Reactor Steam Research Articles

Operation of Rh/Ce0.75Zr0.25O2-δ-ƞ-Al2O3/FeCrAl wire mesh honeycomb catalytic modules in diesel steam and autothermal reforming

The Rh/Ce0·75Zr0·25O2–δ-ƞ-Al2O3/FeCrAl structured catalytic blocks of length 10, 20, and 60 mm were prepared and tested in the reactions of steam and autothermal reforming of n-hexadecane. It was found in a series of experiments on hexadecane steam reforming with the catalyst heating solely through the reactor wall that the complete conversion of hexadecane at a furnace temperature below 750 °C was not achieved even at GHSV = 10,000 h−1. Under these conditions, the formation of carbon on the catalyst surface was observed. At the reactor wall temperature of 800 °C, the complete conversion of hexadecane was achieved even in the 10 mm long catalytic block (GHSV = 60,000 h−1), accompanied by the formation of various intermediate light hydrocarbons. To achieve complete conversion of these intermediate compounds (mainly 1-alkenes), it is necessary to carry out the steam reforming reaction at GHSV = 10,000 h−1. At hexadecane autothermal reforming, heat is supplied to the reaction zone by exothermic oxidation reaction, which makes this process more efficient. In experiments with the use of additional external heat supply through the reactor wall, complete conversion of hexadecane occurred at GHSV = 120,000 h−1. To convert all by-products (mainly 1-alkenes) and achieve a nearly thermodynamic equilibrium distribution of the main reaction products (H2, CO, CO2), the reaction should be carried out at GHSV = 20,000 h−1. Without external heat supply, hexadecane conversion decreased, while the content of light hydrocarbons in the reaction products increased. An increase in the inlet amount of oxygen helps to compensate the heat losses in the reactor and to increase the efficiency of hexadecane autothermal reforming. The performed experiments allow better understanding of the processes which occur during the steam and autothermal reforming of diesel.

CFD analysis and experimental measurements of the liquid aluminum spray formation for an Al–H2O based hydrogen production system

The paper proposes a combined approach between numerical modeling and experimental measurements for the analysis of a cogeneration system based on the reaction of liquid aluminum and water steam. Scrap aluminum is used for hydrogen production and the primary one is employed as an energy carrier to transport the energy from the alumina reduction system to the site of the suggested plant. The analysis focuses on the liquid aluminum injection phase immediately downstream the nozzle.High frequency thermo-cameras are employed to qualitatively assess the thermal behaviour the liquid aluminum jet. Fast imaging techniques are used to capture the multiphase flow pattern of the liquid metal jet during the injection phase.The experimental results are used to validate a 2D multi-phase CFD approach. The computational fluid dynamics model of the injection phase is created and used to extend the measurements and deepen the understanding of the thermo-fluid dynamics behaviour of the system. In particular, the influence of different nozzles diameters and different injection pressures on the liquid aluminum jet is investigated.A modular approach is adopted for the domain subdivision in order to represent accurately all the geometrical features, while the volume of fluid approach is used to model the multi-phase flow distribution in the real geometry under actual operating conditions. Finally, a good agreement between the measurements and the calculations is found.

Comprehensive study on hydrogen production via propane steam reforming inside a reactor

In the proton exchange membrane fuel cells, the required hydrogen must be produced in some way. The power generators in the path of these fuel cells generally include a steam reactor that, through other fuels, provides the needed energy to produce hydrogen. This study investigates a steam reactor powered by propane fuel consisting of a shell and tube heat exchanger. The shell contains a catalyst that receives the mixture of propane and steam, and the tubes embedded inside the reformer contain hot gases that provide a suitable substrate for the reaction. Velocity and temperature fields inside the reformer, species concentration control, and reaction rate are studied. The conversion of reactants and yield of products are investigated according to the reaction rate. The results show that the hydrogen production yield can vary from 77.5 % to 92.2 %. The reaction rate can be controlled by the velocity and temperatures of the hot gases. However, for the T=900 K, full propane consumption is achieved at the reformer outlet.

Study on the systematic thermal-hydraulic characteristics of helical coil once-through steam generator

Due to the compact structure, the high heat transfer efficiency and the powerful ability to withstand the stress caused by thermal expansion, Helical Coil Once-through Steam Generators (HCOTSGs) have been widely used in recent years, especially as the important equipment of Small-medium Modular Reactors (SMRs). In this study, by adopting the finite difference method, the fixed boundary method, the staggered grid to discretize the control equations and the solution regions, and using the GEAR algorithm to carry out the numerical solution, a systematic Thermal-hydraulic Analysis code for HCOTSG called TACS was developed. Compared with the design values and the calculation values of the ONCESG code of the Marine Reactor X (MRX) steam generator in Japan and the System-integrated Modular Advanced ReacTor (SMART) steam generator in Korea, the correctness of the methods and the models used in the TACS was verified. Based on the TACS, the systematic thermal–hydraulic characteristics of the HCOTSG at full load were studied with a simulation object of the steam generator of the International Reactor Innovative and Secure (IRIS). The results showed that the length of each heat transfer zone is greatly different, so heat flux changes sharply along the tube length. Secondary thermal resistances determine the change of total thermal resistance, decrease at first and suddenly rise when dry-out happens. Frictional pressure drops are the main part of secondary pressure drops, accounting for 90% of the pressure drop in the whole flow process. Besides, the transient processes in HCOTSG with the step and linear disturbances of entrance parameters were simulated by the TACS, which conformed to the analysis of the thermal–hydraulic parameters. The final stable states of these processes are the same under two disturbance modes, but the changing processes caused by linear disturbances are gentler.

Reaction and hydrogen production phenomena of ethanol steam reforming in a catalytic membrane reactor

Ethanol steam reforming (ESR) can be performed efficiently using catalytic membrane reactors (CMR) to enhance H2 production. To investigate the reaction of ESR and the effect of membrane on H2 production, a numerical model was developed to predict the chemical reaction phenomena. The simulations suggested that lower Reynolds numbers were conducive to ethanol conversion and H2 recovery. The H2 yield could be increased by recovering H2 from the ESR product gas using the Pd membrane, and the membrane had a better performance at low Reynolds numbers. Alternatively, total H2 production increased at higher Reynolds numbers, but H2 recovery decreased due to shorter residence time in the reactor. Increasing the S/E ratio enhanced the ESR performance to produce H2 due to the excessive steam supplied to the reaction, but the H2 recovery declined slightly and more energy would be required. Although a high inlet temperature increased the H2 concentration on the retentate side, it also caused the membrane to experience a higher risk of melting. An increase in pressure facilitated both the ethanol conversion and H2 recovery, scribing to more H2 permeating through the membrane. Overall, the obtained results in this study are beneficial to ESR operation for H2 production.

Pretreatment of Oil Palm Empty Fruit Bunch (OPEFB) at Bench-Scale High Temperature-Pressure Steam Reactor for Enhancement of Enzymatic Saccharification

Up scaling of biomass pretreatment from laboratory scale to a bench-scale reactor is one of important steps in the application of the pretreatment for pilot or commercial scale. This study reports the optimization of pretreatment conditions, namely reaction temperature and time, by one factor at a time (OFAT) method for the enhancement of enzymatic saccharification of oil palm empty fruit bunch (OPEFB). OPEFB was pretreated using high temperature-pressure steam reactor with different reaction temperatures (160, 170, 180, 190, 200 °C) and times (10, 20, 30, 40, 50 min). The effectiveness of the pretreatment was determined based on chemical compositions of untreated and pretreated OPEFB and sugar production from enzymatic saccharification of the pretreated OPEFB. Solubilized components in the water that generates the steam were also determined. Pretreatment at 180°C for 20 min provides the highest sugar yields (97.30% of glucose yield per initial cellulose and 88.86% of xylose yield per initial hemicellulose). At the optimum condition 34.9% of lignin and 30.75% of hemicellulose were successfully removed from the OPEFB and resulted in 3.43 delignification selectivity. The relationship between severity factor and by-products generated and the sugars obtained after enzymatic saccharification were discussed. The pretreated OPEFB at the optimum condition was also characterized for its morphological characteristic by scanning electron microscopy (SEM) and crystallinity by X-ray diffractometry (XRD) and then compared it with untreated one. The steam pretreatment caused some fiber disruptions with more defined and opened structures and increased of the crystallinity index (CrI) by 2.9% compared to the untreated OPEFB

Dispersion behavior of various single metals on carbonaceous coal supports and their reactivity in methanol steam reforming

Coal as catalytic support is advantageous in many respects. The pore structure and surface composition are controllable, and the high thermal conductivity can increase the thermal efficiency of the reactor. It is stable in acidic or basic media and it is easy to recycle the catalyst after use. In this study, six different coals were evaluated as catalytic supports based on their ability to disperse of the metal and their catalytic performance. Nickel particles with an average diameter of <11nm are typically dispersed on low-rank coals (LRCs). The nickel catalysts supported on LRCs show 60–70% hydrogen yield for methanol steam reforming (MSR), and one of them maintained the activity during 1000h continuous run, confirming the stability as catalyst support. Most of the well-known catalytic metals such as Pt, Pd, Rh, Ru, Mn, Co, Fe, Zn, Bi, Mo, K, Cu, Ce, Mg, Ga, and La, are dispersed on LRC (Eco coal) support uniformly with an average size of <10nm. Much improved dispersion of the metals on LRC confirms the chance of having improved catalytic activity compared to the conventional carbon supports.

Proposal for effective stacking method of structured catalyst

In this study, a micro–partition (MP), structure with micro–scale fins and holes made of aluminum was stacked as a structured catalyst. The effect of this stacking on the reactivity of a methanol steam reforming reaction was examined. The reactivity was improved by promoting the fluid mixing effect in the reactor by the stacking of the characteristic MP structure. However, the reactivity was reduced when the number of MP catalysts (MPCs) to be stacked was increased and packed densely. Moreover, it was suggested that the reactivity could be improved by investigating the factors of the effective stacking method for a catalytic reaction. We proposed the MPC stacking method in terms of the number, position, distance, and orientation of MPCs, such that the fluid mixing effect was promoted and MPC worked uniformly, based on a numerical simulation. The effect of the proposed stacking method on the reactivity was experimentally demonstrated.

Three-Dimensional Profilometry Utilization on VVER Type Reactors

Abstract The paper is focused on the application of three-dimensional (3D) profilometry on water–water energetic reactor (VVER) type nuclear power plant (NPP) equipment. This method is becoming increasingly used in the power industry and replaces conventional methods such as micrometer measurements. One of the greatest benefits is the accurate recording of the 3D profile of the measured surface and the possibility of its comparison with the production documentation or with the results from previous measurements. Centrum Výkumu Řež, s.r.o. (Research Center Řež) uses 3D laser scanner with a measuring arm. This method was, for example, successfully used for reactor pressure vessel (RPV), steam generator (SG), and bolts. The results are used by the NPP operator for the lifetime management of the primary circuit components.

Azeotropic Separation of HCl-Water by Pressure Swing Distillation: Steady State Simulation and Economic Optimization

Copper-Chlorine (Cu-Cl) thermochemical cycle for hydrogen production involves decomposition of water into hydrogen and oxygen with the use of intermediate copper and chlorine compounds and all other reactants are regenerated and recycled to create a closed loop. Our ongoing investigations on copper-chlorine (Cu-Cl) cycle involve electrochemical and thermal reactions constituting six steps. Hydrolysis of cupric chloride to copper oxide and dry hydrogen chloride (HCl) gas is one of the crucial steps. This involves non-catalytic reaction of cupric chloride and steam between 350 and 400oC which needs excess steam for complete conversion of cupric chloride thereby resulting formation of dilute hydrochloric acid rather than dry HCl gas which needs to be recycled to hydrogen generation. Therefore, azeotrope between the HCl and water needs to be eliminated. This work has proposed design and optimization of pressure swing distillation (PSD) for separation of HCl -water by using heat integration of two columns operating at different pressures and temperatures. The first column operating at low pressure concentrates the feed up to the azeotropic point and second column operating at high pressure eliminates the azeotrope and generates dry HCl gas. The reboiler heat of high pressure column (HPC) is reutilized to heat the low pressure column (LPC) and HPC feed which reduces the total annual cost (TAC). Heat integration saves an energy cost by 11.03% of and total annual cost by 6.83 % as compared to non-heat integrated PSD system. Feed composition has strong impact on energy and ultimately economics.

Numerical and analytical predictions of nuclear steam generator secondary side flow field during blowdown due to a feedwater line break

For the structural integrity evaluation of pressurized water reactor (PWR) steam generator (SG) tubes subjected to transient hydraulic loading, determination of the tube-to-tube gap velocity and static pressure distributions along the tubes is prerequisite. This paper addresses both computational fluid dynamics (CFD) and analytical approaches for predicting the tube-to-tube gap velocity and static pressure distributions during blowdown following a feedwater line break (FWLB) accident at a PWR SG. First of all, a comparative study on CFD calculations of the transient velocity and pressure distributions in the SG secondary sides for two different models having 30 or no tubes is performed. The result shows that the velocities of sub-cooled water flowing between any adjacent two tubes of a tubed SG model during blowdown can be roughly estimated by applying the specified SG secondary side porosity to those of the no-tubed SG model. Secondly, simplified analytical approximate solutions for the steady two-dimensional SG secondary flow velocity and pressure distributions under a given discharge flowrate are derived using a line sink model. The simplified analytical solutions are validated by comparing them to the CFD calculations.

Thermodynamic performance study of the CLHG/SOFC combined cycle system with CO2 recovery

In this paper, the chemical looping hydrogen generation (CLHG) and solid oxide fuel cell (SOFC) are combined to achieve efficient power generation and CO2 separation and capture without energy consumption. The system can realize the utilization of H2 produced by CLHG in SOFC to avoid carbon deposition in it. The anode of the SOFC is completely refluxed into the steam reactor (SR) of CLHG without the need to install an afterburner, which avoids the direct combustion of fuel and greatly reduces the generation of NOx. High temperature air at SOFC cathode outlet and high temperature gas at fuel reactor (FR) outlet enter GT to do work. The transcritical carbon dioxide cycle (TRCC) is used to recover waste heat, making the system compact and efficient. The new CLHG/SOFC combined cycle system proposed in this paper has high performance, which can recover CO2 and prevent NOx generation, and also prevent carbon deposition in SOFC. In addition, the anode of SOFC is completely refluxed to SR to further improve the system performance. This paper discusses the effects of fuel flow, fuel utilization, SOFC operating temperature, system operating pressure, and CO2 turbine inlet pressure on system performance. The calculation results show that the total efficiency of the system can reach more than 80%, the power generation efficiency can reach more than 65%, and the exergy efficiency is more than 60%.

Modeling of thermal impacts in a single direct methane steam reforming solid oxide fuel cell

Solid oxide fuel cells (SOFCs) operate at high temperature which enables the direct methane steam reforming but results in high thermal impact. In this research, the developments of thermal impacts (thermal stresses and strains) of solid electrolyte and porous electrodes are investigated in a single direct methane steam reforming SOFC by numerical simulations. To understand thermal impact mechanisms, the heat sources and sinks due to a set of temperature dependent chemical and electrochemical reactions are modelled for predictions of temperature distributions. It is identified from model simulations that the endothermic reactions of methane steam reforming, which are overall dominant, play the key role in improving the thermal loads to the cell. The temperature reductions are developed from a rate of −42.2 K/cm at the inlet to −1.98 K/cm at the centre of the cell. This leads to a maximum thermal stress of 1867.6 MPa generated in solid electrolyte closing to the inlet and 1770.2 MPa at the centre of the cell, associated with a rate of −19.48 MPa/cm at inlet to −3.28 MPa/cm at the centre. It is identified that high operation voltage results 3.1% decrease in thermal stress when the cell operates from 0.4 V to 0.7 V.

Improved Performance of the Natural Gas Steam Reforming by Coupling with Internal Combustor and Target Heat Transfer in an Integrated Reactor

A compact reactor for natural gas steam reforming, in which hydrogen production was coupled with an internal combustor in alternate chambers, was developed and tested. Based on the target heat tran...

Numerical prediction of transient hydraulic loads acting on PWR steam generator tubes and supports during blowdown following a feedwater line break

This paper presents a numerical prediction of the transient hydraulic loads acting on the tubes and external supports of a pressurized water reactor (PWR) steam generator (SG) during blowdown following a sudden feedwater line break (FWLB). A simplified SG model was used to easily demonstrate the prediction. The blowdown discharge flow was treated as a flashing flow to realistically simulate the transient flow fields inside the SG and the connected broken feedwater pipe. The effects of the SG initial pressure or the broken feedwater pipe length on the intensities or magnitudes of transient hydraulic loads were investigated. Then predictions of the decompression pressure wave-induced impulsive pressure differential loads on SG tubes and the transient blowdown loads on SG external supports were demonstrated and the general aspects of transient responses of such transient hydraulic loads to the FWLB were discussed.

A DFT study of the mechanism of H transfer during steam gasification

The chemical reaction between a graphite model edge and H2O is crucial in steam gasification. This study used density functional theory (DFT) calculations to systematically evaluate the reaction path of steam gasification. The research results indicate that a graphite model edge without active cites is more suitable for use as an initial model for steam gasification. The aromaticity of the graphite model edge and the desorption of CO are linearly related. H atoms from H2O are transferred to the graphite model edge, destroying the aromaticity of the edge carbon structure and facilitating the subsequent desorption process, which may be the cause of the higher reactivity of steam compared to CO2 gasification. From a thermodynamic perspective, hydrogen transfer may be the rate-determining step of the overall reaction. The results of this paper can explain the kinetic differences in previous experiments that used water with varying isotopes of H (H2O vs D2O) and graphite in the gasification reaction (Yates and McKee, 1981; Mims and Pabst, 1987; Fletcher and Thomas, 2007). Our results provide new insights into the H transfer mechanism in steam gasification.

How to choose endothermic process for thermochemical waste-heat recuperation?

The thermochemical waste-heat recuperation (TCR) systems by steam reforming of various hydrocarbon fuels are considered. A method for determining the TCR systems efficiency is proposed. The methodology is based on the determination of the heat recuperation rate and heat transformation coefficient. TCR due to steam reforming of methanol, ethanol, glycerol, propane, and methane was analyzed. To obtain the initial data for energy analysis of TCR systems, the thermodynamic analysis was performed. With the help of Aspen HYSYS was determined the synthesis gas composition and reaction enthalpy for all investigated variants. The investigation was performed for a wide temperature range from 400 to 1200 K, for the steam-to-fuel ratio of 1, and pressures of 1 bar. It was established that TCR due to the steam reforming of ethanol, glycerol, and propane in the temperature range above 800 K, it is possible to achieve complete recuperation of the exhaust after the furnace. As a results of investigation, the practical recommendations were given for choosing endothermic reaction for the thermochemical waste-heat recuperation systems: in the temperature range up to 600 K for TCR it is necessary to choose a methanol steam reforming reaction; in the temperature range from 600 to 1000 K - the reaction of steam reforming of ethanol and glycerol; in the temperature range above 1000 K - the reaction of steam reforming propane and methane.

A novel system of biomass-based hydrogen production by combining steam bio-oil reforming and chemical looping process

Biomass to hydrogen is becoming a promising way to produce clean energy with zero or even negative carbon emission. In this study, a novel system containing a biomass pyrolysis process, a catalytic steam reforming of bio-oil process, a chemical looping unit using biochar as the reducing agent and other auxiliary processes including H2 separation and thermal energy circulation processes for hydrogen production is proposed and simulated based on the previous studies. While, a waste heat recovery system is recommended for energy recuperation to make the entire system become auto-thermal. The effects of steam to carbon ratio in the catalytic steam reforming reaction and temperatures at reducing and steam reactors in the chemical looping unit on the system performance are analyzed in details. Under the optimum condition in the proposed system, about 6.9 kg/h of hydrogen could be produced from 100 kg/h of wood biomass with 58.3 kW of net power. Compared with the biomass direct chemical looping process for H2 production, separating the bio-oil and biochar after the pyrolysis process and combining the steam bio-oil reforming process with the chemical looping unit using biochar for H2 production can increase H2 production efficiency from biomass by more than 50%. It is expected that this proposed system could be implemented in a practical application.

Effect of steam addition during carbonation, calcination or hydration on re-activation of CaO sorbent for CO2 capture

Calcium looping (CaL), based on cyclic carbonation/calcination using lime-based sorbents, is a promising technology for post-combustion CO2 capture. An important obstacle of this technology is the decay of sorbent over multiple cycles. Steam re-activation is a potential approach to improve the sorbent reactivity, however, the effects of both in-situ high-temperature steam (in carbonator or/and calcinator) and ex-situ low-temperature steam (steam hydration in hydrator) are still a matter of debate. Here, a bubbling fluidised bed reactor was used to investigate three steam addition options: steam addition during carbonation stage, or during calcination stage, or intermediate steam hydration after each CaL cycle. A CaO sorbent was tested under varying steam concentrations up to 40 vol.% for 10 CaL cycles (carbonation: 650 °C, calcination: 900 °C). Compared to the dry condition, steam addition during carbonation and intermediate steam hydration were both found effective for CaO re-activation. For the former, the improved sorbent reactivity was mainly attributed to an increased pore volume enhancing the extent of carbonation in kinetic regime; while for the latter, the formation of cracks accelerated the rate of diffusion. Nevertheless, decreasing the hydration temperature was detrimental to sorbent reactivity due to enhanced sintering upon cooling. In case of steam addition during calcination, the sorbent was affected negatively or positively depending on the concentration of steam. At higher steam concentrations (20, 40 vol.%), the sorbent reactivity was significantly decreased due to sintering associated with larger pores and lower surface areas. Overall, steam addition during carbonation was recommended for sorbent re-activation.

Sorbent steam reactivation and methane-concentrated calcination for calcium-looping carbon capture: Compatibilities and limitations

This paper investigates the equilibrium performance of CaO hydration and CaCO3/Ca(OH)2 co-calcination in calcium-looping processes. A novel lime hydration configuration is proposed, introducing saturated steam as the reactivating reagent and direct-heat-removal medium. The proposed hydrator generates a substantial amount of superheated steam, used elsewhere as required. The slaked lime and limestone are calcined simultaneously in a methane-concentrated oxy-fuel calciner. The equilibrium performance of the co-calciner is studied at different reactor temperatures, operating pressures, solid/gas feed ratios and feed compositions. A correlation is proposed which estimates the required gaseous feed composition for autothermal, coke-free and complete sorbent regeneration using this novel technology.