Matching Items (5)

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Modeling and characterization of ammonia injection and catalytic reduction in Kyrene Unit-7 HRSG

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ABSTRACT The heat recovery steam generator (HRSG) is a key component of Combined Cycle Power Plants (CCPP). The exhaust (flue gas) from the CCPP gas turbine flows through the HRSG − this gas typically contains a high concentration of NO

ABSTRACT The heat recovery steam generator (HRSG) is a key component of Combined Cycle Power Plants (CCPP). The exhaust (flue gas) from the CCPP gas turbine flows through the HRSG − this gas typically contains a high concentration of NO and cannot be discharged directly to the atmosphere because of environmental restrictions. In the HRSG, one method of reducing the flue gas NO concentration is to inject ammonia into the gas at a plane upstream of the Selective Catalytic Reduction (SCR) unit through an injection grid (AIG); the SCR is where the NO is reduced to N2 and H2O. The amount and spatial distribution of the injected ammonia are key considerations for NO reduction while using the minimum possible amount of ammonia. This work had three objectives. First, a flow network model of the Ammonia Flow Control Unit (AFCU) was to be developed to calculate the quantity of ammonia released into the flue gas from each AIG perforation. Second, CFD simulation of the flue gas flow was to be performed to obtain the velocity, temperature, and species concentration fields in the gas upstream and downstream of the SCR. Finally, performance characteristics of the ammonia injection system were to be evaluated. All three objectives were reached. The AFCU was modeled using JAVA - with a graphical user interface provided for the user. The commercial software Fluent was used for CFD simulation. To evaluate the efficacy of the ammonia injection system in reducing the flue gas NO concentration, the twelve butterfly valves in the AFCU ammonia delivery piping (risers) were throttled by various degrees in the model and the NO concentration distribution computed for each operational scenario. When the valves were kept fully open, it was found that it led to a more uniform reduction in NO concentration compared to throttling the valves such that the riser flows were equal. Additionally, the SCR catalyst was consumed somewhat more uniformly, and ammonia slip (ammonia not consumed in reaction) was found lower. The ammonia use could be decreased by 10 percent while maintaining the NO concentration limit in the flue gas exhausting into the atmosphere.

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Date Created
2011

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Dynamics of Ices and Fluids on Mars and Kuiper Belt Objects

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The seasonal deposition of CO2 on the polar caps is one of the most dynamic processes on Mars and is a dominant driver of the global climate. Remote sensing temperature and albedo data were used to estimate the subliming mass

The seasonal deposition of CO2 on the polar caps is one of the most dynamic processes on Mars and is a dominant driver of the global climate. Remote sensing temperature and albedo data were used to estimate the subliming mass of CO2 ice on south polar gullies near Sisyphi Cavi. Results showed that column mass abundances range from 400 - 1000 kg.m2 in an area less than 60 km2 in late winter. Complete sublimation of the seasonal caps may occur later than estimated by large-scale studies and is geographically dependent. Seasonal ice depth estimates suggested variations of up to 1.5 m in depth or 75% in porosity at any one time. Interannual variations in these data appeared to correlate with dust activity in the southern hemisphere. Correlation coefficients were used to investigate the relationship between frost-free surface properties and the evolution of the seasonal ice in this region. Ice on high thermal inertia units was found to disappear before any other ice, likely caused by inhibited deposition during fall. Seasonal ice springtime albedo appeared to be predominantly controlled by orientation, with north-facing slopes undergoing brightening initially in spring, then subliming before south-facing slopes. Overall, the state of seasonal ice is far more complex than globally and regionally averaged studies can identify.

The discovery of cryovolcanic features on Charon and the presence of ammonia hydrates on the surfaces of other medium-sized Kuiper Belt Objects suggests that cryovolcanism may be important to their evolution. A two-dimensional, center-point finite difference, thermal hydraulic model was developed to explore the behavior of cryovolcanic conduits on midsized KBOs. Conduits on a Charon-surrogate were shown to maintain flow through over 200 km of crust and mantle down to radii of R = 0.20 m. Radii higher than this became turbulent due to high viscous dissipation and low thermal conductivity. This model was adapted to explore the emplacement of Kubrik Mons. Steady state flow was achieved with a conduit of radius R = 0.02 m for a source chamber at 2.3 km depth. Effusion rates computed from this estimated a 122 - 163 Myr upper limit formation timescale.

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Date Created
2019

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Building microbial communities and managing fermentation in microbial electrolysis cells

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Microbial electrochemical cells (MXCs) offer an alternative to methane production in anaerobic water treatment and the recapture of energy in waste waters. MXCs use anode respiring bacteria (ARB) to oxidize organic compounds and generate electrical current. In both

Microbial electrochemical cells (MXCs) offer an alternative to methane production in anaerobic water treatment and the recapture of energy in waste waters. MXCs use anode respiring bacteria (ARB) to oxidize organic compounds and generate electrical current. In both anaerobic digestion and MXCs, an anaerobic food web connects the metabolisms of different microorganisms, using hydrolysis, fermentation and either methanogenesis or anode respiration to break down organic compounds, convert them to acetate and hydrogen, and then convert those intermediates into either methane or current. In this dissertation, understanding and managing the interactions among fermenters, methanogens, and ARB were critical to making developments in MXCs. Deep sequencing technologies were used in order to identify key community members, understand their role in the community, and identify selective pressures that drove the structure of microbial communities. This work goes from developing ARB communities by finding and using the best partners to managing ARB communities with undesirable partners. First, the foundation of MXCs, namely the ARB they rely on, was expanded by identifying novel ARB, the genus Geoalkalibacter, and demonstrating the presence of ARB in 7 out of 13 different environmental samples. Second, a new microbial community which converted butyrate to electricity at ~70% Coulombic efficiency was assembled and demonstrated that mixed communities can be used to assemble efficient ARB communities. Third, varying the concentrations of sugars and ethanol fed to methanogenic communities showed how increasing ED concentration drove decreases in methane production and increases in both fatty acids and the propionate producing genera Bacteroides and Clostridium. Finally, methanogenic batch cultures, fed glucose and sucrose, and exposed to 0.15 – 6 g N-NH4+ L-1 showed that increased NH4+ inhibited methane production, drove fatty acid and lactate production, and enriched Lactobacillales (up to 40% abundance) above 4 g N-NH4+ L-1. Further, 4 g N-NH4+ L-1 improved Coulombic efficiencies in MXCs fed with glucose and sucrose, and showed that MXC communities, especially the biofilm, are more resilient to high NH4+ than comparable methanogenic communities. These developments offer new opportunities for MXC applications, guidance for efficient operation of MXCs, and insights into fermentative microbial communities.

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Date Created
2015

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Nitrogen Recovery from Human Urine by Membrane Processes

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This dissertation investigated the use of membrane processes to selectively separate and concentrate nitrogen in human urine. The targeted nitrogen species to be recovered were urea from fresh human urine and unionized ammonia from hydrolyzed human urine. Chapter 1 investigated

This dissertation investigated the use of membrane processes to selectively separate and concentrate nitrogen in human urine. The targeted nitrogen species to be recovered were urea from fresh human urine and unionized ammonia from hydrolyzed human urine. Chapter 1 investigated a novel two-step process of forward osmosis (FO) and membrane distillation (MD) to recover the urea in fresh human urine. Specifically, FO was used to selectively separate urea from the other components in urine and MD was used to concentrate the separated urea. The combined process was able to produce a product solution that had an average urea concentration that is 45–68% of the urea concentration found in the fresh urine with greater than 90% rejection of total organic carbon (TOC).Chapter 2 determined the transport behavior of low molecular weight neutral nitrogen compounds in order to maximize ammonia recovery from real hydrolyzed human urine by FO. Novel strategic pH manipulation between the feed and the draw solution allowed for up to 86% recovery of ammonia by keeping the draw solution pH <6.5 and the feed solution pH >11. An economic analysis showed that ammonia recovery by FO has the potential to be much more economically favorable compared to ammonia air stripping or ion exchange if the proper draw solute is chosen.
Chapter 3 investigated the dead-end rejection of urea in fresh urine at varying pH and the rejection of unionized ammonia and the ammonium ion in hydrolyzed urine by reverse osmosis (RO), nanofiltration (NF), and microfiltration (MF). When these different membrane separation processes were compared, NF is found to be a promising technology to recover up to 90% of ammonia from hydrolyzed urine with a high rejection of salts and organics.
Chapter 4 investigated the use of the RO and NF to recover ammonia from hydrolyzed human urine in a cross-flow system where both rejection and fouling experiments were performed. For both RO and NF, ammonia rejection was found to be 0% while still achieving high rejection of TOC and salts, and MF pretreatment greatly reduced the extent of fouling on the membrane surface.

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Date Created
2020

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Synthesis of Metal Ternary and Quaternary Nitrides with Applications in Renewable Ammonia Production

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Ammonia is one of the most important chemicals for modern civilization as well as a potentially invaluable intermediary component of a future sustainable H2 economy, yet its current production is decidedly unsustainable. Accordingly, researchers are attempting to devise new paradigms

Ammonia is one of the most important chemicals for modern civilization as well as a potentially invaluable intermediary component of a future sustainable H2 economy, yet its current production is decidedly unsustainable. Accordingly, researchers are attempting to devise new paradigms for ammonia production, one of which would involve the cyclical reaction of H2 with a nitride compound and the renitridation of that compound with N2 - a thermochemical loop that would allow for ammonia production with renewable inputs and at relatively low pressures. In this paper, researchers identified several ternary and quaternary metal nitrides with the potential to exhibit relatively favorable thermodynamics for both the reduction and nitridation steps of that reaction cycle. These compounds were synthesized via co-precipitation and Pechini synthesis and several were tested under gas flows of 75% H2/Ar at 100-700 C and 75% H2/N2 at 700 C to determine their behavior under these conditions. As suggested by the available literature, Co3Mo3N was found to be a far better candidate for thermochemical looping than Fe3Mo3N or Ni2Mo3N - with higher mass loss and mass regain. Interestingly, quaternary nitrides containing Fe and Co in addition to Mo also demonstrated remarkable reduction and nitridation capability under ambient pressures. Ultimately, this paper demonstrates the feasibility of synthesizing a variety of single phase ternary and quaternary nitrides and the potential that several of these nitrides hold for producing ammonia sustainably via cyclic thermochemistry.

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Date Created
2022-05