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Morgantown, WV, United States

Breault R.W.,U.S. National Energy Technology Laboratory | Monazam E.R.,REM Engineering Services PLLC
Applied Energy | Year: 2015

The rate of the reduction reaction of a low cost natural hematite oxygen carrier for chemical looping combustion was investigated in a fixed bed reactor where hematite samples of about 1. kg were exposed to a flowing stream of methane and argon. The investigation aims to develop understanding of the factors that govern the rate of reduction with in larger reactors as compared to mostly TGA investigations in the literature. A comparison of the experimental data with a model indicated that reaction between the methane and the iron oxide shows multi-step reactions. The analysis also shows that the conversion occurs with a process that likely consumes all the oxygen close to the surface of the hematite particles and another process that is likely controlled by the diffusion of oxygen to the surface of the particles. Additional analysis shows that the thickness of the fast layer is on the order of 8 unit crystals. This is only about 0.4% of the hematite; however, it comprises about 20-25% of the conversion for the 10. min reduction cycle. © 2015. Source

Spenik J.L.,REM Engineering Services PLLC | Ludlow J.C.,U.S. National Energy Technology Laboratory
Powder Technology | Year: 2010

A method to determine local mass flux measurements within the riser of a circulating fluidized bed using the rate of impingement of particles on the surface of a piezoelectric pressure transducer is described. Statistically designed experiments with various solids circulation rates and riser gas velocities were conducted in the riser of a cold flow circulating fluidized bed to verify the accuracy of the method. Also, various techniques to relate the impingement rate to mass flux were employed. It is believed that this method delivers results in situations where more standard methods, such as isokinetic sampling, fail. © 2010 Elsevier B.V. Source

Monazam E.R.,REM Engineering Services PLLC | Breault R.W.,U.S. National Energy Technology Laboratory | Siriwardane R.,U.S. National Energy Technology Laboratory | Richards G.,U.S. National Energy Technology Laboratory | Carpenter S.,URS Energy and Construction Inc.
Chemical Engineering Journal | Year: 2013

Chemical-looping combustion (CLC) has emerged as a promising technology for fossil fuel combustion which produces a sequestration ready concentrated CO2 stream in power production. A CLC system is composed with two reactors, an air and a fuel reactor. An oxygen carrier such as hematite (94%Fe2O3) circulates between the reactors, which transfers the oxygen necessary for the fuel combustion from the air to the fuel. An important issue for the CLC process is the selection of metal oxide as oxygen carrier, since it must retain its reactivity through many cycles. The primary objective of this work is to develop a global mechanism with respective kinetics rate parameters such that CFD simulations can be performed for large systems. In this study, thermogravimetric analysis (TGA) of the reduction of hematite (Fe2O3) in a continuous stream of CH4 (15%, 20%, and 35%) was conducted at temperatures ranging from 700 to 825°C over ten reduction cycles. The mass spectroscopy analysis of product gas indicated the presence of CO2 and H2O at the early stage of reaction and H2 and CO at the final stage of reactions. A kinetic model based on two parallel reactions, (1) first-order irreversible rate kinetics and (2) Avrami equation describing nucleation and growth processes, was applied to the reduction data. It was found, that the reaction rates for both reactions increase with, both, temperature and the methane concentration in inlet gas. © 2013. Source

Monazam E.R.,REM Engineering Services PLLC | Breault R.W.,U.S. National Energy Technology Laboratory | Shadle L.J.,U.S. National Energy Technology Laboratory
Powder Technology | Year: 2016

The influence of abrupt exit (T-shaped) configuration on the riser axial pressure profile in a large-scale circulating fluidized bed (CFB) is examined. A new analysis was developed to predict the axial voidage along the length of influence in the exit region with T-shape geometry. The exit region was characterized using non-dimensional analysis of the continuum equations (balances of masses and momenta) that described multiphase flows. In addition to deceleration length due to abrupt exit, the boundary condition for the solid fraction at the top of the riser and the fully developed regions, were measured using an industrial scale circulating fluidized bed (CFB) of 0.3. m diameter and 15. m tall. The operating factors affecting the flow development in the exit region were determined for three materials of various sizes and densities in core annular and dilute regimes of the riser. Performance data were taken from statistically designed experiments over a wide range of Fr (0.5-39), Re (8-600), Ar (29-3600), load ratio (0.2-28), riser to particle diameter ratio (375-5000), and gas to solid density ratio (138-1381). A series of correlations were developed to predict the voidage at the exit of the riser and length of influence due to the exit geometry. The correlations are based on gas and solid properties, operating conditions, and riser geometry. © 2015 Published by Elsevier B.V. Source

Breault R.W.,U.S. National Energy Technology Laboratory | Monazam E.R.,REM Engineering Services PLLC | Carpenter J.T.,U.S. National Energy Technology Laboratory
Applied Energy | Year: 2015

Very little attention has been dedicated to the carrier re-oxidation in chemical looping systems. The work presented in this paper is for the re-oxidation of partially reduced hematite from a cyclic chemical looping fixed bed process. The underlying purpose of this work is to develop engineering rates and mechanisms for the re-oxidation of partially reduced hematite that can be included in CFD models for a chemical looping process. To this end, experiments were run using nominally 1000g of hematite material in a fixed bed reactor cycling between reduction and re-oxidation. The cyclic processing began with the reduction step then proceeded to the oxidation step repeating this analysis for several cycles ranging from 5 to 10. The re-oxidation process was conducted at temperatures ranging from 745°C to 825°C and oxygen concentrations ranging between 9% and 11%. The reduction was carried out at the same temperature as the re-oxidation step at various CH4 concentrations from 5% to 9%. In this paper, cyclic induced variations in performance are presented as well as the kinetic parameters for the first cycle. The re-oxidation of the depleted hematite occurs through a 2 step parallel process in which oxygen reacts to fill the surface of each grain within the particles and then migrates through oxygen vacancy diffusion to the depleted cores of each grain. © 2015 Published by Elsevier Ltd. Source

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