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Numerical study and experimental verification of biomass conversion and potassium release in a 140 kW entrained flow gasifier
Department of Energy Sciences, Division of Fluid Mechanics, Lund University, Lund, Sweden.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.ORCID-id: 0000-0002-7892-8138
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.ORCID-id: 0000-0002-5065-7786
RISE AB, Piteå, Sweden.
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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.

Ort, förlag, år, upplaga, sidor
2023. Vol. 37, nr 2, s. 1116-1130
Nationell ämneskategori
Energiteknik Kemiska processer Atom- och molekylfysik och optik
Identifikatorer
URN: urn:nbn:se:umu:diva-202444DOI: 10.1021/acs.energyfuels.2c03107ISI: 000924910900001PubMedID: 36705624Scopus ID: 2-s2.0-85146130812OAI: oai:DiVA.org:umu-202444DiVA, id: diva2:1725052
Forskningsfinansiär
Energimyndigheten, 22538-4Kempestiftelserna, JCK-1316Knut och Alice Wallenbergs StiftelseEU, Horisont 2020, 637020Energimyndigheten, 50470-1Energimyndigheten, 36160-1Bio4EnergyTillgänglig från: 2023-01-10 Skapad: 2023-01-10 Senast uppdaterad: 2023-09-05Bibliografiskt granskad
Ingår i avhandling
1. Quantitative laser diagnostics of gas-phase potassium species in biomass combustion and gasification
Öppna denna publikation i ny flik eller fönster >>Quantitative laser diagnostics of gas-phase potassium species in biomass combustion and gasification
2023 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Alternativ titel[sv]
Kvantitativ laserdiagnostik av kaliumföreningar i gas-fas vid förbränning och förgasning av biomassa
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
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:nbn:se:umu:diva-207313 (URN)978-91-8070-077-1 (ISBN)978-91-8070-078-8 (ISBN)
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

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