# How to calculate heat loss due to dry flue gas?

Calculating percentage loss of heat due to dry flue gas for determining the boiler efficiency.

## Calculation of % Heat Loss Due to Dry Flue Gas

Heat loss due to dry flue gas is defined as the loss due to gases such as CO2, O2 and N2.The losses occured by these gases in the combustion process is also one of the factor that affects the boiler efficiency. This loss is considered as one of the highest loss in the boiler. Below given the formula to calculate the heat loss due to the dry flue gases. Formula:
L1 = {m x Cp x (Tf - Ta) / GCV of fuel} x 100
Where,
L1 = % Heat loss due to dry flue gas
m = Mass of dry flue gas in kg/kg of fuel
= Combustion products from fuel: CO2 +SO2+ Nitrogen in fuel + Nitrogen in the actual mass of air supplied + O2 in flue gas.
(H2O/Water vapour in the flue gas should not be considered)
Cp = Specific heat of flue gas in kCal/kg
Tp = Flue gas temperature in oC
Tp = Ambient temperature in oC
GCV of fuel = Gross Calorific value of a fuel
Total mass of flue gas (m)/kg of fuel = mass of actual air supplied/kg of fuel + 1 kg of fuel Let us consider an example, on how to calculate the heat loss due to dry flue gas.
Step 1:
Given that,
Total Mass of dry flue gas = 20 kg / kg of oil
Specific heat of flue gas = 0.20 kCal/kg
Flue gas temperature in = 200oC
Ambient temperature in = 25oC
GCV of fuel = 13000 Step 2: Applying the values in the formula,
L1 = {m x Cp x (Tf - Ta) / GCV of fuel} x 100
L1 = {20 x 0.20 x (200 - 25) / 13000} x 100
L1 = 5.38% Result:% Heat loss due to dry flue gas L1 = 5.38% 