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Which burner is better to burn wood chips or pellets ?
30.12.2020

Which burner is better to burn wood chips or pellets ?

Which burner to burn wood chips and pellets?

For the economical combustion of biomass, many burner and feeder solutions are now available. Producers of boilers for pellet and wood chips use various solutions, e.g. drawer feeders, screw feeders, screw feeders, etc. So which burner is the best for burning granulated and shredded biomass or wood chips ?

 The answer is not clear cut because it is impossible to create a perfect solution for every type of fuel and its granulation. Industrial burners, which can burn many different biomass granules, are much more expensive than domestic ones, and they achieve greater power and dimensions. Therefore, among others there is no offer of wood chip boilers below 25 kW - of course we are talking about a special dedicated wood chip boiler with a large capacious fuel basket. Types of boilers and burners for pellets and wood chips Two solutions are usually offered on the market - retort boilers (an obsolete solution, taken from coal combustion technology) and central heating boilers with a slot burner, where the biomass is usually fed through a screw feeder. Screw feeders or screw feeders have the main advantage in their precise operation - we can precisely control the dose of fuel, which cannot be done in a drawer or retort boiler. What's more, in boilers with a feeder and a slot burner we have heaters for firing up automatic fuel - thanks to which the device works on / off like a gas or oil boiler. Retort or drawer boilers usually have a manual ignition of fuel, which is fed continuously to keep the heat in the burner. It is an outdated solution that uses more fuel and energy.

 

Why is a slot burner so much better than a drawer burner?

Drawer feeders, mainly from fine coal boilers that are already banned in Poland, are an old solution that is highly imprecise in operation. We cannot control the fuel dose, we scrape wood chips or granules with a sliding drawer to the hearth. Therefore, it is an outdated and energy-intensive solution. They have long been replaced with stick burners and screw feeders. They have the ability to modulate the power, automatically extinguish and ignite, and provide a precise dose of fuel - which reduces the consumption of pellets and wood chips and, as a result, reduces the operating costs of the device.

 

How does a drawer or piston feeder work? The drawer or piston burner has a simple structure - on the principle of a fuel scraping piston, which is moved to the furnace. Such a structure, although simple, is not very effective: in many constructions the pistons stick or seize up. An undoubted disadvantage from a technical point of view is the inability to precisely adjust the fuel dose. The firebox in the form of grates will burn everything, it is multi-fuel, but its thermal efficiency is negligible - there is no automatic extinguishing and firing up, and you can forget about the efficiency of combustion. Therefore, it works on the principle of sustaining like traditional eco-pea coal retort boilers, we must constantly feed fuel and take care of its proper feeding. According to customers' opinions, the piston retort boiler meets their expectations only as an alternative to traditional dust and coal charging boilers. If someone has had experience with a modern pellet stove with an insertion burner, he will have a bad opinion about a piston stove and will not be satisfied with its use. Therefore, for more demanding experienced users, our company offers innovative burners for biomass: wood chips, pellets and agri-pellets.

 

Construction of a stepped grate burner is really solid

 The construction of the stepped movable burner is based on a screw feeder, through which we can precisely feed as much fuel as we need. The granules or chips are thrown - poured into the burner by a special top inlet and then fed by an additional screw - the so-called stoker to the burner head. It is made of heat-resistant steel and has a movable stepped hearth. Thanks to the sliding movement, it is cleaned of ash, i.e. it slags itself automatically. It works reliably and reliably thanks to the applied servomotors of the Swiss company Belimo. An additional screw feeder in the burner is important for proper combustion.

 

Why is an extra burner screw important?

 Additional screw inside burner supplies the fuel precisely - it increases the furnace efficiency and increases the combustion efficiency. In the case of wood chips, which have irregular shapes and a different fraction - this is crucial. Otherwise, fuel may get stuck in the burner, which can even lead to flashback and fire. Wood chips have much higher requirements in terms of feeding efficiency and combustion itself than pellets. If it is a dry wood chip with a fine fraction, its feeding and combustion is similar to sawdust. There is also industrial, contaminated, much cheaper wood chips on the market, but with a different fraction and moisture content - this requires specialized burners, and basically automatic units for burning comminuted biomass, because apart from the furnace, we must have an appropriate feeder with scrapers. The size of the fuel basket matters For the user, one of the basic operating parameters of the furnace is its autonomy - that is, the operating time without operation. When buying a rather expensive pellet heating device, customers expect at least a few days of work without service. The optimal autonomy time for a pellet heating system is one or two weeks. To ensure this, you need to select an appropriately capacious fuel basket. Many retort, piston or drawer boilers, due to the feeding technique, have very small baskets that are insufficient even for two days of operation of the furnace. By using a screw feeder, we can use a basket with increased fuel capacity and even connect a year-round external silo to the boiler. In a wood chip boiler room, many customers use a wood chip basket in a separate room. It is an optimal solution not only in terms of fire protection of the boiler room, but also allows the use of a larger basket, e.g. 3 or 5 m3. It should also be remembered that in the case of wood chips, access to the feeder is important, because we have to load it mechanically - often with a bulldozer or a forklift. Automatic central heating boilers with a pellet feeder are a modern and ecological source of heat.

 

Which one is better choose?

 

How to properly choose it is described in our guide. We also invite you to contact us by e-mail or telephone, we help our clients choose the optimal heating system for their needs. The use of pellets makes a lot of sense in the case of small home boiler rooms, in the case of higher power and large volumes - we recommend heating with wood chips or briquettes to our customers. Sawdust or straw briquettes are much cheaper than pellets - our boilers burn it fully automatically, just like pellets and wood chips. The cheapest heating fuel is wood chips, it can be obtained from many sources on your own - it is enough to rent or buy a chipper. There are also companies on the market that provide services for chipping materials at the customer. If you have your own biomass resources, rent a chipper will pay for itself in the first month of burning - wood chips from your own source are practically free, i.e. we can save up to several thousand euro a year in relation to pellets.

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