Mixture Of Steam Research Articles

Production of syngas from H2O/CO2 by high-pressure coelectrolysis in tubular solid oxide cells

The conversion of CO2 and steam into syngas in a pressurized solid oxide coelectrolysis (SOC) cell is considered one of the most promising pathways towards the production of sustainable fuels. In this study, a high pressure tubular SOC system was designed and developed that can efficiently convert a mixture of steam and CO2 into valuable syngas fuel. Tubular SOC cells based on a Ni-yttria stabilized zirconia (Ni-YSZ) fuel electrode, scandia stabilized zirconia (ScSZ) electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)-Ce0.8Gd0.2O1.9−δ (GDC) composite air electrode were fabricated and tested at various high pressure conditions to determine the electrochemical and syngas production characteristics. The pressurized tubular SOC cell was first operated at the ambient pressure for various inlet gas conditions and the electrochemical performance of the tubular SOC was studied by current-voltage curves combined with electrochemical impedance spectroscopy at different H2O and CO2 mole% in the inlet gas. The pressurized SOC cell was then operated between 1 and 8 bar pressure at 800 °C in both fuel cell and coelectrolysis modes. In the fuel cell mode, the SOC showed a 44.2% increase in the maximum power density to with a pressure increase of 1–8 bar. The increase in the performance of the cell in the fuel cell mode was attributed to the higher open circuit voltage (OCV) and reduced polarization resistance of the electrodes at higher pressures. In the coelectrolysis mode, the pressure dependency of the electrochemical characteristics on the tubular SOC cell was studied and the relation between different parameters of the system and the pressure conditions was derived. It was found that the higher open circuit voltage (OCV) and the reduced polarization resistance resulted in a significant improvement in the performance of the pressurized tubular SOC cell for the production of syngas. A post-test material characterization by electron microscopy did not show any significant degradation in the tubular SOC cell microstructure during the high pressure operation at 8 bar.

Gasification of Charcoal in Air, Oxygen, and Steam Mixtures over a γ-Al2O3 Fluidized Bed

Charcoal was gasified using air and oxygen as well as with mixtures of oxygen and steam, aiming to produce a gas stream with high hydrogen content. The effects of the equivalence ratio (ER) and steam-to-carbon ratio (S/C) on carbon conversion, producer gas yield, gas heating value, and composition as well as on the apparent energy efficiency (AEE) of the process were studied. The gasification experiments were performed in a laboratory-scale fluidized bed rig working at 1173 K and atmospheric pressure and using γ-Al2O3 as bed material. Results showed that, on a N2-free basis, the composition of the producer gas obtained by gasification with air and pure oxygen were comparable when using the same ER. Furthermore, carbon fraction converted into gas improved when ER was increased from 0.25 up to 0.35, as well as when the S/C was increased to 0.625. The highest producer gas yield was obtained using ER = 0.35 and S/C = 0.625, while the highest hydrogen concentration in the produced gas was achieved using ER = 0...

Effect of a mixture of carbon dioxide and steam on ejector performance: An experimental parametric investigation

The results are presented for an experimental investigation characterizing the performance of a steam ejector when the secondary fluid is a mixture of steam and a non-condensable gas. In the context of post-combustion carbon capture, carbon dioxide was chosen as the non-condensable for this work. In order to study the pure steam ejector over a wide operating range, performance curves were prepared for primary pressures of 350, 450 and 550 kPa, with secondary pressures of 50, 70 and 90 kPa. Effects of the primary nozzle position, the primary pressure, the secondary pressure, and the nozzle diameter were evaluated. For a reference primary pressure of 450 kPa and secondary pressure of 70 kPa, performance curves were prepared for four levels of entrained CO2 in the secondary fluid mixture, up to 45% by mass, and for four nozzle throat diameters ranging from 4.03 to 5.09 mm. It was observed for the first time that in contrast with the pure steam ejector performance curves, increasing amounts of entrained CO2 improved the critical entrainment ratio, but the critical pressure remained unchanged. This behaviour was in sharp contrast with that of a pure steam ejector. A linear relationship was observed between the increase in the entrainment ratio of a steam ejector and the mass fraction of CO2 contained in the ejector secondary fluid.

Gasification under CO2–Steam Mixture: Kinetic Model Study Based on Shared Active Sites

In this work, char gasification of two coals (i.e., Shenfu bituminous coal and Zunyi anthracite) and a petroleum coke under a steam and CO2 mixture (steam/CO2 partial pressures, 0.025–0.075 MPa; total pressures, 0.100 MPa) and CO2/steam chemisorption of char samples were conducted in a Thermogravimetric Analyzer (TGA). Two conventional kinetic models exhibited difficulties in exactly fitting the experimental data of char–steam–CO2 gasification. Hence, a modified model based on Langmuir–Hinshelwood model and assuming that char–CO2 and char–steam reactions partially shared active sites was proposed and had indicated high accuracy for estimating the interactions in char–steam–CO2 reaction. Moreover, it was found that two new model parameters (respectively characterized as the amount ratio of shared active sites to total active sites in char–CO2 and char–steam reactions) in the modified model hardly varied with gasification conditions, and the results of chemisorption indicate that these two new model parameters mainly depended on the carbon active sites in char samples.

Pressurized gasification of lignite in a pilot scale bubbling fluidized bed reactor with air, oxygen, steam and CO2 agents

In this study, 80 h continuously operated gasification experiment was carried out with pilot scale pressurized bubbling fluidized bed gasifier which was operated with the coal feed capacity of 500–520 kWth (80–83 kg/h coal feed rate). The mixture of air, steam, oxygen and CO2 was used as gasification agent with different ratios. The operating pressure of gasifier in this experiment was between 2.4 and 2.7 barg. The effects of ER, steam/carbon ratios and CO2/carbon ratios on syngas composition, carbon conversion ratios and cold gas efficiencies were investigated. According to the results, using CO2 or H2O as gasification agent, may have both advantages and disadvantages for the operation. If CO2 was increased in gasification agent, shift reaction was effected negatively and H2 products were decreased. If steam was increased, cold gas efficiency was slightly decreased.

Energy and exergy analysis of alternating injection of oxygen and steam in the low emission underground gasification of deep thin coal

Recent studies have shown that by coupling the underground coal gasification (UCG) with the carbon capture and storage (CCS), the coal energy can be economically extracted with a low carbon footprint. To investigate the effect of UCG and CCS process parameters on the feasibility of the UCG-CCS process, we utilize a validated mathematical model, previously published by the same authors, that can predict the composition of the UCG product, temperature profile, and coal conversion rate for alternating injection of air and steam for unmineable deep thin coal layers. We use the results of the model to conduct an energy and exergy analysis of the UCG process. We study the effect of various process parameters on the efficiency of the UCG process, the zero-emission recovery factor of coal, and the total CO2 emission of the process. Moreover, we compare the alternating injection of air/steam with the injection of an air and steam mixture.Exergy analysis shows that the alternating injection of air/steam describes a practical process for UCG at low pressure. However, injecting a mixture of steam and oxygen results in a practical recovery factor of coal higher than the alternating injection process. Additionally, we show that the zero-emission conversion of unmineable deep thin coal resources in a coupled UCG-CCS process, that is not practical with the current state of technology, can be realized by increasing the energy efficiency of the carbon dioxide capture process.

Investigation of electrode erosion products of alternating current plasma torch operating on mixture of steam, carbon dioxide, methane and carbon tetrachloride

The most important unit of the plasma torch mainly subjected to the thermal load of the electric arc is electrode. Tungsten, hafnium, yttrium, aluminum, copper, iron and their alloys are used as electrode materials depending on the plasma-forming gas. Copper-based alloys can be rationally used for gases containing oxygen. The experiments were performed on the three-phase alternating current vortex plasma torch with power of 120 kW working on a mixture of steam, carbon dioxide, methane and carbon tetrachloride for the following flow rates 2.9 g/s, 2.9 g/s, 1.21 g/s and 2.44 g/s respectively. The material of erosion of copper rod electrodes was sampled from water-cooled walls of electric arc plasma torch channels made of stainless steel. The sample was divided into magnetized and non-magnetic parts. According to the energy-dispersive elemental analysis the products of electrode erosion contain oxides and chlorides of copper and iron, as well as metallic copper and iron.

High voltage AC plasma torch operating on vapours of organic substances

The article deals with a three-phase high-voltage AC plasma torch with separate supply of gases and vapours during its operation on a mixture of steam, carbon dioxide, methane and organic vapours. Increase in flow rates of organic vapours and methane leads to increase in the arc voltage drop from 875 to 1150 V and electric power from 80 to 102 kW.

Influence of Nonaxisymmetric Flow Injection into the Diffuser on the Turbine LPC Exhaust Nozzle

The data of computational aerodynamic investigations carried out for the diffuser used by the discharge nozzles of modern steam turbines have been given. The calculations were done using the axisymmetric statement for the three options of flow turn to the collection chamber of exhaust nozzles. During the computation, we varied the parameters of special flow injection at the external diffuser by-pass and took into account the above-shroud leakage. The following characteristics were analyzed, in particular the flow injection jet pulse coefficient and the coefficients of net, internal and outlet velocity losses of the diffuser. It was shown that the outlet velocity loss produced the basic influence on the level of net losses of the diffuser due to the flow pattern and the availability of separated circulation zones, and the diffuser flow and the flow of nonaxisymmetric collection chamber of the exhaust nozzle are subjected to the substantial influence of flow injection parameters. Optimal parameters of the injection jet were determined taking into consideration the flow discharge from the exhaust nozzle into the capacitor of a cellar type. The recommendations were given on how to improve the aerodynamic characteristics of the diffuser due to a change in the structure in the region of special injection of the flow. A circumferential change in the size of the output slit of circular channel at the invariable total area of steam output allows for a decrease of mixing losses in the collection chamber and circular nonuniformity of the pressure behind the last cascade for the diffuser cowling flow without separation that results in a decrease of the net losses of exhaust nozzle. Proposed recommendations can be used to provide special injection of the flow of wet steam mixture removed from the circumferential zone of the last stage, increasing thus the efficiency of the exhaust zone of steam turbine with the cellar arrangement of the capacitor and retaining the erosion reliability of the last stage of low pressure cylinder.

Steam and steam-oxygen reforming of methane on NiAl2O3–MxOy (M: La, Ce) based monoliths: effects of catalyst and reaction mixture composition

The effect of rare earth oxides as modifying additives within Ni–MxOy–Al2O3 (M: La, Ce) based catalysts, supported on cordierite monoliths, and the influence of the H2O/CH4 ratio as well as O2 content in the gas reaction mixture on the catalyst activity and selectivity in the steam and steam-oxygen reforming of methane are studied including by means of infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and quasi-equilibrium thermal desorption of ammonia as a probe molecule. The introduction of CeO2 and La2O3 into the catalyst composition as well as oxygen to the reaction mixture of methane steam reforming is shown to enable reducing the water vapor content (up to H2O/CH4 ratios close to stoichiometric) required for stable catalyst operation while maintaining high CH4 conversions and hydrogen yields. The carbon dioxide amount as a by-product in the syngas produced considerably decreases in the presence of Ni–CeO2–Al2O3/cordierite catalysts, which may be explained by slowing the water–gas shift reaction. The introduction of ceria into the catalyst composition leads to a slight decrease in the total number of Lewis acid sites (LAS), whereas the addition of lanthanum oxide causes their increase, which we attribute to formation of two LAS types on the surface of Ni–Al2O3–La2O3/cordierite: lanthanum cations and aluminum ones.

Heat transfer during pseudo-dropwise condensation of water-ethanol vapor mixture on horizontal finned tubes

In the present work experimental data on heat transfer are obtained for the condensation of almost immobile pure steam and water-ethanol vapor mixture on three copper horizontal finned tubes with a cooled length of 100 mm. The fins are rectangular in shape, their height and thickness are 1 mm, and the spacing between fins 1.3, 2.0 and 3.0 mm. The experiments were carried out at pressures of 0.12…0.15 MPa, the vapor-to-surface temperature difference varied from 5 to 35 K. The mass concentration of ethanol in the vapor phase varied from 8.7 to 14.5%. The experimental data are presented in the form of the dependences of heat transfer coefficient on the vapor-to-wall temperature difference. The heat transfer coefficients for the condensation of pure steam are in good agreement with the calculations by the method of Srinivasan et al. According to experimental data for the condensation of the vapor mixture, diffusion thermal resistance and thermal resistance of the liquid phase at various ethanol concentrations and the spacing between fins were calculated.

Simulation and Dynamic Optimization of an Industrial Naphtha Thermal Cracking Furnace Based on Time Variant Feeding Policy

Abstract The main goal of this research is modeling and simulation of ethylene production through naphtha thermal cracking in a coil furnace reactor. The naphtha cracking and decoking processes are modeled based on the mass, energy and momentum balance equations considering a detail kinetic model at pseudo-dynamic condition. To develop a reliable and applicable model, a detail thermal model is considered to predict tube skin temperature. To prove accuracy of developed model and considered assumptions, the simulation results are compared with the plant data. In addition, the results of coke burning in the decoking cycle by mixture of air and steam are presented. It is appeared that ethylene production decreases during the process run time gradually. The simulation results proved that increasing feed temperature, feed pressure and combustion chamber temperature during the process run time is a practical solution to maintain production capacity at an acceptable level. Finally, the optimal operating condition of thermal cracking process is calculated during the process run time based on the time variant feeding policy to achieve maximum ethylene production capacity. It is appeared that applying optimal condition on the system could increase ethylene production capacity from 15.31 ton.h‒1 to 15.49 ton.h‒1.

Moisture content during and after high- and normal-temperature drying processes of wood

ABSTRACTThe aim of the article is to present the results of moisture content of wood during and after the high-temperature steam and air–steam mixture drying processes and after an open air-drying process. The knowledge of moisture content changes of wood in the process of its drying is one of the important parameters to economy drying process and to keep the quality of dried wood. Wood samples, namely, spruce (Picea abies K.) and beech (Fagus silvatica L.) from the northern part of Poland, were subject to steam, air–steam mixture and, air-drying, respectively, with a temperatures about 105, 80, and 25°C. The samples of thickness 70 mm and length about 1,050 of spruce, and about 1,500 mm of beech were used. They were machined by the modern narrow kerf frame sawing machine. Temperature of the cross section of dried wood was measured by thermocouples, wood moisture content was determined during process using moisture sensors. Measurements of moisture content for steam-dried and air-dried samples, as reference, allowed to reveal the effect of drying process on moisture content of wood. It has been recognized that steam wood drying causes almost constant amount of moisture in treated material in comparison to air-drying one.

Local phenomena analysis of steam condensation in the presence of air

In severe accident scenarios (e.g. LOCA), the steam condensation inside the containment area is of vital importance. This is because the containment pressure peak and long-term residual heat removal are closely related to the steam condensation efficiency. Note that the gas inside the containment area is a mixture of steam and air/hydrogen. Steam condensation consisting of non-condensable gases has its own characteristics. Compared to pure steam condensation, it has a much lower heat transfer coefficient and the local phenomena are more complex. Considering that steam condensation is closely related to other phenomena in containment thermal-hydraulic analysis, further studies should be carried out. In the present work, the STAR-CCM+ software is used with a diffusion boundary layer condensation model. Various cases from the COPAIN and Su experiments are simulated and discussed. In the simulation of the COPAIN experiment, the effect of the mesh density (main-stream mesh size and the Y+ value) on the boundary heat flux is compared with the experimental data. Additionally, the local velocity, temperature, and air mass fraction are compared and discussed. In the simulations of the Su experiment, calculated results for the main-stream temperature, near-wall region temperature, and heat transfer coefficient are compared with experimental results and discussed. The COPAIN numerical results indicate that (i) the boundary heat flux decreases linearly with any increase in the air layer thickness of up to 5 mm, and the effect of the air layer weakens with further increases in thickness; (ii) the convective heat flux is only responsible for up to 9.1% of the total boundary heat flux; and (iii) the automatic wall treatment gives a reasonable prediction of steam condensation. The simulations of the Su experiment show that (i) there is no obvious temperature stratification in the main-stream along the vertical direction and (ii) the thickness of the air layer close to the condensation tube is around 6 mm. These results provide basic guidance for the future design of condensation heat transfer enhancement structures.

Chemical Looping Combustion of Hematite Ore with Methane and Steam in a Fluidized Bed Reactor

Chemical looping combustion is considered an indirect method of oxidizing a carbonaceous fuel, utilizing a metal oxide oxygen carrier to provide oxygen to the fuel. The advantage is the significantly reduced energy penalty for separating out the CO2 for reuse or sequestration in a carbon-constrained world. One of the major issues with chemical looping combustion is the cost of the oxygen carrier. Hematite ore is a proposed oxygen carrier due to its high strength and resistance to mechanical attrition, but its reactivity is rather poor compared to tailored oxygen carriers. This problem is further exacerbated by methane cracking, the subsequent deposition of carbon and the inability to transfer oxygen at a sufficient rate from the core of the particle to the surface for fuel conversion to CO2. Oxygen needs to be readily available at the surface to prevent methane cracking. The purpose of this work was to demonstrate the use of steam to overcome this issue and improve the conversion of the natural gas to CO2, as well as to provide data for computational fluid dynamics (CFD) validation. The steam will gasify the deposited carbon to promote the methane conversion. This work studies the performance of hematite ore with methane and steam mixtures in a 5 cm fluidized bed up to approximately 140 kPa. Results show an increased conversion of methane in the presence of steam (from 20–45% without steam to 60–95%) up to a certain point, where performance decreases. Adding steam allows the methane conversion to carbon dioxide to be similar to the overall methane conversion; it also helped to prevent carbon accumulation from occurring on the particle. In general, the addition of steam to the feed gas increased the methane conversion. Furthermore, the addition of steam caused the steam methane reforming reaction to form more hydrogen and carbon monoxide at higher steam and methane concentrations, which was not completely converted at higher concentrations and at these residence times.

Quick Screening of Pareto-Optimal Operating Conditions for Expanding Solvent–Steam Assisted Gravity Drainage Using Hybrid Multi-Objective Optimization Approach

Solvent–steam mixture is a key factor in controlling the economic efficiency of the solvent-aided thermal injection process for producing bitumen in a highly viscous oil sands reservoir. This paper depicts a strategy to quickly provide trade-off operating conditions of the Expanding Solvent–Steam Assisted Gravity Drainage (ES-SAGD) process based on Pareto-optimality. Response surface models are employed to evaluate multiple ES-SAGD scenarios at low computational costs. The surrogate models play a role of objective-estimators in the multi-objective optimization that provides qualified ES-SAGD scenarios regarding bitumen recovery, steam–energy efficiency, and solvent-energy efficiency. The developed hybrid approach detects positive or negative correlations among the performance indicators of the ES-SAGD process. The derived Pareto-optimal operating conditions give flexibility in field development planning and thereby help decision makers determine the operating parameters of the ES-SAGD process based on their preferences.

Development of Cell-Protecting Methods for Carbon-Removal from Porous Ni-YSZ Anodes and Regeneration of the Cell Performance

Carbon deposition is one of the major obstacles that reduce the lifetime of solid oxide fuel cells (SOFCs) and can thus significantly shorten the lifetime of auxiliary power units (APUs). Carbon deposits block the gas pores, cover the catalytic active sites, and induce the microstructure and performance degradation. In order to extend the lifetime of the cells used, effective and cell-protecting strategies for carbon gasification and restoring of the cell performance must be developed. This study scrutinizes various approaches for this purpose. They are based on hydrogen, steam, and oxygen enriched gas mixtures. Gasification strategies, which enable complete carbon removal and performance restoring in a cell-protecting manner and their practicability for industrial usage are examined and summarized in this study.

Steam turbine injection generator performance estimation considering turbine blade cooling

This paper addresses a thermodynamic analysis of steam injection in the combustion chamber of a large size gas turbine considering blades cooling and NOx emissions. Since heat transfer from the mixture of gas and steam is higher than the one from gas alone, the blades would be inefficiently cooled and their material might be affected. Thus, to preserve their temperature below the required limit, two solutions are proposed; the first keeps combustor discharge temperature at its initial value and increases the quantity of coolant and the second keeps the initial quantity of coolant and decreases the combustor discharge temperature. The results show that both solutions lead to the enhancement of performances but the first solution gives better results and allows producing a maximal steam/gas fraction of 14% while for the second solution this fraction is 11%. The power is increased from 270 MW to 388 MW and 302 MW respectively for the first and the second solution and the efficiency from 38% to 42.7% and 40.2%. The results have also shown that the amount of NOx produced is significantly decreased and may reach a value of 10 ppm for the first solution and 14 ppm for the second one.

Experimental study on biomass (eucalyptus spp.) gasification in a two-stage downdraft reactor by using mixtures of air, saturated steam and oxygen as gasifying agents

In this work, biomass (eucalyptus spp.) gasification has been investigated in a two-stage downdraft reactor by using different gasifying agents such as: air, air+saturated steam, and O2+saturated steam. The utilization of low quality saturated steam for gasification in different mixtures with air and O2 is the main novelty of this paper. Thus, the influence of different gasifying agents was assessed on the concentrations of CO, H2 and CH4 and hence, on the lower heating value (LHV), the syngas power and the cold gasification efficiency. Since the type and flow of gasifying agent control the biomass consumption in downdraft gasifiers, the equivalence ratio (ER) and the steam-to-biomass ratio (SBR) were calculated by means of a mass balance. The results showed that low quality steam can increase remarkably the H2 concentration and the LHV of syngas despite its low temperature. Particularly, when O2+saturated steam is fed to the gasifier, the H2 concentration varied between 27.4 and 35.9 vol.%, while the LHV was between 7.13 and 8.35MJ/Nm3, i.e. almost twice the produced when only air or air+saturated steam is used. The optimum ER seems to be below 0.412, while the SBR is found between 0.495 and 1.032. Under this conditions, the cold gasification efficiency was between 70 and 75%. Moreover, the O2 seems to mitigate in a better way the negative effect of the low temperature of the saturated steam given the lower tar concentration in syngas (58.74–64.18mg/Nm3) respect to those found with air+saturated steam (91.41–91.95mg/Nm3). This paper concludes that saturated steam can be used blended either with air or O2 (being better with O2) for biomass gasification in two-stage downdraft reactors and therefore, the requirements of superheated steam are not so important as in other gasification processes.

A study on the reaction of Zircaloy-4 tube with hydrogen/steam mixture

In order to fundamentally understand the secondary hydriding mechanism of zirconium alloy cladding, the reaction of commercial Zircaloy-4 tubes with hydrogen and steam mixture was studied using a thermo-gravimetric analyser with two variables, H2/H2O ratio and temperature. Phenomenological analysis revealed that in the steam starvation condition, i.e., when the H2/H2O ratio is greater than 104, hydriding is the dominant reaction and the weight gain increases linearly after a short incubation time. On the other hand, when the gas ratio is 5 × 102 or 103, both hydriding and oxidation reactions take place simultaneously, leading to three distinct regimes: primary hydriding, enhanced oxidation, and massive hydriding. Microstructural changes of oxide demonstrate that when the weight gain exceeds a certain critical value, massive hydriding takes place due to the significant localized crack development within the oxide, which possibly simulates the secondary hydriding failure in a defective fuel operation. This study reveals that the steam starvation condition above the critical H2/H2O ratio is only a necessary condition for the secondary hydriding failure and, as a sufficient condition, oxide needs to grow sufficiently to reach the critical thickness that produces substantial crack development. In other words, in a real defective fuel operation incident, the secondary failure is initiated only when both steam starvation and oxide degradation conditions are simultaneously met. Therefore, it is concluded that the indispensable time for the critical oxide growth primarily determines the triggering time of massive hydriding failure.