Decomposition Of Sulfur Trioxide Research Articles

A reduced order sulfuric acid decomposition model for a nuclear-powered hybrid sulfur cycle

A reduced order model of sulfuric acid decomposition within a bayonet chemical reactor was developed to support the U. S. Department of Energy Integrated Energy System program, and address the lack of knowledge in scaling and integration for joint chemical and nuclear processes. Sulfuric acid decomposition within a bayonet reactor was modeled to provide chemical and thermodynamic data relevant to advanced nuclear reactor-driven integrated energy systems based on desired operational scale and operational conditions. The temperature range required for high-temperature advanced nuclear reactor integrated energy systems, 750-850 °C, was shown to produce reasonable agreement (within a few percent relative error) with past models and experimental data, and yielded good efficiency results for bayonet reactor operations. The results of the reduced order model agreed with previous work from Savannah River National Labs within a maximum of 3.4% error on the decomposition of sulfur trioxide, and on previous Hybrid Sulfur flowsheets from Gorensek and Summers that showed operational temperature, pressure, and composition ranges for efficiency which made the Hybrid Sulfur cycle competitive with water electrolysis. The agreement with previous high-fidelity models provided a framework for future Integrated Energy System grid evaluations with an advanced nuclear reactor and large-scale hydrogen production using a mathematical model to represent chemical operations.

Thermodynamic modeling of sulfuric acid decomposer integrated with 1 MW tubular SOFC stack for sulfur-based thermochemical hydrogen production

This study developed a thermodynamic model of a set of sulfuric acid decomposers for thermochemical hydrogen production. It was integrated with a 1 MW tubular-type solid oxide fuel cell (SOFC) stack. With the model, we evaluated the feasibility of the combined production of electric power, heat, and sulfur dioxide for thermochemical H2 production. The integrated reactor model consists of three parts: i) SOFC submodel, ii) sulfuric acid decomposition (SAD) submodel, and iii) sulfur trioxide decomposition (STD) submodel with the catalysts Pt/γAl2O3 and WX-1. The efficiency of the integrated system was evaluated at a low-pressure range by polarization and efficiency curves for the SOFC, as well as pinch analysis for the SAD. The highest SOFC efficiency and SO2 production were achieved at 1.25 bar, whereas the lowest fuel consumption and heat demand for SO2 production were achieved at 3.0 bar. Furthermore, WX-1 performed better in the high-temperature range, whereas Pt/γAl2O3 performed better than WX-1 under low-temperature conditions. The Pt-supported catalyst could achieve SO3 conversion of 66% and SO2 yield of 57% at a gas temperature of 1025 K using the proposed integrated reactor design.

Modeling sulfuric acid decomposition in a bayonet heat exchanger in the iodine-sulfur cycle for hydrogen production

Accurate simulations of sulfuric acid decomposition are important for the design and control of sulfuric acid decomposers, which are key equipments for nuclear hydrogen production with the iodine-sulfur cycle driven by heat from a very high temperature gas cooled reactor. The present study included sulfuric acid decomposition experiments with measurements of the decomposition fraction and temperature distribution to verify a user defined boiling model that relaxes the coupling between the phase transition and the chemical reactions modeled using a species transport model based on computational fluid dynamics. The heat transfer in the bayonet heat exchanger was simulated numerically including the liquid sulfuric acid phase change, the reversible sulfuric acid decomposition reaction, and the sulfur trioxide decomposition into sulfur dioxide in the catalyst zone. The results show that the proposed method agrees well with experimental data. The sulfuric acid needs to completely decompose before entering the catalyzer to make full use of the catalyst. The decomposition fraction of sulfuric acid decreases significantly with increasing flow rate due to the inadequate retention time in the catalyst zone. The sulfuric acid decomposition rate increases and then tends towards a stable rate with increasing velocity. This study provides a useful model for engineering designs of high-performance sulfuric acid decomposers.

Evaluating the chemical stability of metal oxides in SO3 and applications of SiO2‐based membranes to O2/SO3 separation

AbstractThe decomposition of sulfur trioxide to produce sulfur dioxide and oxygen using a catalytic membrane reactor is technology that promises to improve the economic viability of the thermochemical water‐splitting Iodine‐Sulfur (IS) process for large‐scale CO2‐free hydrogen production. The chemical stability of membrane materials under SO3, however, is a significant challenge for this strategy. In this study, microporous membranes with a layered structure that consisted of a membrane support prepared from α‐Al2O3, an intermediate layer prepared from silica‐zirconia, and a top layer prepared from bis (triethoxysilyl)ethane‐derived organosilica sols, were examined for stability under SO3 and for use in SO3/O2 separation. An α‐Al2O3 support that features SiO2–ZrO2 intermediate layers with large pore sizes and a high Si/Zr molar ratio showed excellent resistance to SO3, which was confirmed by N2 adsorption, Energy Dispersive X‐ray Spectroscopy (EDS), and Scanning Electron Microscopy (SEM). These membranes also demonstrated a negligible change in gas permeance before and after SO3 exposure. Subsequently, in binary‐component gas separation at 550°C, microporous organosilica‐derived membranes achieved an O2/SO3 selectivity of 10 (much higher than the Knudsen selectivity of 1.6) while maintaining a high O2 permeance of 2.5 × 10−8 mol m–2 s–1 Pa–1.

Enhanced decomposition of sulfur trioxide in the water-splitting iodine–sulfur process via a catalytic membrane reactor

We achieved an enhanced conversion in SO3 decomposition via catalytic membrane reactors at 600 °C and provided the first report on the molecular size of the SO3 molecule.

CFD modeling and simulation of sulfur trioxide decomposition in ceramic plate-fin high temperature heat exchanger and decomposer

Abstract In this study numerical analysis was carried out for four different types of fins namely rectangular, triangular, inverted bolt fins and ripsaw fins and three different types of arrangements namely straight, staggered and top and bottom arrangement. The obtained results were compared with each other and the design with the highest decomposition percentage of sulfur trioxide was selected. The working fluids used in the model were sulfur trioxide, sulfur dioxide, oxygen and water vapor. The operating pressure was 1.5 MPa and the operating temperature ranges from 973 K to 1223 K. From the results it was found that the ripsaw fin design with thickness of 0.05 mm gives the highest decomposition percentage of sulfur trioxide. The inverted bolt fins gives a good heat transfer rate but due to the fin arrangement and the flow disturbances caused by the arrangement the pressure drop was the highest compared to the other fins. The pressure drop and heat transfer obtained for the rectangular and triangular fins were similar to each other. The obtained decomposition percentage of sulfur trioxide for straight, staggered and top and bottom arrangement were 17.60%, 16.74% and 20.55%. The obtained decomposition percentage increased from 16.74% to 85.15% when the channel length of the heat exchanger was increased ten times.

Design of a Compact Ceramic High-Temperature Heat Exchanger and Chemical Decomposer for Hydrogen Production

This article describes a compact silicon carbide ceramic, high-temperature heat exchanger for hydrogen production in the sulfur iodine thermochemical cycle, and in particular, to be used as the sulfuric acid decomposer. In this cycle, hot helium from a nuclear reactor is used to heat the SI (sulfuric acid) feed components (H2O, H2SO4, SO3) to obtain appropriate conditions for the SI decomposition reaction. The inner walls of the SI decomposer channels are coated with platinum to catalytically decompose sulfur trioxide into sulfur dioxide and oxygen. Hydrodynamic, thermal, and the sulfur trioxide decomposition reaction were coupled for numerical modeling. Thermal results of this analysis are exported to perform a probabilistic mechanical failure analysis. This article presents the approach used in modeling the chemical decomposition of sulfur trioxide. Stress analysis of the design is also presented. The second part of the article shows the results of parametric study of the baseline design (linear channels). Several alternate designs of the chemical decomposer channels are also explored. The current study summarizes the results of the parametric calculations whose objective is to maximize the sulfur trioxide decomposition by using various channel geometries within the decomposer. Based on these results, a discussion of the possibilities for improving the productivity of the design is also given.

A thermodynamic analysis of high temperature gas-cooled reactors for optimal waste heat recovery and hydrogen production

In this study the concept of generalized cogeneration has been employed to the analysis of the effective heat recovery from the high temperature gas-cooled reactor (HTGR). Brayton cycle is used as a topping cycle for HTGR with helium as the working fluid. HTR-10 and VHTR, having different power levels of HTGR, have been applied in the present study. The paper investigates the optimal strategy of the heat recovery, which combines the bottoming cycles and the parameters such as the select of different working fluids and the ambient temperatures. The heat recovery has integrated the organic Rankine cycle (ORC) using the fluids, such as alkane and benzene to perform the thermodynamic analysis. The total efficiency could be increased by 13.57% and 3.12% for HTR-10 and VHTR, respectively. Brayton cycle has been employed in the heat recovery for the iodine–sulfur (IS) hydrogen production process of VHTR by integrating the intermediate cooling process with the recuperator. When the sulfur trioxide (SO3) decomposition temperature is the lowest and the efficiency of the power conversion from hydrogen is assumed 0.6, the total thermal efficiency will be increased from 3.12% to 8.60%.

Numerical analysis of operation conditions and design aspects of a sulfur trioxide decomposer for solar energy conversion

A basic concept for a receiver-reactor for solar sulfuric acid decomposition as the key step of the Hybrid Sulfur Cycle for hydrogen production has been developed and realized. A prototype reactor has been built and is specialized for the second part of the reaction, the decomposition of sulfur trioxide. For a detailed understanding of the operational behaviour of the developed reactor type a mathematical model was developed. The reactor model was validated using experimental data from the test operation with a prototype reactor. The present work deals with the optimization of process and design parameters and the evaluation of the achievable performance of the reactor type. Furthermore the reactor model is used for numerical simulations to predict specific operational points of the prototype reactor and the performance of a large-scale reactor on a solar tower. Influences of operational parameters like absorber temperature, feed mass flow, residence time, and initial concentration of the acid are analyzed. In many cases those analyses reveal the existence of an optimum of reactor efficiency. When varying the absorber temperature an optimum of reactor efficiency emerges due to two compensating effects: chemical conversion increases with temperature, whereas re-radiation losses increase disproportionately at the same time. This matches the experimental findings very well. A large scale tower-receiver-reactor consisting of several individual modules is modelled and simulated. The main differences to the prototype system are the reduced gradients of solar flux distribution on the receiver front face and the reduced thermal conduction losses due to the presence of several neighbor modules at a comparable temperature level. This leads to higher chemical conversions and better efficiencies. Reactor efficiencies up to 75 % are predicted.

Modeling of a solar receiver-reactor for sulfur-based thermochemical cycles for hydrogen generation

Sulfur-based thermochemical cycles for hydrogen generation from water have one reaction step in common, which is the decomposition of sulfuric acid, which is one of the most energy-consuming steps. The present work deals with the development of a dynamic mathematical model of a solar reactor for this key step. One of the core parts of the model is a partial model of the reaction kinetics of the decomposition of sulfur trioxide, which is based on experiments investigating the kinetics of the used catalyst platinum coated on a ceramic solar absorber. Other partial models describe, e.g. the absorption of solar radiation, heat conduction in the absorber, convection between gas and the absorber walls and energy losses due to heat radiation. A comprehensive validation of the reactor model is performed using measured data, which is gained in experiments with a prototype reactor. The operating behavior of the real reactor is compared with the results of the numerical simulation with the model. The validation is, in particular, performed by reproducing the influences of individual parameters on the chemical conversion and the reactor efficiency. The relative deviations between the experimental data and the simulation results are mostly within the range of measurement accuracy. In particular, the good agreement of calculated values of the derived parameters, SO3 conversion and reactor efficiency with those determined from the experiments qualifies the model for optimization purposes. Copyright © 2010 John Wiley & Sons, Ltd.

CFD modeling and experimental validation of sulfur trioxide decomposition in bayonet type heat exchanger and chemical decomposer for different packed bed designs

The growth of global energy demand during the 21st century, combined with the necessity to master greenhouse gas emissions has lead to the introduction of a new and universal energy carrier: hydrogen. The Department of Energy (DOE) Nuclear Hydrogen Initiative was investigating thermochemical cycles for hydrogen production using high-temperature heat exchangers. In this study a three-dimensional computational model of high-temperature heat exchanger and decomposer for decomposition of sulfur trioxide by the sulfur–iodine thermochemical water-splitting cycle with different packed bed designs has been done. The decomposer region of the bayonet heat exchanger also called as silicon carbide integrated decomposer (SID) is designed as the packed bed region. Cylindrical, spherical, cubical and hollow cylindrical pellets have been arranged inside the packed bed. The engineering design of the packed bed was very much influenced by the structure of the packing matrix, which was governed by the shape, dimension and the loading of the constituent particles. Staggered and regular packing methods are used for packing the pellets in the packed bed region. The numerical model is created using GAMBIT and fluid, thermal and chemical analyses were performed using FLUENT. The decomposition percentage of sulfur trioxide is found for the packed bed region with different pellets and the numerical results obtained is compared with the experimental results. A comparison is made for the decomposition percentage of SO3 for the packed bed approach and the porous media approach.

Experimental study on sulfur trioxide decomposition in a volumetric solar receiver-reactor

Process conditions for the direct solar decomposition of sulfur trioxide have been investigated and optimized by using a receiver–reactor in a solar furnace. This decomposition reaction is a key step to couple concentrated solar radiation or solar high-temperature heat into promising sulfur-based thermochemical cycles for solar production of hydrogen from water. After proof-of-principle a modified design of the reactor was applied. A separated chamber for the evaporation of the sulfuric acid, which is the precursor of sulfur trioxide in the mentioned thermochemical cycles, a higher mass flow of reactants, an independent control and optimization of the decomposition reactor were possible. Higher mass flows of the reactants improve the reactor efficiency because energy losses are almost independent of the mass flow due to the predominant contribution of re-radiation losses. The influence of absorber temperature, mass flow, reactant initial concentration, acid concentration, and residence time on sulfur trioxide conversion and reactor efficiency has been investigated systematically. The experimental investigation was accompanied by energy balancing of the reactor for typical operational points. The absorber temperature turned out to be the most important parameter with respect to both conversion and efficiency. When the reactor was applied for solar sulfur trioxide decomposition only, reactor efficiencies of up to 40% were achieved at average absorber temperature well below 1000°C. High conversions almost up to the maximum achievable conversion determined by thermodynamic equilibrium were achieved. As the re-radiation of the absorber is the main contribution to energy losses of the reactor, a cavity design is predicted to be the preferable way to further raise the efficiency. Copyright © 2009 John Wiley & Sons, Ltd.

Synthesis of Cu/Fe/Ti/Al2O3 Composite Granules for SO3 Decomposition in SI Cycle

The present paper deals with the catalytic decomposition of SO3 reaction. Cu/Fe/Ti/Al2O3 composite granule catalysts prepared by a combination of Yoldas process and oil-drop method were studied in an attempt to find some suitable catalysts for the decomposition of sulfur trioxide as the oxygen-generating reaction in the thermo-chemical water splitting process. CuFe/Ti:Al-1:2 shows high SO3 conversion (69%) at 800 °C compared with other catalysts because of the high surface area and the support permitted a better dispersion of Ti.

Numerical study of sulfur trioxide decomposition in bayonet type heat exchanger and chemical decomposer with porous media zone and different packed bed designs

The Department of Energy (DOE) Nuclear Hydrogen Initiative was investigating thermochemical cycles for hydrogen production using high temperature heat exchangers. The present work was concerned with use of bayonet type heat exchanger as silicon carbide integrated decomposer (SID) which produces sulfuric acid decomposition product – sulfur dioxide. The product can be used within the sulfur–iodine thermochemical cycle and hybrid sulfur process. A two-dimensional axis-symmetric geometry of the bayonet heat exchanger has been created using GAMBIT software. Fluid, thermal and chemical reaction analyses were performed using FLUENT software. The working fluids in the model were sulfur trioxide, sulfur dioxide, oxygen and water vapor. Silicon carbide with 1 wt% of platinum was used as a catalyst for the chemical reaction. The form of pellets packing was simple cubical packing and porous media approach was used. The chemical reaction for the two-dimensional model was carried out in two cases (ways): (1) constant outer wall temperature and (2) by applying the measured values obtained from the thermocouples placed along the outer wall of the lab scale model of the bayonet heat exchanger in Sandia National Lab (SNL). The decomposition of sulfur trioxide for the two-dimensional model was calculated and the obtained results were compared with the experimental results. But, practically the flow of fluid between the pellets in the decomposer region of the bayonet heat exchanger may have many swirling and recirculation. Hence a further study on three-dimensional model of the decomposer with different arrangement of the pellets in the packed bed region was carried out. The chemical decomposition that occurred in packed bed was of the decomposer. The engineering design of the packed bed was very much influenced by the structure of the packing matrix, which was governed by the shape, dimension and the loading of the constituent particles. The investigations of different types of catalyst in the packed bed region and the decomposition of sulfur trioxide were calculated and the results obtained were consistent with the experimental results.

Numerical modeling of high-temperature shell-and-tube heat exchanger and chemical decomposer for hydrogen production

Numerical simulations of shell-and-tube heat exchanger and chemical decomposer with straight tube configuration and porous media were performed using FLUENT6.2.16 to examine the percentage decomposition of sulfur trioxide. The decomposition process can be a part of sulfur–iodine (S–I) thermochemical water splitting cycle, which is one of the most studied cycles for hydrogen production. A steady-state, laminar, two-dimensional axisymmetric shell-and-tube model with counter flow and parallel flow arrangements and simple uniform cubical packing was developed using porous medium approach to investigate the fluid flow, heat transfer and chemical reactions in the decomposer. As per the investigation, the decomposition percentage of sulfur trioxide for counter flow arrangement was found to be 93% and that of parallel flow was 92%. Also, a high pressure drop was observed in counter flow arrangement compared to parallel flow. The effects of inlet velocity, temperature and the porous medium properties on the pressure drop across the porous medium were studied. The influence of geometric parameters mainly the diameter of the tube, diameter of the shell and the length of the porous zone on the percentage decomposition of sulfur trioxide in the tube was investigated as well. A preliminary parametric study of the mentioned configuration is conducted to explore effects of varying parameters on the decomposition of sulfur trioxide. From the performed calculations, it was found that the Reynolds number played a significant role in affecting the sulfur trioxide decomposition. The percentage decomposition decreases with an increase in Reynolds number. Surface-to-volume area ratio and activation energy were also the important parameters that influenced the decomposition percentage. A high surface-to-volume area ratio enhances the rate of the chemical reaction and high activation energy decreases the decomposition percentage. The decomposition of sulfur trioxide is calculated and compared for both counter and parallel flow arrangements.

Preparation and characterization of Fe/Cu/Al2O3-composite granules for SO3 decomposition to assist hydrogen production

In this work, the activity values of Cu/Al2O3-, Fe/Al2O3- and Cu/Fe/Al2O3-composite granule catalysts prepared by a combination of Yoldas-process and oil-drop method were studied in an attempt to find some suitable catalysts for the decomposition of sulfur trioxide as the oxygen-generating reaction in the thermo-chemical water splitting process. The SO3 decomposition was performed in the temperature range of 750–950 °C at a space velocity of 72,000 mL/g cat. h in a fixed bed reactor. The catalytic activity of Cu/Fe/Al2O3-composite granule catalyst was better than that of Cu/Al2O3- and Fe/Al2O3-composite granule catalysts. The composite of Cu and Fe in the alumina granules increased the catalytic activity and found the optimum ratio of [Cu]/[Fe] = 1/2 with [Cu] + [Fe] = 0.125 M.

Catalytic decomposition of sulfur trioxide on the binary metal oxide catalysts of Fe/Al and Fe/Ti

The iodine–sulfur (IS) cycle has been focused for hydrogen production by water splitting using a very high temperature nuclear reactor (VHTR) which is a high temperature heat source. The nuclear energy was absorbed at the temperature ranges of 750–900 °C by SO 3 decomposition reaction to SO 2 and O 2 in IS cycle. In this work, the activity of Fe/Al and Fe/Ti catalysts prepared by a co-precipitation was studied in an attempt to find some suitable catalysts for the decomposition of sulfur trioxide as the oxygen-generating reaction in the thermo-chemical water splitting process. The SO 3 decomposition was performed in the temperature range of 750–950 °C at a space velocity of 72,000 cm 3/g cat. h in a fixed bed reactor. The catalytic activity of Fe/Al and Fe/Ti catalysts increased with an increase in Fe loadings, indicating that the Fe component should be active. The mechanism for the SO 3 decomposition on metal oxides can be described as follows: the metal sulfate formation (MO + SO 3 → MSO 4) and the decomposition of metal sulfate (MSO 4 → MO 2 + SO 2 and MO 2 → MO + 1/2O 2).

Development of a New Thermochemical and Electrolytic Hybrid Hydrogen Production System for Sodium Cooled FBR

A new thermo-chemical and electrolytic hybrid hydrogen production system in lower temperature range is newly proposed by the Japan Nuclear Cycle Development Institute (JAEA) to realize the hydrogen production from water by using the heat generation of sodium cooled Fast Breeder Reactor (FBR). The system is based on sulfuric acid (H2SO4) synthesis and decomposition process developed earlier (Westinghouse process), and sulfur trioxide (SO3) decomposition process is facilitated by electrolysis with ionic oxygen conductive solid electrolyte to reduce the operation temperature 200-300°C lower than Westinghouse process. SO3 decomposition with the voltage lower than 0.5V was confirmed in the temperature range of 500 to 600°C and theoretical thermal efficiency of the system evaluated based on chemical reactions was within the range of 35% to 55% under the influence of H2SO4 concentration and heat recovery. Furthermore, hydrogen production experiments to substantiate the whole process were performed. Stable hydrogen and oxygen production were observed in the experiments, and maximum duration of the experiments was about 5 hours.

512 熱化学水素製造法ISプロセスの研究開発(III) : 三酸化硫黄分解器の開発(関東支部 茨城講演会)

Japan Atomic Energy Research Institute (JAERI) has been conducting R&D on HTGRs and hydrogen production method focusing on thermochemical IS process. In the IS process, sulfur trioxide (SO_3) decomposition reaction works as the oxygen generation reaction where gaseous SO_3 is decomposed into SO_2 and O_2 in the presence of solid catalysts using high temperature heat of about 900℃ supplied by HTGRs. A concept of SO_3 decomposer was developed which features plate-type heat exchanger made of SiC ceramics, in which the heat of reaction is supplied by high temperature helium gas, and a model of the heat-exchanging units was successfully test-fabricated. Also, a test facility was constructed in order to examine the catalyst performance at temperatures of up to 850℃, and pressures of up to 0.75MPa.

Studies on the nickel-iodine-sulfur process for hydrogen production—III

A thermochemical hydrogen production process utilizing nickel, iodine and sulfur (the NIS process) has been studied and suitable operation conditions examined. Nickel powder dissolution into acid mixtures, nickel iodide decomposition under iodine partial pressure, nickel sulfate decomposition and other steps were studied. Decomposition gas from the sulfate had near equilibrium composition as for the sulfur trioxide decomposition into sulfur dioxide and oxygen. A new process is also under study, utilizing methanol instead of nickel as the circulating reactant.