| 1. |
- Bach Oller, Albert, et al.
(författare)
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Fuel conversion characteristics of black liquor and pyrolysis oil mixture for efficient gasification with inherent catalyst
- 2014
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Ingår i: European biomass conference and exhibition proceedings. - 9788889407523
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Konferensbidrag (refereegranskat)abstract
- This paper describes the technical feasibility of a catalytic co-gasification process using a mixture of black liquor (BL) and pyrolysis oil (PO). A technical concern is if gasifiers can be operated at low temperature (~1000 ºC) without problems of tar, soot or char, as is the case for pure BL due to the catalytic effect of fuel alkali. Hence, we investigated fuel conversion characteristics of BL/PO mixture: conversion of single droplet in flame, and char gasification reactivity. 20wt.% (BP20) and 30wt.% (BP30) were selected for weight fraction of PO because of lignin precipitation in BP30. Single droplet was devolatilized and gasified in a methane flame with a flat flame burner at various droplet sizes. Conversion time and swelling ratio were investigated with imaging. They were more sensitive to initial droplet size and reaction atmosphere than the mixing of BL and PO. Char gasification reactivity was measured in an isothermal thermogravimeter (iTG) at T=880–940 ºC and PCO2=1 bar. Both BP20 and BP30 showed complete char conversion and there was no statistically significant difference in char reactivity among BP20, BP30 and BL. These results show that PO can be co-gasified in BL gasification process without major changes in the operation.
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| 2. |
- Biswas, Amit, et al.
(författare)
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Change of pyrolysis characteristics and structure of woody biomass due to steam explosion pretreatment
- 2011
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Ingår i: Fuel processing technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 92:10, s. 1849-1854
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Tidskriftsartikel (refereegranskat)abstract
- Steam explosion (SE) pretreatment has been implemented for the production of wood pellet. This paper investigated changes in biomass structure due to implication of steam explosion process by its pyrolysis behavior/ characteristics. Salix wood chip was treated by SE at different pretreatment conditions, and then pyrolysis characteristic was examined by thermogravimetric analyzer (TGA) at heating rate of 10 K/min. Both pyrolysis characteristics and structure of biomass were altered due to SE pretreatment. Hemicellulose decomposition region shifted to low temperature range due to the depolymerization caused by SE pretreatment. The peak intensities of cellulose decreased at mild pretreatment condition while they increased at severe conditions. Lignin reactivity also increased due to SE pretreatment. However, severe pretreatment condition resulted in reduction of lignin reactivity due to condensation and re-polymerization reaction. In summary, higher pretreatment temperature provided more active biomass compared with milder pretreatment conditions. © 2011 Elsevier B.V. All rights reserved.
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| 3. |
- Biswas, Amit, et al.
(författare)
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Effect of pelletizing conditions on combustion behaviour of single wood pellet
- 2014
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Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 119:15, s. 79-84
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents how pelletizing die temperature and moisture content affect combustion behaviour of single wood pellet. Pine wood particles with two different moisture contents (i.e. 1 wt.% and 12 wt.%) were pelletized in a laboratory-scale single pelletizer (single die pellets) at die temperature of 20, 100, 150 and 200 °C. The pellets were combusted in a laboratory scale furnace at 800 °C. Time required for single pellet combustion generally increased with both increase of pelletizing temperature and moisture content of biomass. In addition, combustion behaviour of single die pellets was significantly different than those produced in a pilot scale pelletizing plant (semi-industrial scale pellet). That difference was due to variation in physical properties of pellets (e.g. density, and morphology).
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| 4. |
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| 5. |
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| 6. |
- Kramb, Jason, et al.
(författare)
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Modeling biomass char gasification kinetics for improving prediction of carbon conversion in a fluidized bed gasifier
- 2014
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 132, s. 107-115
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Tidskriftsartikel (refereegranskat)abstract
- Gasification of biomass in a fluidized bed (FB) was modeled based on kinetic data obtained from previously conducted thermogravimetric analysis. The thermogravimetric analysis experiments were designed to closely resemble conditions in a real FB gasifier by using high sample heating rates, in situ devolatilization and gas atmospheres of H2O/H2 and CO2/CO mixtures. Several char kinetic models were evaluated based on their ability to predict char conversion based on the thermogravimetric data. A modified version of the random pore model was shown to provide good fitting of the char reactivity and suitability for use in a reactor model. An updated FB reactor model which incorporates the newly developed char kinetic expression and a submodel for the estimation of char residence time is presented and results from simulations were compared against pilot scale gasification data of pine sawdust. The reactor model showed good ability for predicting char conversion and product gas composition.
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| 7. |
- Prabowo, Bayu, et al.
(författare)
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CO2–steam mixture for direct and indirect gasification of rice straw in a downdraft gasifier : Laboratory-scale experiments and performance prediction
- 2014
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 113, s. 670-679
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Tidskriftsartikel (refereegranskat)abstract
- This paper explored the feasibility of CO2 as alternative gasifying agent of steam to obtain higher thermal efficiency in biomass gasification. The effect of the gasifying agent on gas evolution and thermal efficiency was examined by using a lab scale downdraft gasifier. The results were also compared with the output of pyrolysis with N2. The reaction atmosphere in indirect and direct gasification was simulated by carrying out the experiments without and with O2 presence. The reaction conditions were varied in the temperature range from 750 °C to 950 °C by changing the CO2 molar fraction in gasifying agent to the ratio of 0, 30 and 60 vol.% in balance with steam. 40 vol.% of N2 fraction was kept during O2 free experiments, while 31.7 vol.% of N2 and 8.3 vol.% O2 were kept during the experiments with the presence of O2. At all examined condition, gasification yielded more combustible gas than pyrolysis. Furthermore, high CO2 fraction in gasifying agent generally resulted in low H2 yield and high CO yield. These substitutions mostly lowered the energy yield of the producer gas, but in the other hand also reduced the preheating energy of gasifying agent. Thus, optimizations of these changes were investigated for gaining highest thermal efficiency of the gasification process. Highest thermal efficiency of the process without O2 was 52% under N2 (40 vol.%)–CO2 (60 vol.%) atmosphere at the temperature of 850 °C. For the process with O2, where the part of gasifying agent preheating energy supplied by the biomass partial combustion, the highest thermal efficiency was 60% under the CO2 (60 vol.%)–O2 (8.3 vol.%)–N2 (31.7 vol.%) atmosphere at the temperature of 950 °C. CO2 utilization as a gasifying agent potentially increases the thermal efficiency of biomass conversion process compared with pyrolysis or conventional indirect and direct gasification, i.e. pure-steam gasification and O2–steam gasification.
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| 8. |
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| 9. |
- Tanaka, Yasuto, et al.
(författare)
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Performance of a Hybrid Power Generation System Using Biomass Gasification and Concentrated Solar Thermal Processes
- 2014
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Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 61, s. 2149-2153
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Tidskriftsartikel (refereegranskat)abstract
- A hybrid power generation system using biomass gasification and concentrated solar thermal processes (CSTP) was proposed. We analysed the system performance of a combined cycle with a bubbling fluidized bed gasifier (BFG) using CO2-H2O-O2 mixture and CSTP using molten salt. BFG was simulated by a semi-kinetic model, applying a continuously stirred tank reactor (CSTR) model for the bed behaviour and a plug flow reactor (PFR) model for the freeboard reactions. Operating conditions of the plant and heat exchanger network were optimized separately. The current paper shows the effects of gasifying agents and heat input from CSTP on system efficiency among examined parameters. Pure steam at the molar ratio of steam to carbon in biomass around 0.5 was optimum gasifying agent in this system. By increasing heat input from CSTP, marginal efficiency of biomass-to-electricity was enhanced by 6.2-6.5% (from 39.9 ∼41.2% to 46.1∼47.5%).
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| 10. |
- Umeki, Kentaro, et al.
(författare)
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A model of biomass char gasification describing the change in catalytic activity of ash
- 2012
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 207-208, s. 616-624
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensive description of catalytic effects during chargasification under various conditions relevant for biomassgasification was made. A three-parallel reaction model was proposed to describe the dynamic change in catalyticactivity of ash during gasification of biomasschar particles. Three different regimes of conversion were identified by analyzing char reactivity experiments conducted in a vertical TGA with 9 biomasses under a wide range of operating conditions (temperature: 1023-1123 K, pressure: 0.1-3.0 MPa and gasification mixtures of CO2 –CO–H2O–H2): (1) catalyticchargasification with the deactivation of catalyst, (2) non-catalyticchargasification, and (3) catalyticchargasification with small amount of stable ash, without suffering deactivation. Amodel including the three regimes was developed and the measurements were used to fit the kinetic coefficients. It is shown that the model accurately predicts the reactivity of biomasschar in CO2 –CO mixtures during the whole range of conversion. It was detected that chargasification maintains the catalyticactivity during the entire conversion process when: (i) biomasses having small amount of silicon was used, and (ii) steam is used as part of the gasification agent. The model is still useful as predicting tool for these two conditions but its physical significance is contestable on the light of the model developed. For the conditions where the model is valid, it is shown that the model is a useful tool as sub-model in reactor simulations, predicting the conversion rate of single particles fast and accurately at different stages of conversion. The aspects that need to be further investigated for expanding the applicability of the model were identified.
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| 11. |
- Umeki, Kentaro, et al.
(författare)
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A simple expression for the apparent reaction rate of large wood char gasification with steam
- 2010
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Ingår i: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 101:11, s. 4187-4192
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Tidskriftsartikel (refereegranskat)abstract
- A simple expression for the apparent reaction rate of large wood char gasification with steam is proposed. Large char samples were gasified under steam atmosphere using a thermo-balance reactor. The apparent reaction rate was expressed as the product of the intrinsic rate and the effective factor. The effective factor was modified to include the effect of change in char diameter and intrinsic reaction rate during the reaction. Assuming uniform conversion ratio throughout a particle, the simplified reaction scheme was divided into three stages. In the initial stage, the local conversion ratio increases without particle shrinkage. In the middle stage, the particle shrinks following the shrinking core model without change in the local conversion ratio. In the final stage, the local conversion ratio increases without particle shrinkage. The validity of the modified effective value was confirmed by comparison with experimental results. (C) 2010 Elsevier Ltd. All rights reserved.
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| 12. |
- Umeki, Kentaro, et al.
(författare)
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Analysis of an updraft biomass gasifier with high temperature steam using a numerical model
- 2012
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 90:1, s. 38-45
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Tidskriftsartikel (refereegranskat)abstract
- High temperature steam gasification (HTSG) is a gasification technology which utilizes super-heated steam at a temperature above 1273 K. This paper addresses the performance analysis of an updraft HTSG gasifier using a numerical model. The experimental data obtained from a demonstration-scale gasifier was successfully simulated by the developed model. The calculation results showed 150-300 K temperature difference between gas phase and solid phase throughout the bed. Among a number of reactions, char gasification and water-gas shift reaction at char gasification zone played a major role to determine the syn-gas composition. Steam temperature, the ratio of steam to biomass and biomass feed rate affected the syn-gas composition while biomass particle diameter showed no significant effect. For the steam temperature and the ratio of steam to biomass, the difference of solid temperature at the bottom of gasifier determined the syn-gas composition. For biomass feed rate, the ratio of unreacted char extracted from the bottom of gasifier to supplied biomass determined the syn-gas composition.
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| 13. |
- Umeki, Kentaro, et al.
(författare)
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Fuel particle conversion of pulverized biomass during pyrolysis in an entrained flow reactor
- 2012
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 51:43, s. 13973-13979
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Tidskriftsartikel (refereegranskat)abstract
- This study addresses the change of char morphology and fuel conversion during pyrolysis in a laminar entrained flow reactor by experiments and particle simulation. Three experimental parameters were examined: reaction temperature (1073 and 1273 K); particle size (125–250, 250–500, and 500–1000 μm); and the length of reaction zone (650 and 1885 mm). The scanning electron microscopic (SEM) images showed that biomass swelled during heating and shrank during initial stage of pyrolysis. Then, char morphology transformed to cenospheres after the plastic stage. The yields of solid residue from the experiments were reasonably predicted by particle simulation. To give a guideline for the design of laminar entrained flow pyrolysis reactors, the required reactor length for complete conversion of biomass was also calculated for the pyrolysis. High reaction temperature, small particles, and slower gas flow were favorable for high fuel conversion.
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| 14. |
- Umeki, Kentaro, 1982-, et al.
(författare)
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High temperature steam-only gasification of woody biomass
- 2010
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 87:3, s. 791-798
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Tidskriftsartikel (refereegranskat)abstract
- We have studied a high temperature steam gasification process to generate hydrogen-rich fuel gas from woody biomass. In this study, the performance of the gasification system which employs only high temperature steam exceeding 1200 K as the gasifying agent was evaluated in a 1.2 ton/day-scale demonstration plant. A numerical analysis was also carried out to analyze the experimental results. Both the steam temperature and the molar ratio of steam to carbon (S/C ratio) affected the reaction temperature which strongly affects the gasified gas composition. The H2 fraction in the produced gas was 35–55 vol.% at the outlet of the gasifier. Under the experimental conditions, S/C ratio had a significant effect on the gas composition through the dominant reaction, water–gas shift reaction. The tar concentration in the produced gas from the high temperature steam gasification process was higher than that from the oxygen-blown gasification processes. The highest cold gas efficiency was 60.4%. However, the gross cold gas efficiency was 35%, which considers the heat supplied by high temperature steam. The ideal cold gas efficiency of the whole system with heat recovery processes was 71%.
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| 15. |
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| 16. |
- Umeki, Kentaro, et al.
(författare)
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The effect of steam on pyrolysis and char reactions behavior during rice straw gasification
- 2012
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Ingår i: Fuel processing technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 94:1, s. 53-60
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Tidskriftsartikel (refereegranskat)abstract
- Steam gasification of biomass can generate hydrogen-rich, medium heating value gas. We investigated pyrolysis and char reaction behavior during biomass gasification in detail to clarify the effect of steam presence. Rice straw was gasified in a laboratory scale, batch-type gasification reactor. Time-series data for the yields and compositions of gas, tar and char were examined under inert and steam atmosphere at the temperature range of 873–1173 K. Obtained experimental results were categorized into those of pyrolysis stage and char reaction stage. At the pyrolysis stage, low H2, CO and aromatic tar yields were observed under steam atmosphere while total tar yield increased by steam. This result can be interpreted as the dominant, but incomplete steam reforming reactions of primary tar under steam atmosphere. During the char reaction stage, only H2 and CO2 were detected, which were originated from carbonization of char and char gasification with steam (C + H2O→CO + H2). It implies the catalytic effect of char on the water–gas shift reaction. Acceleration of char carbonization by steam was implied by faster hydrogen loss from solid residue.
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