42 Air Monitoring
BEYOND THE STACK: EMISSION AND DISPERSION OF MERCURY SPECIES IN THE VICINITY OF CEMENT PLANT
Mercury (Hg), a naturally occurring trace element, is released into the atmosphere through various human activities, contributing to widespread contamination of air, water, and soil. The release of Hg into the environment has severe implications for human health and ecosystems.
Hg bioaccumulates in aquatic ecosystems, where it can undergo biomagnifi cation, leading to elevated concentrations in predatory fi sh species consumed by humans, thereby posing a signifi cant risk to food safety and security. Among anthropogenic emissions, the cement industry is the second largest source of Hg emission source in Europe. How does Hg come into the cement production unit? What happens to Hg once emitted into the atmosphere? Hg is brought into the cement production system from various raw materials that are ground in raw mills used for the clinker production. For energy effi ciency, a part of hot exhaust gases (along with the dust particles) in the system are re-cycled back to the raw mills to dry raw materials. As a result, Hg is continuously
stripped, sorbed, cycled, and enriched in the inner gas stream. When raw mills are not in operation, fl ue gases are not cycled back for raw materials drying, but passed directed through the fabric fi lter and subsequently released into the atmosphere through the kiln stack, i.e., chimney. Once emitted, atmospheric Hg undergoes various physical and chemical transformations before undergoing wet and/or dry deposition to the ground or water surfaces. Atmospheric Hg is operationally defi ned in three fractions: gaseous elemental (GEM), gaseous oxidized (GOM), and particulate bound Hg (PBM). They are all subject to local, regional, and global transport where GOM, and PBM have more local and regional impact whereas GEM have global effects. Knowledge on Hg emissions and speciation is critical when validating models for predicting Hg emissions, transport, deposition, and fate at local, regional, and global levels.
Figure 1: Representation of the fate of Hg emitted into the atmosphere. Hg undergoes global and regional transport, chemical transformations into reactive species, is deposited into terrestrial environments through wet and dry deposition, and is also re-emitted into the atmosphere from land, water, and vegetation.
IET SEPTEMBER / OCTOBER 2024
Our study aimed to compare Hg emissions from cement production based on the operational status of the plant’s raw mill, to perform Hg speciation in a remote location near the plant, to correlate these measurements with local meteorological parameters such as wind speed and direction, and to investigate the impact of plant emissions on various Hg fractions near the study area. The study area in question is the cement plant, which has been the leading cement producer in Slovenia for over a century. Over the years, the plant has made signifi cant investments in the utilization of alternative fuels to enhance energy-effi cient production. By employing cement kilns for the co-incineration of select waste materials, provided they are free from harmful impurities and possess a high calorifi c value, the facility has emerged as the largest of its kind in Slovenia. This shift towards co-combustion of alternative fuels has resulted in a substantial reduction in the use of fossil fuels, such as coal, petrol coke, and natural gas, as the primary energy source. However, it is worth noting that cement plant has been met with discontent among the local population, particularly due to the co-incineration of waste. Notably, the emissions of Hg from the plant have become a matter of public concern. As part of the methodology, total gaseous mercury (TGM) concentrations in the fl ue gases emitted from the plant were monitored using a continuous emission monitoring system (CEMS) installed in the kiln stack during the study period. Concurrently, for continuous measurements of Hg fractions (GEM, GOM, and PBM), a Tekran Hg speciation unit coupled to the Tekran 2537B Hg vapour analyzer was deployed in the study area, situated approximately 1 kilometer southwest from the plant, in relatively close proximity to the plant chimney. This location was selected due to its alignment with prevailing wind patterns, predominantly
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