Coal gasification - Eulerian - Fixed bed
 

I have performed experiments in a cylindrical reacting char bed were a mixture of gases (CO2, H2O and N2) are injected in the top and passes through the reacting bed. Measurements of pressure drop, gas composition (longitudinal direction) and temperature (radial and longitudinal directions) were made. The char bed height was kept to constant cm due to continuous feeding.

I am trying to model the experiment above using Eulerian (granular > fixed bed). I want to be able to calculate:
* Pressure Drop
* Volume Fraction
* Species production and destruction
* Temperature
* Velocity

Does Fluent 12 have the capability of solving this on its on, or UDF's are required?
Do you have any suggestions?

P.S.: I want to model this in steady state

yes, you can solve your problem with Fluent 12.

if you wish to use Euler-Granular model to simulate gas-solid packed bed you need to write UDF for heterogeneous reactions.

With Euler granular approach, steady state modelling is not possible. you need to carry out unsteady state solution with very small time steps.

There is another software you can work with is MFIX for fixed bed calculations. i haven't used it, as i prefer to work with Fluent.

all the best, regards

Dear Chetan,

i am prishor,currently doing Mtech in thermal sciences. my project work is numerical simulation of biomass gasification in fluidized bed.i am using sawdust as fuel, sand as bed material, air is for fluidization and seperate steam entry for the enhancement of H2 production.
can u please tel me how can i define biomass in material panel as it undergoes pyrolysis before the gasification reaction.pyrolysis products are pure carbon, H2, CH4, CO, CO2 and H2O? Other materials are air, sand, and steam. For homogeneous reactions is it necessary to define each mixture in material panel?
please help me.

thanks and regards,
prishor

QUOTE=coalgas;285296]yes, you can solve your problem with Fluent 12.

if you wish to use Euler-Granular model to simulate gas-solid packed bed you need to write UDF for heterogeneous reactions.

With Euler granular approach, steady state modelling is not possible. you need to carry out unsteady state solution with very small time steps.

There is another software you can work with is MFIX for fixed bed calculations. i haven't used it, as i prefer to work with Fluent.

all the best, regards[/QUOTE]

Using granular flow you can implement solid particle combustion.

Hi Prishor,
You can define biomass as pseudo species, and define a reaction with appropriate E and A values ( experimental or literate values). The reaction will yield carbon, H2, CH4, CO, CO2 and H2O from biomass. Reaction looks like this
Biomass=> C+ H2+ CH4+ CO+ CO2+ H2O and then usual char reactions. Now for the biomass pyrolysis reaction, you can refer research papers. for char gasification you can refer to http://144.206.159.178/FT/158/20493/369881.pdf
This paper is simillar to your work, except fixed bed of char rather saw dust.

One more query, whats role of sand in your simulation? i mean bed of saw dust is nt sufficient for the biomass gasification?

regards
Chetan

dear chetan,

thank you for your reply. first of all sorry to disturb you again. i am using the sand as a bed material because it has better fluidization property.
i can enter biomass decomposition as a heterogeneous reaction..isn't it?
i have another doubt that where i should enter both homogeneous and heterogeneous reactions..whether i have to enter homogeneous reaction in chemical reaction panel and heterogeneous reaction in phase interaction panel.?
or i have to mention both volumetric and particle surface reaction in species transport and have to enter both the reactions in same chemical reaction panel?
how should i mention biomass as a pseudo species.

dear saeed,
i am using euler-euler grannular flow. for solid- air reaction whether i have to consider particle-surface reaction?.
thanks and regards,
prishor p k

Hi Prishor,
You can define all reactions in reaction panel. For solid-gas reactions you need to choose either wall-surface reaction or particle reactions. When you define you reactions you need to specify reaction whether it is homogeneous or wall-surface reaction. You can use mechanisms latter to segregate reactions between homogeneous and heterogeneous reactions.
i hope, this helps you!
cheers
chetan

dear chetan,

thank you very much. i will proceed with this way.now i am going to define every reactions in fluent.
i will contact you if will have any doubt in between.

thanks once again,

prishor p k

dear chetan,
this is prishor again. now my problem is writing udf for the heterogenous phase interaction reaction rate.
do you have any sample udf available with you.
can you help me that how i should start to make UDF code.
if you have any udf for multiphase DEFINE_HET_RXN_RATE please send it to me
my mail id prishor@gmail.com
Expecting your valuable reply
thanking you,
prishor

hi,
did you find how to calculate pressure drop in the CFB or BFB. and do you have any example for homogeneous reaction UDF code?
by calculating reaction rate mass faction C_YI(c,t) or C_YI/MW[][] must be used?
do you have any idea?
thanks in advance?

hi,
I am trying to write code about coal gasification.
did you find how to calculate pressure drop in the CFB or BFB. and do you have any example for homogeneous reaction UDF code?
by calculating reaction rates in homogeneous reaction mass faction C_YI(c,t) or C_YI/MW[][], (or concentration) must be used?
do you have any idea?
thanks in advance?

Dear Chetan,
Can u help me. I have got stuck with the reactions. i have entered homogeneous reactions in reaction panel and heterogeneous reactions in phase interaction panel. i cud not enter both types reactions in reaction panel becoz i defined two mixtures biomass mixture and gas mixture and O2 is defined in gas mixture only. i had entered homogenous reactions in gas mixture. but the pyrolysis products in the biomass mixture should be transfered to gas phase. how can i do it in fluent.
please help me in this regard.
thanks and regards,
prishor p k

Hi Chétan,

why do you think that steady simulation is not possible?
did you try it?

Best!

first of all have you ever tried to solve E-G equation in steady state?? :)
Well, your question has two answers, One- if you are using fluent, you are not able to choose E-G Model with steady-state solver ( i am not sure about V15).
Secondly, E-G model assumes particles are modeled as a continuous medium where all the quantities are assumed to be smooth functions of position and time. further you can refer : (& Governing equations) http://www.ansys.com/staticassets/AN...-ansys-cfd.pdf , I hope that helps.

steady granular flow
 

hi,
I read a recent paper about it. They performed the simulation even in V6.24. It is possible to select steady solver together with Eulerian model.
just try!

Best

i want to simulate a fixed bed coal gasifier in CFD fluent 14.5
plz tell me how to make the gasifier in it. i want to use coal having particle size of 1.5inch. tell me how to make a fixed bed of coal of height 0.6m.

Hi,
You should create the area which you want to fill with particles and then patch it. If you want to have reactions you should write UDF code.
Good luck
QUOTE=nabeelicet;471237]i want to simulate a fixed bed coal gasifier in CFD fluent 14.5
plz tell me how to make the gasifier in it. i want to use coal having particle size of 1.5inch. tell me how to make a fixed bed of coal of height 0.6m.[/QUOTE]

so i should develope the region in design moduler with gasifier geometry where i want to fill with coal particles?

[/QUOTE]

No you should do it in fluent itself. I think you should start with tutorials of fluent (for example tut 22)