Biomass as Fuel in Small Boilers (PDF 6.4 - APO Asian Productivity ...

4. PERFORMANCE EVALUATION OF BIOMASS BOILERS
The performance of boilers declines over time due to poor combustion, heat
transfer surface fouling, and poor operation and maintenance. Even for a new
boiler, deteriorating fuel quality, water quality, and other factors can result
in poor boiler performance. Boiler efficiency tests help us to determine the
deviation of a particular boiler’s efficiency from the highest level of efficiency
and to target problem areas for corrective action.
4.1 BOILER EFFICIENCY
The thermal efficiency of a boiler is defined as the percentage of heat input
that is effectively utilized to generate steam. There are two methods of
assessing boiler efficiency:
1. The Direct Method: Where the energy gain of the working fluid
(water and steam) is compared with the energy content of the boiler fuel.
2. The Indirect Method: Where the efficiency is the difference between
the losses and the energy input.
4.1.1 Direct method
This is also known as “input-output method” due to the fact that only the use
fuel output (steam) and the heat input (i.e. fuel) are required for evaluating
the efficiency.
η =
This efficiency can be evaluated using the formula Parameters to be
monitored for the calculation of boiler efficiency by direct method are:
• The temperature of feed water ( ºC);
Heat Output
Heat Input
• 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;
• Type of fuel and gross calorific value of the fuel (GCV) in kcal/kg of fuel,
Boiler efficiency(η) =
Q×(hg-hf)
q×GCV
×100
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