Browsing by Subject "Ammonia"

Now showing 1 - 4 of 4
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    Enabling Distributed Renewable Energy and Chemical Production through Process Systems Engineering
    (2018-12) Allman, William
    New renewable energy technologies offer the promise of preserving a sustainable energy supply for future generations. Coupling chemical production with renewable energy production can help to address many of the challenges associated with the large-scale implementation of renewable energy, including short time scale variability of electricity production, potential mismatch of supply and demand, and energy stranded in areas of low population density. However, such co-production systems necessitate considering chemical production at scales smaller than what is typically seen in today's infrastructure due to the geospatially dispersed nature of renewable energy resources. This small scale production is economically prohibitive due to economies of scale, which promote building large scale facilities whenever possible. These economic challenges motivate the use of process systems engineering to develop decision making frameworks which minimize the costs of building and operating new renewable energy and chemical production systems. The application of process systems engineering methods to systems producing renewable energy and chemicals presented in this thesis centers around three major themes. First, decomposition, an approach which breaks down large optimization problems into smaller, easier to solve subproblems, is used to solve a challenging problem which finds the optimal design of a combined biorefinery and microgrid system. By doing so, hydrogen production is identified as a critical cost bottleneck in the combined system design. A method for automatically finding subproblems for decomposition for a broad class of optimization problems is also presented. Second, a framework is proposed for considering where new facilities should be built within an existing chemical supply chain. Here, policies and market conditions, such as a carbon tax, are identified that can have a strong effect on reducing emissions from ammonia production. Finally, the connection between the optimal design and operation of renewable energy and chemical systems is analyzed. Here, a framework which determines operating strategies which minimize cost is developed, and the optimal operation of a wind-powered ammonia system in different electricity market structures is analyzed. This framework is used to generate correlations between system design and operating cost which are embedded in a design optimization problem to improve solution efficiency.
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    Evaluating on-farm sampling strategies and corresponding gas emission estimation methods for livestock and poultry barns
    (2022-08) Soriano, Noelle Cielito
    The need for gas emission research is driven by multiple stakeholders to address avariety of concerns and priorities that stem from environmental, human, and animal impacts of gas emissions from barns. In this work, I first provide background on the mechanism of gas emission from these systems and an overview of emission estimation strategies in the literature. This is followed by a presentation of two thesis projects, which demonstrate outcomes and challenges related to different emission estimation strategies. In the first project, I investigate airflow patterns and estimate ammonia (NH3) and carbon dioxide (CO2) emissions using a multi-airspace model for a naturally ventilated deep-pit cattle barn, with discrete gas concentration data. The second project uses a mass balance approach to estimate volatile solids (VS) losses and NH3 emissions from a naturally ventilated poultry barn based on material flows in and out of a barn. Each estimation strategy is evaluated based on the practicality of the sampling approach in specific housing styles, and whether emission estimates are comparable to current emission estimation methods for each system. Findings from these two projects show that, ultimately, there will always be limitations to the various available emission estimation strategies, particularly related to in-barn sample collection. Understanding the appropriate application of each of these approaches is important when selecting an emission estimation approach that will allow researchers to obtain representative emission estimates from a variety of livestock and poultry systems.
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    Investigation into the Performance and Emissions of Ammonia / Hydrogen Blends in a Spark Ignition Engine and Demonstration of Improved Engine Thermal Efficiency using Oxidative Coupling of Methane Pretreatment
    (2022-09) Swift, Evan
    Reducing the impact of internal combustion engines on the global climate is a principal concern of the 21st century. Increasing thermal efficiency and reducing specific emissions are both ways to decrease greenhouse gas emissions from engines and therefore reduce their environmental impact. This thesis presents experimental and simulation studies of two promising concepts for reducing emissions and fuel consumption. The first study identified favorable operating regimes of a spark ignited (SI) engine using ammonia and hydrogen fuels. These fuels are rapidly gaining interest because they contain no carbon and therefore allow an engine to operate without producing any CO2, CO, or hydrocarbons (HC). Because these fuels are a new topic for IC engine research, and burn differently than typical HC fuels, an exploratory study must identify important engine performance trends. With these trends identified, favorable operating conditions may be selected to optimize the engine performance. The experiments show that high thermal efficiency (>40%) and low NOx (<100 ppm) is achievable using rich equivalence ratios. They also show that, unlike a traditional HC fuel, increasing the peak cylinder temperature decreases NOx emissions by facilitating the thermal deNOx mechanism. The fuel blends tested demonstrated a tendency to autoignite - characterized by a two-stage heat release, despite having a high ignition energy. Interestingly, auto-ignition did not lead to intense ringing as it would in a HC engine, which will be the topic of future research. The second study explored how a pretreatment strategy for natural gas could be used to increase the efficiency of a heavy-duty engine. The pretreatment strategy would use an on-board reactor to convert natural gas, primarily CH4, into more reactive C2 species. This process would increase the reactivity of the natural gas fuel and enable natural gas engines to operate in premixed compression ignition (PCI) combustion modes. These combustion modes have a high thermal efficiency but are difficult to realize with natural gas due to its naturally high resistance to autoignition. The analysis done in this thesis will test this strategy by estimating the efficiency gain that could be realized using OCM fuel treatment. First, Cantera simulations found that an engine scale reactor could provide sufficient C2 conversion to enhance the natural gas reactivity significantly. GT-Power software simulated the performance of a natural gas SI engine and found that CI combustion modes were up to 7% more efficient than SI combustion, even when the reactor and required heaters are considered. The benefit is attributed to faster combustion associated with CI combustion, which is accessed more easily using OCM products than with pure natural gas. Future work on this subject will need to investigate alternative combustion control methods and improve reactor performance.
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    Thermochemical Recuperation and Catalytic Strategies for Anhydrous Ammonia in Combustion Systems
    (2021-06) Kane, Seamus
    The carbon intensity of combustion engines poses a major challenge to worldwide efforts to minimize climate change. Anthropogenic carbon dioxide (CO2) is greatest source of atmospheric warming and its emission must be curtailed to affect climate forcing in a meaningful way. Carbon-neutral alternatives such as ethanol and biodiesel recycle atmospheric carbon under ideal conditions yet result in net carbon emissions due to process inefficiencies. Fuels decoupled from chemical carbon are necessary to reduce carbon intensity and halt climate change. Anhydrous ammonia is one such fuel as it can be produced entirely by renewable means and contains no carbon. This body of work investigates combustion applications of anhydrous ammonia in compression ignition (CI) engines, methods of catalytically enhancing ammonia for more efficient combustion and use of the endothermic ammonia decomposition reaction for waste-heat recovery.This thesis presents the applications of catalytic ammonia decomposition, specifically pertaining to, but not limited to internal combustion engines. Ammonia has proved a suitable replacement fuel in spark-ignition (SI) engines and as a secondary fumigated fuel for CI engines. Stability of the ammonia molecule results in poor flame propagation and low ignition reactivity. Using ammonia in a dual-fuel arrangement overcomes these issues in existing engines and combustors designed for hydrocarbon fuels. Alternatively, ammonia can be converted to hydrogen using catalysis, which in turn enhances ammonia combustion without the need for a secondary high reactivity fuel. This work explores hydrogen-enhanced ammonia and diesel combustion in CI engines equipped with catalytic waste-heat recovery. Engines were operated over their full range under various levels of ammonia fuel replacement to determine the effects on engine and combustion efficiency as well as emissions and stability. Thermochemical recuperation and thermal recovery were analyzed across the operability range towards identifying optimal system parameters. The primary finding in the first part of this work is that ammonia effectively recovers waste energy using low-temperature high-active catalysts. Activity is demonstrated as low as 200 °C for Ruthenium-based catalysts, and full conversion to hydrogen results in a net lower heating value increase of 15%. Heat transfer to sustain the decomposing ammonia proved difficult however, as the experimental catalyst unit was undersized for engine operation. Despite low conversion, sufficient hydrogen was generated to enhance flame speed, combustion efficiency and engine thermal efficiency as compared to pure ammonia fumigation. Fuel-bound nitrogen in ammonia generated high oxides of nitrogen (NOx) and N2O emissions upon combustion. However, unburned ammonia present in exhaust was measured to be ideal for passive elimination of these species using selective catalytic reduction (SCR). Emissions and efficiencies measured suggest that future implementation of ammonia dual fuel requires higher rates of heat recovery and higher ammonia replacement rates than those demonstrated in this study. Both conditions can be met using a modified catalyst design and higher flow ammonia fueling system, respectively. Ammonia decomposition catalysis is thoroughly described in literature but heat transfer inside a supporting monolith structure is not. This work presents a computationally efficiency quasi-2D modeling procedure for understanding heat and mass transfer in metal monoliths. A finite difference model was developed to simulate thermal behavior of the decomposition catalyst used in experimental studies. The heat transfer model was calibrated against inert gas experiments and showed excellent agreement with convective and conductive values from literature. Argon, air and CO2 were used under identical thermal conditions to demonstrate robustness in simulating generic flows through the reactor. Agreement of the model against the entire experimental dataset demonstrated robustness in predicting metallic support thermal behavior while the simplicity of the approach presented a computationally inexpensive alternative to CFD or physical prototype design screening. Design screening was then conducted using varied input conditions and showed the relative importance of each parameter on heat exchange effectiveness and wall-average heat transfer coefficient. Optimal performance was quantified, and the effects of design parameters on heat exchange was discussed. High catalyst activity and reaction residence time are needed to achieve high hydrogen yield, promoting efficient combustion of ammonia-hydrogen mixtures. To overcome thermal limitations posed by waste-heat driven decomposition, ammonia partial oxidation can be used to create an endogenous heat source and increase yield. Oxidation and decomposition were combined in an autothermal process and were shown to increase both hydrogen fraction and the hydrogen-to-ammonia ratio of the reformate stream. Autothermal ammonia decomposition (ATD) resulted in fuel heating value decrease, which was comparable to heating value losses expected from poor combustion efficiency in engines. A comprehensive reactor model was developed using two global reaction rates and the previous monolith heat transfer model. Rates were determined through non-linear regression and showed excellent fit across thermal and autothermal regimes. Deficiencies in experimental reactor design were identified using the model, and potential design changes were discussed. The model and experiment both suggest that ATD is a promising alternative to waste-heat recovery approaches alone when a high reactivity reformate mixture is needed. The research shows that ammonia ATD reformate is of sufficient reactivity to enable drop-in replacement of hydrocarbon fuels in unmodified engines and combustors.