BURNER FOR PELLETS The present invention relates to a burner for pellets, which includes - an essentially horizontal combustion head, which can be installed in an opening in the wall of the firebox and which includes a combustion pipe and a surrounding jacket together with the jacket space between them, and in which the combustion pipe has perforations in the area of the jacket space, and a flange surrounding the combustion head, which is set to cover the said opening in the firebox wall, and - a pressure chamber pressurized by a fan and located outside of the flange when viewed from the firebox, and which is connected to the said jacket space, in order to lead air to the combustion pipe through the jacket space and the perforations, and a feed channel connected to the front end of the combustion pipe and led in from above, for leading pellets to the combustion pipe by gravity, and a front wall to the combustion pipe, with openings located in it, for leading air from the pressure chamber to the front end of the combustion pipe.

A pellet is an about 8-mm thick pressed piece of cutter chips or wood sanding dust, compressed at high pressure, which can be used as fuel. No additives are used in a pellet. In this case, the term pellet must be understood more generally as coarse granular solid fuel.

The operating environment of a pellet burner series is energy production. A pellet burner is intended to produce heat in detached houses and in larger buildings, as well as in district-heating plants. Patent publications US 5070798, US 5269233, and WO 01/22003 disclose various burners for pellets.

Generally, these have a feed screw, or some other mechanical

feed device, for feeding pellets to the combustion end of the burner, which protrudes deeply into the firebox. However, such a feed device is in danger of leading the combustion backwards.

In addition, the mechanisms are so complex that they are not economically viable in the low output range (output range 0- 20 kW).

Publication WO 00/75563 discloses a pellet burner construction that is simpler that the above, and which is also intended to achieve better combustion than previously. In this, the fuel is dropped down a relatively high pipe to the combustion pipe, the lower part of which forms, a flange structure. Air is blown from the flange to the ignition core through angled gaps in the base plate. In such a burner, the combustion head is always limited in length, to allow sufficient space to remain in the firebox between the combustion head and the opposite wall. The fuel feed pipe is completely airtight, but the slanting structure leads to fuel unavoidably remaining in the lower part of the pipe, where its combustion heats the front part of the burner unnecessarily. This leads to a danger of back combustion.

The invention is intended to create a burner for pellets that is simpler than before, which nevertheless is highly efficient and in which the drawbacks are avoided. The characteristic features of the invention are stated in the accompanying Claim 1. In this case, the combustion head can be relatively long, as its front part extends outside the flange. According to one embodiment, the pipe acting as the feed channel is cooled by air fed from the pressure chamber, which is directed to the area of an internal cone in the pipe. This keeps the fuel feed pipe cold. In one embodiment, the front wall of the combustion pipe slants and the feed channel connection in the combustion pipe is above this.

Other embodiments and advantages of the invention are examined later in connection with the example of an application.

The product that has been developed differs from burners already on the market and those disclosed in the above publica- tions. The burner differs from other products by its simpler construction and new innovations in combustion technique. The design has also been largely motivated by production-friendli- ness.

The accompanying figures show one burner for pellets according to the invention: Figure 1 shows a side view of the burner in partial cross- section, Figure 2 shows an axonometric view of the main components of the burner, with the protective jacket removed, Figure 3 shows a top view of the main components of the burner, without the drop pipe, Figure 4 shows an exploded view of the main components of the burner, Figure 5 shows the burner with the casing removed, Figure 6a shows the cylindrical blank of the combustion pipe component, Figure 6b shows the blank of the front wall of the combustion pipe.

In Figures 1-3, the component markings are as follows: 10 combustion head, 18 combustion pipe, front wall 11, jacket 14, jacket space 15, flange 16, casing 12, pressure chamber 13, fuel feed channel 17 (including the drop pipe 37, cone 42, and upper pipe 40), fan 20, photosensor 34, switchgear 22, electri- cal connection card 24, protective jacket 26, and quick-release clamps 50.

In the burner, there is an attachment frame A, which mainly includes the jacket 14 and the flange 16. The burner is attached to the wall of the boiler by the flange 16, to which the body component B is attached using the quick-release clamps 50. In Figure 4, the electrical components and fan are detached

from the casing 12 that mainly forms the pressure chamber while the body component C includes the combustion pipe 18, the body flange 16', and the drop pipe 37 with its flange 36. The casing 12 can be placed in this by first passing the upper end of the pipe 37 through the upper opening in the casing 12, so that the casing 12 can be set against the body flange 16'and secured to it.

With reference to Figure 1, the fuel drops from the pipe 37 of the feed channel 17 against the sloping front wall 11 of the combustion pipe 17, where there is an inverted V-shaped divider 30, which divides the flow evenly. It also protects the opening 32, which the photo-resistor 34 monitors in the fan : duct, remaining between the branches of the V. The combustion pipe 18 is extended outwards from the plane of the flange 16 by 10-40 %, preferably 15-30 % of its volume. Thus more space is left in the firebox for the flame and the fuel feed pipe can be brought vertically into the combustion pipe.

Primary air is led through the openings 19 of the lower part of the combustion pipe 18 and the lower perforations 19"of the front wall 11 (Figure 5), as well as from the feed-channel 17 drop pipe 37 (holes 38). Secondary air is fed through the perforations 19'in the rear end of the combustion pipe. The primary-air feed is so effective that it carries all the burned material away. Despite the relatively large amount of primary air, the construction of the burner achieves a high efficiency.

Figure 6a shows the plate blank 11'of the front wall of the combustion pipe. The broken lines show where bends are made.

There is an opening 30'for the divider, and a hole 30 for the flame sensor. In the lower part, there is an opening 18'for the electrical igniter and perforations 19"for the combustion air.

Figure 6b show the plate blank 18'of the combustion pipe. It has ready-made perforations 19 and 19"and an opening for the drop pipe.

The burner is designed in such a way that the burner can be used in boilers fired with any kind of solid fuel. This is a horizontal model (the flame is directed horizontally). The ignition system is electronically controlled, so that rapid gasification and ignition is achieved (hot air rapidly reaches the pellets). The combustion automation includes stepless pellet feed dosing and stepless regulation of the amount of air.

The device is intended for the combustion of wood pellets. The burner is controlled with a microprocessor. When the external thermostat. gives an impulse to start the burner, the feed of pellets to the combustion head 10 starts along the feed channel 17. The pellets fall onto the divider 30, from where they flow evenly to form a layer on the lower surface of the combustion pipe 18. The pellets are ignited with the aid of an ignition resistance 28, which is located close to the lower surface of the combustion pipe 18. Simultaneously with ignition, air is blown into the pellets with the aid of the fan 14. The blast is directed into the jacket space 15 surrounding the combustion pipe 18, from where it flows through the perforations 19 of the combustion pipe 18 into the combustion pipe and, as well, to the feed pipe with the aid of openings 38 in the lower part of the pipe 37, in order to prevent back combustion. A photo- resistor monitors the combustion process. If combustion slows, and the amount of light decreases, the photo-resistor sends a signal to the processor, which sends a feed signal to the pellet-feed system.

Combustion air is blown to the combustion head from holes, which are in the lower part of the combustion head and in the lower end of the drop pipe. When the desired temperate is

reached, the thermostat shuts off the burner in a controlled manner.

Part of the combustion pipe is outside of the firebox in order to achieve a sufficiently large combustion space for the pellets and for there still to be space for the flame in the boiler.

The slant in the front wall of the combustion pipe and in the divider element makes the pellets spread evenly. The divider also prevents the pellets from entering the pressure chamber, from the opening made for the photoelectric eye. Overheating of the drop pipe is prevented by the conical component in the lower part of the pellet drop pipe and the air fed around it.

When air is blown from the pressure chamber from the perforated drop pipe into the space between the drop pipe and the cone, it causes a vacuum in the drop pipe and an airflow from the drop pipe towards the firebox.

The device is designed in such a way that its output range of 0... 20 kW can be fully utilized and the device shuts down completely if heating output is not required.

Gasification takes place in the upper air, which means that ash does not remain to block the air holes or to accumulate in the combustion pipe. The amount of combustion air is great and the amount of secondary air is less.'