[eeheehee]

Hi.

I'm trying to make a UDF about steam reforming using Xu & Froment equation ("Methane Steam Reforming, Methanation and Water-Gas Shift:I.Intrinsic Kinetics")

My problem is unit conversion.
Xu & Froment's rate constant has a unit of (kmol/kg/h).
and
DEFINE_VR_RATE macro guide said that macro has return value of (kgmol/m^3/sec)

what should i do to make it fit in Fluent format.

i tried
1. cell density
2. cell density*(sum of each reaction's reactants mole fraction)

it does not match up with reference value.

anybody who has experience about steam reforming UDF give me some advice,plz.

[pürtelaş]

sorry for late reply, but is there any possibility that you miss the fact that, reaction rate in Xu and Froment is for per kg catalyst rather than per m^3. That means it should be taken as a surface reaction or should be taken into account as porous region. (very thin catalyst thickness which is defined as porous region will do the job.)

[LiJG]

Originally Posted by eeheehee

Hi.

I'm trying to make a UDF about steam reforming using Xu & Froment equation ("Methane Steam Reforming, Methanation and Water-Gas Shift:I.Intrinsic Kinetics")

My problem is unit conversion.
Xu & Froment's rate constant has a unit of (kmol/kg/h).
and
DEFINE_VR_RATE macro guide said that macro has return value of (kgmol/m^3/sec)

what should i do to make it fit in Fluent format.

i tried
1. cell density
2. cell density*(sum of each reaction's reactants mole fraction)

it does not match up with reference value.

anybody who has experience about steam reforming UDF give me some advice,plz.

Hello:

Have you solved this problem? Recently, I have the same question as you. I want to use Xu & Froment equation to make a UDF in fluidized bed and face the unit convertion problem.

[eeheehee]

I couldn't solve the problem.
Instead I used other equation that converted from Xu&Froment rate equation into Arrhenius equation.
It was research paper written in Korean. "A Comparative Study for Steam-Methane Reforming Reaction Analysis Model" (You can find it from "www.dbpia.co.kr")

This paper compared the original Xu&Froment equation written in UDF with three Arrhenius coefficient modified model.

Arrhenius coefficient modified model approximately well followed conversion rate graph of original equation but this paper recommended UDF method.
Because it was more accurate.

Anyway I used model 3 coefficient model.
I don't know it will help for your problem. But it could be alternative solution.

<REFORMING EQUATION>
Equation 1. CH4 + H2O ↔ CO + 3H2
Equation 2. CH4 + 2H2O ↔ CO2 + 4H2
Equation 3. CO + H2O ↔ CO2 + H2

<ARRHENIUS EQUATION>
Ki = Ai * T^(Bi) * exp(-Ei/RT)

<Reaction coefficient for three Arrhenius type reaction models>
model 1
Eq. (1) Ei : 2.40×108 // Ai : 9.490×1016 // Bi : 0
Eq. (2) 2.439×108 // 2.290×1016 // 0
Eq. (3) 6.413×107 // 4.390×104 // 0

model 2
Eq. (1) 2.40×108 // 4.745×1014 // 0
Eq. (2) 2.439×108 // 1.145×1014 // 0
Eq. (3) 6.413×107 // 2.195×102 // 0

model 3
Eq. (1) 2.40×108 // 6.811×1035 // -7
Eq. (2) 2.439×108 // 1.145×1014 // -4
Eq. (3) 6.413×107 // 2.195×102 // 0

[Franchijio]

Li Have you rectified how to sort the issues with XU and Froment rate equation in your fluidized bed as I have similar problem. I thought about multiplying the rate with the density of catalyst

kmol/Kg-cat/s x Kg/m3. this will change the rate to kmol/m3/s.

what do you or anyone think of this method for a fluidized bed system. Please really need your replies and support urgently.

Thanks

[flappy]

Originally Posted by eeheehee

Hi.

I'm trying to make a UDF about steam reforming using Xu & Froment equation ("Methane Steam Reforming, Methanation and Water-Gas Shift:I.Intrinsic Kinetics")

My problem is unit conversion.
Xu & Froment's rate constant has a unit of (kmol/kg/h).
and
DEFINE_VR_RATE macro guide said that macro has return value of (kgmol/m^3/sec)

what should i do to make it fit in Fluent format.

i tried
1. cell density
2. cell density*(sum of each reaction's reactants mole fraction)

it does not match up with reference value.

anybody who has experience about steam reforming UDF give me some advice,plz.

i know this case is old, nevertheless:

In my case I treat the fixed catalyst bed as homogenous. This enables me to convert the units by just multiplying with the total mass of catalyst in my reactor, divide it by the volume of the catalyst bed and by 3600.

does this help?

[chinu007]

Hello Flappy,
Did you solve this problem by
1) multiplying the reaction rate with weight of catalyst divided by catalyst bed volume?
2) multiplying with catalyst density?