Effect Of Steam Addition Research Articles

H2 production enhancement in underground coal gasification with steam addition: Effect of injection conditions

Hydrogen is a clean energy source, and its use helps to mitigate climate change. Underground coal gasification for hydrogen production is a promising method for countries with abundant coal resources and high hydrogen demand. However, the existing coal-to-hydrogen process underground exhibit low production efficiency. This work proposes the use of swirl flow injection to improve hydrogen production efficiency, and also explores the influence of other injection conditions (oxygen flow rate, steam mass flow and steam temperature) on hydrogen production. For straight flow injection, the effect of steam addition on gasification performance depends on the oxygen flow rate, and the highest H2 production is 14.6 L under 1 L/min oxygen and 1 g/L steam. With a swirl flow injection, H2 production increases with steam addition for both 1 L/min and 2 L/min oxygen, which shows a larger H2 production than straight flow injection. The highest H2 production for swirl flow injection is 19 L under 2 L/min oxygen and 1 g/L steam. An increase in steam temperature barely affects the composition of products but apparently increases the amount of products. The fracture effect of high temperature steam might cause a sudden increase of H2 and CH4 at the late stage.

Effect of steam addition on the combustion, performance and emissions characteristics of an HCCI diesel engine

Effect of steam addition on the combustion, performance and emissions characteristics of an HCCI diesel engine

Sustainable conditions for waste tires recycling through gasification in a bubbling fluidized bed

Gasification in a bubbling fluidized bed reactor was introduced as sustainable technology to treat waste such as tires. However, uncertainty arises when defining the most sustainable gasification process conditions. In this paper, eight experimental conditions were analyzed. The experiments were carried out at 700 and 850 °C with different equivalence ratios (ER) while using air as a gasifying agent. At 850 °C the effect of steam addition was also studied. A Life Cycle Assessment (LCA) was assessed to the product gas and its energy content by the following environmental impacts: Climate Change (CC), Ozone Depletion (OD), and Particulate Matter (PM). LCA methodology revealed that optimal gasification conditions provide 74, 69 and 66% environmental impact reductions in CC, PM, and OD, respectively by comparing the best and the worst-case scenarios. The combination of high temperature, low ER, and steam addition offered the most environmentally sustainable process, achieving 8.3·10−2 kg CO2 eq/MJ in CC, 1.3·10−8 kg CFC-11eq/MJ in OD and 4.9·10−5 kg PM2.5eq/MJ in PM. Despite the great savings in environmental impacts, additional efforts are still needed to reduce the energy consumption of the preheating system to ensure the product gas is levelled to conventional natural gas.

Effect of steam addition during calcination on CO2 capture performance and strength of bio-templated Ca-based pellets

Enormous efforts have been devoted to improving the cyclic reactivity of the Ca-based sorbent for cyclic CO2 capture. Steam reactivation is one of the most promising technologies to regenerate the CO2 capture performance of the Ca-based sorbent remarkably. However, the strength of the pellets during the steam reactivation process is insufficiently investigated. This study examined the influences of steam addition during calcination on the CO2 capture capacity and mechanical strength of the bio-templated sorbent over multiple carbonation-calcination cycles. A CO2 uptake of 0.31 g/g was achieved after 20 cycles by adding 30 % steam into the calcination atmosphere, which is 2.2 times higher than the cycles without steam injection. After the long-term test up to 100 cycles with 30 % steam in the calcination environment, a 6-fold increase in the average crushing force of the pellets was observed. The enhancement of the mechanical strength was attributed to the synergy effect of thermal sintering and atmosphere-induced sintering. Generally, steam addition during calcination demonstrated great potential in retaining CO2 capture capacity and improving the mechanical strength of the bio-templated sorbent.

Effect of steam addition and distance between inlet nozzles on non-catalytic POX process under MILD combustion condition

Moderate or intensive low-oxygen dilution (MILD) combustion is a novel combustion technology with high efficiency and low emissions. Few studies have been performed on the application of this technology for partial oxidation processes. In this research, a Computational Fluid Dynamics study for the effect of different parameters on the natural gas partial oxidation under MILD combustion conditions has been carried out. The combustion chamber was in the form of cylinder with a diameter of 300 mm and a length of 1500 mm. The effect of parameters such as different kinetic mechanisms, adding ethane and propane to methane (shale gas feed), adding steam to the feed and distance (interval) between methane and oxygen nozzles were investigated. Results showed that addition of ethane and propane to methane increased the mole fraction of CO and C2H2 so that, in the case of mixed methane with ethane and propane compared to the case of pure methane, an increase of 18.75% and 12.93% was observed for CO and C2H2, respectively. In addition, with increasing the percentage of steam in the inlet feed at a constant flow rate, methane conversion increased so that it in the case of 30% inlet steam was 77.17%, which showed 11% promotion compared to the pure methane case. Also, increasing the distance between the fuel and oxidizer nozzles led to an increase in the maximum temperature in the combustion chamber.

Effect of methane reforming before combustion on emission and calorimetric characteristics of its combustion process

In this study, combustion and emission characteristics of methane mixed with steam (CH4/H2O) and the products of methane reforming with steam (CO/H2/H2O) were compared. Four fuel compositions were analysed: CH4+H2O, CH4+2H2O, and products of complete methane reforming in these mixtures, respectively. A comparison was carried out through the numerical model created via Ansys Fluent 2019 R2. A combustion process was simulated using a non-premixed combustion model, standard k-ϵ turbulence model and P-1 radiation model. The combustor heat capacity for interrelated fuel compositions was kept constant due to air preheating before combustion. The inlet air temperature was varied to gain a better insight into the combustion behaviour at elevated temperatures. The effect of steam addition on the emission characteristics and flame temperatures was also evaluated. NOx formation was assessed on the outlet of the combustion zone. The obtained results indicate that syngas has a higher combustion temperature than methane (in the same combustor heat capacity) and therefore emitted 27% more NOx comparing to methane combustion. With the air inlet temperature increment, the pollutant concentration difference between the two cases decreased. Steam addition to fuel inlet resulted in lesser emissions both for methane and syngas by 57% and 28%, respectively. In summary, syngas combustion occurred at higher temperature and produced more NOx emissions in all cases considered.

The effects of steam addition on the unstable behavior of hydrogen-air lean premixed flames under the adiabatic and non-adiabatic conditions

The effects of steam addition on the unstable behavior of hydrogen-air lean premixed flames under the adiabatic and non-adiabatic conditions were investigated using numerical calculations. We adopted the detailed chemical reaction mechanism for hydrogen-oxygen combustion, modeled with seventeen reversible reactions of eight reactive species and a diluent. Two-dimensional unsteady reactive flow was treated, based on the compressible Navier-Stokes equations. The burning velocity of a planar flame decreased as the steam addition and heat loss increased. A sufficiently small disturbance was superimposed on a planar flame to study the characteristics of intrinsic instability. We obtained the relation between the growth rate and wave number, i.e. the dispersion relation, and the linearly most unstable wavelength, i.e. the critical wavelength. As the steam addition increased, the unstable range became narrower, and the critical wavelength became longer. Taking account of heat loss, we obtained smaller growth rates and narrower unstable range. The superimposed disturbance developed owing to intrinsic instability, and then the cellular shape of flame fronts appeared. In cellular flames, compared with planar flames, high (low) concentration of active chemical species was found in downstream of convex (concave) fronts. This was caused by high (low) temperature at convex (concave) fronts due to the diffusive-thermal effects. The concentration of active chemical species became lower with increasing the steam addition and heat loss, which was because of the reduction of flame temperature. Moreover, the burning velocity of a cellular flame increased monotonically with an increase in the scale of premixed flames. The burning velocity of a cellular flame normalized by that of a planar flame increased as the steam addition and heat loss increased. The numerical results denoted that the steam addition and heat loss had a great influence on the unstable behavior of hydrogen-air lean premixed flames.

Effects of steam addition and/or injection on the combustion characteristics: A review

Due to increasing global energy demand and the fact that a major source of the required energy is generated from fossil fuels, the combustion process has turned into a topic of interest in converting fossil fuels to energy. An ideal combustion system is one that can combine high engine efficiency with low fuel consumption and low emissions. Increasing humidity is a technique used by researchers for influencing the combustion process. The present study aims to review previously conducted researches in this regard. Based on viewpoints of these researches, the reviewed studies were categorized into four groups: the case studies used, the methodology applied, the design guidelines considered, and the performance parameters studied. It can be concluded from the reviewed articles that NOx reduction is the most significant advantage of increasing humidity in the combustion process, and has led to the widespread use of this method. The other studied emissions either remained constant or their respective increases were negligible.

PSI-11 Moisture Content Throughout the Pelleting Process and Subsequent Effects on Pellet Quality

Abstract This experiment was designed to evaluate the effects of steam addition to the conditioner on moisture content throughout the pelleting process and subsequent effects on pellet quality. Treatments consisted of diets pelleted with no steam and steam added to achieve conditioning temperatures of 62.8 and 87.8°C. Conditioner retention time was set at 30 sec and diets were pelleted with a 6.4×63.5 mm pellet die. Pellet samples were collected and immediately placed in an experimental counter-flow cooler for 15 min. All treatments were replicated at 3 separate time points to provide 3 replicates per treatment. Mash (M), conditioned mash (CM), hot pellets (HP), and cooled pellet (CP) samples were collected for moisture content analysis and CP for pellet durability index (PDI). Data were analyzed with pelleting run as the experimental unit and time period as the blocking factor. Moisture samples were analyzed as a 3×4 factorial of steam-conditioning and sample location. There was a steam-conditioning×sample interaction (P< 0.01) for moisture. Mash samples for all treatments were similar (13.3%; 36.2°C). For the no steam treatment, there was no difference in moisture content for the M, CM, and HP; however, moisture decreased in CP, with samples having 13.4, 13.1, 12.9, and 12.0% moisture, respectively. For the 62.7°C treatment, there was an increase in moisture from M to CM, followed by a decrease in both HP and CP, with samples having 13.2, 15.3, 14.9, and 12.7% moisture, respectively. For the 87.8°C treatment, moisture increased from M to CM, and decreased in HP and CP with samples having 13.3, 17.3, 16.3, and 13.4% moisture, respectively. Increasing conditioning temperature from no steam to 87.8°C increased (P< 0.01) PDI from 3.3, 59.1, to 91.1%, respectively. In conclusion, increasing feed temperature from 36.2 to 87.8°C via steam addition increased condition mash moisture content by 4.2% resulting in improved pellet quality.

From O2/CO2 to O2/H2O combustion: The effect of large steam addition on anthracite ignition, burnout and NOx formation

Steam-moderated combustion has been proposed to supress flue gas recycling in oxy-fired units, but the influence of replacing CO2 by H2O has to be deeply studied. In this paper, oxy-fuel combustion of anthracite with large steam addition has been experimentally characterized, and main results are discussed as concerns the influence upon the ignition temperature, the burnout and the NOx formation. The tests have been carried out in an electrically-heated entrained flow reactor for a set of O2/CO2 and O2/H2O/CO2 atmospheres, with steam addition up to 40% vol. The results show that ignition temperature diminishes when steam is added in low rates (maximum decrease of 16 °C), but the trend is reversed for the higher steam concentrations (maximum increase of 18 °C). The effect of steam addition on coal burnout rates is more significant for the 21% vol. O2 atmosphere, with a decrease of 2.2–5.3 percentage points, and almost negligible for the 35% vol. O2. An outstanding reduction of NO specific emissions is detected when adding H2O, with decrements ranging 28–45% compared to the dry conditions. The transition from O2/CO2 combustion to O2/H2O combustion barely affects the anthracite conversion but significantly diminishes NOx formation rates.

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.

Multiscale model for steam enhancement effect on the carbonation of CaO particle

A multiscale model including scales at the surface, grain, and particle was developed to understand the steam enhancement mechanism on the carbonation of CaO particle. The interaction of H2O with CaO occurring at the surface scale exhibited an enhancement effect on the product layer diffusion at the grain scale, while the grain growth due to the product layer diffusion at the grain scale exhibited an important effect on the pore structure and intraparticle gas diffusion at the particle scale. The developed multiscale model was validated with the experimental data, and the effect of steam addition on carbonation performance was discussed. The effect of steam on CaO carbonation at higher temperatures (600 ~ 700 °C) was much less significant than that at lower temperatures (400 ~ 500 °C), due to the pore plugging phenomenon. In addition, the controlling step of the carbonation in the presence of steam was analyzed. Calculated results show that the external gas diffusion resistance is small enough during the reaction process. The controlling step of the carbonation at 400 °C is the chemical reaction step, while the controlling step of the carbonation at 700 °C is the intraparticle gas diffusion step.

Effects of Steam Addition during Calcination on Carbonation Behavior in a Calcination/Carbonation Loop

AbstractThe effects of steam addition during calcination on the carbonation behavior of calcium‐based sorbents in cyclic calcination/carbonation experiments were investigated. Variations in the CaO conversion rate during carbonation were measured to evaluate the influence of operating conditions and particle size on the carbonation reaction in kinetic‐ and diffusion‐controlled reaction regimes. Surface sintering and particle aggregation during cyclic calcination/carbonation affected the sorbent surface area, pore volume, and possibly the pore size, resulting in less sorbent recyclability and a trigger time retard in the fast kinetic‐controlled carbonation. Steam addition during calcination positively affected the recyclability of the sorbents and altered the carbonation behavior.

Effects of steam dilution on laminar flame speeds of H2/air/H2O mixtures at atmospheric and elevated pressures

The laminar flame speeds of H2/air with steam dilution (up to 33 vol%) were measured over a wide range of equivalence ratio (0.9–3.0) at atmospheric and elevated pressures (up to 5 atm) by an improved Bunsen burner method. Burke, Sun, HP (High Pressure H2/O2 mechanism), and Davis mechanisms were employed to calculate the laminar flame speeds and analyze different effects of steam addition. Four studied mechanisms all underestimated the laminar flame speeds of H2/air/H2O mixtures at medium equivalence ratios while the Burke mechanism provided the best estimates. When the steam concentration was lower than 12%, increasing pressure first increased and then decreased the laminar flame speed, the inflection point appeared at 2.5 atm. When the steam concentration was greater than 12%, increasing the pressure monotonously decrease the laminar flame speed. The chemical effect was amplified by elevated pressure and it played an important role for the inhibiting effect of the pressure on laminar flame speed. The fluctuations of the chemical effect at 1 atm were mainly caused by three-body reactions, while the turn at 5 atm was mainly caused by the direct reaction effect. Elevated pressure and steam addition amplified the influences of uncertainties in the rate constants for elementary reactions, which might leaded to the disagreement between experimental and simulation results.

Effect of Steam Addition on the Flow Field and NOx Emissions for Jet-A in an Aircraft Combustor

AbstractThe steam injection technology for aircraft engines is gaining rising importance because of the strong limitations imposed by the legislation for NOx reduction in airports. In order to investigate the impact of steam addition on combustion and NOx emissions, an integrated performance-CFD-chemical reactor network (CRN) methodology was developed. The CFD results showed steam addition reduced the high temperature size and the radical pool moved downstream. Then different post-processing techniques are employed and CRN is generated to predict NOx emissions. This network consists of 14 chemical reactor elements and the results were in close agreement with the ICAO databank. The established CRN model was then used for steam addition study and the results showed under air/steam mixture atmosphere, high steam content could push the NOx formation region to the post-flame zone and a large amount of the NOx emission could be reduced when the steam mass fraction is quite high.

Effect of steam addition on the structure and activity of Pt–Sn catalysts in propane dehydrogenation

To investigate the role of steam on the structure and activities of platinum-based catalyst, a tin modified Pt/γ-Al2O3 catalyst was prepared for propane dehydrogenation in the presence of steam. The propane conversion could be prominently elevated by nearly twofolds with only 1.0% loss of selectivity to propene when an optimum amount of H2O was added. The retarding effects of steam on the activities are also observed at higher H2O/C3H8 molar ratios (>1). Kinetic studies results show that the apparent activation energies for steam dehydrogenations are lower than those without steam addition. The fresh, spent and steam pretreated catalysts were characterized by TG, Raman, H2-chem, HAADF-STEM, XPS and CO adsorption FT-IR (CO-FTIR). It is observed that the platinum particles sizes are smaller in the samples subjected to certain period of steam pretreatment. The changes of platinum dispersion in steam conditions are related to the changes of tin oxidation states and the segregation of platinum from Pt–Sn alloys, as revealed by CO-FTIR and XPS results. More accessible Pt sites that are generated in the steam due to the phase transformation of Pt–Sn catalyst as well as the removal of coke accumulated on the catalyst surface would account for the increase of catalytic activities and the decrease of activation energies in steam atmosphere. Competitive adsorption of H2O and other reagent over Pt sites would lead to the retarding effects of steam on the activities at high H2O partial pressure.

Downhole Heavy Crude Oil Upgrading Using CAPRI: Effect of Steam upon Upgrading and Coke Formation

Heavy crude oil and bitumen are characterized by a low yield of light distillates in the range of 10–30% with a boiling point below 350 °C, high density (low API gravity), high viscosity, and high heteroatom content, which impede their exploitation. In this study, the catalytic upgrading process in situ (developed by the Petroleum Recovery Institute, Canada) add-on to the toe-to-heel air injection for the extraction and upgrading of heavy oil and bitumen downhole was investigated. The effect of steam addition and steam-to-oil ratio upon upgrading, coke formation, sulfur and metal removal were examined using a Co–Mo/γAl2O3 catalyst at a reaction temperature of 425 °C, pressure of 20 bar, gas-to-oil ratio of 500 mL·mL–1, and steam-to-oil ratio in the range of 0.02–0.1 mL·mL–1. It was observed that the coke content of the spent catalyst reduced from 17.02 to 11.3 wt % as the steam-to-oil ratio increased from 0.02 to 0.1 mL·mL–1 compared to 27.53 wt % obtained with only nitrogen atmosphere after 15 h time-on-stream. Over the same range of conditions, 88–92% viscosity reduction was obtained as steam-to-oil ratio increased compared to 85.5% in nitrogen atmosphere only, a substantial reduction from the value of 1.091 Pa·s for the feed oil. It was also found that although desulfurization increased from 3.4% in a steam-free atmosphere to 16–25.6% over the increasing range of steam flows investigated, demetallization increased from 16.8% in a steam-free environment to 43–70.5% depending on the increasing steam-to-oil ratio.

Characterisation of tars from biomass gasification: Effect of the operating conditions

Tars formation remains the main technical hurdle in the development of biomass gasification at commercial scale, due to its associated operating problems (condensation, catalyst deactivation, polymerisation). This work aims to study the effect of the operating conditions (biomass/air ratio, temperature and gasifying agent) on the production and the technical and environmental hazard (tar dew point and carcinogenic potential) of tars produced in a small-scale drop-tube gasifier, dealcoholised marc of grape being used as biomass fuel. An analytical HPLC method has been used for the detection of polycyclic aromatic hydrocarbons (PAHs), benzene, toluene, ethyl-benzene and xylenes (BTEX), phenol, and pyridine. Results show that an increase in the relative biomass/air ratio, a decrease in temperature, and higher steam content lead to a higher tar production. BTEX have been found as the main constituents of tars (60–70% wt.), whereas among PAHs, the most significant are the lighter ones (naphthalene, acenaphtylene, acenaphtene). Phenol production is favoured at lower temperatures or/and higher steam content (around 50% wt. of the tar mixture at 750 °C and steam gasification). A progressive aromatisation of tars has been observed when increasing the temperature, the effect of steam addition on tar composition being not significant at temperatures higher than ∼1000 °C.

Effects of water vapor addition on the laminar burning velocity of oxygen-enriched methane flames

The effects of steam addition on the laminar burning velocity of premixed oxygen-enriched methane flames are investigated at atmospheric pressure. Experiments are carried out with an axisymmetric burner on which laminar conical flames are stabilized. A newly devised steam production system is used to dilute the reactants with water vapor. The oxygen-enrichment ratio in the oxidizer, defined as O 2/(O 2 + N 2) (mol.), is varied from 0.21 (air) to 1.0 (pure oxygen). The equivalence ratio ranges from 0.5 to 1.5 and the steam molar fraction in the reactive mixture is varied from 0 to 0.50. For all compositions examined, the reactive mixture is preheated to a temperature T u = 373 K. Laminar flame speeds are determined with the flame area method using a Schlieren apparatus. The deviations induced by stretch effects due to aerodynamic strain and flame curvature are assessed using Particle Imaging Velocimetry measurements and flame images, and these data are used to estimate the uncertainty of the flame speed measurements. The experiments are completed by numerical simulations conducted with the PREMIX code using different detailed kinetic mechanisms. It is shown that the laminar flame speed of CH 4/O 2/N 2/H 2O ( v) mixtures features a quasi-linear decrease with increasing steam molar fraction, even at high steam dilution rates. Numerical predictions are in good agreement with experimental data for all compositions explored, except for low dilution rates X H 2 O < 0.10 in methane–oxygen mixtures, where the flame speed is slightly underestimated by the calculations. It is also shown that steam addition has a non-negligible chemical impact on the flame speed for methane–air flames, mainly due to water vapor high chaperon efficiency in third-body reactions. This effect is however strongly attenuated when the oxygen concentration is increased in the reactive mixture. For highly oxygen-enriched flames, steam can be considered as an inert diluent.

Reforming performance of a plasma-catalyst hybrid converter using low carbon fuels

The reforming performance of a plasma-catalyst hybrid converter using different low carbon fuels was investigated. The methodology was to use arc from spark discharge combined with an appropriate oxygen/carbon molar ratio (O 2/C) and feeding rate of the supplied mixture. To enhance the mixing and reforming reaction, a gas intake swirl was generated by inducing the mixture tangentially into the reaction chamber. The required energy for fuel processing was provided by heat released through the oxidation of the air–fuel mixture. The reforming temperature as well as the effect of steam addition on the hydrogen production was studied. The results showed that reformate gas temperature had a profound effect on the overall reaction. The H 2/(CO + CO 2) ratio reformed by both methane and propane was shown to increase with temperature and that the optimum ratio was obtained when reforming methane under 650 °C. The conversion efficiency of the fuel was also shown to increase with increasing temperature. The best thermal efficiency of 72.01% was obtained near 750 °C. The theoretical equilibrium calculations and the experimental results were compared.