Test Your Knowledge: Boiler Efficiency

Boiler efficiency is less than 100% because of losses. For most boilers the most significant loss is known as what?

a) Shell loss
This is an incorrect response.
Shell losses (also known as Radiation and Convection Losses) are typically a minor loss component, often less than 1% of fuel input energy.

b) Blowdown loss
This is an incorrect response.
Blowdown losses are typically less than 2% of fuel input energy. It is good to note that blowdown losses can almost be eliminated with simple energy recovery measures.

c) Sootblowing loss

This is an incorrect response.
Sootblowing is used to dislodge ash and other solid materials from heat transfer surfaces of boilers. Sootblowers are typically only used when burning solid fuels and heavy fuel oils. This loss is commonly less than 1% of fuel input energy.

d) Oil heating loss
This is an incorrect response.
Heavy heating oils must be heated to allow proper flow through the burner system. Fuel oil heating is typically less than 1% of fuel input energy and the energy is not totally lost because the heating energy is input to the flame.

e) Stack loss
This is the correct response.
Stack loss characterizes the temperature and combustion aspects of the flue gas. Stack loss ranges between 8% and 25% of fuel input energy. This range is primarily dependent on the fuel type, combustion control characteristics, and heat recovery components of the boiler.

f) Unburned carbon loss, also known as Loss On Ignition (LOI).
This is an incorrect response.
Unburned carbon loss is typically a factor when burning fuels with significant amounts of ash. Most commonly this loss is less than 1% of fuel input energy.

g) Ash loss
This is an incorrect response.
Fuels containing ash (noncombustible material) present a loss associated with the ash removing heat from the boiler as the fuel enters the boiler at a relatively low temperature and the ash exits the boiler with a high temperature. The ash loss is typically less than 1% of fuel input energy.


Test Your Knowledge: Boiler Efficiency