Chemkin Simulation of Mercury Oxidation in a Condensing Heat Exchanger

Mercury oxidation in a slip stream condensing heat exchanger (CHX) developed by the Energy Research Center (ERC) at Lehigh University was modeled using hundreds of possible chemical reactions and tens of species in coal-fired power plant furnace and flue gas downstream of the furnace. The modeling tools, CHEMKIN, SENKIN and PSR were used to conduct equilibrium calculations in the furnace and the kinetic calculations in the flue gas leading to the CHX. The detailed mechanism of mercury speciation at the furnace and downstream of the furnace has been investigated. Atomic chlorine is generated in the furnace and flows downstream of furnace, where it reacts with elemental mercury (Hg0). The predicted results suggest oxidation of Hg0 in the CHX occurs by this mechanism.Performance tests of the CHX at Great River Energy\u27s Coal Creek Station were carried out to study moisture, mercury and acid capture abilities of the CHX. The elemental mercury reduction rate and the amount of condensed water were measured in these tests. The measured results show ~35% of Hg0 was oxidized in the CHX.The mercury oxidation results show agreement between simulation and test within a typical range of HCl concentration of flue gas at furnace exit from 20 ppmv to 50 ppmv. The kinetic calculations downstream of the furnace show the oxidation reaction between Hg0 and atomic Cl primarily occurs at temperature 600K to 300K.The flue gas temperature in the CHX affects condensed water formation and mercury oxidation rate. An analytical model of heat and mass transfer processes in the CHX was used to obtain predictions of flue gas temperature profiles with different CHX inlet cooling water temperatures. The simulation results with lower CHX inlet cooling water temperature, which leads to higher flue gas cooling rate and reduced flue gas moisture content in the CHX, suggest higher Hg0 oxidation rates would be obtained. The predicted Hg0 reduction rate in the CHX increased to ~42% with CHX inlet cooling water temperature of 35℉ and a HCl concentration at the furnace exit of 40 ppmv

Investigation of Geothermal Heat Extraction Using Supercritical Carbon Dioxide (sCO2) and Its Utilization in sCO2-based Power Cycles and Organic Rankine Cycles - A Thermodynamic & Economic Perspective

CO2 capture and sequestration in deep saline aquifers is widely considered to be a leading option for controlling greenhouse gas emissions. One such possibility involves injection of supercritical carbon dioxide (sCO2) into a high-permeability geothermal reservoir. In addition to the benefit of sequestering the CO2 in reservoirs, the CO? can be used to mine geothermal heat for utilization above ground. This study adopts TOUGH2-T2Well/ECO2N multi-phase flow solver which has the capability to model fully coupled geothermal wellbores and reservoir to obtain desirable sCO? production flow rates, temperatures and pressures for power generations.As geothermal energy is widely recognized as a low grade heat source, power cycles with capabilities to convert low grade energy into electricity, such as Organic Rankine Cycle (ORC), have been considered. Additionally, sCO2-based power cycles have also been investigated comprehensively, since the similar temperature profiles between produced sCO2 from geothermal reservoirs and working fluid sCO2 potentially offer the advantages of avoiding pinch points to achieve better cycle performance. Moreover, the unique physical properties near critical point of CO2 are significant contributors for the considerably low compression work leading to higher net power output. Regarding thermodynamic optimization analyses, the maximum net power output is selected as the objective of optimizing cycle performance both for sCO2-based power cycles and ORCs.Possible cycle improvement methods have been taken into consideration and different configurations of sCO2-based power cycles have been analyzed thermodynamically. The direct turbine expansion, sCO2 Brayton cycle with pre-compression and inter-cooling, and transcritical sCO2 cycle have been chosen to perform cost estimation and optimization analyses. On the other hand, working fluid selection criteria have been proposed for ORCs to find out the most suitable working fluids using hot produced sCO2 from geothermal reservoirs. Considering cycle performance, working fluid physical property, operating pressure level and design complexity, a subcritical ORC with R245fa as working fluid is selected as the most competent ORC. Accordingly, to compare with the conventional geothermal power generation system, the cost estimation and optimization analyses have been accomplished by finding the minimum levelized cost of electricity (LCOE) for a nominal power plant capacity of 30 MWe. The plant capital cost, well cost, and operations and maintenance (O&M) cost are taken into account. The optimal results indicate that the LCOEs of selected four promising power generation technologies range from $0.276/kWh to$0.316/kWh in which more than half the portion is contributed by the O&M costs of cooling loads of rejecting heat for power cycles and geothermal loop CO? re-injections.Analyses have been performed to investigate the effects of reducing the cooling O&M cost and counting CO2 credit of sequestration on the LCOEs. It has been found if the cooling O&M cost is reduced to one quarter of the original value, the LCOEs can decrease 43 – 48% without counting the CO2 credit. On the other hand, if the counted CO2 credit is over $2/t for all new proposed power generation options where the largest breakeven point occurs, then they are all competitive compared to conventional geothermal power plants. Furthermore, improvements for reducing LCOEs of power generation options have been discussed and suggested, such as performing more detailed geothermal heat mining simulations, and adopting different cooling techniques to reduce O&M costs

Can Social Networking Sites Alleviate Depression? The Relation between Authentic Online Self-Presentation and Adolescent Depression:a Mediation Model of Perceived Social Support and Rumination

Ample evidence suggests that authentic self-presentation enhances personal well-being including reduced depression in the offline context, but it is unclear yet whether depression can be reduced by authentic self-presentation in the social networking sites (SNSs) environment. The present study investigated whether authentic self-presentation would predict reduced depression in the SNSs context. Further, we explored whether perceived social support and rumination would mediate the link between authentic self-presentation on SNSs and depression. A sample of 365 middle school students completed measures regarding demographics, authentic self-presentation on SNSs, depression, perceived social support, and rumination. The results indicated that: (a) authentic self-presentation on SNSs would predict reduced depression; (b) both perceived social support and rumination mediated the association between authentic self-presentation on SNSs and depression in an unparalleled fashion; and (c) perceived social support and rumination sequentially mediated the relation between authentic self-presentation on SNSs and depression. Implications of taking SNSs as an alternative way to detect and alleviate adolescent depression are discussed

Tectonic evolution and its control on oil–gas accumulation in southern East China Sea since the Jurassic

Based on the results from the previous research on Mesozoic igneous rocks, as well as tectonic environments in the northern South China Sea and southern East China Sea (NSCS-SECS), geophysical parameters, strata, and characteristics of seismic facies in NSCS-SECS were investigated. These findings were combined with results from the analysis of the balanced profile evolution to re-evaluate the tectonic evolution of SECS since the Jurassic. Furthermore, burial history and simulation of wells in the SECS were analyzed using well, seismic and source rock data. Furthermore, favorable models of oil–gas accumulation in the Lower–Middle Jurassic were proposed in combination with studies on elements and conditions of the petroleum system. The results demonstrated that the NSCS-SECS had consistent tectonic settings and comparable strata from the Jurassic to the Cretaceous time. There was a large unified basin in this period. The basin experienced two evolutionary stages, respectively, the fore-arc depression basin in the Early–Middle Jurassic (J1-2) and the back-arc faulted basin in the Late Jurassic–Cretaceous (J3-K). There was considerable deposition of dark mudstones in the SECS during the Lower–Middle Jurassic. The Keelung Sag was the depositional center accumulating the thickest section of the Lower–Middle Jurassic source rocks which entered a high-maturity stage. Hence, it was the hydrocarbon generation center in the SECS. The process of generating hydrocarbons from Lower–Middle Jurassic source rocks was of high complexity from northwest to southeast. The Lower–Middle Jurassic source rock at the northwest edges of the basin experienced two hydrocarbon generation stages, while the Keelung Sag toward the southeast experienced three hydrocarbon generation stages. The models and types of oil–gas accumulation in various evolutionary phases were different due to the control by tectonic evolution. Oil and gas that were generated by Lower–Middle Jurassic source rocks in the Keelung Sag migrated and accumulated in the western high-tectonic units. Research findings provide insights into Mesozoic oil and gas exploration in the NSCS-SECS

Molecular subgroups of adult medulloblastoma: a long-term single-institution study

Background Recent transcriptomic approaches have demonstrated that there are at least 4 distinct subgroups in medulloblastoma (MB); however, survival studies of molecular subgroups in adult MB have been inconclusive because of small sample sizes. The aim of this study is to investigate the molecular subgroups in adult MB and identify their clinical and prognostic implications in a large, single-institution cohort. Methods We determined gene expression profiles for 13 primary adult MBs. Bioinformatics tools were used to establish distinct molecular subgroups based on the most informative genes in the dataset. Immunohistochemistry with subgroup-specific antibodies was then used for validation within an independent cohort of 201 formalin-fixed MB tumors, in conjunction with a systematic analysis of clinical and histological characteristics. Results Three distinct molecular variants of adult MB were identified: the SHH, WNT, and group 4 subgroups. Validation of these subgroups in the 201-tumor cohort by immunohistochemistry identified significant differences in subgroup-specific demographics, histology, and metastatic status. The SHH subgroup accounted for the majority of the tumors (62%), followed by the group 4 subgroup (28%) and the WNT subgroup (10%). Group 4 tumors had significantly worse progression-free and overall survival compared with tumors of the other molecular subtypes. Conclusions We have identified 3 subgroups of adult MB, characterized by distinct expression profiles, clinical features, pathological features, and prognosis. Clinical variables incorporated with molecular subgroup are more significantly informative for predicting adult patient outcome

Supported CuII Single-Ion Catalyst for Total Carbon Utilization of C2 and C3 Biomass-Based Platform Molecules in the N-Formylation of Amines

The shift from fossil carbon sources to renewable ones is vital for developing sustainable chemical processes to produce valuable chemicals. In this work, value-added formamides were synthesized in good yields by the reaction of amines with C2 and C3 biomass-based platform molecules such as glycolic acid, 1,3-dihydroxyacetone and glyceraldehyde. These feedstocks were selectively converted by catalysts based on Cu-containing zeolite 5A through the in situ formation of carbonyl-containing intermediates. To the best of our knowledge, this is the first example in which all the carbon atoms in biomass-based feedstocks could be amidated to produce formamide. Combined catalyst characterization results revealed preferably single CuII sites on the surface of Cu/5A, some of which form small clusters, but without direct linking via oxygen bridges. By combining the results of electron paramagnetic resonance (EPR) spin-trapping, operando attenuated total reflection (ATR) IR spectroscopy and control experiments, it was found that the formation of formamides might involve a HCOOH-like intermediate and .NHPh radicals, in which the selective formation of .OOH radicals might play a key role. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH Gmb