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

Ethylene/Air diffusion flames were studied at sub and super-atmospheric pressures to simulate a microgravity environment at fuel flow rates of 0.482 mg/s and 1.16 mg/s. Flame properties including flame dimensions, soot formation, temperature, and attachment mechanisms were investigated. Overall, luminous flame height decreased with decreasing pressure to the point of visible luminosity disappearance, resulting in blue flames. Flame width increased with decreasing pressure until the flame was almost spherical. Soot formation decreased with decreasing pressure to negligible concentrations in a near vacuum. At 0.482 mg/s, the percentage of carbon converted into soot was between 0.01% and 0.12%, whereas at 1.16 mg/s, this percentage was between 0.5% and 11% at sub-atmospheric pressures. Maximum flame temperatures increased with decreasing pressure. Regardless of fuel flow rate, the diffusion flames remained attached to the exterior of the burner. This attachment point moved further down the burner exterior as pressure decreased until a near vacuum.

Techniques have been developed for measuring the temperature, stable species concentrations, and atomic radical concentrations during a transient combustion event. They combine the features of direct sampling with two spectroscopic techniques to produce relatively simple diagnostic techniques to obtain time-resolved measurements. In this study, a transient event was provided by a propagating hydrogen/air flame. Stable species were detected downstream of the sampling orifice by electron impact fluorimetry, while temperatures and atomic hydrogen concentrations were measured by atomic resonance absorption spectroscopy. The calculation of stable species concentrations from time-varying fluorescence signals was straightforward, however conversion from absorption measurements to temperatures and atomic radical concentrations required the development of a computer model of the radiation source and the absorption by the sample. The model of the source was validated by comparing predicted and recorded spectra of hydrogen Lyman-α emissions, while the absorption model for the sampled gas was tested by comparing the temperatures predicted by absorption measurements with those recorded at a range of known temperatures. These direct sampling spectroscopic techniques minimize time-history distortions inherent in other direct sampling techniques, and are capable of tracking local temperatures and species concentrations during the passage of a propagating flame front. / Graduation date: 1990

Ethylene/Air diffusion flames were studied at sub and super-atmospheric pressures to simulate a microgravity environment at fuel flow rates of 0.482 mg/s and 1.16 mg/s. Flame properties including flame dimensions, soot formation, temperature, and attachment mechanisms were investigated. Overall, luminous flame height decreased with decreasing pressure to the point of visible luminosity disappearance, resulting in blue flames. Flame width increased with decreasing pressure until the flame was almost spherical. Soot formation decreased with decreasing pressure to negligible concentrations in a near vacuum. At 0.482 mg/s, the percentage of carbon converted into soot was between 0.01% and 0.12%, whereas at 1.16 mg/s, this percentage was between 0.5% and 11% at sub-atmospheric pressures. Maximum flame temperatures increased with decreasing pressure. Regardless of fuel flow rate, the diffusion flames remained attached to the exterior of the burner. This attachment point moved further down the burner exterior as pressure decreased until a near vacuum.

The design of combustion devices is very important to society today. They need to be highly efficient, while reducing emissions in order to meet strict environmental standards. These devices, however, are currently not being designed effectively. The most common method of improving them is through parametric studies, where the design parameters are altered one at a time to try and find the best operating point. While this method does work, it is not very enlightening as it neglects the non-linear interactions between the design parameters, requires a large amount of time, and does not guarantee that the best operating point is found. As the environmental standards continue to become stricter, a more robust method of optimizing combustion devices will be required. In this work a robust design optimization algorithm is presented that is capable of mathematically accounting for all of the interactions between the parameters and can find the best operating point of a combustion device. The algorithm uses response surface modeling to model the objective function, thereby reducing computational expense and time as compared to traditional optimization algorithms. The algorithm is tested on three case studies, with the goal of improving the radiant efficiency of a two stage porous radiant burner. The first case studied was one dimensional and involved adjusting the pore diameter of the second stage of the burner. The second case, also one dimensional, involved altering the second stage porosity. The third, and final, case study required that both of the above parameters be altered to improve the radiant efficiency. All three case studies resulted in statistically significantly changes in the efficiency of the burner.

Petroleum coke or petcoke, a refinery byproduct, has generally been considered as an unusable byproduct because of its high sulfur content. However energy industries now view petcoke as a potential feedstock for power generation because it has higher carbon content than other hydrocarbons like coal, biomass and sewage residue. This gives petcoke a great edge over other feedstocks to generate power. Models for the two most common processes for power generation, namely combustion and gasification, were developed using Aspen Plus steady state chemical process simulator. Overall plant layouts for both processes were developed by calculating the heat and mass balance of the unit operations. After conducting wide sensitivity analysis, results indicate that one ton of petcoke feedstock can generate up to 4 MW of net available power. Both processes have rates of return greater than 30%, although gasification offers a slightly more attractive opportunity than combustion.

A comprehensive second law analysis of combustion for a range of conditions and fuels was completed. Constant pressure, constant volume and constant temperature combustion processes were examined. The parameters studied were reactant temperature, reactant pressure, equivalence ratio and the fuels themselves. In addition, the contribution and relative significance of the various components (thermo-mechanical, reactive and diffusion) to the mixture availability was examined. Also, the effect of reactant mixture dissociation was incorporated into the combustion analysis. It was found that for similar initial conditions, constant pressure combustion and constant volume combustion exhibited similar trends. For constant temperature combustion, the trend is significantly different from the constant pressure and constant volume combustion, with almost the entire reactant availability being destroyed due to combustion at lower temperatures. Amongst the parameters examined, reactant mixture temperature had the most significant effect on the fraction of availability destroyed during combustion. The percentage availability destroyed reduced from 25 to 30% at 300 K to about 5% at 6000 K for constant pressure and constant volume combustion processes. The effect of the reactant mixture pressure on the fraction of availability destroyed was more modest. The values for the percentage availability destroyed for pressures ranging from 50 kPa to 5000 kPa were found to lie within a range of 5%. The effect of equivalence ratio on the fraction of reactant mixture availability destroyed was also documented. In general, it was found that the destruction of availability decreased with increasing equivalence ratios. This value, however, accounts for the availability due to fuel like species in the product mixture. Therefore, for practical applications, combustion of the stoichiometric mixture would be preferred over the rich equivalence ratios. It was found that the fraction of reactant availability destroyed increased with increasing complexity of the fuel??s molecular structure. In addition, it was shown that the diffusion availability terms is small and may be neglected, while the reactive availability and thermo-mechanical availability are more significant.

The push toward the miniaturization of electromechanical devices and the resulting need for micro-power generation (milliwatts to watts) with low-weight, long-life devices has led to the recent development of the field of micro-scale combustion. Since batteries have low specific energy (~200 kJ/kg) and liquid hydrocarbon fuels have a very high specific energy (~50000 kJ/kg), a miniaturized power-generating device, even with a relatively inefficient conversion of hydrocarbon fuels to power, would result in increased lifetime and/or reduced weight of an electronic or mechanical system that currently requires batteries for power. Energy conversion from chemical energy to electrical energy without any moving parts can be achieved by a thermophotovoltaic (TPV) system. The TPV system requires a radiation source which is provided by a micro-combustor. Because of the high surface area to volume ratio for micro-combustor, there is high heat loss (proportional to area) compared to heat generation (proportional to volume). Thus the quenching and flammability problems are more critical in a micro-scale combustor. Hence innovative schemes are required to improve the performance of micro-combustion. In the current study, a micro-scale counter flow combustor with heat recirculation is adapted to improve the flame stability in combustion modeled for possible application to a TPV system. The micro-combustor consists of two annular tubes with an inner tube of diameter 3 mm and 30 mm long and an outer tube of 4.2 mm diameter and 30 mm long. The inner tube is supplied with a cold premixed combustible mixture, ignited and burnt. The hot produced gases are then allowed to flow through outer tube which supplies heat to inner tube via convection and conduction. The hot outer tube radiates heat to the TPV system. Methane is selected as the fuel. The model parameters include the following: diameter d , inlet velocity u , equivalence ratio φ and heat recirculation efficiency η between the hot outer flow and cold inner flow. The predicted performance results are as followings: the lean flammability limit increased from 7.69% to 7.86% and the quenching diameter decreased from 1.3 mm to 0.9 mm when heat recirculation was employed. The overall energy conversion efficiency of current configuration is about 2.56.

Growing rates of manure produced from large dairies have increased concern for the environmental quality of nearby streams and watersheds. Typically the manure from the freestalls on these dairies is flushed with water to a mechanical separator. Here, flushed dairy biomass (DB) is parted into separated solids and separated liquid. The separated liquid is discharged into lagoons for treatment and eventual land application. This thesis proposes thermodynamic models for firing DB in small scale boiler systems that would eliminate land application and lagoons, which are being claimed to be the source of nutrient leaching and overloading. Fuel analysis of flushed DB from a dairy in central Texas show that it contains 93%moisture (%M), 3%ash (%A), and 4%combustibles (%Cb), while separated DB solids contain 81%M, 2%A, and 17%Cb. The dry, ash-free higher heating value of DB is approximately 20,000 kJ/kg. Using dry, ash-free results, computations can be made over ranges of %M and %A. For example, DB containing 70%M requires 9.74%Cb to vaporize all moisture and produce gaseous products of combustion at 373 K, but requires 17.82%Cb to burn in a regenerative combustor with a flame temperature of 1200 K. Separated solids that are pressed in an auger to 70%M (3%A and 27%Cb) can burn at 1200 K with exhaust temperatures of up to 1130 K and a minimum required heat exchanger effectiveness of 15%. Pressed solids can thus be fired in a boiler, where the remaining separated liquid can be used as feed water. The pressed solids only can release about 30% of the heat required to vaporize the remaining unclean feed water. However, pressed DB solids can be blended with drier fuels to vaporize almost all the unclean water. The low quality steam produced from the unclean water can be used in thermal processes on the farm. A similar system can be developed for vacuumed DB without the need to vaporize unclean feed water. As for large dairies with anaerobic digester systems already installed, directly firing the produced biogas in a small scale boiler system may be another way to similarly vaporize the remaining effluent.

Th. doct.--Physique expérimentale--Göteborg (Suède)--Chalmers university of technology, Göteborg university, 2004. / Bibliogr. p. 81-90. Annexes.