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The climate models of the Intergovernmental Panel on Climate Change list black carbon (BC) as an important contributor to global warming based on its radiative forcing (RF) impact. Examining closely these models, it becomes apparent that they might underpredict significantly the direct RF for BC, largely due to their assumed spherical BC morphology. Specifically, the light absorption and direct RF of BC agglomerates are enhanced by light scattering between their constituent primary particles as determined by the Rayleigh–Debye–Gans theory interfaced with discrete dipole approximation and recent relations for the refractive index and lensing effect. The light absorption of BC is enhanced by about 20% by the multiple light scattering between BC primary particles regardless of the compactness of their agglomerates. The resulting light absorption agrees very well with the observed absorption aerosol optical depth of BC. ECHAM-HAM simulations accounting for the realistic BC morphology and its coatings reveal high direct RF = 3–5 W/m2 in East, South Asia, sub-Sahara, western Africa, and the Arabian peninsula. These results are in agreement with satellite and AERONET observations of RF and indicate a regional climate warming contribution by 0.75–1.25 °C, solely due to BC emissions., Environmental Science & Technology, 56 (12), ISSN:0013-936X, ISSN:1520-5851

Chemical looping reforming (CLR) is a promising strategy of methane conversion to syngas with low cost and minimal environmental impact. A major challenge for chemical looping reforming systems is the development of oxygen carriers that have high reactivity, high oxygen carrying capacity, and long-term durability. We demonstrate that the addition of a low concentration of cobalt dopant to iron-based oxygen carriers can dramatically enhance the reactivity in CLR processes at low temperatures while maintaining the recyclability. The methane conversion increased by around 300% for Co-doped iron oxide compared to pure iron oxide oxygen carriers from 600 °C to 800 °C. It was found that 2% Co dopant concentration is optimal for methane conversion rate and cost of oxygen carriers at different temperatures. Density functional theory (DFT) calculations reveal that the Co dopant has a short-range effect on the formation of oxygen vacancies. The Co-doping-induced oxygen vacancy significantly reduces energy barriers of CH4 reforming on the surface of iron oxide oxygen carriers, leading to the reactivity enhancement. Our findings provide a pathway to lower the methane reforming temperature in chemical looping systems, while improving the syngas yield with desired oxygen carrier recyclability.

Chemical looping reforming presents an attractive alternative to the conventional processes for chemicals and energy production from carbonaceous fuels with significant reduction in carbon emissions and high exergy efficiency. Production of syngas and hydrogen is important because the former is a critical building block for valuable chemicals and latter is a source of clean energy. The use of copper-iron (Cu-Fe) oxygen carriers for coproducing syngas and hydrogen in a chemical looping reforming process is studied via experiments and process simulations. Three different compositions of Cu and Fe oxides are examined for their properties concerning the reactivity towards fuel and the selectivity towards syngas. The feasibility of using a co-current moving bed reactor configuration for syngas production is probed experimentally in a fixed bed reactor by placing the fully oxidized and reduced oxygen carrier in series. The methane conversion and dry syngas purity as high as 99.5% and 97.5%, respectively, are observed for copper oxide (20 wt%) - iron oxide (60 wt%) - aluminium oxide (20 wt%) oxygen carrier in a simulated co-current moving bed reactor. Key performance parameters including effective thermal efficiency for 5 different configurations of the chemical looping reforming process from ASPEN Plus simulation software are compared against the baseline case of the auto-thermal reforming process. Apart from an improvement in the natural gas conversion and syngas purity in the chemical looping reforming process, the net hydrogen production is increased by 28% and effective thermal efficiency is increased by 10% over that of the auto-thermal reforming process.

Passive cyclonic gas-liquid separators (PCGLSs) are commonly used in microgravity conditions where gravity settling separation is difficult or impossible. In this study, displacement-current phase tomography (DCPT) is used to measure various features of the gas-liquid flow inside of a PCGLS. The liquid holdup, liquid angular velocity, and gas core size are investigated. The liquid holdup is also measured in a gas-liquid flow that simulates the injection flow for a PCGLS. It is found that the gas core contracts and expands in a periodic motion as air is injected with water. This motion becomes more noticeable as the air flow rate is increased. It is also found that the liquid layer angular velocity has a positive linear trend with the air flow rate under constant water flow rates. A basic linear relation is derived to relate the liquid angular velocity to the air and water flow rates. All DCPT and electrical capacitance phase tomography (ECVT) results closely match the visual confirmation methods used for each flow feature.

Chemical looping partial oxidation (CLPO) is a promising strategy of methane conversion to syngas with low cost and minimal environmental impact. A major challenge is the development of oxygen carriers that have high reactivity, high oxygen carrying capacity, and recyclability. We demonstrate that the addition of a low concentration (1%) of copper dopant to iron-based oxygen carriers can dramatically enhance the reactivity in CLPO process at low temperatures while maintaining the recyclability of these carriers. With the dopant, the methane conversion rate at 700 °C is 470% higher than that of carriers without the dopant. These results are substantiated by ab initio DFT + U and thermochemistry analyses. It is noted that operating a chemical looping system at 700 °C can result in energy consumption savings of ∼35% as compared to a chemical looping operation at 1000 °C. Thus, our findings provide a pathway to significantly lowering the methane reaction temperature in chemical looping systems, which will lead to substantial energy savings with desired oxygen carrier recyclability.

Chemical looping combustion (CLC) is an advanced technology for converting fossil fuel while achieving in-situ CO2 capture. The high purity CO generated in the combustion product stream is sequestration/utilization ready, which makes chemical looping one of the most attractive carbon emission control technology. In this paper, the authors present the design, simulation and experimental operation results of the 250 kWth high pressure syngas chemical looping (SCL) pilot plant. The pilot plant’s unique countercurrent moving bed design allows near-full conversion of coal-derived syngas with simultaneous production of high purity, carbon-free H2. Critical aspects of the design efforts, including heat and material balances, reactor sizing approach and solid flow control and measurement devices are presented. An ASPEN Plus® model is constructed to predict the gas and solid conversions of the SCL process the gas and solid conversions of the SCL process under different experimental conditions. The highest syngas conversion achieved was 97.95% with 16.03% oxygen carrier conversion, which were close to the thermodynamic limits for both the gas and solid phases in the reducer. Differences between the experimental results and predicted conversion values were more significant under conditions with lower oxygen carrier to fuel ratio. Greater than 99% purity H2 was produced from the moving bed oxidizer, and the scalability and feasibility of SCL process were successfully demonstrated.

In this perspective article, we illustrate the importance and versatility of the Coulomb criterion that serves as a bridge between the fields of powder technology and rock mechanics/geomechanics. We first describe the essence of the Coulomb criterion and its physical meaning, revealing surprising similarities regarding its applications between both fields. We then discuss the rock mechanics applications and limitations at two extreme scales, the Earth's crust (tens of kilometers) and intact rocks (meters). We finally offer thoughts on bridging these scales. The context of the article is essential not only to the rock mechanics/geomechanics community but also to a broader powder technology community. ISSN:0032-5910 ISSN:1873-328X

Chemical looping methane partial oxidation provides an energy and cost effective route for methane utilization. However, there is considerable CO2 co-production in current chemical looping systems, rendering a decreased productivity in value-added fuels or chemicals. In this work, we demonstrate that the co-production of CO2 can be dramatically suppressed in methane partial oxidation reactions using iron oxide nanoparticles embedded in mesoporous silica matrix. We experimentally obtain near 100% CO selectivity in a cyclic redox system at 750–935 °C, which is a significantly lower temperature range than in conventional oxygen carrier systems. Density functional theory calculations elucidate the origins for such selectivity and show that low-coordinated lattice oxygen atoms on the surface of nanoparticles significantly promote Fe–O bond cleavage and CO formation. We envision that embedded nanostructured oxygen carriers have the potential to serve as a general materials platform for redox reactions with nanomaterials at high temperatures., Chemical looping methane partial oxidation is an effective technology to produce syngas with a minimal energy penalty. Here, the authors design and develop a mesoporous silica supported nanoparticle oxygen carrier that enables a near 100% CO generation with high recyclability and substantially lower operating temperature.

The Biomass-to-Syngas (BTS) chemical looping process is an advanced thermochemical biomass conversion process for the production of sustainable fuels and chemicals. The BTS process is novel in that it converts biomass feedstock to high purity syngas with adjustable H2:CO molar ratio without needing an air separation unit (ASU), a tar reformer, a steam reformer, or a water-gas-shift (WGS) reactor. In the BTS process, biomass feedstock is partially oxidized to produce syngas by oxygen carriers in a reducer that is operated in a co-current gas-solid moving bed contact mode. The reduced oxygen carriers are regenerated in a fluidized bed combustor via the oxidation reaction with air. The BTS process uses the iron-titanium composite metal oxide (ITCMO) material as the oxygen carrier, which is capable of cracking the volatiles produced in biomass pyrolysis as well as regulating the syngas composition. The co-current moving bed reducer eliminates back-mixing, channeling, or bypassing of solid and gas reactants, resulting in a syngas composition that is close to the thermodynamic equilibrium. In this paper, the rationale of a successful BTS process is discussed along with the thermodynamic characteristics of the ITCMO oxygen carrier, that can effectively react with a woody biomass feedstock, analyzed based on an ASPEN Plus model. Bench scale moving bed reducer experiments are presented, indicating the conversion of wood pellets to syngas with a H2:CO ratio of 2, which is suitable for methanol or liquid fuel synthesis. The gas and solid composition produced in the bench scale reducer matches the prediction from the ASPEN Plus thermodynamic model. This model is further used to analyze the performance of the BTS process under autothermal conditions for methanol production, with a comparison with a baseline indirectly heated gasification process. The results indicate that the BTS process significantly reduces the biomass and steam consumption and appreciably improves the biomass conversion efficiency over that obtained from the baseline process.

Chemical looping combustion (CLC) and chemical looping reforming (CLR) are innovative technologies for clean and efficient hydrocarbon conversion into power, fuels, and chemicals through cyclic redox reactions. Metal oxide materials play an essential role in the chemical looping redox processes. During reduction, the oxygen carriers donate the required amount of oxygen ions for hydrocarbon conversion and product synthesis. In the oxidation step, the depleted metal oxide oxygen carriers are replenished with molecular oxygen from the air while heat is released. In recent years, there have been significant advances in oxygen carrier materials for various chemical looping applications. Among these metal oxide materials, iron-based oxygen carriers are attractive due to their high oxygen-carrying capacity, cost benefits, and versatility in applications for chemical looping reactions. Their reactivity can also be enhanced via structural design and modification. This review discusses recent advances in the development of oxygen carrier materials and the mechanisms of hydrocarbon conversion over these materials. These advances will facilitate the development of oxygen carrier materials for more efficient chemical looping technology applications. Keywords: Chemical looping, Oxygen carrier, Hydrocarbon conversion, Ionic diffusion, Mechanism

Commercially viable H2 production from H2S demands a well-designed and efficient technology concept with superior H2 yield. We propose a novel sulfur looping scheme that involves carrier sulfidation and CO2 enabled carrier regeneration to simultaneously utilize H2S and CO2, the two common industrial waste gases, for valuable H2 production. Using Ni3S2 as the active component, a high-performance sulfur carrier design is developed, where the selection of support is key. ZrO2 and MgAl2O4 supports were tested and both substantially improve the recyclability over cycles by imparting structural stability to Ni3S2. ZrO2 dramatically enhances the carrier performance, exhibiting a maximum increase of ~ 100% in sulfur uptake during the redox cycles compared to MgAl2O4. Furthermore, in fixed bed experiments at a high GHSV of 5000 hr-1, ZrO2 supported carrier maintained its superior performance over MgAl2O4 with a ~ 9.5% higher total H2S consumption. Density functional theory calculations were performed to unveil the role of supports. ZrO2 is identified as a support with bifunctional characteristics that not only improves textural properties of the carrier, but also catalytically decomposes H2S and induces a synergistic dynamic with Ni3S2. On the other hand, MgAl2O4 acts only as a conventional inert support for morphology modifications with negligible interaction with H2S. This work demonstrates a novel strategy for H2S and CO2 utilization and provides new insights into effective support selection aiding the design of a robust and efficient sulfur carrier.

We describe an approach, based on electrical capacitance tomography (ECT) sensors, to decompose and continuously monitor multiphase flow components (fractional areas or volumes) in mixtures containing conducting phases. The proposed approach exploits the Maxwell–Wagner–Sillars effect at distinct frequencies to reconstruct each phase of a multiphase flow and is also utilized to estimate the fractional volume of the various phases of the mixture. The approach is illustrated for a three-phase mixture composed of air, water, and oil. This approach utilizes the very same ECT measurement apparatus used for flow imaging and, as such, inherits its high speed of acquisition and suitability for real-time operation.

The fate of sulfur in the coal-direct chemical looping system was investigated in the sub-pilot reactor system. The sulfur balance was successfully closed during the injection of high sulfur coal. More than 69% of the total amount of atomic sulfur in coal was released as SO 2 and H 2 S from the reducer flue gas stream while less than 5% was emitted as SO 2 from the combustor spent air. The remaining atomic sulfur was retained in coal ash as inorganic sulfur compounds. The finding suggests an acid gas removal system targeting both H 2 S and SO 2 is required to meet the recommended quality of CO 2 stream for sequestration and transportation. Using the determined ratio of SO 2 and H 2 S, a properly designed Claus plant can enable the recovery of elemental sulfur as a value-added byproduct. The combustor spent air was found to comply with the US EPA sulfur emission regulation and can be released to the atmosphere without a costly acid removal system. The relationship between the sulfur and carbon capture efficiencies was established experimentally and was found to be proportional to each other throughout the experiment at a slope of 0.8 below 93% of carbon capture efficiency and near 1 above 93%. This was attributed to the delayed release of organic sulfur during incomplete char gasification in the reducer. The finding affirms the effectiveness of the counter-current moving bed design for minimizing the amount of carbon and sulfur emission in the combustor spent air with an average carbon and sulfur capture efficiency of 96.5 and 95%, respectively. Sulfur deposition on the iron based oxygen carriers did not affect the system performance, and complete removal of deposited sulfur was observed during oxidation in a thermogravimetric analyzer. Compared with chemical looping systems using circulating fluidized bed configuration, the use of a moving bed reducer has the additional benefit of minimizing slippage of char into the combustor due to the use of large oxygen carrier; resulting in lower sulfur emission in the combustor spent air. The findings demonstrate the robustness of the coal-direct chemical looping system to handle high sulfur coal without a complicated acid gas cleaning scheme or severe performance penalties.

In this study, a family of second-order process based modified Patankar Runge-Kutta schemes is proposed. The proposed schemes preserve both the mass and mole balance in a stiff reaction network while maintaining the positivity of density and pressure. The accuracy analysis is conducted to derive the sufficient and necessary conditions for the Runge-Kutta and Patankar coefficients. Coupling with the finite volume method, the proposed schemes are extended to Euler equations with non-equilibrium reacting source terms. Benchmark tests are given to prove the prior order of accuracy and validate the positive-preserving property for both density and pressure.

The growth in the global energy consumption demands an increasing use of the renewable energy sources. Nevertheless, fossil fuels are projected to remain as the dominating backbone of petrochemical and consumer industry in the coming decades. As a bridge from the fossil fuel-based to renewable fuel-based economy, chemical looping technology has been developed to achieve sustainable applications by generating highly efficient energy and products through economically viable processes. This article discusses the advances in chemical looping with a focus on the fundamentals of formulation concepts on chemical looping carriers, rationale for reactor configurations, and design consideration from the process analysis. Particularly, the carriers utilized for different chemical looping applications ranging from syngas generation to ammonia synthesis are elaborated. The reactor configurations applied for different chemical looping systems are discussed along with the essentials of the process simulation approach to system optimization. The article also describes the prospects of the future development in the chemical looping technology, and its viability and readiness for industrial deployment.

The growing demand for energy and stringent pollutant emission control in sour fuels makes it essential to develop more efficient approaches in H2S gas removal and subsequent treatment to recover sulfur. Several methods using oxidative or non-oxidative decomposition of H2S to remove or inhibit H2S from gas stream have been extensively explored over the past few decades, including catalytic process, reactive absorption, photocatalysis, electrocatalysis, thermal catalysis, membrane-assisted catalysis, and multistep thermochemical decomposition. This article reviews the recent advances in reactive H2S separation combining computational simulation with experimental development. In particular, material and catalyst design, mechanistic insights of the reactions, and applicable reaction processes are discussed. These pioneering works suggest that understanding H2S decomposition reaction mechanism at molecular level is important in the optimization of material and process design. The perspectives are also given on the viability of oxidative or non-oxidative decomposition of H2S.

Transition metal are heavily used in chemical looping technologies because of their high oxygen carrying capacity and high thermal reactivity. These oxygen activities result in the oxide formation and oxygen vacancy formation that affect the nanoscale crystal phase and morphology within these materials and their subsequent bulk chemical behavior. In this study, two selected earlier transition metals manganese and cobalt as well as two selected later transition metals copper and nickel that are important to chemical looping reactions are investigated when they undergo cyclic redox reactions. We found Co microparticles exhibited increased CoO impurity presence when oxidized to Co3O4 upon cyclic oxidation; CuO redox cycles prefer to be limited to a reduced form of Cu2O and an oxidized form of CuO; Mn microparticles were oxidized to a mixed phases of MnO and Mn3O4, which causes delamination during oxidation. For Ni microparticles, a dense surface were observed during the redox reaction. The atomistic thermodynamics methods and density functional theory (DFT) calculations are carried out to elucidate the effect of oxygen dissociation and migration on the morphological evolution of nanostructures during the redox processes. Our results indicate that the earlier transition metals (Mn and Co) tend to have stronger interaction with O2 than the later transition metals (Ni and Cu). Also, our modified Bronsted−Evans−Polanyi (BEP) relationship for reaction energies and total reaction barriers reveals that reactions of earlier transition metals are more exergonic and have lower oxygen dissociation barriers than those of later transition metals. In addition, it was found that for these transition metal oxides the oxygen vacancy formation energies increase with the depth. The oxide in the higher oxidation state of transition metal has lower vacancy formation energy, which can facilitate forming the defective nanostructures. The fundamental understanding of these metal oxide reactions is essential to designing the metal oxide-based oxygen carriers for chemical looping applications.

Biomass is a promising renewable energy resource despite its low energy density, high moisture content and complex ash components. The use of biomass in energy production is considered to be approximately carbon neutral, and if it is combined with carbon capture technology, the overall energy conversion may even be negative in terms of net CO2 emission, which is known as BECCS (bioenergy with carbon capture and storage). The initial development of BECCS technologies often proposes the installation of a CO2 capture unit downstream of the conventional thermochemical conversion processes, which comprise combustion, pyrolysis or gasification. Although these approaches would benefit from the adaptation of already well developed energy conversion processes and CO2 capture technologies, they are limited in terms of materials and energy integration as well as systems engineering, which could lead to truly disruptive technologies for BECCS. Recently, a new generation of transformative energy conversion technologies including chemical looping have been developed. In particular, chemical looping employs solid looping materials and it uniquely allows inherent capture of CO2 during the conversion of fuels. In this review, the benefits, challenges, and prospects of biomass-based chemical looping technologies in various configurations have been discussed in-depth to provide important insight into the development of innovative BECCS technologies based on chemical looping.

Owing to its high fuel conversion efficiency and in-situ CO2 capture capability, chemical looping is a promising and versatile platform for fossil fuel utilization. Through the circulation of oxygen carriers (OCs), which are usually metal oxides, the carbonaceous fuels are oxidized into power/heat and/or value-added chemicals by lattice oxygen of OC in the fuel reactor. The reactivity of OC towards the carbonaceous fuels is crucial to the success of chemical looping processes. Incorporating low-percentage dopants into OC is a promising strategy to improve their reactivity while maintaining the recyclability. Consequently, a systematic screening strategy in dopant selection with a solid physical foundation is highly desired. Using hematite (α-Fe2O3) as the model OC material, density functional theory calculations were conducted herein to exemplify the impact of transition metal dopants on the surface reactivity with CO and CH4, the two most common C1 reducing agents in fossil fuels. We found that the amount of electrons accumulated on the lattice oxygen that bound with dopants is a key descriptor to evaluating the surface reactivity in the Mars-van Krevelen type reactions, which can be tailored by dopants with different electronegativities. Cu and Ni were predicted to be the most effective dopants, and such theoretical predictions were validated in temperature-programmed reduction and cyclic redox experiments, where a significant reactivity enhancement was observed using only 1% atomic ratio of effective dopants. The proposed screening strategy is expected to facilitate new OC designs and modifications in an energy and cost effective manner, thus significantly expedites the development of chemical looping technologies.

Chemical looping combustion (CLC) is an energy conversion technology that can produce concentrated CO2 stream without the need for a gas separation step, and thus, has the potential to drastically reduce the energy consumption and cost associated with CO2 capture in power generation. The coal-direct chemical looping (CDCL) process is a CLC technology that uses a moving bed reducer configuration that can directly consume coal as a feedstock without requiring an upstream gasification step. An integrated 250 kWth CDCL pilot unit using iron-based oxygen carriers was constructed and demonstrated for over 1000 h of testing. The principles for the CDCL pilot unit design and operation are summarized in this article. During the 288-hour continuous operation testing, the CDCL pilot unit achieved >96% coal conversion with a CO2 purity of >97%. Low carbon carryover into the combustor, i.e.

Chemical looping reforming with CO2 splitting (CLRS) is an attractive process that can be used for conversion of hydrocarbons into syngas, an industrially important intermediate that serves as a building block for other value-added products. Under the chemical looping approach, the oxygen carrier that provides lattice oxygen, instead of molecular oxygen, is used for methane partial oxidation. This work focuses on MgO-supported Ca2Fe2O5 redox materials as the oxygen carriers for simultaneous syngas production and CO2 utilization through thermochemical CO2 splitting using a two-reactor chemical looping system. We experimentally achieve a near 100% CH4 conversion and a high syngas selectivity of >98%, which is by far the highest in chemical looping reforming systems. Complete regeneration of the reduced oxygen carriers is obtained using CO2 with ~78% conversion, thereby operating close to the thermodynamic limit. Density functional theory calculations reveal that the lattice oxygen in corner-sharing octahedra of brownmillerite structure possessed by Ca2Fe2O5 acts as the efficient active sites for CO and H2 production. The formed oxygen vacancy significantly reduces the energy barriers of C-H cleavage and CO formation, leading to the reactivity and selectivity enhancement. MgO assists in reactivity enhancement by enabling higher degree of Ca2Fe2O5 dispersion along with increasing Ca2Fe2O5′s tolerance towards sintering. These findings will contribute to the systematic design of high-performance redox materials and chemical looping processes for syngas production with CO2 utilization.

Chemical looping is a promising technology for fossil fuel utilization due to its high fuel conversion efficiency with in-situ CO2 capture capability. Metal oxide are used as oxygen carriers (OCs) and circulate between a fuel reactor and an air reactor to perform reduction and oxidation reactions, respectively. In general, OC exiting the fuel reactor is not reduced fully to its metallic state due to many factors including carbon deposition and OC deactivation. Therefore, the effect of the initial reduction state on the OC oxidation in the air reactor is a significant parameter for consideration in developing the oxidation kinetic model. The objective of this work is to develop a physically significant kinetic model that applies to the oxidation of both initially fully and partially reduced OC with air. For this study, 1.5 mm Fe-based OC particle supported with TiO2 was used as the model OC particle due to its complex multistep reaction nature. The oxidation kinetics were experimentally investigated in a thermogravimetric analyzer (TGA). Results indicate a significant difference in the oxidation rate profile for the OCs when oxidized from an initially fully reduced compared to an initially partially reduced state. Elemental mapping via energy-dispersive X-ray spectroscopy (EDS) reveals a shrinking-core type topochemical pattern across the OC particle, which was identified to be the cause of the dependency of kinetics on the initial reduction state. A generalized kinetic model was developed based on the observed shrinking-core behavior without presuming any rate-determining steps and experimentally validated over a broad range of temperatures (800–1000 °C) and oxygen concentrations (5, 7, 10, and 15 mol%). Impacts of particle porosity, size, and core-shell structure on the OC oxidation kinetics were analyzed in the developed oxidation kinetic model to suggest methods of improving the oxidation rate of the OC without modifying the chemical composition.

Hydrogen (H 2 ) is a secondary fuel derived from natural gas. Currently, H 2 serves as an important component in refining operations, fertilizer production, and is experiencing increased utilization in the transportation industry as a clean combustion fuel. In recent years, industry and academia have focused on developing technology that reduces carbon emissions. As a result, there has been an increase in the technological developments for producing H 2 from natural gas. These technologies aim to minimize the cost increment associated with clean energy production. The natural gas processing chemical looping technology, developed at The Ohio State University (OSU), employs an iron-based oxygen carrier and a novel gas–solid counter-current moving bed reactor for H 2 production. Specifically, this study examines the theoretical thermodynamic limits for full conversion of natural gas through iron-based oxygen carrier reactions with methane (CH 4 ), by utilizing simulations generated with ASPEN modeling software. This study initially investigates the reducer and the oxidizer thermodynamic phase diagrams then derives an optimal auto-thermal operating condition for the complete loop simulation. This complete loop simulation is initially normalized for analysis on the basis of one mole of carbon input from natural gas. The H 2 production rate is then scaled to match that of the baseline study, using a full-scale ASPEN simulation for computing cooling loads, water requirements and net parasitic energy consumption. The full scale ASPEN simulation is used to analyze the thermal efficiency of multiple energy recovery schemes, for further validation of the chemical looping process. Resulting from this study, the chemical looping technology is found to produce a cold gas efficiency improvement of more than 5 percentage points and an effective thermal efficiency of more than 6 percentage points over the conventional steam methane reforming process, while producing H 2 from natural gas with greater than 90% carbon capture.

Passive cyclonic gas–liquid separators (PCGLSs) have unique advantages compared with other types of gas–liquid separators. In this study, liquid distribution inside a horizontally installed PCGLS is investigated using electrical capacitance volume tomography (ECVT). The liquid distribution is measured under various gas and liquid flow rates. It is found that the inlet liquid flow rate is the dominating factor influencing the liquid distribution. The angular velocity of the liquid layer is found to be proportional to the liquid flow rate when no gas is injected. The center axis of the gas core is observed to be lower than the center axis of the separator cylinder, and it will drift towards the separator׳s center axis with increasing liquid flow rate. A mechanistic model is derived, and flow field parameters are solved analytically to qualitatively explain this phenomenon. The calculated gas core positions match the ECVT images well.

Chemical looping technologies have the potential to reduce the natural-gas conversion cost in a carbon-constrained scenario. Given the increasing importance of natural gas to global energy supply, this work investigates the application of an iron oxide based chemical looping technology for natural gas conversion. A thermodynamic criterion for selecting iron oxide based oxygen carrier material and designing the reaction system is developed using an adapted Ellingham diagram. Equilibrium modeling for detailed thermodynamic analysis is conducted for verifying the Ellingham diagram analysis. The thermodynamic equilibrium model also establishes a system baseline performance, and experimental proof of concept bench-scale demonstration is investigated. The bench-scale testing is used to characterize the effect of parameters like solids to gas ratio and temperature of the reactor on system performance. An optimal set of operating conditions is identified for further testing on a larger scale.

Introduction The conversion of carbonaceous feedstocks into higher value products occurs through two major routes: (1) indirect oxidation; and (2) direct oxidation, as shown in Figure 3.1. In the indirect oxidation approach, carbonaceous feedstock is first oxidized to syngas, which can then be further converted to value-added products. With respect to syngas generation, the thermodynamics and reaction characteristics of metal oxide oxygen carriers are discussed in Chapter 2; chemical looping reactor configurations are discussed in Chapter 4; and the techno-economic analyses of several chemical looping processes are discussed in Chapter 6. In the direct oxidation approach, the carbonaceous feedstock is directly upgraded to the desired product. Conceptually, the direct route simplifies the overall process and reduces costs by removing processing steps, but no commercial-scale system exists. Early research activity on direct oxidation processes, specifically for methane, can be traced back to the 1920s, but the utilization of methane in the chemical industry has been limited due to its high molecular stability. Currently, direct methane utilization involves conversion to value-added products such as aromatics, oxygenates, olefins, and paraffins, of which the three major oxidative processes are partial oxidation to methanol, to formaldehyde, as given in Section 5.4, and to ethylene and ethane via the oxidative coupling of methane (OCM). Volatility in petroleum prices and limited petroleum reserves have made natural gas resources progressively more attractive as an energy source. Recent discoveries of natural gas reserves, increased accessibility to shale gas, and low natural gas prices have propelled a resurgence in methane-to-chemicals research. Monetizing cheap natural gas to obtain higher value-added products would provide a critical opportunity to the petroleum and chemical industry.9 Research into one promising direct route, OCM, has exhibited peaks and troughs, as shown in Figure 3.2. To date, pilot-scale systems were constructed and tested at the Atlantic Richfield Company (ARCO) in the 1990s. In 2012, Honeywell announced plans to scale up a proof-of-concept direct methane conversion process to ethylene. More recently, in 2015 Siluria Technologies began operating a pilot-scale OCM demonstration unit to convert methane to ethylene or gasoline. In this chapter, the direct oxidation of methane to ethylene and higher hydrocarbons through OCM is presented.

Chemical looping processes are characterized as promising carbonaceous fuel conversion technologies with the advantages of manageable CO2 capture and high energy conversion efficiency. Depending on the chemical looping reaction products generated, chemical looping technologies generally can be grouped into two types: chemical looping full oxidation (CLFO) and chemical looping partial oxidation (CLPO). In CLFO, carbonaceous fuels are fully oxidized to CO2 and H2O, as typically represented by chemical looping combustion with electricity as the primary product. In CLPO, however, carbonaceous fuels are partially oxidized, as typically represented by chemical looping gasification with syngas or hydrogen as the primary product. Both CLFO and CLPO share similar operational features; however, the optimum process configurations and the specific oxygen carriers used between them can vary significantly. Progress in both CLFO and CLPO is reviewed and analyzed with specific focus on oxygen carrier developments that characterize these technologies.

The iron-based Coal-Direct Chemical Looping (CDCL) combustion process is an alternative to conventional oxy-combustion technologies, where the oxygen used for fuel conversion in the CDCL process is provided by an iron-oxide based oxygen carrier instead of an air separation unit. The iron oxide is reduced using coal in the reducer reactor, producing highly-pure CO2 in the flue gas, and the reduced iron oxide is regenerated in a separate combustor reactor using air. The CDCL process at Ohio State has been developed and demonstrated in a 25 kWth sub-pilot unit, and it is the first chemical looping demonstration unit with a circulating moving bed reactor for solid fuel conversion. To date, the CDCL sub-pilot unit at OSU has been operated for more than 680 h, with a 200-h continuous operation, providing important data on long term operability as well as parametric optimization. This paper discusses recent parametric operational experience with sub-bituminous coal as the fuel, where dynamic changes in variables were performed to observe the effects on the unit itself. Measurements included temperature, pressure, and gas concentrations from the reducer and combustor. Furthermore, effects of different variables, such as flue gas recycle ratios (enhancer gas flow rates), feed port injection, and temperature, were observed. Tests confirmed high coal conversions with high purity of CO2 achieved in the flue gas. Overall, the moving bed design of the reducer results in nearly full coal conversion with a high purity of CO2, eliminating the need for additional down-stream fuel polishing and/or separation units. The combustor gas contained lean oxygen concentrations with minute amounts of carbonaceous gases detected, indicating proper regeneration of the oxygen carrier as well as good gas sealing between the reducer and combustor.

Spatial resolution represents a key performance aspect in electrical capacitance volume tomography (ECVT) systems. Factors affecting the resolution include the "soft-field" nature of ECVT, the number of capacitance channels used, the ill-conditioned nature of the imaging reconstruction problem, and the signal-to-noise ratio of the measurement apparatus. In this study, the effect of choosing different numbers of capacitance plates on the performance of ECVT is investigated experimentally. Specifically, two ECVT sensors with 12 and 24 capacitance channels but covering equal volumes of a cylinder are used to examine the resulting impact on the image resolution.

Experimental results of the air–water pulsating flows in a trickle bed column were obtained using the electrical capacitance volume tomography (ECVT) system. Detailed 3-D pulse structures in both the fully developed and the transient conditions were illustrated. Pulse frequency, pulse traveling velocity, average liquid holdup and liquid holdup inside the gas-rich and liquid-rich regions, respectively, were measured. Based on a simplified model, the linear liquid velocities inside the gas-rich and liquid-rich regions were estimated. The results revealed that the gas flow rate was the most important parameter in controlling the pulsating flow properties. Discussion on the physical nature of the pulsating flow was also given.

Electrical Capacitance Volume Tomography (ECVT) is a 3D, real-time imaging technique that is recently developed to image the multiphase flow behaviour in columns of regular or irregular geometries. In this study, the ECVT measurements are conducted to obtain phase holdups and flow structures in bubble columns of a straight-cylinder shape and a tapered-cylinder shape with porous and orifice gas distributors. The phase holdups obtained by the ECVT in a straight-cylinder bubble column with porous gas distributor are verified by other measurement techniques and correlation equations reported in the literature. The flow regimes of the bubble columns are also characterized by the ECVT. Particularly, a dynamic 3D flow structure, which is uniquely represented by the spiral motion of the bubble plumes occurring within the heterogeneous regime of the gas-liquid flow in a straight-cylinder shape bubble column with perforated distributor, is captured for the first time instantaneously over the entire flow field with the ECVT. Other flow behaviour such as the converging flow pattern of the gas bubbles in a tapered-cylinder shape bubble column is also revealed by the ECVT.

The CLC process has the potential to be a transformative commercial technology for a carbon-constrained economy. The Ohio State University Coal Direct Chemical Looping (CDCL) process directly converts coal, eliminating the need for a coal gasifier oran air separation unit (ASU). Compared to other solid-fuel CLC processes, the CDCL process is unique in that it consists of a countercurrent moving bed reducer reactor. In the proposed process, coal is injected into the middle of the moving bed, whereby the coal quickly heats up and devolatilizes, splitting the reactor roughly into two sections with no axial mixing. The top section consists of gaseous fuel produced from the coal volatiles, and the bottom section consists of the coal char mixed with the oxygen carrier. A bench-scale moving bed reactor was used to study the coal conversion with CO2 as the enhancing gas. Initial tests using metallurgical cokefines as feedstock were conducted to test the effects of operational variables in the bottom section of the moving bed reducer, e.g., reactor temperature, oxygen carrier to char ratio, enhancer gas CO2 flow rate, and oxygen carrier flow rates. Experiments directly using coal as the feedstock were subsequently carried out based on these test results. Powder River Basin (PRB) coal and Illinois #6 coal were tested as representative sub-bituminous and bituminous coals, respectively. Nearly complete coal conversion was achieved using composite iron oxide particles as the oxygen carriers without any flow problems. The operational results demonstrated that a moving bed reactor design is favorable for the CDCL application.

This work evaluates the environmental impact of conventional and calcium looping processes implemented with CO2 separation to gain broad insight and identify opportunities for future improvement. These systems are assessed at multiple scales: equipment, value chain and economy, and emissions of CO2, water use, land use, and energy return on investment are estimated. The difference in the energy quality of hydrogen and electricity products is considered in developing aggregate metrics. Calcium looping is found to be superior due to its smaller life cycle impacts. However, this process has a smaller energy return on investment due to the higher energy and resource requirements in the calcination and air separation steps. Future efforts for reducing the energy intensity of these steps by developing new technologies and optimizing existing methods are recommended.