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Old   February 23, 2011, 16:50
Default coal gasification using FLUENT-DPM
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Hello...

I am confused over two issues in modeling coal gasification using DPM and species transport....

1. In the coal calculator ultimate analysis, you can only include S when SO2 is included..and the reaction shows at the bottom and also included as reaction 1..
vol+xO2--> mCO+nH2O+pN2+qSO2
what if I don't wan't to consider this reaction at all....
as my volatile species breakup reaction is
Volatile --> aCO+bH2S+cCH4+dH2O+eH2+fN2
What should I do?

2. How do you model moisture release in case of dry coal feed(only inherent moisture is present not in form of slurry)? Is the moisture modeled as water vapor or liquid water?...If it is liquid water, how do you calculate the liquid volume fraction based on proximate analysis and what would be the input options?? Do I have to use wet combustion to model dry coal feed also??

The FLUENT manual(12.1) has confusing statements
pages "15-27,23-24,23-48" says to use wet combustion
page "16-25" says not to use in case of inherent moisture....

Any suggestions will be very helpful...

Thanks in advance..
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Old   March 17, 2011, 05:04
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Michele Vascellari
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Dear Arnab,

Coal calculator is a great help for calculating coal properties on fluent.
However you could use it only to calculate equivalent volatile species (C_x H_y O_z).
One you know the chemical composition of the species, you can balance the chemical reactions that you prefer, and add them to the reaction panel.

Moisture can be add from the injection panel, in wet combustion tab.
Pay attention that you must insert the volume fraction of liquid (not mass fraction).

I hope that is what you need.

Michele
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Old   March 17, 2011, 11:02
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Dear Michele,

Thanks a lot for the reply. Regarding this, could you please help me with combustion simulation strategies in FLUENT?...

What I did and the issues I faced are as following:

1. Set up the model using DPM, Energy equation, k-e turbulent model and all reactions in species transport.
2. Disable the particle/volumetric reactions in Species Transport and product species in Equations tab and run the cold flow simulations.
3. Once converged then enable everything, patch with temperature and run case.

Result:
I get combustion simulation done within 400 iterations (!!) and temperature field shoots upto 4000K and species distribution is unphysical..

Issues:
1. I am using 100 flow iterations per DPM iteration. Is that too high or too low? How to determine that in this kind of flow situations..
2. How do I patch a zone? I tried with marking a reaction zone using the Adapt menu but when I patch that zone doesn't show up. It only shows surface_body..
3. What's the typical range for under relaxation factors and convergence criterion (like 10^-5 for all and 10^-6 for energy)...is that good enough.??

Please let me know your thoughts....I really appreciate your help...

Regards,
Arnab
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Old   March 18, 2011, 06:27
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Dear Arnab,

Generally it is normal to have very high temperature during the first iterations after activating DPM.
They should disappear after few iterations. In order to decrease it, you could use very low DPM under-relaxation factor URF (lower than 0.1) and low temperature and species URF, at least at the beginning until your solution becomes stable.

In some Fluent tutorial/presentation it is suggested to activate at first only DPM without chemical reactions in gas phase. Chemical reactions are activated only in a second step.

Furthermore, you must wait in order to obtain a physical solution, probably you could avoid to patch the temperature, because constant rate volatilization does not depend on temperature as Eddy Break model for homogeneous combustion.

Also grid quality is very important to avoid out of bond temperature and viscosity ratio.

The number of flow iterations per DPM iteration should be a value around 50-100, but there is no a fix rule to set. In order to improve stability of solution an high number of particle tries for discret random walk is recommended.

Considering convergence, residual can not be used as criteria for convergence. It is better to monitor temperature, velocity and one chemical species at a point near the flame and at the outlet, and the volume sum of dpm mass source.

I hope that it could be help you.

Regards

Michele
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Old   March 19, 2011, 08:03
Default Combustion Problem in Gasifier system in Fluent 6.3
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Dear Arnab and sir,

looking to ur problem,i was actually quite happy to see that u had started combustion.I m presently working on a similiar kind of problem.

I'm working on Simulation of Downdraft gasification processes.its my problem of M tech.I want to initiate the combustion in my model, but its not working.

I set up a model by
- activating energy equation
- Enabling the Standard K-E model
- Enabling DPM model
- Enabling species and transport reactions model with eddy dissipation model activated in particle/volumetric reactions.

I'm also facing a problem in adding the species.How do i add the species which i want? help me please.My input material in project is Lignite.

ur help will be very appreciated.

Thanking you,
-Keran
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Old   March 20, 2011, 01:24
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hi karen ,,

if your using species transport model ,, then you have to select a mixture templete at first and you can go to material panel and edit the species you want to use from the fluent database or you can put your own data
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Old   March 20, 2011, 01:27
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can somebody tell me more about how to calculate the Cp, Thermal conductivity and viscosity values for a mixture template,,

Last edited by tirtha; March 22, 2011 at 12:43.
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Old   October 25, 2012, 17:16
Smile inherent moisture of the coal
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hi,

I am the same question of modeling inherent moisture of the coal particle.
I am doing coal combustion and gasification process, and using species transport model and DPM model for coal particles. Currently I use wet combustion sub-model in DPM model to simulate the water vaporation process from coal surface to surroundings. But for water inside of coal (bonded to coal matrix, or inherent moisture), the first process is the inside water go to coal surface, then go to evaporation process. Does Fluent provide any sub-model to simulation this process (water inside of coal go to coal surface)? I read some paper said Fluent used Arrhenius rate to model this process, where I can find it to input A and E (kinetic energy) value?
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Old   February 12, 2013, 06:56
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Quote:
Originally Posted by lvxijia View Post
hi,

I am the same question of modeling inherent moisture of the coal particle.
I am doing coal combustion and gasification process, and using species transport model and DPM model for coal particles. Currently I use wet combustion sub-model in DPM model to simulate the water vaporation process from coal surface to surroundings. But for water inside of coal (bonded to coal matrix, or inherent moisture), the first process is the inside water go to coal surface, then go to evaporation process. Does Fluent provide any sub-model to simulation this process (water inside of coal go to coal surface)? I read some paper said Fluent used Arrhenius rate to model this process, where I can find it to input A and E (kinetic energy) value?
hi all,
i m doing a simulation of biomass gasification in BFB. please help me how to proceed with gasification/species transport/chemical reaction in FLUENT 6.3. Is there any tutorial available for gasification process of Fluidized bed in Fluent.
please help me.
thanks and regards,
prishor
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Old   February 13, 2013, 00:06
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For doing simulation you can select species transport model and use coal as particles.
For AFBC fired boilers there particle size will be little higher like 1 cm also possible. The coal will compose of various components which you have to select as per the ultimate analysis. For ultimate analysis you can refer to any coal data. The coal composition also varies with the source and country of origin. For accounting for moisture you can create the reaction for moisture in coal being converted to steam using enthalpy for inlet coal temperature and the boiler outlet temperature. This method for calculating the heat taken up by coal moisture will be quite accurate enough.
For fluidized bed combustion do not consider 100 % C conversion because in real situations there will be good amount of unburned carbon which is call LOI.
Proceed with species transport reactions for C, N and H. For better accuracy you can also consider the amount of water formed by H2.

Also while simulating do also take care about the heat energy produced during combustion cause in fluent getting the final temperatures in acceptable limits is difficult. For real AFBC boilers the temperatures should be less then 950 Deg C.


Hope my reply will give you some help


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Old   February 19, 2013, 01:14
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thank you Tirtha for your valuable informations...
I am doing gasification process with biomass(CH1.6O0.8) as fuel in bubbling fluidized bed. there are both homogenous and heterogeneous reactions in it. so do i have to enter both of them seperately by considering reactants as mixture(both homogeneous and heterogeneous mixture).?
thanks and regards,
prishor
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Old   February 19, 2013, 06:13
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As in real case yes the reactions will he homogeneous and heterogeneous. As the combustion reaction takes place in steps.

As per my knowledge i believe the volatiles will burn first and are actually responsible for flame generation. After this the surface reactions on the solids will start.

All biomass fuels do contain very high moisture. The moisture can be upto 50 % also in real case scenario.

As VM for biomass is very high in dry basis and rest will be full fixed carbon. As your simulating the Biomass combustion good news for you is biomass contains very less amount of Ash which you can account depending on the type of biomass your simulating.

As for real steady state operation
1. First the water should evaporate (Moisture content)
2. The volatiles will burn
3. The FC will burn
4. The conversion of CO to CO2 and other gas phase reaction will be completed


For simulation purpose you can either consider complete combustion or you can consider some loss in ignition during the operation.


As i am have not been in touch with the simulation part for quite long time only i can advice on the real case scenarios.

Hope you get some direction with this.


Tirtha
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Old   February 20, 2013, 08:54
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dear tirtha,

I got some idea from your explanation. Thanks a lot. i have doubt about that how i should enter devolatilization and decomposition of volatile matters into fluent.the following processes
biomass --> char+volatile+tar+ water(steam)
volatile --> CO+CO2+H2+H2O+CH4
are the initial processes before the homogeneous and heterogeneous reactions.
can you help me how to proceed with these processes. shall I make a separate UDF for this processes?. do you have any sample UDF, for any gasification processes, available with you. if you have, can you send it to me (email: prishor@gmail.com).
with lots of thanks,
prishor

Quote:
Originally Posted by tirtha View Post
As in real case yes the reactions will he homogeneous and heterogeneous. As the combustion reaction takes place in steps.

As per my knowledge i believe the volatiles will burn first and are actually responsible for flame generation. After this the surface reactions on the solids will start.

All biomass fuels do contain very high moisture. The moisture can be upto 50 % also in real case scenario.

As VM for biomass is very high in dry basis and rest will be full fixed carbon. As your simulating the Biomass combustion good news for you is biomass contains very less amount of Ash which you can account depending on the type of biomass your simulating.

As for real steady state operation
1. First the water should evaporate (Moisture content)
2. The volatiles will burn
3. The FC will burn
4. The conversion of CO to CO2 and other gas phase reaction will be completed


For simulation purpose you can either consider complete combustion or you can consider some loss in ignition during the operation.


As i am have not been in touch with the simulation part for quite long time only i can advice on the real case scenarios.

Hope you get some direction with this.


Tirtha
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Old   October 8, 2013, 07:10
Default product composition
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abhijeet bhagat
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can you please tell me...how to find composition of product gas after iteration,
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Old   November 21, 2014, 05:59
Default Coal gasification
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ashish
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hello sir
I am doing my m tech project in CFD simulation of coal gasification.In that i choose the entrainment flow reactor and graw a 3D geometry in design modular and did meshing,but i confuse in fluent i choose the
stsndard K-E model,species transport model,finite rate eddy dissipation turbulence chemistry model,i write reaction in reaction window.
my feed coal is in granular form when i used coal partical injection in coal inlet ,where i put my boundary condition(composition of coal) in coal inlet.
In boundary condition c(s) option not came for granular inlet composition. if you require any more information about my project please contact me on this email id- ashishtonge64@gmail.com
Please help me sir......
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