1 reply to this topic

[Sherif Morsi]

Hi,

 

I calculated the total heat resulting from firing FG in a process heater by multiplying the total gas flow by the LHV of the gas

LHV = 949 Btu/SCF

Flow = 115,000 SCFH

 

Q1 = 109.14 MMBtu/hr

 

I also pulled out the capacity curve of the burners and at 11 psig gas pressure, the heat release per burner is 9 MMBtu/hr.

Q2 = 23 burners x 9MMBtu/hr = 207 MMBtu/hr

 

If I am not mistaken, capacity curves are for a specific gas composition and properties.

 

Why is there such a big difference between the two calculated values given that I am using the same gas properties? P.S: The FG Mol wt is 18 in the datasheet vs. actual Mol wt of 17.6 for the current FG used.

 

Thanks

Sherif

[vishnup11]

Hi, 

Would like you to verify these things before you start the calculations:

1) Accuracy of the flow meter indication

2) The flow meter density is configured as per the flow meter datasheet. Many times, the fuel designed for firing in the initial stages of plant design could be changed over the period (say LPG to natural gas), and appropriate changes are not made to correct the flow meter.

3) The gas burners are installed as per design & no modifications have been made over the lifetime.

4) There is no excess oxygen or high stack temperature in the heater.

 

Such a big difference (~50%), is quite unusual.