Mathematical Modeling Of Pre And Post Combustion Processes In Coal Power Plant

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

THERMODYNAMIC MODELING AND EQUILIBRIUM SYSTEM DESIGN OF A SOLVENT EXTRACTION PROCESS FOR DILUTE RARE EARTH SOLUTIONS

Rare earth elements (REEs) are a group of 15 elements in the lanthanide series along with scandium and yttrium. They are often grouped together because of their similar chemical properties. As a result of their increased application in advanced technologies and electronics including electric vehicles, the demand of REEs and other critical elements has increased in recent decades and is expected to significantly grow over the next decade. As the majority of REEs are produced and utilized within the manufacturing industry in China, concerns over future supplies to support national defense technologies and associated manufacturing industries has generated interest in the recovery of REEs from alternate sources such as coal and recycling. A solvent extraction (SX) process and circuit was developed to concentrate REEs from dilute pregnant leach solutions containing low concentrations of REEs and high concentrations of contaminant ions. The separation processes used for concentrating REEs from leachates generated by conventional sources are not directly applicable to the PLS generated from coal-based sources due to their substantially different composition. Parametric effects associated with the SX process were evaluated and optimized using a model test solution produced based on the composition of typical pregnant leach solution (PLS) generated from the leaching of pre-combustion, bituminous coal-based sources. Di-2(ethylhexyl) phosphoric acid (DEHPA) was used as the extractant to selectively transfer the REEs in the PLS from the aqueous phase to the organic phase. The tests performed on the model PLS found that reduction of Fe3+ to Fe2+ prior to introduction to the SX process provided a four-fold improvement in the rejection of iron during the first loading stage in the SX circuit. The performances on the model system confirmed that the SX process was capable of recovering and concentrating the REEs from a dilute PLS source. Subsequently, the process and optimized parametric values were tested on a continuous basis in a pilot-scale facility using PLS generated from coal coarse refuse. The continuous SX system was comprised of a train of 10 conventional mixer settlers having a volume of 10 liters each. A rare earth oxide (REO) concentrate containing 94.5% by weight REO was generated using a two- stage (rougher and cleaner) solvent extraction process followed by oxalic acid precipitation. The laboratory evaluations using the model PLS revealed issues associated with a third phase formation. Tributyl Phosphate (TBP) is commonly used as a phase modifier in the organic phase to improve the phase separation characteristics and prevent the formation of a third phase. The current study found that the addition of TBP affected the equilibrium extraction behavior of REE as well as the contaminant elements., The effect on each metal was found to be different which resulted in a significant impact on the separation efficiency achieved between individual REEs as well as for REEs and the contaminant elements. The effect of TBP was studied using concentrations of 1% and 2% by volume in the organic phase. A Fourier Transform Infrared (FTIR) analysis on the mixture of TBP and DEHPA and experimental data quantifying the change in the extraction equilibrium for each element provided insight into their interaction and an explanation for the change in the extraction behavior of each metal. The characteristic peak of P-O-C from 1033 cm-1 in pure DEHPA to 1049 cm-1 in the 5%DEHPA-1%TBP mixture which indicated that the bond P-O got shorter suggesting that the addition of TBP resulted in the breaking of the dimeric structure of the DEHPA and formation of a TBP-DEHPA associated molecule with hydrogen bonding. The experimental work leading to a novel SX circuit to treat dilute PLS sources was primarily focused on the separation of REEs from contaminant elements to produce a high purity rare earth oxide mix product. The next step in the process was the production of individual REE concentrates. To identify the conditions needed to achieve this objective, a thermodynamic model was developed for the prediction of distribution coefficients associated with each lanthanide using a cation exchange extractant. The model utilized the initial conditions of the system to estimate the lanthanide complexation and the non-idealities in both aqueous and organic phases to calculate the distribution coefficients. The non-ideality associated with the ions in the aqueous phase was estimated using the Bromley activity coefficient model, whereas the non-ideality in the organic phase was computed as the ratio of the activity coefficient of the extractant molecule and the metal extractant molecule in the organic phase which was calculated as a function of the dimeric concentration of the free extractant in the organic phase. To validate the model, distribution coefficients were predicted and experimentally determined for a lanthanum chloride solution using DEHPA as the extractant. The correlation coefficient defining the agreement of the model predictions with the experimental data was 0.996, which is validated the accuracy of the model. As such, the developed model can be used to design solvent extraction processes for the separation of individual metals without having to generate a large amount of experimental data for distribution coefficients under different conditions

Adiabat_1ph: A new public front-end to the MELTS, pMELTS, and pHMELTS models

The program adiabat_1ph is a simple text-menu driver for subroutine versions of the algorithms MELTS, pMELTS, and pHMELTS [Asimow et al., 2004; Ghiorso et al., 2002; Ghiorso and Sack, 1995]. It may be used to calculate equilibrium assemblages along a thermodynamic path set by the user and can simultaneously calculate trace element distributions. The MELTS family of algorithms is suitable for multicomponent systems, which may be anhydrous, water-undersaturated, or water-saturated, with the options of buffering oxygen fugacity and/or water activity. A wide variety of calculations can be performed either subsolidus or with liquid(s) present; melting and crystallization may be batch, fractional, or continuous. The software is suitable for Linux, MacOS X, and Windows, and many aspects of program execution are controlled by environment variables. Perl scripts are also provided that may be used to invoke adiabat_1ph with some command line options and to produce output that may be easily imported into spreadsheet programs, such as Microsoft Excel. Benefits include a batch mode, which allows almost complete automation of the calculation process when suitable input files are written. This technical brief describes version 1.04, which is provided as ancillary material. Binaries, scripts, documentation, and example files for this and future releases may be downloaded at http://www.gps.caltech.edu/~asimow/adiabat. On a networked computer, adiabat_1ph automatically checks whether a newer version is available

Tracer Applications of Noble Gas Radionuclides in the Geosciences

The noble gas radionuclides, including 81Kr (half-life = 229,000 yr), 85Kr (11 yr), and 39Ar (269 yr), possess nearly ideal chemical and physical properties for studies of earth and environmental processes. Recent advances in Atom Trap Trace Analysis (ATTA), a laser-based atom counting method, have enabled routine measurements of the radiokrypton isotopes, as well as the demonstration of the ability to measure 39Ar in environmental samples. Here we provide an overview of the ATTA technique, and a survey of recent progress made in several laboratories worldwide. We review the application of noble gas radionuclides in the geosciences and discuss how ATTA can help advance these fields, specifically determination of groundwater residence times using 81Kr, 85Kr, and 39Ar; dating old glacial ice using 81Kr; and an 39Ar survey of the main water masses of the oceans, to study circulation pathways and estimate mean residence times. Other scientific questions involving deeper circulation of fluids in the Earth's crust and mantle also are within the scope of future applications. We conclude that the geoscience community would greatly benefit from an ATTA facility dedicated to this field, with instrumentation for routine measurements, as well as for research on further development of ATTA methods

Rare-metal granites as a potential source of critical metals: A geometallurgical case study

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordBecause of their low grades in critical metals such as Light Rare Earth Elements (LREE) or Sn, rare-metal granites are not considered as economic for metal recovery but, when altered, they are often exploited for their industrial minerals. The St Austell rare-metal granite is well known for its world-class kaolin deposits which formed as a result of the extensive weathering and alteration of the underlying granite. The St Austell granite body is composed of several granite components, each having its own accessory minerals assemblage. As a result of the kaolinisation process, some metal-bearing accessory minerals of the granite, such as monazite (LREE) or cassiterite (Sn), are partially liberated from the gangue which allow their pre-concentration in the micaceous residue which is considered as a potential source for critical metals recovery. Similarities with other similar rare-metal granites suggest that topaz granite is the most prospective for disseminated magmatic Sn-Nb-Ta-REE mineralization. However, comparison of the potentiality of 3 granite types i.e., biotite, topaz and tourmaline granites suggest that biotite granites is actually the most prospective due to higher degree of kaolinisation of the biotite granite which favour pre-concentration of its accessory mineral in the micaceous residue. In order to develop a geometallurgical framework for extraction of kaolin and metals from the selected granite component, a field sampling campaign is performed. Core samples are processed in the laboratory using a characterisation program that mimics the full-scale kaolin refining route. Two main products are recovered through this program, viz. MR180 (−180 +53 µm) and P5 (−5 µm), which correspond to a fine micaceous residue and a fine kaolin product respectively. These products are both analysed routinely for major and minor trace elements by XRF and yields are recorded to indicate process performance. A selected number of MR180 samples are also being characterised in terms of particle size by laser light scattering, geochemistry by ICP-MS, and mineralogy by QEMSCAN®. Comparison of characterisation results of MR180 samples and corresponding industrial residue samples shows a good correlation, suggesting that sample analyses are representative for the in-situ deposit and the processing behaviour. Monazite is found to be either fully liberated or fully locked from one sample to the other. Next, pilot-scale gravity concentration tests are performed on micaceous residue samples. Characterisation of the processing products shows that monazite lost in the tailings is mostly locked within tourmaline or micas and is fine grained. Then, predictive regression models for spiral separation performance in terms of recovery, product grade and enrichment as a function of the feed grade are developed for MR180 LREE grade data. Finally, kaolin resources can be classified using quantitative indicators such as yield of the P5 product and the iron oxides content which provides insight into the kaolin quality in terms of whiteness. This geometallurgical classification can be used to delineate zones of interest within the deposit. Although kaolin quality and recovery primarily inform extraction planning, zones which are also of interest for metal recovery can be identified. The proposed model predicts whether the expected LREE grade and recovery satisfy the by-product requirements.European CommissionNatural Environment Research Council (NERC)French National Research Agenc

A Critical Assessment on the Resources and Extraction of Rare Earth Elements from Acid Mine Drainage

Rare earth elements (REEs) are crucial to many modern products used in both civilian and defense applications. Currently, a reliable supply of these elements is uncertain with the clear majority of REE production and refining occurring predominately in China. Furthermore, domestic ore deposits with commercially attractive concentrations of REEs are uncommon in the United States. As a result, the identification of a domestic supply of these technology metals is essential not only for manufacturing consumer merchandise but also for national security. Recently, one promising source of REEs has been identified: coal and coal-byproducts. One of those is acid mine drainage (AMD), the most prevalent water quality impediment in the Appalachian coal mining region. This research found that AMD concentrates REEs through an autogenous process where the presence of sulfide material in an oxidizing environment results in a general lowering of water pH. This acidic water in turn leaches metals, including REEs, from the surrounding geologic strata. Accordingly, this degraded water holds potential value as a REE source. Furthermore, identification of this environmental burden as a reliable supply of REEs could incentivize additional treatment efforts, while providing an additional revenue stream to those responsible for mitigating this substantial source of water pollution. However, current scientific literature lacks systemic studies that describe the content, distribution, and processing amenability of this resource. Therefore, this research details a study that: (1) characterized the REEs contained in AMD and its byproducts; (2) classified the REEs inherent to AMD and identified the size of the resource; (3) designed a process to recover REEs from AMD byproducts; and (4) demonstrated the feasibility of the beneficiation process by generating a concentrated REE product from AMD. This was accomplished by conducting a broad sampling campaign where 185 raw AMD and 623 AMD precipitate (AMDp) samples were collected across the Northern and Central Appalachian coal basins. Next, a series of laboratory experiments were conducted to determine a hydrometallurgical processing route to recover the REEs from AMDp. The results of the laboratory-scale studies were utilized to design a bench-scale plant capable of producing a concentrated REE product. Finally, an acid leaching and solvent extraction demonstration plant was constructed and operated which produced a rare earth oxide product with a purity greater than 60%

Integrated Applications of Geo-Information in Environmental Monitoring

This book focuses on fundamental and applied research on geo-information technology, notably optical and radar remote sensing and algorithm improvements, and their applications in environmental monitoring. This Special Issue presents ten high-quality research papers covering up-to-date research in land cover change and desertification analyses, geo-disaster risk and damage evaluation, mining area restoration assessments, the improvement and development of algorithms, and coastal environmental monitoring and object targeting. The purpose of this Special Issue is to promote exchanges, communications and share the research outcomes of scientists worldwide and to bridge the gap between scientific research and its applications for advancing and improving society