EP1384031B1

EP1384031B1 - Burner for pellets

Info

Publication number: EP1384031B1
Application number: EP02706819A
Authority: EP
Inventors: Markku Muli
Original assignee: HT Engineering Ltd Oy
Current assignee: HT Engineering Ltd Oy
Priority date: 2001-03-29
Filing date: 2002-03-27
Publication date: 2006-03-01
Anticipated expiration: 2022-03-27
Also published as: FI20015036A; EP1384031A1; ATE319043T1; DE60209468D1; FI20015036A0; WO2002079693A1

Abstract

The invention relates to a burner (10) intended for burning a solid fuel, particularly pellets. The burner (10) is intended to be installed in a wall opening of a boiler and its firebox (35) is arranged to form at least a firebox (35) from at least partly delimiting wall constructions (13.1, 13.2, 19, 36) and from hollow grate tubes (11), which are arranged parallel to each other and at a distance to each other, for burning fuel on them in a controlled manner. The burner (10) also includes means (16, 17, 20) for feeding primary air, secondary air, and fuel into the firebox (35). The wall constructions include, at least at the sides of the covered firebox (35), side walls (13.1, 13.2), which are arranged to be essentially encased and to bring secondary air to the firebox (35) through perforations (14) arranged in the casing construction (13.1, 13.2). Primary air is arranged to be brought through the said grate tubes (11) to the ash-collection space (39) beneath them and to then be led to the firebox (35) between the grate tubes (11) and through a perforated front plate (12) arranged in front of the grate tubes (11).

Description

The present invention relates to a burner intended for burning a solid fuel, particularly pellets, which is intended to be installed in a wall opening of a boiler, and the firebox of which is arranged to be formed from at least

wall constructions that at least to some extent delimit the firebox and
hollow grate tubes, which are arranged parallel and at a distance to each other in order to burn the fuel in a controlled manner on top of them,

A burner intended for burning a solid fuel, particularly pellets, is known from Finnish patent application 19992050 and WO application PCT/FI00/00811. In this burner, the grate is formed from adjacent tubes, which are moved backwards and forwards axially. Primary air is introduced to the burning fuel from beneath and between the tubes, while secondary air is introduced to the firebox through the tubes.
Another burner equipped with a tube grate is known from Swedish patent application SE 9702990.
Yet another burner for combusting pallets is known from document US-A-5 070 798.
In the known burners for pellets, the heating of the walls of the firebox reduces the durability of the wall, thermal expansion causing buckling and, in the worst case, results in the wall constructions being burned through while the burner is otherwise still entirely suitable for use.
Further, the heating of the grate structures essentially weakens its durability. Ash that collects in and adheres to the grate and other combustion waste can be difficult to remove, due to the complicated construction of existing burners.
The fireboxes of burners according to the prior art have a construction that is, for example, tubular, with only one end open, or with the upper part fully open over its entire length. In boilers for small heating applications, for example, it is extremely difficult to fit burners that are open at only the end and to create a highly efficient heating effect, because such boilers, both those already installed and new ones, generally have a rather small size, so that their heat transfer surfaces are arranged in the boiler section in such a way that known types of burner construction do not give the best possible heating output.
On the other hand, in solutions in which the upper part of the firebox is left entirely open combustion is unstable, due to the air-feed directions that can be used in them.
In burners according to the prior art, the air feed is generally handled a single blower. This makes it difficult to operate the burner economically, especially in summer, when it would be advantageous to adjust the output of the burner to suit the desired output.
Thus, the known burners for pellets are quite complex in construction and operation while numerous unresolved problems relate to their operation, applicability, and durability.
The present invention is intended to create a new type of burner for pellets, which is essentially simpler, more durable, more applicable, and more reliable in operation. The characteristic features of the burner for pellets according to the invention are stated in Claim 1.
With the aid of the burner according to the invention, durability is substantially improved, by means of the new burner's manner of feeding air and its cleanability by means of the removable grate construction. In addition, the applicability of the burner to small heating boilers is also significantly improved, because the construction of its firebox also takes into account the geometrical characteristics and limitations of small boilers. Further, the new type of air feed creates considerably more stable combustion conditions than in the burner solutions according to the pior art.
The possibilities of regulating the burner for pellets according to the invention are improved substantially, thus permitting, for example, the use of a smaller loading during summer operation.
The other characteristic features of the burner for pellets according to the invention appear in the accompanying Claims while other advantages achieved with the aid of the invention are stated in greater detail in the description section.
The burner for pellets according to the invention, is described with reference to the accompanying drawings, in which

Figure 1: shows the burner for pellets according to the invention, seen at an angle from above,
Figure 2: shows the burner for pellets according to the invention, seen from straight in front,
Figure 3: shows a side view of the burner for pellets according to the invention,
Figure 4: shows a front view of the rear plate of the firebox of the burner for pellets according to the invention,
Figure 5: shows a cross-sectional side view of the burner for pellets according to the invention, and
Figure 6: shows a cross-sectional top view of the burner for pellets according to the invention.

Figures 1 and 2 show the burner 10 intended for burning a solid fuel, particularly pellets, which is the subject of the invention. The burner 10 for pellets is installed by pushing it by its front part 34 into the wall opening (not shown) of the boiler, so that the flange 15 remains outside the wall opening of the boiler. The walls of the firebox 35 of the burner 10 are formed, according to the invention, from a casing construction, which is formed by the enclosed side walls 13.1, 13.2 of the firebox and an enclosed cover part 36 between them. The firebox 35 is bounded by a rear wall 19, which is at the opposite side to the front part 34.
The essential element in the casing construction according to the invention is the perforations arranged in its inner side, which are preferably holes. The holes 14, 24, 25, which have a diameter of 3 - 15 mm, preferably 5 - 12 mm, are in the side walls 13.1, 13.2, in the upper cover part 36, and in the rear wall 19.
A secondary-air blower 17 blows air, through a duct 44 (Figure 5) arranged in the casing 31 behind the rear wall 19 of the firebox 35, into the said casing constructions, i.e. into the sidewalls 13.1, 13.2 and the cover part 36, as well as into the casing 43 behind the rear wall, and from there into the firebox 35 from the holes 14, 24, and 25 arranged in them. By means of this flow of air, the side walls 13.1, 13.2, and the cover part 36 are cooled, while the secondary air being lead into the firebox 35 is simultaneously heated. The cooling effect created substantially improves the durability of the casing constructions of the firebox 35. A primary blower 16 is also arranged in the rear part of the burner 10.
A grate component, which includes hollow grate tubes 11, which are set parallel to and at a distance to each other, for burning the fuel in a controlled manner on them, are located in the firebox 35 in the space bounded by the side walls 13.1, 13.2, and the rear wall 19. Further, the grate component includes a front plate 12 perforated with holes 42, arranged in front of the grate tubes 11 before the boiler section, and an air baffle 37 (Figure 5) beneath them.
A connection 21 is made in the rear wall 19 of the burner 10, to which the fuel-feed duct 41 (Figure 5) is connected, inside of which the fuel is fed by means of the burner screw 20 onto the tubes 11 of the grate component of the firebox 35, according to a selected combustion program. The fuel is led to the duct 41 by a transfer pipe 18. For example, once the desired temperature is achieved in the boiler, the fuel feed stops and the fuel in the burner 10 is burned completely. When the temperature drops below a set value, the burner 10 automatically restarts. The fuel-feed system is protected from a fire starting backwards by means of a thermostatic extinguishing device, which is connected, for example, to the water mains network (not shown).
In the rear wall 19 of the burner 10 there is an opening 23, through which it is possible to arrange, for example, a flame guard for the firebox 35 using photocell monitoring, and an opening for example for a glow igniter 22, by means of which the fuel is ignited in a known manner.
Figures 3 and 5 show a side view of the burner 10 according to the invention. The side walls 13.1, 13.2 of the casing constructions of the firebox 35 are arranged in such a way that the lower part of the casing construction of the firebox 35 extends substantially further than the upper part into the boiler section. The cover part 36, which partly covers the firebox 35, extends over the insulation and material thickness of the wall construction 45 of the boiler section, so that the firebox 35 opens free directly from its upper part into the boiler section. Such a semi-open cover construction 36 permits the burner 10 to be advantageously used in conventional small boilers too, in which case the output produced in the firebox 35 is directed substantially better to the heat transfer surfaces of the boiler than in burners according to the prior art.
In addition, by means of the semi-open cover part 36, a considerably more stable combustion process is achieved than when using burners according to the prior art. By means of the cover part 36, advantageously precisely that area of the firebox 35 in which the fuel feed is arranged to take place is covered and the secondary air is fed through it. Further, the opening angle of the encased cover part 36 is preferably made with small boilers in mind, so that the secondary air feed is advantageously directed towards the boiler section.
Figure 4 shows the rear wall 19 of the firebox 35. Connections 38 are made to the grate tubes 11 in the rear wall 19, so that the grate component 11, 12 can be easily detached for the cleaning of the ash collection space 3.9 (Figure 5) and for changing the grate component 11, 12. According to Figure 5, at the opposite end to the rear wall 19 the grate tubes 11 are attached to the front plate 12 and the air baffle 37. On the boiler section side of the front part 34 of the burner 10 there is a grate support 40, which supports the front plate 12 horizontally, thus permitting the grate component 11, 12 to be easily removed and set in place.
Separate blowers 16, 17 are arranged in the firebox 35 for feeding primary air and secondary air, the air amount of which is regulated by means of the air chokers (not shown) once during the installation of the burner 10. The secondary-air blower 17 blows air into the firebox 35 at the deepest cross-section of Figure 5 and through the duct construction 44 connected to the casing constructions 13.1, 13.2, 19, 36 shown in Figure 6, the duct being set in the burner at a location corresponding to that of the primary-air blower 16.
The air blown by the primary-air blower 16 into the primary-air duct 46 travels to the lower part of the burner 10 and further from the connections 38 (Figure 4) through the grate tubes 11 to the front part 34 of the firebox 35 beneath the front plate 12 and from there under the tubes 11 to the ash-collection space 39 (Figure 5), so that the air enters the firebox 35 from between the grate tubes 11 and from the perforations 42 of the front plate 12. Thus the grate 11, 12 can be advantageously cooled by the primary-air blast. The ash-box door 33 can be pulled out, allowing the ash-collection space 39 to be easily cleaned.
In the burner 10, there are comprehensive operating and maximum alarm functions. An operating alarm is given if there is some fault in the operation of the burner 10. Such an alarm triggers, for example, damping by the flame guard, or trips the motor protector. A maximum alarm is triggered, in turn, by some maximum level, such as the water temperature, being exceeded.
The burner 10 according to the example, in which the firebox 35 length is 330 mm, has an output of about 100 kW. The output can, however, be advantageously adjusted over a range of 0 - 100 %, because the pellet fuel being burned and the glow ignition permit the burner 10 to be shut down temporarily.
The burner 10 permits the selection of separate summer and winter running modes. In the summer running mode, when the thermostat closes, the conveyor screw (not shown) begins to feed fuel through the transfer pipe 18 to the burner screw 20 of the fuel-feed duct 41, which transfers the fuel to the grate tube 11. The glow igniter 22 starts ignition and, after a set delay, the primary-aid blower 16 starts and the control of the resistance of the igniter 22 switches off. Next, after a set delay, the secondary-air blower 17 starts. When the primary-aid blower 16 has started, the photodiode begins to monitor the flame through an aperture 23 and, according to this, controls the fuel transfer screw (not shown) at intervals. When the heat-control thermostat (not shown) cuts the operation, the transfer screw and the burner screw 20 stop and the blowers 16, 17 shut down, each after their own delay.
In the winter running mode, the glow igniter 22 is not used at all when starting the burner 10 as in summer running, instead the intention is to maintain continuous combustion in the burner 10, because the burner 10 is, in practice, stopped for only very short periods. The winter running mode can thus be used to save, for instance, the carbons of the igniter 22 and thus make it last longer. When the burner 10 is resting, the fuel is fed using the transfer screw (not shown) through the transfer pipe 18 to the firebox 35 while the separate primary and secondary- air blowers 16, 17 are started at intervals. The running modes allow the burner 10 to be operated economically in both winter and summer conditions.
The burner 10 according to the invention is simple, because it has only few moving parts and is reliable in operation and lasts for a long time, because the heated parts are cooled with the aid of the combustion-air feed according to the invention.

Claims

A burner (10) intended for burning a solid fuel, particularly pellets, which is intended to be installed in a wall opening of a boiler, the firebox (35) of said burner being formed from at least:
- at least partly delimiting wall constructions (13.1, 13.2, 19, 36) and

- hollow grate tubes (11), which are arranged parallel to each other and at a distance to each other, for burning fuel on them in a controlled manner, the burner (10) also including means (16, 17, 20) for feeding primary air, secondary air, and fuel into the firebox (35), whereby

- the wall constructions include, at least at the sides of the covered firebox (35), side walls (13.1, 13.2), which are formed from an essentially hollow casing construction to bring secondary air to the firebox (35) through perforations (14) arranged in the casing construction (13.1, 13.2) and

- in the said burner the primary air is arranged to be brought through the said grate tubes (11) to an ash-collection space (39) beneath them and to be then led to the firebox (35) between the grate tubes (11) and through a perforated front plate (12) arranged in front of the grate tubes (11).
A burner according to Claim 1, characterized in that the said casing construction is arranged to include a perforated rear wall (19) to the firebox (35) and a perforated cover component (36) that partly covers the firebox (35).
A burner according to Claim 1 or 2, characterized in that the said encasing side walls (13.1, 13.2) of the firebox (35) are shaped in such a way that lower part of the firebox (35) of the burner (10) is arranged to extend substantially further than the upper part into the boiler section.
A burner according to any of Claims 1 - 3, characterized in that said perforations in the casing constructions (13.1, 13.2, 19, 36) one holes (14, 24, 25), the diameter of which is arranged to be 3 - 15 mm, preferably 5 - 12 mm.
A burner according to any of Claims 1 - 4, characterized in that at least a connection (21), to which duct devices (41) fitted with screw devices (20), is arranged in the rear wall (19) for feeding fuel into the firebox (35).
A burner according to any of Claims 1- 5, characterized in that flame-monitoring devices (23) and ignition devices (22) are arranged in connection with the said casing construction (19).
A burner according to any of Claims 1 - 6, characterized in that separate blower devices (16, 17) are arranged for feeding primary air and secondary air into the firebox (35).
A burner according to any of Claims 1 - 7, characterized in that connections (38) are arranged for the grate devices (11) to the rear wall (19) and a grate support (40) is arranged in the boiler-section side end (34) of the burner (10), which is arranged to support the said grate devices (11, 12), to allow them to be cleaned and changed.