| 1. |
- Binti Munajat, Nur Farizan
(författare)
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Combustion of gasified biomass: : Experimental investigation on laminar flame speed, lean blowoff limit and emission levels
- 2013
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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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| 2. |
- Binti Munajat, Nur Farizan, et al.
(författare)
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Correlation of laminar flame speed and lean blowoff limit with the fuel composition of gasified biomass
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Ingår i: Fuel. - 0016-2361 .- 1873-7153.
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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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| 3. |
- Binti Munajat, Nur Farizan, et al.
(författare)
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Influence of water vapour and tar compound on combustion of simulated gasified biomass
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Ingår i: Fuel. - 0016-2361 .- 1873-7153.
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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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| 4. |
- Binti Munajat, Nur Farizan, et al.
(författare)
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Temperature, emission and lean blowoff limit of simulated gasified biomass in a premixed combustor
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Ingår i: Applied Energy. - 0306-2619 .- 1872-9118.
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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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| 5. |
- Birru, Eyerusalem, et al.
(författare)
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A Comparison of Various Technological Options for Improving Energy and Water Use Efficiency in a Traditional Sugar Mill
- 2016
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Ingår i: Sustainability. - : MDPI AG. - 2071-1050. ; 8:12
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Tidskriftsartikel (refereegranskat)abstract
- This study is a comparison of four technological improvements proposed in previous works for the Cuban sugar mill Carlos Balino. These technological options are: (1) utilization of excess wastewater for enhanced imbibition; (2) utilization of waste heat for thermally driven cooling; (3) utilization of excess bagasse for pellets; and (4) modification of the cogeneration unit for maximum electric power generation. The method used for the evaluation of the technological options involves using criteria such as energy saving, financial gains, and CO2 emission saving potential. The results of the analysis show that the first three technological improvement options are attractive only during the crushing season. On the other hand, the last technological improvement option can be attractive if a year round generation of surplus power is sought. The first technological improvement option leads to only minor changes in energy utilization, but the increase in sugar yield of 8.7% leads to attractive profitability with an extremely low payback period. The CO2 emissions saved due to the fourth technological improvement option are the highest (22,000 tonnes/year) and the cost of CO2 emissions saved for the third technological improvement option (lowest) amount to 41 USD/tonne of CO2 emissions saved. The cycle efficiencies of the third and fourth technological improvement options are 37.9% and 36.8%, respectively, with payback periods of 2.3 and 1.6 years. The second technological improvement option is the least attractive alternative of the group.
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| 6. |
- Birru, Eyerusalem, et al.
(författare)
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Assessing the potential of energy saving in a traditional sugar canemill during steady state and transient conditions : part I: basecase plant model
- 2015
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Ingår i: Biomass Conversion and Biorefinery. - : Springer. - 2190-6823 .- 2190-6815.
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Tidskriftsartikel (refereegranskat)abstract
- Sugar cane mills are energy intensive industries andalso have a large potential of providing surplus energy interms of heat or power. Identification of heat and mechanicallosses in sugar mills is one approach in indicating energysaving potential in sugar mills, especially in traditional mills.Such assessment of the energy flows in sugar mills needs to bedone both in steady state and transient conditions (where suddenstoppages occur). In this paper, such an approach is consideredwhere a base case plant is modeled for steady state andtransient state operations. For the transient state study, a typicalstoppage is chosen and three different scenarios aremodeled. Heat loss calculations are done for major cogenerationunits and for the amount accumulated of the surplus bagassewhen the steady state operation is estimated. The resultsof the models show that during steady state operation, thelosses related to mechanical prime movers is on the higherside as the mills and shredder are driven by steamand generatemechanical power higher than what is needed by the mills andthe shredder equipment themselves. In the transient statescenarios, where fuel oil is introduced during press mill stoppage,there is steam wasted (steam that could have been usedfor mechanical power generation) starting from the periodwhere the fuel oil is introduced until the power required duringthe stoppage is reached. The CO2 emission during the use offuel oil is also quite significant during the stoppage.
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| 7. |
- Birru, Eyerusalem Deresse, 1977-
(författare)
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Process Utility Performance Evaluation and Enhancements in the Traditional Sugar Cane Industry
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The need to achieve sustainable development has led to devising various approaches for the efficient utilization of natural resources. Renewable energy technology and energy efficiency measures feature prominently in this regard, and in particular for industries such as sugar production: the sugar cane industry’s eponymous feedstock is a renewable resource, and mills have potential for increased energy savings via improvements to cogeneration units, electric drive retrofitting, and other measures. The overall objective of this research work is to investigate different approaches of efficiency improvements for enhancing sugar cane conversion, thereby increasing the services obtained including surplus electric power delivery. Traditional sugar cane mills, i.e. those that lack modern components such as high-performance boilers and electric drives, are the focus of this investigation. System simulations show that modern mills generate more electrical power as compared to traditional mills, with power-to-heat ratios nearly one order of magnitude higher (i.e. 0.3-0.5). Comparison of the thermodynamic performance of three retrofits showed that such modifications could raise the performance of traditional mills to approach those for their modern counterparts. Results for a base case traditional plant show that losses related to mechanical prime movers are high, since the mills and shredder are driven by steam and generate excess mechanical power. When considering press mill stoppages, steam is wasted during the ensuing fuel oil-fired start-up period. CO2emission for such transient conditions can be decreased owing via bagasse drying and storage. In studying both energy and water impacts, a comparison of four technological improvements demonstrates benefits outside the crushing season for three scenarios: recovery of excess wastewater for enhanced imbibition; recovery of waste heat for thermally-driven cooling; and pelletization of excess bagasse. The fourth option, involving upgrading of the mill’s cogeneration unit, is advantageous for continuous surplus power supply.
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| 8. |
- Birru, Eyerusalem, et al.
(författare)
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Energy performance comparisons and enhancements in the sugar cane industry
- 2019
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Ingår i: Biomass Conversion and Biorefinery. - : Springer Berlin/Heidelberg. - 2190-6815 .- 2190-6823. ; 9:2, s. 267-282
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Tidskriftsartikel (refereegranskat)abstract
- In this study, energy-related operational parameters for modern and traditional (conventional) sugar mills are analyzed, with the goals of identifying improvements in energy efficiency and potential for surplus electricity export. Results show that the power- to-heat ratio of modern and traditional mills is clearly distinct, lying in the ranges of 0.3–0.5 and 0.04–0.07, respectively. Modifications under consideration for the traditional mills include the following upgrades: electric drives and higher capacity back-pressure turbine (case 1); high-pressure boiler, condensing extraction steam turbine and electric drives (case 2); and improvements in case 2 plus bagasse drying (case 3). The thermodynamic impact of these modifications shows that more power is generated as the modification becomes more advanced. Case 1 exhibits a modest increase in cogeneration efficiency (4%) as compared to the base case, while the cogeneration efficiency increase is more marked for cases 2 and 3 (21% and 31%, respectively). Surplus power was studied in a regional context, where it was found that the contribution of 19 retrofitted sugar mills in nine Brazilian regions could supply 30% or more power as compared to current installed power capacity. The economic analysis showed that levelized cost of electricity (LCOE) was lowest for case 1 (11 USD/MWh) and highest for cases 2 and 3 (58 USD/kWh).
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| 9. |
- Birru, Eyerusalem, et al.
(författare)
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Upgrading of a traditional sugar cane mill to a modern milland assessing the potential of energy saving during steady stateand transient conditions : part II: models for a modifiedcogeneration unit
- 2016
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Ingår i: Biomass Conversion and Biorefinery. - : Springer. - 2190-6823 .- 2190-6815. ; 6:2, s. 233-245
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Tidskriftsartikel (refereegranskat)abstract
- It is known that there is a significant amount ofthermal energy used for the sugar cane industry for the purposeof power production and for use in the sugar or ethanolprocessing in cane sugar industries. Likewise, it is understoodthat there are substantial amounts of waste heat that is notbeing recovered, in particular for traditional sugar mills. Regardlessof this, energy conservation is given less considerationas compared to operational convenience due to the factthat sugar mills are self-sufficient in energy (heat and power).The identification of such potential heat loss areas (especiallyduring transient conditions) suggests the sugar mills play avital role in energy saving. In this study, a modified setup ofthe base case plant considered in part I of this paper is assessedfor its energy potential and possible major heat losses duringsteady state and transient conditions where 2-h stoppage of themill presses are considered to occur. For the modified setup,there are two major scenarios considered having two subscenarioseach. The result of the assessment showed that thesteady state assumption scenario of the modified plant (wherebagasse drying is not considered) indicated a 20 % reductionin the losses considered which resulted in a 57 % power generationincrease as compared to the steady state model of thebase case plant. It is also possible to save excess bagasse bydrying the bagasse for later use during unexpected stoppage.The carbon dioxide emission (amounting 29 t/day in case 2aof this study) that occurs during the use of fuel oil during suchstoppages will thus be avoided. The simple economic analysisshowed that it is only in case 2a where fuel oil cost is includedin the operation cost that resulted in a negative NPV. Since therest of the scenarios use bagasse as a fuel which is free, theNPV for all was positive. For the electricity price of 0.04 US$/kWh and discount rate of 15 %, the minimum paybackperiod attained is about 3 years (case 1b) where the bagassemoisture content is 30 % whereas the maximum payback periodis 6 years (case 1a) where there is no bagasse dryingconsidered.
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| 10. |
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