| 1. |
- 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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| 2. |
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| 3. |
- Biswas, Amit
(författare)
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Effect of chemical and physical properties on combustion of biomass particle
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biomass combustion is an interesting alternative to fossil fuel. Modeling and simulation is used for design optimization of biomass boilers and furnace. It is difficult to develop a sufficiently accurate and computationally efficient model because the combustion system is highly complicated multi-scale, multi-phase and multi-physics problem. The study of biomass combustion in different scales allows engineers to understand the combustion process and tochoose necessary simplification to develop a computationally efficient model.The chemical and physical properties of fuels are altered during different fuel preparation methods (i.e. pretreatment and pelletization), and as a result the fuel conversion is also affected. The aim of this thesis is to understand thermal conversion of those chemically or physically altered fuels. Both experimental and modeling techniques were chosen to addressthe aim. Experiments were performed in thermogravimetric analysers, isothermal macro thermogravimeters (iTG), and a pot furnace to account fuel conversion in micro-, meso- and macro scale. In addition, three different types of mathematical model were developed. They are (i) a simplified particle pyrolysis model, (ii) two detailed numerical models that simulate particle pyrolysis and char oxidation and (iii) finally a computational fluid dynamic (CFD) model of combustion of biomass particles in a bed. The results indicate that both the intrinsic and the apparent conversion of the fuel wasinfluenced by the process conditions of fuel preparation methods. Intrinsic pyrolysis reactivitywas reduced due to mild pretreatment; however, it was increased with further increase in pretreatment severity. In contrary, severity of pelletization tends to reduce the apparent reactivity of pellets combustion. It was also investigated that how each physical and chemical parameter should be modelledfor a untreated biomass (i.e. wood logs) and a densified biomass (i.e. pellets) through parametric studies with a detailed particle simulation. The result shows that a model for wood logs should exclude convective heat transfer by volatiles if the fibers align to longitude direction while it is important part in the models for pellets. Devolatilization of wood logs was expressed as endothermic reactions while the model results showed best agreement withexperimental data of wood pellets when the heat of reaction was assumed to be zero, possibly due to the secondary reactions. Then, it was demonstrated that a constitutive equation, i.e. analytical solution of the shrinking core model, is sufficient to express devolatilization rate of thermally-thick particles at the temperature of 1173 K. While studying apparent oxidation of wood pellet char , it was found that change in intrinsic char oxidation reactivity due to different pyrolysis conditions does not influences the model prediction at high temperature. In addition, at high temperature, the reaction front became thin and reaction rate was hardly affected by temperature.It was also found by the simulation of pellet bed combustion that the apparent density of the particle significantly affected the flame velocity.
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| 4. |
- 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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| 5. |
- Biswas, Ashis, et al.
(författare)
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Estimating the role of competing ions on the arsenic mobilization processes in the aquifers of Bengal Basin by surface complexation modeling
- 2013
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Konferensbidrag (refereegranskat)abstract
- This study investigates the relative roles of the different competing ions on the arsenic (As) mobilization in the sedimentary aquifers of Bengal basin by surface complexation modeling of the temporal varaibility of As in shallow (<50 m) groundwater. Two sets of piezometers (2×5 = 10), installed at the two sites with relatively contrasting dissolved As concentration in groundwater, were monitored bi-weekly for As and other hydrogeochemical parameters over a period of 20 months. The estimation of the standard deviation (SD) for As(III) reflects strong temporal variation (SD ≥10 μg/L) in all the piezometers of two sites over the monitoring period. Particularly, the variation is more prominent in the shallowest part of the aquifer, where the site specific cyclic trends are evident. While, As(V) shows significant temporal variation in the piezometers of high As site only and no specific trend is reflected in the variation.Two different surface complexation models (SCMs), developed for ferrihydrite and goethite have been explored to account for the observed temporal variation in As(III) and As(V) concentrations. The SCM for ferrihydrite has provided the better estimation for both As(III) and As(V) variations.Among the different competing ions, PO43- appears as the major competitor of As(III) and As(V) adsorption onto ferrihydrite and the competition ability decreases in the order PO43- >> Fe(II) > H4SiO4 = HCO3-. It is further revealed that a small decrease in pH significantly increases the concentration of As(III) and decreases the As(V) concentration and vice versa. The present study suggests that the reductive dissolution of Fe oxyhydroxides alone cannot explain the observed high As concentration in groundwater of the sedimentary aquifers. Perhaps, the reductive dissolution of Fe oxyhydroxides followed by competitive sorption reactions with the aquifer sediment is the processes conducive for As enrichment in the groundwater of Bengal basin.
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| 6. |
- Biswas, Ashis, et al.
(författare)
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Groundwater chemistry and redox processes : Depth dependent arsenic release mechanism
- 2011
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Ingår i: APPLIED GEOCHEMISTRY. - : Elsevier BV. ; , s. 516-525
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Konferensbidrag (refereegranskat)abstract
- Patchy occurrences of elevated As are often encountered in groundwater from the shallow aquifers (<50 m) of the Bengal Delta Plain (BDP). A clear understanding of various biogeochemical processes, responsible for As mobilization, is very important to explain this patchy occurrence and thus to mitigate the problem. The present study deals with the periodical monitoring of groundwater quality of five nested piezometeric wells between December 2008 and July 2009 to investigate the temporal changes in groundwater chemistry vis-a-vis the prevalent redox processes in the aquifer. Geochemical modeling has been carried out to identify key phases present in groundwater. A correlation study among different aqueous redox parameters has also been performed to evaluate prevailing redox processes in the aquifer. The long term monitoring of hydrochemical parameters in the multilevel wells together with hydrogeochemical equilibrium modeling has shown more subtle differences in the geochemical environment of the aquifer, which control the occurrence of high dissolved As in BDP groundwater. The groundwater is generally of Ca-HCO3 type. The dissolved As concentration in groundwater exceeded both WHO and National drinking water standard (Bureau of Indian Standards; BIS, 10 mu g L-1) throughout the sampling period. The speciation of As and Fe indicate persistent reducing conditions within the aquifer [As(III): 87-97% of As-T and Fe(II): 76-96% of Fe-T]. The concentration of major aqueous solutes is relatively high in the shallow aquifer (wells A and B) and gradually decreases with increasing depth in most cases. The calculation of SI indicates that groundwater in the shallow aquifer is also relatively more saturated with carbonate minerals. This suggests that carbonate mineral dissolution is possibly influencing the groundwater chemistry and thereby controlling the mobilization of As in the monitored shallow aquifer. Hydrogeochemical investigation further suggests that Fe and/or Mn oxyhydroxide reduction is the principal process of As release in groundwater from deeper screened piezometric wells. The positive correlations of U and V with As. Fe and Mn indicate redox processes responsible for mobilization of As in the deeper screened piezometric wells are possibly microbially mediated. Thus, the study advocates that mobilization of As is depth dependent and concentrations of As in groundwater depends on single/combined release mechanisms.
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| 7. |
- Biswas, Ashis, et al.
(författare)
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Hydrogeochemical contrast between brown and grey sand aquifers in shallow depth of Bengal Basin : consequences for sustainable drinking water supply
- 2012
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 431, s. 402-412
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Tidskriftsartikel (refereegranskat)abstract
- Delineation of safe aquifer(s) that can be targeted by cheap drilling technology for tubewell (TW) installation becomes highly imperative to ensure access to safe and sustainable drinking water sources for the arsenic (As) affected population in Bengal Basin. This study investigates the potentiality of brown sand aquifers (BSA) as a safe drinking water source by characterizing its hydrogeochemical contrast to grey sand aquifers (GSA) within shallow depth (<70 m) over an area of 100 km(2) in Chakdaha Block of Nadia district, West Bengal, India. The results indicate that despite close similarity in major ion composition, the redox condition is markedly different in groundwater of the two studied aquifers. The redox condition in the BSA is delineated to be Mn oxy-hydroxide reducing, not sufficiently lowered for As mobilization into groundwater. In contrast, the enrichments of NH4+, PO43-, Fe and As along with lower Eh in groundwater of GSA reflect reductive dis-solution of Fe oxy-hydroxide coupled to microbially mediated oxidation of organic matter as the prevailing redox process causing As mobilization into groundwater of this aquifer type. In some portions of GSA the redox status even has reached to the stage of SO42- reduction, which to some extent might sequester dissolved As from groundwater by co-precipitation with authigenic pyrite. Despite having low concentration of As in groundwater of the BSA the concentration of Mn often exceeds the drinking water guidelines, which warrants rigorous assessment of attendant health risk for Mn prior to considering mass scale exploitation of the BSA for possible sustainable drinking water supply.
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