Mechanical Engineering
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Item INVESTIGATION INTO PYROLYSIS AND GASIFICATION OF SOLID WASTE COMPONENTS AND THEIR MIXTURES(2021) Burra, Kiran Raj Goud; Gupta, Ashwani K; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Unsustainable dependence on fossil fuel reserves for energy and material demands is leading to growing amounts of CO2 concentration in the atmosphere and irreversible climate changes. Carbon neutral sources such as abundant biomass reserves and landfill-destined high energy density wastes such as plastics, and tire-wastes can be utilized together for energy and material production for a sustainable future. Pyrolysis and gasification can convert these variable feedstocks into valuable and uniform synthetic gas (syngas) with versatile downstream applicability to energy, liquid fuels, and other value-added chemicals production. But seasonal availability, high moisture and ash content, and relatively low energy density of biomass can result in significant energy and economic losses during gasification. Furthermore, gasification of plastic wastes separately was found to result in feeding issues due to melt-phase, coking, and agglomerative behavior leading to operational issues. To resolve these issues, co-processing of biomass with these plastics and rubber wastes was found to be promising in addition to providing synergistic interaction leading to enhanced syngas yield and inhibitive behavior in some cases and thus motivating this work. This dissertation provides a deconvoluted understanding and quantification of the source and impact of these interactions for better process performance and alleviation of inhibitive interaction needed to develop reliable co-gasification of feedstock mixtures. To achieve this, plastic and tire wastes were investigated separately and mixed with different biomass species using a series of feedstock arrangements to understand synergistic influence on the syngas yield and kinetics in comparison to mono-conversion. Influence of operating conditions such as feedstock composition, temperature and gasifying agent was also examined for desirable conditions of energy recovery and high-quality syngas yield. Lab-scale semi-batch reactor studies equipped with online product gas analysis, along with thermogravimetric studies were utilized to obtain insight into the products yield, kinetics, and energy conversion. These results provided a better understanding of the influence of feedstocks and their interaction on the syngas and process behavior. They address the knowledge gap in versatile feedstock-flexible gasifier development for efficient and reliable syngas production from varying solid waste and biomass component mixtures with minimal changes to the operating conditions.Item Prediction of Upward Flame Spread over Polymers(2016) Leventon, Isaac Tibor; Stoliarov, Stanislav I; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this work, the existing understanding of flame spread dynamics is enhanced through an extensive study of the heat transfer from flames spreading vertically upwards across 5 cm wide, 20 cm tall samples of extruded Poly (Methyl Methacrylate) (PMMA). These experiments have provided highly spatially resolved measurements of flame to surface heat flux and material burning rate at the critical length scale of interest, with a level of accuracy and detail unmatched by previous empirical or computational studies. Using these measurements, a wall flame model was developed that describes a flame’s heat feedback profile (both in the continuous flame region and the thermal plume above) solely as a function of material burning rate. Additional experiments were conducted to measure flame heat flux and sample mass loss rate as flames spread vertically upwards over the surface of seven other commonly used polymers, two of which are glass reinforced composite materials. Using these measurements, our wall flame model has been generalized such that it can predict heat feedback from flames supported by a wide range of materials. For the seven materials tested here – which present a varied range of burning behaviors including dripping, polymer melt flow, sample burnout, and heavy soot formation – model-predicted flame heat flux has been shown to match experimental measurements (taken across the full length of the flame) with an average accuracy of 3.9 kW m-2 (approximately 10 – 15 % of peak measured flame heat flux). This flame model has since been coupled with a powerful solid phase pyrolysis solver, ThermaKin2D, which computes the transient rate of gaseous fuel production of constituents of a pyrolyzing solid in response to an external heat flux, based on fundamental physical and chemical properties. Together, this unified model captures the two fundamental controlling mechanisms of upward flame spread – gas phase flame heat transfer and solid phase material degradation. This has enabled simulations of flame spread dynamics with a reasonable computational cost and accuracy beyond that of current models. This unified model of material degradation provides the framework to quantitatively study material burning behavior in response to a wide range of common fire scenarios.Item A MULTISCALE APPROACH TO PARAMETERIZATION OF BURNING MODELS FOR POLYMERIC MATERIALS.(2014) Li, Jing; Stoliarov, Stanislav I.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A quantitative understanding of the processes that occur in the condensed phase of burning materials is critical for the prediction of ignition and growth of fires. A number of models have been developed to simulate these condensed phase processes. The main issue that remains to be resolved is the determination of parameters to be input into these models, which are formulated in terms of fundamental physical and chemical properties. This work is focused on developing and applying a systematic methodology for the characterization of polymeric materials based on milligram-scale and bench-scale tests to isolate specific chemical and/or physical processes in each scale level. The entire study is divided into two parts corresponding to two different scale tests and analysis. The first part is concentrated on the measurement of kinetics and thermodynamics of the thermal degradation of polymeric materials at milligram-scale. It employs a simultaneous thermal analysis instrument capable of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). A numerical model is utilized to fit TGA data and obtain thermal degradation kinetics to a continuum pyrolysis model. This model is subsequently employed to analyze DSC heat flow and extract sensible, melting and degradation reaction heats. The extracted set of kinetic and thermodynamic parameters is shown to simultaneously reproduce TGA and DSC curves for a set of 15 widely used commercial polymers. Then the first part of this study was extended to bench-scale gasification experiments that were carried out in a controlled atmosphere pyrolysis apparatus (CAPA) which has been recently developed in our group. The CAPA is used to measure material gravimetric and thermal changes during thermal decomposition in an anaerobic atmosphere with a capability of analyzing material thermal transport properties. These properties, combined with material kinetics and thermodynamics from the first part of this study, were used as inputs for a pyrolysis model to simulate one-dimensional polymer gasification under wide range of external heat fluxes. The predictive power of this model and validity of its parameters are verified against the results of gasification experiments. 7 out of 15 polymers were validated in bench-scale and the parameterized simulations are in reasonable agreement with experimental data under wide range of conditions.