There is
a theoretical amount of fresh air that when mixed with a fixed amount of fuel, and burnt will result in perfect combustion
. In this situation all of the fuel will have been properly burnt and all of the oxygen in the air will have been consumed.
How do I control the excess air in my boiler?
Compensate air flow with Air temperature and pressure. Compensate fuel gas flow with fuel temperature and pressure. High and Low Fuel pressure override control to avoid furnace trip on low or high fuel pressure.
Minimum Air to fuel gas ratio
override control.
How do you calculate excess air in a boiler?
When the air/fuel ratio is optimized, the resulting energy savings usually ranges from 5% to >25%. For example, if the oxygen dry reading in flue gas is 2.5%, then the excess-air calculation would be:
0.895 x 0.025
/ (0.21-0.025) = 12.1% excess air. Too much excess air leads to lower flame temperature.
Why do we use excess air?
Excess air
increase the amount of oxygen to the combustion and the combustion of fuel
. The combustion efficiency increases with increased excess air – until the heat loss in the excess air is larger than the heat provided by more efficient combustion.
How do you reduce excess air?
The simplest method to reduce excess air of an atmospheric burner is
to damper (reduce) the combustion air flow rate to the point that CO emissions are near the upper limit acceptable for
flue gas emissions. This measure is suitable only if the burner operates at almost constant heat output.
What does excess air mean?
The percentage of excess air is
the amount of air above the stoichiometric requirement for complete combustion
. The excess oxygen is the amount of oxygen in the incoming air not used during combustion and is related to percentage excess air. For example, 15% excess air equals 3% oxygen while firing natural gas.
What is the percentage of excess air?
The amount of air in excess of the stoichiometric amount is called excess air. The amount of excess air is usually expressed in terms of the stoichiometric air as percent excess air or percent theoretical air. For example
150% = 1.5 × the theoretical air
.
What causes high CO in a boiler?
If the oxygen level is set too low and something changes the combustion process can become ‘fuel rich
‘ as there is insufficient oxygen for all the fuel to burn. This can cause high levels of CO to be generated and in the extreme enough fuel to enter the boilers flue and ignite (explode) outside the combustion chamber.
What is boiler efficiency?
Definition of Boiler Efficiency is “
The percentage of the total absorption heating value of outlet
.
steam in the total supply heating value
.” In other word, it is a rate how the boiler runs efficiently.
What is the stoichiometric air/fuel ratio?
The ideal (theoretical) air-fuel ratio, for a complete combustion, is called stoichiometric air-fuel ratio. For a gasoline (petrol) engine, the stoichiometric air-fuel ratio is around
14.7:1
. This means that, in order to burn completely 1 kg of fuel, we need 14.7 kg of air.
When a boiler furnace is operated with more air than fuel?
Even so-called “on-ratio” combustion, used in boilers and high temperature process furnaces incorporates a modest amount of excess air –
10 to 20% more than needed to burn the fuel completely
.
What is the purpose of excess combustion air quizlet?
What is the purpose of excess air in furnace combustion? Excess
air insures that all the gas is burned by making sure there is plenty of oxygen available.
How do I lower the temperature on my boiler stack?
Lowering stack temperatures may be as simple as
a day/night set back
. This lowers the operating pressure for steam boilers and the operating temperature for hydronic boilers when idling at night or mild days.
Why boiler combustors are provided with excess air?
Operating your boiler with an optimum amount of excess air will
minimize heat loss up the stack and improve combustion efficiency
. Combustion efficiency is a measure of how effectively the heat content of a fuel is transferred into usable heat.
How excess air control is critical for energy conservation of a boiler?
Low emission burners, excess air is
used to minimize NOx and carbon monoxide production by adjusting the flame temperature inside the burner
. Excess air finally absorbs some of the heat from combustion. As a result, this reduces the efficiency of transferring heat to water in the boiler.
