Flat-flame Burner Research Articles

Comparing gas composition from fast pyrolysis of live foliage measured in bench-scale and fire-scale experiments

Background Fire models have used pyrolysis data from oxidising and non-oxidising environments for flaming combustion. In wildland fires pyrolysis, flaming and smouldering combustion typically occur in an oxidising environment (the atmosphere). Aims Using compositional data analysis methods, determine if the composition of pyrolysis gases measured in non-oxidising and ambient (oxidising) atmospheric conditions were similar. Methods Permanent gases and tars were measured in a fuel-rich (non-oxidising) environment in a flat flame burner (FFB). Permanent and light hydrocarbon gases were measured for the same fuels heated by a fire flame in ambient atmospheric conditions (oxidising environment). Log-ratio balances of the measured gases common to both environments (CO, CO2, CH4, H2, C6H6O (phenol), and other gases) were examined by principal components analysis (PCA), canonical discriminant analysis (CDA) and permutational multivariate analysis of variance (PERMANOVA). Key results Mean composition changed between the non-oxidising and ambient atmosphere samples. PCA showed that flat flame burner (FFB) samples were tightly clustered and distinct from the ambient atmosphere samples. CDA found that the difference between environments was defined by the CO-CO2 log-ratio balance. PERMANOVA and pairwise comparisons found FFB samples differed from the ambient atmosphere samples which did not differ from each other. Conclusion Relative composition of these pyrolysis gases differed between the oxidising and non-oxidising environments. This comparison was one of the first comparisons made between bench-scale and field scale pyrolysis measurements using compositional data analysis. Implications These results indicate the need for more fundamental research on the early time-dependent pyrolysis of vegetation in the presence of oxygen.

Flame Morphology and Characteristic of Co-Firing Ammonia with Pulverized Coal on a Flat Flame Burner

Flame Morphology and Characteristic of Co-Firing Ammonia with Pulverized Coal on a Flat Flame Burner

Study on the formation of PM10 from high-sodium coal under gasification conditions in a flat-flame burner reactor

The deposition of fly ash is a key problem during utilization of high-sodium coal. A flat-flame burner reactor was used to investigate PM10 formation during high-sodium coal entrained flow gasification. The results showed that all particle size of PM10 at different gasification stages exhibits bimodal distributions. It transforms from irregular soot and char particles to square NaCl, spherical aluminosilicate and irregular char particles as gasification proceeds. As gasification time increases, Na and Cl in PM0.1 increases from 20.39 % to 57.61 %, Ca and Mg in PM0.1–1 increases from 22.51 % to 38.74 %, Si and Al in PM0.1–10 increases from 36.87 % to 71.60 %. Besides, a model is established to reveal the formation mechanism of PM10. It well-predicts the PM10 yields, and demonstrates that PM0.154, PM0.154–2.47, and PM2.47–10 come from the nucleation-collision-coagulation of vaporized Na and Cl etcetera, fragmentation of Ca, Mg-contained minerals, and fragmentation and gasification of char, respectively. The results provide valuable information for understanding of PM10 formation during high-sodium coal gasification.

PLIF Flame Study on the Qualitative and Quantitative Measurement of OH Species for Conventional and Alternative Jet Fuels; Experimental and Theoretical Investigations

ABSTRACT The hydroxyl molecule is one of the most important intermediate species in the chemistry of combustion processes and plays an important role in the chemical reactions of a hydrocarbon-air flame. However, investigation on a laser-based quantitative measurement of OH in heavy liquid hydrocarbon flames remains very scarce. Thus, in this study, OH radicals were measured qualitatively with the aid of planar laser-induced fluorescence in atmospheric pressure studies of burner stabilized laminar flames of kerosene and alcohol-to-jet (ATJ) fuel. These qualitative profiles were then put on a quantitative basis by analysis of the impact of temperature on the Boltzmann distribution of OH over the ground electronic state rotational energy levels and the use of a simple methane reference flame and its modeling using ANSYS Chemkin-Pro. The quantitative profiles in turn were used to validate the developed chemical kinetic mechanisms of kerosene and ATJ combustion. An experimental apparatus has been developed to investigate the temperature profile and the OH relative amounts of kerosene and ATJ laminar flames in an optimized premixed flat flame burner, under three different air/fuel ratio conditions. Fine wire type thermocouples were applied to provide reliable temperature profiles for the fuel flames. In general, reasonable agreement were observed between the experimental OH results and the simulations for the target fuel flames in the case of kerosene, while a higher peak value of OH was predicted in the ATJ model output compared to the PLIF derived data.

Experimental Study on Flame Chemical Composition of Coal and Ammonia Gas-Solid Jet in Flat Flame Burner.

Ammonia as a fuel to partially or completely replace fossil fuels is one of the effective ways to reduce carbon dioxide, and the research on ammonia coal cocombustion is of great significance. The combustion characteristics of ammonia are very different from those of pulverized coal, resulting in the ignition and emission characteristics of ammonia and pulverized coal gas flow that is different from traditional pulverized coal flame. In this paper, the effect of pulverized coal concentration in coal and ammonia mixed combustion jet on the ignition distance and gas-phase components at different positions of the jet flame were studied experimentally on the flat flame burner, and the conditions of ignition and ignition stability of coal and ammonia gas-solid fuel were expounded. It was found that the ammonia mixed with pulverized coal changed the temperature field of the flat flame burner and therefore the ignition characteristics of the jet were changed. The ignition delay time at the same jet speed was positively correlated with the pulverized coal concentration, but when the pulverized coal concentration continued to decrease, the influence on the ignition delay time gradually became smaller. The composition of coal ammonia gas-solid fuel changed the heat transfer path and share during combustion, and finally, the flame temperature was negatively correlated with the concentration of pulverized coal. Therefore, the reduction of the pulverized coal concentration was conducive to the stable combustion of coal ammonia mixed fuel. When HAB = 100 mm, the conversion rate of fuel N to NOx per unit mass of coal ammonia mixture increased with the increase of pulverized coal concentration. The NOx production amount first increased and then decreased with the increase of pulverized coal concentration, and the amount of N2O and NO2 decreased rapidly with the increase of HAB. The proportion of NOx in NO exceeded 94%, which was conducive to achieving low nitrogen combustion of coal and ammonia gas-solid fuel. In general, the O2 concentration in the ammonia coal jet flame decreased, the flue gas temperature, and NOx and CO generation increased after mixing ammonia, and the optimal pulverized coal concentration in this experiment was 0.41 kgc/kga (mass ratio of pulverized coal to the sum of N2 and NH3).

Numerical investigation on pyrolysis and ignition of ammonia/coal blends during co-firing

Co-firing ammonia with coal is a promising and feasible technology for reducing coal-related carbon emissions. Pyrolysis and ignition of ammonia-coal blended fuels are the key steps for flame stability and boiler operation safety throughout the conversion process but remain unclear. In this work, an extended Euler–Lagrange framework coupled to detailed solid-phase pyrolysis kinetics and gas-phase reactions mechanism is introduced and validated against experimental results for ammonia-coal co-firing in a two-stage flat flame burner. First, the CRECK-S coal pyrolysis model was validated with TGA experiments and the CPD model at different heating rates to determine parameters for a competing two-step model for CFD simulations. Second, a detailed gas-phase mechanism with 116 species and 1513 elementary reactions was derived from the volatile and ammonia reaction mechanisms. Thirdly, the co-firing simulations were validated for the ignition delay time for various ammonia co-firing ratios. The results show that increasing the co-firing ratios from 0.0 to 1.0 results in gradually increasing ignition delay times in a low-oxygen atmosphere. Further analysis demonstrates that adding ammonia accelerates the coal particle heating rate due to the reduced coal particle number density and ammonia reaction induced gas-phase temperature increase, and thus the coal devolatilization rate is increased. The latter plays a dominant role. Hydrogen produced from ammonia pyrolysis is negligible, so ammonia predominantly participates in the ignition. Time scale analysis shows that homogeneous ignition is dominant during the ignition process. The presence of ammonia inhibits the inward oxygen diffusion and causes the reaction zone to move away from the pulverized coal particle flow. The oxygen diffusion inhibition and low reactivity of ammonia compared to volatiles lead to an increase in ignition delay time for ammonia co-firing, even though pulverized coal devolatilization is accelerated.

An experimental and modeling investigation of the combustion of anisole and guaiacol

Anisole and guaiacol are both used as surrogates for lignin-derived biofuel. However, while the oxidation reaction mechanisms of anisole can be validated against a large set of experimental data, experimental measurements and models for guaiacol are limited. In this context, in addition to measuring adiabatic laminar burning velocities of both fuels using a flat flame burner, the oxidation of guaiacol was investigated at temperatures between 600 and 925 K. A near-atmospheric pressure jet–stirred reactor was used for three equivalence ratios (0.5, 1 and 2) with a high helium dilution. The experiments yielded mole fractions of 22 reaction products, among which two new species, benzodioxole and benzodioxole-2-one, were identified. All the measurements made in this work, along with extensive literature data on anisole, were compared with the predictions of a newly developed kinetic model. A good agreement was found between kinetic modeling and experiments, showing improved prediction for some species relative to the existing literature guaiacol oxidation models. Flow-rate analyses are also discussed both in flames and in the jet-stirred reactor, especially focusing on the formation of the newly detected products.

Experimental and modelling study of phenol combustion and oxidation

Despite of its central importance in the chemistry of aromatic compounds and fuels derived from biomass, only few experimental studies on phenol combustion can be found in literature. In this paper, unique measurements of the adiabatic laminar burning velocities of phenol are presented, together with the first experimental study of the oxidation of this molecule in a jet-stirred reactor. The burning velocities were measured with a flat-flame burner using the heat-flux method for a fresh gas temperature of 398 K and equivalence ratios from 0.7 to 1.35. In the reactor experiments, the oxidation of a stoichiometric mixture of phenol highly diluted in helium was investigated at temperatures between 600 and 1100 K at near-atmospheric pressure. The mole fraction of the reactants, as well as 32 products, mainly carbon monoxide, carbon dioxide, methane, acetylene ethylene, acrolein, cyclopentadiene, benzene, naphthalene and dibenzofuran, were recorded.Based on previous literature work, a new detailed kinetic model is developed based on several published sub-mechanisms and updated considering rate constants taken from recent literature studies or calculated at the CBS-QB3 or G4 level of theory. This model leads to a significantly improved prediction of the phenol burning velocities compared to literature models, as well as a reasonable prediction of most species mole fractions during phenol oxidation in the jet-stirred reactor. Sensitivity analyses as well as flow rate analyses are discussed to explain the obtained model improvements.

Ignition characteristics of the high-velocity pulverized coal jet in MILD combustion mode: Experiments and prediction improvements

The influence of high jet velocity on the ignition characteristics of pulverized coal is very important for the Moderate or Intense Low-oxygen Dilution (MILD) combustion technology of pulverized coal. This paper conducts experimental and numerical simulation research on the ignition characteristics of the pulverized coal jet in a high-temperature environment based on the Hencken-type flat flame burner. The results show that when the ambient temperature is 1873 K and the ambient oxygen mole fraction is 5 %, the ignition delay distance of the pulverized coal jet decreases as the jet velocity increases from 15 m/s to 100 m/s for the formation of MILD combustion. The adoption of the turbulent particle heat transfer model and the non-spherical particle motion model effectively improves the prediction of particle dispersion, ignition delay, and reaction zone in the high-velocity coal jet flame. The enhancement of gas–solid heat transfer by turbulent fluctuation plays a dominant role in advancing the coal ignition in the high-velocity jet, while the non-spherical shape of coal particles mainly improves the uniformity of reaction distribution. The influence of ignition characteristics in the high-velocity jet on the MILD combustion formation of pulverized coal has been also analyzed in detail.

Influence of calcium chloride on the fine particulate matter formation during coal pyrolysis

This study investigated the influence of CaCl2 on fine particulate matter (PM0.5) formation during coal pyrolysis. Two acid-washed coals were loaded with different amount of CaCl2 by physical impregnation. Pyrolysis experiments were conducted in a flat-flame burner at 1400 K, 1600 K, and 1800 K. The PM0.5 yield was evaluated through the size-segregated sampling with a low pressure impactor (DLPI+). Then, the transformation properties of CaCl2 was analyzed with X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES). Finally, the soot properties were analyzed with transmission electron microscopy (TEM), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The results show that PM0.5 yield is affected by coal type, CaCl2 loading level, and pyrolysis temperature. Loading small amount of CaCl2 can reduce the PM0.5 yield through soot inhibition, while high loading of CaCl2 increases the PM0.5 yield by forming mineral particles, the lowest PM0.5 yield occurs at 1.5 % Ca content. The PM0.5 reduction rate of CaCl2 increases then decreases with temperature from 1400 K to 1800 K. On all tested conditions, the PM0.5 yield of low-rank Zhundong subbituminous coal was lower than Shenhua bituminous coal. The release rate of Ca into PM0.5 is positively related to pyrolysis temperature and CaCl2 loading level. Ca loading decreases the sizes of soot primary particles and agglomerates, and leads to smaller amorphous cores and more disordered graphitic shells in the soot primary particles. CaCl2 loading also causes the dealkylation and deoxygenation of soot. The influence of CaCl2 on soot formation can be summarized as the catalytic effect on soot precursor formation, the enhancement of soot nucleation, and the inhibition of soot coagulation.

Laser-induced breakdown spectroscopy using modulated ns-laser pulses for multi-property measurements in high-pressure combustion environments

The present work proposes a novel method to improve the calibration accuracy of laser-induced breakdown spectroscopy (LIBS) in high-pressure combustion environments. Typically, optical plasma breakdown suffers from instability in highly pressurized environments, and the plasma emits photons of noisy and broadened spectra that are unusable for extracting quantitative property information. An improved plasma emission spectrum signal is obtained by modulating or chopping the pulse width of a fundamental 10 Hz Nd:YAG laser pulse by limiting the stochastic inverse-Bremsstrahlung (IB) photon absorption process. The modulated pulse duration is decreased from 9.2 ns to 5 ns utilizing a simple optical setup prior to being focused into a high-pressure combustor. In order to evaluate the impact of the modulated temporal laser pulse profile on the plasma emission, Proper Orthogonal Decomposition (POD) is applied to the emission spectra collected over a customized flat flame burner with varied composition and pressure. POD is capable of decomposing property-sensitive spectrum components that determine the accuracy of the spectrum calibration for property measurements using LIBS. The POD-analyzed database comprises 50 flame cases with pressure and equivalence ratios ranging from 1 to 10 bars and 0.7 to 1.1, respectively. Two Reduced-Order Models (ROMs) are trained with the collected spectra; modulated and original pulse, to predict three distinct flame properties; pressure, equivalence ratio, and adiabatic flame temperature. The output model estimates pressure, equivalence ratio and adiabatic flame temperature with an improved accuracy of 8%, 7% and 55%, respectively when the ROM is trained with chopped spectra over the calibrated pressure range. This is because the reduced pulse width in general lowers the signal level of broadband plasma emission that is sensitive to pressure. The POD-aided spectrum analyses suggest that flexible pulse modulation helps to improve the calibration accuracy in a broad gas density range with varied pressure and temperature.

Mechanism of CO2 and H2O Action on Char in Oxy-fuel Combustion with Wet Flue Gas Recirculation

The mechanism of the combined action of the C–CO2 and C–H2O reactions has yet to be clarified in the study of oxy-fuel combustion with wet flue gas recirculation (WFGR). The ultrahigh temperature (1573 K) and atmosphere of an industrial boiler are simulated in the flat flame burner reaction system (FFB-RS). The measurement of surface reactive groups and combustion reactivity of char uses Fourier transform infrared spectroscopy (FTIR) and a microfluidized bed reaction analyzer (MFBRA). The results show that char combustion reactivity has an excellent positive correlation with an O-containing reactive group. Above a 35% H2O concentration, its physical properties dominate, while below 35%, its chemical properties play a significant role. When the ratio of H2O/CO2 is close to 1, there is a synergistic relationship between the C–CO2 and C–H2O reactions, which did not occupy the same active sites, promoting the formation of O-containing reactive groups (33.83%) and alkyl complexes (19.6%) with a combustion reaction rate of 0.225%/s.

Effect of Jet Velocity on the Formation of Moderate or Intense Low-Oxygen Dilution Combustion of Pulverized Coal.

Moderate or intense low-oxygen dilution (MILD) combustion of pulverized coal is regarded as a new combustion technology with great potential due to its advantages of reducing NO x emission and improving the uniformity of heat flux in the furnace. Increasing the jet velocity has been proved to be an important technical means to achieve MILD oxy-coal combustion, especially without a high level of preheat, but the transition mechanism of coal combustion modes with the increase of jet velocity is not clear enough. In this work, a high-velocity coal-laden jet combustion system on the basis of a flat-flame burner was designed to study the effect of jet velocity on the formation of MILD combustion of pulverized coal. The combustion mode transition of the pulverized coal jet is revealed by analyzing the flame structure, temperature, radiation, and reaction intensity through a variety of optical measurement methods. Theoretical criteria for combustion mode were applied to predict the formation of MILD combustion and were validated by the experimental data. In the environment with an ambient temperature of 1600 °C, the transition velocity of the coal jet into the MILD combustion regime is about 50 m/s and about 100 m/s at 5 and 15% O2 molar fraction, respectively. The dilution effect, jet entrainment, and turbulent mixing in the high-velocity jet, as the key factors to achieve an MILD combustion regime, were analyzed theoretically and experimentally. The dilution effect inherent in the jet significantly reduces the reactant concentration and ultimately reduces the reaction intensity and flame brightness while the entrainment of the jet promotes the radial dispersion of particles and the flame uniformity, which is dominant at lower jet velocities. Strong turbulent mixing promotes the ignition and volatile combustion, which is dominant at higher jet velocities.

Experimental measurement of the rapid mixing of fuel and air in a multi-element diffusion (Hencken) burner

Flat flame burners are valuable tools for studying complex combustion phenomena like particle synthesis due to the well-controlled and well-behaved initial and boundary conditions. In this study, the methane/air flame temperature and tracer density profiles of a multi-element diffusion burner equipped with a central tube were characterized using krypton (Kr) x-ray fluorescence at the Advanced Photon Source at Argonne National Laboratory. The experiments were performed using a fuel-to-oxygen equivalence ratio of 0.8 and 3.3% Kr by volume was added to the reactant gases. One- and two-dimensional scans of non-combusting (i.e., cold flow) and combusting conditions, both with and without flow through the central tube were performed. Spatially-resolved Kr number density profiles were obtained at different planar locations and heights above the surface of the burner. The results show rapid mixing occurred near the exit-plane of the burner and increased spatial uniformity was achieved from 0.1 mm to 0.5 mm above the surface of the burner. The data also showed the impact of the central tube flow on the main methane/air flame, including evidence of the central tube flow mixing with the main flow. Flame temperatures were calculated from the fluorescence measurements at various heights above the burner surface and were in good agreement with model predictions for a burner stabilized flame. These high-fidelity measurements provide accurate baseline data that are particularly valuable for understanding the effects of fuel and air mixing on downstream phenomena, such as the formation of condensed-phase products.

The effects of various flame retardants on the combustion of polypropylene: Combining optical diagnostics and pyrolysis fragment analysis

The assessment of the efficacy and mode of action of flame retardants in polymers requires a thorough knowledge of the coupling of the presence of chemical inhibitors with the underlying heat and mass transport processes. In this experimental work, we combine a thermal decomposition analysis with optical combustion diagnostics in different test environments to gain a comprehensive understanding of the relevant sub-processes and demonstrate how this approach provides future opportunities for the research regarding the mode of action of flame retardants. Four different composites of polypropylene (PP) and 10 wt% of selected flame retardants as well as neat PP are prepared. Flame retardants include pentaerythritol spirobis(methylphosphonate) (PSMP), zinc diethylphosphinate (DEPZn), aluminum hydroxide (i.e. aluminum trihydrate, ATH) and ammonium polyphosphate (APP). The released substances in the gas phase are investigated by using thermogravimetric analysis coupled to Fourier-transform infrared spectroscopy (TGA-FTIR), and the burning behavior regarding carbon monoxide concentration and heat release rate (HRR) is studied in cone calorimeter experiments. The ignition and combustion of flame retarded micrometer-sized particles of PP are experimentally investigated in a laminar flat flame burner by means of simultaneous scanning planar laser-induced fluorescence of OH radicals (OH-PLIF) and diffuse back-illumination (DBI) at a repetition rate of 10 kHz. Particles with gas-phase activity show a decreased normalized OH signal intensity during combustion. A dependency of the dimensionless flame radius on the particle size is found which can be linked to the faster heating and pyrolysis of smaller particles compared to large particles and agglomerations. Eventually, the interaction with an external premixed flame and the subsequent extinction of self-sustaining flames of polymer sticks is investigated using OH-PLIF in an adapted horizontal burning test suited for the application of optical diagnostics. This approach allows to link the findings of investigations encompassing multiple scales, resulting in a thorough understanding of both polymer chemistry and combustion dynamics in flame retarded polymers.

A Study on an Unpressurized Medium-Temperature-Differential Stirling Engine Integrated with a New Spiral-Patterned Flat-Flame Burner and a New Spiral-Finned Hot-End Plate

The present study experimentally investigates the performance of a power generator constituted by an unpressurized Stirling engine coupled with a new flat-flame burner. The operative temperature differential of the Stirling engine is within the medium range (around 400 K or less). In this work, there are two types of the engine’s hot-end-plate designs, a conventional flat plate and the new type with spiral fins developed within this framework. Consequently, the new hot-end-plate design forms spiral-patterned channels to enhance the engine’s heat input rate, thus partly compensating for the inherently low thermal efficiency of an unpressurized engine. The spiral fins are used to increase the resident time of the flue gas and increase the heat-transfer area. In addition, engine performance is measured for two types of fuels, namely, DME (renewable) and propane (fossil). Using propane, the new hot-end plate allows for a maximum electric power output of 24.6 W, which is typically superior to common unpressurized Stirling engines. Compared to the conventional hot-end plate, the new hot-end plate improved electric power output and the thermal-to-electric efficiency up to 63% and 47%, respectively. The study also proved the effectiveness of applying the integration of the new hot-end plate and the new flat-flame burner on boosting the power output of the present Stirling engine generator.

Experimental and modeling study of acetone combustion

The pyrolysis and oxidation of acetone were studied using three complementary experimental setups. Jet-stirred reactor experiments were performed at four equivalence ratios (ϕ = 0.5, 1, 2, and ∞), at pressure of 1.067 bar (800 Torr) and over the temperature range of 700–1200 K for pyrolysis and 600–1150 K for oxidation. The decomposition of acetone starts around 800 K with a conversion rate of 50% obtained around 1000 K in both pyrolysis and oxidation studies. The main stable products detected in both conditions are small hydrocarbons (methane, ethane, and ethylene), with also acetaldehyde, CO and CO2 for oxidation. Oscillation behavior was detected beyond 1000 K under oxidation conditions and the products were followed with on-line mass spectrometry. Ignition delay times were measured using a rapid compression machine at pressures of 20 and 40 bar under non-diluted stoichiometric conditions over the temperature range 850–1100 K. The ignition delay times measured in the present study, combined with shock tube data of literature, exhibit a slight inflexion to the Arrhenius behavior, but no negative temperature coefficient. Laminar burning velocities were measured using a flat flame burner at atmospheric pressure for three fresh gas temperatures: ambient temperature, 358 and 398 K. A detailed kinetic model of the combustion of acetone including 852 species and 3265 reactions was developed. This new kinetic mechanism predicts relatively well the experimental measurements of ignition delay times, the mole fraction of the products in the jet-stirred reactor including oscillations and laminar burning velocities. Related flow rate and sensitivity analysis are also presented providing new insights into the acetone reaction network.

Optical diagnostics on coal ignition and gas-phase combustion in co-firing ammonia with pulverized coal on a two-stage flat flame burner

Gradual substitution of coal with green ammonia is a practical approach for the coal power phasedown at a minimal cost of modification, but the ignition and gas-phase reaction during co-firing NH3 with coal remain largely unclear. In this work, we investigate the co-combustion behaviors of NH3 and a high-volatile coal on a two-stage flat flame burner. Remarkably, the post-flame oxygen mole fraction Xi,O2 of the inner stage can be manipulated to reproduce a proper reducing-to-oxidizing environment that coal particles experience in the practical combustor. We first reveal that, under certain values of Xi,O2 and NH3 co-firing energy ratios ENH3, the reaction intensity (manifested by OH-PLIF signals) in the NH3-coal flame is stronger than burning either pure coal or NH3. This synergetic effect originates from an NH3-combustion-induced enhancement of volatile release. We then propose a characteristic time scale τOH from the OH signals for the initiation of overall reactions in the system. In the case of Xi,O2=0, τOH monotonically increases with ENH3, while for Xi,O2=0.2, the trend transitions to a decreasing one. It can be interpreted by comparing τOH with the characteristic O2 diffusion time, coal particle heating time, and the coal pyrolysis time under different Xi,O2. Furthermore, the coal particle ignition in coal-NH3 flames can no longer be determined by visual images. Instead, we apply CH* chemiluminescence to identify the stages of coal particle ignition and volatile combustion in the NH3-coal flame. While NH3 addition has both positive (elevating temperatures & diluting coal particles) and negative (consuming O2) effects on coal ignition, the combined influence of ENH3 is marginal on coal ignition delay time. On the other hand, the volatile combustion time decreases linearly with ENH3, suggesting a pure effect of reduced coal feed rate.

Visible chemiluminescence of ammonia premixed flames and its application for flame diagnostics

We report a spatially resolved spectroscopic study of the visible chemiluminescence emission from different premixed ammonia-air-oxygen flames stabilized on a laminar flat flame burner, with equivalence ratio ranging from 0.7 to 1.35 and an O2/N2 ratio of 0.4. In the reaction zone of the observed flames, the visible emission was recognized to be the chemiluminescence of excited NH2* radicals, while in the post-flame zone, two types of chemiluminescence were observed: NO2* chemiluminescence dominated in the fuel-lean flames and NH2* chemiluminescence dominated in the fuel-rich flames. The high-resolution spectra of the NO2* and NH2* chemiluminescence in the visible region (400-700 nm) were recorded. The intensity of both spectra increased gradually with wavelength. However, the NO2*-chemiluminescence spectrum appeared to be continuous and unstructured, while the NH2*-chemiluminescence spectrum consisted of groups of distinct emission lines. Based on the spectral feature, the ratios of the integrated chemiluminescence intensities over the 598-603 nm wavelength range to the intensities over the 586-592 nm range and 447-453 nm range were used to sense equivalence ratio. In addition, slightly different colors of the fuel-lean and fuel-rich flames were observed, due to the fact that NO2* chemiluminescence had a relatively stronger signal in the blue region than NH2* chemiluminescence. The difference was used to infer flame equivalence ratio using the flame images recorded by a RGB digital camera, where the ratio of the signal from the red channel to the signal from the blue channel was calculated.

Biomass-coal reburning: Competitive mechanism of gas-solid product activation coal char

Reburning technology combining coal and biomass can effectively reduce NOx emissions and promote carbon neutrality in coal-fired systems. This work is based on the flat-flame burner test bench that decoupled the process of biomass-coal reburning effect on coal in the initial stage. The changes in surface functional groups and carbon skeleton structure of coal char were analyzed using FTIR, XPS, and Raman detection methods. The char's combustion reactivity and NO reduction ability were analyzed based on the micro-reactive fluidized bed test bench. The results showed that biochar and syngas would react with oxygen in the transport medium, and the resulting reactive species would activate the char. The activated effect of syngas is significantly better than that of biochar. The syngas reacts with oxygen while protecting the unnecessary consumption of the coal particle surface, and the generated active substances are enriched on the surface of the coal char to enhance its reactivity. The disordered structure of char was enhanced, and the number of small aromatic ring clusters increased by about 28%. The total alkane group content on the char surface increased by nearly 140%, and the total oxygen-containing group content decreased by nearly 17.8%. The combustion reactivity of char is increased by nearly 44.6%, and the reduced ability of NO is increased by nearly 23.4%. Theoretically, the reburned pulverized coal is reduced by 23.4%.