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Influence of water vapour and tar compound on laminar flame speed of gasified biomass gas
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology.ORCID iD: 0000-0002-2992-6814
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
2012 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 98, 114-121 p.Article in journal (Refereed) Published
Abstract [en]

Biomass can be converted to a gaseous fuel through gasification in order to be used in higher efficiency conversion equipment. Combustion of a gaseous fuel generally allows for higher combustion temperatures than that of a solid fuel leading to the higher efficiency. However, the gasified biomass gas (GBG) contains condensable compounds, such as water vapour and tars, which both will affect the subsequent combustion process with respect to emission levels and flame stability. Cleaning of the GBG prior to combustion is very costly and therefore further research is needed on direct combustion of GBG containing these condensable compounds, in order to develop stable combustion techniques for GBG. The laminar flame speed is a main parameter that relates to other important flame properties such as stability, extinction limit and flashback. Each of GBG components have different chemical and transport properties, which then influences the laminar flame speed of GBG. In this study, the individual effect of water vapour (H2O) and tar compound addition in simulated GBG on laminar flame speed is investigated at atmospheric pressure. The tar compound used is benzene (C6H6) and simulated GBG used is CO/H-2/CH4/CO2/N-2 mixture. Experiments were carried out with conical burner stabilized flame and a Schlieren photography system. The volume fraction of additives in the fuel mixture was varied: for H2O from 0% to 5% and for C6H6 from 0% to 10%. The unburned fuel air mixture was preheated and the temperature was maintained at T-i = 398 K to avoid condensation of the liquid. It was found that measured laminar flame speed of GBG-air mixture decreases with addition of H2O in the fuel mixture. While, non-monotonic behaviour is shown with addition of C6H6. Initially, as the volume fraction of C6H6 incremented, the laminar flame speed decreases, reaching a minimum value, and then increase.

Place, publisher, year, edition, pages
2012. Vol. 98, 114-121 p.
Keyword [en]
Gasified biomass gas, Laminar flame speed, Water vapour, Benzene vapour
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-102606DOI: 10.1016/j.apenergy.2012.03.010ISI: 000306889200013Scopus ID: 2-s2.0-84862204229OAI: oai:DiVA.org:kth-102606DiVA: diva2:555653
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StandUp
Note

QC 20120921

Available from: 2012-09-21 Created: 2012-09-21 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Combustion of gasified biomass:: Experimental investigation on laminar flame speed, lean blowoff limit and emission levels
Open this publication in new window or tab >>Combustion of gasified biomass:: Experimental investigation on laminar flame speed, lean blowoff limit and emission levels
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Biomass is among the primary alternative energy sources that supplements the fossil fuels to meet today’s energy demand. Gasification is an efficient and environmental friendly technology for converting the energy content in the biomass into a combustible gas mixture, which can be used in various applications. The composition of this gas mixture varies greatly depending on the gasification agent, gasifier design and its operation parameters and can be classified as low and medium LHV gasified biomass. The wide range of possible gas composition between each of these classes and even within each class itself can be a challenge in the combustion for heat and/or power production. The difficulty is primarily associated with the range in the combustion properties that may affect the stability and the emission levels. Therefore, this thesis is intended to provide data of combustion properties for improving the operation or design of atmospheric combustion devices operated with such gas mixtures.

The first part of this thesis presents a series of experimental work on combustion of low LHV gasified biomass (a simulated gas mixture of CO/H2/CH4/CO2/N2) with variation in the content of H2O and tar compound (simulated by C6H6). The laminar flame speed, lean blowoff limit and emission levels of low LHV gasified biomass based on the premixed combustion concept are reported in paper I and III. The results show that the presence of H2O and C6H6 in gasified biomass can give positive effects on these combustion parameters (laminar flame speed, lean blowoff limit and emission levels), but also that there are limits for these effects. Addition of a low percentage of H2O in the gasified biomass resulted in almost constant laminar flame speed and combustion temperature of the gas mixture, while its NOx emission and blowoff temperature were decreased. The opposite condition was found when H2O content was further increased. The blowoff limit was shifted to richer fuel equivalence ratio as H2O increased. A temperature limit was observed where CO emission could be maintained at low concentration. With C6H6 addition, the laminar flame speed first decreased, achieved a minimum value, and then increased with further addition of C6H6. The combustion temperature and NOx emission were increased, CO emission was reduced, and blowoff occurs at slightly higher equivalence ratio and temperature when C6H6 content is increased. The comparison with natural gas (simulated by CH4) is also made as can be found in paper I and II. Lower laminar flame speed, combustion temperature, slightly higher CO emission, lower NOx emission and leaner blowoff limit were obtained for low LHV gas mixture in comparison to natural gas.

In the second part of the thesis, the focus is put on the combustion of a wide range of gasified biomass types, ranging from low to medium LHV gas mixture (paper IV). The correlation between laminar flame speed or lean blowoff limit and the composition of various gas mixtures was investigated (paper IV). It was found that H2 and content of diluents have higher influence on the laminar flame speed of the gas mixture compared to its CO and hydrocarbon contents. For lean blowoff limit, the diluents have the greatest impact followed by H2 and CO. The mathematical correlations derived from the study can be used to for models of these two combustion parameters for a wide range of gasified biomass fuel compositions.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 81 p.
Series
TRITA-KRV, ISSN 1100-7990 ; 13:03
Keyword
biomass gasification; gasified biomass; laminar flame speed; blowoff; emissions
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-120570 (URN)978-91-7501-710-5 (ISBN)
Public defence
2013-04-22, M3, Brinellvägen 64, KTH, Stockholm, 10:00 (English)
Opponent
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Note

QC 20130411

Available from: 2013-04-11 Created: 2013-04-11 Last updated: 2014-01-16Bibliographically approved

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