SUBSTANTIATING A MECHANISM TO INCREASE THERMAL RESOURCE OF WATER-BEARING LEVELS AT THE EXPENSE OF UNDERGROUND COAL COMBUSTION

Objective is to study a mechanism increasing thermal resource of water-bearing levels at the expense of underground coal combustion

SENSITIVE ANALYSIS OF A COAL COMBUSTION MODEL ON A DROP TUBE FURNACE

In the present work a one-dimensional model for coal combustion in a Drop Tube Furnace (DTF) is developed. The equations that characterize the flow, heat transfer phenomena and coal combustion reactions are programmed in a FORTRAN90 language code. The results are compared with a reference model and experimental data, showing good agreement. A sensitivity study is performed to understand the behavior of coal combustion due to changes of some working parameters of the DTF. From the variation of the oxygen concentration, working temperature and input flow rates the response of the coal combustion in terms of unburned fraction can be obtained

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

A Reduced Order Model for the Design of Oxy-Coal Combustion Systems

Oxy-coal combustion is one of the more promising technologies currently under development for addressing the issues associated with greenhouse gas emissions from coal-fired power plants. Oxy-coal combustion involves combusting the coal fuel in mixtures of pure oxygen and recycled flue gas (RFG) consisting of mainly carbon dioxide (CO2). As a consequence, many researchers and power plant designers have turned to CFD simulations for the study and design of new oxy-coal combustion power plants, as well as refitting existing air-coal combustion facilities to oxy-coal combustion operations. While CFD is a powerful tool that can provide a vast amount of information, the simulations themselves can be quite expensive in terms of computational resources and time investment. As a remedy, a reduced order model (ROM) for oxy-coal combustion has been developed to supplement the CFD simulations. With this model, it is possible to quickly estimate the average outlet temperature of combustion flue gases given a known set of mass flow rates of fuel and oxidant entering the power plant boiler as well as determine the required reactor inlet mass flow rates for a desired outlet temperature. Several cases have been examined with this model. The results compare quite favorably to full CFD simulation results

Fine Particle and Mercury Formation and Control during Coal Combustion

Pulverized coal combustion is widely used worldwide for the production of electricity. However, it is one of the primary emission sources of air pollutants, including particulate matter (fly ash) and mercury (Hg), into the atmosphere. This dissertation investigated three aspects of pollutant formation and control from the coal combustion process: (1) organic aerosol formation during coal combustion, (2) mercury removal during coal combustion by injection of Vanadium Pentoxide (V2O5), and (3) submicrometer particle formation during oxy-coal combustion. Part. 1. While the characterization and formation of the mineral matter component of aerosol during coal combustion has been well studied and understood, the characterization and fate of corresponding organic matter content was not examined in detail earlier. The first part of this dissertation studies the formation mechanism of organic aerosols during coal combustion. Pilot-scale experiments were conducted in a 1 MW coal combustor, and showed that black carbon aerosol formation was greatly enhanced by increasing the fuel-air equivalence ratio. However, organic carbon aerosol formation was lowered by increasing the fuel-air equivalence ratio, which was opposite to the trend of black carbon aerosol formation. This phenomenon indicates that the formation mechanism of organic carbon aerosol is different from black carbon (soot) aerosol. Detailed organic aerosol formation mechanisms have been studied in a laboratory-scale system. Aerosol mass spectrometry techniques were applied to characterize both coal combustion aerosols from a drop-tube coal combustor and coal pyrolysis products from a flat-flame coal pyrolyzer. The chemical composition of major species for both combustion organic aerosols and pyrolysis products are hydrocarbons, carboxylic acids and aromatic compounds. The similarities of the chemical compositions demonstrate that the products from coal pyrolysis, (the initial step of coal combustion), are the precursors of organic aerosols. More carboxylic acids and oxygenated organic compounds were found in the combustion aerosols, indicating that many pyrolysis products are oxidized before they are converting to organic aerosols. A strong correlation between inorganic and organic aerosol formation mechanisms has been found in this work, demonstrating that inorganic particles play a critical role as carriers of organic species. Sulfate species in inorganic aerosols play a particularly important role in organic aerosol formation. Enhanced organic aerosol formation during the combustion of high sulfur content coal has been observed for the first time. High resolution mass spectra analysis shows the presence of amine-like organics in the aerosols. The correlation between particulate sulfate and organics suggests that acidic sulfate particles may absorb basic amine-like organics, a major coal pyrolysis product, from the gas phase into the particle phase via acid-base neutralization reactions. Part. 2. Coal combustion is a major source of atmospheric mercury. High-temperature sorbent injection is an efficient method to capture metallic species during combustion. This part of the study examines the performance on Hg capture from pulverized coal combustion in a drop-tube furnace. V2O5 was tested as a sorbent and demonstrated good performance on elemental mercury capture, which results from the formation of ultrafine V2O5 particles during the combustion process. It is proposed that the ultrafine V2O5 particles catalyzed Hg0 oxidation on their large surfaces. Hg2+, the oxidation product, may condense on fly ash particle surfaces or on tubing surfaces, thereby being removed from the flue gas. Part. 3. Coal combustion is the largest single contributor to global anthropogenic CO2 emissions. Oxy-coal combustion replaces the air with oxygen and uses recycled flue gas (RFG) as a diluent, resulting in a higher concentration (\u3e98%) of CO2 in the exhaust, which promotes more effective control, capture, and possible conversion of CO2. This part of the dissertation investigates the effects of recycling (up to recycle ratios of 60%) on submicrometer particle formation in a drop-tube furnace system. The recycled exhaust gas containing lower O2 concentration and higher CO2 concentration suppressed submicrometer particle formation. However, it was found that water vapor in recycled exhaust gas greatly enhanced the formation of submicrometer particles. The gas composition changes that result from exhaust-gas recycling significantly affected the size distribution of submicrometer particles at the exit of the combustor. Differences in the particle size distribution with and without the filtration of recycled exhaust gas were insignificant. The composition of the resultant particles in oxy-coal combustion and conventional coal-air combustion as determined by X-ray diffraction was similar

HYDRODYNAMIC CHARACTERISTICS AND COAL COMBUSTION MODELING OF A HIGH VELOCITY FLUIDIZED BED (SOLIDS FRICTION FACTOR, TWO PHASE FLOW, PRESSURE PROFILE, FAST)

A Loop Fluidized Bed (LFB) based on the fast fluidization concept is a novel method for effective solid-gas contact and can play an important role in coal combustion. It can be operated under pressure making it eminently suited for the production of high temperature gas from coal for operating gas turbines for power generation. The LFB can operate over a wide range of gas flow rates and coal can be introduced at various points without excessive pressure drops. Further, it is possible to capture higher amounts of sulfur dioxide due to the use of fine dolomite or limestone particles. This process can also be used for the smelting of mineral ores. However, the LFB concept is relatively new and data in the literature are scarce. In this study a bench scale loop fluidized bed has been designed, fabricated and installed. The unit has been operated using sand, limestone, and gypsum particles. The latter two solids are chosen because of their presence in the coal combustion process for sulfur removal. Data have been collected to study the effect of particle size, particle density, air flux, and solid flux on fluidizing characteristics of the three solids. Extensive data have been obtained to study the effect of particle size, particle density, air flux, and solids flux on fluidizing characteristics of sand, limestone, and gypsum. It is found that solids flow behavior was sensitive to nozzle positions and air flow rates. Three dimensional plots have been prepared for predicting good operating regions for the LFB with respect to nozzle combination, air flow rate and riser solids fraction. Pressure drop data have been correlated with solids velocity and solids fraction to obtain a better solids friction factor equation than available in the literature. A computer program has been developed to predict the static pressure of every point in the LFB. The computer program predictions and the static pressure data show good agreement. Coal combustion and sulfur removal models for the LFB coal combustor have been developed. The predictions from these models agree with commercial data. A conceptual LFB coal combustor has been designed and the results have been compared with commercial coal combustion data. The LFB coal combustion process is found to provide better coal combustion and sulfur removal effectiveness than bubbling bed coal combustion and pulverized coal combustion with limestone injection processes

Estimating Global Environmental Implications of Agricultural Trade Liberalization: A Computable General Equilibrium Analysis

Preliminary results indicate a reduction in agricultural trade barriers offers some benefits to poorer nations at the expense of some richer nations. A positive externality if trade liberalization is a decrease in coal combustion and a slight decrease in global CO2 emissions.Environmental Economics and Policy, International Relations/Trade,

Evaluation of Smoke Detectors for Mining Use

The U.S. Bureau of Mines has constructed a smoke chamber and developed sensitivity tests for smoke detectors. Response of ionization-and optical-type commercially available smoke detectors have been investigated. Six smoke detectors were measured with respect to visually obscuring smoke characterized by a corresponding optical density for smoldering and flaming coal combustion in the smoke chamber. It was determined that for one type of ionization smoke detector the alarm time was nearly equivalent to that of an odor monitor's alarm for smoldering coal combustion experiments and earlier for flaming coal combustion experiments. The experiments showed that an average CO concentration of 5 ppm corresponded to an optical density of 0.022 m-l for smoldering and flaming coal combustion. Two of the commercially available ionization-type smoke detectors were more responsive to flaming than smoldering coal combustion at an optical density of 0.022 m-l, whereas the optical smoke detectors showed the opposite trend. The responsive characteristics of the detectors evaluated with respect to known smoke conditions in the smoke chamber shows their potential for use as mine fire sensors or part of a mine atmospheric monitoring system to improve mine safety

Numerical Study of Single Coal Particle Combustion in O2/N2 and O2/CO2 Atmospheres

No abstract available

REVIEW OF CFD SIMULATION OF OXY-COAL COMBUSTION FOR ELETRICAL POWER GENERATION: OPPORTUNITIES AND CHALLENGES

The oxy-combustion has generated significant interested for reduction of CO2 emission when the fossil fuel is coal, due to simplification on the separation process of CO2 from the flue gas, it can be more easily stored in reservoir. The CFD numerical simulation techniques in oxy-coal combustion has the potential to contribute to designers in cost savings and reduced computational time; Furthermore, such techniques also provide a robust tool for better understanding and description of the aerothermodynamics processes involved, as well as, aiding the design of most efficient furnaces. However, to obtain representative results of the physical phenomena, the numerical models employed by CFD needs to be suitable for oxy-coal combustion. So, the aim of the paper is to carry out a review of the recent models that are being used for turbulence, combustion and pollutant emissions. Moreover, it is shown a comparison of different results obtained in the numerical simulation of oxy-coal combustion among new models, existing models and experiments. The analysis of the models and experiments shows that the challenges that are still being faced to obtain better accuracy of numerical simulation results. Improvements in the models for oxy-coal combustion can be seen like potential opportunities to investigate and optimize the process that occur in the combustion