Thermodynamic study of heavy metals behavior during municipal waste incineration

The incineration of municipal solid waste (MSW) contributes significantly to the presence of heavy metals in urban area aerosols. It is thus important to ascertain the quantities and chemical forms of the heavy metals (HM) that are emitted from the incineration plant stacks. The behaviour of HM, which depends strongly on the thermal and chemical environments, was investigated herein with a modelling approach, consisting of several parts. First, a refuse bed combustion model was developed for simulating on-grate MSW incineration. It describes most of the physico-chemical and thermal phenomena occurring during waste combustion. Second, results from the bed model were taken as boundary conditions to perform 3D simulations of the post-combustion zone and of the boiler. The case studied was of the Strasbourg incineration plant. Finally, the local thermal conditions and the local elementary compositions of gas and solid phases obtained from these simulations were used to carry out thermodynamic calculations of the speciation of HM at each point in the incinerator. The results for four metals (Cd, Zn, Pb, Cr) are presented, discussed and compared to available data. Predicted species are in agreement with observations for volatile metals, except lead, whose volatilization seems overestimated

Energy, exergy and economic analyses of new coal-fired cogeneration hybrid plant with wind energy resource

© 2020 Elsevier Ltd A novel configuration of a coal-fired cogeneration plant is proposed in this paper. This novel system is composed of combustion chamber, Rankine cycle, absorption chiller, alkaline electrolyzer, and methanation plant. In the proposed configuration, the heat of exhaust gas from the combustion chamber can be used in a Rankine cycle to produce electricity. The heat of exhaust gas also powers the absorption chiller to provide cooling. The exhaust gas flows through a sulfur extraction unit to separate sulfur from CO2 gas. To supply electrical power, wind turbines alongside the Rankine cycle are considered. A part of the produced electricity from both the Rankine cycle and the wind turbines can be used by an alkaline electrolyzer to produce hydrogen and oxygen. The CO2 gas from sulfur unit and hydrogen gas (H2) provided by the electrolyzer can be delivered to a methanation unit to produce syngas (CH4) for different applications. The oxygen from the electrolyzer is injected into the combustion chamber to improve the combustion process. Results show that by using 80 units of 1 MW Nordic wind turbine to generate electricity, all of the CO2 in the exhaust gas is converted to syngas. The whole system energy and exergy efficiencies are equal to 16.6% and 16.2%. The highest and lowest energy efficiencies of 85% and 30.1% are related to compressor and steam power plants. The energy and exergy efficiencies of the wind turbine are 30.7% and 11.9%. The system can produce 40920.4 MWh of electricity and 180.5 MWh of cooling. As CO2 is consumed to produce syngas, the proposed system is capable of avoiding a significant amount of 2776 t CO2 emissions while producing 1009.4 t syngas annually. Based on economic analysis, the payback period of the system is 11.2 y, and internal rate of return is found to be 10%, which can prove the viability of the proposed configuration

Oxy-fired fluidized bed combustors with a flexible power output using circulating solids for thermal energy storage

This paper presents a power plant concept based on an oxy-fired circulating fluidized bed combustor (oxy-CFBC) combined with thermal energy storage on a large scale. The concept exploits to full advantage the large circulation flows of high temperature solids that are characteristic of these systems. Two solid storage silos (one for high temperature and the other for low temperature solids) connected to the oxy-fired CFBC allow variability in power output without the need to modify the fuel firing rate and/or the mass flow of O2 to the combustor. During the periods of high power demand the system can deliver additional thermal power by extracting heat from a series of fluidized bed heat exchangers fed with solids from the high temperature silo. Likewise, during period of low power demand, the thermal power output can be reduced by using the energy released in the combustor to heat up the low temperature solids on their way from the low temperature silo to the oxy-CFBC and storing them in the high temperature silo located below the cyclone. A preliminary economic analysis of two designs indicates that this highly flexible system could make this type of power plant more competitive in the electricity markets where fossil fuels with CCS will be required to respond to a large variability in power output.Y.A. Criado thanks the Government of the Principality of Asturias for a Ph.D. fellowship (Severo Ochoa Program). B. Arias thanks the Spanish MINECO for the award of a Ramon y Cajal contract.Peer reviewe

A Review of Solar Thermochemical CO2 Splitting Using Ceria-Based Ceramics With Designed Morphologies and Microstructures

This review explores the advances in the synthesis of ceria materials with specific morphologies or porous macro- and microstructures for the solar-driven production of carbon monoxide (CO) from carbon dioxide (CO2). As the demand for renewable energy and fuels continues to grow, there is a great deal of interest in solar thermochemical fuel production (STFP), with the use of concentrated solar light to power the splitting of carbon dioxide. This can be achieved in a two-step cycle, involving the reduction of CeO2 at high temperatures, followed by oxidation at lower temperatures with CO2, splitting it to produce CO, driven by concentrated solar radiation obtained with concentrating solar technologies (CST) to provide the high reaction temperatures of typically up to 1,500°C. Since cerium oxide was first explored as a solar-driven redox material in 2006, and to specifically split CO2 in 2010, there has been an increasing interest in this material. The solar-to-fuel conversion 1097efficiency is influenced by the material composition itself, but also by the material morphology that mostly determines the available surface area for solid/gas reactions (the material oxidation mechanism is mainly governed by surface reaction). The diffusion length and specific surface area affect, respectively, the reduction and oxidation steps. They both depend on the reactive material morphology that also substantially affects the reaction kinetics and heat and mass transport in the material. Accordingly, the main relevant options for materials shaping are summarized. We explore the effects of microstructure and porosity, and the exploitation of designed structures such as fibers, 3-DOM (three-dimensionally ordered macroporous) materials, reticulated and replicated foams, and the new area of biomimetic/biomorphous porous ceria redox materials produced from natural and sustainable templates such as wood or cork, also known as ecoceramics

Solar thermochemical CO2 splitting using cork-templated ceria ecoceramics

This work addresses the solar-driven thermochemical production of CO and O2 from two-step CO2-splitting cycles, using both ceria granules prepared from cork templates (CG) and ceria foams from polyurethane templates (CF). These materials were cycled in a high-temperature indirectly-irradiated solar tubular reactor using a temperature-swing process. Samples were typically reduced at 1400 °C using concentrated solar power as a heating source and subsequently oxidised with CO2 between 1000-1200 °C. On average, CO production yields for CG were two times higher than for CF, indicating that the morphology of this three-dimensionally ordered macroporous (3-DOM) CeO2 improves the reaction kinetics. Their performance stability was demonstrated by conducting 11 cycles under solar irradiation conditions. Slightly increasing the reduction temperature strongly enhanced the reduction extent, and thus the CO production yield (reaching about 0.2 mmol g-1 after reduction at 1450 °C in inert gas), while decreasing the oxidation temperature mainly improved the CO production rate (up to 1.43 μmol s-1 g-1 at 1000 °C). Characterisation of the 3-DOM structure, by means of XRD and SEM, provided insights into the reactivity behaviour of the developed materials. The pre-sintered ceria granules retained their structure after cycling. The fact that the mean cell size of CG is smaller (at least one order of magnitude) than that of CF suggests that its exposed surfaces enhanced reaction rates by a factor of two. Moreover, the maximum fuel production rate of CG was roughly three times greater than that reported previously for a ceria reticulated porous foam with dual-scale porosity

Dynamic response of an accelerator driven system to accelerator beam interruptions for criticality

Subcritical nuclear reactors driven by intense neutron sources can be very suitable tools for nuclear waste transmutation, particularly in the case of minor actinides with very low fractions of delayed neutrons. A proper control of these systems needs to know at every time the absolute value of the reactor subcriticality (negative reactivity), which must be measured by fully reliable methods, usually conveying a short interruption of the accelerator beam in order to assess the neutron flux reduction. Those interruptions should be very short in time, for not disturbing too much the thermal magnitudes of the reactor. Otherwise, the cladding and the fuel would suffer from thermal fatigue produced by those perturbations, and the mechanical integrity of the reactor would be jeopardized. It is shown in this paper that beam interruptions of the order of 400 ms repeated every second would not disturb significantly the reactor thermal features, while enabling for an adequate measurement of the negative reactivity

Solar Redox Cycling of Ceria Structures Based on Fiber Boards, Foams, and Biomimetic Cork-Derived Ecoceramics for Two-Step Thermochemical H2O and CO2Splitting

Solar thermochemical conversion of H2O and captured CO2 is considered for the production of high-value solar fuels and CO2 valorization, using nonstoichiometric oxygen-exchange redox materials. This work aims to compare the thermochemical cycle performance of different ceria structures, including biomimetic cork-templated ceria (CTCe), ceria foams (CeF), and ceria bulk fiber boards (CeFB), to study the effect of the morphology on fuel production from two-step H2O and CO2 splitting via solar redox cycling. The considered materials underwent thermochemical cycles in a directly irradiated solar reactor under various operating conditions. Typically, a thermal reduction at 1400 °C under Ar at atmospheric pressure, using concentrated solar energy, was carried out followed by an oxidation step with H2O or CO2 between 800 and 1050 °C. The comparison of the fuel production rate and yield from the reactive materials highlighted the importance of the material thermal stability during cycling. CTCe and CeF showed good O2 and fuel production stability over repeated cycles, while CeFB exhibited a decrease of the production because of sintering and thermal gradient due to its low thermal conductivity. Biomimetic CTCe showed a higher fuel production rate compared to the other investigated materials, explained by the favorable microstructure of the cork-based ceramic. The morphology obtained from the cork structure led to the improvement of the redox activity, demonstrating the relevance of studying this material for thermochemical H2O and CO2 splitting cycles. In addition, the impact of the operating conditions was investigated. A decrease of the starting oxidation temperature, an increase of the CO2 molar fraction (lower CO/CO2 ratio), or a high total gas flow rate favoring gas product dilution had a beneficial impact on the CO (or H2) production rate

Testing postcombustion CO2 capture with CaO in a 1.7 MWt pilot facility

AbstractCalcium looping, CaL, is a new and rapidly developing technology that makes use of CaO as a high temperature regenerable sorbent of CO2. Previous theoretical and lab scale studies have shown that this technology could lead to a substantial reduction in the cost of CO2 capture and energy penalties because heat can be effectively recovered from this high temperature solid looping system. We report in this paper on the first results from a pilot plant designed to demonstrate the viability of postcombustion capture of CO2 using CaL under conditions comparable to those expected in a large scale plant. The pilot includes two interconnected circulating fluidized bed reactors of 15 m height: a CO2 absorber (carbonator) able to treat up to 2400kg/h (equivalent to about 1.7 MWth), and an oxy-fired CFB calciner with a firing power between 1-3 MWth. CO2 capture efficiencies over 90% have been experimentally observed, including continuous operation with highly cycled solids in the system (i.e. with modest CO2 carrying capacities). SO2 capture is shown to be extremely high, with concentrations of SO2 well below 10 ppmv at the exit of the carbonator. Closure of carbon and sulfur balances is satisfactory. These results should be valuable base for model validation and scaling up purposes in future stages of the EU FP7 “CaOling” project, under which this investigation has been carried out

␥-Hydroxybutyrate (GHB) in Humans Pharmacodynamics and Pharmacokinetics

ABSTRACT: Despite ␥-hydroxybutyrate (GHB) therapeutic uses and the increasing concern about its toxicity, few studies have addressed GHB dose-related effects under controlled administration and their relationship with its pharmacokinetics. The study design was double-blind, randomized, crossover, and controlled. As a pilot pharmacology phase I study, increasing doses of GHB were given. Single oral sodium GHB doses (40, 50, 60, and 72 mg/kg) were administered to eight volunteers. Plasma and urine were analyzed for GHB by gas chromatographymass spectrometry. Physiological effects, psychomotor performance, and subjective effects were examined simultaneously. GHB produced doserelated changes in subjective effects as measured by questionnaires and VAS. GHB showed a mixed stimulant-sedative pattern, with initially increased scores in subjective feeling of euphoria, high, and liking followed by mild-moderate symptoms of sedation with impairment of performance and balance. Mean peak GHB plasma concentrations were 79.1, 83.1, 113.5, and 130.1 g/L for 40, 50, 60, and 72 mg/kg, respectively. GHB-mediated physiological and subjective effects were dose dependent and related to GHB plasma concentrations. GHB urinary excretion was mainly related to administered doses. GHB-mediate