Pollution is one of the greatest concerns with pulverized coal combustion. With tightening standards on pollution emissions, more information is needed to create better design models. Burner modifications are the most efficient changes that can be made to assure sufficient carbon burnout and low NOx emissions. Experiments were performed in the BYU Flat Flame Burner (FFB) lab, operating under fuel rich conditions for pyrolysis experiments and fuel lean conditions for char oxidation experiments. Effects of temperature, coal rank, residence time, and post flame oxygen content on mass release, nitrogen release, and reactivity were examined. Elemental and Inductively coupled plasma (ICP) analyses were used to determine the mass and nitrogen release of coals and chars. FT-IR was used to determine gas phase nitrogen compositions on selected experiments. Results of char oxidation experiments were fit to a first-order model to obtain an Arrhenius pre-exponential factor, while activation energies were approximated using a published correlation. CPD model calculations were used to find experimental residence times and particle diameters that obtained full pyrolysis yields. Oxy-fuel experiments were performed by switching the burner diluent gas from N2 to CO2. Oxy-fuel experiments exhibited a rank effect in nitrogen release. Bituminous coal tests showed no statistically significant difference in mass or nitrogen release between the two conditions. A sub-bituminous coal exhibited a greater mass and nitrogen release for the same residence time under the CO2 environment, which could be due to early gasification of the char. Two samples of a chemically treated coal with different additive concentrations were tested against an untreated sample for combustion enhancement. The treated samples showed an increase on the order of 15% absolute in pyrolysis yield compared to the untreated sample. An increase in reactivity on the order of 35% was observed for the higher concentrated sample, but not for the lower treatment concentration. Gas phase nitrogen measurements showed both HCN and NH3 at the 1300 K gas temperature condition. HCN and NH3 release during pyrolysis was largely rank dependent, with more HCN formed initially than NH3 for 5 of the 6 samples. However, a Polish bituminous coal was found to have more NH3 than HCN. These nitrogen species data can be used to evaluate or refine nitrogen transformation mechanisms.

Oxy-combustion is a developing technology that enables carbon dioxide (CO2) capture. Flame temperature and emissivity data were taken on a 150 kWth, pulverized-coal, burner flow reactor (BFR) that has been modified to run oxy-combustion with pure CO2 as simulated recycled flue gas. Data were taken at 78 conditions in which three parameters were varied, namely: the swirl angle of the fuel stream, the location of the oxidizer as it exited the burner, and the flow rate of diluent (pure CO2) added to the outer, secondary stream. At each condition, digital color images were obtained using a calibrated RGB camera. The images were used to determine lift-off length, temperature, and emissivity. The mathematical theory of two-color pyrometry and the calibration process used to measure the camera sensitivity is presented. The two most commonly used emissivity models in two-color pyrometry, the Hottel and Broughton and gray models, were investigated to determine which was the most appropriate for use in an oxy-coal flame. A significant difference of 7% in the temperature and 24% in the emissivity results were found when processing an image with the Hottel and Broughton and gray emissivity models. The Hottel and Broughton model was selected for processing, because the Hottel and Broughton model is more appropriate for soot which appeared to dominate flame emissions. Using the two-color data, several trends were documented. Flame temperature was seen to decrease with increasing CO2 flow rate. Within a given flame along the axial direction, temperature was seen to correlate with emissivity. As emissivity increased, flame temperature was seen to decrease. Many flames were lifted from the burner exit. Lift-off length was decreased and the flames became more attached by: 1) Increasing the amount of swirl given to the fuel stream, 2) Adding O2 to the center primary tube or 3) Decreasing the flow of secondary CO2. At higher center oxygen flow rates (above 8.5 kg/hr), the O2 jet velocity was large causing increased entrainment and mixing which degraded burner performance.

This work produced the retrofit of an air-fired, 150 kW reactor for oxy-combustion which was then used in three oxy-combustion studies: strategic oxy-combustion design, oxy-combustion of petroleum coke, and air versus oxy-combustion radiative heat flux measurements. The oxy-combustion retrofit was accomplished using a system of mass flow controllers and automated pressure switches which allowed safe and convenient operation. The system was used successfully in the three studies reported here and was also used in an unrelated study. A study was completed where a novel high oxygen participation burner was investigated for performance while burning coal related to flame stability, NO, and burnout using a burner supplied by Air Liquide. Parameters investigated included oxygen (O2) injection location, burner swirl number and secondary carbon dioxide (CO2) flow rate. The data showed swirl can be used to stabilize the flame while reducing NO and improving burnout. Center O2 injection helped to stabilize the flame but increased NO formation and decreased burnout by reducing particle residence time. Additional CO2 flow lifted the flame and increased NO but was beneficial for burnout. High O2 concentrations up to 100% in the secondary were accomplished without damage to the burner. Petroleum coke was successfully burned using the Air Liquide burner. Swirl of the secondary air and O2 injection into the center tube of the burner were needed to stabilize the flame. Trends in the data similar to those reported for the coal study are apparent. Axial total radiant intensity profiles were obtained for air combustion and three oxy-combustion operating conditions that used hot recycled flue gas in the secondary stream. The oxygen concentration of the oxidizer stream was increased from 25 to 35% O2 by decreasing the flow rate of recycled flue gas. The decrease in secondary flow rate decreased the secondary velocity, overall swirl, and mixing which elongated the flame. Changing from air to neat CO2 as the coal carrier gas also decreased premixing which elongated the flame. Flame elongation caused increased total heat transfer from the flame. The air flame was short and had a higher intensity near the burner, while high O2 concentration conditions produced lower intensities near the burner but higher intensities and temperatures farther downstream. It was shown that oxycombustion can change flame shape, temperature and soot concentration all influencing heat transfer. Differences in gas emission appear negligible in comparison to changes in particle emission.

This work evaluates the relative significance of forces determining the motion of a pulverized coal particle under conditions representative of a pressurized oxy-coal combustor. The gravity force and surface forces of drag, fluid stress, added mass, and Basset history are discussed and appropriate forms of these force equations are chosen, with a consideration of spherical and non-spherical drag and the Basset history kernel. Studies from the literature that emphasize specific forces are used to validate the implementation of the force equations and correlations. Modeling is based on time-averaged, one-dimensional motion of a single non-reacting particle along the centerline of a round, turbulent jet. The numerical methodology employed for solving the particle equation of motion is described in detail, and simulated particle motion is compared to experimental and high-fidelity simulations from the literature. Comparisons show the numerical methodology performs adequately relative to higher fidelity simulations and experimental test cases for one-dimensional, time-invariant conditions. To assess the effect of pressure on particle forces and motion under different conditions, simulation cases are run for particle diameters of 20 μm, 50 μm, 125 μm, gas temperatures of 300 K and 1500 K, and gas pressures of 1.01325 bar, 2 bar, 5 bar, 10 bar, 20 bar, 40 bar. Simulations are conducted over a 0.75-m length in a simplified environment representative of the pressurized oxy-coal (POC) combustor at Brigham Young University. Results show that all surface forces examined can be locally significant at high gas pressures when particle and gas velocity differences, i.e., particle Reynolds numbers, are greatest. The following trends are found for the behavior of surface forces in simplified, POC combustor simulations: 1) The quasi-steady drag force is always significant, though it's relative contribution to particle motion decreases as particles traverse regions with significant fluid velocity gradients or significant values for the substantial derivative of fluid velocity. Furthermore, quasi-steady drag is the only surface force that is significant throughout the entirety of a particle's trajectory. The relative contribution of the drag force decreases with increasing gas pressure. 2) The impact of the fluid stress force on particle motion increases with increasing gas pressure and particle size. The fluid stress force can be locally important for all of the particles sizes when at a gas temperature of 300 K and elevated pressure, as particles traverse regions with significant substantial derivatives of fluid velocity. The local impact of the fluid stress force is largely negligible at 1500 K, except for the case of the largest particle at the greatest pressure. 3) The behavior of the added mass force largely mirrors that of the fluid stress force, though the added mass force is generally of lesser magnitude. Therefore, the added mass force can be locally important for all of the particles sizes when at a gas temperature of 300 K and elevated pressure, as particles traverse regions with significant substantial derivatives of fluid velocity. The added mass force is generally the least significant of the analyzed surface forces. 4) The Basset history force is locally significant for all cases where the particles are traversing regions with significant fluid velocity gradients. The impact of the Basset history force on particle motion increases with increasing gas pressure and particle size, while decreasing as gas temperature increases.

Iron (Fe) oxy-hydroxides such as ferrihydrite (Fh) are ubiquitous in surface environments. Because of their high surface area and high reactive surface, they can immobilize environmental contaminants and nutrients (e.g., oxyanions) through adsorption. Ferrihydrite is metastable and eventually transforms to hematite (Hm), goethite (Gt), and lepidocrocite (Lp). Although the Fh formation and transformation and oxyanion adsorption on its surface have been separately studied, the coupled interaction of these processes is only partly understood. The impact of oxyanion surface complexes on the rate and pathway of Fh transformation was studied. Results show that AsO43- and SO42- inner-sphere complexes decrease the rate of Fh transformation and induce the formation of Hm. In contrast, NO3- outer-sphere complexes promote the formation of Gt. We then investigated the impact of oxyanion (AsO43- and PO43-) surface loading on the rate and pathway of Fh transformation. The results show that the rate of Fh transformation decreases, and more Hm forms with increasing the oxyanion surface loading. Cryogenic transmission electron microscopy (Cryo-TEM) was also used to study the effect of oxyanion surface complexes (NO3- and PO43-) on the nucleation and growth of Gt and Hm during Fh transformation. Our results show that Gt first was formed from Fh dissolution and then grew by oriented attachment. In contrast, Hm formed after the aggregation of Fh particles. We propose that NO3- outer-sphere complexes hydrate the surface and promote the Gt formation through a dissolution/crystallization pathway, while PO43- inner-sphere complexes dehydrate the surface and induce more Hm through an aggregation pathway. In the final project, we investigated the formation of Fh from Fe oxy-hydroxide clusters. The results showed that increasing pH increased the size and structural order of particles that resemble 2-line Fh. Also, the particle size of aged samples at pHs 1.5 and 2.5 increased with time, and they transformed to Gt and Lp. In this work, we develop new ways to study the formation and transformation of Fh. These methods and information can be used to develop further studies towards a comprehensive understanding of Fh formation and transformation in other environmental conditions, such as redox systems. / Doctor of Philosophy / Iron (Fe) oxy-hydroxides nanoparticles are composed of Fe, oxygen (O), and water (H2O). One of the most famous Fe nanoparticles is ferrihydrite (Fh), which is commonly found in soils, sediments, and water. Ferrihydrite surface is positively charged and adsorbs negatively charged ions such as oxyanions, which are important contaminants (e.g., arsenate; AsO43- and sulfate; SO42) and nutrients (e.g., phosphate; PO43- and nitrate; NO3-) in drinking water in the US and around the world. The structure of Fh is not stable, and it transforms to other Fe oxy-hydroxides such as goethite (Gt), hematite (Hm), and lepidocrocite (Lp). Pre-adsorbed oxyanions may release during Fh transformation and impact water and soil quality. Additionally, oxyanion adsorption may affect the formation and transformation of Fh, which is not fully understood. In this work, we investigate how oxyanions change the rate and pathway of Fh transformation. The results show that the strong binding of AsO43- and SO42- slows down the rate of Fh transformation and favors the formation of Hm as opposed to Gt. While weak adsorption of NO3- promotes the formation of more Gt. We also study the transformation of Fh in the presence of different oxyanions (AsO43- and PO43-) concentrations. The results show that the rate at which Fh transforms to Gt and Hm decreases, and more Hm forms with increasing the concentration of oxyanions on the Fh surface. Interestingly, results also show that weekly bounded NO3- and SO42- could be released to the solution phase, while strongly adsorbed AsO43- and PO43- could remain on the surface during the ferrihydrite transformation. We also used an imaging technique (Cryogenic transmission electron microscopy; Cryo-TEM) to study the effect of oxyanion surface complexes (NO3- and PO43-) on the formation and growth of Gt and Hm during the Fh transformation. The results show that Gt first was formed from Fh and then grew to larger particles. In contrast, for the formation of Hm, Fh particles first aggregate, form larger particles, and then transform to Hm. In the final project, we investigate the formation of Fh from Fe oxy-hydroxide cluster precursors. Results show that Fe oxy-hydroxide clusters can be the potential precursors for forming Fh during the rapid hydrolysis of Fe(III) solutions. However, when these precursors are aged, they do not form Fh and transform to Gt and Lp, which have stable structures. In this work, we develop new ways to study the formation and transformation of Fh, which will have implications for understanding how and when contaminant remobilization will occur during Fh formation and transformation.

A new method of power production, called pressurized oxy-fuel combustion, burns coal with CO2 and oxygen, rather than air, bringing us closer to the end goal of developing zero emission coal-fired utility boilers. However, high-pressure, high-temperature systems such as these are under-studied, and their behavior is difficult to measure. An accurate model for previously untested conditions requires data for validation. The heat release profile of flames and their radiative intensity is one of the key data sets required for model validation of an oxy-coal combustion system. A radiometer can be used to obtain the necessary radiative heat flux data. However, several studies show significant measurement errors of past radiometer designs. This work focuses on developing a narrow angle radiometer that can be used to describe radiative heat transfer from a pressurized oxy-coal flame. The sensitivity of the instrument to outside environmental influences is thoroughly examined, making it possible to obtain the axial radiative heat flux profile of the flame in a 100kW pressurized facility by accurately converting the measured quantities into radiative heat flux. Design aspects of the radiometer are chosen to improve the accuracy of radiative heat flux measurements as well as conform to the physical constraints of the 100kW pressurized facility. The radiometer is built with a 0.079-inch aperture, an 8.63-inch probe internally coated with high emissivity coating, four baffles spaced evenly down the length of the probe, no optic lens, a thermopile as the sensor, argon purge gas, and a water-cooled jacket. The radiometer has a viewing angle of 1.33 degrees. The instrument is calibrated with a black body radiator, and these calibration data are used in combination with radiation models to convert the radiometer signal in mV to radiative heat flux in kW/m2. Environmental factors affecting accuracy are studied. The results of the calibration data show that the radiometer measurements will produce a calculated heat flux that is accurate to within 5.98E-04 kW/m2.

The need for electric power across the globe is ever increasing, as is the need to produce electricity in a sustainable method that does not emit CO2 into the atmosphere. A proposed technology for efficiently capturing CO2 while producing electricity is pressurized oxy-combustion (POC). The objective of this work is to design, build, and demonstrate a burner for a 20 atmosphere oxy-coal combustor. Additionally, working engineering drawings for the main pressure vessel and floor plan drawings for the main pressure vessel, exhaust, and fuel feed systems were produced. The POC reactor enables the development of three key POC technologies: a coal dry-feed system, a high pressure burner, and an ash management system. This work focuses on the design of a traditional diffusion flame burner and the design of the main reactor. The burner was designed with the intent to elongate the flame and spread heat flux from the reacting fuel over a longer distance to enable low CO2 recycle rates. This was done by matching the velocities of the fuel and oxidizer in the burner to minimize shear between incoming jets in order to delay the mixing of the coal and oxygen for as long as possible. A spreadsheet model was used to calculate the jet velocities and sizes of holes needed in the burner, comprehensive combustion modeling was outsourced to Reaction Engineering International (REI) to predict the performance of burner designs. Using the guidance of the modeling results, a burner design was selected and assembled. The burner consists of a center tube where the primary fuel will flow, two concentric secondary tubes making an inner and an outer annulus, and eight tertiary lances. The burner and reactor are ready to be tested once issues involving the control system are resolved. Measurements that will be taken once testing begins include: axial gas and wall temperature, radiative heat flux, outlet gas temperature, and ash composition.

One of the challenges facing engineers is to provide clean, sustainable, affordable and reliable electricity. One of the major pollutants associated with coal combustion is CO2. A proposed technology for efficiently capturing CO2 while producing electricity is pressurized oxy-combustion (POC). The first objective of this work is to design, build and demonstrate an exhaust system for a 20 atmosphere oxy-coal combustor. The second objective of this work is to design and build mounts for a two-color laser extinction method in the POC. The POC reactor enables the development of three key technologies: a coal dry-feed system, a high pressure burner, and an ash management system. This work focuses on cooling the flue gas by means of a spray quench and heat exchanger; controlling the reactor pressure and removing ash from the flue gas. Designs and models of each component in the exhaust systems are presented. Methods to test and assemble each system are also discussed. The spray quench flow rate was measured as a function of pump pressure. Theoretical models for the required amount of water in the spray quench, the flue gas composition, the length and number of tubes in the heat exchanger, and the cyclone collection efficiency are presented. The combined exhaust system is assembled and ready to be tested once issues involving the control system and burner are resolved.

The goal of this thesis was to understand what parameters would be most impactful when delivering dry, pulverized coal in a dilute-phase, with a high-pressure feed-system to a pressurized oxy-combustion (POC) reactor. Many studies have conveyed materials in dense-phase plugs at high-pressure or in dilute-phase flows at atmospheric pressure. Very few studies have fluidized and conveyed materials in dilute-phase flows at high pressure, as we needed to. Additionally, studies which might have been applicable based upon system -pressure and -phase delivered findings that were empirically based and therefore not specifically applicable to non-similar systems. 220 different tests were ran using a bench-scale apparatus consisting of a hopper, connecting conveying pipes, and a filter point (representing the future reactor). The system was pressurized to 300 psi using CO2. Dry, pulverized coal with an average diameter of 50 microns and a bulk density of 800.9 kg/m3 was fluidized and conveyed with different combinations of fluidization inlet and fluidization outlet flowrates. Each specific flowrate combination was tested 3 to 5 times. The resulting coal flowrates were recorded and analyzed to see which flowrate combination delivered 13.6 kgs coal/hr and had the least variability between tests. The fluidization inlet and outlet flowrates, coal moisture content, and system geometry were key parameters. In a 2-inch diameter hopper the fluidization inlet flowrate should be kept at 0.119 m/s or below to keep the fluidization regime within the hopper below the transition point to the bubbling fluidization regime. This was beneficial since less CO2 was needed by the system and smaller perturbations within the bed didn't disrupt flow leaving the hopper. The fluidization outlet flowrate could still advance the fluidization regime within the hopper even if the fluidization inlet flowrate is kept at 0.119 m/s. For a ¼ inch diameter the outlet should be kept at 0.005 m/s or above. Additionally, the standard deviation in the measured coal flowrate decreased dramatically when flow of gas was allowed to exit through the top of the coal column (fluidization outlet). The standard deviation was 8.2 kg/hr with the fluidization outlet closed and 3.5 kg/hr with the fluidization outlet flowing to provide 0.005 m/s in the bed above the coal outlet. Coal should have a moisture content between 3% and 6% to ensure that electrostatic interactions between coal particles is kept to a minimum. Finally, these results were found for specific hopper and fluidization inlet and outlet diameters. If these diameters are changed then some calculation must be done for these results to be applicable to systems that are not like the one described later in this thesis.

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