What Are the By-Products of Combustion?

There are three major elements to combustion:

A fuel source
A supply of oxygen
A source of heat or ignition

Let’s talk about how these elements work together to create combustion.

Fuel: Natural Gas and Methane

One of the most popular fuel sources for combustion in heating homes, commercial buildings, institutional buildings, and industrial processes in the United States is natural gas.

Natural gas is mostly composed of methane (CH₄), which typically makes up 84% of natural gas composition. Natural gas also contains ethane, butane, propane, and some additional trace elements, but largely it is the methane that makes up the fuel potential in natural gas.

Oxygen: in the Air we Breathe

The air we breathe contains approximately 78% nitrogen (N), 21% oxygen (O₂), and other trace gases. Mixing air with gas in a controlled environment helps us achieve safe, reliable, and efficient combustion in a predictable manner.

Complete vs. Incomplete Combustion

Complete combustion is the complete oxidation of fuel. When methane (CH₄) mixed with the proper amount of oxygen (O₂) undergoes complete combustion, it produces carbon dioxide (CO₂) and water (H₂O) vapor. This is the most efficient form of combustion, and the most environmentally friendly.

Rich combustion involves the partial oxidation of a fuel when insufficient air is available for complete combustion. This is less efficient, and partial oxidation of methane produces carbon (C) & carbon monoxide (CO) instead of carbon dioxide. Unburned carbon fouls boilers and combustion systems, and carbon monoxide is a poisonous and dangerous gas.

Lean combustion involves mixing too much air with fuel. This excess air reduces heat transfer in boilers, reducing efficiency. The excess air also contains Nitrogen (N) that can bond to the excess O2 in the exhaust, and under high temperatures forms Nitrogen Oxides (NOx) which are greenhouse gases and can endanger the ozone layer.

The By-Products of Combustion

Water vapor is a harmless by-product of complete combustion. Carbon dioxide is considered a greenhouse gas but can partially be absorbed by plants as a normal part of the biological carbon cycle.

Carbon monoxide is an air pollutant and is toxic to the human body. It’s called the “silent killer” because it’s colorless, odorless, tasteless.

Carbon monoxide is often produced by poorly maintained equipment, which is why it’s important to have burners regularly serviced.

Nitrogen Oxides are greenhouse gases which are formed by excess air and nitrogen bonding under high temperatures during the combustion process.

The negative effects of poor combustion can be limited by improving combustion through proper tuning and regular equipment maintenance. Burner and boiler preventative maintenance (PM) programs involve periodic inspections and adjustments to insure equipment is running more safely, efficiently, and cleanly.