Oxy-Coal Combustion: Submicrometer Particle Formation, Mercury Speciation, And Their Capture

Energy is the issue of great importance at the present. Coal, the cheapest and the most abundant reserve fossil fuel, is currently one of the most widely used energy source globally and will continue to be in the foreseeable future. The use of coal has also posed many world-wide environmental challenges, including the control of particulate matter, mercury, and trace metals, and carbon oxide: CO2) emissions. The rising of CO2 level in the atmosphere due to burning of fossil fuels is one of the major factors contributing to the global climate change. Capturing CO2 from coal combustion exhaust has been receiving significant attention; however, the volume fraction of CO2 in conventional coal combustion system: with air) ranges only 13%-15%, making it difficult to cost-effectively design the systems. Oxy-coal combustion or O2/CO2 recycled coal combustion is one of the promising techniques to overcome the limitation of low CO2 concentration in the exhaust. Before this technology can be employed, the effects of oxy-coal combustion on the pollutants associated with coal combustion, including fine particle, gaseous mercury and heavy metal emissions, need to be established. In addition, the influences of oxy-coal combustion on the performance of the current pollution control technologies, such as an electrostatic precipitator: ESP), need to be addressed. This dissertation investigated two aspects of coal combustion process:: 1) pollutant formation, specifically submicrometer particles and mercury, and: 2) pollutant control. The first part of dissertation addresses the impact of oxy-coal combustion on the formation submicrometer particles and the speciation of gaseous mercury. The second part focuses on the performance of two pollutant control technologies, including an ESP for capturing submicrometer particles and nano-structured TiO2 with UV irradiation for mercury capture. The findings presented here can be broadly divided into three parts. The first part reports the influence of oxy-coal combustion on submicrometer particle formation and capture using an ESP. The second part addresses the impacts of oxy-coal combustion on mercury speciation. The third part investigates the performance of nano-structured sorbent for capturing mercury and controlling heavy metal emissions from combustion process. The findings presented here can be used as a guideline for proper operation and control of pollutants generated from both oxy-coal and conventional combustion systems

Homogeneous Mercury Oxidation under Simulated Flue Gas of Oxy-coal Combustion

This study investigated the effects of oxy-coal combustion on Hg-oxidation by HCl using simulated flue gas. Experiments were conducted with different carrier gases that one might find in oxy-coal combustion and conventional coal combustion. The extents of Hg-oxidation in pure CO2, pure N2 and air were also studied for comparison. Our experimental results demonstrated that CO2 weakly assisted Hg-oxidation by HCl; however, its significance was outweighed by the presence of O2. For all carrier gases, the presence of NO or H2O inhibited Hg-oxidation. The inhibitory effects strongly depended on concentrations of NO, but not moisture content. The synergistic inhibitory effects were shown when both NO and H2O were present together. The extents of Hg-oxidation were not significantly different for O2-N2, O2-N2-CO2 and O2-CO2 gas mixtures for all conditions investigated in this study

Removal of Humic Acid by Photocatalytic Process: Effect of Light Intensity

Humic acid is commonly found in natural water as it is one of the by-products from decomposition of plants and animal residues. In a conventional water treatment process, which chlorine is common used as a disinfectant, the presence of humic acid could lead to the formation of carcinogenic substances, such as trihalomethanes and haloacetic acids. Thus, removal of humic acid from raw water before disinfection process is necessary. Photocatalytic reaction using Titanium Dioxide (TiO2) as a catalyst is one of the most effective techniques for degrading humic acid. The efficiency of this process depends on several factors; and, one of these factors is light intensity. This research investigated the effect of light intensity (35, 225 and 435 µW/cm2) and studied kinetic of photocatalytic degradation of humic acid, using commercial TiO2 Degussa P25 as a photocatalyst. Concentration of humic acid in water was monitored using UV254 absorbance and concentration of total organic compound was measured using a Total Organic Carbon Analyzer (TOC) every 30 min. The results showed that the removal efficiency of humic acid increased with increasing light intensity and then becoming asymptotic. At light intensity of 435 µW/cm2 and initial humic acid concentration of 4 mg/L with TiO2 loading of 100 mg/L was found to have highest removal efficiency, nearly 95% of humic acid measured by UV254; however, the removal efficiency of total organic compound was found only 20%. The photocatalytic degradation rate of humic acid was followed by Langmuir - Hinshelwood (L-H) kinetic models, and the reactivity constant kL–H values for the light intensity of 35, 225 and 435 µW/cm2 were found as 0.049, 0.152 and 0.178 mg L-1 min-1, respectively

Seasonal Ammonia Emissions from a Free-Stall Dairy in Central Texas

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Removal of Humic Acid by Photocatalytic Process: Effect of Light Intensity

Humic acid is commonly found in natural water as it is one of the by-products from decomposition of plants and animal residues. In a conventional water treatment process, which chlorine is common used as a disinfectant, the presence of humic acid could lead to the formation of carcinogenic substances, such as trihalomethanes and haloacetic acids. Thus, removal of humic acid from raw water before disinfection process is necessary. Photocatalytic reaction using Titanium Dioxide (TiO2) as a photocatalyst is one of the most effective techniques for degrading humic acid. The efficiency of this process depends on several factors; and, one of these factors is light intensity. This research investigated the effect of light intensity (35, 225 and 435 mu W/cm(2)) and studied the kinetic of photocatalytic degradation of humic acid, using commercial TiO2 Degussa P25 as a photocatalyst. The concentration of humic acid was monitored by using UV254 absorption technique and the concentration of total organic compound was measured using a Total Organic Carbon Analyzer (TOC) every 30 min. The results showed that the removal efficiency of humic acid increased with increasing light intensity and then becoming asymptotic. At light intensity of 435 mu W/cm(2) and initial humic acid concentration of 4 mg/L with TiO2 loading of 100 mg/L, the highest humic acid removal efficiency was found at 99%; however, the removal efficiency of the total organic compound was found only 20%-indicating incomplete mineralization to the end product. The kinetic of the humic acid degradation process was further explained using a Langmuir -Hinshelwood (L-H) model. The reaction rate constants (k(L)-(H)) at the light intensity of 35, 225 and 435 mu W/cm2 were 0.049, 0.152 and 0.178 mg L-1 min(-1), respectively; while the adsorption coefficients (K-ads) were relatively unchanged with light intensity. These findings imply that light intensity has an effect only on the oxidation process

Removal of Humic Acid by Photocatalytic Process: Effect of Light Intensity

Humic acid is commonly found in natural water as it is one of the by-products from decomposition of plants and animal residues. In a conventional water treatment process, which chlorine is common used as a disinfectant, the presence of humic acid could lead to the formation of carcinogenic substances, such as trihalomethanes and haloacetic acids. Thus, removal of humic acid from raw water before disinfection process is necessary. Photocatalytic reaction using Titanium Dioxide (TiO2) as a photocatalyst is one of the most effective techniques for degrading humic acid. The efficiency of this process depends on several factors; and, one of these factors is light intensity. This research investigated the effect of light intensity (35, 225 and 435 mu W/cm(2)) and studied the kinetic of photocatalytic degradation of humic acid, using commercial TiO2 Degussa P25 as a photocatalyst. The concentration of humic acid was monitored by using UV254 absorption technique and the concentration of total organic compound was measured using a Total Organic Carbon Analyzer (TOC) every 30 min. The results showed that the removal efficiency of humic acid increased with increasing light intensity and then becoming asymptotic. At light intensity of 435 mu W/cm(2) and initial humic acid concentration of 4 mg/L with TiO2 loading of 100 mg/L, the highest humic acid removal efficiency was found at 99%; however, the removal efficiency of the total organic compound was found only 20%-indicating incomplete mineralization to the end product. The kinetic of the humic acid degradation process was further explained using a Langmuir -Hinshelwood (L-H) model. The reaction rate constants (k(L)-(H)) at the light intensity of 35, 225 and 435 mu W/cm2 were 0.049, 0.152 and 0.178 mg L-1 min(-1), respectively; while the adsorption coefficients (K-ads) were relatively unchanged with light intensity. These findings imply that light intensity has an effect only on the oxidation process