Modes of Occurrence of Chromium and Their Thermal Stability in Low-Rank Coal Pyrolysis

Chromium (Cr) and the emission of its compounds into the environment have caused long-term environmental contamination. In this study, the modes of occurrence of Cr in low-rank coal and their thermal stability in pyrolysis were investigated by sequential chemical extraction (SCE), single-component samples (SCS) pyrolysis, and thermochemical equilibrium simulation. The results showed that organic matter, aluminosilicate, and carbonate were the dominant modes of occurrence of Cr in low-rank coal. The modes of occurrence and chlorine (Cl) content affected the volatilization of Cr in coal. The characteristic release temperature range of Cr bounded to aluminosilicate was >600 °C and 400–600 °C for Cr bounded to a disulfide. Cr bounded to organic matter almost released completely before 600 °C. Cl enhanced the volatility of Cr and reduced its release temperature in Cr bounded to aluminosilicate. The simulation showed the content of gas products was very low, mainly chlorides. While the content of solid products, sulfides, and oxides, was much higher than gas products, showing their high thermal stability. The sulfides and oxides in chars were closely related to the carbonate and aluminosilicate bound form of Cr. The results of the equilibrium simulation were consistent with the experimental results.

Modes of occurrence of tungsten in alluvial soils and river sediments in the area of the Grantcharitsa tungsten deposit, Western Rhodopes, Bulgaria

A distinct increase in the concentration of W in the topsoil (from 19–20 to 71 ppm) is found in the vertical profile of the alluvial soil at the Grantcharitsa deposit. The distribution of W, Fe, and C is well correlated, which indicates a significant role of organic material and iron oxides/hydroxides formed in the soil in the chemical behavior of W. The role in these processes of scheelite, W-containing goethite and rutile identified in the soil is insignificant.

ANALYSIS OF THE PROCESSES OF OCCURRENCE OF SUBHARMONIC COMPONENTS IN CONTACT POWER SUPPLY NETWORKS WITH NONLINEAR LOADS

The article considers the calculation of the modes of occurrence of subharmonic components in traction power supply networks of railway transport, containing traction converters, controlled and uncontrolled rectifiers. The processes of the appearance of harmonic components during the operation of electric locomotives with zone-phase and pulse control using a four-quadrant 4q-S converter in power circuits are considered. Harmonics related to the fundamental and subharmonic components are determined by the harmonic balance method.

ANALYSIS OF THE PROCESSES OF OCCURRENCE OF SUBHARMONIC COMPONENTS IN CONTACT POWER SUPPLY NETWORKS WITH NONLINEAR LOADS

In the article considers the calculation of the modes of occurrence of subharmonic components in traction power supply networks of railway transport, containing traction converters, controlled and uncontrolled rectifiers. The processes of the occurrence of harmonic components during the operation of electric locomotives with zone-phase and pulse control using a four-quadrant 4q-S converter in power circuits are considered, harmonics related to the main and subharmonic components are determined by the harmonic balance method.