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Sökning: WFRF:(Fransson Torsten)

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41.
  • Baina Veizaga, Fabiola, 1985- (författare)
  • Externally fired gas turbine cycle based on biomass gasification gas as fuel
  • 2015
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Energy services are essential for the development of societies, reduce poverty, and improve the living standards of inhabitants. The conventional routes to provide energy services employ fossil fuels. However, this involves environmental and availability concerns. Environmental issues and the need for energy security demand the use of alternative energy sources. Biomass is a renewable energy source that is advantageous because of its dispatchability and local availability worldwide. Local generation at small scales is interesting because it reduces energy losses when transporting electricity and heat. The development of sustainable decentralized small scale heat and power plants (CHP) using biomass is thus important.In this context, this work is mainly focused on the development of an energy conversion technology based on an externally fired gas turbine using biomass gasification gas as fuel. Although this system is not new, its applicability with biomass gasification gas has not been widely studied. This work is divided in three parts. In the first part, the effect of the fuel composition and fuel inlet temperature on the performance of an externally fired gas turbine prototype is analyzed through simulations. Then, the performances of two types of heat exchangers are compared under the operational conditions of the prototype taking into account different thicknesses of deposit materials. The results shows that the composition of the fuels and the corresponding flue gas temperatures affect the electrical power output of the system. However, this is limited by the operating temperature of the heat exchanger. It is also reported that a decrease in the effectiveness of the heat exchanger has a greater influence on the electrical power output than an increase in the pressure drop as a result of deposit materials. High pressure drops in the hot side of the heat exchanger slightly affect the electrical power output. If biomass gasification gas is to be used after the gasifier with reduced cleaning steps, the effect of contaminants such as tar in the combustion performance is important. The last part in this work describes experimental studies of the effect of benzene as tar representative in the combustion performance of a surrogate mixture of biomass gasification gas. Polyaromatic hydrocarbons such as benzene, present in tar in biomass derived gas, affect the combustion emissions depending on their concentration in the fuel gas.
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42.
  • Binti Munajat, Nur Farizan (författare)
  • Combustion of gasified biomass: : Experimental investigation on laminar flame speed, lean blowoff limit and emission levels
  • 2013
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • 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.
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43.
  • Binti Munajat, Nur Farizan, et al. (författare)
  • Correlation of laminar flame speed and lean blowoff limit with the fuel composition of gasified biomass
  • Ingår i: Fuel. - 0016-2361 .- 1873-7153.
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The composition of the product gas produced from a biomass gasification process varies largely depending on several operational factors. The present study gathers the combustion information of different fuel mixtures that resemble the wide range of product gases from biomass gasification process. Two combustion parameters that are laminar flame speed, SL and lean blowoff limit, ERblowoff have been studied as functions of the content of H2 in the fuel mixture as well as the ratios of CO/H2, hydrocarbons/H2 and diluents/H2. From the plotted graphs, mathematical correlations between the parameter studied and the component of the gas mixture have been derived. The equations developed can be used to calculate the laminar flame speed and blowoff equivalent ratio for a wide range of gasified biomass. The graphs show that the H2 content and diluents/H2 ratio have the greatest influence on the laminar flame speed of the gas mixture and higher effect compared to the influence by the ratio of CO/H2 and hydrocarbons/H2. For the lean blowoff limit, the descending order of influence is the ratio of diluents/H2, H2 content and the ratio of CO/H2. While no importance on the lean blowoff limit is observed for the ratio of hydrocarbons/H2.
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44.
  • Binti Munajat, Nur Farizan, et al. (författare)
  • Influence of water vapour and tar compound on combustion of simulated gasified biomass
  • Ingår i: Fuel. - 0016-2361 .- 1873-7153.
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Gasification is a thermo‐chemical process which converts biomass fuel into a gaseous mixture, gasified biomass, which can be used in various prime movers. For heat and power generation, using gasified biomass in a combustion device, for example, can give lower undesired emission compared to direct combustion of solid biomass. However, with regards to its variety in composition and lower heating value, the combustion behaviour of gasified biomass may differ from natural gas. The main objective of this study is to investigate the influence of water and tar compound on the combustion of simulated gasified biomass, which mainly contains CO, H2, CH4, CO2, N2. The combustion tests are conducted at atmospheric pressure in a premixed combustor. At a fixed input thermal load, CO and NOx emission levels, combustion temperature, and blowoff characteristics of gasified biomass are observed while varying the volume fraction of water (H2O) or benzene (C6H6) vapours in the fuel mixture. With low H2O level in the fuel mixture, the combustion temperature is almost constant, while NOx emission is decreased compared to dry gasified biomass. On the contrary, the combustion temperature decreases and NOx emission is almost constant at higher H2O content. A temperature limit was observed where CO emission could be maintained at low concentration. The blowoff limit was shifted to higher equivalence ratio. The blowoff temperature was first slightly decreased at lower H2O level and raised when H2O level is further increased. With the content of C6H6, the combustion temperature and NOx emission enhanced, while CO emission was reduced. The blowoff occurs at slightly higher equivalence ratio and temperature compared to gasified biomass without C6H6. The study shows that the presence of H2O and C6H6 in gasified biomass may give positive effects on the emission characteristics during combustion, but also that there are limits for these effects.
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45.
  • Binti Munajat, Nur Farizan, et al. (författare)
  • Temperature, emission and lean blowoff limit of simulated gasified biomass in a premixed combustor
  • Ingår i: Applied Energy. - 0306-2619 .- 1872-9118.
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Biomass can be converted to a gaseous fuel through gasification in order to be used in higher efficiency conversion. Combustion of gasified biomass gas (GBG) in gas turbines, for example, potentially reduces the CO2 emission compared to natural gas and diminishes the dependence of fossil fuels. However, the wide variety in the gas composition and its lower heating value will affect the subsequent combustion process with respect to emission levels and flame stability. In this study, premixed combustion of simulated GBG is investigated experimentally at atmospheric pressure and compared with pure CH4 (simulated natural gas). Combustion performance in terms of emission levels and blowoff is observed. The GBG fuel with noncombustible to combustible components ratio of 1.5 is tested in comparison with pure CH4 at fixed input thermal load. The GBG fuel consists of a mixture of CO/H2/CH4/CO2/N2and its proportion reassembles the mixture from air‐blown gasification. The high diluent content decreases the lower heating value (LHV) and increases the volumetric flow compared to CH4. As a result, lower combustion temperature and different flame region than CH4were found in the combustor. However, the GBG combustion still can be stabilized at lower temperature and leaner condition compared to CH4 while maintaining low CO and NOx emissions. As low as ~15 ppm and ~5ppm of CO and NOxemissions, respectively, could be achieved at an equivalence ratio equal to 0.5. It was found that at a combustion temperature below ~800oC, both CO and UHC start to rise from their stable and low concentration. At different input thermal loads, a shift in the optimum operating condition for the GBG combustion was found. No auto‐ignition or flashback events were found during the combustion of GBG in all experiment conditions tested. The results show the possibility to use both GBG and natural gas in one and the same combustor without compromising low emission levels.
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