6 replies to this topic

[starter_2011]

Hi all,

I want to calculate material balance for naphtha steam reformer.I know the reactions.

CnH(2n+2) + nH20 ------->  nCO +(2n+1) H20

 

Since Water Gas Shift reaction(WGS) and reforming reactions are equilibirium limiting,how to calculate product composition (wet basis) if inlet flowrate and outlet temperature and pressure are specified.

 

Thanks in advance.

[S.AHMAD]

Hi,

1. It seems nobody could answer your question since naphtha steam reforming is no longer considered economical in the industry. However, probably in your case, light naphtha is in excess.

2. I worked in an ammonia plant that use a mixture of refinery gas and light naphtha 30 years ago. The ammonia plant is no longer in operation.

3. First of all, you need to determine the MOLECULAR WEIGHT of the light naphtha. Then you can determine the value of n in the above equation. Rounding the value of n (whole no.)

4. Molecular weight can be determined from MeABP (mean average boiling point) and density. There is correlation that relates molecular weight with MeABP and density. For determining MeABP you need the ASTM D86 analysis.

5. API Technical Data Book has the correlations for MW and conversion ASTM D86 to MeABP.

 

Good Luck

Edited by S.AHMAD, 14 January 2014 - 05:10 AM.

[thorium90]

You will need the inlet composition too. First assume all hydrocarbons are converted to CH4. Using the reforming reaction mole balance you can calculate the composition from this step. Now that you only have CH4, use the reforming reaction together with the water gas shift reaction, calculate the composition. You would need kinetics for this step otherwise solve using Gibbs free energy minimization. With this 2 variables solved, you can solve for conversion for each reaction and therefore your reactor outlet composition

[starter_2011]

Hi all.

 

I will make my query clear now.

 

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   150 downloads

Edited by starter_2011, 14 January 2014 - 11:27 AM.

[thorium90]

Calculate the expected exit temperature by using your actual methane slip. Compare it with your actual exit temperature. Wet gas composition is the dry gas composition add any unreacted steam.

[starter_2011]

Dear Thorium,

 

How to calculate unreacted steam,since we dont know the actual conversion of steam/naphtha (any case) methane reforming reaction.

 

The attached excel file is design conditions mass balance of primary reformer.

 

My aim is to calculate wet gas composition based on dry gas composition.So that i can calculate reaction quotient and equilibirium constant.After finding Kp i can calculate Del T(Approach to equilibirium) .This helps me to find the catalyst performance.

Attached Files

•  Primary reformer.xlsx   10.22KB   193 downloads

Edited by starter_2011, 16 January 2014 - 12:49 AM.

[thorium90]

I will consolidate my reply in your other thread.

 

http://www.cheresour...ity/#entry81968