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Quantitative laser diagnostics of gas-phase potassium species in biomass combustion and gasification
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
2023 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)Alternativ titel
Kvantitativ laserdiagnostik av kaliumföreningar i gas-fas vid förbränning och förgasning av biomassa (Svenska)
Abstract [en]

Thermochemical energy conversion processes, such as combustion and gasification, are applied worldwide for generation of electricity, heat and synthesis of chemicals. Today, these processes are mostly run on non-renewable, fossil fuels and constitute a major source of carbon dioxide emissions. A promising renewable energy source with low net carbon dioxide emissions is biomass, in particular rest products from agriculture and forestry. However, biomass usually contains high amounts of volatile inorganic compounds, such as chlorine, potassium (K) and phosphorus (P), which lead to ash-related operational issues, including deposit build-up, slagging and corrosion. Therefore, efficient utilization of biomass requires knowledge of the chemistry and fate of the inorganic compounds during thermochemical conversion. Due to the reactive, high-temperature environments in those processes, gaseous compounds are preferably measured in situ using optical techniques.

This thesis mainly deals with the development of a laser-based technique for simultaneous in situ detection and quantification of the main gaseous K species in biomass combustion and gasification: atomic K, potassium hydroxide (KOH) and potassium chloride (KCl). The novel method combines photofragmentation (PF) with tunable diode laser absorption spectroscopy (TDLAS) and achieves sub-ppm detection limits for all three K species for a path length of 2 cm and a time resolution of 20 ms. Recording the ns-µs PF signal decay due to fragment recombination allows probing the K reaction kinetics. Together with TDLAS sensors for water, methane and gas temperature, the PF-TDLAS system was employed to characterize biomass reactors from laboratory- to pilot-scale. The results were compared to predictions by numerical models. In addition, PF-TDLAS was employed for quantitative wide-field imaging of K species in a laboratory flame during KCl salt and biomass conversion. Finally, in situ detection of phosphorus pentoxide (P4O10) with a time resolution of 140 ms was demonstrated using broadband infrared absorption spectroscopy. Absorption line strengths of P4O10 at temperatures relevant for combustion were determined for the first time. The techniques presented in this thesis can provide unique experimental data for validation and further development of numerical models and advance the understanding of K species chemistry during solid fuel conversion, which is needed to facilitate the utilization of biomass in the energy system.

Ort, förlag, år, upplaga, sidor
Umeå: Umeå University , 2023. , s. 99
Nyckelord [en]
Thermochemical conversion, pyrolysis, phosphorus, single pellet, entrained-flow, in situ, spectroscopy, photofragmentation, imaging, numerical modelling
Nationell ämneskategori
Atom- och molekylfysik och optik Energiteknik
Forskningsämne
fysik
Identifikatorer
URN: urn:nbn:se:umu:diva-207313ISBN: 978-91-8070-077-1 (tryckt)ISBN: 978-91-8070-078-8 (digital)OAI: oai:DiVA.org:umu-207313DiVA, id: diva2:1753481
Disputation
2023-05-25, Lilla hörsalen, KBC-huset, Linnaeus väg 6, Umeå, 09:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2023-05-04 Skapad: 2023-04-27 Senast uppdaterad: 2023-05-03Bibliografiskt granskad
Delarbeten
1. TDLAS-based photofragmentation spectroscopy for detection of K and KOH in flames under optically thick conditions
Öppna denna publikation i ny flik eller fönster >>TDLAS-based photofragmentation spectroscopy for detection of K and KOH in flames under optically thick conditions
2020 (Engelska)Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 45, nr 18, s. 5230-5233Artikel i tidskrift, Letter (Refereegranskat) Published
Abstract [en]

Photofragmentation spectroscopy is combined with tunable diode laser absorption spectroscopy to measure the line shape of the fragment species. This provides flexibility in choosing the UV pulse location within the line shape and accurate quantification of both target species and background fragment concentrations, even under optically thick conditions. The technique is demonstrated by detection of potassium hydroxide (KOH) and atomic potassium K(g) above solid KOH converted in a premixed methane-air flat flame. Time series of KOH(g) and K(g) concentrations are recorded as a function of solid KOH mass and flame stoichiometry. The total substance released during the conversion is in good agreement with the initial solid KOH mass. Under fuel-rich conditions, increased K(g) concentrations at the expense of KOH(g) are observed compared to thermodynamic equilibrium.

Ort, förlag, år, upplaga, sidor
Optical Society of America, 2020
Nyckelord
Atomic spectroscopy, Distributed feedback lasers, Laser induced fluorescence, Line shapes, Spectroscopy, Tunable diode laser absorption spectroscopy
Nationell ämneskategori
Atom- och molekylfysik och optik Kemiteknik
Identifikatorer
urn:nbn:se:umu:diva-174975 (URN)10.1364/OL.400614 (DOI)000577110800071 ()32932498 (PubMedID)2-s2.0-85091054621 (Scopus ID)
Tillgänglig från: 2020-09-14 Skapad: 2020-09-14 Senast uppdaterad: 2023-04-27Bibliografiskt granskad
2. Simultaneous detection of K, KOH, and KCl in flames and released from biomass using photofragmentation TDLAS
Öppna denna publikation i ny flik eller fönster >>Simultaneous detection of K, KOH, and KCl in flames and released from biomass using photofragmentation TDLAS
2021 (Engelska)Ingår i: Optics Express, E-ISSN 1094-4087, Vol. 29, nr 26, artikel-id 42945Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Gaseous potassium (K) species released from biomass during thermochemicalconversion pose challenges to reactors and human health. Photofragmentation tunable diodelaser absorption spectroscopy (PF-TDLAS) was used for simultaneous, high-dynamic rangemeasurements of atomic K, potassium hydroxide (KOH) and potassium chloride (KCl) inflat flames seeded with KCl salt. An expression for the PF-TDLAS signal is presented andexperimentally verified. Axial K species concentration profiles recorded at fuel-air equivalenceratios of 0.8 and 1.3 are compared to 2D axisymmetric reacting flow simulations. An overallgood agreement is found, but KOH is over-predicted in simulations of fuel-rich flames at theexpense of atomic K. Quantification of K species close to softwood and wheat straw particlesconverted in the flames is demonstrated.

Ort, förlag, år, upplaga, sidor
The Optical Society, 2021
Nyckelord
potassium (K), potassium hydroxide (KOH), potassium chloride (KCl), photofragmentation, optical sensors, tunable diode laser absorption spectroscopy, biomass
Nationell ämneskategori
Atom- och molekylfysik och optik Energiteknik Förnyelsebar bioenergi
Identifikatorer
urn:nbn:se:umu:diva-190194 (URN)10.1364/oe.446725 (DOI)000730136600051 ()2-s2.0-85120900645 (Scopus ID)
Forskningsfinansiär
Energimyndigheten, 36160-1Kempestiftelserna, JCK-1316Vetenskapsrådet, 2018-05973Bio4Energy
Tillgänglig från: 2021-12-09 Skapad: 2021-12-09 Senast uppdaterad: 2024-01-19Bibliografiskt granskad
3. Laser-based detection of methane and soot during entrained-flow biomass gasification
Öppna denna publikation i ny flik eller fönster >>Laser-based detection of methane and soot during entrained-flow biomass gasification
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2022 (Engelska)Ingår i: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 237, artikel-id 111886Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Methane is one of the main gas species produced during biomass gasification and may be a desired or undesired product. Syngas CH4 concentrations are typically >5 vol-% (when desired) and 1–3 vol-% even when efforts are made to minimize it, while thermochemical equilibrium calculations (TEC) predict complete CH4 decomposition. How CH4 is generated and sustained in the reactor core is not well understood. To investigate this, accurate quantification of the CH4 concentration during the process is a necessary first step. We present results from rapid in situ measurements of CH4, soot volume fraction, H2O and gas temperature in the reactor core of an atmospheric entrained-flow biomass gasifier, obtained using tunable diode laser absorption spectroscopy (TDLAS) in the near-infrared (1.4 µm) and mid-infrared (3.1 µm) region. An 80/20 wt% mixture of forest residues and wheat straw was converted using oxygen-enriched air (O2>21 vol%) as oxidizer, while the global air-fuel equivalence ratio (AFR) was set to values between 0.3 and 0.7. Combustion at AFR 1.3 was performed as a reference. The results show that the CH4 concentration increased from 1 to 3 vol-% with decreasing AFR, and strongly correlated with soot production. In general, the TDLAS measurements are in good agreement with extractive diagnostics at the reactor outlet and TEC under fuel-lean conditions, but deviate significantly for lower AFR. Detailed 0D chemical reaction kinetics simulations suggest that the CH4 produced in the upper part of the reactor at temperatures >1700 K was fully decomposed, while the CH4 in the final syngas originated from the pyrolysis of fuel particles at temperatures below 1400 K in the lower section of the reactor core. It is shown that the process efficiency was significantly reduced due to the C and H atoms bound in methane and soot.

Ort, förlag, år, upplaga, sidor
Elsevier, 2022
Nyckelord
Entrained-flow reactor, Gasification, Biomass, Methane, Soot, Tunable diode laser absorption spectroscopy (TDLAS)
Nationell ämneskategori
Energiteknik Förnyelsebar bioenergi Atom- och molekylfysik och optik Kemiska processer
Identifikatorer
urn:nbn:se:umu:diva-190099 (URN)10.1016/j.combustflame.2021.111886 (DOI)000735780800001 ()2-s2.0-85120458898 (Scopus ID)
Forskningsfinansiär
EU, Horisont Europa, 637020Energimyndigheten, 50470-1Bio4Energy
Tillgänglig från: 2021-12-06 Skapad: 2021-12-06 Senast uppdaterad: 2023-09-05Bibliografiskt granskad
4. Quantitative real-time in situ measurement of gaseous K, KOH and KCl in a 140 kW entrained-flow biomass gasifier
Öppna denna publikation i ny flik eller fönster >>Quantitative real-time in situ measurement of gaseous K, KOH and KCl in a 140 kW entrained-flow biomass gasifier
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2022 (Engelska)Ingår i: Proceedings of the Combustion Institute, ISSN 1540-7489, E-ISSN 1873-2704Artikel i tidskrift (Refereegranskat) In press
Abstract [en]

Photofragmentation tunable diode laser absorption spectroscopy (PF-TDLAS) was used to simultaneously measure the concentrations of gas phase atomic potassium (K), potassium hydroxide (KOH) and potassium chloride (KCl) in the reactor core of a 140 kWth atmospheric entrained-flow gasifier (EFG). In two gasification experiments at air-to-fuel equivalence ratio of 0.5, the EFG was first run on forest residues (FR) and then on an 80/20 mixture of FR and wheat straw (FR/WS). Combustion at air-to-fuel equivalence ratio of 1.3 was investigated for comparison. A high K(g) absorbance was observed in gasification, requiring the photofragmentation signals from KOH(g) and KCl(g) to be recorded at a fixed detuning of 7.3 cm−1 from the center of the K(g) absorption profile. In combustion, the fragments recombined instantly after the UV pulse within around 10 µs, whereas in gasification, the K(g) fragment concentration first increased further for 30 µs after the UV pulse, before slowly decaying for up to hundreds of µs. According to 0D reaction kinetics simulations, this could be explained by a difference in recombination kinetics, which is dominated by oxygen reactions in combustion and by hydrogen reactions in gasification. The K species concentrations in the EFG were stable on average, but periodic short-term variations due to fuel feeding were observed, as well as a gradual increase in KOH(g) over the day as the reactor approached global equilibrium. A comparison of the average K species concentrations towards the end of each experiment showed a higher total K in the gas phase for FR/WS, with higher K(g) and KCl(g), but lower KOH(g), compared to the FR fuel. The measured values were in reasonable agreement with predictions by thermodynamic equilibrium calculations.

Ort, förlag, år, upplaga, sidor
Elsevier, 2022
Nyckelord
Biomass, Entrained-flow gasification, Potassium (K), Photofragmentation, Tunable diode laser absorption spectroscopy (TDLAS)
Nationell ämneskategori
Annan fysik Atom- och molekylfysik och optik Kemiska processer
Identifikatorer
urn:nbn:se:umu:diva-199816 (URN)10.1016/j.proci.2022.07.180 (DOI)001019037700001 ()2-s2.0-85139508080 (Scopus ID)
Forskningsfinansiär
Bio4EnergyKempestiftelserna, JCK-1316Energimyndigheten, 50470-1Energimyndigheten, 36160-1EU, Horisont 2020, 637020
Tillgänglig från: 2022-09-29 Skapad: 2022-09-29 Senast uppdaterad: 2023-09-05
5. Numerical study and experimental verification of biomass conversion and potassium release in a 140 kW entrained flow gasifier
Öppna denna publikation i ny flik eller fönster >>Numerical study and experimental verification of biomass conversion and potassium release in a 140 kW entrained flow gasifier
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2023 (Engelska)Ingår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 37, nr 2, s. 1116-1130Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

In this study, a Eulerian–Lagrangian model is used to study biomass gasification and release of potassium species in a 140 kW atmospheric entrained flow gasifier (EFG). Experimental measurements of water concentration and temperature inside the reactor, together with the gas composition at the gasifier outlet, are used to validate the model. For the first time, a detailed K-release model is used to predict the concentrations of gas-phase K species inside the gasifier, and the results are compared with experimental measurements from an optical port in the EFG. The prediction errors for atomic potassium (K), potassium chloride (KCl), potassium hydroxide (KOH), and total potassium are 1.4%, 9.8%, 5.5%, and 5.7%, respectively, which are within the uncertainty limits of the measurements. The numerical model is used to identify and study the main phenomena that occur in different zones of the gasifier. Five zones are identified in which drying, pyrolysis, combustion, recirculation, and gasification are active. The model was then used to study the transformation and release of different K species from biomass particles. It was found that, for the forest residue fuel that was used in the present study, the organic part of K is released at the shortest residence time, followed by the release of inorganic K at higher residence times. The release of inorganic salts starts by evaporation of KCl and continues by dissociation of K2CO3 and K2SO4, which forms gas-phase KOH. The major fraction of K is released around the combustion zone (around 0.7–1.3 m downstream of the inlet) due to the high H2O concentration and temperature. These conditions lead to rapid dissociation of K2CO3 and K2SO4, which increases the total K concentration from 336 to 510 ppm in the combustion zone. The dissociation of the inorganic salts and KOH formation continues in the gasification zone at a lower rate; hence, the total K concentration slowly increases from 510 ppm at 1.3 m to 561 ppm at the outlet.

Nationell ämneskategori
Energiteknik Kemiska processer Atom- och molekylfysik och optik
Identifikatorer
urn:nbn:se:umu:diva-202444 (URN)10.1021/acs.energyfuels.2c03107 (DOI)000924910900001 ()36705624 (PubMedID)2-s2.0-85146130812 (Scopus ID)
Forskningsfinansiär
Energimyndigheten, 22538-4Kempestiftelserna, JCK-1316Knut och Alice Wallenbergs StiftelseEU, Horisont 2020, 637020Energimyndigheten, 50470-1Energimyndigheten, 36160-1Bio4Energy
Tillgänglig från: 2023-01-10 Skapad: 2023-01-10 Senast uppdaterad: 2023-09-05Bibliografiskt granskad
6. Quantitative tomographic laser absorption imaging of atomic potassium during combustion of potassium chloride salt and biomass
Öppna denna publikation i ny flik eller fönster >>Quantitative tomographic laser absorption imaging of atomic potassium during combustion of potassium chloride salt and biomass
2023 (Engelska)Ingår i: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 95, nr 2, s. 1140-1148Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Gaseous potassium (K) species play an important role in biomass combustion processes, and imaging techniques are powerful tools to investigate the related gas-phase chemistry. Here, laser absorption imaging of gaseous atomic K in flames is implemented using tunable diode laser absorption spectroscopy at 769.9 nm and a high-speed complementary metal oxide semiconductor (CMOS) camera recording at 30 kfps. Atomic K absorption spectra are acquired for each camera pixel in a field of view of 28 × 28 mm at a rate of 100 Hz. The technique is used to determine the spatial distribution of atomic K concentration during the conversion of potassium chloride (KCl) salt and wheat straw particles in a laminar premixed CH4/air flame with an image pixel resolution of up to 120 μm. Due to axisymmetry in setup geometry and, consequently, atomic K distributions, the radial atomic K concentration fields could be reconstructed by one-dimensional tomography. For the KCl sample, the K concentration field was in excellent agreement with previous point measurements. In the case of wheat straw, atomic K concentrations of around 3 ppm were observed in a cylindrical flame during devolatilization. In the char conversion phase, a spherical layer of atomic K, with concentrations reaching 25 ppm, was found within 5 mm of the particle surface, while the concentration rapidly decreased to sub-ppm levels along the vertical axis. In both cases, a thin (∼1 mm) layer without any atomic K was observed in close vicinity to the particle, suggesting that the potassium was initially not released in its atomic form.

Ort, förlag, år, upplaga, sidor
American Chemical Society (ACS), 2023
Nyckelord
Absorption, Biomass, Lasers, Potassium, Tomography
Nationell ämneskategori
Atom- och molekylfysik och optik Oorganisk kemi Kemiska processer Energiteknik
Identifikatorer
urn:nbn:se:umu:diva-202359 (URN)10.1021/acs.analchem.2c03890 (DOI)000907828300001 ()36584277 (PubMedID)2-s2.0-85145461360 (Scopus ID)
Forskningsfinansiär
Energimyndigheten, 36160-1Kempestiftelserna, JCK-1316Kempestiftelserna, JCK-2025Umeå universitetBio4Energy
Tillgänglig från: 2023-01-09 Skapad: 2023-01-09 Senast uppdaterad: 2023-04-27Bibliografiskt granskad

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