Air Steam Research Articles

Effects of the secondary air inlet position and gasifying agents on grape branch gasification in an improved downdraft gasifier

Gasification experiments on grape branches were carried out in a self-improved downdraft gasifier at 800 °C, under atmospheric pressure, using air, steam, and air–steam as gasifying agents.

Artificial neural network model for single-phase real gas ejectors

Ejector is a passive gas dynamic device used ubiquitously in engineering applications. Applications of ejectors have transited from traditional steam extraction to heat-driven gas compression in supercritical and trans-critical CO 2 power and refrigeration cycles. The non-ideal gas behavior in such applications adds to the existing lack of fundamental understanding of the complex gas dynamics within the ejector. A number of simplified 1-D physics-based low-fidelity models have been proposed in the literature. These models offer reasonably good predictions for most ideal gases such as air and superheated steam. However, significant deviations as high as 20% between the experimental measurements and the model are observed for real gases. On the other hand, CFD simulations for an ejector are not only computationally expensive but also require careful selection and tweaking of the turbulence model. The paper presents a data-driven artificial neural network (ANN) model to predict the critical parameters of a supersonic ejector. The model is trained using a comprehensive experimental database comprising of various working fluids and operating conditions. The framework uses a topology of seven dimensionless input parameters capturing geometry, operating conditions, and working fluid characteristics to predict two output parameters; (a) entrainment ratio and (b) operational regime of the ejector (critical or mixed mode of operation). The model relies on a network of 84 neurons in the hidden layer and uses a split ratio of 0.15 for training the dataset. The trained ANN model is able to predict the entrainment ratio within 10% accuracy, with the ability to classify the operational mode with an accuracy of 91%. • An ANN model is developed to predict the ejector performance and operating regime. • The working fluid is modeled with its molecular weight and isentropic exponent. • ANN predicts ER with a 10% deviation with experimental ER for all working fluids. • The ANN model classifies the operating regime of ejectors with 91% accuracy. • It will be effective in predicting the global performance of ejector-based systems.

Effects of organic carbon content on in situ remediation time using steam–air injection

Abstract Groundwater contamination by chlorinated hydrocarbons (CHC) is a common phenomenon that poses health risks to both humans and animals. These halogenated hydrocarbons infiltrate into the soil matrices and form pools at the bottoms of the aquifers thus contaminating the groundwater sources. Thermally enhanced soil vapour extraction (TSVE) using steam–air injection has gained popularity as an alternative technique to remediate the saturated and vadose source zones contaminated with CHC. This technique has been successfully applied in the remediation of contaminated sites (brownfields, industrial sites) and groundwater. However, the presence of organic carbon (OC) contents within the soil matrices has not been intensively studied. This paper, therefore, intends to contribute toward increasing the understanding of the effects of OC on the remediation time using TSVE. A 2-D flume experimental model was conducted in VEGAS laboratory using coarse sand, fine sand and silty soil with 0, 1 and 2% addition of the activated carbon as OC to investigate the desorption time of PCE and TCE as CHC during TSVE extraction using steam–air injection. 100 kg of soil mixed with the activated carbon was treated with 50 g TCE and 50 g PCE and then remediated using TSVE. The remediation times were recorded and recovered CHC was documented. It was discovered that the presence of OC enhanced the adsorption of the CHC onto the soil matrices thereby increasing the time required for the complete remediation of the contaminant from the soil. An increase of OC by 1% resulted in desorption time by a factor of 4–7.

Neutralizing Aminesin Boiler Steam and Humidified Indoor Air

Objective: The health and comfort of the indoor population have been impacted by the humidity. While people are increasingly spending more time indoors, the presence of pollutants and lack of proper humidification in indoor air have significant risk factors that may lead to multiple health problems. Methods: By applying the right air purification and/or humidification system, the adverse effects of poor indoor air quality can be minimized. Direct steam addition is a common technique to humidify the indoor air of a building. Carbon dioxide or other acidic process contaminants may dissolve in steam or steam condensate that will consequently decrease the pH and make it corrosive for the steam distribution system. To avoid that, neutralizing amines are added to steam that keeps the pH neutral or slightly alkaline(pH 7.5-9.0). However, neutralizing amines have some toxic effects. OSHA, FDA, and NIOSH prescribe maximum concentration limits for them in indoor air. The Central Utility Plant (CUP) of National Institutes of Health (NIH) uses a 50:50 blend of cyclohexylamine and diethylaminoethanol as neutralizing agents for the steam. Results: The CUP at NIH presents the results of monitoring the concentration level of amines through mass balance, online monitoring at specified location of the steam distribution system and field measurement in humidified indoor air at buildings on campus. Conclusion Through theoretical calculation backed up by field measurement, the amine concentration of indoor air is determined to be well below the FDA regulated limits.

Numerical analysis of wave effect on steam–air condensation on a vertical surface

Steam condensation with non-condensable gas is an unavoidable problem for passive containment cooling system (PCCS) in many third generation reactors. The effects of the air mass fraction in steam–air flow and condensing wall subcooling on the steam condensation at the different gas velocities under the different types and amplitudes of solitary or sinusoidal wave walls are numerical analyzed, in the cases that the wavy film is regarded as wavy solid wall. The 41% rise of average condensation flux (ACF) of steam–air flow can be obtained in the channel with large-amplitude solitary wave wall than that of flat wall while the less variation of ACF happens in the mode with sinusoidal wave wall. The sudden expansion and contraction of flow section along the wavy wall as well as vortex generation in the channel influence local condensation flux greatly. All these results are helpful for thermal analysis of condensation in the PCCS.

Degradation of condensation heat transfer on a vertical cylinder by a light noncondensable gas mixed with air-steam mixtures

In this study, the experimental investigation result of steam condensation on a vertical tube in the presence of air and a light noncondensable gas is presented. This study aims at elucidating the effect of hydrogen that may be generated during the progression of a severe accident on the condensation heat transfer. Using helium as a simulant of hydrogen, a series of condensation tests were performed. A novel helium measurement system was introduced to analyze the composition of mixture gas. The condensation heat transfer coefficient was obtained under natural convection conditions on a 1 m long condenser tube having an outer diameter of 21.5 mm. A comprehensive experimental database was obtained to understand the parametric effect of the total mass fraction of noncondensable gases, molar concentration of helium in noncondensable gases, and wall subcooling degree. An empirical correlation for the degradation factor to account for the effect of a light noncondensable gas was proposed for application to the condensation model for the steam–air mixture based on the experimental data. The strategy to adopt the degradation factor was assessed against three steam–air–helium condensation tests.

Uranium nitride advanced fuel: an evaluation of the oxidation resistance of coated and doped grains

The oxidation behaviour of the composite UN-AlN, UN-Cr 2 N/CrN and UN-AlN-Cr 2 N/CrN pellets in air and anoxic steam under thermal transient conditions was investigated and compared with the pure UN pellet. The composite pellets were manufactured to contain the engineered microstructure of coated (the addition of matrix-insoluble AlN) and doped (the addition of matrix-soluble Cr 2 N/CrN) grains. The composite powders were produced by powder metallurgy and sintered into pellets using the SPS method. Sintered composite pellets were subjected to a thermal transient up to 1273 K in an STA-EGA (TGA-DSC-Gas-MS) system, followed by crystallographic characterization by XRD and morphological and elemental analysis by FEG-SEM. Improved oxidation behaviour in air compared to pure UN was demonstrated by the UN-Cr 2 N/CrN composite pellet. The formation of the ternary oxide UCrO 4 from the ternary (U 2 Cr)N 3 phase (doped grain) was observed, consistent with the delayed oxidation onset and slower reaction rates. In an anoxic steam environment UN-Cr 2 N/CrN exhibited a higher onset oxidation temperature relative to UN, although the reaction progressed faster than for UN sample. Composite UN-AlN pellet oxidised at a lower temperature in both air and steam, compared to pure UN, due to internal stresses in the fuel matrix. A mechanism for degradation of the composite materials is proposed and the influence of the individual phases on the oxidation behaviour of the composites is discussed.

CFD simulation of a cold flow model of inter-connected three fluidized reactors applied to chemical looping hydrogen production

The chemical looping hydrogen production (CLHP) process is a new approach for hydrogen (H2) fuel production. The proposed process consists of three reactors which are air reactor (AR), fuel reactor (FR) and steam reactor (SR). In this study, the gas solid flow behaviour in a cold model of the proposed CLHP process was simulated using computational fluid dynamics (CFD) with kinetic theory of granular flow. The effect of drag coefficient models on the pressure profile of each reactor was investigated and the results from the modified Syamlal–O’Brien drag model agreed well with the experimental data. The model was further used to investigate effects of the operating parameters on the hydrodynamics profiles of each reactor. The solid flux increased with the increasing of inlet velocity of AR and FR but decreased with the increasing of the inlet velocity of SR. At the same time, the solid flux increased with the increasing of the solid inventory.

Evaluation of single particle drying characteristics using drying models and curve fitting

ABSTRACT In this study, Turkish lignite dried with hot air and superheated steam was experimentally investigated. Drying experiments were carried out at 120°C drying temperature and atmospheric pressure. Mass, center and surface temperature changes of lignite having a diameter of 30 mm were continuously measured. Hot air and superheated steam drying methods were compared, and it was found that, because of condensation in the initial stage of superheated steam, the moisture content of the lignite sample temporarily increased. On the contrary, the moisture content of the lignite sample dramatically reduced on drying with hot air. Six different thin-layer models describing the drying kinetics of lignite were fitted to the experimental data, with the Pusat model giving the best predictions with superheated steam drying and the Midilli model giving the best predictions with hot air drying of a single particle.

Development of a comprehensive simulation model for H2-rich syngas production by air–steam gasification of biomass

Development of a comprehensive simulation model for H2-rich syngas production by air–steam gasification of biomass

Combustion of liquid hydrocarbon fuel in an evaporative burner with forced supply of superheated steam and air to the reaction zone

Combustion of n-heptane in a laboratory pattern of an original evaporative-type burner with the supply of air or superheated steam to the reaction zone was studied experimentally and numerically. Turbulence was simulated on the basis of the k-ω SST RANS model. Combustion was simulated using the Eddy Dissipation Concept (EDC) model with a detailed kinetic mechanism. The developed mathematical model was verified; a good agreement between calculation results and obtained experimental data is shown. For the first time, a comparative analysis of the effect of forced supply of steam and air on the local and integral characteristics of combustion is carried out. Radical difference in the effect of steam supply in comparison with air supply on reducing emissions of nitrogen oxides and soot from the burner is shown. The burner operating regimes have been studied in detail in a wide range of flow rates of supplied steam and fuel. It has been found that with an increase in steam flow rate, underburning, soot formation and production of nitrogen oxides are significantly reduced.

An approach for waste heat recovery of internal combustion engine: In-cylinder steam-air expansion

• An approach based on CSAE cycle was proposed for IC engine WHR. • Steam temperature has a greater effect on WHR potential compared with steam amount. • The NA mode is recommended for the steam expansion cylinder. • Engine brake efficiency can be increased by 7.0 percent points at most by CSAE cycle. • The proposed WHR approach has little effect on the engine BMEP. To recover waste heat and increase the fuel efficiency of internal combustion engines, an approach based on in-cylinder steam–air expansion is proposed, which has simpler design but higher practicality than previous methods. In the multi-cylinder engine, a cylinder is specially used for steam expansion (called steam expansion cylinder) without fuel entry and firing. The high-temperature steam generated by engine waste heat is injected into the steam expansion cylinder, in which it expands together with air and outputs effective work. The energy-saving potential and influencing factors of this approach were investigated on a six-cylinder natural gas engine through the simulation and some interesting findings were obtained. At the same engine operating conditions, the steam temperature has greater effects on waste heat recovery potential than steam amount. The cycle work of the steam expansion cylinder is improved largely by introducing air. However, if further increase intake pressure (e.g., greater than 0.4 bar), the improvement of cycle work in the steam expansion cylinder is not obvious, thus the naturally aspirated mode is recommended. When this approach is applied, the maximum brake mean effective pressure is approximately equal to the level of the original engine at 1600 rpm and 2000 rpm but slightly lower at 1200 rpm. Nevertheless, the brake efficiency of the engine has an obvious rise at all three speeds, which could increase by up to 5.7, 7.0 and 6.8 percentage points at 1200 rpm, 1600 rpm and 2000 rpm, respectively. Therefore, the proposed approach can effectively recover engine waste heat with little effect on power performance.

Hierarchical porous polystyrene-based activated carbon spheres for CO2 capture.

It is rather essential to design porous carbon adsorbents with high CO2 capture performance for improving global warming and climate change. Activated carbon spheres with high specific surface area and hierarchical porous texture were prepared from polystyrene-based macroreticular resin spheres due to their low ash and mechanical stability by air pre-oxidization and steam activation. The as-prepared carbon spheres had a specific surface area of 1274.95 m2 g-1, total pore volume of 1.09 cm3 g-1 and micropore volume of 0.47 cm3 g-1. Moreover, these carbon spheres showed a hierarchical porous texture composed of ultrafine micropores (0.5-1 nm), micropores (1-2 nm), mesopores (10-50 nm) and macropores (50-100 nm). A CO2 adsorption capacity of 2.82 mmol g-1 for carbon spheres can be obtained at 30 °C and 1 atm. Further, after introducing nitrogen-containing functional groups by gaseous ammonia at 600 °C, these carbon spheres (NPSRCSs) exhibited a high CO2 adsorption capacity of 3.2 mmol g-1. In addition, excellent cyclic stability, low hygroscopicity and regenerability temperature suggested these carbon spheres were favorable for CO2 capture.

Influence of Residence Time on Syngas Composition in CaO Enhanced Air–Steam Gasification of Biomass

Influence of Residence Time on Syngas Composition in CaO Enhanced Air–Steam Gasification of Biomass

Effect of Steam–Air Treatment of Alumina–Chromia Dehydrogenation Catalysts on Their Physicochemical and Catalytic Characteristics

Effect of Steam–Air Treatment of Alumina–Chromia Dehydrogenation Catalysts on Their Physicochemical and Catalytic Characteristics

Reduction entropy generation and condensation by NaCl particle injection in wet steam supersonic nozzle

The supersonic nozzle is very often used in many technical applications, such as fluid-flow machines or devices. If the medium flowing through a supersonic nozzle is a moist gas, moist air or wet steam, non-equilibrium condensation must occur. Such mediums usually contain impurities which affect the condensation phenomenon. The main purpose of this research is a numerical study on the effect of the content of impurities in steam on the non-equilibrium condensation phenomenon. In order to achieve this purpose, salt (NaCl) is used. Sodium chloride (NaCl) is a very common steam impurity. It may occur in a soluble or crystal form. Different concentrations of salt are considered as the input quantity. The results show that the process of steam condensation on salt particles has a significant impact on two-phase variables and flow parameters. In the presence of salt, steam condensation starts whenever the supersaturation ratio is above one. Latent heat of the condensation changes the flow pattern and reduces the nucleation rate and water droplet production. The presence of 1015 particles of salt reduces the outlet average liquid mass fraction and entropy generation by 14.5 % and 15.2 % respectively. The research results prove that steam impurities have a significant impact on non-equilibrium condensation.

Experimental Studies of the Effect of Design and Technological Solutions on the Intensification of an Underground Coal Gasification Process

This paper represents the results of experimental studies of physical modeling of the underground coal gasification process in terms of implementation of design and technological solutions aimed at intensification of a gasification process of thin coal seams. A series of experimental studies were performed in terms of a stand unit with the provided criteria of similarity to field conditions as well as kinetics of thermochemical processes occurring within a gas generator. Hard coal (high volatile bituminous coal) was selected as the raw material to be gasified, as that coal grade prevails in Ukrainian energy balance since it is represented by rather great reserves. Five blow types were tested during the research (air, air–steam, oxygen–steam, oxygen–enriched, and carbon dioxide and oxygen). As a result, the effect of tightness of a gas generator on the quantitative and qualitative parameters of coal gasification while varying the blow by reagents and changing the pressure in a reaction channel has been identified. Special attention was paid to the design solutions involving blow supply immediately into the combustion face of a gas generator. The experimental results demonstrate maximum efficiency of the applied gas generator design involving flexible pipelines and activator in the reaction channel and a blow direction onto the reaction channel face combined with blow stream reversing which will make it possible to improve caloricity of the generator gas up to 18% (i.e., from 8.4 to 12.8 MJ/m3 depending upon a blow type). Consideration of the obtained results of physical modelling can be used with sufficient accuracy to establish modern enterprises based on the underground coal seam gasification; this will help develop more efficiently the substandard coal reserves to generate heat energy as well as power-producing and chemical raw material. The research conclusions can provide technical reference for developing a new generation of underground coal gasification technology.

Model-Free Control of UCG Based on Continual Optimization of Operating Variables: An Experimental Study

The underground coal gasification (UCG) represents an effective coal mining technology, where coal is transformed into syngas underground. Extracted syngas is cleaned and processed for energy production. Various gasification agents can be injected into an underground georeactor, e.g., air, technical oxygen, or water steam, to ensure necessary temperature and produce syngas with the highest possible calorific value. This paper presents an experimental study where dynamic optimization of operating variables maximizes syngas calorific value during gasification. Several experiments performed on an ex situ reactor show that the optimization algorithm increased syngas calorific value. Three operation variables, i.e., airflow, oxygen flow, and syngas exhaust, were continually optimized by an algorithm of gradient method. By optimizing the manipulation variables, the calorific value of the syngas was increased by 5 MJ/m3, both in gasification with air and additional oxygen. Furthermore, a higher average calorific value of 4.8–5.1 MJ/m3 was achieved using supplementary oxygen. The paper describes the proposed ex situ reactor, the mathematical background of the optimization task, and results obtained during optimal control of coal gasification.

Effect of light gas on condensation heat transfer of steam–air mixture and gas stratification

Condensation has been considered for various industrial applications. However, the characteristics of condensation heat transfer have not been fully elucidated. In this study, we identify the characteristics of condensation heat transfer deterioration due to light gas. We measure the condensation heat transfer coefficient by varying the mass fraction of noncondensable gas and the mole fraction of helium to noncondensable gas. We discuss parameters that can affect the condensation heat transfer coefficient, i.e., the gas density, diffusion coefficient, and mole fraction of helium. Gradual deterioration of condensation heat transfer coefficient by increasing mole fraction of helium to noncondensable gas is observed. Furthermore, conditions for helium stratification under condensation are identified. Models for predicting condensation heat transfer are evaluated by varying an effective diffusion coefficient model based on experimental data.

Experimental study of air–steam condensation on the influence of tube diameter and inclination angle

Steam-air condensation is one of the important physical phenomena after reactor accidents, which has direct impacts on the discharge of containment residual heat after the accident. Previously, many researchers have proposed experimental correlations for condensation of non-condensable gas, which include the influence of pressure, concentration, and wall subcooling. However, there are relatively few studies on the influence of tube diameter and inclination angle. In order to investigate the heat transfer characteristics of the condenser at different tube diameters (19 mm, 15 mm, 12 mm) and inclination angles (0 ~ 90°), experiments were carried out in the pressure range of 0.15 ~ 1.6 MPa, air mass fraction of 14 ~ 87%, and wall subcooling of 28 ~ 122 °C. It shows that the condensation heat transfer coefficient (HTC) increases with the decrease of the tube diameter and inclination angle. The condensation HTC with a tube diameter of 12 mm and an inclination angle of 0°(Horizontally) is around 32 ~ 38% larger than that of the heat transfer tube with a tube diameter of 19 mm and an inclination angle of 90°(Vertically). Based on a total of 2276 data points from the present work and related experiments, an experimental correlation containing the effect of tube diameter and inclination angle is proposed, and its deviation is within ± 15% with 95% confidence.