UCG Group

Ahmadābād, India

UCG Group

Ahmadābād, India
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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.


Bhaskaran S.,Indian Institute of Technology Bombay | Samdani G.,Indian Institute of Technology Bombay | Aghalayam P.,Indian Institute of Technology Madras | Ganesh A.,Indian Institute of Technology Bombay | And 4 more authors.
Fuel | Year: 2015

Underground Coal Gasification (UCG) is considered to be a clean coal technology primarily intended to utilize deep underground (>300 m) coal deposits. In this process, a mixture of reactant gases like air/oxygen and steam are injected directly to an ignited portion of underground coal seam. UCG involves complex interactions of different processes like drying, pyrolysis, chemical reactions and spalling. Spalling is detachment of small coal particles from the coal seam due to interconnection of cracks developed in it. It plays an important role by offering higher surface area to give improved performance. The mechanism of spalling and its characterization are not well understood. Furthermore, there are no well established experimental techniques to measure the spalling rates. This paper studies spalling behavior of a lignite coal, which is characterized by high moisture and volatile matter, and suggests a possible underlying mechanism. The rate of spalling was measured using an experimental setup under the UCG-like conditions. In this setup, a reacting coal block was attached to a load cell and suspended in a UCG-like environment. When the experiments were repeated under similar conditions with different blocks of same coal, it was found that there were variations in the rates of spalling. This might be due to the heterogeneity in coal blocks in the form of originally present fissures or weak regions. A UCG process model was used to explain these experimental results and also to investigate the effect of spalling rate on product gas calorific value. We believe that spalling happens due to formation and extension of cracks. Hence a microscopic crack pattern on a heated coal monolith was examined in different stages of heating to understand the mechanism of spalling. It is concluded that cracks are first formed during the initial stage of drying due to the capillary stresses developed due to removal of moisture from the pores and were further extended due to shrinkage of coal during pyrolysis. The detachment of coal particles happens due to horizontal linking of vertical cracks, which might result out of either horizontal cracks, if any, or available fissures and weak regions or relatively weak interlayer bonding at the bedding planes. © 2015 Elsevier Ltd. All rights reserved.


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: 2012

Characterization of reactant gas flow patterns in the underground coal gasification (UCG) cavity is important, because the flow is highly nonideal and likely to influence the quality of the product gas. In our earlier work [Daggupati et al., Energy2010, 35, 2374-2386], we have demonstrated a computational fluid dynamics (CFD)-based modeling approach to analyze the flow patterns in the cavity. A compartment model (network of ideal reactors) for the UCG cavity was developed based on the CFD simulation results. These studies were performed assuming that the UCG cavity is isothermal. In reality, large temperature gradients may prevail under certain conditions and, in turn, may influence the flow patterns. In this work, we consider different possible nonisothermal scenarios in the UCG cavity and propose a simplified compartment modeling strategy to reduce the computational burden. We also examine the effect of various operating and design parameters such as coal spalling, feed flow rate, feed temperature, and orientation of the inlet nozzle. All these effects are quantified by determining the corresponding compartment model parameters. The sensitivity of the compartment model parameters, with respect to the changes in various conditions, is studied. Furthermore, we validate the compartment modeling approach by comparing predicted conversions for a water-gas shift reaction with that of reaction-enabled CFD simulations under nonisothermal conditions. The results presented here provide adequate insight into the UCG process and can be conveniently used in the development of a computationally inexpensive phenomenological process model for the complex UCG process. © 2011 American Chemical Society.


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.
Energy | Year: 2011

Systematic laboratory scale experiments on coal blocks can provide significant insight into the underground coal gasification (UCG) process. Our earlier work has demonstrated the various features of the early UCG cavity shape and rate of growth through lab-scale experiments on coal combustion, wherein the feed gas is oxygen. In this paper, we study the feasibility of in situ gasification of coal in a similar laboratory scale reactor set-up, under conditions relevant for field practice of UCG, using an oxygen-steam mixture as the feed gas. By performing the gasification reaction in a cyclic manner, we have been able to obtain a product gas with hydrogen concentrations as high as 39% and a calorific value of 178. kJ/mol. The effect of various operating parameters such as feed temperature, feed steam to oxygen ratio, initial combustion time and so on, on the product gas composition is studied and the optimum operating conditions in order to achieve desired conversion to syngas, are determined. We also study the effect of various design and operating parameters on the evolution of the gasification cavity. Empirical correlations are proposed for the change in cavity volume and its dimensions in various directions. The results of the previous study on the combustion cavity evolution are compared with this gasification study. © 2011 Elsevier Ltd.


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.


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.


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 the potential in-situ method of converting un-mined coal into combustible syngas which can be served as a fuel for power generation, industrial heating or as chemical feedstock. UCG process provides a source of clean energy with minimal greenhouse gas emissions, when it is compared with the conventional coal mining and gasification. As gasification proceeds underground cavity is formed as the coal burns, and its shape and size changes with time as the coal is consumed. The shape and rate of growth of this cavity will strongly depend on the temperature profile inside the cavity. As underground coal gasification cavities are of irregular three-dimensional shapes, computational fluid dynamics studies (CFD) are essential in order to understand the temperature distribution inside the UCG cavities. A complete knowledge of the transport phenomena inside the UCG cavity is important for both cavity growth modeling and process modeling as it determines the quality and rate of production of the product gas. In the present study, CFD simulations are performed to study the convective heat transfer characteristics of UCG cavities at specified boundary conditions. By changing the feed flow rate, surface heat transfer coefficients are obtained over a wide range of Reynolds number for four different cavity sizes. The methodology of determining heat transfer coefficient through FLUENT is validated by performing simulations for a circular pipe over a wide range of Reynolds number. The predicted heat transfer coefficients are consistent with the correlations.


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.


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.


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.
Energy | Year: 2010

Cavity formation is an important phenomenon in the underground coal gasification (UCG) process. In the early stages of cavity formation, only the combustion reaction is performed in order to stabilize the temperature field. In the present work, we study the formation of the combustion cavity and the effect of various design and operating parameters such as the distance between the wells, feed flow rate and operation time, on its evolution. This paper presents details of laboratory-scale experiments that demonstrate the shape and size of the combustion cavity, and their dependence on various parameters. Empirical correlations for the cavity volume and dimensions in various directions are developed, which indicate the strong effects of mass transport. Results from computational fluid dynamics (CFD), which map the velocity profiles in the cavity, support the experimental observations. © 2010 Elsevier Ltd. All rights reserved.

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