Combustion Test Rig Research Articles

Experimental investigation of combustion characteristics of ammonia with sub-bituminous coal in a pilot circulating fluidized bed combustor

Recent research on power plant technology has focused on employing ammonia as a supplementary fuel with coal to reduce carbon dioxide emissions from coal-fired power plants. However, most of this research has concentrated on pulverized coal systems, with fewer studies on circulating fluidized bed (CFB) combustion systems. Additionally, no research has analyzed combustion and environmental impacts under varying operational conditions with a fixed ammonia co-firing ratio. This study advances the development of coal–ammonia co-firing technology for use in CFB power plants by conducting experiments on a 50 kWth CFB combustion test rig. The co-firing characteristics were evaluated by progressively increasing the ammonia co-combustion rate to 20%, calculated on a high calorific value basis relative to sole coal combustion. Furthermore, this research explored the variations in operational conditions during 20% ammonia co-firing to assess their effects on the temperature distribution within the combustor and the composition of the exhaust gases. The findings elucidate the combustion efficiency, thermal behavior, and emission profiles associated with coal–ammonia co-firing, thereby guiding the optimization of operational strategies to minimize the carbon footprint of CFB power plants.

Two-Photon Planar Laser-Induced Fluorescence Of Near-Wall CO During The Interaction Between A Flame And A Cooling Air Film

Reducing the anthropogenic pollutant emissions is a major concern in the aeronautical community. Implementing high-power density core engines made of lighter materials would undoubtedly increase the thermal efficiency and reduce CO 2 emissions. Nevertheless, near-wall combustion processes will become significant, raising concerns regarding thermal management. As a result, walls in aero-engine combustors are commonly cooled, but it also introduces more complex physical phenomena associated to pollutant formation during flame-cooling air interaction (FCAI). This experimental study aims at elucidating the role of the cooling air film on CO emissions during FCAI. The experiments are conducted in an atmospheric pressure and optically-accessible lab-scale combustion test rig dedicated to near-wall combustion. It generates a lean premixed turbulent methane/air V-shaped flame, with one branch of the flame that interacts with an oil-cooled stainless-steel wall. A splash-cooling plate system enables to generate a momentum-controlled parietal cooling air film. The novelty of this study is to develop and implement planar laser-induced fluorescence of the CO molecule (CO-PLIF), complemented by planar laser-induced fluorescence of the OH radical (OH-PLIF) as well as global CO emissions in the exhaust gases. Results show that the excitation of the Hopfield-Birge system enables to detect the AN ngström bands and the third positive system. However, significant interferences with C 2 and CN emissions are highlighted, being more pronounced in rich combustion conditions, and originating from the incomplete fuel oxidation as well as the high energy density of the two-photon excitation process. A broadband collection strategy of the AN ngström bands is selected, since these interferences are limited in lean combustion regimes. The analysis of the flame dynamics indicates that the increase of the cooling air film momentum shifts the reactive flow away from the wall, but also controls the flame wrinkling through modified aerodynamics. As a result, the flame is not influenced anymore by thermal quenching processes, and can effectively burn further away from the wall. Global emission measurements indicate an increase in CO when the cooling air film momentum increases. While thermal quenching favors a faster oxidation downstream of the flame, the establishment of the cooling air film leads to a longer flame with more production areas. CO-PLIF imaging concurs this phenomenon, with a CO distribution all along the wall when the cooling air film is well established.

Lifetime Extension of Atmospheric and Suspension Plasma-Sprayed Thermal Barrier Coatings in Burner Rig Tests by Pre-Oxidizing the CoNiCrAlY Bond Coats

Lifetime Extension of Atmospheric and Suspension Plasma-Sprayed Thermal Barrier Coatings in Burner Rig Tests by Pre-Oxidizing the CoNiCrAlY Bond Coats

A novel method for stable thermoacoustic system design based on exceptional points - Part I: Conceptualization

In this conceptual study, we introduce the novel EPTD (Exceptional Point-based Thermoacoustic Design)-method for the design of stable thermoacoustic systems: dampen the entire thermoacoustic spectrum by shifting the EP towards smaller growth rates. For this, we first study a generic, linear parametric eigenvalue problem (LPEP) of a non-hermitian matrix featuring an EP. We derive analytical solutions for the eigenvalues and the EP as a function of arbitrary system parameters in the LPEP. Subsequently, we formulate a method for shifting the eigenvalue spectrum by relocating the EP in the complex plane. For this method, we show that not only the location of the EP in the complex plane is of relevance, but also the exceptional parameters, as they enforce the relations of the EP and the eigenvalues in the spectrum. When fixing these while shifting the EP, we demonstrate that the entire eigenvalue spectrum preserves its original shape, such that all eigenvalues only shift with the exact amount the EP was shifted. The derivation and the analysis of the relation between EP and spectrum generally holds for arbitrary system parameter combinations. Additionally, we showcase results for an exemplary configuration, i.e., a configuration with arbitrarily chosen and fixed parameters. We subsequently introduce a generic, thermoacoustic system, a Rijke tube, and study it by means of (semi-) analytical methods to confirm that the findings from the analysis of the LPEP also transfer to thermoacoustic systems. The configuration is modeled as a thermoacoustic network that allows to trace back the full system modes to their respective origins, which are either of acoustic or intrinsic thermoacoustic (ITA) nature. After identifying an EP that is formed by acoustic and ITA driven mode branches, we study its impact on the eigenfrequency spectrum and how this shift impacts the EP’s relation to the mode origins and the remaining eigenvalues. Similar to the analysis of the LPEP, the results show that not only the EP’s location in the CP is of relevance, but also its exceptional parameters: shifting the EP without consideration of the exceptional parameters leads to unsatisfactory shifts of the associated spectrum that becomes distorted. With this, we formulate the EPTD-method: shift the EP towards smaller growth rates while enforcing a well-defined relation between the mode origins and the EP by keeping the exceptional parameters constant. We show that this constraint preserves the relation between EP and mode origins when shifting the EP and finally demonstrate the practicality of the proposed method. For this, we shift the EP of the reference Rijke tube configuration towards smaller growth rates and simultaneously show that the resulting spectrum preserves its overall shape. While this paper covers the derivation and demonstration of the proposed EPTD-method based on a generic configuration, we consider a more complex combustion test rig, featuring a turbulent confined swirl flame, in part II of this study (M. Casel & A. Ghani, Combust. Flame, 2024), where we elaborate on consequences regarding the larger system parameter dimension as well as the existence of two EPs in the spectrum.Novelty and Significance statement:Thermoacoustic instabilities are actively researched for more than half a century. Despite this effort, scientifically sound strategies to design thermoacoustically stable combustors do not exist today. We present a novel method on a conceptual level that takes into account the latest discoveries in our field (e.g. ITA modes between 2014/2015 and Exceptional Points in 2018), connects them into one fast and robust numerical framework and opens the path to design the thermoacoustic stability map. This framework does not require tuning parameters or the like, which translates to an interpretable, parsimonious and computationally cheap design strategy. We demonstrate the Exceptional Point-based Thermoacoustic Design method (called EPTD-method) on two well-known experimental setups with increasing complexity and carefully perform parametric tests to unveil the key aspects of this novel design strategy. Finally, we turn the initially unstable setups into stable ones and explain why and how this was achieved.

Plasma sprayed duplex ytterbium disilicate/monosilicate EBCs and the transformation from ytterbia to ytterbium monosilicate during burner rig testing

Environmental Barrier Coating systems (EBCs) were thermally cycled in a burner rig test facility. Yb2Si2O7 (YbDS) layer was deposited by air plasma spraying while two suspension plasma sprayed Yb2SiO5 (YbMS) microstructures were evaluated in duplex (YbDS/YbMS) systems: columnar and segmentation cracked. EBCs underwent 2000 cycles at a surface temperature of 1300 °C without signs of delamination failure. A porous YbMS layer formed at the base of intercolumnar gaps and segmentation cracks in the duplex systems, presumably due to reactions with entrapped water vapor. Furthermore, Yb2O3 depletion zones were evident at both the surface and YbDS/YbMS interface of the duplex EBCs.

Preparation and thermal cycling performance of Ce-doped YSZ thermal barrier coatings by a novel cathode plasma electrolytic deposition

The preparation and realization of highly reliable thermal barrier coatings (TBCs) on the internal surface of complex cavities is a bottleneck problem. Traditional coating methods are difficult to deposit and fulfil service requirements. In this study, a novel structure of YSZ and Ce-doped YSZ (CeYSZ) TBCs was prepared by a newly cathode plasma electrolytic deposition (CPED) technology. The results suggested that both the CPED-YSZ and CPED-CeYSZ coatings exhibited porous cross-linked dendritic structures. Because Ce doping significantly improved the phase stability of tetragonal structure and enhanced thermal insulation temperature during a burner-rig test at 1300 °C, resulting in a threefold increase in the thermal cycling life of the CPED-CeYSZ coating compared to the CPED-YSZ coating. This work provided a new strategy for tailoring multiple rare-earth principal components of high-performance TBCs and depositing them on the inner surface of complex cavities with high aspect ratios.

Failure mechanisms for Gd2O3–Yb2O3 co-doped YSZ thermal barrier coatings under high-temperature gradient

In this study, Gd2O3–Yb2O3 co-doped YSZ thermal barrier coatings with a top coat thickness of 400 μm were prepared on a nickel-based superalloy by atmospheric plasma spraying. The samples underwent multiple short-term and single long-term thermal exposures through burner rig tests under high-temperature gradients. The short-term thermal exposure duration of the coating was 25 s and the long-term thermal exposure duration was 1200 s. The microstructures and phase compositions of the samples were characterized, and their failure mechanism was discussed. The results demonstrate that during the burner rig tests, the coating surface temperature reached 2600K, resulting in coating sintering and sintered zone formation comprising coarse equiaxed grains. The short-term thermal exposure life of the coating is 3 cycles, and the long-term life is more than 1200s. After the single 1200s thermal exposure, the coating exhibited a stable cubic phase. However, under multiple 25s thermal exposures, the depth of the sintered zone increased with increasing number of cycles, leading to the formation of various vertical and transverse cracks within the coating. Coating failure was due to a combination of sintering and thermal-mismatch-induced stress.The early-stage coating delamination was attributed to sintering-induced transverse cracks, while the overall spallation was primarily ascribed to thermal-mismatch-induced transverse cracks.

Acoustic Design Parameter Change of a Pressurized Combustor Leading to Limit Cycle Oscillations

When aiming to cut down on the emission of nitric oxides by gas turbine engines, it is advantageous to have them operate at low combustion temperatures. This is achieved by lean premixed combustion. Although lean premixed combustion is a proven and promising technology, it is also very sensitive to thermoacoustic instabilities. These instabilities occur due to a coupling between the unsteady heat release rate of the flame and the acoustic field inside the combustion chamber. In this paper, this coupling is investigated in detail. Two acoustic design parameters of a swirl-stabilized pressurized preheated air (300 °C)/natural gas combustor are varied, and the occurrence of thermoacoustic limit cycle oscillations is explored. The sensitivity of the acoustic field as a function of combustion chamber length (0.9 m to 1.8 m) and reflection coefficient (0.7 and 0.9) at the exit of the combustor is investigated first using a hybrid numerical and analytical approach. ANSYS CFX is used for Unsteady Reynolds Averaged Navier-Stokes (URANS) numerical simulations, and a one-dimensional acoustic network model is used for the analytical investigation. Subsequently, the effects of a change in the reflection coefficient are validated on a pressurized combustor test rig at 125 kW and 1.5 bar. With the change in reflection coefficient, the combustor switched to limit cycle oscillation as predicted, and reached a sound pressure level of 150 dB.

Experimental investigation on combustion and emission characteristics of non-premixed ammonia/hydrogen flame

The use of ammonia and hydrogen as fuels to decarbonise the heavy transport industry has attracted worldwide attention. In this work, a swirl-enhanced combustion test rig has been built to investigate the combustion and emission characteristics of non-premixed ammonia/hydrogen flames. The blowoff limits were first examined to ensure that a range of stable flames could be achieved. Emissions containing nitric oxide (NO), nitrous oxide (NO2), ammonia slip (NH3) and unburnt hydrogen (H2) were then measured with a variety of global equivalence ratios, hydrogen blending ratios, inlet gas temperature, swirl numbers and combustion chamber insulation conditions. The structure of non-premixed ammonia/hydrogen flames and the relationship between excited hydroxyl radicals (OH*) and NO emission were revealed using OH* chemiluminescence profiles. The stable non-premixed ammonia/hydrogen flames were achieved when the hydrogen blending ratio was greater than 20%. The optimal emission performance was achieved under stoichiometric conditions, as determined by combustion efficiency. The insulation conditions of the combustor wall played a key role in the emission results, as significant growth of NO and NO2 as well as a reduction of ammonia slip were found. Although a lower swirl number improved the flame stability range, the increases in NO and NO2 emissions were observed.

Combustion Diagnostics and Emissions Measurements of a Novel Low NOx Burner for Industrial Gas Turbine Operated With CO2 Diluted Methane/Air Mixtures

Abstract While the employment of Exhaust Gas Recirculation (EGR) is a well-established technique in Internal Combustion Engines to limit NOx emissions, its adoption in Gas Turbine engines has not yet found a practical application due to its expensive and complex installation that doesn't justify the emissions reduction when compared to already established DLN combustion technologies. EGR becomes an interesting option in GT engines considering the possibility of increasing the CO2 content of the exhaust gases to improve the efficiency of Carbon Capture and Storage (CCS) units. However, the decrease in oxygen content of the combustion air is extremely challenging in terms of combustion stability and therefore of engine operability. In the present work, a low NOx burner was studied at ambient pressure in a reactive single burner test rig. The burner was fed with methane and characterized in terms of emissions and stability limits at different operating conditions. In addition, the flame position and shape were studied through OH* chemiluminescence imaging together with the flow field thanks to PIV measurements. The effects of CO2 addition on the flame were then investigated at different EGR increasing levels, highlighting the impact of the oxygen content on the combustion reaction intensity. Variations in emissions and burner stability limits in terms of maximum sustainable CO2 content were also studied, to detail the burner operating window. Data have been thoroughly analyzed to gather information on the burner behavior to support the design of new technical solutions capable of ensuring both proper flame stability and low CO and NOx emissions.

Effects of elevated pressure on thermochemical states of turbulent flame-wall interaction studied by multi-parameter laser diagnostics

Effects of increased pressure on the thermochemistry of turbulent flame-wall interaction (FWI) were investigated within this study. Quantitative, pointwise measurements of three state parameters, i.e., gas-phase temperature, CO2 and CO mole fraction, were performed by means of dual-pump coherent anti-Stokes Raman spectroscopy (CARS) and two-photon laser-induced fluorescence (LIF) of CO. The flame front was simultaneously tracked by planar OH-LIF imaging. The measurements were carried out in a fully premixed methane-air flame in an enclosed side-wall quenching burner test rig under atmospheric and pressurized conditions (3 bar absolute pressure). An evaluation of near wall flame front topologies showed that the interaction of the flame with the wall is predominantly characterized by one single, extended reaction zone, similar to a so-called head-on quenching configuration. The dominance of this quenching scenario occurred most likely due to the confined burner configuration preventing an unhindered expansion of the hot exhaust gases. Thermochemical states were studied using pairwise correlations of temperature, CO2 and CO mole fraction. Regarding the measurements at atmospheric pressure, an overall good agreement with other studies on atmospheric FWI in a similar unconfined burner was observed considering differences concerning the flow field and the burner configuration. For the thermochemistry measurements at elevated pressure, similar trends as for the atmospheric measurements were identified. A comparison of both operating cases suggested that FWI processes were more strongly affected by heat losses at elevated pressure, but differences are moderately pronounced. To the authors’ best knowledge, these experiments are the first attempt to explore the near-wall thermochemistry of FWI processes at elevated pressure using multi-parameter measurements. As the near-wall measurements were further complicated by effects arising with increasing pressure, e.g., intensified beam steering and reduced length scales, implications on the application of the laser diagnostics are reported.

Innovative Air Bypass System for Low-Emission Multi-Can Combustors

Abstract Gas turbines that are used as compressor drives are often operated in the part load regime because compressor stations are usually designed for operation with full power at extreme weather conditions. Consequently, these gas turbines must comply with strict emission regulations at unfavorably low turbine inlet temperatures. To extend the low-emission operation range of the premixed combustion systems, many gas turbines bypass a part of the compressed air upstream of the combustor and either blow it off into the exhaust stack or reinject it into the secondary combustion zone. This study presents a new approach that overcomes shortcomings by injecting the compressed air in the burner head in the vicinity of the primary combustion zone. This is particularly attractive for multi-can combustors. Atmospheric combustion tests are conducted for two different air injection designs. The first design features lower air injection velocity and the second features higher injection velocities. Both injection strategies are tested with the industrial MGT gas turbine can combustor. The full size burner is tested at atmospheric conditions in a burner test rig with a quartz flame tube and natural gas as fuel. The performance of the air bypass system is assessed by means of CO and NOx emission measurements for different air bypass ratios. Additionally, OH* chemiluminescence camera pictures are presented and compared to numerical calculations. It is found that the air injection in the annular vicinity of the swirl flame does not cause increased CO emissions by quenching or other effects.

Multilayer GZ/YSZ thermal barrier coating from suspension and solution precursor plasma spray

Gas turbines rely on thermal barrier coating (TBC) to thermally insulate the nickel-based superalloys underneath during operation; however, current TBCs, yttria stabilised zirconia (YSZ), limit the operating temperature and hence efficiency. At an operating temperature above 1200 °C, YSZ is susceptible to failure due to phase instability and CMAS (Calcia-Magnesia-Alumina-Silica) attack. Gadolinium zirconates (GZ) could overcome the drawback of YSZ, complementing each other with the multi-layer approach. This study introduces a novel approach utilising axial suspension plasma spray (ASPS) and axial solution precursor plasma spray (ASPPS) to produce a double-layer and a triple-layer TBCs with improved CMAS resistance. The former comprised suspension plasma sprayed GZ and YSZ layers while the latter had an additional dense layer deposited through a solution precursor to minimise the columnar gaps that pre-existed in the SPS GZ layer, thus resisting CMAS infiltration. Both coatings performed similarly in furnace cycling test (FCT) and burner rig testing (BRT). In the CMAS test, the triple-layer coating exhibited better CMAS reactivity, as evidenced by the limited CMAS infiltration observed on the surface.

Acoustic and Optical Investigations of the Flame Dynamics of Rich and Lean Kerosene Flames in the Primary Zone of an Air-Staged Combustion Test-Rig

Abstract In this study, the thermoacoustic behavior of nonpremixed kerosene flames from rich to lean combustion conditions is investigated. Flame-transfer-functions (FTF) measured purely acoustically are compared with results based on flame chemiluminescence. OH*, CH*, C2*, and CO2* were selected as potential measures for representing steady and fluctuating heat release when burning nonpremixed kerosene. In addition, their ability for the quantification of equivalence ratio fluctuations will be highlighted. The measurements were performed in the primary zone of an atmospheric rich-quench-lean (RQL) combustion test-rig. The new experimental approach allows a characterization of the primary zone independent of the secondary zone. Rich and lean operating points were analyzed by fueling an aero-engine prototype injector with and without acoustic excitation. To improve the quality of the acoustic wavefield reconstruction a thermocouple correction method was implemented. The flame dynamics determined with the multimicrophone method (MMM) exhibit a frequency and equivalence ratio depending effect of rich combustion conditions. The results for the steady behavior of the chosen radicals by altering equivalence ratio and thermal power indicate proportionality of the chemiluminescence to thermal power. Furthermore, the CH*/C2* ratio is found to be a promising indicator for the global equivalence ratio in the combustion chamber. The flame-transfer-functions based on chemiluminescence show a good qualitative agreement with the multimicrophone method. Based on the experimental findings a calibration curve for the different radicals to obtain quantitatively correct flame-transfer-functions from chemiluminescence is presented.

Preparation of Highly Durable Columnar Suspension Plasma Spray (SPS) Coatings by Pre-Oxidation of the CoNiCrAlY Bondcoat

Columnar structured thermal barrier coatings (TBCs) have been intensively investigated due to their potential to enhance the durability and reliability of gas turbine engine components. These coatings consist of vertically aligned columns that provide excellent resistance to thermal cycling. In this study, the lifetime of columnar suspension-plasma-sprayed (SPS) TBCs was evaluated using burner rig tests. The tests were carried out under high-temperature conditions. Significantly, the pre-oxidation of the bondcoat during diffusion bonding treatment was found to have a substantial impact on the performance of the SPS TBCs. The optimized treatment resulted in columnar SPS TBCs demonstrating excellent thermal stability and resistance under the test conditions. The lifetime of the coatings was significantly extended compared to conventional TBCs by pre-oxidation of the CoNiCrAlY bondcoat in argon, which suggests that columnar SPS TBCs have great potential for use in gas turbine engines.

Effects of ammonia co-firing ratios and injection positions in the coal–ammonia co-firing process in a circulating fluidized bed combustion test rig

Ammonia (NH3) co-firing is a promising technology for reducing greenhouse gas emissions in coal-fired power plants. Prior to commercialization, an experimental study on coal–NH3 co-firing in a pilot-scale circulating fluidized bed (CFB) combustion test rig was conducted for technical verification. The comprehensive combustion characteristics, including pollutant emission, combustion efficiency, and ash properties, of NH3 co-firing with sub-bituminous coal in a CFB combustion test rig and the CO2 reduction according to NH3 co-firing ratios under two different injection positions (dense bed zone (DBZ) and wind box (WB) with primary air) were investigated. When NH3 was injected at the DBZ, NO emissions decreased as the NH3 co-firing ratio increased and CO emissions increased more rapidly than with only coal-fired combustion. Compared with only coal-fired combustion, a 25.4% NH3 co-firing ratio at the WB position simultaneously reduced NO and CO concentrations, achieving the highest combustion efficiency without ash-related problems. However, N2O emissions increased by > 1.5 times, indicating the formation of N intermediates during NH3 burning. Therefore, with minor retrofitting, coal–NH3 co-firing at the WB position is a feasible solution for simultaneously reducing CO2, NO, and CO emissions in commercial CFB combustion plants.

Large-Eddy Simulation of swirled flame stabilisation using NRP discharges at atmospheric pressure

In this work, the use of Nanosecond Repetitively Pulsed (NRP) discharges is investigated numerically to improve the stabilisation of the flame in a swirl burner. The studied configuration is the PACCI burner test rig set up at KAUST, in which it was experimentally demonstrated that NRP discharges can effectively enhance flame stability. Simulations are performed with the reactive compressible Navier–Stokes solver AVBP, using a recently developed phenomenological model for plasma-assisted combustion of methane-air premixed flame. The ability of the numerical model to reproduce the main flow behaviours is first assessed by comparison with PIV measurements in cold flow conditions. Then, a lean atmospheric pressure case (ϕ=0.67) without plasma actuation is simulated and compared with OH* chemiluminescence image from experiment. Both numerical and experimental results reveal an unstable turbulent flame, with intermittent attachment to the burner exit. Finally, two operating conditions with NRP discharges are simulated. The NRP discharges correspond to 10 kV pulses applied at a frequency of 20 and 30 kHz, respectively corresponding to a discharge power 0.72 and 1.17% of the thermal flame power. First, a significant stabilisation effect is observed when applying the discharges, which efficiently mitigate the flame lifting. This effect is quantitatively demonstrated by tracking the flame centre of gravity, which shows that the flame moves upstream under the influence of the plasma, in good agreement with experimental observations. Results also show that a net power gain is obtained by applying NRP discharges to combustion by comparing the thermal flame power to the plasma power. In particular, an increase of plasma actuation efficiency from 4 to 6 as been observed in the cases studied by increasing the plasma power.

The failure behavior analysis based on finite element simulation of PS-PVD (Gd0.9Yb0.1)2Zr2O7/YSZ coatings during burner rig tests

A double-ceramic-layer (DCL) thermal barrier coating consisting of quasi-columnar structured (Gd0.9Yb0.1)2Zr2O7 (GYbZ) on top and yttria-stabilized zirconia (YSZ) beneath was deposited by plasma spray-physical vapor deposition (PS-PVD). The as-deposited GYbZ/YSZ coating is composed of a dense continuous layer at the bottom and a columnar layer growing on it. The columnar layer comprises taller coarse columns, shorter tapered columns, and particles filling in the gaps between the columns. The thermal shock behavior of the coating is evaluated in a burner rig at 1300 °C, during which the coating mainly fails in the form of delamination. The coating initially delaminates in the regions where the particles are embedded beneath the taller GYbZ columns tips. Subsequently, delamination occurs in the lower region of GYbZ coating and eventually fails at the TGO/YSZ interface. A finite element model tailored to the microstructural characteristics of the DCL coating was established. Stress distributions of the coating indicate that the discontinuities of the strain tolerance caused by abrupt microstructural or componential changes lead to multiple out-of-plane stress (σ22) concentration spots. The position and procedure of the delamination of GYbZ coating obtained based on the energy release rate of each σ22 concentration spot are consistent with experimental results.

Ash deposition and fine particle formation when utilizing biomass and coal fly ash in lab-, pilot- and full-scale

Fine particles were sampled at the 800 MWth Avedøre Power Station Unit 2 (AVV2) as well as at the 900 MWth Studstrup Power Station Unit 3 (SSV3), both utilizing wood pellets together with coal fly ash (CFA), for alkali capturing. In parallel, fine particle formation was quantified in the BoCTeR pilot-scale pulverized-fuel biomass combustion test-rig, at the Technical University of Munich, using the same wood pellets and CFA-additive as was applied in full-scale, to compare the impact of the CFA-addition. A comparison between fine particle formation and concentration in the BoCTeR and in full-scale, revealed a higher quantity of submicron particles (PM1) at AVV2, compared to SSV3, i.e. differences between the two full-scale boilers, while the PM1-values at BoCTeR was found to be substantially higher than what was measured in full-scale, mainly due to differences in temperature–time history between these two combustor scales.Ash deposition during wood pellets firing with CFA-addition, was quantified by an advanced deposit probe at SSV3. The results showed that with a probe surface temperature of 550 °C, and 2 %wt or 3 %wt CFA-addition, no significant amount of deposit was formed. When increasing the probe surface temperature to 650 °C, at 3 %wt CFA-addition, deposit was formed on the upstream side of the probe. No Cl was detected in the deposit samples, indicating that Cl-related corrosion can be effectively suppressed by 2 %wt or 3 %wt coal fly ash addition.Finally, deposit formation when firing different pre-treated biomasses; K- and Cl-rich wheat straw, milled wood pellets, hydrothermally carbonized (HTC)-leaves and steam exploded (SE)-bark, with and without a K-capturing additives, was also investigated in the entrained flow reactor at Technical University of Denmark (DTU-EFR). In terms of deposit formation, the K- and Cl-rich wheat straw proved to be the most problematic fuel, while milled wood pellets, HTC-leaves and SE-bark, had significantly lower deposition propensities. When applying kaolin and two types of CFA (both rich in Al and Si), as K-capturing additive, the deposition propensity of wheat straw decreased significantly, when applying a molar ratio of fuel-K/additive-Al of 1.0.This paper was originally presented at the recent 28th International Conference on Impacts of Fuel Quality on Power Production, the, Aare, Sweden, September 19–23, 2022.

Crystallographic and TEM Features of a TBC/Ti2AlC MAX Phase Interface after 1300 °C Burner Rig Oxidation

A FIB/STEM interfacial study was performed on a TBC/Ti2AlC MAX phase system, oxidized in an aggressive burner rig test (Mach 0.3 at 1300 °C for 500 h). The 7YSZ TBC, α-Al2O3 TGO, and MAXthal 211TM Ti2AlC base were variously characterized by TEM/STEM, EDS, SADP, and HRTEM. The YSZ was a mix of “clean” featureless and “faulted” high contrast grains. The latter exhibited ferro-elastic domains of high Y content tetragonal t″ variants. No martensite was observed. The TGO was essentially a duplex α-Al2O3 structure of inner columnar plus outer equiaxed grains. It maintained a perfectly intact, clean interface with the Ti2AlC substrate. The Ti2AlC substrate exhibited no interfacial Al-depletion zone but, rather, numerous faults along the basal plane of the hexagonal structure. These are believed to offer a means of depleting Al by forming crystallographic, low-Al planar defects, proposed as Ti2.5AlC1.5. These characterizations support and augment prior optical, SEM, and XRD findings that demonstrated remarkable durability for the YSZ/Ti2AlC MAX phase system in aggressive burner tests.