6 replies to this topic

[Boris Dario]

Hello everyone!

I am involved in an ammonia project. I would like that you could help me to calculate the thermal efficiency in a primary reformer for this plant. As you know, to calculate this, you should consider Qin and Qout. I have considered both of them as it follows:

 

Qin:

- Low calorific value of fuel gas (primary)

- Low calorific value of fuel recovery gas (secondary)

- Ha, this is from FLUE gas from gas turbine working with the air compressor used as combustion air in the reformer.

- H GTE, flue gas going to convection section

- Hf 1, heat transefer of fuel gas (primary)

- Hf 2, heat tranfer of recovery gas (secondary)

 

Q out

 

Convection coils:

- Mixed feed

- Process air, hot

- Overheated steam . hot HP

- Overheated steam ,cold  HP

- Preheated NG, hot

- Preheated NG, cold

- Process air, cold

- BFW

- RECOVERY GAS preheated (SECONDARY GAS)

- FUEL GAS preheated (PRIMARY GAS)

 

Also

- Heat transfered trough radiation to catalitic tubes

- Heat transfered to the reaction

- Heat lost in stack

 

So I need to know if each one considered above is OK and maybe you could suggest me some method for the calculation, formules, in order to know if I am going in the right way.

 

I will really apreciate your help.

 

Regards

 

Dario.

Edited by Boris Dario, 22 July 2017 - 06:11 PM.

[Saml]

You can calculate the same way you do in any fired heater.  In theory they should give the same results.

 

Eff = (Heat Input - Losses)/Heat Input

Eff = (Heat to Product)/(Heat Input)

 

In API 560 you have a description on how to calculate the Heat Input. There is a section about externally heated combustion air. That would be your case since you are using the exhaust from a gas turbine (The majority of the ammonia plants do not use this configuration by the way)

 

Now, take into account that many ammonia plants need to reject a lot of heat a relatively low temperature because there is not enough streams that needs to be heated at a lower temperatures. It means that in some designs it woud be wise not to recover heat at the end of the convective section, because otherwise you will need to use cooling water somewhere else. It is easier to reject heat thru a stack rather than thru a cooling tower. If you focus only on reformer efficiency you may be going the wrong way about total plant efficiency.

[spchauhan12]

Hi,

 

  I will also suggest to have a look  - Heat transer text book by D.Q. Kern.

 

 

Regards,

 

SPC

[Waqar1989]

Hi,
Waqar here. I work as a process engineer at ammonia plant. The reformer we have is based on induced draft furnace design. From the info you have shared, i deduce that you are considering a forced draft furnace. You are pretty much on the right track....just a couple of things.

Do take into account heat loss from the furnace and the heat of reaction. If u are using actual plant data remember that there is significant error in flue gas temperatures. Also the measured process gas temperatures at the outlet of reformer (refered to as hot collector or pig tail temperature) are slightly lower due to heat loss to ambient.

I can help u compare results with actual data (though based on different design).

[Boris Dario]

You can calculate the same way you do in any fired heater.  In theory they should give the same results.

 

Eff = (Heat Input - Losses)/Heat Input

Eff = (Heat to Product)/(Heat Input)

 

In API 560 you have a description on how to calculate the Heat Input. There is a section about externally heated combustion air. That would be your case since you are using the exhaust from a gas turbine (The majority of the ammonia plants do not use this configuration by the way)

 

Now, take into account that many ammonia plants need to reject a lot of heat a relatively low temperature because there is not enough streams that needs to be heated at a lower temperatures. It means that in some designs it woud be wise not to recover heat at the end of the convective section, because otherwise you will need to use cooling water somewhere else. It is easier to reject heat thru a stack rather than thru a cooling tower. If you focus only on reformer efficiency you may be going the wrong way about total plant efficiency.

 

Mr. Saml:

Thanks for you suggestion, I am taking into account those consideratons. I would like to know if you have knowledge  of any software to simulate this effciciency analysis.

 

[Boris Dario]

Hi,

 

  I will also suggest to have a look  - Heat transer text book by D.Q. Kern.

 

 

Regards,

 

SPC

Thanks for your recommendation!

[Boris Dario]

Hi,
Waqar here. I work as a process engineer at ammonia plant. The reformer we have is based on induced draft furnace design. From the info you have shared, i deduce that you are considering a forced draft furnace. You are pretty much on the right track....just a couple of things.

Do take into account heat loss from the furnace and the heat of reaction. If u are using actual plant data remember that there is significant error in flue gas temperatures. Also the measured process gas temperatures at the outlet of reformer (refered to as hot collector or pig tail temperature) are slightly lower due to heat loss to ambient.

I can help u compare results with actual data (though based on different design).

Hi Waqar!

Thanks for your reply. The reformer uses an ID fan. The combustion air introduced into the primary reformer comes from the gas turbine, FLUE GAS, used for the air compressor.

On the other hand,we have two sources of fuel for the reformer. One is primary fuel and the other one is secondary fuel coming from recovery gases. The last one doesn´t have a constant flow.