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# Fuel Gas Consumption

fuel fuel gas steam cracker furnace

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### #1 Movers

Movers

Gold Member

• Members
• 52 posts

Posted 26 September 2017 - 03:47 AM

Hi.

We have implemented some efficiency project on steam cracking furnace and I have to evaluate how much fuel consumption was reduced. At the begining I created below formula for comparison situation before and after implementation:

Fuel consumption coeficient [GJ/t of feed] = (Heating value of Fuel Gas [GJ/t]*Fuel consumption [t/h])/amount of the feed [t/h]

But now I see that I should take into account also ambient temperature, feed temperature, fuel gas temperature and amount of combustion air. It is not a problem to evaluate amount of the heat provided to the furnace with these streams, but I have no idea how to incorporate this values into my formula to compare the situation before and after implementation. I would appreciate if someone could give me some advices ho to do that.

Best Regards

### #2 Tdha

Tdha

Brand New Member

• Members
• 3 posts

Posted 24 January 2019 - 04:24 PM

Basically, You have to calculate your heaters' efficiency. For this, you don't even need the amount of fuel gas, but flue gas oxygen content, fuel gas composition, temperatures of stack and atmosphere (self-inspiration burners) - but having fuel gas mass flowrate makes it easier.

1.: Calculate heat duty of furnace (P1=mass flowrate of fuel gas*heating value of fuel gas)

2.: Calculate molar flowrate of flue gas components using oxygen concentration of flue gas for determination of excess air factor (lambda)

3.: Calculate composition of flue gas

4.: Calculate average isobaric heat capacity of flue gas based on its composition

5.: Calculate stack loss using flue gas isobaric heat capacity (P2=flue gas mass flowrate*isobaric heat capacity*(Tstack-Tatmosphere))

6.: Calculate heat recovered in furnace (Pr=Heat duty-Stack loss)

7.: Divide energy recovered by feedstock flowrate to get "fuel consumption coefficient"

Important: it's recommended to make comparison while type os feedstock, its flowrate, COT, HC/Steam ratio and all other settings are the same. A cracking furnace is a very complex system, especially when it's a standalone construction with high level waste heat recovery section.