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Ahmadābād, India

Mandapati R.N.,Indian Institute of Technology Bombay | Sateesh D.,Indian Institute of Technology Bombay | Narseh D.,Indian Institute of Technology Bombay | Mahajani S.M.,Indian Institute of Technology Bombay | And 3 more authors.
27th Annual International Pittsburgh Coal Conference 2010, PCC 2010 | Year: 2010

In the present work, we study gasification of char obtained by pyrolysis of Indian Lignite coal, in a fixed bed reactor. Because of its operational flexibility, the fixed bed reactor (FBR) can be conveniently used to carry out endothermic reactions under controlled conditions. The present work is focused on how various operating parameters such as temperature, flow rate, particle size and pressure affect the extent of the steam and CO2 gasification reactions. A broad objective of this work is to develop a kinetic model, identify mass and heat transfer limitations, if any, based on this data and further support the results obtained by carrying out independent thermogravimetric analysis. Source


Mandapati R.N.,Indian Institute of Technology Bombay | Daggupati S.,Indian Institute of Technology Bombay | Mahajani S.M.,Indian Institute of Technology Bombay | Aghalayam P.,Indian Institute of Technology Madras | And 3 more authors.
Industrial and Engineering Chemistry Research | Year: 2012

Gasification of four Indian coals is carried out in a CO2 atmosphere, using a thermogravimetric analyzer (TGA) to determine the intrinsic kinetics over a temperature range of 800-1050 °C with different partial pressures of CO2. The applicability of three models, viz., the volumetric reaction model, the shrinking core model and the random pore model, is evaluated. Of these three models, the random pore model is found to be the most suitable for all the coals considered in the current study. The dependence of the reaction rate on the gas-phase partial pressures is explained by the Langmuir-Hinshelwood model, and the parameters for the inhibition due to CO and CO2 are determined by performing experiments at different partial pressures. In underground coal gasification, the reaction takes place on reasonably large sized coal particles, wherein diffusion effects are significant. A one-dimensional reaction diffusion model is therefore developed in order to determine the diffusional resistance in the coal particle, and values of diffusivity are estimated. © 2012 American Chemical Society. Source


Daggupati S.,Indian Institute of Technology Bombay | Mandapati R.N.,Indian Institute of Technology Bombay | Mahajani S.M.,Indian Institute of Technology Bombay | Ganesh A.,Indian Institute of Technology Bombay | And 3 more authors.
Industrial and Engineering Chemistry Research | Year: 2011

During underground coal gasification (UCG), a cavity is formed in the coal seam when coal is converted to gaseous products. This cavity grows three dimensionally in a nonlinear fashion as gasification proceeds. The cavity shape is determined by the flow field, which is a strong function of various parameters such as the position and orientation of the inlet nozzle and the temperature distribution and coal properties such as thermal conductivity. In addition to the complex flow patterns in the UCG cavity, several phenomena occur simultaneously. They include chemical reactions (both homogeneous and heterogeneous), water influx, thermomechanical failure of the coal, heat and mass transfer, and so on. Thus, enormous computational efforts are required to simulate the performance of UCG through a mathematical model. It is therefore necessary to simplify the modeling approach for relatively quick but reliable predictions for application in process design and optimization. The primary objective of this work is to understand the velocity distribution and quantify the nonideal flow patterns in a UCG cavity by performing residence time distribution (RTD) studies using computational fluid dynamics (CFD). The methodology of obtaining RTD by CFD is validated by means of of representative laboratory-scale tracer experiments. Based on the RTD studies, the actual UCG cavity at different times is modeled as a simplified network of ideal reactors, called compartments. The compartment model thus obtained could offer a computationally less expensive and easier option for determining UCG process performance at any given time, when used in a reactor-scale model including reactions. The network of ideal reactors can be easily simulated using a flowsheet simulator (e.g., Aspen Plus). We illustrate the proposed modeling approach by presenting selected simulation results for a single gas-phase second-order water-gas shift reaction. © 2010 American Chemical Society. Source


Daggupati S.,Indian Institute of Technology Bombay | Mandapati R.N.,Indian Institute of Technology Bombay | Mahajani S.,Indian Institute of Technology Bombay | Ganesh A.,Indian Institute of Technology Bombay | And 3 more authors.
27th Annual International Pittsburgh Coal Conference 2010, PCC 2010 | Year: 2010

Underground coal gasification (UCG) is a technique which permits access to coal which either lies too deep underground, or is otherwise too costly to exploit using conventional mining techniques. At the same time, it eliminates many of the health, safety and environmental problems of deep mining of coal. An irregular shape cavity is formed in the coal seam when coal is converted to gaseous products and its volume increases progressively as the coal is consumed. The complexity involved in modeling UCG process thus compels one to adopt a rigorous modeling approach that calls for use of computational fluid dynamics (CFD), which solves all balance equations simultaneously on a high speed computer. The simulation tool developed in the present work is capable of simultaneously predicting temperature distribution in the coal seam and profiles of velocity, temperature and species inside the cavity of a given size and shape. Further, with the help of this simulator we study the effect of various inlet conditions such as steam to oxygen ratio, feed temperature etc., on the product gas compositions. Ultimately, this work would help one to obtain the optimum conditions to produce product gas of high calorific value for a given cavity along with the specified inlet and boundary conditions. A broader objective of this simulation work is to track the growth of cavity and the associated changes in the UCG performance. Source


Daggupati S.,Indian Institute of Technology Bombay | Mandapati R.N.,Indian Institute of Technology Bombay | Mahajani S.,Indian Institute of Technology Bombay | Ganesh A.,Indian Institute of Technology Bombay | And 3 more authors.
27th Annual International Pittsburgh Coal Conference 2010, PCC 2010 | Year: 2010

The UCG product gas can be used for electricity generation, or as a chemical feed stock, and gas turbine power generation combined with UCG is one of the promising ways of accomplishing clean coal utilization. In the UCG process, a cavity consisting of ash, char rubble and void space is formed and its size increases three dimensionally in a non-linear fashion. Operational control of the UCG process is difficult because of the several phenomena that are occurring simultaneously such as the detachment of coal from the cavity roof (i.e. spalling), water intrusion, chemical reactions, heat and mass transfer, and so on. These phenomena also lead to a complex flow distribution in the cavity. The characterization and quantification of this non-ideal flow field is necessary as it influences the performance of the UCG process. It is affected by several parameters such as the temperature gradients, inlet nozzle position and orientation, and coal properties such as thermal conductivity. The primary objective of this work is to study the effect of temperature gradients and various thermal boundary conditions on the reactant gas flow patterns in an underground cavity, through mathematical simulations. CFD simulations are performed for each case in order to get the flow pattern and residence time distribution curves. The effects of various thermal boundary conditions in the underground coal gasification cavities are quantified by performing the compartment modeling simulations independently. The results presented here may provide good insight of the UCG cavity under different scenarios of the UCG process. Source

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