Facts about combustion technology


Brief combustion technology

Briefly about combustion technology, chemical reactions during combustion and how flue gas analysis provides you with a good basis for optimal adjustment of your combustion plant.

Facts about flue gas

The purpose of combustion is to create the maximum amount of energy in relation to the fuel supplied. At the same time, the minimum amount of emissions in the form of nitrogen oxides, sulphur oxides, hydrocarbons, etc. must be produced.

In order to determine how well an incinerator works, it is necessary to analyze the gases formed and remaining after combustion, usually oxygen (O2) and/or carbon dioxide (CO2) and carbon monoxide (CO). By far the most common emissions measured are nitrogen oxides (NOx), but depending on the fuel and the plant, sulphur oxides (SOx) and hydrocarbons are also commonly measured.

Flue gas temperature is also important to measure as it is an important factor in calculating the efficiency of the plant and in avoiding condensation in chimneys.

The chemical reactions of combustion.

Combustion involves a large number of chemical reactions. The most important from an energy point of view is the reaction between the carbon in the fuel and the oxygen in the air, resulting in carbon dioxide in the flue gases. Also, depending on the fuel, the reaction between the hydrogen in the fuel and the oxygen in the air. In e.g. natural gas, the hydrogen content is quite high while it is relatively low in biofuels.

The issues

Combustion also produces some environmentally harmful emissions, the most common of which are nitrogen oxides (NOx). Which in normal combustion consists of approx. 95% NO and 5% NO2. These are normally formed at high combustion temperatures. Depending on the fuel and plant, different levels of sulphur oxides, hydrogen sulphide and hydrocarbons are also formed.

Combustion chemical reaction


The theoretically perfect combustion (stoichiometric) means that all the oxygen in the air is consumed during combustion and no oxygen, carbon or hydrogen remains in the flue gases.

Since the world of atoms is sparse, a larger number of oxygen atoms are needed in the supply air (excess air) than will be needed during combustion for all the carbon and hydrogen atoms to find an oxygen atom. To achieve optimal combustion, it is therefore important to mix fuel and air in the right proportions.

Too little air results in an incomplete combustion with high carbon monoxide values and possibly even a fire. soot formation as a result.

Too much air means that you are “burning for the crows”, i.e. the hot flue gases are not fully utilized in the heating system. In addition, combustion is reduced as the flame cools and the carbon monoxide content increases.

Combustion Combustion technology diagram

The flue gas analysis.

The only way to make an optimal adjustment of a combustion plant is to measure the different components of the flue gases with a flue gas meter. These basically have measuring cells to analyze oxygen (O2) and carbon monoxide (CO) and a sensor with a thermocouple to measure temperature. This configuration is sufficient to determine the combustion efficiency of the plant. For slightly larger boilers, the analysis of nitrogen oxides (NOx) is usually also required. For most instruments, an optional NO measuring cell is available. The larger instruments also have measurement cells for other emissions such as those in the atmosphere. sulphur oxide, hydrocarbon, hydrogen sulphide, etc.

The calculations

Most of the parameters used to determine the performance of an installation are calculated from the measured values, e.g. carbon dioxide (CO2), nitrogen oxides (NOx), efficiency, flue gas loss and excess air.

Combustion 320 measures flue gas analysis
Combustion 350 measures flue gas analysis

Flue gas measuring analysis instruments from Nordtec.

Measurement facts testo 300

Entry models

testo 300 Basic is a modern and competent flue gas meter that meets all the basic measurement requirements normally needed for smaller boilers. Measures O2, CO and temperature and calculates CO2, efficiency etc.

For testo 300

Measurement facts testo 330

Professional class

The testo 330 instruments can handle all basic measurement tasks and can also be selected with a NOx function. Many important features such as graphic display, measuring cells with almost double the lifespan, etc.

To testo 330

Measurement facts testo 350

Industrial class

The testo 340 and 350 instruments are primarily designed for larger industrial boilers, turbines and diesel engines where emissions are particularly important to analyze. They can also log measurement data over time.

For testo 350