Heavy Metal Emissions through Particulate Matter from Aluminium Electrolysis

Heavy metal emissions from the aluminium industry are mainly carried from the plant through fugitive particulate matter (PM) originating from the aluminium electrolysis pot room. To evaluate the behaviour of metal-carrying PM, both airborne and settled PM from two different primary aluminium smelters have been characterized and analyzed for composition and particle size distribution, with special emphasis on heavy metals and carbon. In addition, optical particle sensors have been placed at different elevations in one of the plants to determine the concentrations of different particle sizes in fugitive PM. Metals such as Fe and Ni were primarily found as particles together with S and P on partly combusted carbon PM. Settled PM from both plants were generally coarser (mean = 32–39 μm) and had a higher Al:Na ratio compared with airborne PM, with a mean PM of 21–22 μm. The optical sensors measured PM100 concentrations at roof level in the plant 5–6 times higher than the PM10 concentration during fuming events such as anode shift operations.acceptedVersio

Use of a Distributed Micro-sensor System for Monitoring the Indoor Particulate Matter Concentration in the Atmosphere of Ferroalloy Production Plants

Airborne particulate matter (PM) is a concern for both occupational health and the environment, and, in the ferroalloy industry, the level of such particles in the air can be considerable. Small, low-cost sensors for measuring PM have generated interest in recent years, providing widespread monitoring of PM levels in the environment. However, such sensors have not yet been sufficiently tested under conditions relevant for the indoor environment of the metallurgical industry. This study aims to bridge this gap by benchmarking the commercial, low-cost Nova PM SDS011 particle sensor in two different ferroalloy plants. Benchmarking was performed against the Fidas 200S, which has been suitability-tested and certified according to the latest EU requirements (EN 15267, EN 16450). Twelve Nova sensors were tested over 3 months at a silicomanganese alloy (SiMn) plant, and 35 sensors were tested during 1 month at a silicon (Si) plant. The results showed that the low-cost Nova sensors exhibited all the same trends and peaks in terms of PM concentration, but measured lower dust concentrations than the Fidas 200S. The difference was larger at the silicon plant, which is in line with expectations, due to the size and mass fractions of particles in Si dust compared to SiMn dust, and to the larger measurement range of the Fidas, measuring down to 180 nm compared to the Nova which measures down to 300 nm. Despite the difference in absolute values, the Nova sensors were found to provide data for comparing dust levels over time for different processes, at different locations, and under different operational conditions.publishedVersio

Influence of Atmosphere and Temperature on Polycyclic Aromatic Hydrocarbon Emissions from Green Anode Paste Baking

Coal tar pitch, a well-known source of polycyclic aromatic hydrocarbons (PAHs), is used as a binder of petroleum coke in prebaked anodes used for electrolysis of aluminum. Anodes are baked up to 1100 °C over a 20-day period, where flue gas containing PAHs and volatile organic compounds (VOCs) are treated using techniques such as regenerative thermal oxidation, quenching, and washing. Conditions during baking facilitate incomplete combustion of PAHs, and due to the various structures and properties of PAHs, the effect of temperature up to 750 °C and various atmospheres during pyrolysis and combustion were tested. PAH emissions from green anode paste (GAP) dominate in the temperature interval of 251–500 °C, where PAH species of 4–6 rings make up the majority of the emission profile. During pyrolysis in argon atmosphere, a total of 1645 μg EPA-16 PAHs are emitted per gram of GAP. Adding 5 and 10% CO2 to the inert atmosphere does not seem to affect the PAH emission level significantly, at 1547 and 1666 μg/g, respectively. When adding oxygen, concentrations decreased to 569 μg/g and 417 μg/g for 5% and 10% O2, respectively, corresponding to a 65% and 75% decrease in emission.publishedVersio

Assessment of hydrogen quality dispensed for hydrogen refuelling stations in Europe

The fuel quality of hydrogen dispensed from 10 refuelling stations in Europe was assessed. Representative sampling was conducted from the nozzle by use of a sampling adapter allowing to bleed sample gas in parallel while refuelling an FCEV. Samples were split off and distributed to four laboratories for analysis in accordance with ISO 14687 and SAE J2719. The results indicated some inconsistencies between the laboratories but were still conclusive. The fuel quality was generally good. Elevated nitrogen concentrations were detected in two samples but not in violation with the new 300 μmol/mol tolerance limit. Four samples showed water concentrations higher than the 5 μmol/mol tolerance limit estimated by at least one laboratory. The results were ambiguous: none of the four samples showed all laboratories in agreement with the violation. One laboratory reported an elevated oxygen concentration that was not corroborated by the other two laboratories and thus considered an outlier.publishedVersio

Analysis of Polycyclic Aromatic Hydrocarbon Emissions from a Pilot Scale Silicon Process with Flue Gas Recirculation

Flue gas recirculation (FGR) is a method used in several industries to control emissions and process conditions, such as NOx reduction and temperature levels, and increase the CO2 concentration in the off-gas, to be better suited for methods of carbon capture. In this study, the influence of FGR, varying levels of flue gas flow and oxygen concentration on the emissions of polycyclic aromatic hydrocarbons (PAHs) was investigated during Si alloy production. In addition, computational fluid dynamics (CFD) modeling was performed using OpenFOAM for combustion of C2H2 and H2 with varying O2 levels to simulate FGR and to gain better insight into the impact of furnace operations on the PAH evolution. Experimental results show that increasing FGR (0–82.5%) and decreasing levels of oxygen (20.7–13.3 vol %) increase the PAH-42 concentration from 14.1 to 559.7 μg/Nm3. This is supported by the simulations, where increased formation of all PAHs species was observed at high levels of FGR, especially for the lighter aromatic species (like benzene and naphthalene), due to the lower availability of oxygen and the reduction in temperature. Residence time was identified as another key parameter to promote complete combustion of PAHs. Benzene oxidation can be prevented with temperatures lower than 1000 K and residence times smaller than 1 s, while complete oxidation is found at temperatures of around 1500 K.publishedVersio

Validation of QCL CF4 Gas Analyzer for Sensitivity and Selectivity

The final publication is available at https://link.springer.com/chapter/10.1007%2F978-3-030-36408-3_100Quantum cascade lasers (QCL) has open the mid-infrared (mid-IR) spectral range for laser gas monitors. For perfluorocarbon gases (PFCs) such as CF4, continuous emission monitors are now commercially available. Since these instruments can only make use of a narrow IR band, spectral interference from other gas species is not easily resolved. In this paper a commercial QCL CF4 analyser is validated with respect to sensitivity and selectivity. In the laboratory, the laser was mounted on a 0.3-m measurement cell. A gas mixer provided humidified gas mixtures of CF4 and methane. The results indicated that while there was no interference from water in the range up to 8000 ppm H2O, a small interference from methane was observed. This was quantified to be approximately 3 ppb CF4 per ppm of methane. The sensitivity of the instrument was found to be 10.5 ppb CF4 for one-meter light path.acceptedVersio

Aluminium Primary Production Off-Gas Composition and Emissions: An Overview

The raw gas composition from primary aluminium production depends mostly on the process technology applied and the composition of the raw materials. At steady state, a stationary condition is established among the material sources, gas production and sinks: the gas treatment centre and escaping gases. Only a few papers discuss the off-gas composition itself; most papers deal with the gas composition from laboratory-scale experiments performed under inert conditions. In this article, an overview of the literature describing gas production from aluminium electrolysis is given. Effects of temperature and chemical equilibrium on the stationary condition are also discussed. The typical chemical composition of the raw materials is presented to evaluate their input into the gas composition, especially with respect to their impurity levels.publishedVersio

Aluminium Primary Production Off-Gas Composition and Emissions: An Overview

The raw gas composition from primary aluminium production depends mostly on the process technology applied and the composition of the raw materials. At steady state, a stationary condition is established among the material sources, gas production and sinks: the gas treatment centre and escaping gases. Only a few papers discuss the off-gas composition itself; most papers deal with the gas composition from laboratory-scale experiments performed under inert conditions. In this article, an overview of the literature describing gas production from aluminium electrolysis is given. Effects of temperature and chemical equilibrium on the stationary condition are also discussed. The typical chemical composition of the raw materials is presented to evaluate their input into the gas composition, especially with respect to their impurity levels

Particulate emissions from electrolysis cells

In the dry cleaning of the exhaust gas from the aluminium cells impurities are accumulated in the finer fractions of secondary alumina from the dry scrubbers. The present work describes new methods for the determination of dust composition, aiming at increasing the understanding of the effect of cell operation on the amount and the composition of dust in the fume. New and advanced analysis methods are used to characterize a broad specter of emissions. An Electrical Low Pressure Impactor is used to sample and analyze the dust from the cells. The equipment enables real-time particle size distribution analysis of 12 particle classes in the range 30 nm - 10 µm. The size classified samples are analyzed by means of SEM/EDS and XRD to determine the characteristic chemical composition of the different fractions. Understanding the evolution, evaporation, and condensation of particulates in the cell emissions under different operational conditions may facilitate new standards for environmental friendly and energy efficient high amperage electrolysis cells

Particulate emissions from electrolysis cells

In the dry cleaning of the exhaust gas from the aluminium cells impurities are accumulated in the finer fractions of secondary alumina from the dry scrubbers. The present work describes new methods for the determination of dust composition, aiming at increasing the understanding of the effect of cell operation on the amount and the composition of dust in the fume. New and advanced analysis methods are used to characterize a broad specter of emissions. An Electrical Low Pressure Impactor is used to sample and analyze the dust from the cells. The equipment enables real-time particle size distribution analysis of 12 particle classes in the range 30 nm - 10 µm. The size classified samples are analyzed by means of SEM/EDS and XRD to determine the characteristic chemical composition of the different fractions. Understanding the evolution, evaporation, and condensation of particulates in the cell emissions under different operational conditions may facilitate new standards for environmental friendly and energy efficient high amperage electrolysis cells