| 1. |
- Berdugo Vilches, Teresa, 1985, et al.
(författare)
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Shedding light on the governing mechanisms for insufficient CO and H2 burnout in the presence of potassium, chlorine and sulfur
- 2020
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 273
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Tidskriftsartikel (refereegranskat)abstract
- Based on the experiences of insufficient burnout in industrial fluidized bed furnaces despite adequate mixing and availability of oxidizer, the influence of potassium on CO and H2 oxidation in combustion environments was investigated. The combustion environments were provided by a laminar flame burner in a range relevant to industrial furnaces, i.e. 845 °C to 1275 °C and excess air ratios ranging from 1.05 to 1.65. Potassium, in the form of KOH, was homogeneously introduced into the hot gas environments to investigate its effect on the radical pool. To quantitatively determine key species that are involved in the oxidation mechanism (CO, H2, KOH, OH radicals, K atoms), a combination of measurement systems was applied: micro-gas chromatography, broadband UV absorption spectroscopy and tunable diode laser absorption spectroscopy. The inhibition effect of potassium on CO and H2 oxidation in excess air was experimentally confirmed and attributed to the chain-terminating reaction between KOH, K atoms and OH radicals, which enhanced the OH radical consumption. The addition of chlorine or sulfur could reduce the concentrations of KOH and K atoms and consequently eliminated the inhibition on CO and H2 oxidation. Existing kinetic mechanisms underestimate the inhibiting effect of potassium and they fail to predict the effect of temperature on CO and H2 concentration when potassium and sulfur co-exist. This work advances the need to revise existing kinetic mechanisms to fully capture the interplay of K and S in the oxidation of CO and H2 in industrial fluidized bed furnaces.
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| 2. |
- Borggren, Jesper, et al.
(författare)
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Diode laser-based thermometry using two-line atomic fluorescence of indium and gallium
- 2017
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Ingår i: Applied Physics B: Lasers and Optics. - : Springer Science and Business Media LLC. - 0946-2171. ; 123:12
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Tidskriftsartikel (refereegranskat)abstract
- A robust and relatively compact calibration-free thermometric technique using diode lasers two-line atomic fluorescence (TLAF) for reactive flows at atmospheric pressures is investigated. TLAF temperature measurements were conducted using indium and, for the first time, gallium atoms as temperature markers. The temperature was measured in a multi-jet burner running methane/air flames providing variable temperatures ranging from 1600 to 2000 K. Indium and gallium were found to provide a similar accuracy of ~ 2.7% and precision of ~ 1% over the measured temperature range. The reliability of the TLAF thermometry was further tested by performing simultaneous rotational CARS measurements in the same experiments.
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| 3. |
- Borggren, Jesper, et al.
(författare)
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Spatially Resolved Temperature Measurements Above a Burning Wood Pellet Using Diode Laser-Based Two-Line Atomic Fluorescence
- 2018
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 72:6, s. 964-970
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Tidskriftsartikel (refereegranskat)abstract
- Diode laser-based two-line atomic fluorescence (TLAF) thermometry applied to flames of combusting wood pellets is demonstrated. The temperature above burning wood pellets placed in the hot product gas of gallium seeded laminar flames is measured. The calibration-free technique provides spatially resolved temperatures in one dimension with sufficient temporal resolution to resolve all combustion stages of a pellet, even in highly sooting flames. The temperature above a burning pellet was found to decrease due to the release of volatile gases and the accuracy and precision of the technique is assessed at flame temperatures.
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| 4. |
- Chen, Shuang, et al.
(författare)
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CH4/Air反扩散射流火焰多组分同步PLIF诊断
- 2018
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Ingår i: Shiyan Liuti Lixue/Journal of Experiments in Fluid Mechanics. - 1672-9897. ; 32:1, s. 26-32
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Tidskriftsartikel (refereegranskat)abstract
- The simultaneous multi-species Planar Laser Induced Fluorescence technique plays an important role in studying the flame structure and the two-dimensional distribution of intermediate species in combustion. The experimental system of OH/CH2O/Acetone-PLIF was built in order to study the CH4-Air inverse diffusion jet (IDJ) flame. The system consists of two sets of lasers, two intensifier-CCD cameras, a temporal controller and several lenses. The strategy of fluorescence excitation, the method of synchronous timing control and image calibration procedures are discussed. The IDJ flame was studied using the simultaneous multi-species PLIF technique, and the reaction zone, pre-heating zone and fuel zone of IDJ flame were determined. Experimental results suggest that the IDJ flame is different from either the normal diffusion flame or the premixed jet flame. The behavior of this type of flame reveals similarity to the partially premixed flame. Compared to OH chemilumiscence images, simultaneous multi-species PLIF can provide more detail and information about the flame structure and it has huge potential in fundamental combustion studies and industrial burner experiments
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| 5. |
- Fatehi, Hesameddin, et al.
(författare)
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Numerical simulation of ignition mode and ignition delay time of pulverized biomass particles
- 2019
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 206, s. 400-410
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, numerical simulations were carried out to identify the mode of ignition and ignition delay time of pulverized biomass particles in hot flue gas produced by a methane/air flame. In the experiments, it was observed that for most biomass residues the dominant combustion mode was the staged gas-phase ignition in the surrounding gas followed by surface ignition at the char surface. There were some exceptions to this general trend, e.g. wheat straw particles, which ignited at the surface of the particle under some temperature conditions. Moreover, temporally and spectrally resolved images of the single burning particles were obtained in the experiments and CH* chemiluminescence at different stages of biomass conversion was recorded. In this study, by means of a detailed numerical model for conversion of biomass particles and employing detailed gas chemistry mechanism, the ignition mode and ignition delay time of the particles are studied. The model is able to distinguish between different ignition modes of the particles in agreement with the experimental data. The underlying physics behind shifting ignition mode from homogeneous ignition to heterogeneous ignition for wheat straw are discussed. The ignition delay times for different biomass sources at different conditions are calculated and the results are in good agreement with the experimental data. Apart from the detailed model, CFD simulations are performed to assess the flow and combustion process (temperature, O2 concentration and velocity difference between the ambient gas and the particle) around the particle. The CFD results show similar trends compared with the CH* chemiluminescence from the particle at different times during the devolatilization stage.
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| 6. |
- Fatehi, Hesameddin, et al.
(författare)
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Recent Development in Numerical Simulations and Experimental Studies of Biomass Thermochemical Conversion
- 2021
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Ingår i: Energy and Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 35:9, s. 6940-6963
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Forskningsöversikt (refereegranskat)abstract
- Biomass, as a renewable energy source, is available worldwide, is carbon neutral, and can be converted to various types of products depending on the market and on the specific applications. Among different technologies of biomass utilization, thermochemical conversion of biomass is the most efficient method with the shortest time scale of the process. Thermochemical conversion can be used to produce gas or liquid fuels, and it can be used for direct production of heat and electricity. Biomass thermochemical conversion is an active and fast growing field of research. New experimental methods with high spatial and temporal resolution such as laser diagnostics are being introduced, and numerical modeling of the physical and chemical details in biomass conversion is being conducted. In this review, we aim to provide an overview of the recent activities in the field of thermochemical conversion of biomass. Important parameters in the large scale conversion systems, such as temperature distribution, overall conversion rate of fuel, and distribution of different species, are strongly connected to the processes that occur on the scale of a single particle. Understanding the link between transport phenomena, chemical kinetics, and physical transformation on single particle scale can help to unravel issues such as emission and efficiency on the large scale. Hence, the focus of this review is on the single biomass particle, relevant to combustion and gasification systems. Special attention is paid to high fidelity numerical models and state-of-the-art experimental techniques that have been developed or employed over recent years to understand different aspects of biomass thermochemical conversion.
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| 7. |
- Gao, Qiang, et al.
(författare)
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Gas Temperature Measurement Using Differential Optical Absorption Spectroscopy (DOAS)
- 2018
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 72:7, s. 1014-1020
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Tidskriftsartikel (refereegranskat)abstract
- A nonintrusive method for flow gas temperature measurement using differential optical absorption spectroscopy (DOAS) was demonstrated. A temperature-dependent spectra (TDS) originated from the DOAS spectra of sulfur dioxide (SO2) in the wavelength range of 276–310 nm was introduced, and the relationship between the TDS and the temperature was built through experimental calibration process. This relationship is found to be independent of SO2 concentration and can be used for temperature measurements. The experimental results indicated that the precision of the TDS method is < ± 0.3% for SO2 concentrations higher than 150 ppm with the optical path length of 170 mm. For lower concentrations, the precision is estimated to be ± 0.4% at 1 ppm. The relative deviation between the temperature measured by the TDS method and that measured by a thermocouple is within 3% in the temperature range of 298–750 K, and the TDS method has a quicker response to the fast-changing temperature than the thermocouple.
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| 8. |
- Hot, Dina, et al.
(författare)
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Spatially and temporally resolved IR-DFWM measurement of HCN released from gasification of biomass pellets
- 2019
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 37:2, s. 1337-1344
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Tidskriftsartikel (refereegranskat)abstract
- For the first time, to the best of the authors' knowledge, nonintrusive quantitative measurement of hydrogen cyanide (HCN) released during the devolatilization phase of straw pellets gasification is demonstrated with high spatial and temporal resolution. Mid-infrared degenerate four-wave mixing (IR-DFWM) measurements of HCN were performed by probing the interference-free P(20) line in the v 1 vibrational band at around 3 μm and the IR-DFWM signal was detected with an upconversion-based detector, providing discrimination of thermal noise and increased sensitivity. A novel single-pellet setup consisting of a multi-jet burner was used to provide hot flue gas environments with an even and well-defined temperature distribution, for single straw pellet gasification at atmospheric pressure. The environments had temperatures of 1380 K, 1540 K and 1630 K with a constant oxygen concentration of 0.5 vol%. In order to quantify the amount of HCN released during the devolatilization of straw pellets, calibration measurements were performed in well-defined HCN gas flows. Selected hot water lines were probed with IR-DFWM in the interrogated volume to obtain the instantaneous temperature, which were used to correct the temperature effect. HCN concentrations up to 1500 ppm were detected during the devolatilization stage, and the results indicate a strong temperature dependence of the HCN release.
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| 9. |
- Hwang, Ouk, et al.
(författare)
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Development of novel ultrasonic temperature measurement technology for combustion gas as a potential indicator of combustion instability diagnostics
- 2019
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 159
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a high-speed, fast responsive, non-intrusive ultrasonic thermometry system was proposed as a potential candidate for overcoming the disadvantages of thermocouples. The principle of this system is based on the thermal dependence of the speed of sound, and the temperature is measured by detecting the flight time of ultrasonic wave (USW) between the transmitter and the receiver. For a fast and exact measurement, the algorithm was developed as simple as possible, and the exact values of the physical properties, such as specific heat ratio and molecular weight of combustion gas, were taken from the computational calculation of CHEMKIN-Pro with GRI 3.0 mechanism. The performance of the system was verified by two experiments. First, the system was applied to measure the temperature of heated air. Results showed high precision with a 0.3% error when incorporating a modification equation and fast responsive dynamic performance, which directly reflect the rapid temperature change. Second, the combustion gas temperature above a multi-jet burner, which provides a horizontally uniform temperature distribution similar to a flat flame burner, was measured. Five different flame temperatures were measured using a thermocouple and an optic-based measurement method based on two-line atomic fluorescence (TLAF) as well as ultrasonic thermometry to compare their performances. Ultrasonic thermometry showed a slightly lower accuracy than those of TLAF and the thermocouple. This condition could be overcome by correcting the results using linear fitting, as the temperature measured by USW showed the best linearity among them. The USW technique showed excellent performance in terms of the measurement speed of 1000 samples/s and uncertainty under 0.73%. This USW thermometry of combustion gas can be applied to many combustion systems, including boilers and gas turbines. Specifically, fast temperature measurement at a speed of around 1 kHz enables the diagnosis of the combustion instability phenomenon, which is a difficult task when using conventional methods of temperature measurement. Furthermore, both dynamic pressure and temperature can be simultaneously measured at a high rate, thus synergistically increasing the accuracy of combustion instability diagnosis with sufficient information, such as the Rayleigh index or the flame transfer function.
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| 10. |
- Leffler, Tomas, et al.
(författare)
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Experimental investigations of potassium chemistry in premixed flames
- 2017
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 203, s. 802-810
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Tidskriftsartikel (refereegranskat)abstract
- Quantitative potassium species concentrations have been measured in alkali-seeded premixed methane-air flames of different stoichiometry. Potassium chloride (KCl) and hydroxide (KOH) were measured by broadband UV absorption spectroscopy and laser-induced photofragmentation fluorescence, while atomic potassium was measured using tuneable diode-laser spectroscopy. In addition, laser Rayleigh scattering was employed for temperature measurements. Investigations were made for different alkali-seeding levels and chlorine loads resulting in KCl/KOH concentrations up to ∼30 ppm and concentrations of K atoms at ppm levels. Experimental results were compared with predictions from a chemical mechanism used in a homogenous reactor model. The observed trends, decrease in KCl and KOH concentrations and increase in K-atom concentrations with flame equivalence ratio, were well reproduced in simulations and are compared with results reported in literature. In addition, possibilities using the experimental methods for further investigations of alkali-related combustion phenomena and detailed model validation of alkali chemistry are discussed.
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| 11. |
- Li, Shen, et al.
(författare)
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Dual-laser-induced breakdown thermometry via sound speed measurement： A new procedure for improved spatiotemporal resolution
- 2020
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Ingår i: Sensors (Switzerland). - : MDPI AG. - 1424-8220. ; 20:10
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Tidskriftsartikel (refereegranskat)abstract
- Measurement of acoustic waves from laser-induced breakdown has been developed as gas thermometry in combustion atmospheres. In the measurement, two laser-induced breakdown spots are generated and the local gas temperature between these two spots is determined through the measurement of the sound speed between them. In the previous study, it was found that the local gas breakdown can introduce notable system uncertainty, about 5% to the measured temperature. To eliminate the interference, in present work, a new measurement procedure was proposed, where two individual laser pulses with optimized firing order and delay time were employed. With the new measurement procedure, the system uncertainty caused by local gas breakdown can be largely avoided and the temporal and spatial resolutions can reach up to 0.5 ms and 10 mm, respectively. The improved thermometry, dual-laser-induced breakdown thermometry (DLIBT), was applied to measure temperatures of hot flue gases provided by a multijet burner. The measured temperatures covering the range between 1000 K and 2000 K were compared with the ones accurately obtained through the two-line atomic fluorescence (TLAF) thermometry with a measurement uncertainty of ~3%, and a very good agreement was obtained.
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| 12. |
- Li, Shen, et al.
(författare)
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Ignition and combustion behavior of single micron-sized iron particle in hot gas flow
- 2022
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 241
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Tidskriftsartikel (refereegranskat)abstract
- This work investigated the ignition and combustion process of single micron-sized iron particles in the hot gas flow of burned methane-oxygen-nitrogen mixture. The particle emission intensity was recorded by a high-speed camera in different flame conditions. Particle temperature was derived through two-color pyrometry method employing an ICCD camera equipped with a stereoscope. Based on scanning electron microscopy (SEM) image, the microstructure change of iron particles was investigated. Results showed that the temperature of burning particle rose rapidly and was much higher than the ambient temperature. The fresh iron particles mainly went through several stages in hot gas flow: heating, melting, rapid combustion and cooling. Some of them became bright again after cooling. According to the above combustion process, combustion parameters including ignition delay time, accelerated burning time, total burning time and second stage of combustion time were defined. All the above defined parameters were almost linearly increasing with the increase of particle size under the same oxygen concentration. For iron particles with roughly the same size, the ignition delay time, accelerated burning time and total burning time decreased as the effective oxygen concentration increased especially for particle size larger than 40 µm. The second stage of combustion time for particles with similar size were almost the same under different oxygen concentrations. After combustion, most of the particles change from irregular shape to spherical or ellipsoidal shape, and some of them showed hollow shell structure. A phenomenon of nano-sized particles releasing during the iron particles combustion had been identified. The frequently observed luminous tail was attributed to coming from the thermal radiation of the formed nanoparticles, which was supported by the SEM sampling analysis of the combustion products.
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| 13. |
- Liu, Siyu, et al.
(författare)
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A TDLAS-based photofragmentation method for spatially resolved measurement of KOH and KCl as well as its application in biomass combustion processes
- 2024
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Ingår i: Fuel. - 0016-2361. ; 357
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Tidskriftsartikel (refereegranskat)abstract
- The release of gas-phase potassium species, mainly KOH, KCl, and K atoms, from burning biomass fuels can introduce severe problems to boilers, such as fouling, slagging, and corrosion. In the present work, an optical technique combining laser-induced photofragmentation and tunable diode laser absorption spectroscopy is developed for simultaneously measuring the concentration of KOH, KCl and K atoms with a high temporal and spatial resolution. Two laser sheets with a thickness of about 1 mm at wavelengths of 266 and 355 nm, respectively, were adopted to photodissociate KOH and KCl molecules into K atoms. A continuous wave laser at 766 nm generated by a tunable diode laser passed perpendicularly through the laser sheet to detect the K atom. The measured fragmentation-induced K-atom absorbance was correlated to KOH and KCl concertation through a calibration process in a homogenous combustion environment where the concentrations of KOH and KCl were monitored by UV absorption spectroscopy. The calibration curves were verified to be independent of temperature. A typical spatial resolution of 1 mm3 was realized where the value depended on the overlap volume of the UV laser sheet and the 766 nm laser beam. Finally, this technique was applied to measure the release behavior of KOH, KCl and K atoms from burning wood and straw pellets.
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| 14. |
- Schmid, Daniel, et al.
(författare)
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Optical in-situ measurements and modeling of post-flame sulfation of NaOH(g) and NaCl(g)
- 2023
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 332
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Tidskriftsartikel (refereegranskat)abstract
- Post-flame sulfation of gaseous sodium hydroxide (NaOH) and sodium chloride (NaCl) was investigated with optical in situ measurements at 850 to 1475 °C. A multi-jet burner was used to generate well-controlled combustion environments. The multi-jet burner also enabled the separate feeding of the sodium species and SO2 to the combustion environment where the sulfation reactions occurred. Concentrations of NaOH(g) and NaCl(g) were measured in the product gas using broadband UV absorption spectroscopy to follow the degree of sulfation. At 1475 and 1275 °C almost no sulfation occurred with an initial NaOH(g) concentration of 20 ppm and SO2 concentrations between 0 and 150 ppm. At 985 °C, the NaOH(g) concentration decreased to less than 5 ppm with SO2 concentrations above 50 ppm and at 850 °C almost all NaOH(g) was sulfated under these conditions. The experimental results for the gas-phase sulfation of NaOH were compared to previous results for the sulfation of KOH under the same conditions and the results were shown to be similar for NaOH and KOH under these conditions. Sulfation of NaOH(g) generally occurred to a more significant extent than the sulfation of NaCl(g). At 1115 to 1475 °C, no sulfation of NaCl(g) was observed. At the lowest investigated temperature, 850 °C, the NaCl(g) concentration decreased from 20 ppm to 12 ppm after the addition of 150 ppm SO2. Chemical equilibrium calculations and kinetic modeling using an updated kinetic model for the detailed Na-Cl-S chemistry were compared to the experimental results. Above 1100 °C, the system can be described by chemical equilibrium, implying that equilibrium is reached in less than 100 ms. At temperatures below 1100 °C, the measured concentration indicated kinetic control. Under these conditions, the kinetic model was in good agreement with the experimental results for NaOH(g) but over-predicted the sulfation of NaCl(g). The combined experimental data, chemical equilibrium calculations and kinetic modeling of the present study support that sulfation of alkali species can occur in the gas phase through homogeneous reactions.
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| 15. |
- Tong, Yiheng, et al.
(författare)
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Experimental Investigation on Effects of Central Air Jet on the Bluff-body Stabilized Premixed Methane-air Flame
- 2017
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Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 107, s. 23-32
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Tidskriftsartikel (refereegranskat)abstract
- Flame stabilized by a bluff-body is a common scene in many engineering applications due to the enhanced mixing characteristics, improved flame stability, and ease of combustion control. We recently designed a burner which has a conical bluff body with a central air injector. In the current work, effects of the central air jet on the heat load of the bluff body, the flame structures and the flame blowoff limits were investigated. It was found that the central air jet can significantly reduce the heat load to the bluff body. It is a considerable solution to the problem caused by the high heat load in practical applications. The flame structures and blowout limits were altered with the addition of central air jet as well. Different blowout behaviors caused by the air jet were observed and reported. The bluff-body could be cooled down by the center air injection but then it seems not to stabilize the flame any more.
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| 16. |
- Wang, Zhihua, et al.
(författare)
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Alkali metal release in thermochemical conversion of biomass and coal : Optical measurements and modeling
- 2024
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Ingår i: Progress in Energy and Combustion Science. - 0360-1285. ; 100
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Forskningsöversikt (refereegranskat)abstract
- Alkali metals, mainly K and Na, which are present in solid fuels such as biomass and coal, play an important role during their thermal conversion, e.g., in combustion or gasification. At high temperatures, alkali elements will be released in gas phase as alkali atoms, alkali chlorides, alkali hydroxides and alkali sulphates. In biomass/coal-fired boilers, the release of these alkali species can cause problems such as corrosion, slagging and fouling, threatening the safe operation of the facilities. The information on the release dynamic is important for developing proper models for alkali metal transformation in solid fuel combustion and gasification. Therefore, accurate quantitative measurements of the release of different alkali species during thermal-chemical conversion processes of biomass/coal are important. In this paper, we review literatures published over the last few decades in the field of quantitative optical measurements of alkali metals performed in combustion/gasification processes, and the release modeling based on those optical measurements. Firstly, the current situation of biomass and coal utilization is discussed, including the speciation of alkali metals in biomass/coal and their adverse effects on facilities. Secondly, requirements for optical measurements as well as several quantitative optical techniques are introduced including the general principles, typical setups, calibration methods and major advantages and drawbacks. In contrast to off-line techniques, these optical techniques provide nonintrusive measurements with high temporal and spatial resolution, which are indispensable for alkali release modeling. Furthermore, the alkali release behaviors based on optical measurements in thermochemical conversion processes are discussed. Based on the experimental results, the kinetic data for alkali release were summarized. Alkali release modeling was fulfilled relying on the knowledge of alkali release mechanisms and the kinetic data. In addition, simulations of alkali metal release with computational fluid dynamics during the biomass/coal combustion processes are also discussed, providing valuable information for industrial processes. Finally, typical examples of industrial applications of optical measurement methods in solid fuel thermochemical conversion processes as well as waste incineration and other processes are presented.
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| 17. |
- Weng, Wubin, et al.
(författare)
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A novel multi-jet burner for hot flue gases of wide range of temperatures and compositions for optical diagnostics of solid fuels gasification/combustion
- 2017
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 88:4
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Tidskriftsartikel (refereegranskat)abstract
- A novel multi-jet burner was built to provide one-dimensional laminar flat flames with a wide range of variable parameters for multipurpose quantitative optical measurements. The burner is characterized by two independent plenum chambers, one supporting a matrix of 181 laminar jet flames and the other supporting a co-flow from a perforated plate with small holes evenly distributed among the jets. A uniform rectangular burned gas region of 70 mm × 40 mm can be generated, with a wide range of temperatures and equivalence ratios by controlling independently the gas supplies to the two plenum chambers. The temperature of the hot gas can be adjusted from 1000 K to 2000 K with different flame conditions. The burner is designed to seed additives in gas or liquid phase to study homogeneous reactions. The large uniform region can be used to burn solid fuels and study heterogeneous reactions. The temperature was measured using two-line atomic fluorescence thermometry and the temperature profile at a given height above the burner was found to be flat. Different types of optical diagnostic techniques, such as line of sight absorption or laser-induced fluorescence, can be easily applied in the burner, and as examples, two typical measurements concerning biomass combustion are demonstrated.
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| 18. |
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| 19. |
- Weng, Wubin, et al.
(författare)
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Insight into KOH and KCl release behavior of burning wood and straw pellets using quantitative in situ optical measurements
- 2023
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 39:3, s. 3239-3248
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional laser-induced photofragmentation fluorescence (LIPF) was employed to quantitatively visualize the potassium hydroxide (KOH) and potassium chloride (KCl) vapor in the plume above burning wood and straw pellets. In the LIPF measurement, two excitation lasers at 266 and 193 nm were adopted to discriminate KOH and KCl. Meanwhile, tunable diode laser absorption spectroscopy (TDLAS), laser-induced breakdown spectroscopy (LIBS) and two-color pyrometry were used to measure the atomic potassium concentration, total elemental potassium concentration and surface temperature of the burning pellets, respectively. The combustion environment had a temperature of 1550 K and an oxygen concentration of 4.6 vol.%. Two peaks were observed from the temporal potassium release profile of the burning wood, corresponding to the devolatilization and char oxidation stage, while only a single release peak was observed from the burning straw attributed to its high ash content. During the char oxidation and ash cooking stages, KOH was observed to be the dominant potassium species released from the wood, while only KCl was observed for the straw which had a high content of chlorine. About 45% of the total potassium in the wood samples and about 10% in the straw samples were measured to be released during the combustion process. The high content of silicon in the straw retained a considerable amount of potassium in the ash. The wood had the potassium release mainly in the char oxidation stage (53% of the total release), while the straw had the main release during the ash cooking stage (49% of the total release). During the char oxidation and ash cooking stages, about 32% of Cl was released from the straw pellets in KCl, while the other part of Cl was considered to be released during the devolatilization stage in other Cl species form, such as HCl.
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| 20. |
- Weng, Wubin, et al.
(författare)
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Investigation of formaldehyde enhancement by ozone addition in CH4/air premixed flames
- 2015
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 162:4, s. 1284-1293
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Tidskriftsartikel (refereegranskat)abstract
- Abstract The ozone (O3) decomposition in the pre-heat zone of flames can initiate and accelerate the chain-branching reactions. In the present study, formaldehyde (CH2O) was investigated by both experiment and simulation methods in methane/air laminar premixed flames under atmospheric conditions. The formaldehyde concentration profiles in the flames were measured with CH2O-PLIF. When 4500 ppm of ozone was added, the formaldehyde concentration in Bunsen type laminar flame was enhanced by 58.5% at fuel-rich condition (Ï = 1.4) and 15.5% at stoichiometric condition. In the simulation work, the most recent ozone sub-mechanism was coupled with GRI-mech 3.0 kinetic mechanism. It showed that with 4500 ppm ozone addition, the formaldehyde concentration was enhanced by about 48.1% at rich condition (Ï = 1.4) and about 14.7% in stoichiometric mixture. The simulation suggested an early production of CH2O with ozone addition, especially in rich conditions. These reactions occurred at relatively low temperature, around 500 K. In order to isolate these reactions from the flame, experiments with preheated unburned mixtures were carried out. A larger amount of formaldehyde was produced in the zone far from the flame as the preheating temperature was increased. It indicated that the combustion enhancement with ozone could be caused by the additional reactions of ozone at relatively low temperature. Simulations showed that methoxy radical (CH3O) is the key specie for production of formaldehyde at lower temperatures. Early in the pre-heat zone of the laminar flame, formaldehyde occurs via decomposition of CH3O while in the pre-heated gas mixture via reaction of CH3O with O2. Furthermore, the O3 effect on turbulent flames was investigated showing a greater enhancement in formaldehyde signal than that in the laminar cases. This difference in formaldehyde signal enhancement could be attributed to the expansion of the preheat zone, due to turbulence.
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| 21. |
- Weng, Wubin
(författare)
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Optical Diagnostics for Quantitative Potassium Chemistry in Biomass Thermochemical Conversion Processes
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biomass is an essential sustainable and carbon-neutral energy source. Through thermochemical conversion processes, such as combustion and gasification, biomass can generally be used in boilers to provide heat and/or power. Biomass fuels contain varying amounts of potassium, chlorine and sulfur. The release of these elements, especially in the form of potassium chloride (KCl), in the thermal conversion processes causes crucial problems such as slagging and corrosion of heat transfer surface, and bed material agglomeration in operating furnaces. Potassium sulfate (K2SO4) is less corrosive and has a higher melting point than KCl. K2SO4 could be formed through sulfation of potassium using sulfur-containing additives, such as sulfur oxides (SO2). Between KCl/KOH and SO2, the sulfation can occur through gas-phase reactions. The understanding of the sulfation processes is based on gas-phase K-Cl-S chemistry, and the work in this thesis focuses on the development and application of in-situ optical diagnostics for quantitative measurements of key species in the K-Cl-S chemistry.As a preliminary investigation (Paper I) of the homogeneous sulfation between gas-phase KCl/KOH and SO2, a specially designed counter-flow reactor was adopted, where neither wall-based reactions nor other heterogeneous reactions could be involved. Homogenous sulfation was observed in the reactor, and the sulfation of KOH was observed to be more rapid than that of KCl. However, due to the counter-flow structure, quantitative measurement of potassium species was hard to be achieved. In order to achieve quantitative measurement and evaluate a detailed K-Cl-S mechanism, a laminar flame burner (Paper II) was designed to provide well-defined homogenous hot gas environments. The homogenous hot gas could be widely adjusted both in temperature and gas composition to mimic real operation conditions of furnaces. The temperature was measured using two-line atomic fluorescence (TLAF) thermometry. Different homogenous reactions could be investigated with seeding certain additives in gas or liquid phase, such as K2CO3, KCl and SO2.UV absorption spectroscopy was used to quantify concentrations of KOH, KCl, OH radicals and SO2. However, UV absorption cross sections of KOH, KCl and SO2 at the temperature over 1200 K were absent. Thus, they were accurately measured in this work (Paper III, IV). Tunable diode laser absorption spectroscopy (TDLAS) was adopted for the measurement of the concentration of K atoms. Two TDLAS systems, at 769.9 nm and 404.4 nm, were employed to extend the measurement dynamic range of potassium atoms, from below ppb-level to over ten ppm.The K-Cl-S chemistry (Paper V, VI) was investigated in oxidative and reducing environments having temperatures from 1120 K to 1950 K with additives of K2CO3, KCl and SO2. Based on the quantitative measurements of KOH, KCl, K atoms and OH radicals, a detailed K-Cl-S mechanism was evaluated and a reasonable agreement between the modelling and experimental results was obtained. SO2 sulfated KOH/KCl to K2SO4 in an oxidative environment at a temperature below 1550 K. The sulfation of KOH was more rapid compared to that of KCl. The chain-terminating reactions between KOH / K atoms and OH radicals promoted the consumption of OH radicals and inhibited the oxidation of CO and H2 as the environment temperature below 1550 K (Paper VII). Sulfation reactions consumed KOH and K atoms and eliminated the chain terminating reactions. In a reducing environment with SO2 seeding, potassium was only transformed into KOSO, and UV absorption spectrum of KOSO was obtained for the first time.
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| 22. |
- Weng, Wubin, et al.
(författare)
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Optical investigation of gas-phase KCl/KOH sulfation in post flame conditions
- 2018
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 224, s. 461-468
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Tidskriftsartikel (refereegranskat)abstract
- A counter-flow reactor setup was designed to investigate the gas-phase sulfation and homogeneous nucleation of potassium salts. Gaseous KOH and KCl were introduced into the post-flame zone of a laminar flat flame. The hot flame products mixed in the counter-flow with cold N2, with or without addition of SO2. The aerosols formed in the flow were detected through Mie scattering of a 355 nm laser beam. The temperature distribution of the flow was measured by molecular Rayleigh scattering thermometry. From the temperature where nucleation occurred, it was possible to identify the aerosols formed. Depending on the potassium speciation in the inlet and the presence of SO2, they consisted of K2SO4, KCl, or K2CO3, respectively. The experiments showed that KOH was sulphated more readily than KCl, resulting in larger quantities of aerosols. The sulfation process in the counter-flow setup was simulated using a chemical kinetic model including a detailed subset for the Cl/S/K chemistry. Similar to the experimental results, much more potassium sulfate was predicted when seeding KOH compared to seeding KCl. For both KOH and KCl, sulfation was predicted to occur primarily through the reactions among atomic K, O2 and SO2, forming KHSO4 and K2SO4. The higher propensity for sulfation of KOH compared to KCl was mostly attributed to the lower thermal stability of KOH, facilitating formation of atomic K. According to the model, sulfation also happened through SO3, especially for KCl (KCl → KSO3Cl → K2SO4).
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| 23. |
- Weng, Wubin, et al.
(författare)
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Optical measurements of KOH, KCl and K for quantitative K-Cl chemistry in thermochemical conversion processes
- 2020
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 271
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Tidskriftsartikel (refereegranskat)abstract
- Potassium and chlorine chemistry at high temperature is of great importance in biomass utilization through thermal conversion. In well-defined hot environments, we performed quantitative measurements of main potassium species, i.e., potassium hydroxide (KOH), potassium chloride (KCl) and K atoms, and the important radical OH. The concentrations of KOH, KCl and OH radicals were measured through a newly developed UV absorption spectroscopy technique. Quantitative measurements of potassium atoms were performed using tunable diode laser absorption spectroscopy at the wavelength of 404.4 and 769.9 nm to cover a wide concentration dynamic range. The reaction environment was provided by a laminar flame burner, covering a temperature range of 1120–1950 K and global fuel-oxygen equivalence ratios from 0.67 to 1.32. Potassium and chlorine were introduced into the combustion atmosphere by atomized K2CO3 or KCl water solution fog. The experimental results were compared to modeling predictions to evaluate a detailed K-Cl mechanism. For most cases, the experimental and simulation results were in reasonable agreement. However, the over-prediction of K atom concentration at low temperature fuel-rich condition and the overall under-prediction of KCl concentration call for further investigation. It was demonstrated that the optical methods and the well-defined hot environments could provide quantitative investigations widely applicable to different homogeneous reactions in thermochemical conversion processes, and in evaluation of corresponding reaction mechanisms with reliable data.
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| 24. |
- Weng, Wubin, et al.
(författare)
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Participation of alkali and sulfur in ammonia combustion chemistry : Investigation for ammonia/solid fuel co-firing applications
- 2022
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 244
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Tidskriftsartikel (refereegranskat)abstract
- Ammonia (NH3) is a promising carbon-free energy carrier. Co-firing of ammonia in solid fuel-fired facilities is a feasible solution to reduce carbon dioxide (CO2) emissions. Solid fuels, such as coal and biomass, contain various trace elements, such as alkali metals and sulfur, which are released to the gas phase during combustion. Experimental characterization and modeling are used to study the participation of alkali and sulfur species in ammonia conversion in a post-flame environment, focusing on the characteristics of NO emissions and NH3 slip. The combustion environment was provided by a laminar flame burner with a temperature decreasing from about 2000 K in reaction zone to 1500 or 1100 K in flue gas zone and an equivalence ratio of around 0.65 or 1.3. Known amounts of ammonia (up to 20,000 ppm), potassium hydroxide (KOH, representative of alkaline substances, up to 25 ppm), and sulfur dioxide (SO2, up to 1500 ppm) were uniformly introduced into the burner for high-temperature thermochemical research. The concentrations of NH3, nitric oxide (NO), KOH, SO2, and hydroxyl radicals (OH) downstream of the burner were measured quantitatively in situ using broadband UV (ultraviolet) absorption spectroscopy. In the oxidizing reaction environments, the influence of SO2 on the NO formation was negligible, while KOH significantly reduced the concentration of NO, and even led to residual ammonia in the low temperature case. Under reducing conditions, both SO2 and KOH significantly inhibited the decomposition of ammonia, especially at relatively low temperature. Meanwhile, consumption of KOH/K was observed after the mixing with ammonia, possibly due to a direct reaction of KOH/K with ammonia. One dimensional modeling using a detailed mechanism containing N/S/K chemistry qualitatively predicted the impact of S/K on ammonia oxidation and decomposition. The effect was mainly contributed to the enhanced radical consumption by SO2 and KOH. However, the model could not describe the observed consumption KOH/K by ammonia. Potassium amide (KNH2) can be generated through KOH + NH3 = KNH2 + H2O. However, according to quantum chemistry calculations for KNH2, this reaction is endothermic by 80 kJ mol−1, shifting the equilibrium strongly towards KOH + NH3, and more work is required to clarify the mechanism of removal of potassium by NH3.
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| 25. |
- Weng, Wubin, et al.
(författare)
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Particle temperature and potassium release during combustion of single pulverized biomass char particles
- 2021
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 38:3, s. 3949-3958
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Tidskriftsartikel (refereegranskat)abstract
- This work investigated the combustion characteristics of single pulverized biomass-derived char particles. The char particles, in the size range 224-250 μm, were prepared in a drop tube furnace at pyrolysis temperatures of 1273 or 1473 K from four types of biomass particles - wheat straw, grape pomace, kiwi branches and rice husk. Subsequently, the char particles were injected upward into a confined region of hot combustion products produced by flat flames stabilized on a McKenna burner, with mean temperatures of 1460, 1580 and 1670 K and mean O2 concentrations of 4.5, 6.5 and 8.5 vol%. The data reported include particle temperature, obtained using a two-color pyrometry technique, and potassium release rate, measured using a laser-induced photofragmentation fluorescence imaging technique. In addition, particle ignition delay time and burning time, obtained from the temporal evolution of the thermal radiation intensity of the burning char particles, are also reported. The results indicated that ignition of the char particles occurs simultaneously with the starting of the potassium release, then the particle burning intensity increases rapidly until it reaches a maximum, after which both the particle temperature and the potassium release rate remain approximately constant until the end of the char oxidation process. The char ignition process is temperature controlled, and the char oxidation process is oxygen diffusion controlled, with the total potassium release being independent of the oxygen concentration and the temperature of the combustion products. The combustion behavior of the chars studied is more affected by the char type than by the conditions used to prepare them.
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| 26. |
- Weng, Wubin, et al.
(författare)
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Planar laser-induced photofragmentation fluorescence for quantitative ammonia imaging in combustion environments
- 2022
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 235
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Tidskriftsartikel (refereegranskat)abstract
- Ammonia is regarded as a potential carbon-free alternative fuel. To have a better understanding of its combustion characteristics, development of feasible techniques for ammonia detection in combustion environments is essential. In the present work, planar laser-induced photofragmentation fluorescence (LIPF) was developed for quantitative measurements of ammonia in hot gas flows. A 193 nm ArF excimer laser was used to photo-dissociate ammonia. As a fragment, NH* radicals were generated, and the fluorescence at 336 nm was used for ammonia detection. Quantitative calibration of the LIPF signal was performed in hot flows either from laminar flames or an electric heating-pipe with a known amount of ammonia and temperature. Ultraviolet absorption was used to obtain accurate concentrations of ammonia in the hot flows from laminar flames. The single-shot detection limit of the LIPF technique was estimated to be ∼50 ppm and ∼130 ppm in hot flue gas at 1140 and 1750 K, respectively, and ∼0.2 ppm in a room-temperature nitrogen flow. The technique was applied to detect the slip of ammonia in a premixed laminar ammonia-air flame with a fuel-air equivalence ratio of 1.2. Over 5000 ppm unburned ammonia was detected in the post-flame region and measurements showed good agreement with predictions of a chemical model.
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| 27. |
- Weng, Wubin, et al.
(författare)
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Quantitative Hydrogen Chloride Detection in Combustion Environments Using Tunable Diode Laser Absorption Spectroscopy with Comprehensive Investigation of Hot Water Interference
- 2022
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530.
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen chloride (HCl) monitoring during combustion/gasification of biomass fuels and municipal solid waste, such as polyvinyl chloride (PVC) and food residues, is demanded to avoid the adverse effect of HCl to furnace operation and to improve the quality of the gas products. Infrared tunable diode laser absorption spectroscopy (IR-TDLAS) is a feasible nonintrusive in-situ method for HCl measurements in harsh environments. In the present work, the measurement was performed using the R(3) line of the ν2 vibrational band of HCl at 5739.25 cm–1 (1742.4 nm). Water vapor is ubiquitous in combustion/gasification environments, and its spectral interference is one of the most common challenges for IR-TDLAS. Spectral analysis based on the current well-known databases was found to be insufficient to achieve an accurate measurement. The lack of accurate temperature-dependent water spectra can introduce thousands parts per million (ppm) HCl overestimation. For the first time, accurate spectroscopic data of temperature-dependent water spectra near 5739.3 cm–1 were obtained based on a systematic experimental investigation of the hot water lines in a well-controlled, hot flue gas with a temperature varying from 1100 to 1950 K. With the accurate knowledge of hot water interference, the HCl TDLAS system can achieve a detection limit of about 100 ppm⋅m at around 1500 K, and simultaneously the gas temperature can be derived. The technique was applied to measure the temporally resolved HCl release and local temperature over burning PVC particles in hot flue gas at 1790 K.
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| 28. |
- Weng, Wubin, et al.
(författare)
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Quantitative imaging of KOH vapor in combustion environments using 266 nm laser-induced photofragmentation fluorescence
- 2022
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 235
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Tidskriftsartikel (refereegranskat)abstract
- In biomass thermal conversion processes, the release of potassium in high temperature environments crucially influences the operating efficiency and safety. The dominant potassium species can be potassium hydroxide (KOH) and/or potassium chloride (KCl). We report a species-specified quantitative measurement of potassium hydroxide (KOH) in combustion environments using laser-induced photofragmentation fluorescence (LIPF). Ultraviolet (UV) light sources with different wavelengths (193, 213 and 266 nm) were investigated to select a proper source ensuring that the excited potassium atoms in the 42P state could be only generated from the KOH molecules, not another major potassium compound, potassium chloride (KCl), and emit fluorescence at 766/769 nm after the photodissociation. After direct comparison, the fourth-harmonic of Nd:YAG laser at 266 nm was found to be the most proper light source. The fluorescence signal was strongly influenced by temperature as KOH molecules at thermally populated excited vibrational levels were needed to produce excited potassium atoms after the 266 nm photolysis. After the calibration using broadband UV absorption spectroscopy, the detection limit of the LIPF planar imaging system was determined to be about 3 ppm at 1750 K under a harsh condition, where about 80% of the fluorescence was re-absorbed by the potassium atoms present in the background gas. The technique was applied to quantitatively measure KOH concentration in the hot flue gasses provided by potassium carbonate seeded flames with varying equivalence ratios, and it was also used to visualize the distribution of KOH vapor above a piece of burning wood char.
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| 29. |
- Weng, Wubin, et al.
(författare)
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Quantitative imaging of potassium release from single burning pulverized biomass char particles
- 2020
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 264
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Tidskriftsartikel (refereegranskat)abstract
- The release of potassium from single burning pulverized wheat straw char particles was quantitatively measured using laser-induced photofragmentation fluorescence (LIPF). The char particles were prepared in a drop tube furnace at 1000 °C from wheat straw particles with sizes in the range 224–250 µm. Subsequently, the char particles were injected upward into a hot flue gas flow produced by a premixed CH4/air flame anchored on a McKenna burner. The flue gas had a mean temperature of 1580 K and a mean O2 concentration of 6.5 vol%. The 193 nm laser beam from an ArF Excimer laser was formed into a collimated laser sheet to photodissociate potassium hydroxide (KOH) and potassium chloride (KCl) around the burning char particles, and the signal of the produced fluorescence was captured by a camera. The measurements were conducted for char particles during residence times in the flue gas between 10 and 70 ms. Quantitative data was obtained from a direct calibration of the LIPF signal in hot gas products doped with known amounts of KOH and KCl. The maximum potassium concentration measured surrounding the burning char particles was over 40 ppm. During the oxidation period until 70 ms, the measured potassium release rate remained almost constant at around 0.5 µg/s, with more than 60% of the potassium being released in the form of KOH. The results indicate that the LIPF imaging method can be used to study the potassium release from burning biomass fuels.
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| 30. |
- Weng, Wubin, et al.
(författare)
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Quantitative K-Cl-S chemistry in thermochemical conversion processes using in situ optical diagnostics
- 2021
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 38:4, s. 5219-5227
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Tidskriftsartikel (refereegranskat)abstract
- The sulfation of gas-phase KOH and KCl was investigated in both oxidizing and reducing atmospheres at temperatures of 1120 K, 1260 K, 1390 K, and 1550 K. Well-defined gas environments were generated in a laminar flame burner fuelled with CH4/air/O2/N2. Atomized K2CO3 and KCl water solution fog and SO2 were introduced into the hot gas as sources of potassium, chlorine, and sulfur, respectively. The in situ concentrations of KOH, KCl, and OH radicals were measured using broadband UV absorption spectroscopy, and the concentration of K atom was measured using TDLAS at 769.9 nm and 404.4 nm. The nucleated and condensed K2SO4 aerosols were visualized as illuminated by a green laser sheet. With SO2 addition, reduced concentrations of KOH, KCl, and K atom were measured in the hot gas. The sulfation was more significant for the low temperature cases. KOH was sulfated more rapidly than KCl. K2SO4 aerosols, formed by homogeneous nucleation, were observed at temperatures below 1260 K. At 1390 K, no aerosols were formed, indicating that the consumed KOH was transformed into gaseous KHSO4 or K2SO4. K atoms formed in the hot flue gas with KOH addition enhanced the consumption of OH radicals except at the high-temperature case at 1550 K. At 1120 K and 1260 K, the sulfation of KOH with SO2 seeding reduced the concentration of K atom, resulting in less OH radical consumption. Studies were also conducted in a hot reducing environment at 1140 K, with the flame at an equivalence ratio of 1.31. Similar to the observation in the oxidizing atmosphere, the concentrations of KOH and K atom decreased dramatically with SO2 seeding. An unknown absorption spectrum observed was attributed to UV absorption by KOSO. The experimental results were used to evaluate a detailed K-Cl-S reaction mechanism, and a reasonable agreement was obtained.
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| 31. |
- Weng, Wubin, et al.
(författare)
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Quantitative Measurement of Atomic Potassium in Plumes over Burning Solid Fuels Using Infrared-Diode Laser Spectroscopy
- 2017
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Ingår i: Energy and Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 31:3, s. 2831-2837
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Tidskriftsartikel (refereegranskat)abstract
- Solid fuels, such as coal and biomass, comprise a large portion of the current annual world energy supply, roughly equal to the annual oil consumption. During solid fuel combustion, certain species, though they are fairly benign outside of the combustion system, can cause damage in and around the combustion chamber. Alkali release from coal and biomass is known to cause severe problems in solid fuel fired boilers, such as fouling and corrosion of the heat transfer surfaces. In this work, the amount of atomic potassium in the plume of burning single coal, wood, and straw pellets (∼170 mg/piece) was measured using tunable diode laser absorption spectroscopy (TDLAS) of the potassium D1 line at 769.9 nm. The sample pellets were burned in an environment with stable temperature and gas composition provided by a laminar flame burner. More atomic potassium existed in the plume of burning biomass pellets compared with coal pellets, and the two temporal concentration profiles were dissimilar. This was attributed to the difference in the respective combustible components, ash compositions, potassium concentrations, and potassium compound state found in the two fuels. A high proportion of fixed carbon in coal induces potassium release mostly during the char-burnout period. In contrast, biomass has its strongest release during the devolatilization stage since its potassium presents mostly in a water-soluble form. Measurements of atomic potassium concentration during wood pellet gasification were performed in an oxygen deprived hot flue gas environment. The concentration of atomic potassium was found to be halved relative to combustion. The distribution of atomic potassium in the plume at different height above the pellets was also measured and is discussed in brief.
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| 32. |
- Weng, Wubin, et al.
(författare)
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Quantitative SO2 Detection in Combustion Environments Using Broad Band Ultraviolet Absorption and Laser-Induced Fluorescence
- 2019
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 91:16, s. 10849-10855
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Tidskriftsartikel (refereegranskat)abstract
- Spectrally resolved ultraviolet (UV) absorption cross sections of SO2 in combustion environments at temperatures from 1120 to 1950 K were measured for the first time in well-controlled conditions through applying broad band UV absorption spectroscopy in specially designed one-dimensional laminar flat flames. The temperature was observed to have a significant effect on the absorption cross-section profiles at wavelength shorter than 260 nm, while at the longer wavelength side, the absorption cross-section profiles have much less dependence on temperature. The absorption cross section at 277.8 nm with a value of 0.68 × 10-18 cm2/molecule was suggested for the evaluation of the SO2 concentration because of the weak dependence on temperature. To make spatially resolved measurements, laser-induced fluorescence (LIF) of SO2 excited by a 266 nm laser was investigated. Spectrally resolved LIF signal was analyzed at different temperatures. The LIF signal showed strong dependence on temperature, which can potentially be used for temperature measurements. At elevated temperatures, spatially resolved LIF SO2 detection up to a few ppm sensitivity was achieved. Combining UV broad band absorption spectroscopy and LIF, highly sensitive and spatially resolved quantitative measurements of SO2 in the combustion environment can be achieved.
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| 33. |
- Weng, Wubin, et al.
(författare)
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Simultaneous quantitative detection of hcn and c2h2 in combustion environment using tdlas
- 2021
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Ingår i: Processes. - : MDPI AG. - 2227-9717. ; 9:11
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Tidskriftsartikel (refereegranskat)abstract
- Emission of nitrogen oxides (NOx ) and soot particles during the combustion of biomass fuels and municipal solid waste is a major environmental issue. Hydrogen cyanide (HCN) and acetylene (C2H2 ) are important precursors of NOx and soot particles, respectively. In the current work, infrared tunable diode laser absorption spectroscopy (IR-TDLAS), as a non-intrusive in situ technique, was applied to quantitatively measure HCN and C2H2 in a combustion environment. The P(11e) line of the first overtone vibrational band v1 of HCN at 6484.78 cm−1 and the P(27e) line of the v1 + v3 combination band of C2H2 at 6484.03 cm−1 were selected. However, the infrared absorption of the ubiquitous water vapor in the combustion environment brings great uncertainty to the measurement. To obtain accurate temperature-dependent water spectra between 6483.8 and 6485.8 cm−1, a homogenous hot gas environment with controllable temperatures varying from 1100 to 1950 K provided by a laminar flame was employed to perform systematic IR-TDLAS measurements. By fitting the obtained water spectra, water interference to the HCN and C2H2 measurement was sufficiently mitigated and the concentrations of HCN and C2H2 were obtained. The technique was applied to simultaneously measure the temporally resolved release of HCN and C2H2 over burning nylon 66 strips in a hot oxidizing environment of 1790 K.
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| 34. |
- Weng, Wubin, et al.
(författare)
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Single particle ignition and combustion of pulverized pine wood, wheat straw, rice husk and grape pomace
- 2019
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 37:3, s. 2663-2671
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Tidskriftsartikel (refereegranskat)abstract
- This work examines the combustion behavior of single pulverized biomass particles from ignition to early stages of char oxidation. The biomass residues investigated were pine wood, wheat straw, rice husk and grape pomace. The biomass particles, in the size range 224-250 μm, were injected upward into a confined region with hot combustion products, produced by a flat flame McKenna burner, with a mean temperature of 1610 K and a mean O2 concentration of 6.5 vol%. Temporally and spectrally resolved images of the single burning particles were recorded with an intensified charge-coupled device camera equipped with different band-pass spectral filters. Data are reported for CH*, C2*, Na* and K* chemiluminescence, and thermal radiation from soot and char burning particles. The data on CH* and C2* chemiluminescence and soot thermal radiation permits to identify important differences between the ignition delay time, volatiles combustion time and soot formation propensity of the four biomass residues, which are mainly affected by their volatile matter content. The Na* and K* emission signals follow the same trends of the CH* and C2* emission signals until the end of the volatiles combustion stage, beyond which, unlike the CH* and C2* emission signals, they persist owing to their release from the char burning particles. Moreover, during the volatiles combustion stage, the Na*/CH* and K*/CH* ratios present constant values for each biomass residue. The CH* and thermal radiation emission data suggest that all biomass char particles experienced heterogeneous oxidation at or immediately after the extinction of the homogeneous volatiles combustion.
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| 35. |
- Weng, Wubin, et al.
(författare)
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Spectrally Resolved UV Absorption Cross-Sections of Alkali Hydroxides and Chlorides Measured in Hot Flue Gases
- 2018
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 72:9, s. 1388-1395
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Tidskriftsartikel (refereegranskat)abstract
- Spectrally resolved ultraviolet (UV) absorption cross-sections of gas-phase sodium chloride (NaCl), potassium hydroxide (KOH), and sodium hydroxide (NaOH) were measured, for the first time, in hot flue gases at different temperatures. Homogenous gas-phase NaCl, KCl (potassium chloride), NaOH, and KOH at temperatures 1200 K, 1400 K, 1600 K, and 1850 K were prepared in the post-flame zone of laminar flames by seeding nebulized droplets out of aqueous solution of corresponding alkali species. The amount of droplets seeded into the flame was kept constant, so the relative concentration of different alkali species can be derived. The broadband UV absorption cross-section of KCl vapor reported by Leffler et al. was adopted to derive the absorption cross-section curves of NaCl, NaOH, and KOH with the corresponding measured spectrally resolved absorbance spectra. No significant changes in the spectral structures in the absorption cross-sections were found as the temperature varied between 1200 K and 1850 K, except for NaOH at around 320 nm. The difference between the absorption spectral curves of alkali chlorides and hydroxides is significant at wavelengths above 300 nm, which thus can be used to distinguish and obtain the concentrations of alkali chlorides and hydroxides in the broadband UV absorption measurements.
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| 36. |
- Weng, Wubin, et al.
(författare)
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Temporal temperature measurement on burning biomass pellets using phosphor thermometry and two-line atomic fluorescence
- 2021
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 38:3, s. 3929-3938
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Tidskriftsartikel (refereegranskat)abstract
- We report accurate in-situ optical measurements of surface temperature, volatile gas temperature, and polycyclic aromatic hydrocarbon (PAH) emission over the whole burning history of individual biomass pellets in various combustion atmospheres. Two biomass fuels, wood and straw, were prepared in cylindrical pellets of ~300 mg. The pellets were burned in a well-controlled combustion atmosphere provided by a laminar flame burner with temperature ranging from 1390 K to 1840 K, and oxygen concentration from zero to 4.5%. The surface temperature of burning biomass pellets was accurately measured, for the first time, using phosphor thermometry, and the volatile gas temperature was measured using two-line atomic fluorescence thermometry. PAH emission was monitored using two-dimensional laser-induced fluorescence. During the devolatilization stage, a relatively low surface temperature, ~700 K, was observed on the burning pellets. The volatile gas temperature was ~1100 K and ~1500 K 5 mm above the top of the pellets in a gas environment of ~1800 K with 0.5% and 4.5% oxygen, respectively. PAH mainly released when the temperature of the pellet exceeded ~600 K with the highest concentration close to the surface and being consumed downstream. The weight of the released PAH molecules shifted towards lighter with a reduction of gas environment temperature. The wood and straw pellets had almost the same surface and volatile gas temperature but different compositions in the released volatile gases. The temperature information provided in the present work aids in revealing the reactions in the burning biomass fuels regarding species release, such as various hydrocarbons, nitrogen compounds, and potassium species, and is valuable for further development of biomass thermal conversion models.
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| 37. |
- Weng, Wubin, et al.
(författare)
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Temporally and spectrally resolved images of single burning pulverized wheat straw particles
- 2018
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 224, s. 434-441
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Tidskriftsartikel (refereegranskat)abstract
- This work focuses into the combustion behaviour of single wheat straw particles with the aim of providing a quantitative description of the particle burning process from ignition to the early stages of the char oxidation. The single particles, in the size range 224–250 µm, were injected upward into a confined region with hot combustion products, produced by a flat flame McKenna burner, with a mean temperature of 1550 K and a mean dry O2 concentration of 6.5 vol%. Spectral emission data and temporally resolved images of the single burning particles were obtained with a spectrometer and an ICCD camera, respectively. To obtain spectrally resolved images the camera was equipped with different band-pass filters. Overall, the results demonstrate the ability of the present experimental setup and associated optical diagnostics to gather quantitative information of the combustion process of single pulverized solid fuel particles. The emission spectra from the burning wheat straw particles showed that the emission was mainly originated from CH∗, C2 ∗, Na∗ and K∗ chemiluminescence, and thermal radiation from soot and char burning particles. The ICCD images show that the emission from excited CH, C2, Na and K is initially detected almost at the same time, the burning of the soot particles initiates soon after the ignition, and the char particles experience ignition after the extinction of the homogeneous combustion. During the volatiles combustion stage, the temporal evolution of the normalized emission intensity of the excited CH, C2, atomic sodium and atomic potassium is quite similar; during the char oxidation stage, however, the decrease of the emission intensity of the excited atomic sodium and potassium is delayed in relation to the decrease in the emission intensity of CH and C2 because of the continuous release of atomic sodium and potassium from the burning char particles.
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| 38. |
- Weng, Wubin, et al.
(författare)
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Ultraviolet Absorption Cross-Sections of Ammonia at Elevated Temperatures for Nonintrusive Quantitative Detection in Combustion Environments
- 2021
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 75:9, s. 1168-1177
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Tidskriftsartikel (refereegranskat)abstract
- Ammonia (NH3) is regarded as an important nitrogen oxides (NOx) precursor and also as an effective reductant for NOx removal in energy utilization through combustion, and it has recently become an attractive non-carbon alternative fuel. To have a better understanding of thermochemical properties of NH3, accurate in situ detection of NH3 in high temperature environments is desirable. Ultraviolet (UV) absorption spectroscopy is a feasible technique. To achieve quantitative measurements, spectrally resolved UV absorption cross-sections of NH3 in hot gas environments at different temperatures from 295 K to 590 K were experimentally measured for the first time. Based on the experimental results, vibrational constants of NH3 were determined and used for the calculation of the absorption cross-section of NH3 at high temperatures above 590 K using the PGOPHER software. The investigated UV spectra covered the range of wavelengths from 190 nm to 230 nm, where spectral structures of the (Formula presented.) transition of NH3 in the umbrella bending mode, v2, were recognized. The absorption cross-section was found to decrease at higher temperatures. For example, the absorption cross-section peak of the (6, 0) vibrational band of NH3 decreases from ∼2 × 10−17 to ∼0.5 × 10−17 cm2/molecule with the increase of temperature from 295 K to 1570 K. Using the obtained absorption cross-section, in situ nonintrusive quantification of NH3 in different hot gas environments was achieved with a detection limit varying from below 10 parts per million (ppm) to around 200 ppm as temperature increased from 295 K to 1570 K. The quantitative measurement was applied to an experimental investigation of NH3 combustion process. The concentrations of NH3 and nitric oxide (NO) in the post flame zone of NH3–methane (CH4)–air premixed flames at different equivalence ratios were measured.
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| 39. |
- Weng, Wubin, et al.
(författare)
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Ultraviolet Absorption Cross Sections of KOH and KCl for Nonintrusive Species-Specific Quantitative Detection in Hot Flue Gases
- 2019
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882.
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Tidskriftsartikel (refereegranskat)abstract
- An understanding of potassium chemistry in energy conversion processes supports the development of complex biomass utilization with high efficiency and low pollutant emissions. Potassium exists mainly as potassium hydroxide (KOH), potassium chloride (KCl), and atomic potassium (K) in combustion and related thermochemical processes. We report, for the first time, the measurement of the ultraviolet (UV) absorption cross sections of KOH and KCl at temperatures between 1300 K and 1800 K, using a newly developed method. Using the spectrally resolved UV absorption cross sections, the concentrations of KOH and KCl were measured simultaneously. In addition, we measured the concentrations of atomic K using tunable diode laser absorption spectroscopy, both at 404.4 and 769.9 nm. The 404.4 nm line was utilized to expand the measurement dynamic range to higher concentrations. A constant amount of KCl was seeded into premixed CH 4 /air flames with equivalence ratios varied from 0.67 to 1.32, and the concentrations of KOH, KCl, and atomic K in the hot flue gas were measured nonintrusively. The results indicate that these techniques can provide comprehensive data for quantitative understanding of the potassium chemistry in biomass combustion/gasification.
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| 40. |
- Weng, Wubin, et al.
(författare)
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Visible chemiluminescence of ammonia premixed flames and its application for flame diagnostics
- 2023
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 39:4, s. 4327-4334
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 41. |
- Yang, Li, et al.
(författare)
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Investigation of dilution effect on CH4/air premixed turbulent flame using OH and CH2O planar laser-induced fluorescence
- 2020
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 13:2
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Tidskriftsartikel (refereegranskat)abstract
- Diluting the combustion mixtures is one of the advanced approaches to reduce the NOx emission of methane/air premixed turbulent flame, especially with high diluents to create a distributed reaction zone and mild combustion, which can lower the temperature of reaction zone and reduce the formation of NOx. The effect of N2/CO2 dilution on the combustion characteristics of methane/air premixed turbulent flame with different dilution ratio and different exit Reynolds number was conducted by OH-PLIF and CH2O-PLIF. Results show that the increase of dilution ratio can sharply reduce the concentration of OH and CH2O, and postpone the burning of fuel. Compared with the ultra-lean combustion, the dilution weakens the combustion more obviously. For different dilution gases, the concentration of OH in the combustion zone varies greatly, while the concentration of CH2O in the unburned zone is less affected by different dilution gas. The CO2 dilution has a more significant effect on OH concentration than N2 with the given dilution ratio, but a similar effect on the concentration of CH2O in the preheat zone of flame. However, dilution does not have much influence on the flame structure with the given turbulent intensity.
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| 42. |
- Yang, Li, et al.
(författare)
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Investigation of hydrogen content and dilution effect on syngas/air premixed turbulent flame using OH planar laser-induced fluorescence
- 2021
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Ingår i: Processes. - : MDPI AG. - 2227-9717. ; 9:11
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Tidskriftsartikel (refereegranskat)abstract
- Syngas produced by gasification, which contains a high hydrogen content, has significant potential. The variation in the hydrogen content and dilution combustion are effective means to improve the steady combustion of syngas and reduce NOx emissions. OH planar laser-induced fluorescence technology (OH-PLIF) was applied in the present investigation of the turbulence of a premixed flame of syngas with varied compositions of H2/CO. The flame front structure and turbulent flame velocities of syngas with varied compositions and turbulent intensities were analyzed and calculated. Results showed that the trend in the turbulent flame speed with different hydrogen proportions and dilutions was similar to that of the laminar flame speed of the corresponding syngas. A higher hydrogen proportion induced a higher turbulent flame speed, higher OH concentration, and a smaller flame. Dilution had the opposite effect. Increasing the Reynolds number also increased the turbulent flame speed and OH concentration. In addition, the effect of the turbulence on the combustion of syngas was independent of the composition of syngas after the analysis of the ratio between the turbulent flame speed and the corresponding laminar flame speed, for the turbulent flames under low turbulent intensity. These research results provide a theoretical basis for the practical application of syngas with a complex composition in gas turbine power generation.
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