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Avdhesh Kr Sharma - One of the best experts on this subject based on the ideXlab platform.

  • modeling and simulation of a downdraft Biomass Gasifier 1 model development and validation
    Energy Conversion and Management, 2011
    Co-Authors: Avdhesh Kr Sharma
    Abstract:

    An ‘EQB’ computer program for a downdraft Gasifier has been developed to predict steady state performance. Moving porous bed of suction Gasifier is modeled as one-dimensional (1-D) with finite control volumes (CVs), where conservation of mass, momentum and energy is represented by fluid flow, heat transfer analysis, drying, pyrolysis, oxidation and reduction reaction modules; which have solved in integral form using tri-diagonal matrix algorithm (TDMA) for reaction temperatures, pressure drop, energetics and product composition. Fluid flow module relates the flow rate with pressure drop, while Biomass drying is described by mass transfer 1-D diffusion equation coupled with vapour–liquid-equilibrium relation. When chemical equilibrium is used in oxidation zone, the empirically predicted pyrolysis products (volatiles and char) and kinetic modeling approach for reduction zone constitutes an efficient algorithm allowing rapid convergence with adequate fidelity. Predictions for pressure drop and power output (Gasifier) are found to be very sensitive, while gas composition or calorific value, temperature profile and gasification efficiency are less sensitive within the encountered range of gas flow rate.

  • experimental study on 75 kwth downdraft Biomass Gasifier system
    Renewable Energy, 2009
    Co-Authors: Avdhesh Kr Sharma
    Abstract:

    Experimental study on 75kWth, downdraft (Biomass) Gasifier system has been carried out to obtain temperature profile, gas composition, calorific value and trends for pressure drop across the porous Gasifier bed, cooling–cleaning train and across the system as a whole in both firing as well as non-firing mode. Some issues related to re-fabrication of damaged components/parts have been discussed in order to avoid any kind of leakage. In firing mode, the pressure drop across the porous bed, cooling–cleaning train, bed temperature profile, gas composition and gas calorific value are found to be sensitive to the gas flow rate. The rise in the bed temperature due to chemical reactions strongly influences the pressure drop through the porous Gasifier bed. In non-firing mode, the extinguished Gasifier bed arrangement (progressively decreasing particle size distribution) gives much higher resistance to flow as compared to a freshly charged Gasifier bed (uniformly distributed particle size). The influence of ash deposition in fired-Gasifier bed and tar deposition in sand filters is also examined on the pressure drop through them. The experimental data generated in this article may be useful for validation of any simulation codes for Gasifiers and the pressure drop characteristics may be useful towards the coupling of a Gasifier to the gas engine for motive power generation or decentralized electrification applications.

  • equilibrium and kinetic modeling of char reduction reactions in a downdraft Biomass Gasifier a comparison
    Solar Energy, 2008
    Co-Authors: Avdhesh Kr Sharma
    Abstract:

    Abstract The thermodynamic and kinetic modeling of char reduction reactions in a downdraft (Biomass) Gasifier has been presented. Mass and energy balance are coupled with equilibrium relations or kinetic rate parameters (using varying char reactivity factor) in order to predict status of un-converted char in addition to gas composition, calorific value, conversion efficiency, exit gas temperature, endothermic heat absorption rate and Gasifier power output. Both modeling predictions are compared against experimental data for their validity. The influence of char bed length and reaction temperature in reduction zone has been examined. CO and H 2 component, calorific value of product gas and the endothermic heat absorption rate in reduction zone are found to be sensitive with reaction temperature, while char bed length is less sensitive to equilibrium predictions. For present case, all char conversion takes place at critical reaction temperature of 932 K for equilibrium, while for kinetic modeling critical reaction temperature and critical char bed length of 950 K and ∼25 cm have been identified, comparing the predictions. The critical reaction temperatures and critical char bed length also depend on inlet components composition and initial temperature supplied to the reduction reaction zone model.

  • equilibrium modeling of global reduction reactions for a downdraft Biomass Gasifier
    Energy Conversion and Management, 2008
    Co-Authors: Avdhesh Kr Sharma
    Abstract:

    Abstract This article proposed a full equilibrium model of global reduction reactions for a downdraft Biomass Gasifier in order to predict the accurate distribution of various gas species, unconverted char and reaction temperature. Full equilibrium of the global reduction reactions has been described using thermodynamics principles based on the stoichiometric approach. Model predictions for equilibrium constants for reduction reactions and dry gas composition have been validated by comparing the data collected from various sources. Simulations modeling the influences of moisture content in feedstocks, pressure, equivalence ratio and initial temperature input on dry gas composition, unconverted char, calorific value of gas, gasification efficiency, outlet gas temperature and endothermic heat released in char bed. For optimal energy conversion of Douglas fir bark, the range of moisture content and equivalence ratio should be limited to 10–20% and 0.3–0.45 respectively, while the initial temperature in the reduction reaction zone should not be less than 1200 K. The accuracy of the prediction of the equilibrium model depends on the correctness of the initial conditions of temperature and reactants concentrations.

  • Equilibrium and kinetic modeling of char reduction reactions in a downdraft Biomass Gasifier: A comparison
    Solar Energy, 2008
    Co-Authors: Avdhesh Kr Sharma
    Abstract:

    The thermodynamic and kinetic modeling of char reduction reactions in a downdraft (Biomass) Gasifier has been presented. Mass and energy balance are coupled with equilibrium relations or kinetic rate parameters (using varying char reactivity factor) in order to predict status of un-converted char in addition to gas composition, calorific value, conversion efficiency, exit gas temperature, endothermic heat absorption rate and Gasifier power output. Both modeling predictions are compared against experimental data for their validity. The influence of char bed length and reaction temperature in reduction zone has been examined. CO and H2component, calorific value of product gas and the endothermic heat absorption rate in reduction zone are found to be sensitive with reaction temperature, while char bed length is less sensitive to equilibrium predictions. For present case, all char conversion takes place at critical reaction temperature of 932 K for equilibrium, while for kinetic modeling critical reaction temperature and critical char bed length of 950 K and ∼25 cm have been identified, comparing the predictions. The critical reaction temperatures and critical char bed length also depend on inlet components composition and initial temperature supplied to the reduction reaction zone model. © 2008 Elsevier Ltd. All rights reserved.

W. Zhang - One of the best experts on this subject based on the ideXlab platform.

  • experimental test on a novel dual fluidised bed Biomass Gasifier for synthetic fuel production
    Fuel, 2011
    Co-Authors: Kristina Göransson, Ulf Söderlind, W. Zhang
    Abstract:

    This article presents a preliminary test on the 150 kWth allothermal Biomass Gasifier at MIUN (Mid Sweden University) in Harnosand, Sweden. The MIUN Gasifier is a combination of a fluidised bed gas ...

  • Experimental test on a novel dual fluidised bed Biomass Gasifier for synthetic fuel production
    Fuel, 2011
    Co-Authors: Kristina Göransson, Ulf Söderlind, W. Zhang
    Abstract:

    This article presents a preliminary test on the 150 kWthallothermal Biomass Gasifier at Mid Sweden University (MIUN) in Härnösand, Sweden. The MIUN Gasifier is a combination of a fluidised bed Gasifier and a CFB riser as a combustor with a design suitable for in-built tar/CH4catalytic reforming. The test was carried out by two steps: (1) fluid-dynamic study; (2) measurements of gas composition and tar. A novel solid circulation measurement system which works at high bed temperatures is developed in the presented work. The results show the dependency of bed material circulation rate on the superficial gas velocity in the combustor, the bed material inventory and the aeration of solids flow between the bottoms of the Gasifier and the combustor. A strong influence of circulation rate on the temperature difference between the combustor and the Gasifier was identified. The syngas analysis showed that, as steam/Biomass (S/B) ratio increases, CH4content decreases and H2/CO ratio increases. Furthermore the total tar content decreases with increasing steam/Biomass ratio and increasing temperature. The Biomass gasification technology at MIUN is simple, cheap, reliable, and can obtain a syngas of high CO+H2concentration with sufficient high ratio of H2to CO, which may be suitable for synthesis of methane, DME, FT-fuels or alcohol fuels. The measurement results of MIUN Gasifier have been compared with other Gasifiers. The main differences can be observed in the H2and the CO content, as well as the tar content. These can be explained by differences in the feed systems, operating temperature, S/B ratio or bed material catalytic effect, etc. © 2011 Elsevier Ltd All rights reserved.

  • Experimental test on a novel dual fluidised bed Biomass Gasifier for synthetic fuel production
    Fuel, 2011
    Co-Authors: K Goeransson, U Soederlind, W. Zhang
    Abstract:

    This article presents a preliminary test on the 150 kW allothermal Biomass Gasifier at Mid Sweden University (MIUN) in Haernoesand, Sweden. The MIUN Gasifier is a combination of a fluidised bed Gasifier and a CFB riser as a combustor with a design suitable for in-built tar/CH sub(4) catalytic reforming. The test was carried out by two steps: (1) fluid-dynamic study; (2) measurements of gas composition and tar. A novel solid circulation measurement system which works at high bed temperatures is developed in the presented work. The results show the dependency of bed material circulation rate on the superficial gas velocity in the combustor, the bed material inventory and the aeration of solids flow between the bottoms of the Gasifier and the combustor. A strong influence of circulation rate on the temperature difference between the combustor and the Gasifier was identified. The syngas analysis showed that, as steam/Biomass (S/B) ratio increases, CH sub(4) content decreases and H sub(2)/CO ratio increases. Furthermore the total tar content decreases with increasing steam/Biomass ratio and increasing temperature. The Biomass gasification technology at MIUN is simple, cheap, reliable, and can obtain a syngas of high CO + H sub(2) concentration with sufficient high ratio of H sub(2) to CO, which may be suitable for synthesis of methane, DME, FT-fuels or alcohol fuels. The measurement results of MIUN Gasifier have been compared with other Gasifiers. The main differences can be observed in the H sub(2) and the CO content, as well as the tar content. These can be explained by differences in the feed systems, operating temperature, S/B ratio or bed material catalytic effect, etc.

Rubenildo V. Andrade - One of the best experts on this subject based on the ideXlab platform.

  • Theoretical and experimental investigations of a downdraft Biomass Gasifier-spark ignition engine power system
    Renewable Energy, 2012
    Co-Authors: Felipe Centeno, Khamid Mahkamov, Electo E. Silva Lora, Rubenildo V. Andrade
    Abstract:

    A mathematical model which was developed to predict steady state performance of a Biomass downdraft Gasifier/spark ignition engine power system is described. A mathematical model of the integrated system consists of two parts: the fixed bed downdraft Gasifier and spark ignition internal combustion engine models. For calculations the Gasifier is split into three zones, namely drying - pyrolysis, oxidation and reduction sections. The Gasifier's mathematical model consists of three separate sub-models, each describing the processes in the corresponding zone. The process taking place in the reduction zone has been described using chemical kinetic principles in order to avoid introduction of assumptions related to achievement of the thermo-chemical equilibrium state during Gasifier's operation. The model is capable to accurately predict molar concentrations of different species in syngas (CO2, CO, H2O, H2, CH4and N2) and the temperature profile in the Gasifier along its height. This information then can be used for sizing the reactor and material selection. The engine's model is based on the fuel-air thermodynamic cycle for spark ignition engines and such model takes into account the composition of syngas used as fuel. The engine's model also takes into account effects of heat losses in the cycle through the walls of the cylinders and due to the gas blow by. Finally, the influence of dissociation processes during the combustion and the residual gases remaining in the cylinders at the beginning of the compression stroke is accounted for computations of the engine's performance. The numerical results obtained using the proposed model are in a good agreement with data produced with the use of other theoretical models and experimental data published in open literature and with experimental data obtained in these investigations. The proposed model is applicable for modelling integrated downdraft Gasifier/engine Biomass energy systems and can be used for more accurate adjustment of design parameters of the Gasifier and the engine in order to provide the higher overall efficiency of the system. © 2011 Elsevier Ltd.

  • theoretical and experimental investigations of a downdraft Biomass Gasifier spark ignition engine power system
    Renewable Energy, 2012
    Co-Authors: Felipe Centeno, Khamid Mahkamov, Electo Eduardo Silva Lora, Rubenildo V. Andrade
    Abstract:

    A mathematical model which was developed to predict steady state performance of a Biomass downdraft Gasifier/spark ignition engine power system is described. A mathematical model of the integrated system consists of two parts: the fixed bed downdraft Gasifier and spark ignition internal combustion engine models. For calculations the Gasifier is split into three zones, namely drying – pyrolysis, oxidation and reduction sections. The Gasifier’s mathematical model consists of three separate sub-models, each describing the processes in the corresponding zone. The process taking place in the reduction zone has been described using chemical kinetic principles in order to avoid introduction of assumptions related to achievement of the thermo-chemical equilibrium state during Gasifier’s operation. The model is capable to accurately predict molar concentrations of different species in syngas (CO2, CO, H2O, H2, CH4 and N2) and the temperature profile in the Gasifier along its height. This information then can be used for sizing the reactor and material selection. The engine’s model is based on the fuel–air thermodynamic cycle for spark ignition engines and such model takes into account the composition of syngas used as fuel. The engine’s model also takes into account effects of heat losses in the cycle through the walls of the cylinders and due to the gas blow by. Finally, the influence of dissociation processes during the combustion and the residual gases remaining in the cylinders at the beginning of the compression stroke is accounted for computations of the engine’s performance. The numerical results obtained using the proposed model are in a good agreement with data produced with the use of other theoretical models and experimental data published in open literature and with experimental data obtained in these investigations. The proposed model is applicable for modelling integrated downdraft Gasifier/engine Biomass energy systems and can be used for more accurate adjustment of design parameters of the Gasifier and the engine in order to provide the higher overall efficiency of the system.

Henrik Thunman - One of the best experts on this subject based on the ideXlab platform.

  • comparing active bed materials in a dual fluidized bed Biomass Gasifier olivine bauxite quartz sand and ilmenite
    Energy & Fuels, 2016
    Co-Authors: Teresa Berdugo Vilches, Jelena Marinkovic, Martin Seemann, Henrik Thunman
    Abstract:

    Active bed materials are in this work investigated for in situ gas upgrading of Biomass-derived gas. Previous research on in situ gas upgrading has focused on assessing gas quality, in terms of the concentrations of tar and permanent gases. Other aspects of fuel conversion, such as char conversion and the impact of oxygen transport on the final gas, are not as well documented in the literature on gasification. In this paper, the overall Biomass conversion in a dual fluidized bed Biomass Gasifier is investigated in the presence of the catalytic material olivine and the alkali-binding material bauxite. The impact of these materials on fuel conversion is described as the combination of four effects, which are induced by the bed material: thermal, catalytic, ash-enhanced catalytic effect, and oxygen transport. Quartz-sand and ilmenite are here used as the reference materials for the thermal and the oxygen transport effects, respectively. Olivine and bauxite show activity toward tar species compared to quartz-...

  • Importance of Decomposition Reactions for Catalytic Conversion of Tar and Light Hydrocarbons: An Application with an Ilmenite Catalyst
    Industrial and Engineering Chemistry Research, 2016
    Co-Authors: Huong N.t. Nguyen, Georg L. Schwebel, Nicolas Berguerand, Henrik Thunman
    Abstract:

    This work elucidates the contributions of different decomposition reactions, namely, steam reforming, hydro-cracking, dry reforming, and (thermal) cracking reactions, to the conversion of tar and light hydrocarbons during the catalytic cleaning of a Biomass-derived raw gas. A raw gas that contained a high content of steam and that was produced in the Chalmers indirect Biomass Gasifier was taken as the reference. The representative reactions associated with the upgrading of the given raw gas were identified to investigate the individual effects and thereafter reassembled to investigate the synergistic effects. Ilmenite was used as the catalyst, and the temperature range of 750°–900 °C was the focus. For this process, it was discovered that the complete steam reforming, steam dealkylation, and hydro-cracking reactions are important, whereas the dry reforming reaction is not relevant. In addition, the water gas shift reaction occurs significantly and can promote the hydro-cracking reaction. These results pro...

  • characteristics of olivine as a bed material in an indirect Biomass Gasifier
    Chemical Engineering Journal, 2015
    Co-Authors: Jelena Marinkovic, Henrik Thunman, Pavleta Knutsson, Martin Seemann
    Abstract:

    The use of untreated olivine as the bed material in a Biomass Gasifier is investigated in this work, in which activation of the material is the main focus. The experiments were carried out in the Chalmers 2–4-MWth indirect Biomass gasification unit and comprised analyses of the gas composition and bed material, as well as changes in tar yield. Starting from the raw material, the first signs of activation, in the form of a reduction in the tar yield, were observed already during the second day of the operation. The tar yield continued to decrease with time, and by the fourth day it was reduced by 30%, as compared to the yield on the first day of the operation. Analysis of the bed samples showed accumulation of inorganics within the bed material, with a share of potassium being present in leachable form. Thermodynamic calculations support the indications from the experiment that potassium can be released under gasification conditions and may play an important role in the activation of olivine. To examine the impacts of S and silica on the activity of olivine, two experiments were conducted. The addition of S to the combustion side gave a positive effect in terms of the tar levels in the raw gasification gas. The addition of silica sand revealed, as expected given the affinity of potassium for silicone, negative influences on the tar yield and gas composition that could not be attributed to mere dilution, as compared with the gas produced during operation with pure olivine.

  • Manganese oxide as catalyst for tar cleaning of Biomass-derived gas
    Biomass Conversion and Biorefinery, 2012
    Co-Authors: Fredrik Lind, Martin Seemann, Mikael Israelsson, Henrik Thunman
    Abstract:

    The possibilities to upgrade raw gas with the use of a manganese oxide have been investigated in an application for secondary tar cleaning of Biomass-derived gas. Experiments were conducted in a reactor system where a novel technique that combines tar cleaning with catalyst regeneration is applied. Raw gas from the Chalmers non-catalytic steam Biomass Gasifier—containing roughly 32 g_tar/Nm _gas ^3 —was fed to the tar cleaning reactor. The tar reforming qualities of the manganese oxide were evaluated in the reactor system using a mixture of 23 wt.% catalysts in silica sand at the temperatures 700 and 800°C. Experiments showed that the catalyst was continuously regenerated from carbon deposits and that the total amount of tars was decreased by as much as 44.5 % at a gas residence time of 0.4 s in the bed. The catalyst showed activity in water–gas shift reaction and the H_2/CO ratio increased from 0.6 in the raw gas to a peak value of 1 in the reformed gas at 800°C. Only a slight decrease in methane and acetylene content was observed for both operating temperatures.

B. V. Babu - One of the best experts on this subject based on the ideXlab platform.

  • Production of hydrogen energy through Biomass (waste wood) gasification
    International Journal of Hydrogen Energy, 2010
    Co-Authors: Pratik N. Sheth, B. V. Babu
    Abstract:

    Biomass gasification, conversion of solid carbonaceous fuel into combustible gas by partial combustion, is a prominent technology for the production of hydrogen from Biomass. The concentration of hydrogen in the gas generated from gasification depends mainly upon moisture content, type and composition of Biomass, operating conditions and configuration of the Biomass Gasifier. The potential of production of hydrogen from wood waste by applying downdraft gasification technology is investigated. An experimental study is carried out using an Imbert downdraft Biomass Gasifier covering a wide range of operating parameters. The producer gas generated in the downdraft Gasifier is analyzed using a gas chromatograph (NUCON 5765) with thermal conductivity detector (TCD). The effects of air flow rate and moisture content on the quality of producer gas are studied by performing experiments. The performance of the Biomass Gasifier is evaluated in terms of equivalence ratio, composition of producer gas, and rate of hydrogen production. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

  • experimental studies on producer gas generation from wood waste in a downdraft Biomass Gasifier
    Bioresource Technology, 2009
    Co-Authors: Pratik N. Sheth, B. V. Babu
    Abstract:

    A process of conversion of solid carbonaceous fuel into combustible gas by partial combustion is known as gasification. The resulting gas, known as producer gas, is more versatile in its use than the original solid Biomass. In the present study, a downdraft Biomass Gasifier is used to carry out the gasification experiments with the waste generated while making furniture in the carpentry section of the institute’s workshop. Dalbergia sisoo, generally known as sesame wood or rose wood is mainly used in the furniture and wastage of the same is used as a Biomass material in the present gasification studies. The effects of air flow rate and moisture content on Biomass consumption rate and quality of the producer gas generated are studied by performing experiments. The performance of the Biomass Gasifier system is evaluated in terms of equivalence ratio, producer gas composition, calorific value of the producer gas, gas production rate, zone temperatures and cold gas efficiency. Material balance is carried out to examine the reliability of the results generated. The experimental results are compared with those reported in the literature.

  • Experimental studies on producer gas generation from wood waste in a downdraft Biomass Gasifier
    Bioresource Technology, 2009
    Co-Authors: Pratik N. Sheth, B. V. Babu
    Abstract:

    A process of conversion of solid carbonaceous fuel into combustible gas by partial combustion is known as gasification. The resulting gas, known as producer gas, is more versatile in its use than the original solid Biomass. In the present study, a downdraft Biomass Gasifier is used to carry out the gasification experiments with the waste generated while making furniture in the carpentry section of the institute's workshop. Dalbergia sisoo, generally known as sesame wood or rose wood is mainly used in the furniture and wastage of the same is used as a Biomass material in the present gasification studies. The effects of air flow rate and moisture content on Biomass consumption rate and quality of the producer gas generated are studied by performing experiments. The performance of the Biomass Gasifier system is evaluated in terms of equivalence ratio, producer gas composition, calorific value of the producer gas, gas production rate, zone temperatures and cold gas efficiency. Material balance is carried out to examine the reliability of the results generated. The experimental results are compared with those reported in the literature. © 2009 Elsevier Ltd. All rights reserved.

  • modeling and simulation of reduction zone of downdraft Biomass Gasifier effect of char reactivity factor
    Energy Conversion and Management, 2006
    Co-Authors: B. V. Babu, Pratik N. Sheth
    Abstract:

    Abstract Biomass and waste are recognized to be major potential sources for energy production. Gasification enables the conversion of these materials into combustible gas, mechanical and electrical power, synthetic fuels and chemicals. In view of the considerable interest in the gasification process worldwide, it is necessary to model and predict the performance of the Gasifier in priori. Modeling of Biomass gasification implies the representation of chemical and physical phenomena constituting pyrolysis, combustion, reduction and drying in a mathematical form. In the present study, steady state composition and temperature profiles for the reduction zone of a downdraft Biomass Gasifier are predicted. A model reported in the literature is modified by incorporating the variation of the char reactivity factor (CRF) along the reduction zone of the downdraft Biomass Gasifier. Increasing the CRF exponentially along the reduction bed length in the model gave better predictions of the temperature and composition profiles when compared with the experimental data and earlier models reported in the literature.