A. Ya. Travyanov

Possibility of cyanide formation in blast furnaces

5There is great concern currently about the presence of cyanides (salts of hydrocyanic acid) and other compounds containing the CN radical in metallurgical emissions. Cyanides are highly toxic and have a very deleterious impact on human health and on the environment. Cyanide formation is highly likely in ferrous metallurgy. In particular, cyanides may be formed from the components involved in blast-furnace processes: carbon, nitrogen, hydrogen, and alkali metals. The temperature in the working space of the blast furnace varies widely: from 100‐200 ° C (at the charge hole) to 2000‐ 2300 ° C (in the tuyeres). Various compounds containing the CN group are stable within this region. Analysis of the chemical composition of metallurgical emissions confirms the presence of cyanides. Thus, in the water of the slurry tank at Kosogorsk metallurgical plant, an elevated concentration of CN radicals is observed. This tank contains the byproducts obtained in purifying blast-furnace gas: charge-hole dust and slurry. In the present work, we analyze the thermodynamic conditions of cyanide stability in various temperature zones of the blast furnace, for different compositions of the batch and atmosphere, using IVTANTERMO thermodynamic-simulation software. This software permits the calculation of complex chemical equilibria in multicomponent, multiphase systems. The equilibrium composition of the reagents in the system may be calculated for specified temperature, pressure, and concentrations of the elements. The computational algorithm is based on minimizing the Gibbs energy of the system. The distinguishing feature of the IVTANTERMO software used in the present work is that the thermodynamic parameters employed are obtained by the analysis of primary data in the literature [1, 2]. A special calculation procedure has been developed for thermodynamic simulation of the blast-furnace process. The chemical elements in the system are selected on the basis of information regarding their presence in the blast furnace for specified conditions. Thus, the initial system includes nine elements: C, O 2 , H 2 , N 2 , Fe, K, Na, Cl, and F. Preliminary calculations show that the other elements in the blast furnace, such as Si, Ca, Al, Mg, Mn, etc., have little influence on the formation and decomposition of materials containing cyanides. Research shows that most of the cyanides formed in the blast furnace are the compounds CN, CN 2 , HCN, KCN, and NaCN. The salts NaCN and KCN and hydrocyanic acid HCN are most stable, i.e., correspond to the broadest interval of existence with variation in the external conditions, such as temperature, pressure, chemical composition, and redox potential. Thermodynamic analysis indicates that the quantity of each material formed in the blast furnace is determined by the following parameters: