Boiler Efficiency

Effisiensi boiler dapat dihitung:

1. Direct Method
The direct method of determining boiler efficiency is also known as the “input-output” method. This is because it only needs the useful output, which is steam, and the heat input, which is fuel, in order to evaluate the efficiency. The efficiency is evaluated by using this formula where hg is the enthalpy of saturated steam and hf is the enthalpy of feed water.



Ket:
hg -the enthalpy of saturated steam in kcal/kg of steam
hf -the enthalpy of feed water in kcal/kg of water
Quantity of steam generated per hour (Q) in kg/hr
Quantity of fuel used per hour (q) in kg/hr
The working pressure (in kg/cm2(g)) and superheat temperature (oC), if any
The temperature of feed water (oC)
Type of fuel and gross calorific value of the fuel (GCV) in kcal/kg of fuel

Kelebihan dan kekurangan:
Advantages
- Quick evaluation
- Few parameters for computation
- Few monitoring instruments
- Easy to compare evaporation ratios with benchmark figures
Disadvantages
- No explanation of low efficiency
- Various losses not calculated

2. Indirect Method
This is also referred to as the heat loss method. The boiler efficiency can be calculated by subtracting the heat loss fractions from 100 as shown here. The principle losses that occur in a boiler are due to: Dry flue gas; evaporation of water and evaporation of moisture in fuel; moisture present in combustion air; unburnt fuel in fly ash; unburnt fuel in bottom ash, radiation and other unaccounted losses.



Ket:
i) Dry flue gas
ii) Evaporation of water formed due to H2 in fuel
iii) Evaporation of moisture in fuel
iv) Moisture present in combustion air
v) Unburnt fuel in fly ash
vi) Unburnt fuel in bottom ash
vii) Radiation and other unaccounted losses

Kelebihan dan Kekurangan
Advantages
- Complete mass and energy balance for each individual stream
- Makes it easier to identify options to improve boiler efficiency
Disadvantages
- Time consuming
- Requires lab facilities for analysis