10 replies to this topic

[ravindra@096]

How do we perform material and energy balances over a steam methane reformer using natural gas (89 mole% methane) as the feedstock?

[PingPong]

One normally uses a process simulator. But to simulate a steam reformer one has to be familiar with the process scheme, required operating conditions, et cetera.

 

It goes to far to explain here the whole process with all its ins and outs, but you can start using google to obtain some typical info about the process.

Use also the search function of this forum.

 

Any specific questions related to what is not clear you can then post here.

[ravindra@096]

Our objective is to use natural gas to produce 100 kg/hr Hydrogen with no export steam using Conventional Steam Methane Reforming, only steam required for the process. We have assumed steam to carbon ratio 2. Temperature and pressure conditions are such that 1073 K and 20 bar are maintained in the reformer tubes. PSA beds are used for product recovery.

[PingPong]

An S/C ratio of 2 is very low.

A coil outlet temperature of 800 ^oC is also very low.

 

Where did you get those numbers?

[ravindra@096]

We are working on senior year project titled "Design and Simulation of Hydrogen production plant using natural gas as the feedstock. We have assumed 800 degrees Celsius as the reformer temperature because our Natural gas contains 89 mole percent Methane in addition to the fact that our production objective is to produce only 100 kg/hr of hydrogen for saponification process. Our assumption of S/C of 2 relies on the fact that we do not intend to produce any steam for export other than what is required for the process.

[PingPong]

Your question looks very much like that of MurtazaHakim

https://www.cheresou...of-an-smr-unit/

You both use natural gas with 89 % methane, an S/C ratio of 2 (which is unrealistically low) and a reformer outlet pressure of 20 bar, except that you moreover use an unrealistic reformer outlet temperature of 800 ^oC.

 

Normally SMR units operate on an S/C ratio of 2.5 - 4

Too low an S/C ratio can result in coke formation on the reformer catalyst.

We have assumed 800 degrees Celsius as the reformer temperature because our Natural gas contains 89 mole percent Methane

So what? Your natural gas is nothing special.

That low reformer outlet temperature will result in a relatively large natural gas feed required and a very large heating value of the PSA tailgas that is used as fuel in the reformer furnace. Normally the reformer outlet temperature is controlled by additional natural gas firing, but you now run the risk that you will have more PSA tailgas than you can burn.

Our assumption of S/C of 2 relies on the fact that we do not intend to produce any steam for export other than what is required for the process.

The S/C ratio is to protect the catalyst from coking, not to make it easier for you to close the steam balance.

[ravindra@096]

As you have suggested I have taken into consideration the S/C ratio of 3 and I have prepared a preliminary material balance spreadsheet in MS excel. Kindly look into it and suggest the changes required. I am stuck in deciding the conversion rates of CH₄, C₂H₆, C₃H₈, C₄H₁₀ in Water-gas shift reactor which will further determine the flowrates of tail gas into the reformer furnace.

Attached Files

•  SMR Mass balance.xlsx   12.57KB   110 downloads

[PingPong]

You should follow my explanations in that other topic.

 

As described there you must work with atom-balances for all elements (C, H, O and N) in the system in combination with the two reaction equilibria that are applicable. That gives a set of 7 equations with 7 unknowns that can be solved to give the reformer furnace outlet composition.

[MurtazaHakim]

It appears that I have mistakenly deleted the topic titled "Heat balance of a steam reformer unit".

I would like to continue that discussion in this topic.

 

So far we have calculated the reformer and water gas shift reactor outlet composition and quantity. We are stuck in deciding the amount of condensate which will be formed before the shifted gas reaches the PSA inlet.

 

 

@PingPong

In your last message, you suggested to use a steam table. Please elaborate more on that procedure. An additional question is that will there be any other component (from the shifted gas) other than steam in the condensate ?

[PingPong]

MurtazaHakim,

I put a lot of effort in your topic

https://www.cheresou...of-an-smr-unit/

so that my advise would also be available for other interested readers in future. I would be a pity if all that were lost.

 

Please contact a moderator or administrator of this forum and request to reactivate the topic so that we can continue there.

[MurtazaHakim]

@PingPong

The topic 

https://www.cheresou...of-an-smr-unit/ of our discussion has been restored. I request you to continue the discussion from there.