13 replies to this topic

[aeidy]

Hello.

 

Hope that someone can help me in doing the material balance of a prereformer. What I have now are the conversions, steam to carbon ratio and reactions for the process as follows:

                                                                                                              Conversion

CH4 + H2O => CO + 3H2                                                                              4%

C2H6 + 2H2O=> 2CO + 5H2                                                                         85%

C3H8 + 3H2O=> 3CO + 7H2                                                                         95%

CnHm + nH2O => nCO + (n+m/2)H2                                                            100%

n>=4

Steam to carbon ratio: 3

 

I have already tried to make one but it ended up not balance. I could not figure out where I did wrong. What I did was just a simple molecular species balance. Attached herewith is the excel of the material balance I did. Thanks!

Attached Files

•  book1.xlsx   17.23KB   60 downloads

Edited by aeidy, 29 May 2013 - 03:25 AM.

[thorium90]

I see you have calculated 50714 ton in and out as shown in cell W59 and W60. The number of moles may not be the same after a reaction but the mass will be the same. Thats why its a mass balance.

[abbaschemical]

Hi aeidy,

             I could find some mistakes in your calculation.

1. Conversion of steam mass to moles is wrong

2. You have not considered Carbon available in CO2 in feed. You had taken it as zero. It is to be considered as single carbon of that moles/hr.

Edited by abbaschemical, 29 May 2013 - 02:41 PM.

[thorium90]

Apologies to aeidy for not looking into such detail into your calculations at first.. I only looked at the final number that was in red.
 
To note abbas's points, aeidy appears to be converting moles to mass and the conversion appears correct.
aeidy appears not to have considered water gas shift reactions, therefore no CO2 was considered.

Edited by thorium90, 29 May 2013 - 10:09 PM.

[aeidy]

Abbaschemical:

 

Sir, thanks for the help. At first I included the Carbon in CO2 but I  thought that the Carbon to be used in S/C ratio is the carbon in the Hydrocarbons only that`s why I did not include it in the calculation of total C. Anyways, I already changed my calculation wherein I included the C available in CO2. 

 

In calculating the amount of Steam to be used in this process, I used the Steam/Carbon ratio (in terms of moles) of 3 so that`s 3 multiplied by the total carbon of the feed. Then to have its mass I multiplied it by H2O`s Molar Mass then divided it by 1000 to have metric ton. 

[aeidy]

Thoriium:

 

Thanks for the help! 

[aeidy]

This is the revised copy of my calculation. Hope that this is the correct one.

Attached Files

•  book1 (3).xlsx   17.21KB   72 downloads

[aeidy]

Thorium:

 

What you`ve said here is definitely correct. Sorry for I was not able to immediately recognize that. In fact, I have encountered such problems during our exam in our kinetics subject. Thanks sir anyways. :

[thorium90]

I would also like to point out that after the pre reformer, there will not be any more C2+. Also, about 10 to 15% of the total reforming happens in the pre reformer.

I think you also forgot to add the water gas shift reaction to your reaction columns.

 

I wouldn't quite say your spreadsheet is correct yet. May I ask, what is the purpose of this exercise and where you got this data?

Edited by thorium90, 31 May 2013 - 10:57 AM.

[aeidy]

Thorium:
 

Such exercise is part of our material balance for our H2 Plant Design. In such design, I included two water gas shift reaction reactors: high temperature and low temperature. Data are gathered from different related articles and websites.

[thorium90]

If you are doing the design work, you should be using data from laboratory performance tests of the catalyst you will be using. Don't use values from articles and websites. Are you sure conversion values of 85%, 95% etc are even from articles? They look so nice that I suspect you are simply making assumptions. You will have a hard time convincing your client on your reformer design with assumed values for catalyst performance.

 

To be frank, your simple spreadsheet cannot be be the basis for your design, and it is not completely correct either.

The water gas shift reaction takes some CO and H2O and makes CO2 and H2. As you can see, the molecules you are balancing are also in it and your outlet will not simply be the outcome from the reaction of just the hydrocarbons. The equilibrium reaction will play a part. What abbas has pointed out is to imply the use in this reaction which apparently you have not fully understood.

 

Anyway, such design work should be based upon actual catalyst kinetics and not simple balance of molecular species. I'm guessing you and your company are very new to the engineering industry and since reformers are already very widely used in the world, you have alot of expertise and experience to catch up on.

 

If you are really just a student in school, perhaps only the 2nd paragraph would really be very applicable to you.

Edited by thorium90, 01 June 2013 - 12:34 AM.

[aeidy]

Thorium:

 

Sir, I`m a Chemical Engineering student and all of the data I used are just assumptions. The design I uploaded here is part of our Plant Design which is a requirement in our course. 

[thorium90]

I understand. You can upload your amendments if you still need clarification.

[chancock]

aeidy,

 

Hi, I am also a chemical engineering student doing the prereformer as part of my plant design module.

I've had a look at your work and i think it looks good.

 

I've just started mine and I'm struggling with how exactly to do this and was wondering if you'd be able to give me some pointers?

 

Thanks