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

A study of anode baking gas composition

The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-319-72284-9_180A method has been developed to measure gas composition inside the pit in open anode baking furnaces. The gas composition can be used to understand attack on and degradation of the refractory lining, baking behavior and combustion energy contribution through the baking cycle. A probe was installed in the packing coke near the bottom of the pit while extracting gas over several days with continuous analysis with an FTIR spectrometer. The results show a clear temperature dependence of CO and CO2 composition. Methane was found to be the dominating gas species at the beginning of the measuring cycle. Fluoride gases was also present, indicated by reactions with the glass wool filter to yield SiF4 that was detected in small amounts. PAH condensates were observed but not systematically determined in the present campaign. Earlier results from PAH measurements before the scrubbing, showing large fluctuations, will be discussed in relation to present findings.acceptedVersio

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

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.acceptedVersionCopyright © 2011 The Minerals, Metals & Materials Society. This is the authors manuscript to the article

Improved cyclability of Nickel-rich layered oxides

This study compares the physico- and electro- chemical properties of LiNi0.8Mn0.10Co0.1O2 (NMC811) and LiNi0.83Mn0.06Co0.09Al0.1O2 (NMCA) prepared by an oxalic acid co-precipitation. Deposition of a SiO2 surface coating was attempted via reaction of the powder with an amino silane prior to the final heat treatment. It was found that either the presence of small amounts of Al3+, or the compositional gradient resulting from a two step co-precipitation, caused increased crystal growth of the NMCA in comparison to NMC811. This led to improved cyclability in LP40 electrolyte. However, the SiO2 coating appeared incomplete and negatively impacted performance. Crystal cleavage preferably on the {001} planes was observed after 100 charge-discharge cycles, Downloaded from https://www.cambridge.org/core. SINTEF, on 13 Jun 2020 at 10:36:09, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2020.90 with consequent cathode electrolyte interphase formation in the crystal cracks. This is believed to cause capacity decay via lithium loss, and increased charge transfer resistance. An FEC based electrolyte improved the cyclability in all cases and even under extreme conditions (45°C and upper cycling potential of 4.5 V) NMCA showed a capacity retention of 85% after 100 cyclespublishedVersio

Validation of Online Monitoring of PFC by QCL with FTIR Spectroscopy

Monitoring of perfluorocarbon (PFC) evolution from aluminium smelting is gaining attention, not only because of their high greenhouse gas potentials but also due to process optimization purposes. Conventionally, PFC monitoring has been conducted by extractive sampling and subsequent analysis by fourier transform infrared (FTIR) spectroscopy. With FTIR, the quantification can be performed by IR spectral features specific for PFC. The downside is a requirement of gas scrubbing to remove HF detrimental to the instrument as well as relatively poor gas dynamics due to the large internal gas volume of the instrument. With emerging quantum cascade laser (QCL) technology, online monitoring can now be conducted with duct mounted lasers with calcium fluoride optical windows. However, due to a strong spectral overlap of CF4 and other gas constituents present in the process (e.g. methane), the QCL instruments currently suffer from some cross-interference. In this work, QCL single cell PFC monitoring has been validated by simultaneous monitoring with FTIR.acceptedVersio

In situ monitoring of pit gas composition during baking of anodes for aluminum electrolysis

Carbon anodes, which are consumed in aluminum electrolysis, are fabricated in separate anode plants where coke and pitch are mixed and vibrocompacted to green anode blocks before being baked in anode baking furnaces. The chemical environment inside an anode baking furnace is found to play an important role in the degradation of the furnace refractory lining. In this work, the pit gas composition was recorded during anode baking by a Fourier transformed infrared spectroscopy (FTIR) spectrometer and a gas chromatograph. The temperature dependence of the concentration of gas species during baking was obtained based on three measurement campaigns. The concentrations of CO and CO2 were found to be dependent on temperature, where the concentration of CO peaked around the maximum firing temperature. In addition to varying concentrations of CH4 and HF, water was found in large amounts in the first part of the baking cycle. The water originates to some extent from the cooling of the green anodes after vibrocompaction and is potentially important with respect to the chemical stability of the refractory lining. The variations in pit gas composition are related to operational parameters and are discussed in relation to refractory degradation phenomena

Extent of Ore Prereduction in Pilot-scale Production of High Carbon Ferromanganese

Three pilot-scale experiments have been conducted at SINTEF/NTNU in a 440 kVA AC electric furnace to demonstrate the process operation, energy requirements and CO2 emissions in the production of high carbon ferromanganese alloys. Comilog, UMK and Nchwaning (Assmang) ores blended with other materials, such as sinter and flux, thus achieving different charge mixtures have been utilized in the experiments. In the prereduction zone, higher manganese oxides in the ore are reduced to MnO through solid-gas exothermic reactions and at a temperature around 800oC, the unwanted endothermic Boudouard reaction is also active. As such, the total coke and energy consumption is highly dependent on if the prereduction occurs by CO gas or solid C. The pilot furnace has been excavated after each experiment and the extent of prereduction of the ore has been investigated by collecting samples from specific regions in the prereduction zone. In addition, material, and energy balance calculations for the three pilot experiments have been calculated using HSC Chemistry software. The HSC material and energy balance calculations have shown that the slag/alloy ratios, metal analyses, carbon consumption and the overall energy consumption are mainly affected by the composition of the charge mixtures. The relationship between the specific carbon consumption, the off-gas CO2/(CO2+CO) ratio and energy consumption to produce 1 tonne of HCFeMn alloy is discussed for the three different pilot-scale scenarios

A study of anode baking gas composition

A method has been developed to measure gas composition inside the pit in open anode baking furnaces. The gas composition can be used to understand attack on and degradation of the refractory lining, baking behavior and combustion energy contribution through the baking cycle. A probe was installed in the packing coke near the bottom of the pit while extracting gas over several days with continuous analysis with an FTIR spectrometer. The results show a clear temperature dependence of CO and CO2 composition. Methane was found to be the dominating gas species at the beginning of the measuring cycle. Fluoride gases was also present, indicated by reactions with the glass wool filter to yield SiF4 that was detected in small amounts. PAH condensates were observed but not systematically determined in the present campaign. Earlier results from PAH measurements before the scrubbing, showing large fluctuations, will be discussed in relation to present findings