Hot Combustion Gases Research Articles

Investigation of Combustion and Thermal-Flow Inside a Petroleum Coke Rotary Calcining Kiln With Potential Energy Saving Considerations

Calcined coke is a competitive material for making carbon anodes for smelting of alumina to aluminum. Calcining is an energy intensive industry and a significant amount of heat is exhausted in the calcining process. Efficiently managing this energy resource is tied to the profit margin and survivability of a calcining plant. To help improve the energy efficiency and reduce natural gas consumption of the calcining process, a 3D computational model is developed to gain insight of the thermal-flow and combustion behavior in the calciner. Comprehensive models are employed to simulate the moving petcoke bed with a uniform distribution of moisture evaporation, devolatilization, and coke fines entrainment rate with a conjugate radiation-convection-conduction calculation. The following parametric studies are conducted: rotation angles, tertiary air injection angles, devolatilization zone length, discharge end gas extractions without injecting natural gas, variations of coke bed properties (thermal conductivity and heat capacity), and coke bed sliding speed. A total of 19 cases have been simulated. The results of studying the effect of tertiary air injection angles show that employing 15 deg tertiary air injection angle provides the best calcining condition than using 30 deg and 45 deg injection angles by achieving a higher coke bed temperature and less coke fines entrainment and attrition rate. In an attempt to reduce natural gas consumption, employing gas extraction at the discharge end successfully draws the hot combustion gas from the tertiary air zone towards the discharge end without burning natural gas. The coke bed temperature between 6 and 21 m from the discharge end is successfully raised 10–100 K higher, but discharge end temperature is reduced 150 K without burning natural gas. The extracted gas at 1000 K is too low to be returned to the kiln, but it could be used to preheat the tertiary air.

GTL (Gas To Liquid) and RME (Rapeseed Methyl Ester) combustion analysis in a transparent CI (compression ignition) engine by means of IR (infrared) digital imaging

In the present paper, (infrared) IR measurements were performed in order to study the behaviour of biofuels combustion in a transparent Euro 5 diesel engine operating in premixed mode. (Commercial diesel fuel) REF, (Gas To Liquid) GTL and (Rapeseed Methyl Ester) RME biofuels have been used. An elongated single-cylinder transparent engine equipped with the multi-cylinder head of commercial passenger car and (common rail) CR injection system was used. A sapphire window was set in the bottom of the combustion chamber, and a sapphire ring was placed in the upper part of the cylinder. Measurements were carried out through both accesses by means of high-speed infrared digital imaging system. IR camera was able to detect the emitted light in the wavelength range 1.5–5 μm. Infrared imaging allowed acquiring larger amount of information than UV (ultraviolet) and visible cameras. In particular the IR camera was used for the characterization of injection and combustion process. Analysing the IR images, it was possible to identify clearly the seven jets of vaporized fuel that react with air in the bowl. During the late combustion phase, the IR image showed a good capability to follow the hot burned gas both in the bowl and above the piston. The IR camera has shown high sensibility permitting to follow carefully the soot oxidation process within the cylinder. The GTL shows an advance of about 8° crank angles in the evolution of combustion process with respect to the RME. On the contrary a longer chemical activity has been detected for the latter biofuel. Finally, the IR camera was revealed very useful tool to characterize the combustion process for long time allowing high quality of the results. Images of the reactions that happen in the combustion chamber and above the piston head were clearly acquired even if the optical windows were obscured by the soot produced from the previous combustion cycles.

Improvement of the adhesion properties of silicone rubber by the incorporation of silane‐modified montmorillonite

AbstractA silicone rubber precursor was amended by the incorporation of γ‐aminopropyl triethoxysilane (APS) into siloxane to prepare an elastomeric thermal insulator adhering to the isocyanate‐group‐containing liner sheets, which are actually used to envelop rocket propellants. This improved adhesion may protect the liners of the rocket motor cases efficiently against the hot combustion gas. Clay was modified by cationic exchange with an amine compound, and the resulting clay was further treated with APS and N‐(2‐aminoethyl)‐3‐aminopropyl trimethoxysilane to introduce amine groups onto the surface of the clay to further improve the adhesion of the silicone rubber to the liner. The neat and modified clays were compounded with the APS‐amended silicone rubber [room‐temperature vulcanizate (RTV)]. The effects of the clay modification on the adhesion properties were explored. The peel strength between the liner and the room‐temperature silicone rubber (RTV) based on siloxane was 0, whereas the peel strength increased to 3.7 N/cm when the silicone rubber was amended with APS. The peel strength between APS–RTV and the liner was lower than 3.7 N/cm when clay was added, whereas the peel strength became higher than 5.7 N/cm so that APS–RTV could not withstand the peeling force and was torn off before the delamination when the amine silane modified clay was added instead of clay. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Determination of Heat Release Rate Disturbances in Unconfined Flames Based on Fluctuations in the Travel Time of Ultrasonic Waves

The article presents a new method to measure heat release rate disturbances from flames when optical access is limited. The technique is based on the determination of the travel time of ultrasonic waves propagating through the flow. The link between heat release rate and sound travel time disturbances depends on the configuration considered. An expression is established here for the case of unconfined premixed flames driven by buoyancy forces associated with the Kelvin–Helmholtz instability formed by the interaction between accelerating hot burned gases and cold ambient air at rest. The system and the principle used for the determination of the sound travel time are then presented and validated under nonreacting conditions. Effects of the main parameters on the precision of this detection technique are examined experimentally. Measurements in reacting conditions are compared to heat release rate data obtained with another technique based on the chemiluminescence emission. A good agreement is obtained between both signals for the different cases explored demonstrating the sensitivity of the proposed technique.

Degradation of Microstructure after Service in ZhS6k Superalloy with Diffusive Aluminide Coating

This paper presents the degradation of hollow turbine blades made of ZhS6K nickel-based superalloy after service in DV2 aero engines. The blades were coated with a diffusive aluminide coating (Al-Si) to improve the oxidation and hot corrosion resistance. Turbine blades work under extreme conditions and a complex state of stress. During service, creep and fatigue of various natures take place. The interaction among hot combustion gases causes oxidation of the surface layer and hot corrosion and micro cracking of the coating. Moreover, changes in morphology of the γ’ phase just under the coating and transformations of the primary carbides take place. The factors limiting the lifetime of turbine blades are the quality of the aluminide coating andmicrostructure of the superalloy, depending on the service parameters—the temperature and the duration of service. It was found that exposure to high temperatures above the critical value for several seconds substantially decreased the engine power and its durability. In this paper, analysis of the microstructure, chemical composition and phase composition of the turbine blades after service were carried out. Evaluation of the extent of degradation was performed using the scanning electron microscopy (SEM), energy dispersive X-ray microanalysis (EDS) and electron backscatter diffraction (EBSD) techniques. The EBSD technique was used to analyse the phase composition in micro areas, especially to identify carbides before and after transformations.

Application of in situ oxidation-resistant coating technology to a home-made 100 kW class gas turbine and its performance analysis

Abstract An axial type 100 kW class gas turbine power generation system equipped with an additive supply system was fabricated and tested for the performance evaluation experimentally and analytically, in order to confirm the advantage of in situ oxidation-resistant coatings on gas turbine components toward the performance of a gas turbine power generation system directly. The gas turbine was operated up to the rated speed of 74,000 rpm, and to the turbine inlet temperature (TIT) of ∼1200 °C. At the early stage of this test operation, an oxide film precursor (tetraethylorthosilicate/methanol mixture, 10 vol.%) was fed into the combustion chamber by the additive supply system to in situ deposit silica based layers and thus to protect the metallic components from hot combustion gas during operation. After the test operation, in situ deposited silica layers were observed on the surface of the combustion chamber, turbine nozzles and rotor blade. Due to these protective layers the gas turbine could be harmless tested at TIT = 950 °C, much higher than its design temperature of 850 °C. According to the performance analysis, a TIT increase of 100 °C was expected to be accompanied by ∼5% increase in the turbine rotation speed by consuming more fuel and air by 22% and 8%, respectively. As a result, the power output increased by 42% and the thermal efficiency from 12% to 14%. This result was well accorded with that of empirically obtained, indicating that no noticeable impacts on the performance due to in situ deposited layers on the components.

A sulfuric acid management strategy for the production of liquid hydrocarbon fuels via catalytic conversion of biomass-derived levulinic acid

In this study, we first develop an integrated strategy for the catalytic conversion of lignocellulose into liquid fuels based on the production of levulinic acid (LA) followed by its hydrogenation to γ-valerolactone (GVL). Our integrated strategy involves a novel catalytic conversion process employing alkylphenol-based separation to extract LA from the sulfuric acid containing aqueous solution following the sulfuric acid catalyzed deconstruction of cellulose. To minimize utility consumption, we perform heat integration, while the remaining heating requirement is satisfied by the combustion of residual biomass. Hot combustion gases are also used to generate electricity, which meets the electricity requirement of the process, while the excess electricity is sold to the grid. We perform a technoeconomic analysis for the alkylphenol-based strategy and compare its economics with a previously reported strategy, in which butyl acetate was used as an extractive solvent to separate GVL from sulfuric acid following the LA hydrogenation step. With some improvements in the process configuration, the alkylphenol strategy leads to a minimum selling price (MSP) of $4.40 per gallon of gasoline equivalent (GGE) for compatible biofuel components, whereas the butyl acetate strategy leads to a MSP of $4.68 per GGE. We show that the alkylphenol strategy becomes a significantly better choice when the catalyst lifetime for the hydrogenation of LA becomes less than 6 months.

Drying medium - modelling and process evaluation

Natural gas is used as a heat source in the majority of modern drying plants in agriculture. The input gas is a mixture of natural gas and atmospheric air. With burning, the composition of this mixture changes. Drying medium is a mixture of hot combustion gases from natural gas and atmospheric air added. The thermic parameters of natural gas and atmospheric air are permanently constant. The authors present their method of the calculation of thermodynamic parameters of the drying medium. They elaborated two computer programmes in Q-Basic for the calculation related to the drying medium with temperatures in the range 100–200°C.

Full-scale experimental and numerical studies on compartment fire under low ambient temperature

Abstract A fire experiment with wood crib was conducted in a concrete building under low ambient temperature of −10 °C to explore fire development and temperature distribution. The concrete building consists of a two-storey compartment with the size of 9.0 m by 5.0 m by 4.8 m high and a four-storey stairwell with the size of 5.0 m by 2.4 m by 10.0 m high. The fuel mass loss rate and temperatures at different positions were measured. Two fire cases, with different assumed ambient temperatures of −10 °C and 20 °C respectively, were then simulated by using FDS software to investigate the effect of ambient temperature and compare with the experimental results. The numerical results show that the calculated heat release rate is in reasonably good agreement with the measured full-scale result before water suppression. The calculated temperatures in the hot combustion gas layer at different positions agree also very well with the measured values. However, the measured fresh air temperature at the floor level near the fire source is higher than the calculated value. This discrepancy may partly depend on measuring errors as analyzed in the paper.

Passive control of premixed lifted flame in a dump combustor

This paper reports an experimental investigation of the dynamics of premixed lifted flame inside a dump combustor with tapered exit. The pressure and heat release measurements along with flame visualization were carried out to understand the combustion phenomenon inside the combustion chamber. High levels of combustion driven oscillations in pressure were observed in the lifted flame due to the coupling of the heat release and flow oscillations. The dominant mode of oscillations was seen to be governed by the convection of hot burned gases into the combustion zone due to flow reversal from the exit section. The fluctuations of pressure decreased in the presence of a stabilizing rod due to mistuning of heat release and pressure oscillations resulting in a decrease in their correlation and coupling as the dominant frequency of oscillation in the presence of rod resembled the frequency of vortex shedding from the rod. Consequently, a 4dB decrease in overall sound pressure level could be achieved by passive control in the dump combustor.

Degradation Characteristics of Inconel738LC with Thermal Exposure

Gas turbine components operated by hot combustion gas undergo material degradation due to the thermal cycle by daily startup and shutdown. The failure mechanism of the hot gas components is accompanied by degradation in the properties of high temperature strength and creep rupture time. Many hot gas components in gas turbines are made of Ni-based superalloy because of their high temperature performance. In this work, we survey the time and temperature dependent degradation of Ni-based superalloy. We prepared specimens from Inconel738LC that were then exposed at 871~982°C in 1,000~5,000hours. We carried out stress-rupture tests and microstructural investigation.

Effects of High Temperature Deformation and Thermal Exposure on Microstructure and Mechanical Properties of Co-Based Superalloy

The gas turbine components operated in hot combustion gas undergo material degradation due to the thermal cycles. The failure mechanism of the hot gas components would be accompanied by material degradation in the properties of high temperature strength and creep rupture time. Many stationary parts in gas turbine are made of Co-based superalloy because of their high temperature performance. In this work, we survey the time and temperature dependent degradation of Co-based superalloy. We prepared the specimens of Co-based superalloy ECY768 that are exposed at 871 and 982 oC in 1000 ~ 5000 hours. We carried out the mechanical test and microstructural observation.

Solid particle erosion of thermal spray and physical vapour deposition thermal barrier coatings

Thermal barrier coatings (TBC) are used to protect hot path components of gas turbines from hot combustion gases. For a number of decades, in the case of aero engines TBCs are usually deposited by ...

Investigation of nitrogen-diluted syngas non-premixed flames measured by planar laser-induced fluorescence of hydroxyl and particle image velocimetry

In order to investigate the effects of nitrogen dilution on combustion behaviour of syngas flames, a model combustor with optical access for swirl non-premixed flames was developed. Experimental results from planar laser-induced fluorescence (PLIF) of OH and particle image velocimetry (PIV) are presented. The syngas consists of hydrogen and carbon monoxide of volume fraction ratio kept at 0.78. Up to 60 per cent (by volume) of nitrogen was added into syngas, as well as reference fuels including methane, hydrogen, and carbon monoxide, for dilution. Flow fields obtained by PIV reveal that the averaged typical swirling flow structure is not influenced by dilution content, which has more effect on turbulence intensities in recirculation zones and shear layers. Additionally, analysis of reaction zones and regions of burnt gas from OH-PLIF measurement shows that although syngas flame burns closer to fuel spray exit than methane, the latter shows more combustion stability, probably because of the different stabilization mechanisms for these two flames. With less support from hot burned gases in recirculation zones, the content of hydrogen plays a crucial role in syngas flame stabilization. Experimental results also imply that the increase of dilution content in fuel leads to less flame opening angle and thinner flame base.

PENETRATION OF A SHOCK WAVE IN A FULLY SUPERSONIC FLAME FRONT WITH THE FORMATION OF AN EXPANSION FAN

In a previous paper (3) was treated the ,,simple penetration of an incident shock wave through a fully supersonic flame front in the space of the hot burnt gases, situated in a supersonic two-dimensional flow of an ideal homogeneous /combustible gas was treated in a previous paper (3). In the present paper takes into consideration, a configuration, in which an expansion fan is produced, is take into consideration the shock polar and expansion polar are used for the analyze of the interference phenomena.

Discussions of some myths and concerned practices of film cooling research

This paper focuses on discussing four myths and concerned conventional practices of film cooling research guided by a series of computational simulations. The issues that have been discussed include: (a) the film cooling effectiveness ( φ) is given a constant (0.6) to calculate the heat flux ratio HFR = q ″ / q o ″ between film-cooled and no-film cases; (b) the adiabatic wall temperature is the driving temperature of film cooling; (c) the adiabatic film heat transfer coefficient can be obtained from an isoenergetic film experiment ( T j = T g); (d) using a heated surface can provide a simplified approach to simulate the film-cooling condition. The result shows that the adiabatic wall temperature is not always the driving temperature (i.e. T aw is not always larger than T w), but T aw does act well as the reference temperature in correctly predicting the heat flux direction and giving an always positive adiabatic film heat transfer coefficient. Using a constant value for φ is questionable and may lead to un-realistic or false HFR. The conventional equation of HFR was not theoretically exact and can lead to an error of up to 20%. A revised HFR equation is provided in this paper. The dominant energy passage in turbine airfoil film cooling is always from hot combustion gas flows into the airfoil; therefore, employing a heated wall as a boundary condition with hotter main stream flow and cold film injection to simulate the actual film cooling condition is found to be fundamentally questionable. A conjugate simulation that includes wall heat transfer and internal flow cooling shows that reversed heat transfer from blade to gas that gives a negative HFR is possible, due to the heat conduction from the downstream hotter region into the near film hole cooler region.

220203 エタノール噴霧の既燃ガスジェット着火現象(OS12 燃焼工学の新展開,オーガナイズド・セッション)

In this study, we experimentally investigated the effects of burnt gas jet ignition on ethanol spray combustion using a constant volume combustion vessel with a sub chamber. The ignition and combustion phenomena were observed by using a high-speed video camera, and combustion pressure history was measured as well. In case of burnt gas jet ignition, compared with a conventional spark plug ignition, stronger luminous flames were observed, and rate of pressure rise and maximum overpressure much increased. Moreover, it was confirmed that measured HCHO concentration of the burnt gas in the combustion vessel remained at low level although the amount of ethanol related to combustion reaction increased. It is mainly due to the strong turbulent mixing effects of the hot burnt gas jet and the spray flows.

Efficiency analysis of radiative slab heating in a walking-beam-type reheating furnace

Abstract The thermal efficiency of a reheating furnace was predicted by considering radiative heat transfer to the slabs and the furnace wall. The entire furnace was divided into fourteen sub-zones, and each sub-zone was assumed to be homogeneous in temperature distribution with one medium temperature and wall temperature, which were computed on the basis of the overall heat balance for all of the sub-zones. The thermal energy inflow, thermal energy outflow, heat generation by fuel combustion, heat loss by the skid system, and heat loss by radiation through the boundary of each sub-zone were considered to give the two temperatures of each sub-zone. The radiative heat transfer was solved by the FVM radiation method, and a blocked-off procedure was applied to the treatment of the slabs. The temperature field of a slab was calculated by solving the transient heat conduction equation with the boundary condition of impinging radiation heat flux from the hot combustion gas and furnace wall. Additionally, the slab heating characteristics and thermal behavior of the furnace were analyzed for various fuel feed conditions.

Predicting toxic gas concentrations at locations remote from the fire source

AbstractA toxicity model capable of predicting toxic gas concentrations within fire enclosures utilizing the concept of the local equivalence ratio (LER) was recently developed. This paper describes an enhancement of the original model that improves its accuracy in predicting species concentrations at remote locations from the room of fire origin. The enhanced technique involves dividing the CFD computational domain into two regions for species calculation, a control region (CR) and a transport region. Toxic gas concentrations in the CR are calculated using the formulation developed in the earlier study whereas in the transport region, gas concentrations are determined as a result of the mixing of hot combustion gases with fresh air. The concept of a critical equivalence ratio, which is derived from the effective heat release rate (or combustion efficiency) of the fire scenario being simulated, is introduced to perform the domain division. Predictions of temperatures and species concentrations at various locations made by the new model are compared with the results from two experiments. Compared with the earlier model, the modified model provides considerable improvements in the predictions of toxic species levels. Copyright © 2010 John Wiley & Sons, Ltd.

가스터빈 단결정 블레이드 사용품의 특성변화

The material properties of gas turbine components change during the daily start/stop thermal cycle because of exposure to the hot combustion gas. Recently, single-crystal Ni-based superalloys have been used to manufacture many hot-gas components for gas turbines. However, the user needs to depend on the manufacturer for maintenance issues because of the lack of data required for predicting blade life and material degradation. In this study, we investigate the time-dependent degradation of first-stage blades at various operating facilities to collect the basic data for life assessment and damage analysis. The blade material is a single-crystal Ni-based superalloy, CMSX-4, and the EOH (equivalent operating hours) are 25,000 and 52,000, respectively. We prepared the test specimen directly from used blades and carried out mechanical tests and microstructural observations.