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•Underground coal gasification (UCG) is a process which converts

coal to syn gas at the underground coal seam itself. This process

involves injection of reactive gases to the coal seam and bringing

the product gases to the surface through a production well.

•UCG can help meet the rising energy demand by utilizing coal

resources that otherwise would be too deep, or of poor quality, or

simply not economical to mine. As UCG takes place, a cavity is

formed underground in the coal seam which grows three-

dimensionally.

• The growth of the cavity is affected by various factors such as

flow field in the cavity, spalling of char/coal, temperature

distribution in the cavity, etc. Because of complexity of the

process, a simplified process model is needed to predict the

performance of the UCG. This work presents one such model.

INTRODUCTION

OBJECTIVE

RESULTS

Some of the representative results are shown in Fig.3, Fig.4 and

Fig.5. The distribution of char density at time = 140 minutes is

shown in Figure3 where it can be seen that the char near the inlet

has been consumed till this time.

CONCLUSIONS The model is able to predict the composition of product gas and its

calorific value. The important aspect of the model is that it can

foresee the growth of the cavity even after it has hit the

overburden, which is the reality for the UCG of thin coal seam.

REFERENCES

1) Tsang, Tat Hang Tate;Modeling of heat and mass transfer during

coal block gasification; ProQuest Dissertations and Theses; 1980.

2) E.Shafirovich, A.Varma; U.C.G: A brief Review of current Status,

(Ind Eng. Chem. Res. 2009, 48, 7865 -7875

3) C.B.Thorsness, E.A.Grens, A.Sherwood; A one dimensional

model for in situ coal gasification; Lawrence Livermore;1978.

4) A.N.Khadse, M.Qayyumiy, S.Mahajani, P.Aghalayam. Reactor

Model for the Underground Coal Gasification (UCG) Channel;

International journal of Chemical Reactor Engineering; Volume 4,

Article A37, 2006.

The objective of this work is to develop a two-dimensional model of

the cavity to analyse its growth and product gas composition

during the UCG process. The two-dimensional model is a reduced

form of the actual three-dimensional cavity where the geometry for

modeling is a vertical plane passing through the injection and

production well.

Figure 2. 2-D Geometry of the UCG process (COMSOL model)

As shown in Figure 4, oxygen concentration is very low at places

away from the inlet as it gets consumed very fast due to the high

rate of the combustion reaction. Carbon dioxide is generated from

this combustion reaction and it gets consumed due to the

gasification reaction. Hence, its concentration profile depends on

the position of the reaction front of these two reactions. Figure 5

shows the profile of carbon dioxide where a maxima can be seen

due to this very reason.

1) Solid Balance Equation- 2) Gas Balance Equation -

𝝏𝑪𝑪𝒉𝒂𝒓

𝝏𝒕= 𝑹𝑪𝒉𝒂𝒓

𝝏𝑪𝒊

𝝏𝒕+ 𝜵. −𝑫𝒊𝛁𝑪𝒊 + 𝒖. 𝛁𝑪𝒊 = 𝑹𝒊

3) Heat balance Equation -

(𝝆𝑪𝒑)𝒆𝒇𝒇𝝏𝑻𝒔𝝏𝒕+ 𝛁. (𝝆𝒈𝒖𝑪𝒑,𝒈𝑻𝒔) = 𝜵. −𝒌𝒆𝒇𝒇𝛁𝑻𝒔 + (∆𝑯𝒊

𝟑

𝒊=𝟏

∗ 𝑹𝒊)

(i) Transport in dilute species; (ii) Heat transfer in porous media;

(iii) Brinkman’s equation are solved in the Segregated Time

Dependent Solver in COMSOL.

Figure 1. Schematic of the UCG process

COMPUTATIONAL METHOD

1 Department of Chemical Engineering, Indian Institute of Technology Bombay, Mumbai, India

2 Indian Institute of Technology Madras, Chennai, India

S. Srikantiah1, S. Mahajani1, G. Samdani1, A. Ganesh1, P. Aghalayam2

2-D Modeling of Underground Coal Gasification (UCG)

Figure 3. Concentration of char in the coal bed at time=140mins

Figure 4. Concentration of oxygen(O2) in the coal bed at time=140mins

Figure 5. Concentration of carbon dioxide(CO2) in the coal bed at time=140mins