Vol 60, No 4 (2017)

The oxidation index is an important characteristic of coal and coal batch, indicating the change in coking properties on oxidation. The coke obtained from coal batch containing poorly clinkering oxidized coal has a higher content of isotropic carbon and a lower content of anisotropic carbon. That explains its increased reactivity and impaired mechanical and postreactive strength. The oxidation on storage is greatest for small coal classes (<0.5 mm). Preliminary removal of <0.5 mm oxidized coal markedly improves the reactivity and also the mechanical and postreactive strength. A method of preparing oxidized coal for coking is proposed: finer grinding (until the content of the ≤1 mm class is 100%). That considerably reduces the influence of the oxidized coal on the quality of the coke produced.

Under non-isothermal conditions, thermogravimetric analysis was applied to study carbon dioxide gasification of three metallurgical cokes. The cokes selected for the study were named Coke A, Coke B and Coke C. The experimental data are fitted using four common gas-solid kinetic models: the homogeneous model, the sharp interface model, the traditional model and the random pore model. It is found that the random pore model most closely reflects the kinetic behavior of coke gasification characteristics. Using the random pore model, the apparent activation energies for gasification of Coke A, Coke B, and Coke C were calculated to be 139.08, 127.78, and 116.32 kJ mol^–1, respectively.

The semicoking of regular lignite from the Berezovsk field in Kansko-Achinsk Basin (moisture content 1.6–19.6 wt %) at 450–550°C in a reactor with solid heat carrier is studied. The products are semicoke (up to 68.1%), tar (up to 9.5%), gas (up to 31.9%), and pyrogenetic water. The composition of the semicoking gas is quantitatively determined. Its main components are hydrogen (up to 71.7%) and methane (up to 17.2%). The heat of combustion of the semicoking gas is 12.39–16.25 MJ/m³. The yield of phenolic fractions in the semicoking tar, consisting of phenol and its alkyl derivatives with one or two short substituents (C₁–C₃), is 10.5–14.6%. After hydraulic purification of the gasoline fraction in the semicoking tar (below 180°C), gasoline with octane rating 75.8 (by the motor method) is obtained. It consists of aromatic, saturated, and unsaturated hydrocarbons (C₅–C₈). The diesel fuel derived from tar fractions distilled off at temperatures up to 350°C are of good quality, except for their low cetane rating. The high-boiling tar fractions may be used to produce lignite pitch and pitch coke. The semicoke obtained is a very effective reducing agent in the production of phosphorus. It may also be used as a lean additive in coking batch and as a component in enriched domestic coal briquets.

The final purification of coke-plant wastewater after biochemical treatment by nitrification–denitrification is considered. All the methods that reduce the chemical oxygen demand, color, and suspended substances content are complex and expensive. Only two methods reduce the salt content (dry residue) to the standard levels for water added to circulatory cooling systems: thermal distillation and membrane purification. Of these, thermal distillation is best in practice.