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Strandberg, A., Carlborg, M., Boman, C. & Broström, M. (2019). Ash Transformation During Single-Pellet Combustion of a Silicon-Poor Woody Biomass. Energy & Fuels, 33(8), 7770-7777
Open this publication in new window or tab >>Ash Transformation During Single-Pellet Combustion of a Silicon-Poor Woody Biomass
2019 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 33, no 8, p. 7770-7777Article in journal (Refereed) Published
Abstract [en]

Biomass fuels with calcium and potassium as the main ash-forming elements are expected to form ash consisting mainly of carbonates and oxides. These carbonates are stable in a rather narrow temperature range, which in turn depends on the Ca/K ratio, as well as on the surrounding atmosphere. The objective of the present study was to perform a detailed characterization of ash formation and transformation at a single-pellet level during combustion of silicon-poor woody biomass fuel. Combustion tests were performed with poplar in a single-pellet isothermal thermogravimetric analyzer operated at different temperatures and atmospheres and quenched at different stages of fuel conversion. The char and residual ashes were characterized for morphology and chemical composition. The focus of the experimental work in this study was on the time (conversion) resolved ash formation and transformations at the late part of the char combustion phase. Thermodynamic equilibrium calculations were used both to design the experiments and to support the interpretation of experimental results. It was concluded that carbonates were, in general, stable at low temperatures (here, 600–800 °C), identified as CaCO3, K2Ca2(CO3)3, and K2Ca(CO3)2, and decomposed at higher temperatures. In addition, a combined carbonate and phosphate phase in the form of carbonate apatite, Ca9.9(PO4)6(CO3)0.9, was also found, mainly at lower temperatures. However, for char/ash samples quenched before full conversion, CaCO3 was still found at temperatures higher than expected, possibly explained by the stabilizing effect of locally higher CO2 partial pressure within the burning fuel particles. Thus, the results of the present study provide new insights into conversion-based ash formation and transformation in a burning fuel particle with relevance for combustion of Si-poor woody biomass fuels.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
National Category
Bioenergy
Identifiers
urn:nbn:se:umu:diva-163274 (URN)10.1021/acs.energyfuels.9b00937 (DOI)000481569100090 ()2-s2.0-85070870382 (Scopus ID)
Available from: 2019-09-12 Created: 2019-09-12 Last updated: 2019-09-16Bibliographically approved
Sandström, K., Boman, C., Weidemann, E. & Broström, M. (2019). Fluorine reactions in MSW combustion. In: EUBCE 2019: . Paper presented at EUBCE 2019, 27th European Biomass Conference & Exhibition, 27-30 May, Lisbon, Portugal.
Open this publication in new window or tab >>Fluorine reactions in MSW combustion
2019 (English)In: EUBCE 2019, 2019Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

Fluorine is of increasing concern in waste combustion since fluorinated plastics constitute anincreasing share of waste fractions entering CHP plants. Alkali fluorides could potentially causesimilar problems as are well known for the corresponding chlorides. However, there are somefundamental differences in thermodynamic stabilities. Available literature essentially lacks theexperimental evidence needed to draw any further conclusions on the extent of any fluorine relatedproblems, but recently a MSW fired CHP reported alarming deposit growth rates, possibly relatedto a delivery of fluorine containing fuels. The objective of the present study was to experimentallyevaluate some of the thermodynamic considerations mentioned. Fuels were prepared by addingNaCl, NaF and S to softwood pellets. Deposit and aerosol samples were analyzed with SEM-EDSand XRD, and evaluated together with fundamental thermodynamic phase equilibriumconsiderations to provide new and important information on the ash forming reactions and theirimplications. The results from the combustion tests showed that the fluorine found on the depositprobe was in form of NaF and Na3F(SO4) in qualitative agreement with thermodynamicequilibrium calculations.

National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-162798 (URN)
Conference
EUBCE 2019, 27th European Biomass Conference & Exhibition, 27-30 May, Lisbon, Portugal
Available from: 2019-08-28 Created: 2019-08-28 Last updated: 2019-09-06Bibliographically approved
Strandberg, A., Skoglund, N., Thyrel, M., Lestander, T. A., Broström, M. & Backman, R. (2019). Time-Resolved Study of Silicate Slag Formation During Combustion of Wheat Straw Pellets. Energy & Fuels, 33(3), 2308-2318
Open this publication in new window or tab >>Time-Resolved Study of Silicate Slag Formation During Combustion of Wheat Straw Pellets
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2019 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 33, no 3, p. 2308-2318Article in journal (Refereed) Published
Abstract [en]

Ash formation during single-fuel pellet combustion of wheat straw at 700 and 1000 °C was studied throughout fuel conversion by quench cooling and analysis at different char conversion degrees. The combination of X-ray microtomography analysis and scanning electronic microscopy with energy-dispersive X-ray spectroscopy showed that ash accumulated in rigid net structures at 700 °C with streaks or small beads surrounding the char, and the pellet mostly maintained its size during the entire fuel conversion. At 1000 °C, the ash formed high-density melts that developed into bubbles on the surface. As the conversion proceeded, these bubbles grew in size and covered parts of the active char surface area, but without entirely blocking the gas transport. The successive char conversion dissolved increasing amounts of calcium in the potassium silicate melts, probably causing differences in the release of potassium to the gas phase. Similarities were found with slag from a combustion experiment in a domestic boiler, with regard to relative composition and estimated and apparent viscosity of the slag. Complete char encapsulation by ash layers limiting char burnout was not found at the single pellet level, nor to any greater extent from the experiment performed in a small domestic boiler.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
National Category
Inorganic Chemistry Other Environmental Engineering
Identifiers
urn:nbn:se:umu:diva-157725 (URN)10.1021/acs.energyfuels.8b04294 (DOI)000462260600064 ()
Projects
Bio4Energy
Funder
Swedish Research Council, 2014-5041Bio4Energy
Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-08-30Bibliographically approved
Strandberg, A., Skoglund, N., Thyrel, M., Lestander, T. A., Broström, M. & Backman, R. (2019). Wheat straw pellet combustion – characterization with X-ray micro-tomography and SEM-EDS analysis. In: : . Paper presented at World Sustainable Energy Days, 28 February, 2019, Wels, Austria.
Open this publication in new window or tab >>Wheat straw pellet combustion – characterization with X-ray micro-tomography and SEM-EDS analysis
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2019 (English)Conference paper, Oral presentation with published abstract (Refereed)
National Category
Energy Engineering
Identifiers
urn:nbn:se:umu:diva-157286 (URN)
Conference
World Sustainable Energy Days, 28 February, 2019, Wels, Austria
Funder
Swedish Research Council, 2014-5041Swedish Research Council Formas, 2017-01613
Available from: 2019-03-13 Created: 2019-03-13 Last updated: 2019-03-19
Broström, M., Holmgren, P. & Backman, R. (2018). Ash fractionation and slag formation during entrained flow biomass gasification. In: : . Paper presented at The 27th International Conference on the Impacts of Fuel Quality on Power Production and the Environment, Lake Louise, Alberta, Canada, September 24-28 2018..
Open this publication in new window or tab >>Ash fractionation and slag formation during entrained flow biomass gasification
2018 (English)Conference paper, Oral presentation only (Other academic)
National Category
Chemical Engineering Bioenergy
Identifiers
urn:nbn:se:umu:diva-152042 (URN)
Conference
The 27th International Conference on the Impacts of Fuel Quality on Power Production and the Environment, Lake Louise, Alberta, Canada, September 24-28 2018.
Available from: 2018-09-25 Created: 2018-09-25 Last updated: 2018-11-22Bibliographically approved
Strandberg, A., Thyrel, M., Skoglund, N., Lestander, T. A., Broström, M. & Backman, R. (2018). Biomass pellet combustion: cavities and ash formation characterized by synchrotron X-ray micro-tomography. Fuel processing technology, 176, 211-220
Open this publication in new window or tab >>Biomass pellet combustion: cavities and ash formation characterized by synchrotron X-ray micro-tomography
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2018 (English)In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 176, p. 211-220Article in journal (Refereed) Published
Abstract [en]

Ash formation during thermochemical conversion of biomass-based pellets influences both char conversion rates and ash-related operational problems. The objective of the present study was to provide detailed insights into changes in fuel and ash properties during fuel conversion. Pellets of poplar wood and wheat straw were used as model biofuels, representing vastly different compositions of ash-forming elements. Pellet samples at different char conversion phases were analyzed by synchrotron-based 3D X-ray micro-tomography, to map and visualize the development of cracks, internal cavities, and ash layers during conversion. The analysis of ash layers was complemented by scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. The results provide new insights into how large cracks and internal cavities are developed already during devolatilization, for example, the poplar wood pellets had a 64% void fraction after the devolatilization stage. As expected, there were large variations between the ash layer properties for the two fuels. A porous, low density, and calcium-rich ash was formed from the poplar fuel, whereas the wheat straw ash was a high-density silicate melt that developed into bubbles on the surface. As the conversion proceeded, the wheat straw ash covered parts of the active char surface area, but without blocking the gas transport.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
ash composition, pellet, thermochemical conversion, wheat straw, poplar, SEM-EDS
National Category
Chemical Process Engineering Bioenergy
Identifiers
urn:nbn:se:umu:diva-146673 (URN)10.1016/j.fuproc.2018.03.023 (DOI)
Projects
Bio4Energy
Available from: 2018-04-17 Created: 2018-04-17 Last updated: 2019-09-02Bibliographically approved
Trubetskaya, A., Brown, A., Tompsett, G. A., Timko, M. T., Kling, J., Broström, M., . . . Umeki, K. (2018). Characterization and reactivity of soot from fast pyrolysis of lignocellulosic compounds and monolignols. Applied Energy, 212, 1489-1500
Open this publication in new window or tab >>Characterization and reactivity of soot from fast pyrolysis of lignocellulosic compounds and monolignols
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2018 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 212, p. 1489-1500Article in journal (Refereed) Published
Abstract [en]

This study presents the effect of lignocellulosic compounds and monolignols on the yield, nanostructure and reactivity of soot generated at 1250 °C in a drop tube furnace. The structure of soot was characterized by electron microscopy techniques, Raman spectroscopy and electron spin resonance spectroscopy. The CO2 reactivity of soot was investigated by thermogravimetric analysis. Soot from cellulose was more reactive than soot produced from extractives, lignin and monolignols. Soot reactivity was correlated with the separation distances between adjacent graphene layers, as measured using transmission electron microscopy. Particle size, free radical concentration, differences in a degree of curvature and multi-core structures influenced the soot reactivity less than the interlayer separation distances. Soot yield was correlated with the lignin content of the feedstock. The selection of the extraction solvent had a strong influence on the soot reactivity. The Soxhlet extraction of softwood and wheat straw lignin soot using methanol decreased the soot reactivity, whereas acetone extraction had only a modest effect.

Place, publisher, year, edition, pages
Oxford: Elsevier, 2018
Keywords
Fast pyrolysis, Lignocellulosic compounds and monolignols, Soot, Reactivity, Nanostructure
National Category
Energy Engineering
Identifiers
urn:nbn:se:umu:diva-142747 (URN)10.1016/j.apenergy.2017.12.068 (DOI)000425200700110 ()
Available from: 2017-12-11 Created: 2017-12-11 Last updated: 2018-06-09Bibliographically approved
Wagner, D. R., Holmgren, P., Skoglund, N. & Broström, M. (2018). Design and validation of an advanced entrained flow reactor system for studies of rapid solid biomass fuel particle conversion and ash formation reactions. Review of Scientific Instruments, 89(6), Article ID 065101.
Open this publication in new window or tab >>Design and validation of an advanced entrained flow reactor system for studies of rapid solid biomass fuel particle conversion and ash formation reactions
2018 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 89, no 6, article id 065101Article in journal (Refereed) Published
Abstract [en]

The design and validation of a newly commissioned entrained flow reactor is described in the present paper. The reactor was designed for advanced studies of fuel conversion and ash formation in powder flames, and the capabilities of the reactor were experimentally validated using two different solid biomass fuels. The drop tube geometry was equipped with a flat flame burner to heat and support the powder flame, optical access ports, a particle image velocimetry (PIV) system for in situ conversion monitoring, and probes for extraction of gases and particulate matter. A detailed description of the system is provided based on simulations and measurements, establishing the detailed temperature distribution and gas flow profiles. Mass balance closures of approximately 98% were achieved by combining gas analysis and particle extraction. Biomass fuel particles were successfully tracked using shadow imaging PIV, and the resulting data were used to determine the size, shape, velocity, and residence time of converting particles. Successful extractive sampling of coarse and fine particles during combustion while retaining their morphology was demonstrated, and it opens up for detailed time resolved studies of rapid ash transformation reactions; in the validation experiments, clear and systematic fractionation trends for K, Cl, S, and Si were observed for the two fuels tested. The combination of in situ access, accurate residence time estimations, and precise particle sampling for subsequent chemical analysis allows for a wide range of future studies, with implications and possibilities discussed in the paper.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2018
National Category
Other Physics Topics
Identifiers
urn:nbn:se:umu:diva-147729 (URN)10.1063/1.5030603 (DOI)000437195200054 ()29960572 (PubMedID)2-s2.0-85048128383 (Scopus ID)
Projects
Bio4Energy
Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2019-09-02Bibliographically approved
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
Wiinikka, H., Toth, P., Jansson, K., Molinder, R., Broström, M., Sandström, L., . . . Weiland, F. (2018). Particle formation during pressurized entrained flow gasification of wood powder: effects of process conditions on chemical composition, nanostructure, and reactivity. Combustion and Flame, 189, 240-256
Open this publication in new window or tab >>Particle formation during pressurized entrained flow gasification of wood powder: effects of process conditions on chemical composition, nanostructure, and reactivity
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2018 (English)In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 189, p. 240-256Article in journal (Refereed) Published
Abstract [en]

The influence of operating condition on particle formation during pressurized, oxygen blown gasification of wood powder with an ash content of 0.4 wt% was investigated. The investigation was performed with a pilot scale gasifier operated at 7 bar(a). Two loads, 400 and 600 kW were tested, with the oxygen equivalence ratio (λ) varied between 0.25 and 0.50. Particle concentration and mass size distribution was analyzed with a low pressure cascade impactor and the collected particles were characterized for morphology, elemental composition, nanostructure, and reactivity using scanning electron microscopy/high resolution transmission electron microscopy/energy dispersive spectroscopy, and thermogravimetric analysis. In order to quantify the nanostructure of the particles and identify prevalent sub-structures, a novel image analysis framework was used. It was found that the process temperature, affected both by λ and the load of the gasifier, had a significant influence on the particle formation processes. At low temperature (1060 °C), the formed soot particles seemed to be resistant to the oxidation process; however, when the oxidation process started at 1119 °C, the internal burning of the more reactive particle core began. A further increase in temperature ( > 1313 °C) lead to the oxidation of the less reactive particle shell. When the shell finally collapsed due to severe oxidation, the original soot particle shape and nanostructure also disappeared and the resulting particle could not be considered as a soot anymore. Instead, the particle shape and nanostructure at the highest temperatures ( > 1430 °C) were a function of the inorganic content and of the inorganic elements the individual particle consisted of. All of these effects together lead to the soot particles in the real gasifier environment having less and less ordered nanostructure and higher and higher reactivity as the temperature increased; i.e., they followed the opposite trend of what is observed during laboratory-scale studies with fuels not containing any ash-forming elements and where the temperature was not controlled by λ.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Gasification, Biomass, Soot, Nanostructure, HRTEM
National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-142615 (URN)10.1016/j.combustflame.2017.10.025 (DOI)000426535500020 ()
Available from: 2017-12-05 Created: 2017-12-05 Last updated: 2018-06-09Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-1095-9154

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