Modeling Of Coal Gasification Research Articles

A coupled thermal-force-chemical-displacement multi-field model for underground coal gasification based on controlled retraction injection point technology and its thermal analysis

Underground coal gasification is an essential means of meeting the growing energy needs of some countries. In this paper, a new numerical simulation method of thermal-force-chemical-displacement multi-field coupling is developed, and in order to better adapt to the actual working conditions, taking Shanjiaoshu Coal Mine as the geological background, the first gasification working face of No. 12 coal seam is simulated based on the controlled retraction injection point technology. This method is used to simulate the heating of coal body by the ignition device at the initial stage of UCG, the chemical-thermal changes triggered by spontaneous combustion of the coal body under the continuous backward movement of the injection point, and the simulation of the formation of the cavity after the coal gasification reaction. Finally, the evolution of temperature and displacement fields in No.12 coal seam after gasification reaction is analyzed. Therefore, this study aims to simulate the actual working conditions more realistically, optimize the UCG technology, and produce more clean energy syngas to improve the energy situation in China.

Simulation of co-production system based on coal partial gasification under different reactant gas atmospheres

In order to explore the comparison of coal partial gasification hydrogen-electricity cogeneration systems under different gasification agent atmospheres, based coal partial gasification, including steam cycle power generation and syngas processing for hydrogen production, a hydrogen-electric co-production system and its model of partial coal gasification and semi-coke combustion are constructed, respectively using (H2O/O2) and (CO2/O2) as gasification reactant gas. The effects of oxygen-coal ratio and carbon conversion on exergy efficiency and syngas composition under different gasification reaction gas atmospheres were studied by Aspen Plus simulation. The exergy efficiency under different gasification agent atmospheres increases first and then decreases with the increase of oxygen-coal ratio and carbon conversion rate. Using (CO2/O2) as gasification agent has higher exergy efficiency. The composition of syngas changes little under different oxygen-coal ratios, while the overall content of H2, CO and CH4in syngas will increase with the increase of carbon conversion rate, but the growth rate will continue to decline.

Calculation of a Direct-Flow Anthracite Culm Gasification Process with Liquid Slag Removal

Abstract A program for calculating the gasification process based on a mathematical model of direct-flow coal gasification with liquid ash removal, in which a mixture of oxygen and water vapor is used as a blast, is considered. Calculations were carried out for anthracite culm from the Eastern Donbass coal basin as a raw material.

Artificial neural network model of catalytic coal gasification in fixed bed

Catalytic coal gasification is a cost-effective way to utilize coal to produce hydrogen or methane. Because of complex interactions among hydrodynamics and chemical reactions with catalyst, it was very difficult to predict hydrogen yield and carbon conversion. Therefore, three kinds of artificial neural network (ANN) models, including feed-forward back propagation neural network (FFBP), cascade-forward back propagation neural network with Levenberge Marquardt algorithms (CFBP), and cascade-forward back propagation neural network with genetic algorithm (CFBP-GA) were used to predict these processes. Three kinds of input parameters were used, such as coal ultimate analyses, coal proximate analyses and operation conditions. Gas yield and carbon conversion were taken as output parameters. R2 of all three established ANN models were above 0.9. The CFBP-GA showed good performance with E2 = 0.000241 and R2 = 0.9978 than the other two ANN models. And then, the model was used to predict the effects of temperature, catalyst type and catalyst loading on carbon conversion and hydrogen yield. The most important three factors for carbon conversion and hydrogen yield were catalyst type, catalyst loading and temperature based on relative importance analysis. The good performances were indicated the ANN model was an effective way to predict hydrogen production and carbon conversion of catalytic coal gasification in fixed bed quickly and accurately, and it could be also extended to other carbon resources to produce hydrogen.

Establishment and application of a two‐stage reaction equilibrium model for underground coal gasification

Establishment and application of a two‐stage reaction equilibrium model for underground coal gasification

A comprehensive simulation of catalytic coal gasification in a pressurized jetting fluidized bed

A steady-state multi-zone empirical model for catalytic coal gasification in a pressurized jetting fluidized bed was developed, which took account of pressurized hydrodynamics, mass and heat transfers and catalytic reaction kinetics. The effects of combustion product distribution coefficient and steam gasification product distribution coefficient on hydrodynamic parameters, particle temperature, gas temperature and compositions were conducted to find the suitable ones. The calculated bed temperature and gas compositions showed good agreement with experimental results. The hydrodynamics behaviors and gas compositions in different zones were analyzed in detail. The effects of control parameters on catalytic reactions were further conducted. Results showed that the most important factors for methanation were particle size, bed height and catalyst loading. The effects of particle size and steam flow rate on steam gasification reaction and water gas shift reaction were also obviously. The model would provide basically information to support design and scale-up of catalytic coal gasification.

Physics-Informed Neural Network for Unreacted-Core Shrinking Model of Coal Gasification

Physics-informed neural network (PINN) has achieved success in many science and engineering disciplines by encoding physical laws into the loss functions of the neural network. Compared with traditional numerical method, PINN transformed the problem of solving differential equations into the optimization of loss functions by automatic differentiation. In this work, PINN is apply to solve the coal gasification chemical kinetic problems of gas-solid reactions in the form of the unreacted-core shrinking model with governing ordinary differential equations (ODEs). The results show that the prediction performance of the developed PINN is comparable with that of the widely-used Runge-Kutta method, and thus it opens the possibility for the application of deep learning to the modelling of complex chemical kinetics systems.

CFD Simulation of Temperature Variation in Carboniferous Rock Strata During UCG

The numerical simulation was based on the computational fluid dynamics formalism in order to identify the change of temperature in rock strata during underground coal gasification (UCG). The calculations simulated the coal gasification process using oxygen and water vapour as a gasification agent in 120 hours. Based on the selected software (Ansys-Fluent) a model of underground coal gasification (UCG) process was developed. The flow of the gasification agent, the description of the turbulence model, the heat-exchange model and the method of simulation of chemical reactions of gasification are presented herein.

Critical Analysis of Underground Coal Gasification Models. Part II: Kinetic and Computational Fluid Dynamics Models

Purpose Underground coal gasification, as a complex and technically difficult process, in many aspects requires the support provided by computer simulations. There are a lot of mathematical models of UCG, some of them are concentrated with the forecast of syngas composition. The most important may be divided into three groups: equilibrium, kinetic and CFD models. The purpose of this work was the detailed critical analysis of more advanced approaches (than equilibrium considerations) applied in simulations of the coal conversion process – both kinetic and based on computational fluid dynamics. The other aim of this paper was the comparative analysis of the most important models of underground coal gasification. Methods Literary studies, concerned with the features and mathematical description of kinetic and CFD models of coal gasification, were used as the research method applied in the work presented. Compilation of the kinetic parameters of gasification reactions was an important part of this article. For that purpose the analysis of Polish and foreign papers, monographs and university handbooks was undertaken. Results Critical analysis of kinetic and CFD models of coal gasification (together with their mathematical formulation) was the result of considerations presented in this article. Kinetic equations were shown separately for pyrolysis, homogenous and heterogeneous reactions. In the case of CDF models, except for the presentation of the conservation equation, the most important methods of modeling turbulence are described (for the reason that this phenomenon may have significant influence on the final results). Practical implications The work presented describes practical issues connected with kinetic and CFD models, focusing on their capabilities, drawbacks and possible application problems. Originality/value This paper presents state of art in the field of coal gasification modeling using kinetic and computational fluid dynamics approach. The paper also presents own comparative analysis (concerned with mathematical formulation, input data and parameters, basic assumptions, obtained results etc.) of the most important models of underground coal gasification.

Critical Analysis of Underground Coal Gasification Models. Part I: Equilibrium Models – Literary Studies

Purpose Underground coal gasification is a very difficult process due to changes in the parameters over time and within the space of the reactor and a variety of phenomena that occurs there. Consequently, it is necessary to create appropriate mathematical models, which simplify the optimization and forecast of future results (especially final gas properties). The purpose of this work was the detailed critical analysis of the simplest coal gasification simulations methods, based on thermodynamic calculations of the process. These models, called equilibrium models, can be divided into two groups: stoichiometric and non-stoichiometric. The other aim of this paper was to characterize various engineering methods used in the calculation of equilibrium gasification processes. Methods Literary studies, concerned with general aspects of underground coal gasification modeling and the modeling of coal gasification in the manner of equilibrium calculations, were used as a research method applied in presented work. Results The critical analysis of equilibrium models of coal gasification and the characterization (including mathematical formulation of process, range of required parameters, rate of convergence of calculations and methodology of searching solutions) of stoichiometric and non-stoichiometric methods were results of numerous considerations presented in this article. Practical implications The work presented describes practical issues connected with equilibrium models – their advantages, limitations and possible problems (for example with the determination of required constants) and potential applications (preliminary analysis, point of reference to more complex simulations etc.). Originality/value This paper presents state of the art in field of equilibrium coal gasification modeling. This article is also attempt to elaborate on the most important problems connected with thermodynamic models of coal gasification.

Calculation of a Direct-Flow Coal Gasification Process with Liquid Slag Removal

A program for the calculation of a gasification process based on a mathematical model of direct-flow coal gasification with liquid slag removal is proposed. Calculations were performed for Chinese gas coals. A good agreement between the experimental and calculated data of the process is demonstrated.

Assessment of coal gasification in a pressurized fixed bed gasifier using an ASPEN plus and Euler\u2013Euler model

With the help of Aspen Plus, a two-dimensional unsteady CFD model is developed to simulate the coal gasification process in a fixed bed gasifier. A developed and validated two dimensional CFD model for coal gasification has been used to predict and assess the viability of the syngas generation from coal gasification employing the updraft fixed bed gasifier. The process rate model and the sub-model of gas generation are determined. The particle size variation and char burning during gasification are also taken into account. In order to verify the model and increase the understanding of gasification characteristics, a set of experiments and numerical comparisons have been carried out. The simulated results in the bed are used to predict the composition of syngas and the conversion of carbon. The model proposed in this paper is a promising tool for simulating the coal gasification process in a fixed bed gasifier.

Modeling and simulation of coal gasification on an entrained flow coal gasifier

In this paper, the recent researches and developments on coal gasification modeling and simulation are described. Numerical models for the three chemical processes such as devolatilization, char gasification, and gas-phase reaction are reviewed and discussed for further development to improve accuracy. Recently the devolatilization models to describe the coal chemical structure with a simple expression have been proposed and validated on the laboratory-scale flames. It is essential to precisely model char gasification reaction as a rate-determining step and the formulation of the active sites sharing by the mixture and the pore structure formation are important in the modeling. It will become significant to take the elementary reactions into account in the gas phase reaction model. Large-eddy simulation of coal gasification on the laboratory-scale entrained flow gasifier is performed to demonstrate the numerical procedure. Results show the predicted temperature distribution qualitatively agrees with the experiment. Moreover, the gas-liquid-solid three-phase reacting flow simulation is preliminarily performed to capture the molten slag flow behavior within the gasifier. It is revealed that the three-phase simulation can give insight into the complex multiphase and multiphysics phenomena taking place within the gasifier to assess the design and the operating condition.

Gasification of Coal Dust in a Cyclone Furnace in an O2/H2O Atmosphere

This paper presents the results of the modeling of coal dust gasification using oxygen and steam in a cyclone furnace. The combustion process leads to the release of gas composed mainly of CO and H2. The composition of this gas can be controlled through changes in the content of O2 and H2O in the gasifying agent. It is possible for the process conditions adopted in the study to obtain the CO content at the level of 50% with the content of the gasifying agent O2/H2O of 50/50. In the case of the composition of the gasifying agent O2/H2O of 80/20, the H2 content was 50%. The maximal calorific value of the gas was obtained for O2/H2O 50/50 (11.2 MJ/kg).

Thermal analysis of methanol production from low grade coal of Thar coalfield: an alternate route to utilise indigenous coal efficiently

In this paper, we developed an integrated model of coal gasification with methanol synthesis reactor using Aspen Plus®. Gasification process and methanol synthesis are modelled and simulated based on low grade coal of Thar coalfield. After validation of the simulation results with experimental data, the thermodynamic analysis of integrated process is carried out to predict the optimal methanol yield. Moreover, the influence of reactor operating temperature and pressure, CO2/H2 ratio and amount of catalyst, on the methanol synthesis is investigated. The results indicated that for coal input feed of 60 kg/s, the syngas flow rate of 9.4 kg/s was obtained in the gasification section. Whereas, the optimal methanol yield of 23.8% and 28.2% are obtained for Vanden Bussche (VB) and Graaf model, respectively in methanol synthesis reactor. Furthermore, the optimal operating temperature in methanol reactor was 210°C and 240°C for Graaf model and VB model, respectively.

Thermal analysis of methanol production from low grade coal of Thar coalfield: an alternate route to utilise indigenous coal efficiently

In this paper, we developed an integrated model of coal gasification with methanol synthesis reactor using Aspen Plus®. Gasification process and methanol synthesis are modelled and simulated based on low grade coal of Thar coalfield. After validation of the simulation results with experimental data, the thermodynamic analysis of integrated process is carried out to predict the optimal methanol yield. Moreover, the influence of reactor operating temperature and pressure, CO2/H2 ratio and amount of catalyst, on the methanol synthesis is investigated. The results indicated that for coal input feed of 60 kg/s, the syngas flow rate of 9.4 kg/s was obtained in the gasification section. Whereas, the optimal methanol yield of 23.8% and 28.2% are obtained for Vanden Bussche (VB) and Graaf model, respectively in methanol synthesis reactor. Furthermore, the optimal operating temperature in methanol reactor was 210°C and 240°C for Graaf model and VB model, respectively.

A 0-dimensional cavity growth submodel for use in reactor models of underground coal gasification

Modelling of the underground coal gasification process is dependent upon a range of sub-models. One of the most important is the calculation of the cavity growth rate as a function of various operating conditions and coal properties. While detailed 1-dimensional models of coal block gasification are available, it is not easy to couple them directly with reactor models, which aim to simulate the complete process. In this paper, a 0-dimensional cavity growth sub-model is presented. The model is based on the concept of a surface reaction and incorporates physics to account for moisture evaporation, water influx, coal pyrolysis, coal thermo-mechanical fragmentation and the build up of an ash layer on the char. The model is validated using measurements from laboratory experiments on coal cores and coal blocks. A comparison of calculated results from several UCG field trials shows that the model can provide good estimates of cavity growth rate for reasonable input parameters. Finally, simulation results of cavity growth in the combustion and gasification zones as a function of the bulk gas temperature, gas pressure, water influx rate, ash layer thickness and coal fragmentation behaviour are presented.

Contribution to creating a mathematical model of underground coal gasification process

Underground coal gasification, as an auto thermal process, includes processes of degasification, pyrolysis, and the gasification itself. These processes occur as a result of a high temperature and the management of coal combustion during addition of gasification agent. Air, water vapor mixed with air, air or water vapor enriched with oxygen, or pure oxygen, may be used as gasification agents. Resulting gas that is extracted in this process may vary in chemical composition, so it is necessary to adjust it. That is the reason why it is necessary to develop a mathematical model of the underground gasification process prior to any operations in coal deposit, in order to obtain as much accurate prediction of the process as possible. Numerical calculation provides prediction of gas mixture?s chemical composition, which enables calculation of gas components? energy contents and total energy content of the gas in predicted underground coal gasification process. It is one of the main criteria in the economic assessment of underground coal gasification process. This paper, based on available data on researches in this area, provides a contribution to creation of mathematical model of underground coal gasification.

A coupled thermal-mechanical numerical model of underground coal gasification (UCG) including spontaneous coal combustion and its effects

Underground coal gasification (UCG) is a promising option for extracting energy from coal in unworked or hard to access areas of the subsurface. From a geotechnical perspective, UCG involves various complex phenomena resulting from the elevated temperatures induced within the rock surrounding the UCG burn. This paper presents a coupled thermal-mechanical numerical model developed to represent a UCG trial in Wieczorek, Poland. Temperature dependent mechanical properties were assigned according to results obtained from laboratory experiments and data available in the literature. The coal burning process was simulated by modifying the energy balance equation with an additional term related to the calorific value of coal as a source. This source term was described using a time decay function to reflect the fact that the energy release from coal gradually decreases with time. The mechanical degradation of coal due to burning was simulated by removing the burned zone from the calculation after a specific time, which depended on zone size and type of coal. In this study, it was found that the maximum temperature at the burning zone was always <1000 °C, which agrees with previous research carried out for other UCG trials. The size of the burning zone was predicted to spread about 15 m laterally after 20 days of burning. Ground subsidence was evaluated for single and multiple (parallel) panel simulations; subsidence at the top of the numerical mesh, corresponding to a depth of 395 m below the surface, ranged from 23 mm for a single panel to 85 mm for seven panels. The degradation of mechanical properties of the rock surrounding the burned zone due to heating was found to have a marginal effect on the ground subsidence when parallel burning was carried out. The numerical modelling results obtained from this study may provide guidance for the design and operation of UCG processes.

A process model for underground coal gasification – Part-III: Parametric studies and UCG process performance

Underground gas gasification (UCG) is a clean coal technology which involves in-situ gasification of deep-seated underground coal. The process can be divided in two phases based on state of coal seam and direction of cavity growth. In phase-I, cavity grows mainly in vertical direction while in phase-II it grows in horizontal direction. The in-house simulator developed for both the phases of UCG has been reported earlier Samdani et al. (2016a,b). It incorporates reaction kinetics, flow patterns, spalling, heat and mass transfer effects. In this work, we take further insight and perform parametric studies to examine the effects of different operating conditions, coal properties and design parameters on key performance indicators i.e. exit gas quality, energy generation rates etc. The investigation revealed that the exit gas quality and rate of coal consumption are strong functions of spalling rates and kinetics of reactions; the coal having very low spalling tendency or less reactivity may not be favorable for the UCG process. An important parameter called critical spalling rate has emerged through this analysis. It is the property of given coal above which UCG is sustainable. In addition, model performance is also sensitive to inlet gas temperature, pressure and composition. Optimum performance of UCG is obtained at a steam to oxygen ratio of 2.5 and at the highest possible inlet gas temperature, operating pressure, and oxygen content in the feed. Among the design parameters, the length of outflow channel is very important as it strongly affects both the exit gas calorific value and its fluctuations with time. The predicted effects of different parameters are in accord with the observations during lab-scale UCG experiments and different field trials. This study demonstrates the importance of a process model to determine the best conditions for UCG process and to evaluate feasibility of the process for a coal seam under consideration.