Presence Of Steam Research Articles

Comparative study of CrAlSiN monolayer and CrN/AlSiN superlattice multilayer coatings: Behavior at high temperature in steam atmosphere

Protective coatings that retard ionic diffusion at high temperature in the presence of steam are of interest for the energy industry. A CrAlSiN monolayer and two CrN/AlSiN coatings of periodic layers of different thicknesses deposited on P92 steel by cathodic arc evaporation (CAE) were studied. Their protection capabilities under the working conditions of ultrasupercritical steam turbines (at 650 °C in 100% steam atmosphere) up to 2000 h were assessed. Several characterization techniques were used to achieve this objective, such as gravimetric analysis, X-ray diffraction (XRD), scanning electron microscopy with an energy dispersive detector (SEM-EDS), field emission scanning electron microscopy (FE-SEM) and glow discharge optical emission spectrometry (GDOES).After 2000 h, the oxidation resistance of the coated samples showed a significant improvement compared to that of the bare substrate. This behavior is explained by the formation of a protective outer layer of chromia (Cr2O3), which prevents or reduces the inward and outward diffusion of oxygen and metallic cations, respectively, leading to a reduction of the oxidation rate at working conditions. Oxidation kinetics of the coated samples follows a parabolic trend at the first stages of oxidation, according with the development of a protective oxide on the surface during the thermal treatment. However, after a certain time an apparent change in the kinetics of the oxide growth is observed, that has been related to the detachment of the oxidized macrodroplets of the evaporated materials, which are characteristic of the CAE technique. Nevertheless, this phenomenon does not decrease the oxidation resistance of the coatings.

The role of steam in selective oxidation of methacrolein over H3PMo12O40

Role of steam in selective oxidation of methacrolein with molecular oxygen over H3PMo12O40 catalyst was investigated. Addition of steam to feed gas significantly enhanced both catalytic activity and selectivity to methacrylic acid, which were fivefold and twice increases, respectively, under the optimal steam pressure (PH2O = 0.13 atm). Kinetic analysis demonstrated that the addition of steam caused 200-fold increase in the pre-exponential factor for the formation of methacrylic acid, leading to the significant increase in the activity. The steam in the feed gas varied hydrous state of H3PMo12O40 under the reaction conditions, while did not alter redox property, molecular and crystalline structures, and surface area of the catalyst. In the presence of steam at 573 K, three H2O per one H3PMo12O40 were absorbed and hydrated protons like [H3O]+ were formed in the bulk of H3PMo12O40. Methacrolein was adsorbed on the surface of the hydrous catalyst, but not on anhydrous one at all. Based on the results, it was concluded that activation of methacrolein readily occurred on the catalyst in the presence of steam, leading to the significant increase in the pre–exponential factor. Quantum chemical calculation supported the smooth activation of methacrolein by the reaction with [H3O]+ without any transition state.

Combined sorbent and catalyst material for sorption enhanced reforming of methane under cyclic regeneration in presence of H2O and CO2

An investigation on an innovative calcium‑nickel Combined Sorbent and Catalyst Material (CSCM) for Sorption Enhanced Reforming (SER) of methane is presented in this paper. After hydrothermal synthesis, a nominal 30 wt% CaO-based sorbent supported on mayenite was physically mixed with a commercial reforming catalyst and granulated to obtain bifunctional particles of 200–300 μm. Materials were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller surface analysis (BET) and Mercury- intrusion prosimetry (Hg-porosimetry). A novel thermo-gravimetric analysis (TGA) approach was employed for investigating SER activity, particularly the materials performance during multicycling methane reforming and sorbent carbonation followed by regeneration in oxidative atmosphere – either in the presence of steam or CO2 at high temperature. When regeneration is carried out in 100 vol% CO2 at 925 °C, an intermediate reduction step between cycles was crucial to maintain the catalytic activity of the CSCM for 100 consecutive sorption-regeneration cycles. In spite of a stable catalytic activity, the initial sorption capacity of the CSCM sorbent function (~16gCO2/100gCSCM) declined progressively with cyclic runs and stabilized at ~10gCO2/100gCSCM from cycle 90 onwards. This decline in capacity has been related to CaO depletion by solid phase reaction with the catalyst support.

Structure of the Mo-Containing Dispersed Catalyst During Heavy Oil Upgrading in the Presence of Steam And Hydrogen

XRD, TEM, EXAFS/XANES methods are first used to study the structure and morphology of Mocontaining phases of carbon residues of heavy oil refining during catalytic steam cracking, catalytic cracking without water, and hydrocracking. According to the results obtained from physical and chemical studies of Mo-based catalytic phases, the reaction medium affects structural features of Mo-containing phases, e.g. the amount of oxide and sulphide forms, the particle size, and particle morphology.

Zircaloy-4 high temperature oxidation in atmospheres representative of SFP-LOCA: Investigation of the influence of a low temperature pre-oxidation scale

Within the framework of the French DENOPI project dedicated to the study of Spent Fuel Pool accidents, the high temperature degradation of Zircaloy-4 cladding material has been investigated in the 700–950 °C range, in air and air-steam atmospheres. In particular, we focused on the effect of the pre-transient corrosion-oxide scale formed on the cladding materiel during in-reactor use, here simulated by an out-off-pile low-temperature pre-oxidation step. In-situ X-Ray Diffraction evidenced strong evolutions of the stress state and grain size of these laboratory-grown pre-oxidation scales upon high temperature exposures. From 18O tracer experiments and thermogravimetric analysis, the pre-oxide was shown to be a rather efficient barrier against further high temperature attack by the nitrogen-containing atmosphere, despite its multi-layered, porous microstructure. Oxygen apparent diffusion coefficients were derived from the 18O tracer experiments. These diffusion coefficients suggest that the pre-oxide rather behaves like a dense monoclinic zirconia layer. The protective effect was sometimes observed to be maintained during very long exposure times at high temperature, depending on the presence of defects in the scale. Where the protective effect was first lost, the nitrogen-“catalyzed” oxidation initiated and progressively propagated to the whole specimen surface. A propagation mechanism is proposed, which involves progressive mechanical failure of the pre-oxide scale, below which the high temperature, nitrogen-assisted, porous oxidation formation occurs. The cladding degradation kinetics, driven by this propagation mechanism, is only weakly affected by the presence of steam. However, where the porous oxide formed, strong hydrogen pick-up in the underlying metallic substrate was observed.

Sustainable Use of Natural Geological Materials and Marble Wastes as Promising Calcium Looping Sorbents for CO2 Capture in the Cement Industry: Comparative Study

The present work focuses on the comparative study of the Calcium looping CO2 capture capacity and stability along 10 or 20 calcination-carbonation cycles, of three different marble powder wastes (MW) and two calcite samples (one from West Bank and another provided by CIMPOR) using a gas mixture with a /sub>CO2 concentration of 25% to mimic the real flue gases CO2 concentration in the cement industry. Very high initial carbonation (first cycle) conversions were obtained using the MW sorbents tested, which is a very interesting and promising result when compared with the initial carbonation conversions of the natural calcite sorbent currently used in industry as raw material for the cement production. For the Calcium-looping conditions used, the MW sorbent tested on the fixed bed reactor unit exhibits better cyclic stability with a lower sorbent deactivation with the number of cycles than the natural calcite resource used for the cement production. The presence of 5% of steam in the feed gas mixture with air atmosphere leads to significant differences on the sorbents cyclic performance when comparing with the results obtained for the standard calcination conditions. For both MW and calcite sorbent samples selected and tested on the fixed bed rector unit in the presence of steam, a lower CaO carbonation conversion is observed along the first 7 cycles, but a higher cyclic stability reaching a CaO conversion plateau, with a lower deactivation after 20 cycles, when comparing with the results for the standard calcination conditions. An improved sorbent stability for Ca-looping CO2 capture was observed during the carbonation-calcination cycles in the presence of steam which could allow reducing the make-up of CaO frequency along the time and the costs associated. The selection of suitable marble wastes as CaO-based sorbents, the improvement of their performance and the incorporation of exhausted sorbents in the clinker, can contribute to reducing the CO2 footprint of cement production and avoid the production of wastes associated to the marble producers.

Influence of H2O on NO formation during char oxidation of biomass

The present study investigates conversion of char-N to NO in mixtures of O2/N2 and in O2/H2O/N2. Biomass particles of spruce bark were combusted in an electrically heated single particle reactor at 900 °C at various O2/H2O/N2 concentrations. NO concentrations of the product gases were measured during the char combustion stage. The conversion of char-N to NO was significantly higher with H2O as compared to without H2O in the gas. Additional fixed bed experiments were conducted to investigate the products of the reaction between H2O and spruce bark char. The results showed that NH3 is the primary product in the reaction between char-N and steam. These results explain the observation that more NO is formed during char combustion in the presence of steam: the char-N reacts partly with H2O to form NH3, which reacts further to NO.

Gas phase dehydration using hydrogels

Hydrogels are cross-linked networks of water soluble polymers that have the potential to be used in the dehydration of wet gas. In this work, the uptake of hydrogels and molecular sieves were assessed in controlled humidity environments including in the presence of steam (100% relative humidity) and under pressurized conditions (6 MPa). The recyclability of the hydrogels and molecular sieves at 115 °C was also studied. At 98% humidity, the hydrogel was able to absorb twice its own mass while molecular sieves were only able to adsorb 0.3% of their mass. In the presence of steam (100% relative humidity), hydrogels absorb a maximum of approximately 23 times the absorbent's own mass while the molecular sieves merely adsorb an average of 0.4 times the adsorbent's mass under the identical experimental condition. Under pressurized conditions, hydrogels were able to absorb a maximum of approximately 6 times the absorbent's initial mass and an approximate of 0.25 times the adsorbent's initial mass. In terms of the recyclability, regeneration time and temperature the hydrogels show improved performance compared to molecular sieves. The superior uptake is due to the fundamentally different mechanism of dehydration of the hydrogel which results from swelling of the particles. This creates issues in terms of swelling and blocking of a dehydration column so methods to overcome this were explored by supporting the hydrogel. Owing to the outstanding water uptake performance, fast and complete regeneration, and readily available commercial supply, the hydrogel is considered as a viable and economical alternative to the commonly applied molecular sieve for gas phase dehydration.

Promotion effect of proton-conducting oxide BaZr0.1Ce0.7Y0.2O3−δ on the catalytic activity of Ni towards ammonia synthesis from hydrogen and nitrogen

In this report, for the first time, it has been observed that proton-conducting oxide BaZr0.1Ce0.7Y0.2O3−δ (BZCY) has significant promotion effect on the catalytic activity of Ni towards ammonia synthesis from hydrogen and nitrogen. Renewable hydrogen can be used for ammonia synthesis to save CO2 emission. By investigating the operating parameters of the reaction the optimal conditions for this catalyst were identified. It was found that at 620 °C with a total flow rate of 200 mL min−1 and a H2/N2 mol ratio of 3, an activity of approximately 250 μmol g−1 h−1 can be achieved. This is ten times larger than that for the unpromoted Ni catalyst under the same conditions although the stability of both catalysts in the presence of steam was not good. The specific activity of Ni supported on proton-conducting oxide BZCY is approximately 72 times higher than that of Ni supported on non-proton conductor MgOCeO2. These promotion effects were suspected to be due to the proton conducting nature of the support. Therefore it is proposed that the use of proton conducting support materials with highly active ammonia synthesis catalysts such as Ru and Fe will provide improved activity of at lower temperatures.

Propylphenol to Phenol and Propylene over Acidic Zeolites: Role of Shape Selectivity and Presence of Steam

This contribution studies the steam-assisted dealkylation of 4-n-propylphenol (4-n-PP), one of the major products derived from lignin, into phenol and propylene over several micro- and mesoporous acidic aluminosilicates in gas phase. A series of acidic zeolites with different topology (e.g., FER, TON, MFI, BEA, and FAU) are studied, of which ZSM-5 outperforms the others. The catalytic results, including zeolite topology and water stability effects, are rationalized in terms of thermodynamics and kinetics. A reaction mechanism is proposed by (i) analyzing products distribution under varying temperature and contact time conditions, (ii) investigating the dealkylation of different regio- and geometric isomers of propylphenol, and (iii) studying the reverse alkylation of phenol and propylene. The mechanism accords to the classic carbenium chemistry including isomerization, disproportionation, transalkylation, and dealkylation, as the most important reactions. The exceptional selectivity of ZSM-5 is attributed...

Effects of Secondary reaction of Primary Volatiles on Oil/gas Yield and Quality from Oil Shale Pyrolysis

The reaction behaviors of primary volatiles from oil shale pyrolysis were investigated using a two-stage reactor under different in-situ thermal reaction conditions. The reaction parameters of secondary reactor, such as, reactor temperature, atmosphere and residence time, were studied for their effects on the pyrolysis oil/gas yield and quality. The results showed that the reaction temperature had profound influence on the oil and gas yield. The pyrolyzed shale oil and gas yield reduced by 15% and 20% (mass) respectively, with the temperature of 2nd stage reactor increasing from 600 to 650 °C under optimized reaction condition of 1st stage. Comparing with nitrogen atmosphere, the liquid oil yield could be enhanced by 5% when steam was added as the reaction atmosphere in the second stage, and the corresponding oil was mainly concentrated in the gasoline and diesel distillations (that is, boiling point < 350 °C). The GC-MS analysis illustrated that the secondary reaction at the residence time of 0−3 s was mainly pyrolysis while the presence of steam could increase the content of aromatics in the oil and meanwhile suppress the condensation of aromatics. When the residence time was greater than 3−5 s, the secondary reaction was mainly condensation of poly-aromatics, which led to the increase of coke. Meanwhile, the gasoline and diesel oil yield remained stable, and the VGO fractions decreased by about 30%.

Stable complete methane oxidation over palladium based zeolite catalysts

Increasing the use of natural gas engines is an important step to reduce the carbon footprint of mobility and power generation sectors. To avoid emissions of unburnt methane and the associated severe greenhouse effect of lean-burn engines, the stability of methane oxidation catalysts against steam-induced sintering at low temperatures (<500 °C) needs to be improved. Here we demonstrate how the combination of catalyst development and improved process control yields a highly efficient solution for complete methane oxidation. We design a material based on palladium and hierarchical zeolite with fully sodium-exchanged acid sites, which improves the support stability and prevents steam-induced palladium sintering under reaction conditions by confining the metal within the zeolite. Repeated short reducing pulses enable the use of a highly active transient state of the catalyst, which in combination with its high stability provides excellent performance without deactivation for over 90 h in the presence of steam.

Steam Influence and Effect of Oxidant Amount on Propane Oxidation over Multi Metal Oxide Catalyst Using High-Throughput Experiment

The high-throughput experimentation technique was used to verify the testing conditions due to the effects of catalyst structure modifications and/or due to reaction parameter variation in parallel. In this paper, the design of experiment and catalytic results are discussed in the development of selective oxidation catalyst, to demonstrate the importance and versatility of such technology. It is used for the automated parallel testing of selective oxidation of propane to acrylic acid over some types of multi metal oxide catalysts. The catalysts used for performance test were Mo (molybdenum), cat-1 (unsupported Mo1V0.3Te0.23Nb0.125O), and cat-2 (supported Mo1V0.3Te0.23Nb0.125O). All catalysts were dried using spray drier. The effect of some reaction parameters, such as the amount of oxidant, presence of steam and reaction temperature was also investigated during the test. The configuration of the ‘nanoflow’ is shown to be suitable to screen catalytic performance. The results obtained gave very good reproducibility.

New Insight into SO2 Poisoning and Regeneration of CeO2-WO3/TiO2 and V2O5-WO3/TiO2 Catalysts for Low-Temperature NH3-SCR.

In this study, the poisoning effects of SO2 on the V2O5-WO3/TiO2 (1%VWTi) and CeO2-WO3/TiO2 (5%CeWTi) selective catalytic reduction (SCR) catalysts were investigated in the presence of steam, and also the regeneration of deactivated catalysts was studied. After pretreating the catalysts in a flow of NH3 + SO2 + H2O + O2 at 200 °C for 24 h, it was observed that the low-temperature SCR (LT-SCR) activity decreased significantly over the 1%VWTi and 5%CeWTi catalysts. For 1%VWTi, NH4HSO4 (ABS) was the main product detected after the poisoning process. Both of NH4HSO4 and cerium sulfate species were formed on the poisoned 5%CeWTi catalyst, indicating that SO2 reacted with Ce3+/Ce4+, even in the presence of high concentration of NH3. The decrease of BET specific surface area, NO x adsorption capacity, the ratio of chemisorbed oxygen, and reducibility were responsible for the irreversible deactivation of the poisoned 5%CeWTi catalyst. Meanwhile, the LT-SCR activity could be recovered over the poisoned 1%VWTi after regeneration at 400 °C, but not for the 5%CeWTi catalyst. For industrial application, it is suggested that the regeneration process can be utilized for 1%VWTi catalysts after a period of time after NH4HSO4 accumulated on the catalysts.

A Scoping Study of the Chemical Behavior of Cesium Iodide in the Presence of Boron in the Condensed Phase (650°C and 400°C) Under Primary Circuit Conditions

This work is a contribution toward understanding the chemical reactions on the primary circuit surfaces involving gaseous iodine release during a severe nuclear reactor accident. Cesium iodide was used as a nonradioactive precursor material in order to highlight the effects of carrier gas composition (Ar/H2O, Ar/H2O/H2, and Ar/Air), temperature, the initial cesium/iodine (Cs/I) molar ratio by adding cesium hydroxide, and the presence of boron on the molar composition of the deposited iodine compound and on the release of gaseous iodine from the deposit. The results from the experiments involving only cesium iodide as a precursor revealed a slight decomposition of cesium iodide and a release of gaseous iodine. Furthermore, the measured gaseous iodine mass decreased with the addition of hydrogen to the carrier gas at 650°C. At 400°C, the amount of released material (aerosol and gas) was decreased. However, whereas at 650°C the sampled iodine existed mainly as aerosols, the mass concentration recorded from the experiment at 400°C indicated a predominance of gaseous iodine. When the initial Cs/I molar ratio was significantly greater than unity (1.5 < Cs/I < 4.5), the mass of produced gaseous iodine was barely detectable, suggesting a reaction between cesium hydroxide and the gaseous iodine released from cesium iodide decomposition. In the presence of boron, the transport of gaseous iodine was increased as a result of the formation of glassy cesium borate in the evaporation crucible. The presence of steam and its quantity were shown to have an enhancing influence on the cesium borate formation and on the release of gaseous iodine.

Combined effect of nanoporous diluent and steam on catalytic upgrading of fuel oil to olefins and fuels over USY catalyst

ABSTRACTThis paper explores the effect of incorporation of a nanoporous silica as diluent for a USY catalyst in the presence or absence of steam, as a cost-effective hydrogen donor and regenerative agent, in the fuel oil upgrading. We found that the incorporation of inert silica in the catalyst particles in the presence of steam could produce more than 40 wt% of olefinic products, mainly propylene, in the cracked products. With the elimination of steam, the olefins yield became less than a half (about 17 wt%) and the reaction tended towards higher liquid yields (74.8 wt%) including gasoline and diesel fuel.

Sustainable hydrogen production options from food wastes

In this study, two thermochemical processes, namely steam gasification and supercritical water gasification (SCWG), were comparatively studied to produce hydrogen from food wastes containing about 90% water. The SCWG experiments were performed at 400 and 450 °C in presence of catalyst (Trona, K2CO3 and seaweed ash). The maximum hydrogen yield was obtained at 450 °C in presence of K2CO3 catalyst. In second process, hydrothermal carbonization was used to convert food wastes into a high-quality solid fuel (hydrochar) that was further gasified in a dual-bed reactor in presence of steam. The steam gasification of hydrochar was carried out with and without catalysts (iron−ceria catalyst and dolomite). The maximum hydrogen yield obtained from steam gasification process was 28.08 mmol/g dry waste, about 7.7 times of that from SCWG. This study proposed a new concept for hydrogen production from wet biomass, combination of hydrothermal carbonization following steam gasification.

Effect of alkali metal ions presence on the products of xylan steam assisted slow pyrolysis

Biomass pyrolysis has been extensively investigated during the last decades both as a stand-alone process for the production of bio-based fuels and as intermediate stage in other thermochemical processes such as gasification and combustion. The comprehension of biomass pyrolysis mechanisms can greatly benefit from the study of the pyrolysis behavior of separated biomass organic components as well as of the effect of metal ions on their decomposition pathways. Only few works reported the metal ions effect on the pyrolysis of hemicellulose. In the present paper the influence of metal ions on hemicellulose pyrolysis was studied choosing commercial xylan as reference. The thermal behavior of raw and demineralized xylan samples was studied in a thermogravimetric apparatus at atmospheric pressure under nitrogen from 323 K up to 973 K with a heating rate of 5 K/min. Then steam assisted pyrolysis tests were carried out up to two different final temperatures, 873 and 973 K, at pressure P = 5 × 105 Pa and heating rate HR = 5 K/min. Products yields, gas releasing rates as a function of the temperature, gas and liquid compositions were compared for raw and demineralized samples. The raw and demineralized xylan exhibited different pyrolytic behaviors both in nitrogen and steam atmospheres. Raw xylan produced a higher amount of char compared to the demineralized one in nitrogen atmosphere, whereas negligible differences in char yields were observed in presence of steam. Demineralization pretreatment resulted in the recovery of a greater amount of furfural and depressed the production of gas in both the pyrolysis and the gasification stages.

Hydrogen from Pyrolysis Oil by Chemical Looping of a Sol–Gel‐Prepared Iron(III) Oxide on Magnesium Aluminate as Oxygen Carrier

AbstractChemical looping of iron oxides has emerged as a promising approach to produce hydrogen with inherent gas separation. In this work, we use sol–gel‐prepared Fe2O3/MgAl2O4 as an oxygen carrier to produce hydrogen from biomass pyrolysis oil. The results showed that 950 °C was the optimum gasification temperature to achieve a high carbon conversion and gas yield. At this temperature, we produced hydrogen by chemical looping. However, the produced hydrogen was polluted severely by CO and CO2 because of coke formation during reduction. To solve this problem, we adjusted the reduction atmosphere by adding steam, which was an effective method to enhance the hydrogen purity. At a steam‐to‐oil ratio of 1.5, the purity of hydrogen reached 96 % in contrast to 84 % without steam. In the presence of steam, we also found a more stable porosity, which led to improved cyclic performance. Our current results demonstrate an approach to enhance hydrogen purity and material recyclability. This can be extended to improve other thermochemical hydrogen‐production processes.

Development of sustainable coal to liquid processes: Minimising process CO2 emissions

Traditional coal-to-liquid (CTL) plants are synonymous with the production of carbon dioxide. Coal may be gasified in the presence of steam and oxygen to produce gas comprising carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), hydrogen (H2) and steam (H2O). The gases can be reacted to a myriad of chemicals and fuels via the Fischer-Tropsch (FT) reaction. However, excess carbon dioxide is generated via the Water-Gas-Shift reaction during preparation of CO:H2 ratios for FT. Here, a process development is represented on a CHO phase diagram, where unique regions are identified for autothermal operations for coal conversion. Considerations are given to develop idealised processes for the production of liquid chemicals from coal which emit minimal process CO2, require minimal energy input and do not require steam. This is achieved by co-feeding coal with methane and identifying endothermic-exothermic process pairs for methane-coal dry reforming. Furthermore, it is shown that a preferred method to produce liquid fuels from coal is by first creating dimethyl ether (DME) as an intermediate, followed by the dehydration of DME to liquid fuels (gasoline range). For this route, via DME, the CO2 emission was found to be four times less than idealised CTL processes.