As discussed in the last few blogs, different types of biomass pellets produce different types and quantities of ash and clinker. Proper pellet burner maintenance is essential to efficient combustion and fuel efficiency. If the pellet burner is not cleaned to a sufficient standard, this can impact the combustion process and reduce efficiency, and result in higher levels of noxious gases, through inefficient combustion. Also if the rest of the burn chamber is not properly cleaned this can reduce the amount of useful heat that is extracted. For example in a pellet boiler if there is a large build up of deposits around the heat exchanger tube, this insulates the tubes and stops heat getting into the boiler. This means more fuel is used to get up to temperature.
Wood Pellet Maintenance
Wood pellets as discussed in earlier articles produce varying levels of ash depending on whether they are premium wood pellets or not. The ash percentage will vary between 0.5-3%, but the chance of sintering or clinker is very low. Some boilers and stoves have heat exchanger tube spring cleaners. The springs are positioned inside the heat exchanger tubes, and a mechanism lift and drops the springs to clean deposit built up. In some pellet burners this is manually carried out by the user, or in some systems is automated and can be set to clean at certain times. Some pellet burners are also water-jacketed, so making sure there is minimal deposit build up in the rest of the burn chamber is also important. Finally fly ash collects within the inside of the chimney, and if not maintained can effect combustion through poor ventilation of the combustion gases.
It is generally recommended that once a year several components should be removed and the burner should be given a thorough clean. This obviously should be carried out during the summer months when the burner isn’t required.
Straw Pellet Maintenance
Straw pellets create a higher ash content than wood pellets, but the same basic cleaning principles apply, however they need to be carried out more regularly. As stated in earlier articles burning straw pellets create clinkers and slag formation on the heat exchanger tubes. The clinker must be removed so that it does not affect combustion. Depending on the type of boiler and burn pot design this may be required every few hours, every 6-8 hours or every day or week. Another factor is slag build up in the heat exchanger tubes. Slag is similar to a clinker, where ash melting has formed a sold deposit to form. Unlike wood ash in the heat exchanger tubes, slag is a hard despot that needs to scraped off. Cleaning springs may not be suitable to remove slag deposits, as they may not provide sufficient force.
Therefore maintenance for straw pellets is more frequent and labour intensive compared to burning wood pellets. However there are sufficient cost incentives and other benefits.
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