Date of Award

5-1-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Energy Engineering

First Advisor

Michael D. Mann

Abstract

Coal is a brownish-black sedimentary rock with organic and inorganic constituents. It has been a vital energy resource for humans for millennia. Coal accounts for approximately one quarter of the world’s energy consumption, with 65% of this is energy utilized by residential consumers, and 35% by industrial consumers. Coal operated power stations provide 42% of U.S. electricity supply. The United States hold 96% of coal reserves in North America region, out of which 26% are known for commercial usage. The coal combusted in these power generating facilities requires certain pre-combustion processing, while by-products of coal combustion go through certain post-combustion processing. The application of hydrometallurgical extraction of Rare Earth Elements (REE) from North Dakota Lignite coal feedstock can assist coal value amplification. Extraction of REE from lignite coals liberates REEs and CMs that are vital to electronics, power storage, aviation, and magnets industries. The REE extraction process also reduces the sulfur content of ND lignite coal, along with ash components that foul heat exchange surfaces and can have benefits for post-combustion scrubbing units. When coal is combusted, the exhaust gasses contain carbon dioxide (CO2), sulfur dioxide (SO2), oxides of nitrogen (NOx), water (H2O) and nitrogen (N2). Carbon dioxide comprises approximately 8-10 vol% of the flue gas and is reported to contribute to the greenhouse effect, a primary reason for climate change. Carbon Capture and Storage (CCS) involves of CO2 by use of liquid or solid absorbents to separate CO2 from combustion flue gas. Little data is available on gas-liquid interfacial area correlations in the literature for use of second generation solvents, such as MonoEthanolAmine (MEA), in structured packing absorber columns consisting of thin corrugated metal plates or gauzes, designed to force fluids on complicated paths. While mathematical model development for existing post-combustion carbon capture (PCCC) technologies, such as carbon capture simulations using computational fluid dynamics (CFD) for prediction of mass transfer coefficients is well developed, models describing the behavior of third generation solvents is lacking. Two main research opportunities exist: (i) due to the complex chemistry of coal, there is a requirement for a modeling tool that can account for the coal composition and complex hydrometallurgical extraction processes to assist in designing and sizing pre-combustion REE extraction plants; and (ii) CFD models are required that can capture the mass transfer coefficients of third generation CO2 solvents using structured packing. Two primary hypotheses have been developed to address the research opportunities: (1.) Process modeling of hydrometallurgical extraction of REE provides some theory-based understanding that is complementary to experimental validation and, with the help of chemical kinetics and percentage carboxylation existing in feedstocks, can forecast the efficiency and leachability of other feedstocks, and (2.) A detailed Volume of Fluid (VOF) simulation of coupled mass and momentum transfer problems in small intricate regions of corrugated structured and packed panels placed at 45° angle can be used to predict mass transfer coefficients for third generation solvents by using open-source numerical C/C++ based framework called Open Fields-Operations-And-Manipulations (OpenFOAM). The hydrometallurgical process modeling is developed using METSIM, a leading hydrometallurgical process modeling software tool. The steady state process model provides an overview of REE production along with equipment inventory sizing. The model also has functions to define percentage of organic carboxylic acid bonds present in coal, since, the prior research has identified that the primary association of REE in lignite coal is as weakly-bonded complexes of carboxyl groups, which are targets of the extraction technology. The CFD modeling work is expected to determine critical mass transfer coefficients for CO2 capture using structured packing columns. Further, the developed CFD model and its validity will be tested against experimental data from various industrial and literature sources.

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