Behaviors of Chromium in Coal-Fired Power Plants and Associated Atmospheric Emissions in Guizhou, Southwest China

Abstract

Coal burning is a main concern for a range of atmospheric pollutants, including the environmentally sensitive element chromium (Cr). Cr migrates to the environment through stack emissions and can leach out from solid coal-burning byproducts, thereby causing adverse effects on the ecosystem. In this study, atmospheric emissions of Cr from six coal-fired power plants (CFPPs), as well as the distribution of Cr inside these CFPPs in Guizhou Province, Southwest China, were investigated. Among the six CFPPs, one was a circulating fluidized bed boiler and the others were pulverized coal boilers. The results showed that Cr in the feed fuel of these CFPPs ranged from 39.5 to 101.5 mg·kg−1 (average: 68.0 ± 24.8 mg·kg−1) and was approximately four times higher than the national and global average. Cr in the feed fuel correlated significantly with the ash yield, demonstrating that Cr in coal is closely associated with ash-forming minerals. After the coal combustion and the treatment by different air pollution control devices, most Cr (>92%) in the installation was retained in the captured fly ash and bottom ash, with less as gypsum (0.69–7.94%); eventually, only 0.01–0.03% of Cr was emitted into the atmosphere with a concentration of 1.4–2.2 μg·Nm−3. The atmospheric emission factors of Cr for these utility boilers were as low as 14.86 ± 3.62 mg Cr·t−1 coal, 7.72 ± 2.53 μg Cr (kW·h)−1, and 0.70 ± 0.19 g Cr·TJ−1, respectively. About 981 kg·y−1 of Cr was discharged into the atmosphere from Guizhuo’s CFPPs in 2017, much lower than previous reported values. Most of the Cr in the CFPPs ended up in solid combustion products, identifying the need for the careful disposal of high-Cr-containing ashes (up to 500 mg·kg−1) to prevent possible mobilization into the environment.

Chromium in Chinese coals: geochemistry and environmental impacts associated with coal-fired power plants

“…Following the explication by Clarke ( 1993 ) and Meij et al ( 2004 ), Cr in coals could be categorized as an element between nonvolatile and semi-volatile and was mainly retained in solid wastes after coal combustion. Researchers have reported that air pollution control devices (APCDs) in CFPPs had remarkable impacts on the partitioning of Cr in solid wastes (Li et al, 2020 ). This paper compared the Cr concentrations in different solid wastes from CFPPs in China over recent years, and presented them in detail in Table 5 .…”

“…As shown in Table 5 , compared with the feed coal, Cr was enriched in the fly ash and bottom ash after coal combustion, whereas existed less in the flue gas desulfurization (FGD) gypsum. For most CFPPs, a higher Cr concentration in fly ash could be observed, and the reasons for this phenomenon were described as follows: (1) in comparison with bottom ash, fly ash had smaller particle size and stronger adsorption capacity for the condensation of Cr (Han et al, 2021 ; Tang et al, 2013 , 2022b ), (2) the occurrence of Cr in coals was an important influencing factor for its redistribution in solid wastes, and Cr in the form of organic/sulfide combinations was more likely to partially evaporate and thus coagulate on the fly ash (Fu et al, 2019 ; Li et al, 2020 ). In summary, the solid wastes from CFPPs needed to be carefully disposed to prevent their possible mobilization into the environment.…”

“…Although the removal efficiency of APCDs in CFPPs had reached a relatively high level, part of Cr in the stack gas could still escape to the atmosphere and cause potential hazards (Han et al, 2021 ; Li et al, 2020 ). Identifying the atmospheric Cr emissions from CFPPs was inherent in improving air quality and human health.…”

Substance Flow Analysis of Zinc in Two Preheater–Precalciner Cement Plants and the Associated Atmospheric Emissions

“…Trace elements in the Earth's surface system are critical to livestock wellbeing due to their biological functions or toxicities [1]. The abundance of trace elements in the ambient environment is affected by both natural and anthropogenic sources [2,3]. In modern society, human activities are more extensive than at any previous time in the Earth's history and have deeply influenced the biogeocycling of trace metals [4][5][6].…”

Special Issue Editorial: Air Pollution Estimation

“…Trace elements, contained in coal, migrate with coal combustion products. In one study, atmospheric emissions of Cr from six coal-fired power plants (CFPPs), as well as the distribution of Cr inside these CFPPs, were measured in Guizhou Province, Southwest China [8]. The results showed that Cr in the feed fuel of these CFPPs ranged from 39.5 to 101.5 mg•kg −1 (average: 68.0 ± 24.8 mg•kg −1 ) and was approximately four times higher than the national and global average.…”