Morgantown, WV, United States
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Monazam E.R.,REM Engineering Services PLLC | Breault R.W.,U.S. National Energy Technology Laboratory | Weber J.,U.S. National Energy Technology Laboratory | Layfield K.,REM Engineering Services PLLC
Powder Technology | Year: 2017

The elutriation of fine particles from a binary mixture of particles with different densities and diameters has been investigated in bubbling fluidized bed (BFB). A series of experiments were conducted in a 10 cm diameter, 170 cm tall cylindrical bubbling fluidized bed under various operating conditions. Bed materials with different particle sizes, ranging from 93 μm to 1000 μm powder, and particle densities ranging from 7.9 to 2.45 g/cm3 were used in these experiments. Various combinations of these solids were mixed and fluidized at several superficial gas velocities. Solid elutriation was measured by collecting the carryover solids exiting the column with a filter. Experimental data on the effects of particle density, particle size, and gas velocity on the elutriation of particles from bubbling fluidized bed of binary mixture are examined. Influence of weight fraction of fines in the binary mixture on coarse particles was also investigated and discussed. The results indicated that the elutriation rate constant increases with increasing superficial gas velocities and weight fraction of fines in the bed. A generalized correlation for the elutriation rate constant is proposed using the ratio of Ug/Ut, weight fraction of fines, and fines to coarse particle density ratio. © 2016


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

Chemical looping combustion is a promising technology for the capture of CO2, which involves the reduction and oxidation of materials known as oxygen carriers. One particular carrier is hematite as it is readily available, relatively inexpensive, and nontoxic. We present a new particle model and reaction kinetics that can be applied to Barracuda simulations of the fuel reactor. This was performed as Barracuda does not allow for the Johnson–Mehl–Avrami (JMA) (nucleation and growth)-type kinetics that were developed from the results of an analytical study, thermogravimetric analysis, and fixed-bed experiments. We summarize the analytical analysis of the fixed-bed reduction experiments conducted in a cycling fixed-bed reactor and subsequently modeled with Barracuda computational fluid dynamics software to develop the new model. The experiments were conducted using 1000 g of hematite material. The cyclic processing began with the reduction step then proceeded to the oxidation step, and this analysis was repeated for several cycles (5–10). The effect of fuel partial pressure (8.4, 7.2, and 5 mol %) on the conversion was investigated. The JMA analysis assumed that the reactions occurred in the shell that surrounds the particle grains with the diffusion of oxygen to the grain surface from the core. In contrast, working with the particle kinetics allowed in Barracuda, the reactions occur with different hematite species (surface and core) mixed homogeneously. Therefore, it is necessary to develop a new particle model in which the rates are related to the amount of reactant (surface or core) in the particle. We present the development of such a particle model and compare the results with experimental values. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim


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.


Monazam E.R.,U.S. National Energy Technology Laboratory | Monazam E.R.,REM Engineering Services PLLC | Spenik J.,U.S. National Energy Technology Laboratory | Spenik J.,REM Engineering Services PLLC | Shadle L.J.,U.S. National Energy Technology Laboratory
Chemical Engineering Journal | Year: 2013

The adsorption of carbon dioxide (CO2) by immobilized polyethylenimine (PEI) on mesoporous silica was investigated in a fluid bed. The tests were performed to determine breakthrough behavior with varying bed temperature, flow rates and feed concentrations. Experimental breakthrough curves were analyzed using a theoretical 1D model developed by Bohart and Adams. The results showed that Bohart-Adams model was suitable for the normal description of breakthrough curve for the temperature ranges of 40-90°C. The maximum capacity increased with temperature up to 70°C and then decreased. The adsorption rate constant exhibited a negative temperature dependence decreasing as the temperature increased. Parameters characteristic of a fluid bed adsorber were inferred from these breakthrough curves including the breakthrough time, saturation time, critical reactor length, and length of mass transfer zone LMTZ. These parameters can be used to design fluid bed adsorption system without resolving the mechanistic contributions of dispersion, mixing, and intraparticle diffusion. © 2013.


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.


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.


Monazam E.R.,REM Engineering Services PLLC | Shadle L.J.,U.S. National Energy Technology Laboratory | Siriwardane R.,U.S. National Energy Technology Laboratory
AIChE Journal | Year: 2011

The equilibrium and conversion-time data on the absorption of carbon dioxide (CO2) with amine-based solid sorbent were analyzed over the range of 303-373 K. Data on CO2 loading on amine based solid sorbent at these temperatures and CO2 partial pressure between 10 and 760 mm Hg obtained from volumetric adsorption apparatus were fitted to a simple equilibrium model to generate the different parameters (including equilibrium constant) in the model. Using these constants, a correlation was obtained to define equilibrium constant and maximum CO2 loading as a function of temperature. In this study, a shrinking core model (SCM) was applied to elucidate the relative importance of pore diffusion and surface chemical reaction in controlling the rate of reaction. Application of SCM to the data suggested a surface reaction-controlled mechanism for the temperature of up to 40°C and pore-diffusion mechanism at higher temperature. Published 2011 American Institute of Chemical Engineers (AIChE).


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.


Monazam E.R.,REM Engineering Services PLLC | Breault R.W.,U.S. National Energy Technology Laboratory | Siriwardane R.,U.S. National Energy Technology Laboratory
Chemical Engineering Journal | Year: 2014

Thermogravimetric analysis (TGA) of the reduction behavior of hematite by using continuous streams of 5%, 10%, and 20% CO concentrations in N2 was conducted at temperatures ranging from 750 to 900°C over ten cycles. The reduced hematite was then oxidized using dry air. The rate of reduction was determined by the sample weight loss. Analysis of the data indicated that the reduction behavior can be described by single rate-determining step and it was controlled by the chemical reaction at the particle surface. The mass spectroscopy analysis of product gas indicated that no carbon deposition was found when operating at these temperature ranges (750-900°C). The analysis of reduction showed that two reduction steps (Fe2O3→Fe3O4, Fe3O4→FeO) proceed simultaneously. The activation energy was estimated to be 19.0±0.14kJ/mole. © 2013 .


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.

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