Browsing by Subject "reduction"
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Item Advanced Reduction Processes - A New Class of Treatment Processes(2012-10-19) Vellanki, Bhanu PrakashA new class of treatment processes called Advanced Reduction Processes (ARP) has been proposed. The ARPs combine activation methods and reducing agents to form highly reactive reducing radicals that degrade oxidized contaminants. Batch screening experiments were conducted to identify effective ARP by applying several combinations of activation methods (ultraviolet light, ultrasound, electron beam, microwaves) and reducing agents (dithionite, sulfite, ferrous iron, sulfide) to degradation of five target contaminants (perchlorate, nitrate, perfluorooctanoic acid, 2,4 dichlorophenol, 1,2 dichloroethane) at 3 pH levels (2.4, 7.0, 11.2). These experiments identified the combination of sulfite activated by ultraviolet light produced by a low pressure mercury vapor lamp as an effective ARP. More detailed kinetic experiments were conducted with nitrate and perchlorate as target compounds and nitrate was found to degrade more rapidly than perchlorate. The effects of pH, sulfite concentration, and light intensity on perchlorate and nitrate degradation were investigated. The effectiveness of the sulfite/UV-L treatment process improved with increasing pH for both perchlorate and nitrate.Item An Analysis of the Impact of Reducing Pedestrian-Walking-Speed on Intersection Traffic MOEs(2015-01-26) Li, XiaohanPedestrian traffic is an important element in signalized intersection analysis. As a low-speed traffic component, pedestrians crossing the street may take up time that could be utilized by vehicles on the other street to pass through the intersection, and this causes an increase in the total delay at the intersection. Therefore, to minimize traffic delays and increase traffic efficiency, it is important to study the impact of pedestrian walking speed. This study was conducted to analyze the impacts of pedestrian speed under different lane group combinations, median widths, volumes on major and minor streets, and pedestrian pushbutton horizontal offsets. The idea originated came from the reduction of pedestrian walking speed used for calculating the pedestrian intervals. The 2003 MUTCD specified a value of 3.5 ft/sec to calculate the pedestrian clearance time and this speed was reduced to 4.0 ft/sec in the 2009 MUTCD. Moreover, a second method using 3.0 ft/sec to calculate the total pedestrian intervals was added to the 2009 MUTCD. This change is likely to influence the signal timing plan of entire intersections and further increasing the intersection total delay. The researcher used one of the most popular simulation software programs, Synchro 7, to simulate various types of intersections under different traffic circumstances and yield a series of datasets to analyze the impacts of the reduction in pedestrian walking speed. The data was analyzed both horizontally and vertically. By comparing the intersection total delay as well as the through lane group and the approach average delay, the researcher analyzed their differences mathematically as well as practically. According to the analysis results, if the cycle length of an intersection can be optimized, the change of pedestrian walking speed would not make significant impact on intersection delay; however, if under a given cycle length other than its optimum one, the intersection delay would increase significantly after the change of pedestrian walking speed in some circumstance. The extended pushbutton press function can be used to alleviate such delay increase.Item Non-Reacting Flow Characteristics and Emissions Reduction on Blends of Coal and Dairy Biomass in 30 kW_(t) Low NO_(x) Down-Fired Furnace(2014-08-07) Tiyawongsakul, TiyawutRecently, coal-fired power plants have considered either to retire themselves or to use natural gas as the main energy source instead of coal due to more stringent air pollution regulations for nitrogen oxides (NO_(x)), mercury (Hg) and more recently the required CO_(2) reduction of 30% by 2030. Clean coal technology must be continuously developed in order to prevent people from losing their jobs and to decrease the negative impacts of firing coal on environment. The present research focuses on NO_(x) emissions which arise mainly due to oxidation of fuel-bound nitrogen using low NO_(x) burner (LNB) when fired with Wyoming Powder River Basin coal (PRB) and blends of coal and dairy biomass (DB). The DB was selected as co-fired fuel for possible elimination of DB from dairy feedlots which result in land, air and water pollution if not properly disposed of. LNB adopts staged air introduction in order to limit the availability of oxygen when nitrogen from fuel is released. To achieve the objective, the mixing patterns between fuel particle and air were predicted using non-reacting flow (NRF) simulation inside the cylindrical combustion chamber. The effects of varying burner parameters, fuel particle sizes, main burner equivalence ratios (ER_(mb)) and overall equivalence ratios (ER_(oa)) on mixing characteristics were investigated. Then, the LNB components were modified based on the results from NRF simulation. The modified main burner is a partially premixed swirl burner (fuel mixes with the primary air inside the fuel/primary air nozzle, and the secondary air is swirled by the straight-vane swirler) whose swirl angle and secondary air swirl number are 59? and 1.42 respectively. The circular over-fire air (OFA) nozzles are located 484 mm below the main burner exit, and the OFA is injected into the combustion chamber in the radial direction. The fuels used in the research were: 1) pure PRB and 2) the fuel blend of PRB and DB with the PRB-to-DB ratio of 90 to 10 on mass basis (90-10 PRB-DB blend). Fuel characteristics were first obtained, and empirical chemical formulae were deduced. The CO_(2), O_(2) and NO were measured as a function of ER_(oa) and ER_(mb) (ER_(mb) based on air flow without inclusion of OFA). The gas analyses were used to obtain the burnt fraction, respiratory quotient (RQ, = CO_(2) moles produced/O_(2) moles consumed) and equivalence ratio which is then checked against measured values. Uncertainty analyses were also performed. The optimum conditions for minimum NO_(x) emission that pass the EPA limit (210 g/GJ) were obtained as follows. With ER_(oa) = 0.95, firing pure PRB produced NO_(x) 220 g/GJ without OFA, and 179 g/GJ with OFA (ER_(mb) = 1.10) which is about 18.6 % reduction. Under same conditions, the co-firing of 90-10 PRB-DB blend decreased NO_(x) by 3.6% without OFA, and 22.2% with OFA (ER_(mb) = 1.10) compared to firing pure PRB at ER_(oa) = 0.95 without OFA. Furthermore, co-firing 90-10 PRB-DB blend with OFA at ER_(mb) = 1.10 and ER_(oa) = 0.95 (excess air 5.26%) emitted NO_(x) approximately 171 g/GJ whilst firing pure PRB without OFA at ER_(oa) = 0.85 (excess air 17.65%) emitted NO_(x) approximately 330 g/GJ which is 48% reduction and less than 210 g/GJ (the current EPA limit). This reduction could benefit 500-MWt power plants approximately $113,500 per year in case the efficiency of power plants is 35% and NO_(x) are traded at $15.89 per short ton.Item Synthesis, characterization, anion complexation and electrochemistry of cationic Lewis acids(2009-05-15) Chiu, Ching-WenOwing to the favored Coulombic attraction between the ammonium group and anion which stabilizes the B-F/B-CN bond against heterolysis, cationic borane [25]+ has great affinity toward anions than its neutral analog, and is capable of capturing fluoride or cyanide from water under bi-phasic conditions. By placing the fluorophilic silyl group adjacent to an electrophilic carbocation, a novel fluoride sensor [45]+ was obtained. Sensing occurs via a fluoride induced methyl migration from the silicon to adjacent electrophilic methylium center which is unprecedented. As a result of its strong fluoride affinity, [45]+ is able to react with KF in aqueous media at pH 7.0. The electrochemistry study of these cationic Lewis boranes reveals that the cationic character of these boranes serves to decrease their reduction potential and increase the stability of the resulting radicals. In this part of the research, we have prepared a cationic borane [27]+, which features two reversible reduction waves at -0.86 and -1.56 (vs. Fc/Fc+) corresponding to the formation of stable neutral and anionic derivatives. The one-electron reduction of [27]+ leads to the formation of a boron containing neutral radical featuring an unusual boron-carbon one-electron ? bond. Further reduction of 27? results in the formation of the borataalkene derivative [27]-, which features a formal B=C double bond. The structural changes accompanying the stepwise population of the B-C ?-bond are also determined, and this sequential population of B-C ?-bonding orbital is also supported by theoretical computations. In order to understand the impact of the cationic nature of these boranes on their oxidative power, three novel cationic boranes ([34]+, [35]2+, and [36]3+) have been synthesized and their oxidative power were examined via cyclic voltammetry. The CV data of these compounds shows that the reduction potential of these triarylboranes is linearly proportional to the number of the pendant cationic substituents. Substitution of a mesityl group by an ArN+ group leads to an increase of the reduction potential by 260 mV.Item Thermal signature reduction through liquid nitrogen and water injection(Texas A&M University, 2005-02-17) Guarnieri, Jason AntonioThe protection of aircraft against shoulder fired heat seeking missiles is of growing concern in the aviation community. This thesis presents a simple method for shielding the infrared signature of a jet engine from heat seeking missiles. The research efforts investigated two approaches to shield the thermal signature of the Noel Penny Type 401 turbojet at the Texas A&M University Propulsion Lab Test Cell. First, liquid nitrogen was injected through a manifold at a flow rate equivalent to the flow rate of exhaust gases, producing a small temperature reduction in the exhaust but no infrared shielding. Second, water was injected at a flow rate of 13% of the flow of exhaust gases, producing a greater temperature reduction and some shielding. Water was then injected through a manifold at a ?ow rate of 118% of the flow rate of exhaust gases, producing a substantial reduction in temperature and complete shielding of the infrared signature. Additionally, numerical simulations were performed using FLUENT to support these experiments. Results are presented in the form of thermocouple data and thermal images from the experiments, and in the form of temperature contours and streamtraces from the simulations.Item Time-dependent release of iron from soot particles by acid extraction and the reduction of fe3+ by elemental carbon(2009-05-15) Drake, Stephen JamesElemental carbon reduces Fe3+ to Fe2+ in aqueous solutions. This process has potential implications in the adverse health effects of fine particles in air pollution, because both elemental carbon and iron are major components in atmospheric particulate matter. In this study we measured the time-dependent release of iron from laboratory flames and standard reference soot particles that contained iron, and the reduction of Fe3+ to Fe2+ in an acid extraction process. The concentration of Fe3+ and Fe2+ ions in the extraction solutions was measured by a spectrophotometric method. The results showed that while Fe3+ was the dominant valence state in the dry soot particles, significant fraction of iron was reduced to Fe2+ in the aqueous solution. Further investigation is needed to assess the significance of this phenomenon in the biological effects of particles that contain iron and elemental carbon.