Flue Gas Waste Heat Boiler Thermal Efficiency Calculation

Boiler heat efficiency refers to the heat input into the boiler, most of which are absorbed by the boiler heating surface to produce water vapor, which is the heat that is effectively utilized, and the remaining heat is called heat loss. The heat efficiency of a flue gas waste heat boiler is the percentage of the effective heat in the heat injected into the fuel.

The anti-balance test method is usually used to measure boiler thermal efficiency.

The calculation formula for the thermal efficiency of the anti balance method: η= 100- (q2+q3+q4+q5+q6)

1. q2-flue gas heat loss
The exhaust heat loss is the heat loss caused by a part of the heat that is taken away by the smoke of the boiler. Its size is related to the amount of smoke, the smoke exhaust and the reference temperature and the sensible heat of the water vapor in the flue gas. q2 can be used as a simplified calculation formula: q2 = (3.55αpy +0.44) (tpy-t0) / 100
In the formula, αpy - exhaust air excess coefficient
tpy - exhaust gas temperature (℃)
t0 - reference temperature (° C)

2. chemical incomplete combustion heat loss q3
Chemical incomplete combustion heat loss is due to flue gas containing combustible gas CO, mainly affected by the fuel property, excess air coefficient, the temperature inside the furnace and air force condition and so on, can be calculated using the following empirical formula:
q3 = 0.032αpy + 100%
In the formula, αpy - exhaust air excess coefficient
CO - the percentage of carbon monoxide in dry flue gas (%)

3. Incomplete combustion heat loss q4
Incomplete combustion heat loss q4 is taken away by the boiler flue gas discharged fly ash and slag, depending on the nature of the fuel and the operating level of the operator, the simplified calculation formula is:
q4 = 337.27 × Aar × Cfh / [Qnet.ar × (100-Cfh)]
Aar – fuel sh content percentage (%)
Cfh - fly ash combustible content (%)
Qnet.ar - low calorific value (kJ / kg)

4. heat loss q5
The heat dissipation loss Q5 is the percentage of total heat input from the furnace wall and pipe to the surrounding environment in the boiler range. The formula is q5 = 5.82 × De0.62 / D
De - boiler rated load (t / h)
D - boiler actual load (t / h)

5. physical heat loss of slag q6