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June 1983 - October 2013
Publications
Publications (526)
Solar thermochemical hydrogen (STCH) produced by heat-driven water-splitting is a promising route for producing green hydrogen and other zero-emission synfuels. However, the efficiency of STCH must be dramatically increased for it to make an impact on decarbonization efforts. We have previously presented a novel Reactor Train System (RTS) for signi...
The aim of this work is to investigate the effect of exhaust gas recirculation (EGR: water vapor and CO2), with and without O2 enrichment, on non-premixed turbulent flames stabilized on a swirl burner. The motivation includes CO2 capture applications using O2 and CO2, combustion of biogas that containing CO2 and the use of EGR or H2O in certain ind...
Cerium oxide (CeO2) is the state-of-the-art material for syngas production from CO2 and H2O splitting via (methane assisted-) solar-driven thermochemical cycles. This technology consists of two separate processes: (1) a partial reduction of the oxide with methane at ~900 ◦C that produces syngas and generates oxygen vacancies in the oxide lattice; a...
Solar Thermochemical Hydrogen Production (STCH) is a promising technology that uses high-temperature heat directly to split water. The authors have previously proposed a Reactor Train System (RTS) that addresses the largest source of inefficiency in state-of-the-art STCH systems — solid heat recovery — by using multiple moving reactors that exchang...
This paper details the use of nanosecond repetitively pulsed discharges to attenuate combustion instabilities in a 14 kW swirl-stabilized methane/air combustor. The combustor exhibits large-amplitude pressure oscillations ranging from 1 to 4% of the mean pressure during which the flame exhibits bulk motion in each instability cycle, upstream and do...
Biomass is a promising renewable source that can reduce fossil fuel consumption and associated greenhouse gas emissions, but some of its characteristics make it difficult to use in its raw form. Torrefaction has been proposed as a thermochemical pretreatment to upgrade biomass for direct applications such as combustion and gasification, biochar and...
Torrefaction of biomass is a promising pre-treatment process capable of substantially improving the properties of raw biomass for its use as a solid biofuel, among many other potential applications. Oxygen-lean torrefaction can effectively reduce the cost and complexity of inert torrefaction. In this work, torrefaction tests of crushed olive stones...
Thermochemical redox cycles are a promising route for the production of solar fuels. In this work a novel Reactor Train System (RTS) is proposed for efficient conversion of solar thermal energy to hydrogen. This system is capable of recovering thermal energy from redox materials, which is necessary for achieving high efficiency, but has been diffic...
Industrial scale fluidized bed reactors are characterized by limited mixing rates, either local or global, especially when using low-pressure drop gas distributors to reduce operational costs. In this work, partitioning of wide beds using vertical internals is proposed as an effective technique to improve local mixing in large reactors, i.e., mixin...
The precessing vortex core (PVC) is a self-excited flow oscillation state occurring in swirl nozzles. This is caused by the presence of a marginally unstable hydrodynamic helical mode that induces precession of the vortex breakdown bubble (VBB) around the flow axis. The PVC can impact emissions and thermoacoustic stability characteristics of combus...
The time required to achieve steady state operation is an important factor in biomass conversion reactors, especially at a pilot or higher scale. The present work analyses the start-up, shutdown, and transient timescales of the laboratory-scale biomass reactor set-up using theoretical framework, for the case study of biomass torrefaction. The exper...
This presentation reports on an application of the annular jet vortex contactor (ANJEVOC) for high-temperature pyrolysis of methane. The unique ANJEVOC technology stems from one analytical solution of NSE describing tornado-like flows. Particularly, a conical annular converging-diverging jet develops and becomes very thin and fast as forcing increa...
Thermochemical redox cycles are a promising route for the production of solar fuels. In this paper we present a novel Reactor Train system for efficient conversion of solar thermal energy to hydrogen. This system is capable of recovering thermal energy from redox materials, which is necessary for achieving high efficiency, but has been difficult to...
Mixed ionic-electronic conducting (MIEC) membranes have gained
growing interest recently for various promising environmental and energy
applications, such as H2 and O2 production, CO2 reduction, O2 and H2
separation, CO2 separation, membrane reactors for production of chemicals,
cathode development for solid oxide fuel cells, solar-driven evaporati...
We present the development and application of a two‐phase stirred reactor model for heavy oil upgrading in the presence of supercritical water (SCW), with coupled phase‐specific thermolysis reaction kinetics and multicomponent hydrocarbon–water phase equilibrium. We demonstrate the inference of oil and water phase kinetics parameters for a compact...
Moving or fixed bed reactors are commonly used for continuous processing of biomass in a wide range of applications, such as torrefaction, slow pyrolysis, gasification, and incineration. Many of these moving bed reactors for biomass applications behave like a quasi-fixed bed reactor because of longer solid residence times in comparison to fluid. In...
Oil palm residues, such as palm oil empty fruit bunches (PEFBs), are typically abandoned due to high moisture and bulky. Pelletization and downdraft gasification constitute a promising solution for small-scale power and heat production. In this study, the two-dimensional, steady-state computational fluid dynamics (CFD) model of a modified Imbert do...
The precessing vortex core (PVC) is a self-excited flow oscillation state occurring in swirl nozzles. This is caused by the presence of a marginally unstable hydrodynamic helical mode that induces precession of the vortex breakdown bubble (VBB) around the flow axis. The PVC can impact emissions and thermoacoustic stability characteristics of combus...
We present the development and application of a two-phase stirred reactor model for heavy oil upgrading in the presence of supercritical water (SCW), with coupled phase-specific thermolysis reaction kinetics and multicomponent hydrocarbon water phase equilibrium. We demonstrate the inference of oil and water phase kinetics parameters for a compact...
Although biomass gasification using concentrated solar energy is an attractive technology for the production of storable renewable energy and CO2 reduction, several challenges have stalled its deployment over the last decades: high temperature and/or large reactor volume required for complete fuel (char) conversion, the achievement of a steady syng...
jats:title>Abstract The precessing vortex core (PVC) is a self-excited flow oscillation state occurring in swirl nozzles. This is caused by the presence of a marginally unstable hydrodynamic helical mode that induces precession of the vortex breakdown bubble (VBB) around the flow axis. The PVC can impact emissions and thermoacoustic stability chara...
Growing concerns of emissions from wildfires and burning of crop residues demand cleaner and efficient technologies to convert and utilize this residual biomass. The present study demonstrates a pilot scale moving bed biomass torrefaction reactor operating in oxidative medium to produce biochar for soil amendment. A series of experiments are conduc...
Growing concerns of emissions from wildfires and burning of crop residues demand cleaner and efficient technologies to convert and utilize this residual biomass. The present study demonstrates a pilot scale moving bed biomass torrefaction reactor operating in oxidative medium to produce biochar for soil amendment. A series of experiments are conduc...
Increasing the performance of Solid Oxide Electrolysis Cells (SOECs) for the production of hydrogen (H 2 ) from water (H 2 O) splitting requires the use of cathodes with low polarization resistance. In-situ growth of metal catalysts from perovskite oxides (termed catalyst exsolution) has been proposed as a means to decorate the porous electrode wit...
Minimizing energy consumption and reducing pollutant emissions during the carbon anode baking process is critically important for the aluminum industry. The present study investigates the effects of oxidizer inlet temperature, inlet oxygen concentration, equivalence ratio, refractory wall thermal conductivity, and refractory wall emissivity on the...
The published torrefaction design analysis either ignore thermal loss or assume a generic value in their characterization of biomass thermochemical reactors. This study, using a small-scale biomass reactor prototype for torrefaction as an example, demonstrates a low-cost but scientifically rigorous way to measure thermal losses, and proposes a math...
A new approach to conduct allothermal steam-gasification of biomass in a dual fluidized bed gasifier (DFBG), using concentrating solar energy and solid particles as thermal energy carrier and storage media, is presented. The advantage of this configuration is that the solar receiver and the reactor are uncoupled, while thermal integration is highly...
Utilization of rice husk, an abundant global residual biomass, represent a large opportunity for increasing the share of bioenergy in the power sector. The present work assesses the life cycle emissions of rice husk torrefaction in different reaction conditions and the techno-economic prospects for decentralized torrefaction facilities at rice mill...
Coal power plants play an important role in supplying affordable and reliable electricity. It is necessary to develop high‐efficiency and low‐cost carbon capture (CC) technologies to mitigate the associated global warming. Using H2S‐tolerant oxygen transport membranes (OTMs) for hydrogen production and CO2 separation can significantly reduce the en...
Precombustion carbon capture is an effective strategy to reduce large‐scale CO2 emissions, which is mainly used in the area of integrated gasification combined cycle (IGCC) power plants. Oxygen transport membranes (OTMs) were suggested as the air separation unit to produce high purity oxygen for the gasifier. However, the improvement in efficiency...
Increasing the performance of Solid Oxide Electrolysis Cells (SOECs) for the production of hydrogen (H 2 ) from water (H 2 O) splitting requires the use of cathodes with low polarization resistance. In-situ growth of metal catalysts from perovskite oxides (termed catalyst exsolution) has been proposed as a means to decorate the porous electrode wit...
The dynamic response of a bubbling fluidized-bed biomass gasifier (FBG) is examined. A transient model is developed by extending a previous steady-state model to account for key processes occurring during the ramp-up and/or changes in loading of fuel and gasification agent. The model is validated against measurements from transient tests in a labor...
Pulsating flame jets have been widely used in open-top carbon anode baking furnaces for aluminum electrolysis. Reducing energy consumption and pollutant emissions are still major challenges in baking (heat-treatment) carbon anode blocks. It is also of immense significance to bake all the anodes uniformly irrespective of their position in the furnac...
Copyright © 2019 ASME. Pulsating flame jets have been widely used in open-top carbon anode baking furnaces for aluminum electrolysis. Reducing energy consumption and pollutant emissions are still major challenges in baking (heat-treatment) carbon anode blocks. It is also of immense significance to bake all the anodes uniformly irrespective of their...
Intermediate temperature membrane-supported CO 2 thermochemical reduction using renewable energy is a clean approach for reusing CO 2 . To implement this technology at scale, stable catalytic membrane materials with fast kinetics should be developed, and reactor designs and system integrations should be optimized. In this review, we highlight major...
The stabilization of turbulent lean premixed flames in a backward-facing step combustor is investigated using large eddy simulations, with a reduced 2-step reaction kinetics mechanism and one of two detailed mechanisms. Although all reaction mechanisms predict similar laminar flame velocities and adiabatic flame temperatures, significant instabilit...
We examine the redox activity of nickel/nickel oxide foils. Thin nickel foils (2.5 µm, 10 µm, and 100 µm) were subjected to redox conditions in a fixed-bed reactor within 800–1000 °C, and samples were examined using SEM at different stages of conversion. We identify some key features or the process that are used to guide model development: (1) Oxid...
Drying is a crucial process in many thermochemical processes for bioenergy. However, most existing drying models often have the following shortcomings: they are feedstock-dependent, or they are unable to describe the spatial inhomogeneity that often develops within thermally thick biomass particles under higher temperature gradients. In this paper,...
This work demonstrates and assesses the concept of in situ catalyst exsolution in ceramic membrane reactors for the co-production of carbon monoxide (CO) and syngas through carbon dioxide (CO2) splitting and methane (CH4) partial oxidation, respectively. We use dense pellets of La0.85Ca0.10Fe0.95Ni0.05O3-δ (LCFN) as a model membrane reactor system....
In this study, we analyze experimental time series temperature data and infer the transient behaviors of the test reactor, as well as how it changes with reactor scaling. We show that the thermal mass of the reactor has a significant part to play in the reactor's temporal response to changes, and demonstrate that in our design, it is possible to ac...
A small-to medium-scale, mobile torrefaction system has the potential to improve the economics of biomass torrefaction and expand its deployment in decentralized, rural areas. In order to simplify the reactor design for deployment in these contexts, a torrefaction reactor prototype operating under oxygen-lean conditions was proposed and developed i...
Recent major discoveries of gas and oil in the U.S. in shale plays have significantly increased the amount of ethane available for steam cracking to produce ethylene; and numerous large petrochemical companies have built new ethane crackers on the U.S. Gulf Coast since 2016. Steam cracking, however, is energy intensive; and there is a need to devel...
Minimizing energy consumption and reducing pollutant emissions during carbon anode baking process are critically important for improving the efficiency and sustainability of the aluminum production. Usually, fifteen to twenty carbon anodes, each one of them of approximately one ton, are kept inside a single pit. It is a significant challenge to bak...
In the aluminum anode baking furnace, the operational parameters have a significant influence on the furnace performance and the resulting anode quality. For this furnace, an important parameter is the fire-cycle, which determines the production rate of the baking kiln and the anodes quality. Shorter fire-cycle results in a higher furnace productio...
In this study, a combined experimental and Large Eddy Simulation (LES) investigation is performed to identify the vortical structures, their dynamics, and interaction with a turbulent premixed flame in a swirl-stabilized combustor. Our non-reacting flow experiment shows the existence of large scale precessing motion, commonly observed for such flow...
This paper presents a novel Exergy Loss based (EL) allocation method for the electricity produced in hybrid renewable-fossil power plants. The rationale behind this approach is that the electricity allocated to the fossil and renewable resources are obtained by subtracting from the respective source input exergies, the corresponding exergy losses,...
In this paper, we demonstrate CO 2 thermochemical reduction to CO in a La 0.9 Ca 0.1 FeO 3-d oxygen ion transport membrane reactor. For process intensification, we also show that methane can be used on the sweep side, producing two streams: a CO stream from CO 2 reduction on the feed side, and a syngas stream on the other. We show that surface reac...
The rotary chemical looping combustion reactor design - which utilizes oxygen carriers in a matrix of micro channels for indirect fuel conversion - provides a viable path for fossil-based electric power generation with CO2 capture. Its thermally integrated matrix of micro channels minimizes irreversibilities associated with heat transfer in the rea...
In Part I of the study, we proposed a simplified biomass torrefaction moving bed reactor design capable of decentralized, small-scale, and mobile deployment operated under an oxygen-lean condition. We built and validated a laboratory-scale test reactor. In the present study, we develop a mathematical description of the reactor and show that it prod...
A new, simplified biomass torrefaction reactor concept that operates under oxygen-lean conditions is proposed as a potential way to downscale torrefaction reactors for small- and medium-scale applications. To verify the feasibility of the concept, a multi-scale analysis was conducted to understand the design requirements, underlying chemistry, intr...
In this work, the mixing of a hydrocarbon droplet in near- and super-critical water (NCW/SCW) is mathematically modeled, coupling thermodynamic properties calculation with transport processes. In non-ideal systems, mass transfer is captured using the generalized Maxwell-Stefan equations with the driving force expressed in terms of the fugacity grad...
The cost and quality of aluminum produced by the reduction process are strongly dependent on heat treated (baked) carbon anodes. A typical aluminum smelter requires more than half a million tons of carbon anodes for producing one million ton of aluminum. The anode baking process is very energy intensive, approximately requires 2GJ of energy per ton...
Copyright © 2018 ASME. The cost and quality of aluminum produced by the reduction process are strongly dependent on heat treated (baked) carbon anodes. A typical aluminum smelter requires more than half a million tons of carbon anodes for producing one million ton of aluminum. The anode baking process is very energy intensive, approximately require...
A novel system based on the indirect oxy-combustion of coal in a liquid Sb anode solid oxide fuel cell (SOFC) has been used to produce electricity for over 48 h. Pulverized anthracite was fed to the liquid-antimony-anode of the fuel cell, and a peak power density of 47 mW cm-2 was reached at 1023 K and 35 mW cm-2 at 973 K. The fuel cell was prepare...
For 2030, Spain has set ambitious targets for increasing intermittent renewable electricity generation. Concentrated Solar Power (CSP) plants have the capability of store solar energy during operation allowing a reduction of the external support to renewable generation to cover the demand. A model has been developed for the estimation of the impact...
This paper presents a numerical study of ultra-lean hydrogen-methane flames stabilized behind a rectangular, highly conducting metallic bluff body acting as a flame holder. Using high fidelity numerical simulations, we show that lean inverted steady flames exist below normal flammability limits. They have distinct stabilization mechanism from pure...
Two key flame macrostructures in swirling flows have been observed in experiments of oxy-combustion (as well as air-combustion); as the equivalence ratio is raised, the flame moves from being stabilized on just the inner shear layer (Flame III) to getting stabilized on both the inner and outer shear layers (Flame IV). We report results of an LES in...
The development of CFD-DEM is critical for investigating particle phenomena and their coupling with reactor transport. However, there continues to be considerable uncertainty in the selection of model parameters because of limitations in: (a) experimental measurements of multi-particle interactions, and (b) computational resources which have restri...
This paper presents a global hydrodynamic stability analysis of flow fields in a backward-facing step combustor, assuming weakly nonparallel flow. The baseline experiments in a “long” combustor of length of 5.0 m shows the presence of two combustion instability states characterized by coherent low- and high-amplitude acoustic pressure oscillations....
The flame stabilization and blowout velocity of lean premixed turbulent flames in a backward-facing step combustor were investigated experimentally with well-defined stable flames. The dynamic pressure in the combustor was monitored to select a stable regime among overall flame behaviors. The responses in the flame behaviors to changes in the initi...
In this paper, we demonstrate CO2 thermochemical reduction to CO in a La0.9Ca0.1FeO3-δ oxygen ion transport membrane reactor. For process intensification, we also show that methane can be used on the sweep side, producing two streams: a CO stream from CO2 reduction on the feed side, and a syngas stream on the other. We show that surface reactions a...
With growing concerns over greenhouse gas emission, novel combustion technologies are timely and critical. Fossil fuels will continue to contribute a large fraction of energy production in the near and intermediate future, making carbon capture and storage an important part of the solution. System studies show that oxy-combustion can play an import...
Partially miscible fluids often exhibit complex behavior. While previous studies have focused on the phase characteristics, the coupled phase equilibrium and transport processes under near-critical/supercritical conditions are not well studied. Here, the binary/ternary phase equilibria of light oil (maltenes)—heavy oil (asphaltenes)—water mixtures,...
This paper examines the dynamics of the flame leading edge in a laminar premixed CH4/air flame stabilized on a bluff body in a channel. Harmonic fluctuations and step velocity change are used to simulate the flame response to acoustic oscillations, which are of primary importance in the study of thermo-acoustic instabilities. We use a fully resolve...
This paper presents a fundamental study of ultra-lean flames stabilized behind a thin, highly conducting metallic rectangular bluff body acting as a flame holder. Using high fidelity numerical simulations, we reproduce a phenomenon observed experimentally, showing that in this configuration steady hydrogen–methane flames can exist at equivalence ra...
Renewable power intermittency requires storage for load matching. A system combining a solid oxide electrolysis cell (SOEC) and a methanation reactor (MR) could be an efficient way to convert excess electricity into methane, which can be integrated with the existing natural-gas network. In this paper, a comprehensive exergy analysis is performed fo...
Thin rectangular fluidized beds enable detailed optical diagnostics providing high quality data for validating numerical simulations. Because of their lower computational costs, 2D CFD continues to be employed despite the high wall surface-area to bed-volume ratio characterizing this geometric setup. 2D simulations do not resolve the gas and solids...
Kinetics data for CO2 thermochemical reduction in an isothermal membrane reactor is required to identify the rate-limiting steps. Here, we report a detailed reaction kinetics study on this process supported by an La0.9Ca0.1FeO3-δ (LCF-91) membrane. The dependence of CO2 reduction rate on various operating conditions is examined such as CO2 concentr...
This study investigates stoichiometric premixed CH4/O2/CO2 flames. Our recent studies show that these oxy flames behave differently under turbulent versus laminar conditions, with the extinction strain rate being the key parameter for comparing flame stability. This work builds on that conclusion by investigating why there are differences in extinc...
The thermochemical conversion of biomass via gasification and pyrolysis over attractive routes to drop-in-ready fuels and renewably-derived chemicals from a variety of different biomass feedstocks. For both of these conversion pathways prediction of the growth of Polycyclic Aromatic Hydrocarbon (PAH) compounds is of particular importance since they...
Kinetics data for CO2 thermochemical reduction in an isothermal membrane reactor is required to identify the rate-limiting steps. Here, we report a detailed reaction kinetics study on this process supported by an La0.9Ca0.1FeO3-δ (LCF-91) membrane. The dependence of CO2 reduction rate on various operating conditions is examined such as CO2 concentr...
CO 2 splitting via thermo-chemical or reactive redox has emerged as a novel and promising carbon-neutral energy solution. Its performance depends critically on the properties of the oxygen carriers (OC). Ceria is recognized as one of the most promising OC candidates, because of its fast chemistry, high ionic diffusivity, and large oxygen storage ca...
Hydrogen production from water-splitting has attracted significant interest because of its use in refining, chemicals’ production and as an alternative fuel. A promising technology for hydrogen production through water-splitting at moderate temperatures is the use of mixed ionic-electronic conducting (MIEC) membranes [1-2]. Using an inert gas on th...
CO2 splitting via thermo-chemical or reactive redox has emerged as a novel and promising carbon-neutral energy solution. Its performance depends critically on the properties of the oxygen carriers (OC). Ceria is recognized as one of the most promising OC candidates, because of its fast chemistry, high ionic diffusivity, and large oxygen storage cap...
Recently, next-generation HVAC technologies have gained attention as potential alternatives to the conventional vapor-compression system (VCS) for dehumidification and cooling. Previous studies have primarily focused on analyzing a specific technology or its application to a particular climate. A comparison of these technologies is necessary to elu...
This paper presents a global hydrodynamic stability analysis of flow fields in a backward-facing step combustor, assuming weakly nonparallel flow. The baseline experiments in a “long” combustor of length of 5.0 m shows the presence of two combustion instability states characterized by coherent low- and high-amplitude acoustic pressure oscillations....
Rotary reactor concept showing rotating drum with oxygen carrier-coated micro-channels
Power-to-methane (PtM) systems coupling solid oxide electrolysis cell (SOEC) and Sabatier reactors offers an efficient and promising pathway to integrate the renewable/nuclear power with the existing natural gas network. SOEC operates at a higher temperature and yet produce hydrogen or syngas with a controllable H 2 /CO ratio with higher efficiency...
Solids mixing affects thermal and concentration gradients in fluidized bed reactors and is, therefore, critical to their performance. Despite substantial effort over the past decades, understanding of solids mixing continues to be lacking because of technical limitations of diagnostics in large pilot and commercial-scale reactors. This study is foc...
Water and energy systems have often been treated as separate “silo” systems over the entire pathway from production to consumption. However, their close interdependence requires some perspective of the water-energy nexus (WEN), especially in regions with very high water stresses combined with a myriad of rapid changes in resource production and con...
