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Qu, Zhechao
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Publications (10 of 18) Show all publications
Qu, Z., Holmgren, P., Skoglund, N., Wagner, D. R., Broström, M. & Schmidt, F. M. (2018). Distribution of temperature, H2O and atomic potassium during entrained flow biomass combustion: coupling in situ TDLAS with modeling approaches and ash chemistry. Combustion and Flame, 188, 488-497
Open this publication in new window or tab >>Distribution of temperature, H2O and atomic potassium during entrained flow biomass combustion: coupling in situ TDLAS with modeling approaches and ash chemistry
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2018 (English)In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 188, p. 488-497Article in journal (Refereed) Published
Abstract [en]

Tunable diode laser absorption spectroscopy (TDLAS) is employed for simultaneous detection of gas temperature, water vapor (H2O) and gas-phase atomic potassium, K(g), in an atmospheric, research-scale entrained flow reactor (EFR). In situ measurements are conducted at four different locations in the EFR core to study the progress of thermochemical conversion of softwood and Miscanthus powders with focus on the primary potassium reactions. In an initial validation step during propane flame operation, the measured axial EFR profiles of H2O density-weighted, path-averaged temperature, path-averaged H2O concentration and H2O column density are found in good agreement with 2D CFD simulations and standard flue gas analysis. During biomass conversion, temperature and H2O are significantly higher than for the propane flame, up to 1500 K and 9%, respectively, and K(g) concentrations between 0.2 and 270 ppbv are observed. Despite the large difference in initial potassium content between the fuels, the K(g) concentrations obtained at each EFR location are comparable, which highlights the importance of considering all major ash-forming elements in the fuel matrix. For both fuels, temperature and K(g) decrease with residence time, and in the lower part of the EFR, K(g) is in excellent agreement with thermodynamic equilibrium calculations evaluated at the TDLAS-measured temperatures and H2O concentrations. However, in the upper part of the EFR, where the measured H2O suggested a global equivalence ratio smaller than unity, K(g) is far below the predicted equilibrium values. This indicates that, in contrast to the organic compounds, potassium species rapidly undergo primary ash transformation reactions even if the fuel particles reside in an oxygen-deficient environment.

Place, publisher, year, edition, pages
New York: Elsevier, 2018
Keywords
Tunable diode laser absorption spectroscopy (TDLAS), Atomic potassium, Entrained flow reactor, Biomass combustion, Thermodynamic equilibrium calculations, Computational fluid dynamics (CFD)
National Category
Atom and Molecular Physics and Optics Chemical Process Engineering Inorganic Chemistry
Identifiers
urn:nbn:se:umu:diva-141456 (URN)10.1016/j.combustflame.2017.10.013 (DOI)000424859100040 ()
Projects
Bio4Energy
Available from: 2017-11-06 Created: 2017-11-06 Last updated: 2019-09-02Bibliographically approved
Ögren, Y., Sepman, A., Qu, Z., Schmidt, F. M. & Wiinikka, H. (2017). Comparison of measurement techniques for temperature and soot concentration in premixed, small-scale burner flames. Energy & Fuels, 31(10), 11328-11336
Open this publication in new window or tab >>Comparison of measurement techniques for temperature and soot concentration in premixed, small-scale burner flames
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2017 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, no 10, p. 11328-11336Article in journal (Refereed) Published
Abstract [en]

Optical and intrusive measurement techniques for temperature and soot concentration in hot reacting flows were tested on a small-scale burner in fuel-rich, oxygen-enriched atmospheric flat flames produced to simulate the environment inside an entrained flow reactor. The optical techniques comprised two-color pyrometry (2C-PYR), laser extinction (LE), and tunable diode laser absorption spectroscopy (TDLAS), and the intrusive methods included fine-wire thermocouple thermometry (TC) and electrical low pressure impactor (ELPI) particle analysis. Vertical profiles of temperature and soot concentration were recorded in flames with different equivalence and O2/N2 ratios. The 2C-PYR and LE data were derived assuming mature soot. Gas temperatures up to 2200 K and soot concentrations up to 3 ppmv were measured. Close to the burner surface, the temperatures obtained with the pyrometer were up to 300 K higher than those measured by TDLAS. Further away from the burner, the difference was within 100 K. The TC-derived temperatures were within 100 K from the TDLAS results for most of the flames. At high signal-to-noise ratio and in flame regions with mature soot, the temperatures measured by 2C-PYR and TDLAS were similar. The soot concentrations determined with 2C-PYR were close to those obtained with LE but lower than the ELPI results. It is concluded that the three optical techniques have good potential for process control applications in combustion and gasification processes. 2C-PYR offers simpler installation and 2D imaging, whereas TDLAS and LE provide better accuracy and dynamic range without calibration procedures.

Place, publisher, year, edition, pages
Washington: American Chemical Society (ACS), 2017
Keywords
flow coal gasifier, volume fraction, wavelength dependence, optical diagnostics, refractive index, gas temperature, pyrometry, biomass, size, extinction
National Category
Atom and Molecular Physics and Optics Energy Systems Chemical Process Engineering
Identifiers
urn:nbn:se:umu:diva-141034 (URN)10.1021/acs.energyfuels.7b01168 (DOI)000413710300104 ()
Available from: 2017-10-22 Created: 2017-10-22 Last updated: 2018-06-09Bibliographically approved
Fatehi, H., Qu, Z., Schmidt, F. M. & Bai, X.-S. (2017). Effect of Volatile Reactions on the Thermochemical Conversion of Biomass Particles. In: Yan, J Sun, F Chou, SK Desideri, U Li, H Campana, P Xiong, R (Ed.), 8TH INTERNATIONAL CONFERENCE ON APPLIED ENERGY (ICAE2016): . Paper presented at 8th International Conference on Applied Energy (ICAE), OCT 08-11, 2016, Beijing, PEOPLES R CHINA. ELSEVIER SCIENCE BV, 105
Open this publication in new window or tab >>Effect of Volatile Reactions on the Thermochemical Conversion of Biomass Particles
2017 (English)In: 8TH INTERNATIONAL CONFERENCE ON APPLIED ENERGY (ICAE2016) / [ed] Yan, J Sun, F Chou, SK Desideri, U Li, H Campana, P Xiong, R, ELSEVIER SCIENCE BV , 2017, Vol. 105Conference paper, Published paper (Refereed)
Abstract [en]

A numerical and experimental study on the conversion of a biomass particle is carried out to quantify the effect of homogeneous volatile combustion on the biomass pyrolysis. The numerical domain consists of a particle and its surrounding and the model considers detailed chemical kinetic mechanism for reaction of pyrolysis products. A detailed pyrolysis model is employed which provides the composition of pyrolysis products. The effect of gas phase reaction on the conversion time and temperature of the particle is analyzed and it was shown that the gas phase reactions results in shorter pyrolysis time. H2O mole fraction and temperature above a biomass pellet from wheat straw (WS) and stem wood (SW) were experimentally measured using tunable diode laser absorption spectroscopy (TDLAS) while recording the particle mass loss. The TDLAS data were used to validate the numerical model developed for biomass conversion. The results showed that by considering the gas phase reactions a good agreement between the measurement and the model prediction for mass loss and temperature can be achieved. For H2O mole fraction on top of the particle, on the other hand, some discrepancy between the model prediction and the experimental data was observed. Nevertheless, the difference in H2O mole fraction would be much larger by neglecting the gas phase reaction at the particle boundary.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2017
Series
Energy Procedia, ISSN 1876-6102 ; 105
Keywords
Biomass Particle, Boundary Layer, Combustion, Numerical Modeling
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:umu:diva-140928 (URN)10.1016/j.egypro.2017.03.1007 (DOI)000404967904114 ()
Conference
8th International Conference on Applied Energy (ICAE), OCT 08-11, 2016, Beijing, PEOPLES R CHINA
Available from: 2017-10-23 Created: 2017-10-23 Last updated: 2018-06-09Bibliographically approved
Qu, Z., Holmgren, P., Skoglund, N., Wagner, D. R., Broström, M. & Schmidt, F. M. (2017). Investigation of H2O, temperature and potassium in entrained flow biomass combustion – coupling in situ TDLAS with modelling. In: Nordic Flame Days 2017, 10-11 October, Stockholm: . Paper presented at Nordic Flame Days 2017, 10-11 October, Stockholm.
Open this publication in new window or tab >>Investigation of H2O, temperature and potassium in entrained flow biomass combustion – coupling in situ TDLAS with modelling
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2017 (English)In: Nordic Flame Days 2017, 10-11 October, Stockholm, 2017Conference paper, Oral presentation with published abstract (Refereed)
National Category
Atom and Molecular Physics and Optics Chemical Process Engineering Inorganic Chemistry
Identifiers
urn:nbn:se:umu:diva-141520 (URN)
Conference
Nordic Flame Days 2017, 10-11 October, Stockholm
Available from: 2017-11-06 Created: 2017-11-06 Last updated: 2018-06-09
Sepman, A., Ögren, Y., Qu, Z., Wiinikka, H. & Schmidt, F. M. (2017). Real-time in situ multi-parameter TDLAS sensing in the reactor core of an entrained-flow biomass gasifier. Proceedings of the Combustion Institute, 36(3), 4541-4548
Open this publication in new window or tab >>Real-time in situ multi-parameter TDLAS sensing in the reactor core of an entrained-flow biomass gasifier
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2017 (English)In: Proceedings of the Combustion Institute, ISSN 1540-7489, E-ISSN 1873-2704, Vol. 36, no 3, p. 4541-4548Article in journal (Refereed) Published
Abstract [en]

Tunable diode laser absorption spectroscopy (TDLAS) was used to measure several important process parameters at two different locations inside the reactor of an atmospheric, air-blown 0.1 MWth biomass gasifier. Direct TDLAS at 2298 nm was employed for carbon monoxide (CO) and water vapor (H2O), calibration-free scanned wavelength modulation spectroscopy at 1398 nm for H2O and gas temperature, and direct TDLAS at 770 nm for gaseous elemental potassium, K(g), under optically thick conditions. These constitute the first in situ measurements of K(g) and temperature in a reactor core and in biomass gasification, respectively. In addition, soot volume fractions were determined at all TDLAS wavelengths, and employing fixed-wavelength laser extinction at 639 nm. Issues concerning the determination of the actual optical path length, as well as temperature and species non-uniformities along the line-of-sight are addressed. During a 2-day measurement campaign, peat and stem wood powder were first combusted at an air equivalence ratio (lambda) of 1.2 and then gasified at lambdas of 0.7, 0.6, 0.5, 0.4 and 0.35. Compared to uncorrected thermocouple measurements in the gas stream, actual average temperatures in the reactor core were significantly higher. The CO concentrations at the lower optical access port were comparable to those obtained by gas chromatography at the exhaust. In gasification mode, similar H2O values were obtained by the two different TDLAS instruments. The measured K(g) concentrations were compared to equilibrium calculations. Overall, the reaction time was found to be faster for peat than for stem wood. All sensors showed good performance even in the presence of high soot concentrations, and real-time detection was useful in resolving fast, transient behaviors, such as changes in stoichiometry. Practical implications of in-situ TDLAS monitoring on the understanding and control of gasification processes are discussed.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Tunable diode laser absorption spectroscopy, Biomass gasification, Gas temperature, Potassium, Carbon monoxide
National Category
Chemical Process Engineering Atom and Molecular Physics and Optics Energy Systems Bioenergy Energy Engineering
Identifiers
urn:nbn:se:umu:diva-124706 (URN)10.1016/j.proci.2016.07.011 (DOI)000393412600136 ()
Available from: 2016-08-22 Created: 2016-08-22 Last updated: 2018-06-07Bibliographically approved
Valiev, D., Qu, Z., Steinvall, E. & Schmidt, F. (2016). Measurement and simulation of atomic potassium in the plume above potassium hydroxide in a methane-air flat flame. In: : . Paper presented at 36th International Symposium on Combustion, Seoul, Korea, July 31 - August 5, 2016. , Article ID 4P057.
Open this publication in new window or tab >>Measurement and simulation of atomic potassium in the plume above potassium hydroxide in a methane-air flat flame
2016 (English)Conference paper, Poster (with or without abstract) (Other academic)
National Category
Other Mechanical Engineering Other Physics Topics
Identifiers
urn:nbn:se:umu:diva-124996 (URN)
External cooperation:
Conference
36th International Symposium on Combustion, Seoul, Korea, July 31 - August 5, 2016
Available from: 2016-09-01 Created: 2016-09-01 Last updated: 2018-06-07
Rutkowski, L., Khodabakhsh, A., Johansson, A. C., Valiev, D. M., Lodi, L., Qu, Z., . . . Foltynowicz, A. (2016). Measurement of H2O and OH in a Flame by Optical Frequency Comb Spectroscopy. In: Proceedings Conference on Lasers and Electro-Optics: . Paper presented at Conference on Lasers and Electro-Optics (CLEO), JUN 05-10, 2016, San Jose, CA.
Open this publication in new window or tab >>Measurement of H2O and OH in a Flame by Optical Frequency Comb Spectroscopy
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2016 (English)In: Proceedings Conference on Lasers and Electro-Optics, 2016Conference paper, Published paper (Refereed)
Abstract [en]

We measure broadband H2O and OH spectra in a flame using near-infrared cavity-enhanced Fourier transform optical frequency comb spectroscopy, we retrieve temperature and OH concentration, and compare water spectra to an improved line list.

Series
Conference on Lasers and Electro-Optics, ISSN 2160-9020
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-132064 (URN)000391286403500 ()978-1-9435-8011-8 (ISBN)
Conference
Conference on Lasers and Electro-Optics (CLEO), JUN 05-10, 2016, San Jose, CA
Available from: 2017-03-17 Created: 2017-03-17 Last updated: 2018-06-09Bibliographically approved
Qu, Z., Holmgren, P., Skoglund, N., Wagner, D. R., Broström, M. & Schmidt, F. M. (2016). TDLAS-based in situ detection of atomic potassium during combustion of biomass in an entrained flow reactor. In: : . Paper presented at 22nd International Conference of Impacts of Fuel Quality on Power Production, Prague, Czech Republic, September 19-23, 2016.
Open this publication in new window or tab >>TDLAS-based in situ detection of atomic potassium during combustion of biomass in an entrained flow reactor
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2016 (English)Conference paper, Oral presentation only (Other academic)
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:umu:diva-126922 (URN)
Conference
22nd International Conference of Impacts of Fuel Quality on Power Production, Prague, Czech Republic, September 19-23, 2016
Available from: 2016-10-21 Created: 2016-10-21 Last updated: 2019-06-19Bibliographically approved
Qu, Z., Steinvall, E., Ghorbani, R. & Schmidt, F. M. (2016). Tunable Diode Laser Atomic Absorption Spectroscopy for Detection of Potassium under Optically Thick Conditions. Analytical Chemistry, 88(7), 3754-3760
Open this publication in new window or tab >>Tunable Diode Laser Atomic Absorption Spectroscopy for Detection of Potassium under Optically Thick Conditions
2016 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 88, no 7, p. 3754-3760Article in journal (Refereed) Published
Abstract [en]

Potassium (K) is an important element related to ash and fine-particle formation in biomass combustion processes. In situ measurements of gaseous atomic potassium, K(g), using robust optical absorption techniques can provide valuable insight into the K chemistry. However, for typical parts per billion K(g) concentrations in biomass flames and reactor gases, the product of atomic line strength and absorption path length can give rise to such high absorbance that the sample becomes opaque around the transition line center. We present a tunable diode laser atomic absorption spectroscopy (TDLAAS) methodology that enables accurate, calibration-free species quantification even under optically thick conditions, given that Beer−Lambert’s law is valid. Analyte concentration and collisional line shape broadening are simultaneously determined by a least-squares fit of simulated to measured absorption profiles. Method validation measurements of K(g) concentrations in saturated potassium hydroxide vapor in the temperature range 950−1200 K showed excellent agreement with equilibrium calculations, and a dynamic range from 40 pptv cm to 40 ppmv cm. The applicability of the compact TDLAAS sensor is demonstrated by real-time detection of K(g) concentrations close to biomass pellets during atmospheric combustion in a laboratory reactor. 

National Category
Analytical Chemistry
Identifiers
urn:nbn:se:umu:diva-118864 (URN)10.1021/acs.analchem.5b04610 (DOI)000373656300046 ()
Available from: 2016-04-05 Created: 2016-04-05 Last updated: 2018-06-07Bibliographically approved
Qu, Z., Ghorbani, R., Valiev, D. & Schmidt, F. M. (2015). Calibration-free scanned wavelength modulation spectroscopy – application to H2O and temperature sensing in flames. Optics Express, 23(12), 16492-16499
Open this publication in new window or tab >>Calibration-free scanned wavelength modulation spectroscopy – application to H2O and temperature sensing in flames
2015 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 12, p. 16492-16499Article in journal (Refereed) Published
Abstract [en]

A calibration-free scanned wavelength modulation spectroscopy scheme requiring minimal laser characterization is presented. Species concentration and temperature are retrieved simultaneously from a single fit to a group of 2f/1f-WMS lineshapes acquired in one laser scan. The fitting algorithm includes a novel method to obtain the phase shift between laser intensity and wavelength modulation, and allows for a wavelengthdependent modulation amplitude. The scheme is demonstrated by detection of H2O concentration and temperature in atmospheric, premixed CH4/air flat flames using a sensor operating near 1.4 μm. The detection sensitivity for H2O at 2000 K was 4 × 10−5 cm−1 Hz-1/2, and temperature was determined with a precision of 10 K and absolute accuracy of ~50 K. A parametric study of the dependence of H2O and temperature on distance to the burner and total fuel mass flow rate shows good agreement with 1D simulations.

National Category
Atom and Molecular Physics and Optics Energy Systems
Identifiers
urn:nbn:se:umu:diva-105147 (URN)10.1364/OE.23.016492 (DOI)000356902500128 ()
Available from: 2015-06-18 Created: 2015-06-18 Last updated: 2018-06-07Bibliographically approved
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