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Modelling of a downdraft biomass gasifier with finite rate kinetics in the reduction zone
Abstract
A model of a downdraft gasifier has been developed based on chemical equilibrium in the pyro-oxidation zone and finite rate kinetic-controlled chemical reactions in the reduction zone. The char reactivity factor (CRF) in the reduction zone, representing the number of active sites on the char and its degree of burn out, has been optimized by comparing the model predictions against the experimental results from the literature. The model predictions agree well with the temperature distribution and exit gas composition obtained from the experiments at CRF=100. A detailed parametric study has been performed at different equivalence ratios (between 2 and 3.4) and moisture content (in the range of 0–40%) in the fuel to obtain the composition of the producer gas as well as its heating value. It is observed that the heating value of the producer gas increases with the increase in the equivalence ratio and decrease in the biomass moisture content. The effect of divergence angle of the reduction zone geometry (in the range of 30–150°) on the temperature and species concentration distributions in the gasifier has been studied. An optimum divergence angle, giving the best quality of the producer gas, has been identified for a particular height of the reduction zone. Copyright © 2009 John Wiley & Sons, Ltd.
... The waste tyre gasification process for the co-production of gaseous and high value solid products in three different gasifiers (fixed bed reactor, fluidized bed reactor and rotary kiln reactor) were simulated and modelled using Aspen simulation software. A one-dimensional kinetic model was employed to model the fixed bed and rotary kiln while the fluidized bed was modelled using a semi-empirical model [37,168,169]. ...
... In kinetic model, two distinct zones are identified in the reactor which are the pyro-oxidation (Zone -I) and reduction zones (Zone -II) [168]. Equilibrium assumptions are assumed in the pyrooxidation zone and these assumptions were used to simulate the drying, pyrolysis and combustion zones while the kinetic model is applied to the reduction zone to compute the final products [172]. ...
... A general formula (CHmOn) can be obtained for the combustible part of the waste tyre sample with the assumption that the feedstock contains only C, H and O [168]. The values of m and n can be N Balance: 3.76a = x 6 3.10 ...
The high level of waste tyres in stockpiles has contributed tremendously to environmental pollution and global warming on daily basis. These tyres have also been known to serve as breeding sites for mosquitoes and other disease-causing microbes. Gasification has been identified as one of the alternative pathways that can be used to recover energy from waste tyres. In addition to the gaseous products (syngas), high-value solid products like carbon black, activated carbon and carbon nanotubes can also be obtained from the gasification of waste tyres.
This study has evaluated the simultaneous production of syngas and solid carbon (activated carbon) in three different reactor configurations namely; fluidized bed, fixed bed, and rotary kiln. A single stage gasification and activation process was employed in the production process by using Aspen Plus® software. This study also evaluated the effects of gasification parameters like the equivalence ratio (ER), the steam-to-fuel ratio (SFR) and the gasifier temperature (GT) on the gasification products from the three reactor configurations. The ER was varied from 0.18 to 0.38, the SFR from 0.1 to 0.25 and the GT from 700 ℃ to 1000 ℃. BET analysis was used in the determination of the surface area of the activated carbon formed at the end of the char activation stage.
The optimum conditions for the co-production process in the fluidized bed gasifier occurred at ER of 0.3, SFR of 0.2 and GT of 800 ℃. At this condition, the fluidized bed gasifier has a syngas (CO + H2) composition of 50.2%, the gas yield of 4.81 Nm3/kg, gas LHV of 6.29 MJ/kg, cold gas efficiency of 84.8%, 89.2 kg (2.02% AC to carbon in feedstock ratio) with BET surface area of 2236 m2/g and carbon conversion ratio of 97.8%.
The optimum conditions for the co-production process in the fixed bed gasifier occurred at ER of 0.3, SFR of 0.25 and GT of 800 oC. At this condition, the fixed bed gasifier has a syngas (CO + H2) composition of 51.76%, gas yield of 4.92 Nm3/kg, gas LHV of 6.25 MJ/kg, cold gas efficiency of 85.9%, 0.53 kg (3.22% AC to carbon in feedstock ratio) with BET surface area of 822.25 m2/g and carbon conversion ratio of 96.8%.
The optimum conditions for the co-production process in the rotary kiln reactor occurred at ER of 0.3, SFR of 0.25 and GT of 800 ℃. At this condition, the rotary kiln gasifier has a syngas (CO + H2) composition of 48.8%, the gas yield of 4.91 Nm3/kg, gas LHV of 6.05 MJ/kg, cold gas efficiency of 83.1%, 0.91 kg (5.56% AC to carbon in feedstock ratio) with BET surface area of 664.94 m2/g and carbon conversion ratio of 94.4%.
A comparative analysis was also done for the three reactor configurations, from the results obtained, the fluidized bed reactor performed best for the waste tyre gasification production process of both syngas and value-added solid activated carbon product followed by the fixed bed. The rotary kiln reactor did not perform well as the others in the co-production process.
... Producción ( Barman (2012), Jarungthammachote (2008) y Roy et al. (2009) validaron su modelo para predecir la composición del gas pobre con los datos experimentales de Jayah et al. (2003), pero solo para fragmentos de biomasa menores a 3.3 cm de diámetro. Cuando se aplica el modelo de Roy a los fragmentos de biomasa (3.3, 4.4 y 5.5cm), la composición de los gases para diferentes tamaños de fragmentos presenta errores promedios predictivos que varían en el rango de 2.56% a 17.81%. ...
... El objetivo de esta investigación es estimar el potencial energético del gas pobre obtenido a partir de la cáscara de cacao y racimos de frutos vacíos de palma aceitera en base al modelo matemático de Serrato (2016), pero aplicado a procesos de gasificación propuesto por el modelo de gasificación de Roy et al. (2009) basados en el equilibrio termodinámico en la zona de pirooxidación y la cinética de las reacciones en la zona de reducción. Las operaciones matemáticas no son complejas, aunque sí incluye un aceptable análisis fisicoquímico que lo hace adecuado para realizar un buen estudio para la optimización de gasificadores de lecho fijo. ...
... Tomando como referencia el gasificador de Jayah et al. (2003), Roy et al. (2009) divide el gasificador en dos zonas, y considera dos submodelos matemáticos. El primer submodelo es aplicado en la zona de pirooxidación, cuyas temperaturas son las más elevadas en el gasificador por lo que se aplica el modelo de equilibrio químico; el segundo submodelo es aplicado en la zona de gasificación o reducción, basada en el modelo cinético químico del "char" presentando un gran número de volúmenes de control elemental a lo largo de la zona reducción. ...
The objective of this research study is to estimate the energy potential of producer gas obtained from agro-industrial residues of cocoa and oil palm in Peru by using downdraft gasifier technology. This is performed based on the Serrato mathematical model, but applied to gasification processes proposed by Roy's model. The equilibrium constants and the kinetic velocity of the Roy's model are adjusted with multiplicative factors for fragments raging from 3.3 to 5.5 cm. This is validated using experimental data obtained from the literature. The maximum energy potential of the producer gas from the cocoa pod husk and oil palm empty fruit in Peru is estimated to be 4016.4 and 2108.7 TJ / year, respectively, for 3.3cm fragments. It is concluded that gasification using downdraft gasifiers is a good option to generate agro-industrial waste bioenergy to solve electrical and thermal energy shortages in Peruvian remote areas.
... Thus, using a chemical equilibrium model to simulate the downdraft fixed bed gasification process will produce large errors [17]. To control the simulation errors, a combined model of the chemical equilibrium and the kinetics control reactions is widely used for the fixed bed gasification process simulation [3,27,28]. Although the combined model has been successfully used for wood and animal manure gasification simulation, no study has used it for poultry gasification simulation to date [15]. ...
... Because the fuel and air inputs to the gasifier are from the top, the gasifier can be separated into four zones of drying, pyrolysis, combustion, and reduction from the top to the bottom (shown in Figure 2b). According to the research of Roy et al. (2009 and2015), the combustion and reduction zones include the major reactions of gasification process [27,31]. Therefore, in the simulation process, the total gasifier was re-grouped into two reaction zones: a pyro-oxidation zone and a reduction zone. ...
... Because the fuel and air inputs to the gasifier are from the top, the gasifier can be separated into four zones of drying, pyrolysis, combustion, and reduction from the top to the bottom (shown in Figure 2b). According to the research of Roy et al. (2009 and2015), the combustion and reduction zones include the major reactions of gasification process [27,31]. Therefore, in the simulation process, the total gasifier was re-grouped into two reaction zones: a pyro-oxidation zone and a reduction zone. ...
Despite growing attention has been paid to waste material gasification for high-efficiency energy conversion, the application of gasification technology in meat waste management is still limited. To fill this gap, this study designed two systems which evaluated the potential of using gasification technology to manage the poultry waste that has been exposed to highly pathogenic avian influenza (HPAI). Two systems are simulated by using Aspen plus combined with a one-dimensional kinetics control gasification model, and wood or dried poultry is selected as the feedstock for the gasifier. The results show that the energy efficiency of the poultry drying system (wood gasification) is 14.5%, which is 12% lower than that of the poultry gasification system when the poultry energy is accounted as energy input. Even though the economic analysis indicates the poultry elimination cost of the poultry gasification system is only 30 $/tonne lower than the poultry drying system, taking the absence of dried poultry burial into consideration, the poultry gasification system has development potentials. The sensitivity analysis shows that labor fee and variable factor has larger effects on the poultry elimination cost, while the uncertainty analysis determines the uncertainty level of the economic analysis results.
... Different from the fluidized bed gasifier, the fixed bed gasifier does not have good mixing characters (Ma et al., 2012), which results in the chemical equilibrium model is not suitable for the fixed bed gasification simulation (Patra and Sheth, 2015). Therefore, a combined model of reaction kinetics and chemical equilibrium has been widely used to simulate the fixed bed gasification process (Ratnadhariya and Channiwala, 2009;Roy et al., 2009). Even though the combination model has been successfully used to simulate the gasification of wood and animal manure, it has not been applied for the gasification of tire yet (Jia et al., 2015(Jia et al., , 2018Roy et al., 2009Roy et al., , 2010. ...
... Therefore, a combined model of reaction kinetics and chemical equilibrium has been widely used to simulate the fixed bed gasification process (Ratnadhariya and Channiwala, 2009;Roy et al., 2009). Even though the combination model has been successfully used to simulate the gasification of wood and animal manure, it has not been applied for the gasification of tire yet (Jia et al., 2015(Jia et al., , 2018Roy et al., 2009Roy et al., , 2010. ...
... The objective of this study is to find an economic and efficient pathway for the syngas product derived from waste tires gasification process. To achieve this goal, two most commonly used gasifier types of fluidized bed and fixed bed have been simulated by using a semi-empirical model (Hannula and Kurkela, 2010) and a one-dimensional kinetics model (Roy et al., 2009), respectively. ...
Waste tires have an organic-matter composition of more than 90% and have been proposed as an excellent calorific fuel material. The objective of this study is to find an economic and efficient pathway for producing syngas by waste tires gasification. To achieve this goal, two most commonly used gasifier types of fluidized bed and fixed bed have been simulated and compared by using a semi-empirical model and a one-dimensional kinetics model, respectively. Moreover, economic analysis of the levelized cost of syngas is used to compare economic indicators of different gasifiers. Results show that the lower heating value of the tire-syngas product is 2.5–7.4 MJ/Nm ³ , moreover, equivalence ratio and tire mixture ratio have negative impacts on syngas heating value and syngas efficiency. Furthermore, the levelized cost of syngas of tire gasification is 0.33–0.60 ¢/kWh that is lower than the market price of natural gas at 0.68 ¢/kW, which indicates tire gasification is a potential technology for syngas production. Finally, compared with the fluidized bed tire gasification, the fixed bed tire gasification has worse performance but better economic indicators, indicating that fixed bed gasification is an economic pathway for the syngas product.
... Un processus de pyro-gazéification comporte généralement quatre phases : déshydratation, pyrolyse, oxydation et gazéification. Pour le présent modèle, un modèle à deux zones de réaction est considéré [62,[120][121][122]. Les trois premières étapes sont regroupées dans une même zone, appelée « zone de pyro-oxydation ». ...
... Cette première zone est décrite suivant un modèle d'équilibre chimique, également adoptés dans les travaux de Melgar et al. [58] ainsi que ceux effectués par Roy et al. [62]. La réaction globale décrivant cette zone est donnée par l'équation 5.1 : ...
... Avec ∆G 0 ( T, i) étant l'énergie libre de Gibbs de la réaction i et dépendant de la température T ; R désigne la constante universelle des gaz parfaits (kJ.mol −1 .K −1 ). En considérant que le rendement en char de la biomasse, représenté par le taux de carbone fixe obtenu par analyse immédiate, se compose de solide carboné et de méthane rattaché à la surface de ce char [62], l'équation 5.15 est établie : ...
Les résidus agricoles constituent un potentiel bioénergétique important à l’échelle d’un territoire comme Madagascar. L’utilisation de ces ressources locales comme vecteurs d’énergie est primordiale afin de diversifier et trouver des solutions alternatives à la précarité énergétique notamment en milieu rural. La pyro-gazéification est un procédé thermochimique très prometteur pouvant convertir des matrices carbonées solides, comme les résidus de biomasse, en gaz de synthèse (syngaz). Deux types de résidus agricoles, balle de riz (RH) et paille de riz (RS), ont ainsi été étudiés. Les analyses physico-chimiques et thermiques des résidus bruts de RH et RS ont révélé de faibles pouvoirs calorifiques par rapport à d’autres types de biomasse, mais avec une forte teneur en cendres, typique de la présence d’éléments inorganiques. Les expérimentations sur réacteur à échelle laboratoire ont montré que les produits issus de la conversion thermochimique se présentent sous forme gazeux (syngaz), solide (biochar) et liquide (goudron). Des analyses de caractérisations physico-chimiques de ces produits ont alors été réalisées et des analyses prospectives de leur valorisation sont suggérées. Un modèle de réacteur de pyro-gazéification des résidus agricoles a été développé en se basant sur l’équilibre chimique et la cinétique des réactions. Les résultats de simulation sont en accord avec ceux dans la littérature. Une analyse de sensibilité globale (GSA) sur le modèle a été réalisée afin de déterminer les paramètres clés influençant le rendement exergétique du processus de pyro-gazéification.
... For the reduction zone, Giltrap et al. [1] have studied a steady state kinetic model with the plentiful char condition and incorporated several factors such as particle size and number of active carbon site into their pre-multiplier that are called 'Char Reactivity Factor' (CRF) which represents the relative reactivity of different char types [1]. Roy et al. [15][16] and Sharma [17] developed the finite kinetic model of reduction zone related the height, angle and diameter of gasifier which can be used for gasifier design. ...
... The moisture content of biomass feedstock vaporized in this module by heat supplying from the oxidation module. The model of drying module was adopted from the finite rate kinetic model of Roy et al. [15] for applying the drying process. The temperature of drying module rises from initial temperature (T0 = 298 K) until temperature reach 368 K and then the vaporization of moisture content starts. ...
... where CRF is the char reactivity factor, Tr is the temperature of the reduction module, yi is the mol fraction of gas species i, KR1-R4 are the equilibrium constant of reduction reaction of 1 to 4 which can be determined from the standard Gibbs function of formation [5]. Roy et al. [15] found that the suitable value of CRF should be equal to 100 when compared to experimental data. The finite rate kinetic model of Roy et al. [15][16] was used in this study. ...
A mathematical model of a biomass downdraft gasification process has been developed. The model was considered to be four modules that are drying, pyrolysis, oxidation, and reduction which the products of upper module will be the reactants of the next. The one-dimensional kinetic finite rate models were applied to drying and reduction modules. The pyrolysis model took place when drying temperature reached 473 K. The equilibrium sequence model was used to describe the oxidation process by considering the sequence of order of reaction rates. For the model validation the comparison showed a good agreement. In the parametric study the moisture content increasing affected the height of drying, and pyrolysis zones increasing while the critical char bed length of reduction zone decreased from 0.53 to 0.25 m. The height of these zones decreased along A/F increasing. The results of this study can be used in the reactor design evaluation.
... Thus, it requires a well-planned and time/cost consuming experimental facilities. On the other hand, numerical modelling proves a strong ability to simulate the gasification process considering the wide variety of variables in the process ( [8][9][10]).Different modelling approaches are been used in the gasification process e.g., equilibrium ( [11][12][13][14]), kinetic ( [15][16][17][18]), and Computational Fluid Dynamics (CFD) ( [19,20]). ...
... For the same working conditions, increasing z from 0 to 1 produces higher carbon conversion efficiency by 35%. While for the optimum working parameters z= (0.25-0.5), it tends to producer higher carbon conversion efficiency than air by (10)(11)(12)(13)(14)(15)(16)(17)(18)(19) %. On the other hand, the gasification efficiency found to decrease while increasing z values between (0.1-0.25), then it tends to show a gradual increase for higher z values. ...
The gasification process in a 20-kW downdraft gasifier is investigated using Computational Fluid Dynamics. The research aims to examine the feasibility of air and producer gas co-injectionas a gasifying medium on the performance of the whole process. To this end, the effect of varying the injected amount of the producer gas on producer gas composition, emissions, H2 production, producer gas yield and higher heating value (HHV), the gasification, and carbon conversion efficiencies are reported. The results reveal promising findings for boosting the producer hydrogen amounts, and the corresponding heating values, with lower CO2 levels. The ratio of the injected producer gas (within the gasifying medium) to the total required amount of air for gasification is defined by z (eqn. (10)), and it is found that optimum z values are around (0.25–0.5). For the same working conditions of moisture content (MC), feedstock, and equivalence ratio (ER), the gasifying medium of z= (0.25–0.5) has higher HHV, gasification, and carbon conversion efficiencies than air gasification up to 33%, 31%, and 19% respectively. Additionally, for the same optimum range of z, it is found that the producer gas yield, and H2 production are higher than air gasification by 10%, and 34% respectively, with a reduction in CO2 by 18%. Consequently, the research presents a significant potential for higher yield, rich H2, and CO2-free syngas production, while demonstrating a promising novelty and technique that is applicable to any sort of the gasification units’ type and capacity.
... A similar model was presented by Sharma [22], in which a reduction in computation times was pursued while maintaining model validity. Giltrap et al. [23], Babu and Sheth [24], and Roy et al. [25] presented similar models focused on the catalytic effect of char on the heterogeneous reactions occurring in the reduction zone. Gao and Li [26] modeled the process of downdraft gasification by considering a kinetic model of pyrolysis within an equilibrium setting for the reduction zone and taking into account pyrolysis temperature as a model input. ...
... Heat transfer by convection for spherical particles in the bed was modeled by taking into account its analogy with mass transfer. The h sg coefficient was calculated using equation (25) [36,42,57]. The Nusselt number was estimated from a correlation proposed by Wakao and Kaguei [58] who studied energy and mass transfer in packed beds; see equation (26). ...
SUMMARY This study aimed at presenting a model to simulate downdraft biomass gasification under steady-state or unsteady-state conditions. The model takes into account several processes that are relevant to the transformation of solid biomass into fuel gas, such as drying; devolatilization; oxidation; CO2, H2O, and H2 reduction with char, pressure losses, solid and gas temperature, particle diameter, and bed void fraction evolution; and heat transfer by several mechanisms such as solid–gas convection, bed–wall convection, and radiation in the solid phase. Model validation is carried out by performing experiments in two lab-scale downdraft fixed bed reactors (unsteady-state conditions) and in a novel industrial pilot plant of 400 kWth–100 kWe (steady-state conditions). The capability of the model to predict the effect of several factors (reactor diameter, air superficial velocity, and particle size and biomass moisture) on key response variables (temperature field, maximum temperature inside the bed, flame front velocity, biomass consumption rate, and composition and calorific value of the producer gas) is evaluated. For most response variables, a good agreement between experimental and estimated values is attained, and the model is able to reproduce the trend of variation of the experimental results. In general terms, the process performance improves with higher reactor diameter and lesser air superficial velocity, particle size, and moisture content of biomass. The steady-state simulation appears to be a versatile tool for simulating different reactor configurations (preheating systems, variable geometry, and different materials). Copyright © 2013 John Wiley & Sons, Ltd.
... The primary focus of this work in the biomass thermochemical conversion was directed towards the optimization of the process to reduce the amount of unwanted products and maximize the syngas production. Several researchers have worked on the reduction zone of biomass gasifier [5][6][7][8][9]. Simulation has been done on the equilibrium models of reduction zone [3,4,[9][10][11] and kinetic models [8], whereas Sharma has studied a combined effect of both in his work [5]. ...
... Several researchers have worked on the reduction zone of biomass gasifier [5][6][7][8][9]. Simulation has been done on the equilibrium models of reduction zone [3,4,[9][10][11] and kinetic models [8], whereas Sharma has studied a combined effect of both in his work [5]. This study is entirely about the simulation of kinetic rate models under both isothermal and non-isothermal conditions for different kinds of biomass such as douglas fir bark, rice husk, peanut hull, bagasse and wood sawdust. ...
Gasification of biomass is becoming common technology now a days; it is convenient to apply numerical simulation to the process to save time and energy as compared to the lengthy experimentation.
Syngas produced as a result of gasification has many applications. Keeping in view those applications the objective of this work is to maximize the yield of syngas, using five different biomass like bagasse, wood sawdust, douglas fir bark, peanut hull and rice husk. The maximum yield of syngas is calculated using rate equations under isothermal and non-isothermal conditions. For isothermal conditions, the kinetic model is simulated over the temperature range of 1000–1300 K by taking a step size 50 K to estimate optimum temperature. For non-isothermal conditions, the kinetic equations are solved for heating rate range of 25–75 K/s by taking a step size 10 K/s to assess optimum value of heating rate.
... Different modelling tools are used in the gasication process varying from equilibrium 12,13 to kinetic, 11,[14][15][16][17] and Computational Fluid Dynamics (CFD). 10,[18][19][20] Equilibrium 12,13,21,22 and kineti [15][16][17]23,24 models are widely used in pyrolysis and gasication of biomass. However, there are some limitations which restrict the applicability of both the kinetic and equilibrium models. ...
The gasification process in a downdraft biomass gasifier is investigated using Computational Fluid Dynamics (CFD). The aim is to develop a novel approach to reduce CO2 emissions from producer syngas while increasing the higher heating value (HHV). To this end, the effects of varying the throat diameter of the gasifier and gasifying media (air and oxygen) on the performance of gasification are investigated. The results reveal that as the throat ratio decreases for oxy-gasification, more CO, H2, and CH4 are produced, thus resulting in a HHV of 12.1 MJ Nm-3. For the same working conditions (ER, MC, and feedstock), the suggested design/optimum throat ratio of 0.14 is found to reduce CO2 by ∼55% compared to any other higher throat ratios, while simultaneously increasing HHV by ∼20% for both air and oxy-gasification cases. Additionally, the suggested throat ratio increases the gasification efficiency, carbon conversion and producer gas yield by 19%, 33%, and 22% respectively. Therefore, it shows a significant potential for CO2-free syngas production in the gasification process, demonstrating a promising technique that does not require any solvents, catalysts, absorbers, or additional CO2 removal. Lower throat ratios further favour the higher yield of syngas, HHV, gasification and conversion efficiencies, with better gasifier performance.
... As a result, researchers are paying more attention towards modelling techniques e.g., equilibrium, kinetic, and CFD models [8][9][10][11]. Although equilibrium ( [12][13][14]) and kinetic models [15][16][17][18] are widely investigated and could perfectly accommodate the process gasification, but it still have some limitations. This includes gasifier design effect, hydrodynamics, and the variations of different gas and solid species along the gasifier. ...
The gasification process is investigated using 2D Computational Fluid Dynamics (CFD) model. A 2D gasifier is presented in which biomass is fed from the side of the gasifier, while the gasifying medium is injected from nozzles at the bottom and top/downstream of the gasifier.
The aim of the current research is to develop novel approach for maximizing H2 production, and CO2 reduction from biomass gasification. To this end, the effect of using different gasifying mediums (oxygen, steam, air, and CO2) on the gasifier performance are investigated. Additionally, the injection of such mediums from bottom (with the gasifying medium) and top of the gasifier (within reduction zone) is also studied. The results showed that higher heating values are achieved for steam, and oxy-gasification. Additionally, for the proposed design, at the gasifier bottom, the temperature reached ∼1500 K, which is favourable in reducing tar, ash, and residual amounts during the gasification process. Furthermore, the optimum results are achieved when injecting steam with (SB = 0.5), within the downstream of the gasifier. The novel idea results in higher H2 production, and lower CO2 emissions by (5–80) %, (12–40) % respectively, and correspondingly, higher heating values for the produced gas than air, and oxy-gasification for the same working conditions. As a result, the study presents significant outcomes for maximizing H2 yield, and the potential for CO2-free syngas, which demonstrates the promising technology and novelty that does not require any catalysts, absorbents, solvents, or additional CO2 removal. Such findings are applicable for different gasifier scales and fuel types.
... Gao and Li [9] combined reduction zone and pyrolysis zone models in order to simulate the whole process of fixed-bed biomass gasification. Roy et al. [10] studied the reduction zone reaction process based on the coke chemical kinetics model, and examined the influence of cone angle on the temperature and composition of production. Salem and Paul [11] established a kinetic model for the downdraft gasifier, and discussed the effect of reduction zone height on the gas concentration of different products. ...
The fixed bed gasifier has simple structure, convenient operation and maintenance, and is suitable for use in rural areas. In this paper, a downdraft fixed bed gasifier was designed for biomass gasification using corn cob as raw material. COMSOL Multiphysics software was used to simulate the reduction zone of biomass gasifier. The temperature field and concentration distribution of the reduction zone were studied. The influence of structural parameters of the reduction zone on the composition of syngas was analyzed. The rates of major chemical reactions in the reduction zone were also compared in detail.
... In order to reduce the costs of experimentations, various modeling approaches (equilibrium [3][4][5][6], onedimensional kinetic [7,8], and CFD [9][10][11][12]) have been employed to predict the performance of a gasifier under different operating and design conditions. Among these approaches, the multi-dimensional CFD provides the greatest detailed and most accurate results. ...
Municipal solid waste (MSW) is the largest waste stream around the world and has a great potential for syngas generation through gasification process. Many researchers have worked on biomass and coal gasification; however, a few of them have considered MSW as feedstock. The present study employs a combination of computational fluid dynamics (CFD) approach, response surface method (RSM), and genetic algorithm (GA) to optimize a MSW-driven gasifier with the simultaneous consideration of efficiency and environmental effects. This study is conducted for Rasht city which is located in the north of Iran and highly suffers from waste disposal problems. This work is to investigate the influence of major parameters on the performance of the gasifier and to find out the optimal set of design variables. The results illustrate that the efficiency of the gasifier is more influenced by the geometric parameters rather than equivalence ratio; however, the effects of equivalence ratio and geometrical parameters on total emission of pollutants are comparable. The efficiency and total emission of pollutants of the best trade-off design (or optimal design) are observed to be 32.2% and 4.8 ppm, respectively.
... At this temperature the pyrolysis begins automatically, thus the devolatization of biomass occurs [10]. The rate at which the drying reaction taking place is determined by the equation below ( [10,17]). Constant drying temperature is used in calculations as 400 K to ensure that the drying process is complete. ...
A kinetic model was built to estimate the optimum working parameters of a downdraft gasifier, in which a set of chemical kinetics at each zone of the gasifier was described. The model deals with a wide range of biomass types with elemental composition ranges of (38 ≤ C ≤ 52) %, (5.5 ≤ H ≤ 7) %, and (36 ≤ O ≤ 45) %. This model is able to predict gas composition, tar content, temperature and height of each zone, as well as temperature, velocity and pressure distribution at reduction zone with heating value of product gas. The model also gives full design dimensions of a downdraft gasifier. The final results, which proved to be in a good agreement with experimental works under different working conditions of biomass type, moisture content, and air-to-fuel ratio, are based on a new approach that includes calculation of the optimum height of the reduction zone. Calculation based on the optimum height ensures that all the char produced is consumed in the reduction zone, thus leading to the production of the maximum amount of gases. Results conclude that biomass with a moisture content less than 10% and equivalence ratio of 0.3–0.35 leads to the production of higher yield of syngas with low tar content. In particular, woody biomass materials are found to give the higher heating value for producer gas with a reasonable amount of tar.
... The latter complication causes mass transfer to play an important role in the gasification of solids [119]. Nevertheless, numerous researchers have focused extensively on kinetic models of biomass gasification: Wang and Kinoshita [120] [133]. Kinetic models describe the char reduction process using kinetic rate expressions obtained from experiments and permit better simulation of the experimental data where the residence time of gas and biomass is relatively short. ...
This chapter focuses on multiphase reactors' applications and challenges encountered in their applications to biomass processing and conversions to heat, power, biofuels, and chemicals. A number of multiphase reactors have been used for biomass combustion, including fixed bed, fluidized bed (FB), and entrained bed (pulverized fuel) combustors. Bed agglomeration, slagging, fouling, and corrosion are the major issues related to biomass combustion due to the relatively high salts (AAEMs), nitrogen, and chlorine contents of biomass feedstocks. The major problems for biomass feeding are blockage and plug seal failure to the reactor. Densified biomass (e.g., wood pellets and briquettes) is much more appropriate for transportation, handling, storage, and feeding. The high costs of pelletization can be justified by better operability of the fuel leading to improved boiler and combustion performance. The desirable moisture content of biomass feedstock must be lower than 15% (wb) for storage and various thermochemical applications.
... The processes are largely dependent on the parent biomass composition, moisture content, reactivity of biomass, local stoichiometry and the gasifier design. Figure 1: The down-draught fixed bed gasifier [3] A suitable model of the downdraft gasifier can predict the optimum performance parameters for its operation [4]. ...
... Roy et al. [18] combined an equilibrium model for the combustion and pyrolysis zones with a one-dimensional steady state model to simulate the char gasification stage. They focused on the catalytic effect of char on the heterogeneous reactions in the reduction zone. ...
A detailed sensitivity analysis is performed on a one-dimensional fixed bed downdraft biomass gasification model. The aim of this work is to analyze how the heat transfer mechanisms and rates are affected as reaction front progresses along the bed with its main reactive stages (drying, pyrolysis, combustion and reduction) under auto-thermal conditions. To this end, a batch type fixed-bed gasifier was simulated and used to study process propagation velocity of biomass gasification. The previously proposed model was validated with experimental data as a function of particle size. The model was capable of predicting coherently the physicochemical processes of gasification allowing an agreement between experimental and calculated data with an average error of 8%. Model sensitivity to parametric changes in several model and process parameters was evaluated by analyzing their effect on heat transfer mechanisms of reaction front (solid-gas, bed-wall and radiative in the solid phase) and key response variables (temperature field, maximum solid and gas temperatures inside the bed, flame front velocity, biomass consumption and fuel/air ratio). The model coefficients analyzed were the solid-gas heat transfer, radiation absorption, bed-wall heat transfer, pyrolysis kinetic rates and reactor-environment heat transfer. On the other hand, particle size, bed void fraction, air intake temperature, gasifying agent composition and gasifier wall material were analyzed as process parameters. The solid-gas heat transfer coefficient (0.02 < correction factor < 1.0) and particle size (4 < diameter < 30 mm) were the most significant parameters affecting process behavior. They led to variations of 88% and 68% in process velocity, respectively.
... There is considerable literature also available which deal with the modelling of gasification processes. These models can be mainly classified into three broad categories: 1) Kinetic rate models [5][6][7]; 2) Thermodynamic equilibrium model [8,9] of which ASPEN Plus model can belong to this category [10,11]; and 3) neural network based gasification model [12,13]. Except thermodynamics equilibrium model, other two models are computationally expensive or contain parameters that limit their applicability for a special scenario of power plant. ...
In this study the merits of hydrogen production using solar energy are discussed. The primary focus of the paper is to perform thermodynamics analysis of coal gasification via solar energy. Initially the chemical properties of coal are determined using proximate analysis, ultimate analysis and calorimeter. Using the coal properties a thermodynamics model bases on equilibrium constant approach is developed. The model is tested against the experimental data and further exergetic and cold gas efficiency is calculated. The effect of temperature and moisture contents is studied which shows that efficiency as high as 70% can be achieved with hydrogen yield of around 57% by volume. The model is further used to explore the potential of solar energy along with the partial combustion of coal. The result shows a sharp decline in the CO 2 emission, while 43% increase in the yield of Hydrogen is calculated.
... The quality of the fuel depends on the moisture content, which affects the heating value [68] . The moisture content in the biomass is one of the important parameters that affects the performance of the gasifier through the variation in the producer gas composition and conversion efficiency [69]. The amount of moisture content may be due to the inherent water content in the raw biomass specie or due to prevailing weather conditions. ...
Charcoal has found enormous application in both agriculture (AKA biochar) and other sectors. Despite its potential benefits, small scale technologies relevant for its production remain a challenge. Technologies striking a balance between user friendliness, energy efficiency, ease of adaptation and limited emissions could easily be integrated into the local community for the sustainable production of biochar answering both technical and socioeconomic aspects. These technologies can be customized to recover the produced heat alongside biochar and the producer gas. The purpose of this work is to review the state of the art in small scale technologies, their associated risks and challenges as well as research gaps for future work. Factors affecting biochar production have been discussed and temperature is known to heavily influence the biomass to biochar conversion process. Based on the reviewed work, there is a need to develop and promote sustainable and efficient technologies that can be integrated into biochar production systems. There is also further need to develop portable, economically viable technologies that could be integrated into the biochar production process without compromising the quality of produced biochar. Such technologies at midscale level can be channeled into conventional small scale farmer use in order that the farmers can process their own biochar.
... Estudos recentes sugerem a combinação das abordagens de equilíbrio e cinética. Roy et al. (2009) desenvolvem um modelo de 2 zonas baseado em equilíbrio químico e cinética química. Os autores dividem o processo de gaseificação em 2 zonas: (1) zona de piro-oxidação (secagem, pirólise e oxidação) e (2) zona de redução. ...
Gasification is a thermochemical conversion of a carbon-based fuel into a gas with useful calorific value. Modeling and simulation of gasification is difficult since involves complex chemical and physical processes. In that context, a simplified phenomenological model able to estimate the major variables becomes convenient. In the literature there are basically 2 approaches: equilibrium and kinetics. An equilibrium approach requires a smaller number of information for simulation, but can only be valid in chemical equilibrium conditions. A kinetic approach considers the mechanisms of chemical reactions and requires a much larger number of parameters for simulation. This paper proposes a new hybrid model that represents a gasification process for a combined equilibrium and kinetic approach. The new model is then compared with experimental values and estimated values of similar literature models.
... Ruggerio and Manfrida [19] have attempted to predict the product gas composition and overall efficiency of gasifier using thermodynamic model. Some other studies using equilibrium and/or kinetic models are from Altafini et al. [20], Melgar et al. [21], Brown et al. [22], Vera et al. [23], Roy et al. [24], Chowdhury et al. [25,26], Dasappa and Paul [27] and Saxena and Thomas [28]. ...
Biomass gasification has been a viable alternative for decentralized electricity generation in developing countries. The efficiency of the biomass gasification process for operation of the engine-generator set is mapped in terms of quality and quantity of the producer gas. In this study, we have attempted to devise generalized correlations for four principal parameters that form the benchmark for the performance of the gasifier. These parameters are lower heating value and net yield (per unit biomass) of producer gas, and volume fractions of CO and CO2 in the gas resulting from biomass gasification process. The correlations have been constituted using simulations of gasification of three common biomass feedstocks (viz. rice husk, saw dust and corn cobs) using semi-equilibrium non-stoichiometric thermodynamic model. The independent variables used in the simulations are air ratio, carbon conversion, gasification temperature and three elemental ratios in the gasification mixture, viz. H/C, O/H and O/C. As many as eight expressions of linear and non-linear type have been evaluated to best fit the simulations data for each performance parameter. On the basis of statistical indicators, the compatibility of the correlations for best fit of the data has been assessed. Finally, the predictions of the correlation have been tested against experimental data on gasification of different biomass. The best correlation for each performance parameter was chosen on the basis of least average absolute error and highest (absolute) regression coefficient. It was found that the set of best correlations could predict the values of performance parameters within engineering accuracy of ± 10–20%. The correlations proposed in this work are independent of the type of biomass gasifier. These correlations can form a useful tool for design and optimization of fixed or fluidized bed gasifier for any biomass feedstock. Copyright © 2011 John Wiley & Sons, Ltd.
... There are also commercial models or features of chemical engineering software like ASPENplus [137,138,139]. This software was only used in this work for biodiesel modeling in Chapter 7. Moreover in the gasifiers models it is important to distinguish models that treat only a part of the reactor, such as char reduction [140,141,142,143] or pyrolysis [144,145,146], or models that investigates the fluid dynamic of reactors and the multiphase flow in fluidized and bubble bed gasifiers [147,148,149,150]. ...
Research on the utilization of biomasses for energy purposes is playing a key role for the assessment and the development of new solutions for the world energy scenario. In fact, the demand and price of primary energy are constantly increasing, along with the development of new national and international strategies providing incentives and development policies for renewable technologies. This work aims at investigating the biomass gasification in downdraft stratified reactors used for energy production. First, different solutions for the production of electrical energy starting from woodsy biomasses are discussed, pointing out the major parameters involved in the pursuit of an optimal solution. Then, the technologies and principles of gasification are explained focusing on downdraft stratified reactors. Different reactors are analyzed, ranging from lab-scale to full-scale power-plant stratified gasifiers: the main thermo-chemical parameters have been acquired adopting different methods and instruments depending on the reactor scale and ultimate aim. The reactors are modeled using different approaches: from energy and mass balances to kinetic chemical modeling. During the experimental campaigns, particular attention has been paid to the development of a calorimetric approach for tar content evaluation and gas composition calculation. The scaling of the equation set used in the stratified reactors modeling highlights a distinctive feature of the modeling approach. The diameter of the gasifier seems to have no influence on the reactor performance, despite experimental data acquired during this work had provided different results. For this reason, the influence of the diameter on the behavior of the gasifiers is investigated and its correlation with thermal and rheological parameters is discussed. Results show the capability of these reactors to be used under several operating conditions, even where other gasifiers have running difficulties. Advantages and disadvantages of this technology are discussed, some new solutions for downdraft reactors are proposed, with an emphasis on micro-scale application.
... In downdraft gasifier, compared to air gasification, oxygen/ steam gasification improves H 2 yield and nearly doubles the heating value of fuel gas [5]. Roy et al. [6] presented a mathematical model of a throated downdraft gasifier predicting the syngas composition and gasification temperature. They also studied the effect of equivalence ratio and fuel moisture content on the performance of the downdraft gasifier to optimize the operating condition. ...
Gasification is a thermo-chemical conversion process used to produce syngas through partial oxidation. Gasification technology provides the opportunity to convert a feedstock into fuel gases or synthetic gases. Raw syngas produced by gasification needs cleaning before being used subsequently. One of the impurities in raw syngas is tar, a group of long-chain sticky hydrocarbons that clog the subsequent devices. One useful way of removing tar is to degrade it thermally into simple fuel gases (e.g., hydrogen, methane). This adds to the heat value of syngas too. In this work, an equilibrium model is reported that simulates the thermal cracking of three representative tars, viz. toluene, benzene and naphthalene, by steam reforming and hydrogenation and estimates the cracking products. Parametric studies have also been carried out to understand the influence of different operating conditions such as temperature and reactant concentrations on the composition of product gas mixture. Reported results may be useful to determine optimum operating conditions in tar cracking systems.
The article is focused on demostrating the combined effects of reaction and insulation parameters on syngas compostion during gasification process. A kinetic model is developed and implemented using FORTRAN program to simulate a downdraft gasifier using rubber wood as feedstock. The gasifier model consists of three zones: the pyrolysis, oxidation zone, and reduction zone; the gas composition and temperature distribution are estimated for each zone taking into account equilibrium ratios and reaction kinetics. To study the effect of heat loss, a novel expression in terms of insulation parameters is included for each zone. The properties of biomass composition and oxidant along with reaction constants is supplied as input parameter to the model.The results obtained from the model have been validated with experimental values. The effect of air supply and moisture content, coupled with properties of thermal insulation on final syngas composition and temperture is discussed. The analysis is useful for understanding the effects of energy interaction and it's losses, chemical reactions and operating conditions to maximize the energy output of the gasification process.
A robust mathematical model is developed for prediction and optimization of syngas in a downdraft gasifier. The gasifier is modelled for two distinct zones i.e. pyro-oxidation zone (zone I) and reduction zone (zone II). A thermodynamic equilibrium model is implemented for the prediction of syngas composition in zone I, while zone II is modelled by implementing a finite kinetic approach. For each zone five control parameters are identified for sequential maximization of carbon conversion efficiency (CCE). Maximization of H2 and CO yield in syngas and minimization of char contaminants is the main objective in the present analysis. The Taguchi method is implemented for process optimization while ANOVA is used to determine the most influential parameter. The optimized model gives 17.79% improvement in calorific value of syngas, while the final CCE obtained was 96.04%. For zone I the equivalence ratio was found to be the most influential parameter with 97% contribution, while for zone II the reduction zone temperature was the most influential parameter with 88% contribution.
La implementación de fuentes no convencionales de generación de energía eléctrica se ha realizado por medio de microrredes, en las cuales los sistemas de gestión de energía juegan un papel importante, ya que, por medio de estos, se busca el suministro económico de potencia a la carga. El objetivo de este estudio fue el desarrollo de un sistema de gestión de energía que considera el comportamiento de un sistema gasificador-generador mediante el uso de modelos matemáticos en la generación de electricidad basada en biomasa en una microrred con inclusión de fuentes convencionales y no convencionales de generación de energía eléctrica, almacenamiento en baterías, respuesta a la demanda y conexión a la red para el suministro económico de potencia a la carga. Para ello, se realizó la formulación matemática, tanto de la función objetivo de optimización, como de las restricciones de las fuentes y cargas que componen la microrred, y se implementó un algoritmo en Matlab para la ejecución de simulaciones y obtención de resultados, los cuales mostraron que el sistema de gestión opera satisfactoriamente a la microrred aislada y conectada a la red, aprovechando la fuente de biomasa para atender a la carga en un entorno de operación económica, combinando cada una de las fuentes y almacenamiento que componen el sistema. Finalmente, el uso de modelos matemáticos permite la incorporación del comportamiento de fuentes como la biomasa en la generación de potencia para diferentes valores de parámetros como la humedad de la biomasa y el factor de aire en esquemas de gestión económica de microrredes.
El análisis del uso de biomasa como fuente de energía y el desarrollo de las investigaciones relacionadas con el proceso de gasificación; han originado el planteamiento de diversos modelos para explicar y entender este complejo proceso, tanto en su diseño, como en su simulación, optimización y análisis; los cuales van encaminados a satisfacer la necesidad de cuantificar la producción de energía y su eficiencia. Este artículo presenta un análisis de varios modelos de gasificación basados en el equilibrio termodinámico, la cinética y control basado en redes neuronales artificiales.
The aim of this work is to investigate a novel integrated cooling, heating, and power (CCHP) system with biomass gasification, solid oxide fuel cells (SOFC), micro‐gas turbine, and absorption chiller. The performance of this system is analyzed by mathematical models consisting of lumped models of SOFC and absorption chiller and one‐dimensional model of a downdraft biomass gasifier. Effects of main operating parameters such as moisture content of biomass, air flow rate in the gasifier, and temperature of fuel gas on the overall energy and exergy performance of CCHP system are evaluated. The net present value (NPV) method is used to analyze the economic prospects of this system. The results show that higher flow rate of air for the gasifier with lower moisture content of biomass are beneficial for the improvement of the output of cooling, heating, and power of CCHP, and, accordingly, the electrical efficiency as well as overall energy and exergy efficiency of CCHP rises. Increasing mass flow rate of air for the gasifier can increase exergy efficiency by 10%. Moisture content less than 0.2 could result in exergy efficiency greater than 45% and CCHP efficiency over 65%.The decrease of the exhaust gas temperature further boosts the production of cooling and heating of the CCHP system. Specifically, a 10% improvement of overall efficiency of CCHP is obtained when the exhaust gas temperature is reduced to 90°C. In this work, an electrical efficiency over 50%, exergy efficiency more than 40%, and CCHP efficiency up to 80% can be achieved. Economic assessment shows that the initial investment of SOFC is above 50%‐60% of the total investment of the CCHP and the payback period is about 7‐8 years.
Biomass is considered as a potential source of energy production.Gasification can be employed to convert dilute biomass energy source in to gaseous products holding concentrated form of energy. A steady state model for fluidized bed biomass gasifier is developed based on reaction kinetics and hydrodynamic aspects of fluidization. The presence of sorbent for absorption of carbon dioxide from the product gas is also incorporated in the model.The developed model predicts the variation of syngas composition, temperature, pressure and velocity along the height of gasifier. Experiments were carried out in a lab scale fluidized bed biomass gasifier and the results were used to validate the model.An increase of 50.35% in H 2 mole fraction and a decrease of 50.88 % in CO 2 mole fraction were observed when CaO was used as the sorbent.
Biomass gasification is widely recognized as an effective method to obtain renewable energy. It is very challenging to accurately predict the syngas and tar compositions. In this work, a chemical reaction kinetics Model based on comprehensive gasification kinetics is proposed to simulate downdraft biomass gasification. The Kinetic Model is validated by direct comparison to experimental results of two downdraft gasifiers available in the literature and is found to be more accurate than the widely used Gibbs energy minimizing model (GEM Model). The Kinetic Model is then applied to investigate the effects of equivalence ratio (ER), gasification temperature, biomass moisture content and biomass composition on syngas and tar production. Accurate water‐gas shift and CO shift reaction kinetics are found critical to achieving good agreement with experimental results.
Ziel der thermochemischen Vergasung ist die Erzeugung eines brennbaren Produktgases aus einem festen Kohlenstoffträger bei unterstöchiometrischer Sauerstoffzufuhr mit möglichst hoher Effizienz. Gerade im kleinen und mittleren Leistungsbereich haben sich luftgeblasene, autotherme, atmosphärische Festbettverfahren etabliert. Eine wesentliche Herausforderung speziell bei „stratified downdraft“ Reaktoren („throatless gasifier“) stellt die Prozessstabilität und damit die Wanderung der Reaktionsfront im Schüttbett dar. Damit verbundene Inhomogenitäten können zu Kanalbildung und damit zu erhöhtem Teergehalt im Produktgas führen. Ziel der vorliegenden Arbeit ist es, mittels experimenteller Untersuchungen und mathematischer Modellierung die Transparenz des Prozesses der autothermen luftgeblasenen Festbettvergasung von Holz in „stratified downdraft“ Reaktoren zu verbessern. Es wird eine Versuchsanlage im Technikumsmaßstab konzipiert und aufgebaut, um die gewonnenen Ergebnisse und Betriebserfahrungen auf technische Anwendungen übertragen zu können. Im praktischen Versuchsbetrieb wird der Einfluss der Betriebsparameter Vergasungsgutfeuchte und Leerrohrgeschwindigkeit im Hinblick auf die Stabilisierung der Reaktionsfront bei gleichzeitiger Optimierung der Leistungsparameter der Vergasungsanlage und Minimierung des Gehalts an kondensierbaren Kohlenwasserstoffen untersucht. Vorgeschaltet ist eine kritische Analyse und Bewertung der eingesetzten Messmethoden, um den Vergleich mit bisherigen Untersuchungen zu ermöglichen. Weiterhin wird ein zweistufiges mathematisches Modell vorgeschlagen, das erste Voraussagen bezüglich der Auslegung von Vergasungsreaktoren einerseits und des Betriebsverhaltens bestehender Systeme in Abhängigkeit der gewählten Betriebsparameter und Einsatzstoffe andererseits erlaubt. Das Modell wird anhand der praktischen Versuchsergebnisse validiert.
Gasification has been one of the most attractive and common biomass conversion processes for recent years. The existence of an accurate and dynamic model frees us from carrying out time-consuming and expensive tests. In this study, to eliminate the complexity of dynamic models, a hybrid model is used for modeling the process of wood-fixed bed gasification. Firstly, an equilibrium model is developed to obtain the mole fractions of product flow and the equilibrium temperature of the flaming pyrolysis zone. The equilibrium model is applied as the initial condition of the unsteady one-dimensional kinetic model for the reduction zone. The couple of heat and mass equations in the gas phase are solved by considering the kinetic of main reactions in the reduction zone using MATLAB software. Oxygen is considered gasifying agent instead of air. The results indicate a good agreement with previous relevant researches. In the equivalence ratio of 0.35, the maximum mole fraction of hydrogen as the most valuable syngas has obtained. In this optimum ER, the equilibrium temperature of flaming pyrolysis zone has been calculated to be 1012 K, and the gasifier outlet temperature at gas-phase velocity within 0.1–1 m/s is 890–952 K. The final mole fractions of CO and H2 as the main products of the process are 0.46 and 0.36, respectively. The heating value of produced syngas equals 10.8 MJ/m³ that is 120% higher than the average heating value when the air is utilized as the gasifier agent.
Co-gasification of woody biomass and animal manure is an effective technology to utilize animal manure. In this work, the thermodynamic and economic analysis of an integration of co-gasification of woody biomass and animal manure with solid oxide fuel cell (SOFC) and micro gas turbine is carried out. The overall thermodynamic performance of this combined heat and power (CHP) system is investigated by a mathematics model consisting of simple zero-dimensional model of SOFC and one-dimensional model of downdraft biomass gasifier. The net present value (NPV) method is adopted to investigate the economic feasible of the CHP system.
The gasifier model includes two parts. The pyrolysis-oxidation zone includes pyrolysis zone and combustion zone, and a lumped capacitance method and chemical equilibrium are used to simulate the species in pyrolysis-oxidation zone, while one-dimensional kinetic model is adopted to analyze the performance of reduction zone, which considering geometrical dimensions of downdraft gasifier and actual char conversion process.
Effects of three operating parameters such as air flow rate in gasifier, moisture content of blended fuel and mass fraction of woody biomass in blended fuel on overall performance of CHP system are evaluated. The results show that decreased mass fraction of animal manure and increased mass flow rate of gasification air have positive effect on conversion of char owing to higher reaction temperature. Entire conversion of char in gasifier and electrical efficiency of the CHP power system above 45% can be achieved on the condition that mass fraction of animal manure is less than 0.4, moisture content is less than 0.4 and mass flow rate of gasification air is more than 47 kg h⁻¹ as the total mass flow rate of blended fuel equal to 28 kg h⁻¹.
Economic analysis shows that more woody biomass rather than animal mature in blend fuel is more economically attractive despite of the low cost of animal mature. The particular high initial capital investment of SOFC is the main part of the whole CHP system. In this work, the payback time is less than eight years. If the target cost less than 3000 €/kW for SOFC in a future year will be reached and the optimized operating parameter is adopted, the investment of a co-gasification of woody biomass and animal manure, SOFC and MGT hybrid system will be more competitive for the user.
The chapter gives an overview of new techniques developed and used in coal, biomass and waste materials gasification. All of the above-mentioned materials have similar properties for hydrocarbon content. As a consequence, most of them are used for power and heat generation through gasification technology. The chapter discusses advanced kinetic as well as computational fluid dynamics (CFD) modelling schemes valid for a wide range of coal and biomass materials using a downdraft gasifier. The models show validated results with experimental data. Underground coal gasification (UCG) is also discussed, modelled and verified to some extent. Applications leading to the combined heat and power (CHP) generation from syngas produced through the gasification of such feedstocks are presented.
This chapter begins with the presentation of the exergy analysis of biomass gasification, which is a key thermochemical conversion technology. Syngas produced from biomass can be used for many applications, including heat and power generation as well as synthesis of transport fuels and chemicals. Gasification, along with combustion and pyrolysis, belongs to thermochemical conversion processes that can be applied to almost all kinds of biomass feedstocks. Gasification models are useful engineering tools to study the influence of the biomass composition, kind of gasifying agent, and process conditions on the syngas production process. The chapter considers the exergy analysis of gasification of pure solid carbon, which gives the reader an insight into the efficiency of elemental steps involved in the gasification process. The chapter demonstrates that exergy losses during gasification, particularly the losses due to the heating up of the gasifying agent to the reactor temperature, can be reduced using oxygen as a gasifying agent.
Gasification is a thermochemical conversion process consisting of partial oxidation of a fuel to convert it to a gas mixture ("syngas"). Generally, the gasification process modeling uses a kinetic detailed description, or approach it to a chemical equilibrium state. Both approaches have advantages and disadvantages, as well as limitations. The objective of this work was to develop a new phenomenological modeling of gasification processes through a "hybrid" model here called hybrid adaptive zone model (HAZ). This proposed modeling assumed the gasifier is represented by two types of zones: one dominated by chemical kinetics, represented by a kinetic model, and another where chemical kinetics is fast so chemical species are assumed in chemical equilibrium states, represented by an equilibrium model. A transition criterion between zones was defined by a Damköhler number (Da) which relates residence time and chemical reaction time. Therefore, the HAZ model can adapted according to the dominant processes in each zone. Firstly, a multi-phase equilibrium model (ME) was developed and applied to study the coal-biomass co-gasification of Brazilian sources. Hereafter, the HAZ model was built using the technique of equivalent reactor network (ERN) with the ME model and a kinetic model developed in this work. A methodology of use of the HAZ model was proposed, applied and validated for two configurations of gasifiers: two cases of biomass bubbling fluidized-bed gasifiers and one case of coal entrained-flow gasifier. In the first two cases the transition was estimated to occur on Da ≥ 10^(+5) and in the last case; it was estimated on Da ≥ 10^(+3). The application of the HAZ model proved to be satisfactory since it could reduce the computation time by at least 40% compared to a pure kinetic approach. It should already be emphasized that the HAZ model allowed a better physical and chemical understanding of gasification by identifying the dominant local processes.
El analisis del uso de biomasa como fuente de energia y el desarrollo de las investigaciones relacionadas con el proceso de gasificacion; han originado el planteamiento de diversos modelos para explicar y entender este complejo proceso, tanto en su diseno, como en su simulacion, optimizacion y analisis; los cuales van encaminados a satisfacer la necesidad de cuantificar la produccion de energia y su eficiencia. Este articulo presenta un analisis de varios modelos de gasificacion basados en el equilibrio termodinamico, la cinetica y control basado en redes neuronales artificiales.
The use of biomass gasification system for the generation of combined heat and power has gained importance because it is considered to be one of the most promising renewable energy technologies. Widespread research has been already carried out on downdraft gasifier with single biomass as feedstock. However limited work is available to ascertain the feasibility of utilising blends of biomasses. In this paper, theoretical and experimental studies have been carried out on a 50 kWth downdraft gasifier with the blends of coconut shell and rubber seed shell, which are available abundantly in the rural villages of South India. Two-Zone kinetic modelling is followed for the theoretical studies. Experimental study has been carried out to prove the validity of the modelling approach. The results show that the mixing of rubber seed shell and coconut shell with various compositions yields the performance which is on par with the woody biomasses. Besides, the maximum values of the performance parameters are obtained when the equivalence ratio is maintained between 0.2 and 0.3.
Alternative energy resources are becoming increasingly important because of dwindling petroleum reserves and increasing environmental concerns. As a result, biobased fuels are emerging as an alternative solution. In order to fully utilize biomass resources, a versatile, robust, and cost-effective conversion process needs to be developed. Biomass gasification and fast pyrolysis are promising methods that can be used to transform lignocellulosic biomass into fuels and chemicals. This chapter discusses gasification and fast pyrolysis technologies in detail. Factors that affect gasification and fast pyrolysis processes are discussed. Bio-oil applications and upgrading techniques are also delineated.
Alternative fuels, mainly generated from waste, constitute a possible option to reduce the demand for fossil fuels. For instance, biogas can be obtained from cow manure using anaerobic digesters, a technology that is currently being implemented in several dairy farms. Synthesis gas, also known as syngas, is a mixture of hydrogen and carbon monoxide that may have fractions of other components such as nitrogen, carbon dioxide, and methane, depending on the gasifying method used. However, before a change to alternative fuels can be made, the performance of common appliances and industrial equipment using these fuels needs to be investigated. In this paper, a computational analysis of the performance of an air heater using natural gas, biogas, and syngas is performed. The results show that alternative fuels with heat values almost an order of magnitude lower than natural gas can be used in commercial air heaters with only minor variations in thermal performance. The main drawback is the higher flow rates required for alternative fuels, specially for syngas.
An integrated process of biomass gasification and solid oxide fuel cells (SOFC) is investigated using energy and exergy analyses. The performance of the system is assessed by calculating several parameters such as electrical efficiency, combined heat and power efficiency, power to heat ratio, exergy destruction ratio, and exergy efficiency. A performance comparison of power systems for different gasification agents is given by thermodynamic analysis. Exergy analysis is applied to investigate exergy destruction in components in the power systems. When using oxygen-enriched air as gasification agent, the gasifier reactor causes the greatest exergy destruction. About 29% of the chemical energy of the biomass is converted into net electric power, while about 17% of it is used to for producing hot water for district heating purposes. The total exergy efficiency of combined heat and power is 29%. For the case in which steam as the gasification agent, the highest exergy destruction lies in the air preheater due to the great temperature difference between the hot and cold side. The net electrical efficiency is about 40%. The exergy combined heat and power efficiency is above 36%, which is higher than that when air or oxygen-enriched air as gasification agent.
In this study, gasification of different biomass feedstocks, including pine wood chips, sawdust, peanut hulls, and poultry litter (the latter three in pelletized form), was conducted in a 25 kW e commercially available, mobile downdraft gasifier. Ultimate and proximate analyses were carried out to characterize the biomass feedstocks used for gasification. The synthesis gas obtained from different feedstocks and different operating conditions (biomass flow rate and moisture content) was analyzed using an on-site gas analyzer. Gasification of peanut hull pellets showed the highest heating value (6.1 MJ per normal cubic meter, Nm -3) of synthesis gas, whereas poultry litter gasification gave the lowest heating value (4.8 MJ Nm -3). © 2011 American Society of Agricultural and Biological Engineers ISSN 2151-0032.
An integrated power system of biomass gasification with solid oxide fuel cells (SOFC) and micro gas turbine has been investigated by thermodynamic model. A zero-dimensional electrochemical model of SOFC and one-dimensional chemical kinetics model of downdraft biomass gasifier have been developed to analyze overall performance of the power system. Effects of various parameters such as moisture content in biomass, equivalence ratio and mass flow rate of dry biomass on the overall performance of system have been studied by energy analysis.
It is found that char in the biomass tends to be converted with decreasing of moisture content and increasing of equivalence ratio due to higher temperature in reduction zone of gasifier. Electric and combined heat and power efficiencies of the power system increase with decreasing of moisture content and increasing of equivalence ratio, the electrical efficiency of this system could reach a level of approximately 56%.Regarding entire conversion of char in gasifier and acceptable electrical efficiency above 45%, operating condition in this study is suggested to be in the range of moisture content less than 0.2, equivalence ratio more than 0.46 and mass flow rate of biomass less than 20 kg h⁻¹.
Hydrogen has a great potential as fuel of the future and biomass can be a useful resource for the production of hydrogen. In the present work, a thermodynamic model has been developed to evaluate the yield of hydrogen from biomass through gasification in an oxygen-rich environment followed by carbon monoxide shift reaction with the injection of water. The effects of operating conditions, like gasifier equivalence ratio, quantity of water injected in the shift reactor and oxygen percentage in the gasifying agent, on the hydrogen concentration in the product gas from biomass have been evaluated. It is predicted that the process can generate 102 g hydrogen per kg of biomass, resulting in a cold gas efficiency of 65.4%. However, the air separation unit consumes a considerable amount of work in compression and refrigeration and these would decrease the overall efficiency by about 3.6 percentage points in a 5-stage compressor system.
A performance analysis of downdraft biomass gasifier has been done using an equilibrium model for the pyro-oxidation zone and kinetic model for the reduction zone. The motivation of the analysis is to find out the suitable operating parameters when different biomass feedstocks are used in the gasifier as fuel. The study has been carried out with three woody biomass (rubber wood, eucalyptus wood and bamboo wood), two agricultural wastes (wheat straw and rice straw) and coconut shell. The fuel feed rate, equivalence ratio and feed particle size are adjusted to target the critical char bed length, constant gas production rate and pressure drop with every biomass, such that the gasifier with its accessories can be optimally used. However, it is found that the heating value of the producer gas and the bio-energy generation rate in the gasification process would change with the variation in the gasifier fuel. This will result in a change in rating of the engine coupled with the gasifier for producing power. Finally, an economic analysis based on fuel price is made for the corresponding operating conditions of all the fuels. It is found that wheat straw gives the maximum bio-energy generation rate and the minimum specific fuel cost (Rs./MJ of energy) among the fuels compared.
This thesis presents the development of a methodology for simulation, techno-economic
optimization and design of a quad-generation energy system based on biomass gasification.
An efficient way of reducing CO2 emission from the environment is by increasing the use of
biomass in the energy sector. Different biomass resources are used to generate heat and
electricity, to produce gas fuel like bio-SNG (synthetic natural gas) and also to produce liquid
fuels, such as ethanol, methanol and biodiesel. Due to the fact that the trend of establishing new
and modern plants for handling and processing biomass, it is possible to lay a foundation for
future gasification based power plants to produce flexible output such as electricity, heat,
chemicals or bio-fuels by improving the flexibility of existing DHP (district heating plant)
integrating gasification technology.
The present study investigates energy system alternatives by upgrading existing district
heating plant. It provides a generic modeling framework to design flexible energy system for the
near future. This framework addresses three main issues arising in the planning and designing of
energy systems: a) socio impact at both planning and process design levels; b) technical impact
to select different technologies and types of equipment from available options; and c) economic
concern to validate new technology with existing ones. To resolve the above issues a life cycle
assessment (LCA) analysis and techno-economic analysis of quad-generation systems are
included in this study.
The overall aim of this work is to provide a complete assessment of the technical potential of
biomass gasification for local heat and power supply in Denmark and replacement of natural gas
for the production. This study also finds and defines future areas of research in gasification
technology in Denmark within the development of green syngas or liquid fuels for sectors such
as the transportation sector. Computational models of whole system component for steady-state
operation are developed and also system concepts as well as key performance parameters are
identified. The main contribution of this project to ascertain new and flexible technologies that
could contribute for local heat demand and supply, national gas grid connection, and short term
power marketing perspective in an economic evaluation.
An exergetic analysis has been performed on a gasification-based bio-hydrogen generation system consisting of an ASU (air separation unit), a gasifier and a water gas shift reactor. The biomass feed in the system is rice straw. The influences of oxygen percentage in the gasifying agent (in the range 85–99%) and gasifier equivalence ratio (in the range 2–4) on the system exergetic efficiency have been studied. The analysis also investigates the effect of the above mentioned operating parameters on the hydrogen yield and cold gas efficiency. It is observed that, with 95% oxygen in the gasifying agent and with gasifier equivalence ratio of 4.0, the process generates 107.8 g hydrogen per kg of dry biomass (on ash free basis) with a cold gas efficiency of 70%. An increase in gasifier equivalence ratio is found to increase the exergetic efficiency of the system. However, the exergetic efficiency remains almost immune to the change in oxygen percentage in the gasifying agent. The maximum destruction of exergy, in quantitative term, is found to be in the gasifier due to the irreversible chemical reactions occurring there. However, in terms of percentage of exergy input, the highest exergy destruction and exergy loss are observed to occur in the ASU.
Modeling of biomass gasification has been an active area of research for past two decades. In the published literature, three approaches have been adopted for the modeling of this process, viz. thermodynamic equilibrium, semi-equilibrium and kinetic. In this paper, we have attempted to present a comparative assessment of these three types of models for predicting outcome of the gasification process in a circulating fluidized bed gasifier. Two model biomass, viz. rice husk and wood particles, have been chosen for analysis, with gasification medium being air. Although the trends in molar composition, net yield and LHV of the producer gas predicted by three models are in concurrence, significant quantitative difference is seen in the results. Due to rather slow kinetics of char gasification and tar oxidation, carbon conversion achieved in single pass of biomass through the gasifier, calculated using kinetic model, is quite low, which adversely affects the yield and LHV of the producer gas. Although equilibrium and semi-equilibrium models reveal relative insensitivity of producer gas characteristics towards temperature, the kinetic model shows significant effect of temperature on LHV of the gas at low air ratios. Kinetic models also reveal volume of the gasifier to be an insignificant parameter, as the net yield and LHV of the gas resulting from 6 m and 10 m riser is same. On a whole, the analysis presented in this paper indicates that thermodynamic models are useful tools for quantitative assessment of the gasification process, while kinetic models provide physically more realistic picture.
In the development of rural India, employment generation is the most fundamental issue to be addressed, which, in today's context, is very closely connected to the power supply to villages. Decentralised power supply is being increasingly recognised as having much greater potential for supplying quality power to the remote areas as compared to the conventional centralised supply. Biomass gasification has emerged as a very promising technology for decentralised power generation and hence must be utilised for rural electrification to its full potential. In this paper, an effort has been made to draw attention to the suitability of this technology for power supply to villages and also to the challenges which must be addressed for effective use of the technology for this purpose. Many issues which need careful consideration, like resource and demand assessment, various aspects of plant management, economics and the government policies have been discussed. Many of these are pertaining to field situations and hence pose considerable challenge for effective handling. The paper is directed towards a wide class of readership – from those responsible for rural electrification including policy makers and implementers, who may need to know even the basics of the technology to those familiar with technology but with little or no experience in field implementation. It is hoped that such a paper will provide the concerned people with adequate exposure to the complexities associated with rural electrification using biomass gasification and hence help in its more effective implementation.
One of the major obstacles for the application of biomass gasification systems is the high tar content of the producer gas that prevents the use in engines, turbines or fuel cells without further gas cleaning. In this work, features of a novel tar free gasifier are described. Producer gas, containing 2 mg/Nm 3 of tar and dust was obtained. This gas can be used directly to fuel cycle Otto engines to produce electricity and heat. Biomass was converted in producer gas with up to 78% efficiency. Typically from 1.3 kg of woody biomass in dry base, 1 kWh e and up to 2 kWh t can be obtained. Operations and maintenance are very simple and can be carried out by non-skilled operators.
1 . India an oil -importing country, with nearly 70% of its population living in half million villages and hamlets across the country and rich in bio -resources is ideally suited for biomass-based technologies. The Ministry of Non - conventional Energy Sources (MNES) has taken the initi- ative to develop research groups within India for techno - logy and manpower development. As a consequence, one of the premier institutions namely, the Indian Institute of Science (IISc) has been involved in the field of biomass combustion and gasification over twenty years by con - ducting innovative research, technology development, dis - semination, training, technology demonstration and testing of system in accordance to the international protocols. It is also involved in areas of con sultancy, technology trans- fers and imparting training to the international participants. It is important to begin this article by enunciating the motivation behind the development of gasifiers at IISc. Early in 1979, the attention of Shrinivasa and Mukun da 2
The performance and impact of a decentralized biomass gasifier-based power generation system in an unelectrified village are presented. In Hosahalli village, Karnataka, India, lighting, drinking water, irrigation water and flour-milling services are provided using power derived from the biomass gasifier-based power generation system. The system consists of a 20 kW gasifier-engine generator system with all the accessories for fuel processing and electricity distribution. The biomass power system has functioned for over 14 years (1988-2004) in Hosahalli village (population of 218 during 2003), meeting all the electricity needs of the village. Lighting and piped drinking water supply using biomass electricity, was provided for over 85% of the days during the past six years. The fuel, operation and maintenance cost ranged from Rs 5.85/kWh at a load of 5 kW to Rs 3.34/kWh at a load of 20 kW. Technical, social, economic and management-related lessons learnt are presented here.
Equilibrium modeling has been used to predict the gasification process in a downdraft gasifier. The composition of the producer gas and, hence, the calorific value have been determined. The effects of initial moisture content in the wood and the temperature in the gasification zone on the calorific value have been investigated. The predicted values compare reasonably well with experimental data. The calorific value of the producer gas decreases with increase in moisture content in the raw material. The calorific value of the producer gas decreases as the gasification temperature increases in the range of temperatures investigated.
The management of municipal solid waste (MSW) and the current status of world energy resources crisis are important problems. Gasification is a kind of waste-to- energy conversion scheme that offers the most attractive solution to both waste disposal and energy problems. In this study, the thermodynamic equilibrium model based on equilibrium constant for predicting the composition of producer gas in a downdraft waste gasifier was developed. To enhance the performance of the model, further modification was made by multiplying the equilibrium constants with coefficients. The modified model was validated with the data reported by different researchers. MSW in Thailand was then used to simulate and to study the effects of moisture content (MC) of the waste on the gasifier's performance. The results showed that the mole fraction of H2 gradually increases; CO decreases; CH4, which has a very low percentage in the producer gas increases; N2 slightly decreases; and CO2 increases with increasing MC. The reaction temperature, the calorific value, and the second law efficiency, decrease when MC increases.
This paper discusses the contribution of biomass in the future global energy supply. The discussion is based on a review of 17 earlier studies on the subject. These studies have arrived at widely different conclusions about the possible contribution of biomass in the future global energy supply (e.g., from below 100 EJ yr−1 to above 400 EJ yr−1 in 2050). The major reason for the differences is that the two most crucial parameters—land availability and yield levels in energy crop production—are very uncertain, and subject to widely different opinions (e.g., the assessed 2050 plantation supply ranges from below 50 EJ yr−1 to almost 240 EJ yr−1). However, also the expectations about future availability of forest wood and of residues from agriculture and forestry vary substantially among the studies.The question how an expanding bioenergy sector would interact with other land uses, such as food production, biodiversity, soil and nature conservation, and carbon sequestration has been insufficiently analyzed in the studies. It is therefore difficult to establish to what extent bioenergy is an attractive option for climate change mitigation in the energy sector. A refined modeling of interactions between different uses and bioenergy, food and materials production—i.e., of competition for resources, and of synergies between different uses—would facilitate an improved understanding of the prospects for large-scale bioenergy and of future land-use and biomass management in general
The conversion of biomass by gasification into a fuel suitable for use in a gas engine increases greatly the potential usefulness of biomass as a renewable resource. Gasification is a robust proven technology that can be operated either as a simple, low technology system based on a fixed-bed gasifier, or as a more sophisticated system using fluidized-bed technology. The properties of the biomass feedstock and its preparation are key design parameters when selecting the gasifier system. Electricity generation using a gas engine operating on gas produced by the gasification of biomass is applicable equally to both the developed world (as a means of reducing greenhouse gas emissions by replacing fossil fuel) and to the developing world (by providing electricity in rural areas derived from traditional biomass).
Measurements of CO2 (direct GHG) and CO, SO2, NO (indirect GHGs) were conducted on-line at some of the coal-based thermal power plants in India. The objective of the study was three-fold: to quantify the measured emissions in terms of emission coefficient per kg of coal and per kWh of electricity, to calculate the total possible emission from Indian thermal power plants, and subsequently to compare them with some previous studies. Instrument IMR 2800P Flue Gas Analyzer was used on-line to measure the emission rates of CO2, CO, SO2, and NO at 11 numbers of generating units of different ratings. Certain quality assurance (QA) and quality control (QC) techniques were also adopted to gather the data so as to avoid any ambiguity in subsequent data interpretation. For the betterment of data interpretation, the requisite statistical parameters (standard deviation and arithmetic mean) for the measured emissions have been also calculated. The emission coefficients determined for CO2, CO, SO2, and NO have been compared with their corresponding values as obtained in the studies conducted by other groups. The total emissions of CO2, CO, SO2, and NO calculated on the basis of the emission coefficients for the year 2003–2004 have been found to be 465.667, 1.583, 4.058, and 1.129 Tg, respectively.
This handbook has been prepared by the Solar Energy Research Institute under the US Department of Energy /bold Solar Technical Information Program/. It is intended as a guide to the design, testing, operation, and manufacture of small-scale (less than 200 kW (270 hp)) gasifiers. A great deal of the information will be useful for all levels of biomass gasification. The handbook is meant to be a practical guide to gasifier systems, and a minimum amount of space is devoted to questions of more theoretical interest.
A kinetic model for biomass gasification is developed based on the mechanism of surface reactions. The apparent rate constants are computed by minimizing the differences between experimental data and theoretical results for different residence times and different temperatures. The kinetic model is validated by comparing experimental data with the theoretical results for different equivalence ratios; the simulations agree well with the experimental data. Simulations modeling the influence of char particle size on the time required to achieve 90% carbon conversion agree with the results of tests performed by other investigators. Simulations are performed to evaluate the effects of the following parameters on biomass gasification: (a) type of oxidant, (b) residence time, (c) char particle size, (d) temperature, (e) pressure, (f) equivalence ratio, and (g) moisture.
A phenomenological model of downdraft gasification under steady state operation is developed based on previously published values for the reaction kinetics in the reduction zone. The model predicts a product gas with a composition similar to that found experimentally, although the model over-predicts the methane concentration. The accuracy of the model is limited by the availability of data on the initial conditions at the top of the reduction zone.
This paper deals with the computational simulation of a wood waste (sawdust) gasifier using an equilibrium model based on minimization of the Gibbs free energy. The gasifier has been tested with Pinus Elliotis sawdust, an exotic specie largely cultivated in the South of Brazil. The biomass used in the tests presented a moisture of nearly 10% (wt% on wet basis), and the average composition results of the gas produced (without tar) are compared with the equilibrium models used. Sensitivity studies to verify the influence of the moisture sawdust content on the fuel gas composition and on its heating value were made. More complex models to reproduce with better accuracy the gasifier studied were elaborated. Although the equilibrium models do not represent the reactions that occur at relatively high temperatures (≈800 °C) very well, these models can be useful to show some tendencies on the working parameter variations of a gasifier.
Given a set of operating and input conditions, the equilibrium models can predict the temperature, gas composition and char yield at the exits of the flaming-pyrolysis (FP) zone and of the gasifier. Based on the equilibrium models, parametric studies have been conducted to assess the influences of the important operating parameters, including the air/feed ratio, moisture/feed ratio and heat loss rate, on the performance of the FP zone and of the entire gasifier. To facilitate the implementation of thermodynamic equilibrium models, two highly efficient calculation methods for the carbon-hydrogen-oxygen-inert (CHOI) system have been developed. The first, an analytic method, can calculate the equilibrium gas composition in a heterogeneous CHOI system, and the second, a single-variable numerical solution based on the first method, can determine the equilibrium gas composition in a general CHOI system, either heterogeneous or homogeneous. The pyrolysis of a single large biomass particle in the flaming-pyrolysis zone of a downdraft gasifier was simulated by a kinetic model, featuring (1) first-order Arrhenius kinetics for the pyrolysis, (2) particle heat capacity and thermal conductivity dependent on the degree of pyrolysis, and (3) a thermal environment approximating that of the FP zone. A numerical solution method based on the Crank and Nicholson method has been developed for the model. Transient temperature and density profiles, and the rate of evolution of volatiles from the particle have been obtained from simulations. Parametric studies have indicated the trends of decreasing time for completion of flaming-pyrolysis with increasing flame temperature, with increasing convective heat transfer coefficient between the flame and the particle, with decreasing particle size and with increasing exothermicity of pyrolysis reaction; these trends are all in agreement with expectations.
A Texas lignite, an anthracite and two bituminous coals, Pittsburgh number8 and Illinois number6, were pyrolyzed in a nitrogen atmosphere to prepare chars. Optical microscopy, mercury porosimetry and gas adsorption techniques using nitrogen, CO/sub 2/ and CO, were employed for pore structure characterization. The lignite char exhibited the fastest rates of gaseous diffusion, followed in order of decreasing diffusivities by the Illinois number6, Pittsburgh number8 and anthracite chars. The changes in reactivities and pore structures of chars were measured experimentally during their reaction with oxygen (400-550C) and CO/sub 2/ (800-1000C). For a particular char-gas system, the normalized rate-conversion pattern was invariant with respect to temperature and gaseous concentration. In the case of lignite and Pittsburgh number8 chars, the rate-conversion pattern was similar during reaction with oxygen and CO/sub 2/. Adsorption experiments on partially reacted chars indicated that the micropores in the lignite char were accessible to both reactants. The micropores in the Illinois number6 char were, however, not accessible during its reaction with oxygen. The evolution of pore structure during reaction was modeled by using a probabilistic approach which accounts for overlapping pores with different shapes and sizes. The kinetics of gasification of the lignite and the Pittsburgh number8 chars was studied using a Langmuir-Hinshelwood type kinetic expression to correlate the experimental data. CO was found to inhibit the reaction substantially. The effect of a potassium carbonate catalyst on the reaction of these two chars was also investigated. Substantial increases in reaction rates were observed, and the enhancement was approximately proportional to the catalyst loading.
The paper reports the development of a novel multifuel biomass reactor for direct heating applications such as water heating, air heating or steam generation. Studies were conducted on the reactor to maximize its heat release rate by evaluation of the sensitivities of the fuel and charging parameters to firing rate. Maximum firing rates measured for the different fuels were in the range of 8–43 kg/h for the natural draft mode and 45–130 kg/h for the forced draft mode. It is observed that the heat release rate is enhanced by up to 360% by preheating of the charge, increase of the surface-area/volume ratio of the fuel charge, decrease of the charge per feed, and adoption of forced draft mode. For wood, a fuel preheat to 80°C, a surface-area/volume ratio of 600 m−1 and a charge per feed of 0.5–1.0 kg give a higher heat release and minimize gas temperature fluctuations.
The behaviour of an updraft moving bed gasifier of diameter 76 mm and height 787 mm, with rice husk as a fuel, has been studied. The gasification rate of the rice husk was varied in the range of 3.5–12.5 × 10−3 kg/m2 s. The air velocity was varied in the range of 0.07–0.11 m/s. The producer gas obtained from the gasifier has a calorific value in the range of 3712–4464 kJ/m3. A set of theoretical kinetic equations on the assumption of nonequilibrium conditions has been developed and solved numerically. The simulated temperature profile and outlet gas composition have been compared with those obtained from experimental runs. This model, which is developed from a mechanistic approach, can appreciably explain the behaviour of the present system within the range of variables studied.
The behaviour of a downdraft rice husk gasifier of diameter 200 mm and a height 940 mm has been studied. The gasification rate was varied in the range 1.8–4.3 × 10−2 kg/m2s. The air velocity was varied in the range 0.032–0.099 m/s. The producer gas obtained from the gasifier has a calorific value in the range 3240–4382 kJ/m3. A set of theoretical kinetic equations on the assumption of nonequilibrium conditions has been developed and solved numerically. The simulated temperature profile and outlet gas composition have been compared with those obtained from experimental runs. The model developed from a mechanistic approach is found to explain the behaviour of the present system appreciably within the range of variables studied.
The U.S. Department of Energy and the National Renewable Energy Laboratory are developing technologies to produce hydrogen from renewable, sustainable sources. A cost goal of $2.00–$3.00 kg−1 of hydrogen has been identified as the range at which delivered hydrogen becomes cost competitive with gasoline for passenger vehicles. Electrolysis of water is a standard commercial technology for producing hydrogen. Using wind and solar resources to produce the electricity for the process creates a renewable system. Biomass-to-hydrogen processes, including gasification, pyrolysis, and fermentation, are less well-developed technologies. These processes offer the possibility of producing hydrogen from energy crops and from biomass materials such as forest residue and municipal sewage. Solar energy can be used to produce hydrogen from water and biomass by several conversion pathways. Concentrated solar energy can generate high temperatures at which thermochemical reactions can be used to split water. Photoelectrochemical water splitting and photobiology are long-term options for producing hydrogen from water using solar energy. All these technologies are in the development stage. Copyright © 2007 John Wiley & Sons, Ltd.
A one-dimensional, steady state, numerical model for coal pyrolysis by solid heat carrier in moving-bed has been developed. The multiple-reaction model of coal pyrolysis and the gas–solid–solid three phases heat transfer theory in packed bed have been applied to account for the pyrolysis process. The results show that the axial temperature distribution of the coal particles increase with a heating rate more than 600 K/min. Coal particle size has significant influence on the heating rate, while blending ratio is the determinant factor of pyrolysis temperature. Given the main operating parameters, product distributions (H2, CO, CH4, tar, etc) are calculated by the model. The modeling results are found to agree the experimental data using a moving-bed pyrolyzer with processing capacity 10 kg h−1 of coal.
An analysis of the performance of a gas turbine–steam turbine combined cycle with supplementary firing has been carried out. Natural gas is fired in the main combustor of the cycle, whereas biomass fuel is considered as the supplementary fuel. Although, supplementary firing is found to reduce the overall cycle efficiency, the low cost of biomass and the CO2-neutral attribute of its combustion reduce the specific fuel cost and specific CO2 emission. The effects of pressure and temperature ratios of the topping cycle and main steam conditions of the bottoming cycle on the performance parameters of the combined cycle have been studied at different degrees of supplementary firing. The topping cycle temperature ratio is found to be the most critical parameter and its low value gives substantial advantages in lowering the fuel cost and CO2 emission. Marginal advantages are also achieved at higher pressure ratio and better bottoming cycle main steam conditions. Copyright © 2008 John Wiley & Sons, Ltd.
A scenario based entirely on renewable energy with possible use of hydrogen as an energy carrier is constructed for a group of North European countries. Temporal simulation of the demand–supply matching is carried out for various system configurations. The role of hydrogen technologies for energy storage and fuel cell applications is studied and applied to both stationary energy use and transportation sectors. As an alternative, biofuels may take the role of hydrogen both as a storable fuel and for direct use in the transportation sector. It is shown that there is scope for considerable amounts of energy trade between the countries, due to the different endowments of different countries with particular renewable energy sources, and to the particular benefit that intermittent energy sources, such as wind and solar, can derive from exchange of power. The establishment of a smoothly functioning renewable energy supply system is demonstrated with the use of the seasonal reservoir-based hydrocomponents in the northern parts of the region. The outcome of the competition between biofuels and hydrogen in the transportation sector is dependent on the development of viable fuel cells and on efficient technologies for converting biomass residues to fuels. Copyright © 2007 John Wiley & Sons, Ltd.
With the fast economic growth, the energy demand in China has increased two-fold in the past three decades. Various energy resources have been exploited and utilized and biomass is one of the energy resources that is abundant and has been widely used in China for a long time. Biomass gasification is an efficient and advanced technology for extracting the energy from biomass and has received increasing attention in the energy market. In this paper the development of biomass gasification for various energy applications in China is reviewed and their prospects are discussed. Among the different biomass gasification technologies, biomass gasification and power generation is found to be the most promising biomass gasification technology that has great potential to be further developed in China.
This paper examines the potential roles of Fischer–Tropsch (FT) synfuels in the 21st century with a global energy model treating the entire fuel supply chain in detail. The major conclusions are the following. First, FT synfuels become a major alternative fuel regardless of CO2 policy due to their low transportation costs and compatibility with existing petroleum infrastructure and vehicles. Secondly, the FT process brings stranded gas to world markets until around 2050. In a 550 ppm CO2 stabilization case thereafter, producing FT synfuels from biomass, whose competitiveness is robust against its capital costs, and their interregional trade enable a worldwide diffusion of carbon-neutral fuels. This provides a significant source of income for developing regions, such as Latin America and Sub-Saharan Africa. Thirdly, FT synfuels play a crucial role in meeting the growing transportation energy demand and assuring diversified supplies of transportation fuels. Increasing portions of FT liquids are refined to FT-kerosene to be provided for the rapidly growing aviation sector in the second half of the century. Furthermore, upgrading FT-naphtha into FT-gasoline proves to be critically important. FT synfuels’ participation could help the development in Africa through technological contributions of the South African leading companies in the world synfuel industry.
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 H2 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.
This article discusses a mathematical model for the thermochemical processes in a downdraft biomass gasifier. The model combines the chemical equilibrium and the thermodynamic equilibrium of the global reaction, predicting the final composition of the producer gas as well as its reaction temperature. Once the composition of the producer gas is obtained, a range of parameters can be derived, such as the cold gas efficiency of the gasifier, the amount of dissociated water in the process and the heating value and engine fuel quality of the gas. The model has been validated experimentally. This work includes a parametric study of the influence of the gasifying relative fuel/air ratio and the moisture content of the biomass on the characteristics of the process and the producer gas composition. The model helps to predict the behaviour of different biomass types and is a useful tool for optimizing the design and operation of downdraft biomass gasifiers.
A gasifier has been fabricated in Sri Lanka for the tea industry, but there is a lack of knowledge of the effect of certain key operating parameters and design features on its performance. Experimental testing of the design under various conditions has produced data that has then been used to calibrate a computer program, developed to investigate the impact of those parameters and features on conversion efficiency. The program consists of two sub-models of the pyrolysis and gasification zones, respectively. The pyrolysis sub-model has been used to determine the maximum temperature and the composition of the gas entering the gasification zone. The gasification zone sub-model has been calibrated using data gathered from the experiments. It was found that a wood chip size of 3– with a moisture content below 15% (d.b.) should be used in this gasifier. Feed material with a fixed carbon content of higher than 30% and heat losses of more than 15% should be avoided. For the above parameters, the gasification zone should be long to achieve an acceptable conversion efficiency.
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.
Four open core throatless batch fed rice husk gasifier reactors having internal diameters of 15.2, 20.3, 24.4 and 34.3 cm were designed and fabricated. Each reactor connected with gas cleaning unit was tested for its performance characteristics. On each reactor ten trial runs were conducted varying the air flow rate or specific gasification rate. Gas quality, gas production rate, gasification efficiency specific gasification rate, and equivalence ratio were determined for every run on each of the four reactors. It was found that for each reactor the gasifier performance was the best at a specific gasification rate of around 192.5 kg/h-m2. Under the best operating conditions, the equivalence ratio was 0.40 and the gasification efficiency was around 65%. These parameters may be used for designing rice husk operated throatless gasifiers in the capacity range of 3–15 kW.
In this work, a possible way for partial CO2 emissions reduction from gas turbine exhausts by co-firing with biomass is investigated. The basic principle is the recirculation of a fraction of the exhausts (still rich in oxygen) to a gasifier, in order to produce syngas to mix with natural gas fuel. As biomass is a CO2 neutral fuel, the fraction of replaced natural gas is a measure of CO2 removal potential of the powerplant.The investigated solution considers the conversion of solid fuel to a gaseous fuel into an atmospheric gasifier, which is blown with a recirculated fraction of hot gas turbine exhausts, typically still rich in air. In this way, the heat content of the exhausts may be exploited to partially sustain the gasification section.The produced syngas, after the tar removal into the high temperature cracker, is thus sent to the cooling section, consisting of three main components: (I) gas turbine recuperator, (II) heat recovery steam generator and (III) condensing heat exchanger to cool down the syngas close to the environmental temperature before the subsequent recompression and mixing with natural gas fuel into the combustion chamber. The water stream produced within the condensing heat exchanger upstream the syngas compression is vaporised and sent back to the gasifier.If very limited modification to the existing gas turbine has to be applied in order to keep the additional costs limited, only a relatively reduced fraction of the low calorific value syngas may be mixed with natural gas. The analysis at different levels of co-firing has shown that no appreciable redesign has to be applied to the target GE5 machine up to 25–30% (heat rate based) renewable fraction. With an accurate heat recovery from the cooling/cleaning system of the syngas, the same levels of efficiency of the original machine have been achieved, in spite of the relatively large power consumption of the syngas recompression. Very interesting results have been obtained within the 10–30% range of biomass co-firing, with CO2 removal levels between 30% and 50% with reference to the values of the base GE5 gas turbine powerplant.The economic analysis has shown that, in spite of the high investment required for the syngas fuel production chain (gasifier, coolers, cleaners and fuel compressor), approximately at the same level of gas turbine itself, there is an interesting attractiveness due to the possibility of selling high-value green certificates and CO2 allowances, which reduce the payback time to 2–4 years.The uncertainty on the calculated economic parameters are greatly influenced by the uncertainty on actual biomass availability and yearly working time of powerplant, whereas off design operation, which affects mainly the uncertainty of compressor and turbine efficiency, is mainly reflected on the uncertainty of electric power output and efficiency.
This paper presents an extended integral model using char oxidation under different ambient oxygen concentrations to predict the pyrolysis of wood. The char oxidation kinetics from TGA experiments is embedded in an integral model. Comparison with experimental data shows that the predictions of mass loss rates and temperature profiles within the charring material are in reasonably good agreement with the experiments. (c) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
In the current overview paper, various issues related to the combustion of agricultural residues are discussed. Attention has been given to the problems associated with the properties of the residues such as low bulk density, low ash melting points, high volatile matter contents and the presence of nitrogen, sulfur, chlorine and sometimes high moisture contents. Consequently the issues discussed include densification, the combustion mechanisms of agricultural residues, problems of low melting point of ash such as agglomeration and fouling, emissions and co-combustion. Further, design considerations of facilities for the combustion of agricultural residues are discussed.
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.
Energy conversion systems based on biomass utilisation are particularly interesting because of their contribution to the limitation of global CO2 emissions; within the possible methods for energy-based biomass utilisation, thermal gasification appears as the most mature technology. In the first design stage, the designer of these systems, or the user looking for performance predictions under different operating conditions, has advantages of running thermochemical simulations allowing a prediction of the syngas composition and calorific value. The equilibrium model described in this paper is very simple, but it considers chemical species typically encountered by biomass gasifiers, and was tested against published experimental data.
Handbook of Biomass Downdraft Gasifier Engine System. SERI: Golden, CO, 1988. MODELLING OF A DOWNDRAFT BIOMASS GASIFIER 851 Copyright r
- Reed Tb Das
Reed TB, Das A. Handbook of Biomass Downdraft Gasifier Engine System. SERI: Golden, CO, 1988. MODELLING OF A DOWNDRAFT BIOMASS GASIFIER 851 Copyright r 2009 John Wiley & Sons, Ltd. Int. J. Energy Res. 2009; 33:833–851 DOI: 10.1002/er
Handbook of Biomass Downdraft Gasifier Engine System. SERI: Golden, CO, 1988. MODELLING OF A DOWNDRAFT BIOMASS GASIFIER Copyright r
- T B Reed
- A Das
Reed TB, Das A. Handbook of Biomass Downdraft Gasifier
Engine System. SERI: Golden, CO, 1988.
MODELLING OF A DOWNDRAFT BIOMASS GASIFIER
Copyright r 2009 John Wiley & Sons, Ltd.
Int. J. Energy Res. (2009)
DOI: 10.1002/er
- Reed