Hot Gas Stream Research Articles

Heavy hydrocarbon recovery with integration of turboexpander and JT valve from highly CO2-containing natural gas for gas transmission pipeline

Demand of natural gas is predicted to increase since many valuable products can be produced. Water and heavy hydrocarbon content are the key for gas pipeline facility. To meet requirement of natural gas transportation, dehydration unit (DHU) and hydrocarbon dew point control unit (DPCU) are necessary to avoid water and hydrocarbon condensation during transmission. The conventional dehydration technology, TEG contactor, can lower water content from 1,304 mg/m3 to 80.35 mg/m3 where the maximum limit of water content in natural gas is 97 mg/m3 to prevent hydrate formation. DPCU is installed to remove heavy hydrocarbon, especially C5+. Integration of JT valve and turboexpander was employed to obtain the low gas dew point. The hot gas stream that entered the JT valve was observed. The lower hot bypass gas was applied, the lower hydrocarbon dew point and the more condensate flowrate was achieved. The highest power generation can be gained at low hot gas flow ratio which also influenced the exit pressure and temperature of compressor. In pipeline simulation, the pressure and temperature drop occurred at the high hot gas rate. To examine the arrival condition, dew point curves were generated and showed that the limitation of hot gas flow ratio has to be below 0.6 to prevent heavy hydrocarbon condensation in pipeline.

Effect of oxygen on the temperatures and conversion of tobacco in an electrically heated system

The goal of Heated Tobacco products (HTPs) is to devolatilize nicotine from the tobacco by a controlled electrical heating without inducing combustion and to thereby reduce the formation of harmful and potentially harmful compounds typically related to self-sustained combustion of tobacco as in conventional cigarettes. Here, we have instrumented a commercial puffing machine and an HTP with a micro-positioning system of a thin thermocouple (0.25 mm). The puffing was conducted under N2 or air. We provide the evolution of temperature as a function of time during standard puffing cycles and along the radial position within the tobacco plugs of tobacco sticks used as part of an electrically heated tobacco system (EHTS) during operation. The temperature profiles are nearly the same for the two atmospheres showing only minor influences of oxygen (maximum temperatures: 318 °C in air, 308 °C in N2, at the end of the puffing cycle). The thermal degradation of the tobacco remains always globally endothermic due to the high flow rate of the cold air flowing the tobacco during the puffing. To better understand the differences between air or N2 puffing, we have imaged the solid residues collected in the tobacco plugs by FTIR spectroscopy. The residues are clearly differentiated whatever their radial positions between air or N2 by principal component analysis of the FTIR spectra. This result highlights similar surface oxidation phenomena of the solid residue independent of the positions. Moreover, analysis of the FTIR spectra indicates that the heating of the tobacco in the EHTS is relatively uniform along the electrically-controlled heater without signs of local hot spots. These experiments were also completed by calorimetry of tobacco upon pyrolysis or oxidation, in a 3D sensor and under a fixed bed configuration (not in the EHTS). We evidence significant exothermic phenomena from about 230 °C mainly due to gas-phase oxidation of primary volatiles in the hot gas stream. During the operation of the EHTS, such potential exothermicity is counter-balanced by strong heat losses and the high flow rate of cold air flowing through the tobacco bed during the puffing. This leads to the observed net endothermic degradation of tobacco during EHTS operation.

Reducing carbon emissions in cement production through solarization of the calcination process and thermochemical energy storage

The conceptual design of a novel cement production process has been developed during the SolCement research project. Fossil fuels used for limestone calcination are replaced by concentrated solar energy. Also, a Thermochemical energy Storage Reactor - TSR is used for transferring energy between daytime and nighttime operation. Additionally, the process enables energy recovery from waste gases and integration with carbon capture systems by isolating the rich carbon dioxide stream produced by the decomposition of limestone. A computational study simulates and compares a conventional with two different versions of the SolCement process (with and without the TSR). Simulations show that the use of a solar calciner operated at 1000 °C increases energy savings, while shifting the production capacity towards daytime improves the overall performance. The proposed scheme can lead to a 33 % reduction in fossil fuel consumption, but only a 9 % reduction in overall emissions, corresponding to 493 kg CO2/tonne clinker, since most of the carbon dioxide is produced due to limestone calcination. However, with storage and further utilization of the CO2 rich gaseous outlet stream, the predicted reduction of emissions may reach 82 %. The TSR provides 22 % of the energy required for preheating during the night operation, while simple Rankine cycles can recover from the otherwise rejected hot gas streams, 49 % and 40 % of the electrical energy required for compressing the produced carbon dioxide during daytime and nighttime operation, respectively. This results in 33 kg CO2-eq per tonne of clinker less, or an additional 0.6 % emissions reduction.

Droplet entrainment characteristics of HTPB/Paraffin blended fuels for hybrid rocket motors

Droplet entrainment contributes to excellent regression rates of HTPB/paraffin blended fuels in hybrid rocket motors, but also leads to more complicated mass transfer mechanisms in application. The liquid film dynamic behaviors and droplet entrainment mechanisms of the fuels in a windowed two-dimensional slab facility under hot gas stream were investigated using the backlight method, image processing technique and fast Fourier transform. The results showed that the liquid film with a thickness of less than 3 mm could be formed on the fuel surface, and the gas-liquid interface experienced rolling and ripple waves before evolving into singlet disturbance-crests, bags and ligaments, the sources of entrained droplets. Moreover, interfacial waves propagated periodically at frequencies within 100 Hz, which was stimulated by gas shear stress and inhibited by liquid film viscosity damping, thus the regression rate was positively correlated with the temperature and mass flux of hot gas stream, while negatively correlated with the chamber pressure and the HTPB concentration. Additionally, the burst of the main part and the rim of bag provided polarized droplet diameters among the three droplet entrainment mechanisms involving the ligament break-up and the shearing-off of crest. Therefore, the averaged droplet diameter and its coefficient of variation even reduced to 47.98 μm and 0.48 with the disappearance of bag break-up, when the HTPB content increased to 40 wt%.

Simulasi pemasangan sebuah model kerugian minor perubahan penampang di konektor loop mesin termoakustik

A custom-designed thermoacoustic engine model has been created with the open source Delta EC simulation software. The specific design of the engine lies in the part of the heat exchanger, which allows it to receive heat from the hot gas stream resulting from the combustion of low grade biomass directly. The engine model can be coupled with a loudspeaker model that functions as a liner alternator, resulting in a simple power generator engine model. In this study, further simulations were carried out to increase the total efficiency of converting heat energy into electricity from the previous model. After that a model of minor loss of cross-sectional change was also added to the model. In a certain set of engine model parameter values without minor losses, the efficiency of converting heat energy to acoustic energy is 12.76%, equivalent to the amplification of acoustic energy by a regenerator of 33.26 W. The total efficiency of the engine model in converting heat energy into electrical energy is 10.53%. After the addition of a sub-program of minor losses due to the effect of one conical segment, there was an acoustic energy loss of 0.11 W. So that the efficiency of converting heat energy to acoustic energy was reduced by 0.01% to 12.75%. As a result, relatively small change occur in the total efficiency of the engine model.

Review of Porous Ceramics for Hot Gas Cleanup of Biomass Syngas Using Catalytic Ceramic Filters to Produce Green Hydrogen/Fuels/Chemicals

Biomass gasification is one of the most promising routes to produce green hydrogen, power, fuels, and chemicals, which has drawn much attention as the world moves away from fossil fuels. Syngas produced from gasification needs to go through an essential gas cleanup step for the removal of tars and particulates for further processing, which is one of the cost-inducing steps. Existing hot gas cleanup strategies involve the particulate removal step followed by catalytic tar reforming, which could be integrated into a single unit operation using porous ceramics owing to their advantages including high-temperature resistance, high corrosion resistance, flexibility, and robust mechanical integrity. Ceramic filters have proven to be effective at filtering particulates from hot gas streams in various applications including combustion, incineration, gasification, and pyrolysis. These materials have also been evaluated and used to an extent as catalyst support to remove contaminants such as nitrogen oxides (NOx), volatile organic compounds (VOC), and in particular, tars, however, the use of these ceramic materials to remove both tars and particulates in one unit has not received much attention, although it has a promising potential to be a cost-effective hot gas cleanup strategy. Thus, this review presents the ability of catalytic ceramic filters to boost energy efficiency by converting unwanted byproducts while simultaneously eliminating PM in a single unit and is shown to be valuable in industrial processes across the board. This article presents a comprehensive and systematic overview and current state of knowledge of the use of porous ceramics for catalytic hot gas filtration applications with an emphasis on biomass syngas cleanup. In addition, a similar strategy for other applications such as combustion exhaust streams is presented. Prospects and challenges of taking this approach, and the necessary research and development to advance the novel use of reactive ceramic filters within biomass-fed thermal systems are presented. Major challenges include the low surface area of the ceramic filter media and high-pressure drop across the filter media, which can be overcome by wash coating or dip coating mechanisms and porosity tailored to meet the requirements. Owing to limited R&D efforts in this area, a systematic approach toward developing these integrated hot gas filtration systems is much needed, which will ultimately contribute to cost-effective green hydrogen production.

A design model for spiral wound heat exchangers which accounts for property variation, longitudinal heat conduction, and heat-in-leak

• A combined analytical-numerical design model for cryogenic SWHE is developed. • Analytical sizing module finds the optimum configuration of SWHE. • The effects of property variation, LHC, and heat-in-leak are investigated. • LHC impact is negligible compared to property variation and heat-in-leak. • A sensitivity analysis on the input constraint is performed. Spiral Wound Heat Exchangers (SWHEs) can be a good and reliable choice for serving as the main heat exchanger in the cryogenic gas liquefaction cycles using throttling process such as the Linde-Hampson cycle. In this application, a high pressure hot gas stream has to be cooled down via transferring heat to a low pressure cold gas in a high-effectiveness heat exchanger. Present research has been organized to develop a design model which is able to find the optimum SWHE configuration for gas liquefaction cycles. The model has to be capable of considering the important physical phenomena in the cryogenic temperature ranges, including variation of fluid properties with temperature, longitudinal heat conduction (LHC) through separating walls, and heat-in-leak. Therefore, a combined analytical-numerical design model has been developed in the present study. The design model is essentially composed of two stand-alone modules, i.e. an analytical sizing module and a numerical performance evaluation module. To develop the design model, first, the geometrical characteristics of SWHE are studied and primary geometrical parameters are recognized. Then, the analytical sizing module is developed which is able to determine the optimum values of primary geometrical parameters of SWHE minimizing the heat transfer surface area based on the input design requirements. Afterwards, a 1D finite difference numerical module is presented in which important physical phenomena can be considered in the evaluation of the thermo-hydraulic performance of all types of counter flow or parallel flow heat exchangers as well as SWHEs. Finally, the two modules are combined to construct a design model. Two examples in which the low pressure superheated vapor helium is intended to cool down the high pressure supercritical helium flowing inside the tubes are also provided to demonstrate the applicability of the proposed combined model, and also, to elucidate its sensitivity to the input constraints. It was concluded that while variations of fluid properties and the external heat fluxes due to the radiation and convection have significant influence on the performance of cryogenic SWHE, the LHC is of minor importance and can be neglected. Moreover, decreasing the shell-side allowable pressure drop from 10 kPa to 2 kPa, causes the heat exchanger length and its outside diameter to increase by 79% and 48%, respectively.

Ceramic Raw Materials from the Pulsating Hot Gas Stream

Ceramic Raw Materials from the Pulsating Hot Gas Stream

Feasibility of high-temperature electrostatic precipitation for the removal of nanoparticles: A case study on iron oxide separation at up to 800 °C

The removal of nanoparticles from hot gas streams is a challenging task. However, there is a huge potential for heat recovery from waste gas incineration, glass furnaces, ceramic, metallurgical, pyrolytic and many other high temperature processes. A prototype application is the separation of nanoparticles formed by condensation in thermal post-combustion processes, in order to achieve efficient heat recovery at high temperatures.This case study evaluates the performance of a high-temperature electrostatic precipitator (HT-ESP) between 400 and 800 °C for both discharge polarities. The tube-type ESP with 150 mm diameter and 1500 mm length is operated isothermally. Two electrode designs are tested by separating flame-generated iron oxide nanoparticles from a flue gas atmosphere. The total number concentration in the raw gas is around 2·107 cm−3 with a temperature-dependent mode diameter of 20–40 nm.Between 400 and 600 °C very high separation efficiencies around 99.998% (number-based) were found with just 1.5 s of residence time and negative polarity, using a wire discharge electrode. In fact, the separation is more efficient than at room temperature which is explained by particle charging with free electrons leading to an exceptionally high particle charge. At 700 °C and 800 °C, thermionic emissions become more relevant for ESP operation. In this range the best separation efficiencies of 99.96% and 99.5% respectively were obtained using a rod discharge electrode operated below the corona onset voltage. The specific input of energy required for 99% separation efficiency at any temperature is less than 250 J/m³.These findings clearly prove that HT-ESPs are a feasible and highly performing alternative for nanoparticle removal from hot gases at up to 800 °C.

Эффективность применения дезинфицирующего средства с использованием генератора горячего тумана

The sporicidal and bactericidal effect of hydrogen peroxide using a hot fog generator on the viability and ultrastructure of spores of the vaccine strain Bacillus anthracis STI-1 was studied using a bacteriological method and electron microscopy. The high efficiency of disinfection treatment of various surfaces has been established, which consists in the fact that within 10-20 minutes there is a complete death of test microorganism that contaminate the surfaces treated with hot fog. It has been experimentally proven that in the process of generating hot fog, the concentration of working disinfectant solution increases, which is based on the partial evaporation of moisture from solution of disinfectant during the formation of hot fog and its transfer by a stream of hot gas. Based on the results obtained, it is advisable to use hot fog generators to achieve a pronounced biocidal effect when carrying out disinfection measures in medical organizations, as well as when performing scientific research. Keywords: microorganisms, spores, bacteria, hydrogen peroxide, hot fog generator.

Novel Synthesis of Si/Rgo Anode Materials for Lithium-Ion Batteries Via Reactive Spray Drying

In recent years, lithium-ion batteries (LiB) with Si anodes attracted increasing attention, particularly due to their high specific energy density. An optimization of this characteristic is extremely important for their extended use as power source not only in portable devices but also in larger applications, such as electric vehicles.The main disadvantage of using silicon as anode material in LIBs is its high volume expansion during lithiation, which leads to various negative effects, such as pulverization, delamination, and an unstable solid electrolyte interface (SEI) [1]. This eventually results in a reduced cell performance, especially in terms of cycling stability. One promising approach to mitigate these issues is to wrap silicon nanoparticles in a graphene-like matrix via spray drying. A suitable starting material for this approach is graphite oxide (GO) [2, 3, 4].In all processes described so far, an additional time- and energy-intensive calcination step is necessary to obtain the graphene-like “reduced graphene oxide” (rGO) structure. Here, we present a new reactive spray drying process for a simplified one-step synthesis of Si/rGO composites using water as solvent. To design the reactor properly, it is necessary to understand the reaction kinetics. Therefore, the reaction is investigated by simultaneous thermal analysis (STA) in various atmospheres. We can describe the thermal decomposition of GO to rGO as a second-order reaction (Arrhenius behaviour). The STA data also show that the additional presence of water in the atmosphere due to the one-step synthesis is negligible at temperatures below 600 °C for both the reaction of GO and the unwanted additional oxidation of Si. We use crystalline silicon nanoparticles (dp ≈ 100 nm) and micrometer-sized graphite oxide prepared via modified hummers method as starting materials. Si and GO are dispersed in water and ultrasonically treated to obtain a stable dispersion. The prepared dispersion is sprayed continuously into a hot reactor (> 500 °C), where the droplets dry in the first reaction zone, forming a Si/GO composite, followed by a thermal decomposition reaction to Si/rGO in the second one. The Si/rGO particles are separated from the hot gas stream via a cyclone. To prevent oxidation, the entire system is operated in an inert atmosphere. To evaluate the electrochemical performance, the as-prepared composites are coated on a copper foil using a water-based binder mixture of styrene-butadiene rubber and caboxymethyl cellulose (SBR:CMC = 1:1). The electrodes are cycled against Li/Li+ in a half cell setup.The specific capacity after cell formation is raised from 275 mAh g-1 for GO to 335 mAh g-1 for rGO due to the reactive spray drying process. A Si/rGO composite with a Si content of 11.5 % shows a capacity of 505 mAh g-1 after the formation. Future studies will focus on further reduction of the oxygen content of rGO and an improved integration of silicon in the carbon matrix.[1] J.W. Choi, D. Aurbach, Nature Reviews Materials 2016, 1 (4), 16013.[2] M. Li et al., Journal of Power Sources 2014, 248, 721-728.[3] J. Lee, J.H. Moon, Korean Journal of Chemical Engineering 2017, 34 (12), 3195-3199.[4] Y. Huang et al., Energy Fuels 2020, 34 (6), 7639-7647. Figure 1

Reliability assessment and lifetime prediction of TBCs on gas turbine blades considering thermal mismatch and interfacial oxidation

Thermal barrier coatings (TBCs) – as porous ceramic materials – have varying lifetimes because of their unstable mechanical properties and harsh working conditions. In this paper, a probabilistic approach to quantify the risk of interface spallation in TBCs by thermally grown oxide (TGO) growth and thermal mismatch, along with a lifetime prediction method based on the critical failure probability is proposed. First, a failure criterion for TBCs is set to determine a boundary between the failure and safe region. Second, parameters relating to failure, along with the stochastic characteristics of these parameters, are analysed thoroughly. Third, the failure probability is calculated. Finally, the lifetime of TBCs on turbine blades in a hot gas stream is predicted. Under furnace isothermal cycling, the predictive failure probabilities of TBCs are 0.1% (300 cycles), 1.5% (600 cycles), and 7.49% (1000 cycles). The experiment results for turbine blades are 1.03% (300 cycles), 1.73% (600 cycles), and 5.12% (1000 cycles). Under a hot gas stream, the maximum failure probabilities of TBCs after 200, 300, 500, and 1000 h are 40%, 45% 50%, and 70%, respectively. The lifetimes of TBCs are 273, 332, 406, and 523 h if the critical area ratio of the metal substrate exposed to the hot gas is 5%, 10%, 15%, and 20%, respectively.

Marker Compounds Adsorbed on Dust Particles (PM10) Sampled According to Standard EN 12341 in the Outdoor Air Near the Cement Plant

Compounds adsorbed onto PM10 in the air near the cement plant were determined. Several side reactions that occur in the hot flue gas stream at the same time as the actual main reactions are also possible. This leads to the formation of traces of organic nitrogen compounds. For the GC/MS determination of polar organic compounds silylation as a derivatization method was used. Organic compounds detected are derivatives of sugars, sugar alcohols, and mono-, di- and tri-carboxylic acids. The composition is characteristic for pollution of the urbane atmosphere. Nitrogen organic compounds formed during the urea thermolytic process in hot cement kiln gases represent parabanic acid, 5-hydroxyhydantoin, 4,5-dihydroxyhydantoin, 5-oxoproline, and cyanuric acid. The inorganic part of aerosols detected includes oxyanions of sulfamic acid, sulfate, sulfite, phosphate, and vanadate(V) with ammonium as a cation. Chemical compositions of particles are crucial to assess the health impacts since the biological responses to aerosols are not always linked with major constituents but rather with toxicologically potent minor components.

A flat-plate spiral-channeled membrane heat exchanger for methane dehumidification: Comparison of kraft paper and thin-film composite membrane

Membrane heat exchangers were used for moisture and heat recovery from a hot and humid natural gas stream in indirect contact with an air stream. A plate membrane module with spiral channels on each side was designed to configure gas and air streams in co-current and counter-current flow. Two types of membranes, a commercial kraft paper, and a laboratory-made thin-film composite membrane, were used as the module core. The thermal efficiency and the water recovery from the humid gas were calculated and compared under different operating conditions. At a unit flow ratio of air/gas, the greatest effectiveness was achieved at a methane flow of 100 cm3/min, but water recovery increased at higher gas flows. For the counterflow configuration, an air/methane flow ratio of 2 was sufficient to achieve the highest total effectiveness and water recovery; however, larger air/gas ratios were beneficial to improve heat and moisture transfer for the co-current configuration. The highest water recovery by the kraft paper and composite membrane was achieved (approximately 15 mgH2O/cm2.h) for the input gas with the highest humidity. The dehumidification performance of kraft paper as a porous and hydrophilic membrane was slightly better than that of the composite membrane containing a dense hydrophilic polymer thin film in most cases. A relatively low heat transfer coefficient was found for the module, which was increased by using higher gas flow rates at higher humidity conditions.

Pyrolysis and Combustion Characteristics of Leaf-like Fuel under Convection and Radiation Heating

ABSTRACT The heating of a fuel element representing a vertically oriented living manzanita leaf was computationally investigated. The computational conditions resembled a previous experimental setup where manzanita leaves were exposed to an upward stream of hot gases supplying the convective heating and a radiant panel providing the radiative heating. The simulations confirmed the experimental observations as to what the impact of the heating mode is on ignition. The convection-only and combined convection and radiation modes resulted in ignition and flaming whereas the radiation-only mode did not. The leaf mass loss versus time, the heating pattern of the leaf, the ignition time, and the flame spread pattern in simulations were in good agreement with the experimental findings. Furthermore, the simulations revealed the impact of the heating mode on thermochemical evolution of the leaves, formation of boundary layers on the leaf faces, ignition, and formation and propagation of the flame. An analysis based on the postprocessing of the numerical data showed that except for the first second, the fuel may be considered thermally thin. Ignition occurred near the lower corners of the leaf, which were exposed to the highest heat fluxes compared to the rest of the leaf. In the combined heating mode, the fuel pyrolyzed faster and ignition occurred earlier because the overall heat flux was larger. The computed heat release rates per unit volume showed that the flame is formed in the lower part of the leaf, and then moves and propagates upward. The computations revealed that the overall heat release by combustion of pyrolysis gas was not sensitive to the mode of heating.

Experimental study for choosing an active substance in a microcracks detection system in the turbine blade

In this work, an experiment was carried out that allows choosing an active substance in the system for early detection of microcracks in the blades of gas turbine engines. The aim of the work is to compare several active substances by measuring the signal generated by each of them at the same temperatures and concentrations of the active substance. A current signal is obtained by applying a voltage between two electrodes placed in a stream of hot gas. The strength of the electric current arising between the electrodes in the hot gas flow depends on the ionization of the gas caused by the active substance. The current signal is the main criterion for choosing an active substance. A study was also carried out on the effect of gas temperature on the strength of the signal caused by the active substance. This experiment is one of the main stages in the creation of a system for detecting microcracks in gas turbine blades.

Influence on the Electrical Efficiency of a Hybrid MGT-SOFC-System by μ-fogging in a-Two-Staged Compressor System

Hybrid combinations of solid oxide fuel cell and recuperated micro gas turbines can convert the chemical energy of hydrocarbon-based fuels in electrical energy with high electrical efficiency. With an integrated and improved cycle management, more than 70% of the energy content of the fuel could be converted. Therefore, the systems are highly suitable for the Power-To-Gas conversion. In particular, a pressure charging of the SOFC fuel cell leads to an increase in stack performance. By a downstream turbo set, after residual fuels are intentionally oxidized with an afterburner, additional electrical energy can be gained from the expansion of the hot exhaust gas stream and the overall efficiency can be increased. In order to increase the electrical efficiency of the system, it is proposed, to ensure the required compression of the process air in particular by a-two-staged turbo compressor with an intermediate cooling system. By thus achievable reduction of the dissipation of the compressor and by targeted condensation of finest drops in front of the second compressor stage affected by intermediate cooling, an increase in efficiency of the system is possible. This is achieved by targeted cooling of the process air behind a low pressure compression, so that it is saturated over 100% relative air humidity. As a result, a slightly supersaturated airflow is available for the second compressor stage, which enters the compressor after heat removal via an intermediate cooling having a small number of microdroplets. Therefore, the condensed water evaporates again by the heat of compression in the second stage and the compressed flow ultimately enters the recuperation at a lower temperature than during normal compression. Thus, more heat can be recovered within the recuperation system. Therefore, the electrical energy of the system can be produced having higher efficiency, because the heat dissipation of the overall system decreases. In this article it is presented, how such a process is thermodynamically modelled and how a technical realization can be built after optimization by simulations. Finally, in this study, the process-influencing factors are analyzed to show the highest possible electrical yield of such a system.

A computational study of burning of vertically oriented leaves with various fuel moisture contents by upward convective heating

Pyrolysis and combustion of a solid fuel representing a vertically oriented leaf of manzanita (Arctostaphylos glandulosa) were computationally investigated. Various fuel moisture content (FMC) values corresponding to four manzanita leaf treatments studied experimentally by others, were considered. The fuel was exposed to an upward stream of hot gases in a computational configuration resembling the experimental setup where leaves were burned. Time evolution of the normalized mass of the leaves was used to validate the simulations against the experimental data. Examining the time history of heat release rate confirmed that increasing FMC delays ignition time. The ignition times in simulations were in good agreement with those determined by empirical correlations for all FMCs. The burnout times were somewhat shorter in simulations than the empirically-determined ones. Simulations showed that thermal, momentum and concentration boundary layers are formed on the leaf faces. The boundary layers played a significant role in heating, and subsequent moisture evaporation and pyrolysis of the leaves. Within the leaves, an evaporation front propagating inward from the edges, was detected. A considerable amount of liquid moisture remained in the leaf after ignition. Accumulation of water and fuel vapor around the leaf, as a consequence of the leaf moisture evaporation and pyrolysis, displaced oxygen, decreasing the oxygen concentration therein. A post ignition time was characterized by a high temperature zone around the leaf. At such times, oxygen consumption by gas phase combustion resulted in a noticeable decrease in oxygen concentration around the leaf. The flaming pattern after ignition was qualitatively in agreement with previously reported experimental observations.

Insights on the role of primary and secondary tar reactions in soot inception during fast pyrolysis of coal

In the present work fast pyrolysis of coal in N2 and CO2 atmospheres was studied in a drop tube reactor (DTR) and in a heated strip reactor (HSR). In the DTR the volatiles generated by coal pyrolysis were entrained in a hot gas stream and were collected at the reactor outlet by tar traps. In the HSR, the volatiles were ejected from the hot coal particles into a cool environment and the condensable species, including primary tar, deposited and/or condensed on a glass bridge located above the heated strip. The composition of tars produced in the two reactors was compared to study the role of gas tar reactions in soot inception, and reference compounds for each class of tar species produced were identified.In the DTR the formation and growth of polycyclic aromatic hydrocarbons (PAH) were found higher than in the HSR. Soot formation occurred only in the DTR, being negligible in the HSR.It was concluded that the hot gas environment of the DTR favours secondary tar reactions, formation of PAH and eventually soot, while in the HSR this path was prevented due to prompt cooling down of volatiles. The presence of large concentration of CO2 in the pyrolysis atmospheres further promoted formation of heavy PAH and soot in the DTR, but not in the HSR, where the cooler environment limits soot-CO2 reactions in the gas phase.

Erosion Testing of Environmental Barrier-Coated Ceramic Matrix Composite and Its Behavior on an Aero-Engine Turbine Vane Under Particle-Laden Hot Gas Stream

Abstract Ceramic matrix composite (CMC) has better durability at high temperature and lower material density, as compared to nickel-based superalloys which have been the standard material for hot section components of aero-engines. Among the CMC materials, SiC–SiC CMC is especially promising with its superior mechanical property at a higher temperature. It, however, inevitably needs environmental barrier coating (EBC) to protect the substrate against oxidation. The EBC also needs to have other functions and to meet various requirements. One such very critical requirement is the resistance to sand erosion, although the issue has not been investigated well so far. The primary contribution of this work is to reveal the erosion resistance of the CMC + EBC material with wind tunnel test data of good quality and to demonstrate what erosion behavior the material exhibits in a turbine cascade under particle-laden hot gas stream. In the present work, erosion tests were first carried out in a testing facility with an erosion media of 50 μm silica sand. The tests were conducted under a flow velocity of 225 m/s and a temperature of 1311 K to simulate typical aero-engine conditions, and impact angles of 30, 60, and 80 deg were investigated. The obtained data showed a typical brittle erosion mode, where the erosion rate had a positive dependence on the impact angles. A typical erosion model, Neilson–Gilchrist model, was applied to correlate the data, and the model was shown to have a good agreement with the experimental data once it was properly calibrated. Then, the numerical computation solving particle-laden flow was carried out to predict three-dimensional flow field and particle trajectories across the target turbine cascade. The erosion profile along the airfoil was calculated based on the obtained trajectories and the calibrated erosion model. The trajectories showed that the particles mostly impinged the airfoil pressure surface first and then the rebounded particles attacked the opposite suction surface as well. Accordingly, the predicted erosion profile showed a broad erosion band across the pressure surface and also some slight erosion peak at around the mid-chord of the suction surface.