Information On The Workings Of Wood Pellet Burners
It is becoming more popular to use pellet burners such as boilers and stoves to generate heat and energy. So how do they work and why are pellets the ideal fuel for these automatic systems. Most pellet stoves, boiler and burners operate on a hopper system, which feeds a burn pot.
The pellets in the hopper are fed to the burn pot via an auger system. The auger system will be variable speed. The variable speed on the auger system is important to regulate temperature, and for adjustments on the different types of pellets. For increased temperature the auger will feed for longer. In many systems the auger will feed the burn pot every 30 seconds, how many seconds it feeds for is what can be adjusted to get more or less heat. The auger speed and timing also needs to be adjusted as not all pellets burn the same and generate the same amount of heat. Some pellets are denser and contain more energy; these pellets will be feed slower and less often into the burn pot than fast burning low energy pellets.
A consistent room temperature is clearly the objective, and so the stove must be flexible enough to reach that temperature with a range of different pellets. Most pellet stoves are controlled via a wall thermostat, and the stove will monitor its own temperature, actual and desired room temperature to make the necessary adjustments, for example auger feed rate and timing. Today some stoves can even be started by mobile phone. The owner on their way home can send a txt message to the stove and it will start up. This means by the time the owner gets home the house is up to temperature.
What makes fuel pellets ideal for stoves and boilers? The reasons are based around several qualities pellets have. Firstly pellets flow like a liquid, and so are ideal for hopper and auger feed systems. They have a uniform size and shape and so are less likely to cause issues in the auger. Wood chip boilers tend to have issues with oddly shaped chips every so often, which can block the auger. The second reason is pellets have a much higher density than unprocessed biomass such as wood chips, and increased density means increased combustion efficiency. Finally pellets have very low moisture content, generally below 10%, compared to between 30-50% for wood chip. Combustion efficiency is also achieved through low fuel moisture content. To summarise the features of pellets, it is their standardised form and features, which makes them more efficient, predictable and reliable in burning equipment. The small size, high energy content of pellets also means pellet burners can be a lot smaller than other types of biomass burners such as wood chip burners.
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