CFD of Underground Coal Gasification

Presented By Himanshu Arora

What is UCG ?

• Coal is converted insitu into a combustible gas.

• Out coming gases used as fuel

Source : www.coal-ucg.com

Why UCG ?

• Mining and conversion accomplished in a single step.

• Eliminates the cost of mining, transportation etc.

• Exploit resources, uneconomic to work by conventional underground coal extraction.

Overview of the process

• Chemical reactions occurs in 3 steps

1. Oxidation2. Reduction3. Pyrolysis

Source:www.coal-ucg.com

Overview of the process…(contd.) • Cavity Growth

1. Growth occurs between injection well and production well.

2. Cavity consists of four zones.

Source :Britten et al, 1989

Objective of the project

• Study the flow pattern and RTD of UCG.

• Reactions not included.• Compare RTD with network of

reactors.• Predict conversion of UCG on

the basis of network model.• Get conversion from

experiments.• Compare experimental and

modeling results.

CFD study of a model UCG reactor • Geometric details.• Length = 1m• Width = 0.226m• Depth = 0.226m• Diameter of inlet = 0.02m

CFD modeling …(contd.)

• Meshing Details

• Mixture of tetragonal and hexagonal cells.

• 2,50,000 volume cells in the whole volume.

• Volume of reactor = 0.0365m3

CFD modeling …(contd.)

• Boundary conditions.

• Mass flow rate = 0.012kg/hr• Outlet Pressure = 1 atm.• Fluid Porosities

Ash = 0.2 Char = 0.4 Coal = 0.6 Void = 1

Flow Pattern

• Steady state velocity profile.

Velocity vectors at plane y=0

Flow Pattern…(contd.)

• Tracer named Air1 with mole fraction = 0.05 introduced at the inlet.

• F curve and E curve are studied.

Comparison of RTD with network of reactors.

• Different networks were tried.

• PFR and CSTR in series.• PFR and CSTR in parallel.• Tank in series.

• Tanks in series fitted the best with

n=3 and τ = 5.50e+4 sec

• Τ of UCG = 109062.66sec

Comparison of E(t) curvesimulated vs. fitted

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

x 106

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5x 10

-6

time(sec)

E(t

)E(t) vs. t

simulationfit

CFD study of more complicated geometry

• Geometry details.• Length = 9m• Depth = 5.5m• Diameter of inlet = 0.2m

CFD modeling…(contd.)

• Meshing Details• Mixture of tetrahedral and

hexagonal cells.• Total of 2,26,330 volume cells.• Volume of UCG = 36.3m3

Flow pattern

• Due to complexity of the geometry steady state was not achieved.

Conclusion

• Studied the velocity profiles in UCG.

• RTD of the UCG. • Compared it with network

of reactors.

Future Work

• A comprehensive model that includes a network of CSTR’s and PFR’s which has same RTD as the UCG has to be developed.

• RTD results should be compared with the experiments.

Thank You!

Equations solved

For n tanks in series, E(t) is