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Online investigation of steam gasification kinetics of biomass chars up to high temperatures
Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för bygg- och energiteknik (BE). (Bioenergy)
Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för bygg- och energiteknik (BE).
2014 (engelsk)Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, nr 1, s. 607-613Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

In this study, a novel aerosol-based method has been further developed and applied for on-line investigating of steam gasification kinetics of suspended biomass char particles. By combining the aerosol method with thermogravimetric analysis, the gasification kinetics were established in steam (33 vol%)-N2 atmosphere from 800°C to 1300°C for char samples produced from pelletized wood, straw, and miscanthus. The aerosol method includes steps for generating, suspending, and gasifying char particles. The conversion of the char particles was established by measuring the change in particle size distributions and mass concentrations using an aerodynamic particle sizer (APS) spectrometer and a tapered element oscillating microbalance (TEOM), respectively. The reactivity of three char samples could be ranked as wood > miscanthus > straw. The activation energy was 155 kJ·mol-1 for wood char, 199 kJ·mol-1 for miscanthus char, and 222 kJ·mol-1 for straw char. Results interpreted from TEOM and APS measurements indicated that the effective density of char particles initially decreased until a certain level of conversion was reached, and then remained constant. 

sted, utgiver, år, opplag, sider
American Chemical Society (ACS), 2014. Vol. 28, nr 1, s. 607-613
Emneord [en]
biomass, steam gasification, char, kinetics, aerosol, APS, TEOM
HSV kategori
Forskningsprogram
Teknik, Bioenergiteknik/Energi- och Miljöteknik
Identifikatorer
URN: urn:nbn:se:lnu:diva-31344DOI: 10.1021/ef402343xISI: 000330018200068Scopus ID: 2-s2.0-84892729774OAI: oai:DiVA.org:lnu-31344DiVA, id: diva2:682040
Tilgjengelig fra: 2013-12-21 Laget: 2013-12-21 Sist oppdatert: 2017-12-06bibliografisk kontrollert
Inngår i avhandling
1. Char conversion kinetics and aerosol characterization in biomass gasification
Åpne denne publikasjonen i ny fane eller vindu >>Char conversion kinetics and aerosol characterization in biomass gasification
2013 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Biomass gasification is a thermochemical conversion by partial oxidation at elevated temperature of solid biomass into a gaseous energy carrier. The product gas contains the major components CO, H2, CO2, CH4, as well as some tar and inorganic impurities and solid particles such as ash, bed material, soot and char. The aim of this work is to develop an aerosol-based method to investigate on-line the reactivity of the suspended biomass char particles at high temperatures, and to apply aerosol measurement systems for sampling and characterizing particulate matter in the hot product gas from gasifiers.

An aerosol-based method including the steps for generating, transporting, and oxidizing suspended char particles (0.5–10 µm) was proposed and developed for investigation of char reactivity at high temperatures. An aerodynamic particle sizer (APS) spectrometer was used to measure the particle size distributions. A tapered element oscillating microbalance (TEOM) was used to measure the change of mass concentrations of particles in the carrier gas, before and after conversion. The intrinsic kinetics of various biomass (wood, straw, miscanthus) char particles have been experimentally established in a wide temperature range for both combustion (in air/oxygen) and gasification (in 33 vol% CO2 or 33 vol% steam), up to 800°C and 1300°C, respectively, by combining the aerosol method with thermogravimetric analysis (TGA). The general CO2 or steam gasification reactivity of chars from different biomass could be ranked as wood > miscanthus > straw. In CO2 or steam gasification, the reactivity of char samples measured by the aerosol method at 1300°C would vary by a factor of 4-9 comparing with the extrapolated estimation from the TGA results at the low temperatures. This indicates that high-temperature reactivity estimation by extrapolation should be used with care. Variations of the morphology and the effective density of char particles during conversion indicated that in the initial stage of char conversion (either combustion or gasification), pore growth was dominant up to a certain conversion, and shrinkage or fusing would occur in the later stage. The aerosol-based method presents a set of benefits which are advantageous compared to previously established techniques: no mass transfer limitation at high temperatures; the flexibility to switch to different gas agent combined with continuous feeding of char sample; and the on-line measurement of particle mass and size. The aerosol method is not applicable under the conditions where the reaction rate is slow, since longer residence time will increase the probability of particle losses. In addition to laboratory applications, the aerosol method has potentials for on-line investigation of concentration and reactivity of suspended char fragments sampled directly from the product gas in different types of gasifiers.

Particulate matter (10 nm–10 µm) in the product gas was characterized for the size distribution, morphology and elemental composition by both on-line and off-line techniques. An aerosol particle measurement system including a dilution probe connected in series with a packed activated carbon bed was applied to extract aerosol from the hot product gas produced in the gasifiers using wood as feedstock: an indirect bubbling fluidized bed gasifier and a circulating fluidized bed (CFB) gasifier. The fine and coarse particles from the CFB gasifier contained calcium and magnesium, indicating the contributions from the ash and the magnesite bed material. From the indirect gasifier, the fine-mode (<0.5 µm) particles were dominated by potassium and chlorine whereas the coarse-mode (>0.5 µm) particles were dominated by calcium and silicon, probably from the ash and the bed material. Char fragments were identified in the hot product gas and contribute to the coarse-mode particles in both gasifiers.

 

sted, utgiver, år, opplag, sider
Växjö: Linnaeus University Press, 2013
Serie
Linnaeus University Dissertations ; 150/2013
Emneord
Biomass gasification, fluidized bed, char, kinetics, aerosol, APS, TEOM
HSV kategori
Forskningsprogram
Teknik, Bioenergiteknik/Energi- och Miljöteknik
Identifikatorer
urn:nbn:se:lnu:diva-31347 (URN)978-91-87427-56-5 (ISBN)
Disputas
2013-10-18, M1083, Hus M, Växjö, 10:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2014-02-25 Laget: 2013-12-23 Sist oppdatert: 2014-02-25bibliografisk kontrollert

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