CFD Online Discussion Forums - Coal gasification: reactions not working

Dear all,

First of all thanks for reading the thread, I really appreciate it.

I am trying to model coal gasification process in fluent using the species transport. The step that I follow to perform the analysis are given below.
The parameters that are not mentioned are taken by default.

I am only performing this exercise to see the potential of species transport for the coal gasification, but at the end of the day the simulation was not working ... yyyyyyyyyyyyyyyyyy ... I don’t have any clue

Anyway, the steps are given below,

1) Import the mesh file in Ansys Fluent 12.1.4.
The geometry is a 2D rectangle (10m by 1m), have a nozzle in the center and an end face as outlet. (fairly simple geometry)

2) Define>model>energy equation> ON

3) Define>model>viscous model>K-epsilon

4)define>model>species model>species transport.

5) under species transport, the volumetric and particle surface reaction are unabled.

6) similary, finate rate/eddy dissipation model is selected.

7) species mode> coal calculator> default values selected that generate a mixture material “coal-volatiles air”.

8) now in the material panel: material are selected and edited for mixture so that it contain “vol, o2, h2, co and n2” in the fluid speices and “C<s>” in the solid species.

9) now the two reaction are defined as,

a) volumetric reaction

vol + 0.885 o2 = 1.898 co + 2.381 h2 + 0.017 n2

b) particle surface

c<s> + 0.5 o2 = co2

10) define injection >new

Injection type>surface> “NOZZLE surface”

b) Particle type>combusting

c) Custom law> ticked

d) Temp>450, velocity>5 m/s, flow rate>0.1 kg/s

11) Material>combusting particle>combustion model> “multiple surface reaction” is selected.

12) Define>boundary condition>nozzle (velocity inlet)> velocity =10 m/s, species > o2 mole fraction =0.21, temperature=450

13) Initialized and run for couple of thousand iterations.

The only check I have that I check the temperature contours. Because if reactions are working than the temperature should go up. Remember, the temperature I am putting for air inlet and injecting particle are above the devolatalization temperature.

But I never get any reaction happening and maximum temperature remain the same as inlet conditions

Any comments and suggestions are welcome.

At this point I can try anything because the grid is fairly small so it will not take any time.

If anything is unclear then just shoot a question.

Thanks