908 research outputs found

    An overview of advances in biomass gasification

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    Biomass gasification is a widely used thermochemical process for obtaining products with more value and potential applications than the raw material itself. Cutting-edge, innovative and economical gasification techniques with high efficiencies are a prerequisite for the development of this technology. This paper delivers an assessment on the fundamentals such as feedstock types, the impact of different operating parameters, tar formation and cracking, and modelling approaches for biomass gasification. Furthermore, the authors comparatively discuss various conventional mechanisms for gasification as well as recent advances in biomass gasification. Unique gasifiers along with multi-generation strategies are discussed as a means to promote this technology into alternative applications, which require higher flexibility and greater efficiency. A strategy to improve the feasibility and sustainability of biomass gasification is via technological advancement and the minimization of socio-environmental effects. This paper sheds light on diverse areas of biomass gasification as a potentially sustainable and environmentally friendly technology

    Biomass gasification for syngas and biochar co-production: Energy application and economic evaluation

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    Syngas and biochar are two main products from biomass gasification. To facilitate the optimization of the energy efficiency and economic viability of gasification systems, a comprehensive fixed-bed gasification model has been developed to predict the product rate and quality of both biochar and syngas. A coupled transient representative particle and fix-bed model was developed to describe the entire fixed-bed in the flow direction of primary air. A three-region approach has been incorporated into the model, which divided the reactor into three regions in terms of different fluid velocity profiles, i.e. natural convection region, mixed convection region, and forced convection region, respectively. The model could provide accurate predictions against experimental data with a deviation generally smaller than 10%. The model is applicable for efficient analysis of fixed-bed biomass gasification under variable operating conditions, such as equivalence ratio, moisture content of feedstock, and air inlet location. The optimal equivalence ratio was found to be 0.25 for maximizing the economic benefits of the gasification process

    Experimental and numerical investigation on tar production and recycling in fixed bed biomass gasifiers

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    Bioenergy has been utilized for domestic purposes since pre-recorded history and it catches the highlight in the recent decades because it naturally benefits the world climate and energy security. Gasification is one of the key technologies to efficiently and economically convert biomass into syngas and further into biofuels. Despite these outstanding advantages, biomass gasification suffers from the formation of unfavorable byproduct tar and the consequential tar elimination. Moreover, the collected tar is toxic and thus requires storage and strict deposit method to avoid environmental pollution. To understand the mechanisms of biomass gasification and tar production, simulations with Aspen Plus were conducted for both downdraft and updraft gasifiers, which are presented in the Paper I and II, respectively. The kinetic models are implanted with reaction kinetics to ensure their ability to approximate the tar production, which are superior to the widely used Gibbs Energy Minimization model for predicting syngas compositions. Paper III focuses on the investigation of the impact of tar recycling on syngas compositions under various operating conditions including different reactor scales (4\u27\u27, 8\u27\u27, 12\u27\u27), different biomass feedstocks (pellets, picks, and flakes) and different equivalence ratios (0.15, 0.20, 0.25). --Abstract, page iv

    Thermodynamic evaluation of the gasification of municipal solid waste

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    The dependency on energy use is unavoidable in modern civilization. The burning of fossil fuels for energy use is regarded as one of the human activities that has a harmful environmental impact. Waste to energy is slowly becoming an evident argument that energy can be obtained from waste at a level that is enough to meet energy demands. Waste is viewed as a renewable source of energy and can lower emissions from the greenhouse gas (GHG) and mitigate climate change. The exploitation of municipal solid waste (MSW) can be implemented using various routes, either through thermal or biological conversion. The thermal conversion can be achieved through combustion, gasification, or pyrolysis. This study aimed to evaluate the gasification of municipal solid waste. The investigation focused on the effects the selected operating parameters have on the syngas composition, H2/CO ratio, and calorific value. The selection of the modelling approach focused on the problem statement. It was necessary to use a model that did not have a lot of limitations or relied on the geometry of the gasifier. A mathematical model that could analyse the selected operating parameters of the gasification process was utilized. A step-by-step procedure of the thermodynamic equilibrium model was implemented using MATLAB. The model was validated by comparing the predicted results of this study and empirical data in published literature. The results showed that operating parameters affected the amount of syngas quality, calorific value, and H2/CO ratio. The amount of carbon monoxide and nitrogen reduced with an increase in moisture content, and the amount of carbon dioxide increased with increased moisture content. A small amount of methane was recorded, with increased moisture content. Enhanced temperature brought about increased hydrogen while the amount of nitrogen remained constant. With high temperature, carbon dioxide composition reduced, and just over 1% of methane was recorded. The increased (ER) from 0.2 to 0.6 showed that ER has a notable impact on nitrogen. A sharp increase in nitrogen was noted when the ER increased while the amount of hydrogen and carbon monoxide decreased. Results showed acceptable agreement between the modelled data from this investigation and the experimental values reported in the literature. The overall conclusion is that the thermodynamic model gives accurate prediction results of the gasification process. Additionally, when the investigated operating parameters were adjusted, syngas composition, H2/CO ratio and calorific value were all affected (they either increased or reduced). Furthermore, it is concluded that the ER ratio is the most influential parameter in the gasification process

    Mathematical modelling of a small biomass gasifier for synthesis gas production

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    The depletion of fossil fuels coupled with the growing demands of the world energy has ignited the interest for renewable energies including biomass for energy production. A reliable affordable and clean energy supply is of major importance to the environment and economy of the society. In this context, modern use of biomass is considered a promising clean energy alternative for the reduction of greenhouse gas emissions and energy dependency. The use of biomass as a renewable energy source for industrial application has increased over the last decade and is now considered as one of the most promising renewable sources. The direct combustion of biomass in small scales often results in incomplete and inconsistent burning process which could produce carbon monoxide, particulates and other pollutants. Therefore, biomass is required to be transformed into more easily handled fuel such as gases, liquids and charcoal using technologies such as pyrolysis, gasification, fermentation, digestion etc. Biomass gasification upon which this thesis focuses is one of the promising routes amongst the renewable energy options for future deployment. Gasification is a process of conversion of solid biomass into combustible gas, known as producer gas by partial oxidation. This research work is carried out to investigate various methods employed for modelling biomass gasifiers, it also studies the chemistry of gasification and reviews various gasification models. In this work, a mathematical model is developed to simulate the behaviour of downdraft gasifiers operating under steady state and determine the synthesis gas composition. The model distinctly analyses the processes in each of the three zones of the gasifier; pyrolysis, oxidation and reduction zones. Air is used as the gasifying agent and is introduced into the pyrolysis and oxidation zones of the gasifier for both single and double air operations. These zones have been modelled based on thermodynamic equilibrium and kinetic modelling; the model equations are solved in MATLAB. Given the biomass properties, consumption, air input, moisture content and gasifier specifications, the MATLAB model is able to accurately predict the temperature and distribution of the molar concentrations of the synthesis gas constituents. The downdraft gasifier is also represented in Aspen HYSYS based on the same models to study the effect of both single and double air gasification operation. For known biomass properties, consumption, air input, moisture content and gasifier operating conditions, the Aspen HYSYS model can accurately predict the distributions of the molar concentrations of the syngas constituents (CO, CO2, H2, CH4, and N2). The models were validated by comparing obtained theoretical results with experimental data published in the open literature. Parametric studies were carried out to study the effects of equivalence ratio, moisture content, temperature on the gas compositions and its energy content. The proposed equilibrium model displayed a variable ability for the prediction of various product yields with this being a function of the feedstock studied. It also demonstrated the ability to predict product gases from various biomasses using both single and double stage air input. In the case of gasification with double air stage supply, higher amounts of methane are obtained with specific tendencies of the gases reaching a peak at certain conditions. The kinetic model was partially successful in predicting results and comparable with experimentally published results for a range of conditions. There were discrepancies particularly with CH4 formation and the operating temperatures predictions which were usually consistently lower than those actually measured experimentally. The use of the PFR, however, did show a greater potential for the use in further modelling

    Performance modelling and validation of biomass gasifiers for trigeneration plants

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    Esta tesis desarrolla un modelo sencillo pero riguroso de plantas de trigeneración con gasificación de biomasa para su simulación, diseño y evaluación preliminar. Incluye una revisión y estudio de diferentes modelos propuestos para el proceso de gasificación de biomasa.Desarrolla un modelo modificado de equilibrio termodinámico para su aplicación a procesos reales que no alcanzan el equilibrio así comodos modelos de redes neuronales basados en datos experimentales publicados: uno para gasificadores BFB y otro para gasificadores CFB. Ambos modelos, ofrecen la oportunidad de evaluar la influencia de las variaciones de la biomasa y las condiciones de operación en la calidad del gas producido. Estos modelos se integran en el modelo de la planta de trigeneración con gasificación de biomasa de pequeña-mediana escala y se proponen tres configuraciones para la generación de electricidad, frío y calor. Estas configuraciones se aplican a la planta de poligeneración ST-2 prevista en Cerdanyola del Vallés.This thesis develops a simple but rigorous model for simulation, design and preliminary evaluation of trigeneration plants based on biomass gasification. It includes a review and study of various models proposed for the biomass gasification process and different plant configurations. A modified thermodynamic equilibrium model is developed for application to real processes that do not reach equilibrium. In addition, two artificial neural network models, based on experimental published data, are also developed: one for BFB gasifiers and one for CFB gasifiers. Both models offer the opportunity to evaluate the influence of variations of biomass and operating conditions on the quality of gas produced. The different models are integrated into the global model of a small-medium scale biomass gasification trigeneration plant proposing three different configurations for the generation of electricity, heat and cold. These configurations are applied to a case study of the ST-2 polygeneration plant foreseen inCerdanyola del Valles

    Mathematical Modeling and Simulation of a One-Dimensional Transient Entrained-flow GEE/Texaco Coal Gasifier

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    Numerous gasifier models of varying complexity have been developed to study the various aspects of gasifier performance. These range from simple one-dimensional (1D) models to rigorous higher order 3D models based on computational fluid dynamics (CFD). Even though high-fidelity CFD models can accurately predict many key aspects of gasifier performance, they are computationally expensive and typically take hours to days to execute even on high-performance computers. Therefore, faster 1D partial differential equation (PDE)-based models are required for use in dynamic simulation studies, control system analysis, and training applications.;In the current study, a 1D transient model of a single-stage downward-firing entrained flow General Electric Energy (GEE)/Texaco-type gasifier has been developed. The model comprises mass, momentum and energy balances for the gas and solid phases. A detailed energy balance across the wall of the gasifier has been incorporated in the model to calculate the wall temperature profile along the gasifier length. This balance considers a detailed radiative transfer model with variable view factors between the various surfaces of the gasifier and with the solid particles. The model considers the initial gasification processes of water evaporation and coal devolatilization. In addition, the key heterogeneous and homogeneous chemical reactions have been modeled. The resulting time-dependent PDE model is solved using the method of lines in Aspen Custom ModelerRTM, whereby the PDEs are discretized in the spatial domain and the resulting differential algebraic equations (DAEs) are then integrated over time using a variable step integrator.;Results from the steady-state model and parametric studies have been presented. These results include the gas, solid, and wall temperature profiles, concentrations profiles of the solid and gas species, effects of the oxygen-to-coal ratio and water-to-coal ratio on temperature, conversion, cold gas efficiency, and species compositions. In addition, the dynamic response of the gasifier to the disturbances commonly encountered in real-life is presented. These disturbances include ramp and step changes in input variables such as coal flow rate, oxygen-to-coal ratio, and water-to-coal ratio among others. The results from the steady-state and dynamic models compare very well with the data from pilot plants, operating plants, and previous studies

    Modeling Of USS Gasification To Evaluate New Gasifier Design In Aspen Plus

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    Evaluation of ultra-superheated-steam (USS) gasification efficiency of coals to produce hydrogen enriched syngas is the research motive of this joint project between the University of North Dakota and Ohio University. A new USS bubbling fuidized bed gasifier was built in Ohio and several tasks were assigned to assess the gasifier\u27s performance and the feasibility of producing tar-free and hydrogen-rich producer gas. This thesis presents a thermo-equilibrium model of USS gasification. The model calculates the syngas composition and heating value for the base case fuel Clarion 4A coal using input data from experiments completed at Ohio. The RGIBBS reactor module in ASPEN PLUS, which performs calculation using the Gibbs free energy minimization concept is used to simulate the gasification process. The model compositions were then compared with the experimental syngas composition. The simulation was performed with four other coals and the output for all coals is compared on both wet and dry basis. A sensitivity analysis estimated the effect of temperature and steam flow rate variation on syngas composition and heating value on a wet and dry basis. The model estimates the syngas composition of mainly 39% H2, 19% CO, 13% CO2, and 28% H2O and a heating value of 4300 Btu/lb (254 Btu/scf). The composition comparison among all coals provided a favorable syngas composition trend for the low-moisture Clarion 4A and Pittsburgh #8 coals, but gave almost the same H2 composition when gas compositions were compared on a dry basis. This implies that drying of high moisture coal before gasification would imporve gas composition. Temperature variation for all coals gives the same trend for gas composition and heating value. The data on temperature variation suggests that gasification at 1320degF gives the maximum H2 composition in the syngas and a gasification temperature of 1410degF produces the highest heating value syngas for this gasifier. The steam flow reate was varied and the effect of H2O/C on syngas composition and heating value was evaluated and compared with experimental data. H2 concentration decreased with an increasing H2O/C range of 0.85 to 3.5 compared on a dry basis. Comparisons of model results to experimental data indicate a higher CO and lower H2 composition for the experimental data as compared to the model. This indicates the water-gas shift reaction may not be in equilibrium. Since this is a fast reaction it indicates there may be transport/diffusino limitations in the experimental gasifier. This work tested two hypotheses. The first hypothesis, that a zero-order thermo-equilibrium model accurately predicts the performance of experimental set-up USS gasifier at Ohio with syngas composition and heating value calculation was not valid. A three-dimensional model that includes both kinetics and transport phenomena is required. The model sensitivity analysis determined the maximum gasification temperature and H2O to carbon ratio for maximum hydrogen concentration in syngas. This proves the hypothesis that the model provides useful information for the improvement of the experiment
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