Three Ts of Combustion: Time, Turbulence and Temperature

The process of combustion is probably the most important process taking place inside the boiler. Through combustion, the energy contained within the fossil fuels is released and then used to generate steam or hot water as the process demands. The purpose of combustion is to release the heat from fuel and make it available for the further use. It is essential that the combustion is
  • Complete so that the complete amount of energy present in the fuel is utilised
  • Quick so that the required heat output is produced
In coal fired boilers or any boiler for that matter, efficiency of combustion plays an important role in determining the overall boiler efficiency. The combustion of fuel should be quick and complete.

The process of combustion is complex in nature and multiple parameters affect the combustion efficiency. Out of these several parameters, time, turbulence and temperature are referred to as 3 Ts of combustion. It is very important to control and optimise these 3 Ts to get maximum out of the combustion process.

1.    Time
When a fuel is being burned, it is important that sufficient time is available so that the fuel burns completely. 100% combustion means that the fuel is fully oxidized and full oxidation of the carbon, hydrogen and other combustible elements has taken place.

If fuel remains in the combustion zone for a time lesser than necessary, it will be partially burned which increases the un-burnt losses. On the other hand, if it remains for a time higher than the required, the power output of the boiler will drop as new fuel will not be able to come in and get burned. Ideally, the fuel should stay for a time sufficient for the complete combustion and then replaced by the fresh fuel. Thus, the time plays a very important role in determining the combustion efficiency.

2.    Turbulence
Oxygen makes an essential part of the process of combustion. While burning the fuel, it is essential that it is broken down in small particles. This increases the surface area of the fuel and ensures that sufficient air i.e. oxygen is made available. Turbulence ensures a thorough mixing of the air and the fuel. If turbulence is not maintained, certain part of the fuel will have excess oxygen available for the combustion while the remaining having too little. This will result in incomplete combustion of carbon forming carbon monoxide instead of carbon dioxide. If proper turbulence is not maintained, some part of the fuel will go out of the chimney without even getting oxidized. This will increase the un-burnt losses.

3.    Temperature
During the combustion, if the temperature is not sufficiently high, fuel will take some time to ignite thus increasing the time of the combustion. This will affect the heat output. Hence, it is very important to maintain correct temperature which ensures that fuel is quickly burnt releasing the complete energy.

As it can be seen, the 3 Ts discussed above impact the process of combustion and can significantly affect the efficiency if not monitored closely.