Technology and function with pellet heat!

Pellet burner
You can describe today's technology of pellet burners being generally divided into three different categories based upon their method of operation. The three different types of burners are known as under fed, horizontal fed and vertical fed. An under fed burner often has rotary arm feeders (with a small internal storage) and a built-in dosage auger fitted inside the burner unit. The same method also goes for the horizontal pellet fed burner. Finally with the vertical pellet fed solution the burner has a fall shaft and the fuel is dosed directly via an external auger.
Under fed function Horizontal fed function Over fed function
Under fed technology
As shown on the picture to the right, the BioLine20 burner from EcoTec is a typical example of an under fed burner. The burner takes in the pellet fuel from an external auger that drops down the fuel to the lock on the burner. The lock wheel and its valves then dose the pellets further down to the internal feed auger. Here the fuel is fed via the internal auger with even feeding intervals and is then fed up into the burner cup and combusted. Regular cleaning of heating surfaces should be performed and the burner cup should also be cleaned from ash residues created by the combustion. The burner ignites the fuel automatically via a hot-air heater. This construction of burner requires space above the burner cup so that the flame does not reach the ceiling within the hearth.
Horizontal fed technology
PellEco 2000 is a typical horizontal fed burner. The burner has an internal storage dosed by an external auger. Within the bottom of the internal storage a rotary arm feeder handles the dosage to the internal auger via a fall shaft. The fuel is then fed forward to the burner cup. This burner does not have an electronic ignition but is simply lit with fire-lighting fluid to start the combustion. This construction of burner requires space above the burner cup, so that the flame does not reach the ceiling within the hearth. There are flame pointers so that the flame can be directed forward if needed. The burner has been tested with bark pellets and handles that well, since it more or less works as a stoker fed burner. This opens up new ways for a wider variety of fuel options.
Over fed technology
As an example shown to the right, we have the PX21 burner from Ariterm which functions very well as an over fed pellet burner. The dosage is made via an external auger and therefore the burner, other than that, does not have any other moveable parts other than the fan. When the boiler calls for heat via its own temperature regulator separate from the burner, the burner is then first dosed with a so called start up dose. After that the fuel is ignited via a hot-air heater, in co-operation with the fan. During the heating up phase the burner is dosed with a smaller amount of fuel that then changes during full operation. When the desired temperature of the boiler has been reached, the fuel feeding is then automatically disconnected and only the fan then runs for a couple of minutes so that the fuel is fully combusted and the greater part of the ash is then blown out into the hearth. The burner operates with start and stop function and does not have a continuous fire. Instead it can be compared with the operation of an oil burner. The burner requires cleaning once a week to be cleaned from ash residues within the burner pipe.
1.Fall pipe
2.Hearth pipe
3.Terminals
4.Electronical steering
5.Combustion air fan
6.Hot-air ignition
Fuel dosage
Burner constructions which have an internal storage are not so sensitive and dependent on an even dosage of the fuel from the external auger to the burner. As a result, they then require less maintenance and can be fired longer periods. The fuel is being fed to the internal storage and by batch feeding and via the fall shaft the burner is then being dosed with an internal auger that gives a more exact dosage to achieve a more even combustion. Burners with a vertical fall shaft being dosed with the external auger are more dependent upon a more frequent cleaning with for example, weekly storage of fuel. The external auger pipe should be cleaned approximately one to two times per year, to achieve an even dosage. Please note that cleaning of storage and feeding augers should be made continuously and frequently regardless of dosage rates to keep a problem free heating system. All bulk storages should be cleaned before every filling, to remove chip residues that could cause arching problems and internal wear of the augers.
Ignition function
If looking at the ignition function of the burners, it varies depending on what technology the burners is being operated with. The ignition of the burners, on most products, takes place with the help of a so called ignition element that could be compared to a kettle element with an encapsulated resistance wire that is generally being heated up for a few minutes for combustion of the fuel to occur. At the same time a fan blows out hot air towards the fuel which is then finally ignited. The life cycle on these products varies between 1.5 to 5 years, depending on the amount of use. Some burner brands need to be ignited manually with a drop of fire-lighting fluid that then starts a flame and produces a so called maintenance fire (such as that of a pilot light in a typical gas central heating system). The control system within the burner then takes over and with even intervals automatically feeds in pellets and adds oxygen via the fan. Please note that you should be observant that the maintenance fire is not recommended when firing with an accumulator tank, as this can cause an unnecessary amount of soot build up during the summer. This is caused by an increase in drafty conditions which often increase during warmer outdoor temperatures. Due to this fact a burner with an automatic ignition can be viewed as an advantage. The advantage with the maintenance fire however is that when using a lot of hot water within a house, this function then gives a faster effect and keeps the temperature of the boiler more constant and balanced. Since burners with ignition elements require time before the pellets have been ignited, this therefore can cause the temperature of the boiler to sink to a lower level before it stabilizes.
Ash handling
Ash handling varies a lot between different burner brands. As an example, BioNordic's B16GL has solved the ash build up problem by using compressed air. Here there are two nozzles on the bottom of the fuel cup that go in and blow the burner clean before start-up. These nozzles are shaped so that they cut off slag residues and ash like air deposits. In effect this burner then also becomes less sensitive to bark pellets and peat pellets, which produce a substantially larger amount of ash. Ulma AB has chosen a stick sweeping method on their burner, the ULMA 2000. Via their burner system you can easily, when needed, turn a wheel to the left and bring the scraper back, turn it down again and push the scraper forward and clean the burner pipe from ash. This scraper also acts as a pellet brake so that the pellets stay in the combustion pipe.
Pellet stoves
The pellet stove is built to be a primary heat source i.e. to be responsible for the main part of the heat demand of a house. It works fully automatically with a room thermostat and in best cases only needs to be filled one to two times per week, depending on the model and heat demand. The stoves spread heat via an integrated fan system, or water jacketed models which can also be connected to the existing radiator system within the house. It is relatively easy to install since it can be installed to simple gas flues and at the same time it is a simple construction that does not require any load bearing foundations. Security against back fire is a typical fire prevention system within pellet stoves and in Sweden these fulfill the security measures required by the Swedish P-marking. A pellet stove can easily replace at least 70-80 % of the electric heating demand within a normal sized house and operates at its best when set against the lowest outdoor temperature. At the same time it is a very nice looking piece of furniture that spreads well-being and good comfort to your house. A pellet stove needs 50-60 watts of electricity (similar to that of a light-bulb) to work. With a simple convertor from 12V to 230V a pellet stove could work problem free for several days using an ordinary car battery. Thus, this can also provide a welcome security for home-owners during unforeseen power cuts.

Example of the function of a pellet stove
The pellet stoves can in most cases be delivered with different designs to fit within your home environment. The stoves are encased with everything from marble, coloured metal sheet and soapstone etc. The stove can as a suggestion, be placed centrally within the house. By doing so, the heat it produces can then effectively spread further to other rooms within the house. If you keep the doors open the temperature normally does not differ more than two degrees between the rooms and it works at its best in a house with open planning. This mostly applies to stoves which spread heat via integrated fan systems.
Pellet boilers
Integrated pellet boilers operate with a high efficiency. Both the burner and boiler are assembled together to create one unit. The pellet boiler is like a traditional boiler where you have built in a pellet burner inside the actual boiler. This is normally the best technology since the parts are designed and adjusted right from the start to work effectively together. Since an integrated pellet boiler and burner is specifically adjusted to the fuel you are using, they normally reach a better performance than when you put a burner into an existing boiler that is a couple of years old for example. As an example, below we can see the function of the integrated pellet boiler and burner called Bionet.
Example of one of Ariterm's pellet systems - complete from storage to boiler/burner.
Inside Ariterm's Bionet a compact pellet boiler has been combined with a BeQuem pellet burner to create a reliable and efficient unit. Comfort, environmental performance and efficiency are produced to the highest degree imaginable to meet the requirements of the user and create efficient pellet combustion. The Bionet has a standing convection system which makes the boiler able to keep a high efficiency between service intervals. The service requirement depends on the pellet quailty being used and the selected effect (fuel consumption), which varies between seasons. It is the same when it comes to the maintenance requirement of the burner. The 20 litre ash box is of a good size and is easy to take out and empty.
Adjust automatics
For pellet combustion, there are now automatic controls which make it possible to adjust the effect in up to 3 steps. Within the display of the automatics, you can get information about the operating status of the boiler, such as boiler temperature, flue-gas temperature, pellet consumption, pellet storage, alarm function etc.
Many-sided additional heat
An additional advantage of the Bionet boiler and burner is that it can be adjusted to be integrated into an existing waterbourne heating system. Bionet is easily to handle and an economic choice when used in combination with a modern oil boiler, wood boiler, heat pump or solar energy system. The effect of 12 kW is enough for most house systems. For hot water production, the Bionet is connected to a separate water heater. The compact dimension of the Bionet also makes installation even possible in narrow spaces.

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AFAB (UK) Ltd
9, Strand
Teignmouth
Devon
TQ14 8BW
United Kingdom

Phone: +44 777 3316 994