A mathematical modeling framework for the methane steam reforming reaction operating in steady state has been developed. Performances are compared between the classic catalytic packed bed reactor and a Pd-based catalytic membrane reactor. Isothermal simulations on MATLAB © has first been conducted and show a higher performance of the membrane reactor over the packed bed reactor. Methane conversion of 1 can be reached for lower temperatures than used with industrial PBR, and better performances are shown for an increase in the operating pressure. Optimum conditions were defined for Temperature (500-600 Celsius), reaction side pressure (16-40 bars), membrane thickness (1-7 micrometers), steam/methane ratio (3-4), reactor length (5-10 meters) and permeate sweep ratio (20 or more). This model was validated by multiple recognized sources. Adiabatic simulations were conducted in order to develop a mathematical model base for non-isothermal simulations. The membrane reactor is again showing a higher conversion of methane compared to the packed bed reactor, however the heat loss due to the membrane and the hydrogen leaving through the tube is decreasing the performances of the MR over the PBR compared to the isothermal case. Results show also that most of the reaction occurs at the very beginning of the reactor.

No description available.

No description available.

Cleats are natural fractures in coal that serve as permeability avenues for darcy flow of gas and water to the well bore during production. Theoretically, the development of cleat and coal-seam permeability is related to the rank, type and grade of the coal concerned. The permeability of a coal seam, moreover, may change during gas production, due to either matrix shrinkage, cleat closure or both. Matrix shrinkage and cleat closure are also affected by numerous geological factors, including coal rank, desorption character and geological setting. A method integrating geochemical and petrographic analysis, reservoir engineering diagnosis, geophysical data and production characteristics has been developed, and used to determine the initial permeability of coal seam on a metre by metre scale. This overcomes the constraint of conventional well test by refining the test intervals. The effect of coal rank, grade and type on the initial permeability of coal seams was also investigated, with the special reference to the coals of the Galilee Basin. The permeability was estimated using analytical equations based on the permeability data obtained from well tests and from cleat descriptions within the seam section. This aspect of the study showed that the coal type, rank and grade strongly influence the initial permeability of individual coal seams. Increase in ash content has negative effect on cleat development and permeability. On contrast, increasing coal rank and proportion of bright coal lead to reduction in cleat spacing and increase in permeability. Twenty three core samples collected from the Qinshui Basin in China were evaluated in the laboratory to investigate the effects of coal grade, rank and type on the change in permeability during pressure depletion. The experimental factors included the coal's geochemical properties, the permeability against changing pressure, and strain with pore pressure depletion. This part of the study fund that permeability changes with pore pressure depletion in relation to coal rank, grade and type. The strain values determined by the experiments with pressure depletion were used to identify the mechanical principles associated with changes in permeability during pressure depletion in relation to the rank, grade and type of the coal concerned. A reservoir simulation study was used to investigate the effects of desorption pressure, geological setting and coal rank on the variation in permeability under in-situ conditions during coalbed methane production, based on a study in the Hedong area, Ordos Basin, China. The simulations allowed history matching of gas and water production from 12 wells with the actual well conditions specified as the model pressure. Good agreement was achieved between the model yields and the actual production data, suggesting that the changing permeability interpreted from the simulation is a realistic representation of the in-situ reservoir properties. The reservoir simulation study found that the decreases in permeability with production exceeded the increase in permeability caused by matrix shrinkage for nearly all wells in the Hedong area. The magnitude of the decrease in permeability increases as the gap between initial pressure and desorption pressure increases. The decrease in permeability is slower in the zone closest to the fault. The reservoir simulation has demonstrated that coal rank influences significantly the change in permeability during coalbed methane production.

We develop and use a new version of the Terrestrial Ecosystem Model (TEM) to study how rates of methane (CH4) emissions and consumption in high-latitude soils of the Northern Hemisphere have changed over the past century in response to observed changes in the region’s climate. We estimate that the net emissions of CH4 (emissions minus consumption) from these soils have increased by an average 0.08 Tg CH4 per year during the 20th century. Our estimate of the annual net emission rate at the end of the century for the region is 51 Tg CH4 per year. Russia, Canada, and Alaska are the major CH4 regional sources to the atmosphere; responsible for 64%, 11%, and 7% of these net emissions, respectively. Our simulations indicate that large inter-annual variability in net CH4 emissions occurred over the last century. If CH4 emissions from the soils of the pan-Arctic region respond to future climate changes as our simulations suggest they have responded to observed climate changes over the 20th century, a large increase in high latitude CH4 emissions is likely and could lead to a major positive feedback to the climate system. / Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/). / This study was supported by a NSF biocomplexity grant (ATM-0120468), the NASA Land Cover and Land Use Change Program (NAG5-6257), and by funding from MIT Joint Program on the Science and Policy of Global Change, which is supported by a consortium of government, industry and foundation sponsors.

This research was aimed at investigating a counter-diffusive catalytic reactor for mitigation of methane and BTEX emissions from the natural gas dehydration process. A commercial radiant heater unit was used in the experiments and the effect of methane flow rate on its conversion was studied. Methane conversion decreased with increasing methane feed rate. It was found that the external diffusion of oxygen through the boundary layer was the limiting factor in the system. Complete methane conversion was achieved when the oxygen diffusion limitation was overcome by inducing convective air flux in the boundary layer in front of the catalyst pad. To simulate natural gas dehydration emissions, which contain excess amount of water, the effect of addition of liquid water and water vapor on methane combustion was also studied. Small volumes of liquid water did not affect the methane combustion, however, at 2 g/min liquid water, which is comparable to the amount of water produced during the reaction, combustion was inhibited. Added water vapor did not show any influence on combustion efficiency. The presence of pentane and toluene, representing the non-aromatic hydrocarbons and BTEX substances in the emissions, inhibited methane conversion due to the competition for oxygen since pentane and toluene are easier to oxidize compared to methane. Two-dimensional modeling of the radiant heater system was conducted using the COMSOL Multiphysics software package. Comparing the model data for methane conversion with experimental results revealed similar decreasing trend in conversion with increasing the methane flow rate; however, the model under-predicted the conversion. Increasing the mass transfer coefficient, resulted in improved methane conversion, confirming the dominance of mass diffusion limitation in the system. In fact, the real mass transfer coefficient was 1.5-2 times higher than the values originally used in the model. Changing the kinetic parameters did not significantly improve the conversion leading to the conclusion that the catalytic radiant heater system is not kinetically controlled. Developing the three-dimensional model of the system in Fluent revealed that the fuel distribution in the system is not a significant factor, in agreement with experimental observation. / Chemical Engineering

Thesis (Ph. D.)--College of William and Mary. / Vita. Includes bibliographical references.

A greenhouse study was conducted to investigate the mechanisms causing diurnal variations in methane emission from rice plants (Oryza sativa L.). Methane emission was measured using a closed chamber system on individual rice plants at five stages of development. The role of the rice plant as the primary methane transport component was examined by comparing emission from intact plants to plants severed above and below the water. No diurnal variations were present in the severed plants and the emission was greatly reduced when compared to the intact plant. Results from the vascular transport experiment showed that transpiration is a major factor in methane emission. Emission dependence on soil temperature was examined to test the hypothesis that soil temperature affects emission. With some plants, soil temperature was held constant using a water bath, otherwise the soil temperature was allowed to vary with environmental conditions in the greenhouse. Diurnal variations in emissions were higher for plants with uncontrolled soil temperature than for plants with controlled soil temperature. Soil temperature at a 5 cm depth explained 46% of the emission variation. Soil temperature affects the source of methane in the soil while transpiration promotes the uptake of water and subsequently the emission of methane. Methane emission was negatively correlated with biomass, probably due to effects of root biomass on soil water methane concentration. Methane concentration in soil water was negatively correlated with root biomass, most likely due to increases in soil oxidation with increasing biomass in a fixed soil volume, and change in root conductance with age.

Heavy-duty natural gas engines offer air pollution and energy diversity benefits. However, current homogeneous-charge lean-burn engines suffer from impaired efficiency and high unburned fuel emissions. Natural gas direct-injection engines offer the potential of diesel-like efficiencies, but require further research. To improve understanding of the autoignition and emission characteristics of natural gas direct-injection compression-ignition combustion, the effects of key operating parameters (including injection pressure, injection duration, and pre-combustion temperature) and gaseous fuel composition(including the effects of ethane, hydrogen and nitrogen addition) were studied. An experimental investigation was carried out on a shock tube facility. Ignition delay, ignition kernel location, and NOx emissions were measured. The results indicated that the addition of ethane to the fuel resulted in a decrease in ignition delay and a significant increase in NOx emissions. The addition of hydrogen to the fuel resulted in a decrease in ignition delay and a significant decrease in NOx emissions. Diluting the fuel with nitrogen resulted in an increase in ignition delay and a significant decrease in NOx emissions. Increasing pre-combustion temperature resulted in a significant reduction in ignition delay, and a significant increase in NOx emissions. Modest increase in injection pressure reduced the ignition delay; increasing injection pressure resulted in higher NOx emissions. The effects of ethane, hydrogen, and nitrogen addition on the ignition delay of methane were also successfully predicted by FlameMaster simulation. OH radical distribution in the flame was visualized utilizing Planar Laser Induced Fluorescence (PLIF). Single-shot OH-PLIF images revealed the stochastic nature of the autoignition process of non-premixed methane jets. Examination of the convergence of the ensemble-averaged OH-PLIF images showed that increasing the number of repeat experiments was the most effective way to achieve a more converged result. A combustion model, which incorporated the Conditional Source-term Estimation(CSE) method for the closure of the chemical source term and the Trajectory Generated Low-Dimensional Manifold (TGLDM) method for the reduction of detailed chemistry, was applied to predict the OH distribution in a combusting non-premixed methane jet. The model failed to predict the OH distribution as indicated by the ensemble-averaged OH-PLIF images, since it cannot account for fluctuations in either turbulence or chemistry.

Northern peatlands play a significant role in the global carbon (C) cycle by functioning as sources of atmospheric methane (CH4). Peatlands are becoming polluted as a result of nitrogen (N) deposition, which is likely to impact CH4 dynamics. This thesis presents research at the Mer Bleue bog (Ottawa, Canada) in the longest known simulated atmospheric nutrient deposition experiment. After 8 years of simulated N (and other nutrient) deposition, activities of microbial communities involved in CH4 cycling have been analyzed in the laboratory and CH4 fluxes measured using chamber techniques in the field. High rates (>10 times ambient deposition) of simulated N deposition decreased CH4 production, and enhanced CH4 oxidation in vitro. However, in situ CH4¬ emissions were greater in the high N plots. I hypothesize that CH4 production is therefore driven by short-lived root exudates in the field, consistent with increased shrub biomass that occurs concomitantly with high N deposition.