What is primary air and secondary air?

Asked By: Gene Traynor | Last Updated: 1st March, 2020
Category: home and garden indoor environmental quality
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What is Primary Air and Secondary Air? Definition. Primary air: Air supplied to the burner with the fuel that controls the rate of combustion as well as the amount of fuel that can be burned. Secondary: Air supplied to the combustion process that controls combustion efficiency; How completely the fuel is burned. Term.

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People also ask, what is primary and secondary air in boiler?

Primary air provides a percentage of the combustion air, but more importantly, controls the amount of fuel that can be burned. Secondary air improves combustion efficiency by promoting the fuel to burn completely. Power burners generally do not require secondary air.

Also, what are the symptoms of a shortage of primary air? A small hard blue flame or a flame blowing off the burner ports or lighting back at the burner orifice indicates too much primary air and the air shutter should be closed. A soft, blurred or yellow tipped flame indicates lack of primary air and the air shutter should be opened.

Just so, what is secondary air in a furnace?

secondary air. 1. Air which is introduced into a furnace (in addition to the primary air which enters either as a mixture with fuel or as blast underneath a stoker) above or around the flames to promote combustion.

What is excess air?

Excess air ensures that there is enough air for complete combustion. Excess air is expressed as a percentage of theoretical air required. Thus, 10% excess air indicates that 110% total air is being supplied. In boiler operation, excess air represents a heat loss.

39 Related Question Answers Found

What is the purpose of primary air?

Definition. Primary air: Air supplied to the burner with the fuel that controls the rate of combustion as well as the amount of fuel that can be burned. Secondary: Air supplied to the combustion process that controls combustion efficiency; How completely the fuel is burned.

What does a secondary air pump do?

What Does a Secondary Air Pump Do? The secondary air injection pump (also referred to as a smog pump or SAI pump) is responsible for lowering the number of carbon emissions that come out of the tailpipe of a vehicle. This is necessary since a vehicle engine is never 100% efficient in the combustion process.

How much air is required for combustion?

∴ Oxygen required from air for the complete combustion of fuel will be (2.66C + 8H + S – O) which can be written as 2.66C + 8 (H – O/8) + S, the term in the bracket being known as the available hydrogen.

What is primary air in HVAC?

Primary air is the main supply of air that mixes with the gas for the fire in the burners themselves. Secondary air is the air which flows around the outside of the burners and is not directly mixed with the gas in the burners. It is needed for combustion but mostly to allow draft to occur thru the furnace.

Why air is required for combustion?


There must be enough air in the combustion chamber for complete combustion to occur. The addition of excess air greatly lowers the formation of CO (carbon monoxide) by allowing CO to react with O2. The less CO remaining in the flue gas, the closer to complete combustion the reaction becomes.

What is SA fan?

Secondary Fans or SA Fans
The secondary fans (SA fans) play an important supporting role in power plants. The secondary fan allows for complete combustion of the fuel inside the furnace. As and when required the SA fan is used to increase the air flow to improve the efficiency and avoid wastage of fuel.

What is primary air fan?

Primary air fan is used to transport thepulverized coal from mills to the furnace area. So its main function is the carry the fuel to the furnace for the combustion. Whearas the FD fan provides the secondary air to the furnace area in the boiler where combustion takes place.

Is nitrogen needed for burning?

Nitrogen gas has strong triple bond between the two nitrogen atoms, it is almost inert. Nitrogen present 78% by volume in the atmosphere mainly inhibits the interaction of oxygen with substances present on the surface of the earth. So nitrogen gas no role to play in the burning.

What is primary air?

Definition of primary air. : air admitted to the fuel stream or area ahead of the combustion zone in a burner or furnace.

Why do we preheat the combustion of air?


For fuel-fired industrial heating processes, one of the most potent ways to improve efficiency and productivity is to preheat the combustion air going to the burners. The source of this heat energy is the exhaust gas stream, which leaves the process at elevated temperatures.

What is tertiary air?

Tertiary Air = Pre heated air comes in through air bars on the back of the stove, tertiary air is not controllable, but is there to inject more oxygen and air into the chamber to improve the efficiency as it is burning as well as providing the air for the secondary combustion, where the gases from the primary

Where does furnace draw air from?

In a traditional (80% efficiency) furnace, combustion air is drawn from inside the home. This is a poor choice for many reasons; it pulls in unconditioned outside air through cracks in windows, doors, and chimneys which causes issues with poor humidity and drafts.

What is combustion air?

Combustion air is the air that is used to actually burn the fuel. Without combustion air, which is normally forced into the furnace, combustion is impossible. Infiltration Air. Infiltration air is the outdoor air that is not deliberately in the boiler.

What is Windbox in boiler?

(The windbox is the area behind the burner throats that supplies combustion air to the burners.) On many boilers, air flow is the measured differential between the furnace inlet and the boiler outlet.

Where is secondary air induced into the burner?


Secondary air - Air which is introduced into a furnace (in addition to the primary air which enters either as a mixture with fuel or as blast underneath a stoker) above or around the flames to promote combustion.

Why excess air is required for the complete combustion of fuel?

Because the air and fuel cannot mix perfectly in a burner, excess air is needed to completely burn the fuel. Also, with the furnace or boiler firebox operating at a slightly negative gauge pressure, any leaks in the heater will suck air into firebox that doesn't go through the burners.

What is tertiary air in boiler?

The tertiary air is added to the WTE at a distance from the secondary air, in a boiler region of relatively lower temperatures. The SNCR additives are introduced to the WTE boiler proximate to the tertiary air.