Reactor Conversion Research Articles

Enhanced solar radiation absorption by carbon dioxide in thermodynamic nonequilibrium: A computational study

The conversion of carbon dioxide (CO2) into higher value products using solar energy can help fulfill the increasing need for fuels and chemicals while mitigating environmental emissions. Solar thermochemical conversion approaches rely on the absorption of radiative energy by a solid catalytic medium. The direct absorption of solar energy by CO2 before reaching the catalyst could lead to more efficient conversion. Greater solar photon absorption can be achieved through the use of an electrical discharge to drive CO2 to a low-temperature plasma state in which free electrons and heavy-species are in a state of Non-Local Thermodynamic-Equilibrium (NLTE). The absorption of solar energy by a plasma-enhanced solar reactor for atmospheric pressure CO2 conversion is analyzed via zero- and one-dimensional models. The models are comprised by the spectral radiative transfer equation (RTE) and energy conservation equations for electrons and heavy-species. Radiative properties are computed by a line-by-line radiative code and transport properties using kinetic theory. Simulation results for a representative 10 cm long solar-plasma reactor show up to 48% and 90% net-absorption of solar radiation by CO2 in NLTE at electron temperatures of 1 and 2 eV, respectively, and heavy-species temperatures of ~2000 K, common in solar thermochemical processes. In contrast, less than 0.2% of solar radiation is absorbed by CO2 in LTE under similar conditions. The results suggest that solar-plasma direct-receiver reactors, due to increased direct solar energy absorption, have the potential for greater efficiency CO2 decomposition processes.

Model and sensitivity analysis of the reciprocating biomass conversion reactor (RBCR)

In this work, the capabilities of a pilot-scale reciprocating biomass conversion reactor (RBCR) are assessed by modeling. The RBCR is a novel means to produce bio-oil by fast-pyrolysis whose core is a re-purposed 4-cycle internal combustion engine. Inert gas and a small volume-fraction of pulverized biomass are input into the RBCR intake, and the crankshaft is cycled by an external energy source to supply the process heat. The biomass is converted during the compression stroke, and then the bio-products are exhausted. The cycle is: intake, compression/heating, expansion, and exhaust. A control-volume energy balance to assess the steady-state flow of mass and energy through the RBCR is presented. The RBCR calculations are quantitatively compared to experimental results from the state of the art considered to be a lab-scale fluidized-bed reactor (FBR) found in the literature. This FBR is chosen for comparison because the RBCR and FBR have nearly the same size/footprint and, thus, by crude assumption, similar capital costs. Relative to the state-of-the-art (SOA), calculations predict that the RBCR will increase the biomass throughput, decrease the mass-specific energy requirement to thermochemically convert biomass to bio-oil, bio-char, and bio-gas by fast-pyrolysis. Moreover, calculations predict that at bench scale, the RBCR process results in a bio-oil product with a heating value approximately 6.8 times higher than the energy required to drive the cycle (there is a 6.8 times “return on energy investment”).

Performance of conical ammonia dissociation reactors for solar thermochemical energy storage

Solar thermochemical energy storage cannot only have a high energy density but the capability of storing energy at ambient temperature with little heat loss. Recently, lots of research has been done to advance the heat recovery process of an ammonia synthesis system in the context of ammonia-based solar thermochemical energy storage. However, there has not been much enhancement proposed to improve the conversion of the ammonia dissociation reactor, which determines the solar energy absorbed. This paper explores the effects of geometry and configuration on the conversion of ammonia dissociation reactors. A two-dimensional pseudo-homogeneous model has been developed to simulate reaction kinetics and thermodynamics in conical as well as cylindrical ammonia dissociation reactors. The model has been validated by comparing model-predicted and experimentally measured reactor wall temperature profiles and conversions. The effect of the configuration, i.e., cylindrical, diverging and converging, on reactor performance has been investigated. The results show that converging reactors can achieve a higher conversion with a fixed preheating heat exchanger, i.e., a 5.3% increase in the conversion with less than a 1° slope in the tube wall.

Leveraging Advanced Manufactured Catalysts and Reactors for Electrochemical CO2 Conversion

With the realization of the global impact of waste carbon on the atmosphere, coupled with a clear and growing demand for abundant electricity, there are both environmental and economic driving forces for capturing and electrochemically converting carbon dioxide (CO2) into high value hydrocarbon products. While much of the recent focus in this area has been driven by catalyst discovery, there is a lack of understanding on how the partnership of the catalyst and the reactor can be optimized for product selectivity and overall performance. The development of novel and optimized electrochemical reactors for this reaction is critically important; to address this gap, we report the use of advanced materials and manufacturing capabilities to design and construct electrocatalysts and electrochemical reactors for CO2 reduction. We report that by 3D printing catalysts and reactors, we can affect catalyst morphology, environment and reaction conditions, and thereby improve performance of Ag and Cu catalysts for electrochemical CO2 reduction. Our work at LLNL demonstrates our ability to leverage 3D printing and advanced manufacturing as tools to help study and improve catalyst activity, product faradaic efficiency, and overall energy efficiency.

(Invited) High-Temperature Mixed Conducting Membranes and Reactors for Direct CO2 Capture and Conversion

Direct CO2 capture and conversion have been an active research area in recent years due to its importance in addressing the current global warming/climate change and future depletion of fossil fuels and creating a carbon neutral ecosystem. The benchmark technology for CO2 capture is the post-combustion amine absorption, which is energy intensive and cost prohibitive to large-scale commercial implementation. In comparison, the CO2 conversion technologies are still at their infancy with many technical challenges in efficiency and selectivity to be overcome, but primarily being explored in low-temperature solution-based and high-temperature solid-oxide-based electrochemical cells with solar or electrical energy as the input. Here we present a new type of high-temperature membrane reactors operated on mixed conducting chemistry for direct CO2 separation and instant conversion. In the presentation, we will first discuss the chemistries of three basic types of mixed ionic/electronic conductors designed for CO2 separation and conversion. We will then present materials and synthesis of the membranes, followed by testing the performance of membrane reactors with mock-up flue gas as the feeding gas and methane/ethane as the sweeping gases. The performances of oxidative conversions of methane and ethane are characterized by conversion rate of the reactants, selectivity and yield of the products and flux density of both reactant and product species. Finally, the fundamental separation and conversion mechanisms will be discussed in detail.

Nanocrystalline ZrN thin film development via atomic layer deposition for U-Mo powder

Zirconium nitride (ZrN) thin film deposited via thermal atomic layer deposition (ALD) has been recently chosen as a candidate technology for application of a diffusion barrier coating on the low enriched uranium alloy powder considered in the NNSA research reactor conversion program. Reported here is the first instance of using ALD for coating actinide materials. For this study, a modified ALD system was constructed to produce one micron thick zirconium nitride (ZrN) coating over spherical particulate of natural uranium-molybdenum (U-Mo) based fuel. The ALD system was designed to have a rotating drum system, with provisions for facilitating sequential exposures of chemicals such as tetrakis dimethyl amido zirconium (TDMAZr) and ammonia (NH3) in order to deposit ZrN. The ALD system was successful in developing a highly conformal ZrN coating covering every individual U-7Mo particle. This article describes the ZrN film synthesis details and reports the produced microstructure and composition of the ALD ZrN as deposited on fuel particulates. The as-fabricated coating was determined to have a nanocrystalline structure in the cubic-ZrN (cF8) phase. It exhibited a dense microstructure with adequate interfacial bonding. TEM-EELS characterization demonstrated that the coating contains a very low amount of oxygen impurity. To understand the potential microstructural evolution for ALD ZrN during reactor operation, an in-situ heavy ion (Kr) irradiation experiment was performed at the IVEM-Tandem facility. A total fluence of 7.5 × 1015 ions/cm2 (∼10 dpa) was achieved, and apart from minor grain coarsening in the ALD ZrN coating, no significant radiation effects were observed.

110th Anniversary: Characterization of a Condensing CO2 to Methanol Reactor

A novel condensing reactor for conversion of CO2 to methanol is characterized under forced convective conditions, both experimentally and by modeling. The goal of the study is to optimize the opera...

Design of an Air-Cooled Sabatier Reactor for Thermocatalytic Hydrogenation of CO2: Experimental Proof-of-Concept and Model-Based Feasibility Analysis

This study assesses the techno-economic feasibility of using a single-pass, air-cooled Sabatier reactor for the thermocatalytic conversion of CO2 into renewable natural gas (RNG). The reactor was first analyzed numerically using a dynamic mathematical model. Effects of the feed rate, coolant type (compressed air vs molten salt), and cooling rate on the reactor performance were investigated. Next, the experimental proof-of-concept was provided using an autonomous Sabatier reactor (62 g of Ni/Al2O3 catalyst), including stability tests up to 100 h time-on-stream. Both simulations and experimental investigation have shown that, with a proper selection of operating parameters, it is possible to achieve CO2 conversions higher than 90%, while keeping the selectivity to CH4 production at 100%. On the basis of these results, a large-scale system for RNG generation from landfill gas has been designed, simulated, and analyzed, resulting in the RNG production cost as low as $15/GJ for the electricity price of $0.05/kWh.

Process Modeling and Simulation of Levulinate Esters Production Using Commercial Software

This paper presents the conceptual design and simulation of a biofuels (Levulinic esters) synthesizing process by esterification of Levulinic acid with lower alcohols using H2SO4 as catalyst. Levulinic esters are used as valuable fuels and fuel additives due to their high octane number, low water solubility, and high content of oxygen. Furthermore, they have less negative environmental impacts compared to the base fossil fuels. The Levulinic esters production process was simulated using HYSYS V8.8 software. The thermodynamic properties and kinetic data are obtained from open literature and used in the Aspen HYSYS model. The process simulation method involved selecting thermodynamic model, defining chemical components, selecting suitable operating units and identifying operating conditions. A detailed process flow sheet for production of Levulinate esters was developed. Effects of pressure, temperature and type of alcohol on biofuel yield were investigated and optimum values of temperature, pressure and types of alcohol were obtained. The optimum conversion was achieved when the conversion reactor operates at a pressure and temperature of 5 bar and 150°C respectively. Maximum conversion was obtained using methanol compared to other considered types of alcohols.

CO₂ Conversion by Membrane Reactors.

Membrane reactors technology represents a promising tool for the CO₂ capture and reuse by conversion to valuable products. After a preliminary presentation of the fundamentals of this technology, a critical overview of the last achievements and new perspectives in the CO₂ conversion by membrane reactors is given, highlighting the still existing limitations for large scale applications. Among the low temperature (≤100 °C) membrane reactor for CO₂ conversion, electrochemical membrane reactors and photocatalytic reactors, represent the two mainly pursued systems and they were discussed starting from selected case studies. Dry reforming of methane and CO₂ hydrogenation to methanol were selected as interesting examples of high temperature (>100 °C) membrane based conversion of CO₂ to energy bearing products.

A commissioning rod assembly for the Jamaican SLOWPOKE-2 nuclear reactor.

Within the framework of the Material Management and Minimization Conversion Program of the U.S. Department of Energy's National Nuclear Security Administration, the Argonne National Laboratory approved the manufacturing of a Jamaica's SLOWPOKE-2 nuclear reactor (JM-1) mock-up, reactor removal tools, and commissioning rods by Polytechnique Montreal. This mock-up reactor was then used to practice dry runs of the JM-1 high enriched uranium core removal activities and fresh low enriched uranium core loading operations of the JM-1 reactor conversion. One of the most crucial elements in the commissioning of a new reactor core is the commissioning rod assembly. Hence, this paper presents the design, the fabrication, the calibration, and the dry runs performed at Polytechnique Montreal with commissioning rod assembly. The work was then resumed at Jamaica's International Centre for Environmental and Nuclear Sciences.

SIMULATION AND OPTIMIZATION OF CONTINUOUS BIODIESEL PRODUCTION FROM SOYBEAN OIL

It is known that oil and its derivatives were the main energetics of the last century, although the fact that these inputs are finite and generate several pollutant harmful to human health and the environment. Economic and environmental aspects have contributed to the gradual disuse of fossil fuels and to the growth of research on renewable and clean energy, such as biodiesel, that has been gaining representativeness in the national and world market. Brazilian biodiesel production has been led by soybean oil for many years, then, aiming to make the simulation of the biodiesel plant closer to the brazilian reality (based on biodiesel process described by Zhang et al., 2003) the raw material (triolein) was changed to (trilinolein) through the use of the predictive methods of Constantinou e Gani (1994) and (1995) to estimate base and critical properties. Besides, a kinetic equation based on the experimental data of Noureddini and Zhu (1997) was proposed to represent the rate of soybean transesterification in function of temperature. Finally, optimization studies were made with the objective of maximizing biodiesel production; minimize the consumption of energy and inputs; outline great scenarios from the environmental perspective. The optimization results indicated that the temperature of the conversion reactor has a great influence on the biodiesel production due to the linear relationship. In addition, the change in the flow of water inserted in the liquid-liquid extractor is insignificant in view of the influence of the reactor temperature.It is known that oil and its derivatives were the main energetics of the last century, although the fact that these inputs are finite and generate several pollutant harmful to human health and the environment. Economic and environmental aspects have contributed to the gradual disuse of fossil fuels and to the growth of research on renewable and clean energy, such as biodiesel, that has been gaining representativeness in the national and world market. Brazilian biodiesel production has been led by soybean oil for many years, then, aiming to make the simulation of the biodiesel plant closer to the brazilian reality (based on biodiesel process described by Zhang et al., 2003) the raw material (triolein) was changed to (trilinolein) through the use of the predictive methods of Constantinou e Gani (1994) and (1995) to estimate base and critical properties. Besides, a kinetic equation based on the experimental data of Noureddini and Zhu (1997) was proposed to represent the rate of soybean transesterification in function of temperature. Finally, optimization studies were made with the objective of maximizing biodiesel production; minimize the consumption of energy and inputs; outline great scenarios from the environmental perspective. The optimization results indicated that the temperature of the conversion reactor has a great influence on the biodiesel production due to the linear relationship. In addition, the change in the flow of water inserted in the liquid-liquid extractor is insignificant in view of the influence of the reactor temperature.

3D Eulerian-Eulerian modeling of a screw reactor for biomass thermochemical conversion. Part 1: Solids flow dynamics and back-mixing

Three-dimensional (3D) computational fluid dynamics (CFD) simulations were performed to study solids flow dynamics and solids back-mixing behavior in a screw reactor (designed for thermal conversion of dry biomass particles) based on the Eulerian-Eulerian method. Simulation results were compared against experimental data with respect to filling degree and mean residence time of particles. The mean deviations for filling degree and for mean residence time between simulation and experiment were about 0.01 and 11.4 s, respectively, which shows that the model is reasonably accurate in predicting solids flow behavior in the screw reactor. The solids flow dynamics inside the reactor were discussed. The solids residence time distribution (RTD) was calculated and the degree of solids back-mixing in the forward transportation direction of the reactor was analyzed. It was found that solids being flung over the shaft and solids back-leakage, resulting from the low solids forward transportation velocity at the clearance between the flight and the bottom shell of the screw reactor, were responsible for solids back-mixing. The degree of solids back-mixing can be reduced at higher screw rotating speeds when keeping inlet mass flow rate of solids constant.

3D Eulerian-Eulerian modeling of a screw reactor for biomass thermochemical conversion. Part 2: Slow pyrolysis for char production

Biomass slow pyrolysis inside a screw reactor was studied using three-dimensional (3D) computational fluid dynamics (CFD) modeling. A multi-component (cellulose, hemicellulose and lignin with detailed elemental composition), multi-step kinetic model was incorporated into the CFD model. Modeling results were compared with experimental results with respect to the steady-state axial temperature distribution in the reactor (mean deviation, MD, of 12.6 K at the operating temperature of 598 K), the product yields (MDs of 7.7 wt%, 6.2 wt% and 1.7 wt% for the mass yields of char, liquid product, and gas product, respectively) and the elemental composition of char (MD of 1.6 wt%, 0.9 wt% and 2.5 wt% for the mass fractions of C, H and O, respectively). The model was then used to predict the energy density (higher heating value, HHV) and the energy yield of char, and these modeling results were compared against experimental data (MD of about 1.0 MJ kg−1 for the HHV and of about 9.4 wt% for the energy yield). Simulation results indicate that the model can well predict biomass pyrolysis and can predict the quality (e.g. HHV) and the energy yield in the resulting char.

A membrane-assisted hydrogen and carbon oxides separation from flare gas and recovery to a commercial methanol reactor

The push to control the greenhouse gas emissions is motivated by environmental regulations. For the aim to be achieved, the suggestion of eliminating or at least reducing gas flaring is currently taken under environment. In this regard, a new configuration for flare gas treatment is proposed in this study. This configuration is aimed to collect H2 and CO2 from flare gas, simultaneously. The collected components would be sent to the methanol synthesis reactor in the upstream section. The proposed configuration is made up of a multi-step membrane-assisted separation unit. In order to clarify what lies behind the idea, we proposed a mathematical formulation which is composed of conservation equations and kinetic rate equations is developed. H2 and CO2 elimination in the first step followed by a membrane-assisted water gas shift reactor for catalytic CO conversion and H2 recovery in tandem, and removing the remaining CO2 in the supplementary step is investigated numerically. The collected H2/CO2 mixture is aimed to recover into the upstream methanol synthesis reactor. The obtained results reveal that by utilizing such a strategy, about 2500 kmol/day CO2 (almost 98% of total input) is eliminated from the flare gas stream. Moreover, by considering the converted CO, about 4050 kmol/day CO2 is recovered to the methanol reactor. As a whole, 0.68% enhancement in the methanol generation and the reduction of about 4050 kmol/day flare gas pollutants are achieved in tandem when 98% N2 and 92.9% CH4 is separated the from purge gas.

Kinetics-free transformation from non-isothermal discontinuous to continuous tubular reactors

Focusing on tubular reactors with continuously distributed side injections, a general procedure to evaluate the operating mode able to reproduce the performance of a given semi-batch reactor is worked out. Namely, such operating mode is expressed as axial profiles of feed flowrate and temperature of the cooling/heating medium inside the reactor jacket. This transformation procedure, previously limited to isothermal reactors, is extended here to non-isothermal systems. The process performance (selectivity and conversion) of the original discontinuous reactor are fully reproduced using the continuous intensified reactor, while its productivity remains a degree of freedom. Notably, like in the isothermal case, the transformation procedure is kinetics-free, i.e. the knowledge of the reaction kinetics is not a precondition.As case study, a copolymerisation reaction is considered to demonstrate the potential of the method. Even though any SBR feed policy could be considered when applying this methodology, the optimal feed policy of the semi-batch reactor evaluated according to the so-called “power feed” procedure is examined considering the reactor non-isothermal. Afterwards, the proposed transformation method is applied and the performance of the two systems, discontinuous and continuous, are comparatively evaluated. Finally, given the practical difficulties associated with continuously distributed side injections, a discretisation approach is proposed based on the use of discrete lateral feeds and more realistic reactor configurations.

Exergy analysis and performance evaluation of a newly developed integrated energy system for quenchable generation

This paper presents an innovative use of waste heat recovered from a cement slag for multigeneration purposes, including power, ammonia, heat, hot water and oxygen production. A novel approach of ammonia production is employed in this study. The proposed system consists of four major subsystems; copper-chlorine (Cu-Cl) cycle, cryogenic Air Separation Unit (ASU), ammonia synthesis reactor and two steam Rankine cycles. The Aspen plus 9.0 version is employed for modeling and simulation of the proposed system. A comparative study is also conducted considering the different CuCl cycle based integrated systems for multigenerational purpose with numerous energy sources. The parametric studies are carried out by varying parameters, namely flow rate, compressor and turbine discharge pressures and ammonia reactor conversion rate. The exergy analysis is comprehensively conducted for each of the system components through exergy balance equations and exergy efficiencies. The overall exergy efficiency of the designed system is found to be 36.1%. Further results are also presented and discussed.

NTP reactor for a single stage methane conversion to methanol: Influence of catalyst addition and effect of promoters

Partial oxidation of methane to methanol is one of the best routes for liquid oxygenates preparation. The present study describes the application of a non-thermal plasma reactor operated under dielectric barrier discharge mode with/without catalyst addition for a single stage methane conversion to methanol. Air has been chosen as the oxidant for methane partial oxidation. It is found that both the reactant conversion and product distribution are strongly dependent on the reactor configuration, feed gases composition and also catalyst addition. A series of γ-Al2O3 supported Cu catalyst with metal oxide promoters (ZnO, ZrO2 and MgO) were integrated with plasma zone as to obtain in-plasma catalytic reactor. Typical results show that the synergistic effect due to plasma activation and catalytic action, significantly improves both CH4 conversion and CH3OH selectivity. The best methanol selectivity of ∼28% is achieved over the CuZrAl catalyst with a CH4 conversion of ∼11%, while plasma reactor provides only ∼18% CH3OH selectivity. The possible reaction mechanism of methanol formation inside the plasma reactor has been discussed, which highlights that the catalyst facilitates the adsorption of plasma excited species and improves the performance of the reactor.

Numerical modelling of a low power non-transferred arc plasma reactor for methane conversion

Thermal flow characteristics and the methane conversion reaction in a low power arc plasma reactor for efficient storage and transport of methane, which is the main component of shale gas, were simulated. The temperature and velocity distributions were calculated according to the type of discharge gases and arc current level by a self-developed magnetohydrodynamics (MHD) code and a commercial ANSYS-FLUENT code; the transport of chemical species was analyzed as including the chemical reactions of methane conversion. The simulated results were verified by the comparison of calculated and measured arc voltages with permissible low error as under 4%. Three C2 hydrocarbon gases with ethane (C2H6), ethylene (C2H4), and acetylene (C2H2) were selected as the converted species of methane from experimental data. The mass fraction of C2 hydrocarbons and hydrogen as the product of the conversion reaction at the reactor was also calculated. Those values show good agreement with the actual experimental results in that the major conversion reaction occurred in C2H2 and hydrogen, and the conversions to C2H6, C2H4, and hydrogen were minor reactions of methane pyrolysis conversion.

Multilayer Operability Framework for Process Design, Intensification, and Modularization of Nonlinear Energy Systems

An optimization-based multilayer operability framework is introduced for the process design of nonlinear energy systems that are challenged by complexity and highly constrained environments. In the first layer of this framework, a mixed-integer linear programming (MILP)-based iterative algorithm considers the minimization of the footprint and the achievement of process intensification targets. Then, in the second layer, an operability analysis is performed to incorporate into the approach key features for optimality and feasibility, accounting for the system operation with changeable input conditions. The outcome of the framework consists of a set of modular designs, considering the aspects of both size and process operability. For this study, the nonlinear system is represented by multiple linearized models, resulting in low computational expense and efficient quantification of operability regions. The developed framework is applied to a membrane reactor for direct methane aromatization conversion to hyd...