Iron Transformation and Ash Fusibility during Coal Combustion in Air and O₂/CO₂ Medium

Abstract

Little work has been performed on the transformation of iron and ash fusibility during oxy-coal combustion, which is of great significance to assessing ash deposition propensity. A high-iron bituminous coal was burnt at 1300°C in a laboratory drop-tube furnace under four conditions: (1) 21 vol % O 2 /79 vol % N 2 (air-firing), (2) 21 vol % O 2 /79 vol % CO 2 (oxy-firing), (3) 27 vol % O 2 /73 vol % CO 2 (oxy-firing), and (4) 32 vol % O 2 /68 vol % CO 2 (oxy-firing). The bulk ash samples were subjected to X-ray fluorescence and Mossbauer spectroscopic analyses. The effects of changing from air combustion to O 2 / CO 2 combustion and the effects of varying the O 2 level in O 2 /CO 2 combustion on iron transformation and ash fusibility were investigated. The results show that varying the combustion condition has insignificant effects on the elemental composition of coal ashes but has appreciable effects on the relative proportions of iron combustion products that were identified as hematite, magnetite, and Fe−glass phases. This indicates that speciation analysis is as important as bulk analysis for thorough ash characterization. Replacing N 2 in air with CO 2 results in a higher content of hematite but a lower content of magnetite. Increasing the O 2 level in O 2 /CO 2 combustion increases the formation of hematite but decreases the formation of magnetite. In contrast, the amount of Fe−glass phases remains almost unchanged. An appreciable fraction (about 8% Fe) of hematite/ magnetite seems to crystallize out of the molten glass phases during combustion, and it is not significantly affected by changing combustion conditions. The fusion temperatures of the oxy-fired ashes are higher than those of the air-fired ash and increase with the inlet O 2 level. A positive correlation between the hematite content and the ash fusion temperatures is observed.

Anthropogenic combustion iron as a complex climate forcer

“…In NEW simulation, the fraction of AN magnetite to AN iron (magnetite fraction) was assumed to be 40% in offline estimation of the total and the soluble iron concentrations and their deposition flux. This magnetite fraction has not been constrained by observations and might be much higher or lower than 40% depending on the combustion sources 25 , 26 (Supplementary Note 1 ). We define the uncertainty range of the magnetite fraction between 20% and 80%, and discuss the total and the soluble iron estimates within this uncertainty range (Supplementary Note 1 ).…”

Characterization of Ash Particles from Co-combustion with a Zhundong Coal for Understanding Ash Deposition Behavior

“…The drop tube furnace (DTF) used in this work is the same one as described elsewhere. 8 Briefly, the furnace tube has a length of 2 m and an inner diameter of 56 mm. It is electrically heated and the working temperature can be well-controlled.…”

Abundance of Light‐Absorbing Anthropogenic Iron Oxide Aerosols in the Urban Atmosphere and Their Emission Sources

“…In addition to natural sources, magnetite and hematite particles are also emitted through human activities involving combustion or other high‐temperature processes. Previously reported anthropogenic sources of these particles include integrated steel plants (Machemer, ), motor vehicle exhaust (i.e., the wearing down and melting of engine fragments; Liati et al, ), brake discs and brake pads in motor vehicles and trains (Karlsson et al, ; Kukutschová et al, ; Salma et al, ), welding operations in construction projects and industrial plants (Berlinger et al, ), and coal and heavy oil combustion (Fu et al, ; Linak et al, ; Yu et al, ). Hu et al () suggested that the dominant source of FeO x aerosols sampled in the Beijing metropolitan region was steel plants, which operated around their observatory at distances ranging from 6 to 25 km.…”