9 replies to this topic

[starter_2011]

Hi all

 

How to calculate activity of the catalyst based on outlet gas composition from steam methane reformer or any reactor.Please provide me correlations if any.

 

Thanks in advance

[S.AHMAD]

Hi

1. As far as I know, there is no general correlations to determine catalyst activity of steam reforming.

2. The company that supply the technology normally ask for the data required and they will let you know the activity coefficient. of the steam reforming. They have the confidential correlation only for their use only.

[starter_2011]

Dear Ahamad,

 

Thank you for your information.

 

I am working in ammonia plant.I have calculated ATE equilibirium for HT , LT based on following procedure

 

Step 1: Calculation of  equilibirium constant and equlibirium conversion of CO:

 

I used the following relation :

 

Keq = exp(4577.8/T - 4.33)

 

Based on the above relation I calculated equilibirium conversion.

 

Step 2:

 

Then i assumed approach to equilibirium as 40 deg C and fixed outlet temperature of the bed.

 

Based on this i calculated actual conversion.Then i calculated outlet composition.

 

I made these calculation using Excel and cross check with HYSYS.

 

It was found to be correct.

 

But in case steam methane reforming or naphtha steam reforming i dont know how to calculate approach to equilibirium.

In reformer two reactions takes place,reforming reaction and WGS reaction.

 

At the reformer outlet WGS reaction is assumed to be in equilibirium.Reforming reaction is approaching equilibirium.

 

Here I want to calculate ATE for reformer.Based on the attached file ATE can be calculated.

In reformer outlet gas samples are based on dry basis.How to convert it into wet basis,if inlet composition and steam to carbon ratio,based on ATE without specifying conversion.

Attached Files

•  steamreforming-approachtoequilibrium-130925135459-phpapp01.pdf   1.68MB   86 downloads

Edited by starter_2011, 14 January 2014 - 11:23 AM.

[thorium90]

It would be better if you consolidated all your related queries in one thread. No use starting new ones all over the place. It is actually counter productive...

 

Catalyst activity is defined by a number called Turnover Frequency. However, such a precise term is not commonly used by operators of industrial reactors. It is alot more common to simply compare past against current data for outlet compositions, temperature etc to evaluate the performance of the reactor catalyst.

[S.AHMAD]

Hi Starter

1. If I understand correctly, you problem is to determine the outlet composition on wet basis since laboratory analysis is normally reported on dry basis. Is that correct?

2. If so then you need to do hydrogen & carbon balance across the reforming reactor then use excel spreadsheet SOLVER to reconciled the results. It always the case that the reformer calculated results will never equal the laboratory analysis but we can minimize the error. Errors are from laboratory analysis and the flowrate of feedstock and steam fed into the reformer.

3. You need to assume either feedstock flowrate is correct or the steam is the correct one. Then use the incorrect flowrate as the variable in SOLVER.

4. The objective or target of the SOLVER is the sum of the square of the error between calculated and laboratory analysis.

5. The constraint is the methane composition (dry basis) equal the laboratory methane composition. We need to assume that one component of the outlet gas is correct. You can choose methane or CO2 or try several cases such that the objective is the lower minimum.

6. I have done this type of calculation 4 years ago on natural gas steam reforming but I could not find ,the spreadsheet. I try to explain the method based on my poor memory. The right way is for you to try and submit your spreadsheet so I can give my comments.

Edited by S.AHMAD, 14 January 2014 - 09:52 PM.

[starter_2011]

Dear ahamad,

 

You are right! As you told i will calculate and provide you the spreadsheet. 

 

I tried atomic balance across the reformer based on the attached file(section: Mass Balance calculation method for the reformed gas compositions).But i did not get the correct answer.I googled for atomic balance across reformer but i didnot get any example problems.If you have any example or link pls share with me.

 

My aim is to prepare a spread sheet ,

The input should be

 

(i)  Naphtha /Methane flow rate

(ii) Steam flow rate

(iii) Reformer outlet temperature

(iv) Approach to equilibirium

 

Output should be

 

(i) Reformer outlet gas composition

(ii) Enthaphy of outlet gas

 

After preparing my spreadsheet ,I want check my calculated values with my plant design Heat and mass balance.

I prepared the spreadsheet for HT,Quench flow rate,LT and Methanator.Then checked with design case and HYSYS everything matches accurately.But i dont know how to calculate for primary reformer and secondary reformer.

 

I think i mam clear with my queries.

Attached Files

•  Atomic balance.pdf   1.47MB   123 downloads

Edited by starter_2011, 16 January 2014 - 12:02 AM.

[S.AHMAD]

Hi starter

1. Have got the MW of the naphtha? You can assume the naphtha to be paraffinic..

2. All naphtha will be converted to CH4. Then you have the knowledge to do the mass balance.

[starter_2011]

Dear Ahamad,

 

I have attached the naphtha spec for you reference. Molecular weight was taken as 100.  naphtha spec.xlsx   9.62KB   58 downloads

Edited by starter_2011, 16 January 2014 - 01:51 PM.

[tumza]

please help me out with material balance of naptha feed c11h24 reaction with steam in the primary reformer and secondary reformer,how much carbon to steam ratio must i use for this reaction,and how do i calculate conversion per reformer?sulphur content is22ppm by weight 

 

Component

Mol%

Hydrogen

52.01

Carbon

0.84

Sulphur

22ppm by weight

 

naphtha contains 15.3% hydrogen by mass. The average molecular formula of this naphtha is C₁₁H₂₄.

[P.K.Rao]

I think C/H ratio is better than assuming the molecular formula  of naphtha as C11H14. You can calculate hydrogen in naphtha using the formula,

 

% w Hydrogen  26 - 15d, where d is the density at 15C . % Carbon = 100   H - S