Volume 60, Nº 5 (2017)
- Ano: 2017
- Artigos: 7
- URL: https://journals.rcsi.science/1068-364X/issue/view/13940
Coal
The oxidization of coal
Resumo
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.
Coke
Coking of batch with modifying additives at ChAO zaporozhkoks
Resumo
Efforts to improve the quality of blast-furnace coke produced from modified batch at ChAO Zaporozhkoks are described. The batch is modified by introducing fine-grain electrocorundum and carborundum (silicon carbide). The introduction of a fixed quantity (0.25 wt %) of nonclinkering additives permits adjustment of the processes in the plastic state so as to improve the coke strength. The effect of such modification on coke quality depends significantly of the rank composition of the batch. The use of additives is especially important for batch with poor clinkering properties.
Chemistry
Influence of the coke filler on the carcinogenicity of pitch–coke mixtures on carbonization
Resumo
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 (Tso = 100°C) than for electrode pitch (Tso = 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.
Efficiency of a Claus furnace in the coke-oven gas desulphurization circuit of MMK
Resumo
The poor efficiency of the Claus furnace in sulfur removal at the coke plant of OAO Magnitogorskii Metallurgicheskii Kombinat (MMK) is analyzed on the basis of monitoring data for the sulfur recovery unit and thermodynamic calculations. The low level of sulfur removal from coke-oven gas (~60%) at OAO MMK is mainly due to thermodynamic limitations on the thermal stage of hydrogen-sulfide oxidation with the specific composition of the sour gas at coke plants: low hydrogen-sulfide concentration and combustion of the additional fuel (natural gas). With the kinetic constraints in the Claus furnace, the high CO2 content in the sour gas (up to 37 vol %) results in increased yield of carbonyl sulfide (~14%). That calls for particular care in optimizing the temperature during the catalytic stages and selecting the best catalysts.
Thiophene extraction from the gasoline fraction of LTC shale tar
Resumo
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.
Utilization of Production Wastes
Droplet ignition of coal–water slurries prepared from typical coal- and oil-processing wastes
Resumo
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.