extract thiophene and its homologs from these fractions by extractive rectification using selective extractants.

The requirements for stable ignition (and subsequent combustion) of fuel suspensions prepared from typical coal- and oil-processing wastes are studied experimentally. Attention focuses on the differences between the ignition characteristics of coal–water slurries (containing petrochemicals) obtained on the basis of filter cakes containing T, K, SS, Zh, D, and G coal. To eliminate the influence of the droplet holder (traditionally, thermocouple junctions, ceramic rods, or metal wire) on the ignition characteristics of the fuel droplet, the experiments employ a special model combustion chamber and a device for introducing a single drop of suspension. The ignition time and the minimum temperature of stable ignition of a droplet of coal–water slurries suspended in an oxidant flux are established. The influence of the following factors on the initiation of fuel combustion is determined: the oxidant temperature, the droplet size, the size of the coal dust, and the properties and concentrations of the components. The compositions of the coal–water slurries corresponding to optimal ignition (minimum inertia) are identified.