Fuel gas consumption

[padovano]

I am writing my first end of month report as energy analyst in a small refinery. I have calculated the efficiency of the furnace of the hydrotreatment of naphtha using the formular which takes into consideration excess air and the temperature of flue gas leaving the stack. I would like to estimate the quantity of fuel gas which was consumed by the furnace as a result of excess oxygen which was not well regulated( design excess air is 15%,but during the month the average excess air was 25%)
Design Temperature of Flue gas is 320°C,Excess air is 15%.
At the end of the month of July flue gas temperature is 322°C and excess air is 25%.
The low heating value of fuel gas is 12500kcal/kg.
The heat absorbed by the process fluid is about 4Gkcal/h.
In my calculations, the design efficiency is 81% and the efficiency at the end of the month is 79.4%.
I obtained an excess of 8kg/h of fuel gas consumed by the furnace. I would guys to do some calculations so that I can verify my method to see if its good or not.

 

[25362]

Using the efficiency figures obtained by you:

If the heat absorbed is 4[×]10⁶ kcal/h, the "xs" fuel consumed per hour: 10⁶(4/0.794-4/0.81)[÷]12,500 = 7.96 kg/h.

Please note the heat absorbed is 4 Gcal/h, not Gkcal/h as written.

If it were 4 Tcal/h, then the resulting figure would have to be multiplied by 1000.

 

[padovano]

Thanks. Using my method I obtained similar results but I think your method is less complicated.
You are right, it is Gcal/h and not GKcal/h.