1,720,985 research outputs found
Assessment of the carbon looping (CarboLoop) concept in a novel twin fluidized bed reactor
No full textCarboLoop is an innovative method, developed and patented by Salatino and Senneca (2009, 2010) and Salatino et al. (2010), for combustion of coal with inherent separation of CO2 which represents an alternative to chemical looping combustion (CLC) for solid carbon. Unlike other CLC processes, in CarboLoop there is no need for oxygen carriers because the property of carbons to uptake oxygen at low temperatures, forming oxygenated surface complexes, and to release them as CO and CO2 at higher temperatures is exploited (Haynes, 2001). The CarboLoop concept requires the utilization of two reactors (in particular two interconnected fluidized beds): an Oxidizer, where the coal is kept in contact with air at relatively mild temperature (4400°C) to foster oxygen chemisorption, and a Desorber, operating at higher temperature (7700°C) where the oxygenated C-O compounds are desorbed in an almost pure CO2 stream. The first proof-of-concept of CarboLoop has been given by discontinuous experiments in a thermogravimetric analyzer (Salatino and Senneca, 2009, Salatino et al., 2010, Senneca et al.,2013). Experiments have been carried out using different solid carbon materials and aimed at assessing the extent and rate of oxygen uptake at different temperatures. In this study the CarboLoop concept is tested in a looping apparatus. The "Twin Bed Reactor" (Coppola et al., 2016) has been purposely developed for the characterization of looping processes at the bench scale while preserving the time-temperature history that particles experience in a real looping plant. It consists of two lab-scale bubbling beds of silica sand, acting as thermal ballast, operated batchwise, connected by a rapid solids transfer line. Carbon samples are fed to the system and undergo sequential steps of Oxidization and Desorption of pre-set duration by rapid transfer from one reactor to the other. The fuel tested is a bituminous coal char with size range of 400-1000μm. The Oxidizer was operated in air at different temperatures in the range 200-300°C with a holding time of 20 min. The desorption stage was carried out at 700-800°C with the same holding time of 20 min in N2. The progress of char oxidation was monitored following the profiles of CO and CO2 concentration in the exhaust. Moreover, the effect of multiple cycles on char oxidation/desorption propensity was investigated. Results pave the way for validation of the Carboloop concept and optimization of the process conditions
Reply to the letter 'Kinetics of decomposition measured using thermobalance' by Juan A. Conesa
No full textThe Influence of Heat Treatment and Weathering on the Gasification Reactivity of Montana Lignite
No full textThermogravimetric analysis and temperature programmed desorption have been used to assess the influence of annealing and of char weathering on the gasification reactivity of a Montana lignite. To this end, lignite samples were heat treated at 900 °C for different times in a nitrogen atmosphere. Samples either weathered under ambient conditions for six months or nonweathered were tested to assess their reactivity toward oxygen and carbon dioxide and their propensity to chemisorb either reactants. Reactivity and chemisorption capacity of heat-treated chars were found to be closely related to each other. Annealing mainly affects the availability of sites that are active toward oxygen chemisorption, a property that is directly reflected by char oxyreactivity. Also, the effect of weathering is strongly emphasized by the previous temperature history of the chars. On the contrary, the ability of chars to chemisorb carbon dioxide and related gasification reactivity are negligibly affected by heat treatment. Results are analyzed considering possible relationships between the reactivity, chemisorption capacity, and chemical and microstructural modifications induced by heat treatment in low-rank coals. It is believed that modifications of the organic structure, rather than mineral matter transformations, are responsible for the observed phenomena
The Influence of Heat Treatment and Weathering on the Gasification Reactivity of Montana Lignite
No full textThermal degradation of pesticides under oxidative conditions
No full textThe paper addresses thermal decomposition under oxidative conditions of 16 pesticides. Within the scope of the paper such 16 substances have been divided in four groups:(1)Pesticides with linear molecule belonging to the family of aldoxime carbamates.(2)Benzimidazolylcarbamates.(3)Pyrethroids.(4)Pesticides containing one aromatic (heterocyclic in one case) ring within their structure. The experimental work consists of non isothermal thermogravimetric analysis with 5% oxygen in helium, using a TG-DSC-MS system equipped with a Skimmer device that ensures the simultaneousness of thermogravimetric analysis with the analysis of evolved gas and rules out the possibility of secondary reactions in the gas phase. Results have been analyzed in order to highlight similarities and differences in the modes of decomposition of pesticides within and among the four mentioned groups. The influence of oxygen and the yield in gaseous products has also been addressed. © 2007 Elsevier B.V. All rights reserved
Looping cycles for low carbon technologies: A survey of recent research activities in Naples
No full textIn the last decades several looping processes for clean utilization of fossil resources have been proposed with the aim of providing transient/long-term solutions to the challenge of near-zero emission energy production. A selection of solids looping processes for both carbon oxidation/gasification and CO2 capture/utilization will be surveyed, with a specific focus on the contribution given by the research group active in Naples. A novel concept has been developed (CarboLoop) to accomplish capture-ready combustion/gasification of carbon through iterated oxidation/desorption cycles. The idea is that alternated oxygen chemisorption on carbon followed by thermal desorption of oxides as CO/CO2 provide a path with inherent oxygen separation and concentrated CO/CO2 streams. The path to exploitation of the CarboLoop is laid by elucidation of the thermochemistry of carbon oxidation throughout dynamic oxidizing/reducing cycles. Calcium Looping (CaL) provides a feasible path to accomplish carbon capture from CO2-bearing exhaust. Its efficiency is affected by sorbent thermal sintering and by particle attrition/fragmentation. There is still a lack of characterization of the concurrent effect of steam and SO2 in terms of sorbent availability and selective uptake of CO2. The performance of Ca-based sorbents has been scrutinized in the frame of ternary CO2-SO2-H2O environments. Methanation is an attractive path to CO2 utilization. Sorption-Enhanced Methanation (SEM) exploits the favourable effect on thermodynamics of continuous in-situ removal of steam generated by methanation by a sorbent. SEM is conveniently performed as a looping process, whose performance has been characterized by means of a novel test rig configuration based on two-interconnected fluidized beds
Characterization of surface-oxides on char under periodically changing oxidation/desorption conditions
No full textA novel experimental method based on periodic swinging of oxidation/desorption reaction stages is used to investigate the formation and release of surface oxides on carbon under mild oxidation conditions. The chemical nature of the carbon-oxygen complex and the key mechanistic features of the interaction between solid carbon and oxygen are assessed by continuous monitoring of CO/CO2 release during the experiments and by probing - via XPS - the chemical nature of oxygen moieties at different stages of the experiments. Sub-bituminous char is used as carbon substrate. The proposed technique turns out to be a simple though effective method to assess the nature and extent of surface oxides formed under different reaction conditions. Results show that oxygen is extensively chemisorbed on carbon as epoxy moieties below ~750 K. At higher temperatures, isomerization into “edge” oxides (ether-hydroxyl and carbonyl-carboxyl functionalities) takes place, followed by oxide decomposition and desorption as CO and CO2. Estimates of the oxygen chemisorption rate as a function of temperature are given. The study provides new insights into the extent and chemical nature of surface oxides on carbons, that represent one key to their successful application in several areas of energy conversion and storage. Oxides affect surface physico-chemical (polarity, wettability) and electrical (capacitance, resistivity) properties, relevant to application of carbons in batteries, supercapacitors and fuel cells. Moreover, understanding surface oxides on carbon is helpful in designing novel concepts of energy conversion from carbon through chemical looping, transient operation of stationary combustors, synthesis of carbon-based catalysts, beneficiation of ash
Pyrolysis and combustion of a solid refinery waste
No full textThis study addresses pyrolysis and combustion of a heavy hydrocarbon residue of the refinery industry. The material has good calorific value (HHV = 34050 kJ/kg), is solid at room temperature and has a high content of metals, in particular Mo, and impurities. The effect of these metals on pyrolysis and combustion has been investigated. The activity included first of all the physical and chemical characterization of the raw sample before and of samples of char and ash by means of several techniques: ICP, SEM EDAX. Moreover pyrolysis and combustion have been investigated by TGA and in small scale reactors of the fixed and fluidized bed type. Mo, very abundant in the raw sample, is relatively stable upon pyrolysis at 500–600 °C, but is only marginally retained in the ash after combustion, because of the large volatility of this metal in the oxidized state. The metal content has interesting effects on the pyrolysis and char combustion behavior: when the sample is heated up under mildly oxidizing atmospheres (i.e oxygen concentration of < 1%), the metals promote the uptake of oxygen in parallel with char formation and affect the degree of graphitization of the carbon structure The composition of the pyrolysis gas is strongly affected by the presence of even low concentration of oxygen. Despite the fact that a catalytic action of the metals could be expected, reaction times in a fluidized bed reactor are relatively large compared to other conventional and non conventional solid fuels
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