Investigation on the transformation behaviours of Fe-bearing minerals of coal in O2/CO2 combustion atmosphere containing H2O.

The transformation behaviors of Fe-bearing minerals in coals of Xinjiang (XJC) and Shenhua (SHC) were investigated in an O2/CO2 atmosphere containing H2O in a drop-tube-furnace (DTF). The solid products were characterized using XRD, Mössbauer spectroscopy, particle size analyzer and SEM-EDX techniques. The results show that the change in the combustion atmosphere does not significantly alter the main phases of Fe-bearing minerals in the coal ashes, but does affect their relative contents. The ratio of Fe2+-glass to Fe3+-glass in the ashes produced from the O2/CO2 combustion atmosphere was significantly increased. During the XJC combustion and under different combustion conditions examined, the content of Fe-glass phases remained almost unaltered. However, in SHC samples, combustion under O2/CO2 atmosphere resulted in a higher amount of iron melting into Fe-glass phases and less amount of iron oxide formation. This could be attributed mainly to the presence of Fe-bearing minerals mostly included in nature in SHC samples, which more easily interacted with clays or other silicates inside coal-formed Fe-glass phases. Increasing the O2 level of the O2/CO2 atmosphere during SHC combustion could promote the formation of iron oxides. In O2/CO2 atmosphere, with the same oxygen level, the replacement of 10% of CO2 with H2O promoted the formation of iron oxides, regardless of the occurrence form (included or excluded) of iron minerals in coal. Furthermore, the addition of steam resulted in an increase in the size of the particles in ash, resulting probably in a decrease in the deposition and slagging propensity of coal ash.

Torrefaction of herbal medicine wastes: Characterization of the physicochemical properties and combustion behaviors.

To explore the feasibility of using herbal medicine waste (HMW) as solid fuel, HMW was torrefied under different temperatures and atmospheres. The physicochemical properties and combustion behaviors of the torrefied HMW were investigated. Temperature was found to be the most influential factor affecting the torrefaction. Torrefaction improved the hydrophobicity of HMW and decreased the equilibrated moisture uptake from 24.48(0.083) % to 15.22(0.054) %. The HMW samples torrefied under different conditions are easy to ignite. The comprehensive combustibility index (S) of the torrefied HMW increased by 3-5 folds compared to that of the raw sample. In general, the HMW torrefied under lower temperatures and under CO2 and O2 have better flammability. The present results revealed that the torrefied HMW exhibited good combustion characteristics and can thus be used for solid fuel production, such as fuels for co-combustion or raw materials for pelletization.

The thermal transformation mechanism of chlorinated paraffins: An experimental and density functional theory study.

The increasing production and usage of chlorinated paraffins (CPs) correspondently increase the amount of CPs that experience thermal processes. Our previous study revealed that a significant amount of medium-chain chlorinated paraffins (MCCPs), short-chain chlorinated paraffins (SCCPs) as well as aromatic and chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) were formed synergistically during the thermal decomposition of CP-52 (a class of CP products). However, the transformation mechanisms of CP-52 to these compounds are still not very clear. This article presents a mechanistic analysis on the decomposition of CP-52 experimentally and theoretically. It was found that CP-52 initially undergoes dehydrochlorination and carbon chain cleavage and it transformed into chlorinated and unsaturated hydrocarbons. Cyclization and aromatization were the most accessible pathways at low temperatures (200-400°C), both of which produce mostly aromatic hydrocarbons. As the temperature exceeds 400°C, the hydrocarbons could decompose into small molecules, and the subsequent radical-induced reactions become the predominant pathways, leading to the formation of Cl-PAHs. The decomposition of CP-52 was investigated by using density functional theory and calculations demonstrating the feasibility and rationality of PCB and PCN formation from chlorobenzene. The results improve the understanding of the transformation processes from CP-52 to SCCPs and Cl-PAHs as well as provide data for reducing their emissions during thermal-related processes.

Occurrence and Human Exposure Assessment of Short- and Medium-Chain Chlorinated Paraffins in Dusts from Plastic Sports Courts and Synthetic Turf in Beijing, China.

This study presents the first investigation of concentrations and congener group patterns of short- and medium-chain chlorinated paraffins (SCCPs and MCCPs) in 159 dust samples from plastic sports courts and synthetic turf in Beijing, China. The geometric mean concentration of SCCPs and MCCPs in dusts from plastic tracks (5429 and 15157 µg g-1) and basketball courts (5139 and 11878 µg g-1) were significantly higher than those from plastic tennis courts, badminton courts, and synthetic turf; meanwhile, they were 1-3 orders of magnitude higher than in dusts from other indoor environments. The friction between sneaker soles and plastic track materials may lead to the wear and decomposition of rubber, which may be an important source of chlorinated paraffins (CPs) in the dust from plastic tracks. The mean estimated daily intakes of CPs from plastic tracks and basketball courts are generally higher than those estimated from dietary, breast milk, or other indoor dust sources. The margin of exposure for adults and children was greater than 1000 both at mean and high-exposure scenarios, indicating that no significant health risks were posed by CPs in the dust from plastic sports courts and synthetic turf.

Identification of the Released and Transformed Products during the Thermal Decomposition of a Highly Chlorinated Paraffin.

As plasticizers and flame retardants, highly chlorinated paraffin (CP70) and related products will experience thermal processes during their lifecycle stages. However, the thermal transformation data for CP70 is limited. In this study, we investigated the release and transformation of chlorinated and unchlorinated products during the thermal decomposition of CP70. Large quantities of short- and medium-chain chlorinated paraffins (SCCPs and MCCPs) and unsaturated analogues (Cl-polyenes or chlorinated olefins) as well as toxic chlorinated aromatic hydrocarbons were formed synergistically under different thermal conditions. The yield of SCCPs increased gradually in the gas phase, while it decreased in the residue at 200-400 °C. SCCPs can be transformed further and generated mostly polychlorinated biphenyls (PCBs). Oxygen promoted the thermal transformation of SCCPs and MCCPs and decreased the yield in the gas phase at >400-500 °C. In contrast, the yield of both SCCPs and MCCPs increased notably under N2 at 800 °C. Chlorobenzene (CBz), PCBs, and polychlorinated naphthalenes (PCNs) were the main chlorinated aromatic hydrocarbons and obtained a maximum yield at 500-600 °C. The present findings indicate that CP70-containing materials may synergistically generate SCCPs, MCCPs, and other toxic chlorinated compounds during their life cycles.

Thermochemical emission and transformation of chlorinated paraffins in inert and oxidizing atmospheres.

Chlorinated paraffins (CPs) generally function as flame retardants and plasticizers in various materials. They are most likely to be processed by thermal processes during the entire life cycle. However, data on the formation and emission of CPs during thermal processes are still not fully understood. In this study, we simulated industrial thermal processes to investigate the emission of medium-chain chlorinated paraffins (MCCPs) and short-chain chlorinated paraffins (SCCPs) using commercial CP52 as the feedstock. We found that CP52 decomposed very easily at 210-320 °C. The decomposition of CPs generated large quantities of MCCPs and SCCPs. These remained in the residue at low temperature (∼200 °C) and were gradually released into the gas phase at higher temperatures. MCCPs and SCCPs were not detected in either the residue or the gas phase when the temperature exceeded 400 °C. However, considerable concentrations of aromatic and chlorinated aromatic hydrocarbons (Cl-PAHs) were identified in the gas phase, and they were formed as the amount of SCCPs and MCCPs decreased. Cl-PAHs were dominated by low-chlorinated chlorobenzenes, polychlorinated biphenyls, and polychlorinated naphthalenes. Oxygen promoted the release and decomposition of SCCPs in the gas phase. The results of the present study revealed the release of MCCPs and SCCPs and their synergistic emission with Cl-PAHs when CPs were subjected to heat. This work may also provide data for developing multiple techniques to control the emission of CPs and Cl-PAHs.