Wood pellet boiler

Abstract

The present application relates to improvements to granular fuel burning boilers such as wood pellet boilers and burners therefor. In particular, there is disclosed a wood pellet boiler having a combustion chamber, wherein an access door for said combustion chamber comprises a wood pellet burner assembly mounted on the interior side thereof. In this way, the wood pellet burner assembly is movable from and into the combustion chamber of the wood pellet boiler when the access door is opened and closed, respectively.

Claims

1. An access door for a combustion chamber of a wood pellet boiler, the access door comprises a wood pellet burner assembly, characterised in that the wood pellet burner assembly comprises: a housing having a surface adapted to support a combustion pot of the wood pellet burner; a grate comprising a plurality of spaced apart bars; a cleaning mechanism to dislodge residual ash and clinker from the grate, the cleaning mechanism comprising one or more movable members adapted to move in upwards and downwards reciprocating motion between the bars of the grate, wherein each movable member comprises a substantially planar blade member having an upper in use end that projects above the upper surface of the wood pellet burner housing, wherein motion of each blade member is affected by a rotatable rod that extends through and engages in a cam-action with a lower in use end of each blade member, the rotatable rod being rotated in use by a motor provided within the access door; and wherein the access door comprises an aperture for air to be drawn by a circulation fan of the wood pellet boiler through the access door, the aperture being in fluid communication with the wood pellet burner assembly, whereby air circulated through the aperture provides combustion air for the combustion pot, cooling air for the housing of the wood pellet burner assembly, and cooling air for the cleaning mechanism and its motor.

2. The access door of claim 1, wherein the access door is hinge mountable to the wood pellet boiler.

3. The access door of claim 1, wherein the combustion pot is removably demountable with respect to the wood pellet burner assembly.

4. The access door of claim 3, wherein the combustion pot comprises a substantially annular member having spaced apart and generally concentric outer and inner walls joined by a cap member.

5. The access door of claim 4, wherein the combustion pot is generally hollow and comprises a plurality of apertures provided in its inner wall and/or cap member.

6. The access door of claim 4, wherein the upper surface of the housing comprises a plurality of apertures for air drawn by the circulating fan of the wood pellet boiler can travel through the housing and into a space defined by the inner and outer walls of the combustion pot.

7. The access door of claim 1, wherein the spaced apart bars of the grate are defined by a plurality of slots formed in a base plate of the combustion pot.

8. The access door of claim 1, wherein the spaced apart bars of the grate are supported on the upper surface of the wood pellet burner housing.

9. The access door of claim 1, wherein each blade member comprises respective upper and lower elongate slots through which respective upper and lower guide rods extend in use, the guide rods being operable to maintain the blade members in a substantially vertical orientation.

10. A wood pellet boiler comprising an access door for a combustion chamber, the access door comprising: a wood pellet burner assembly, characterised in that the wood pellet burner assembly comprises: a housing having a surface adapted to support a combustion pot of the wood pellet burner; a grate comprising a plurality of spaced apart bars; a cleaning mechanism to dislodge residual ash and clinker from the grate, the cleaning mechanism comprising one or more movable members adapted to move in upwards and downwards reciprocating motion between the bars of the grate, wherein each movable member comprises a substantially planar blade member having an upper in use end that projects above the upper surface of the wood pellet burner housing, wherein motion of each blade member is affected by a rotatable rod that extends through and engages in a cam-action with a lower in use end of each blade member, the rotatable rod being rotated in use by a motor provided within the access door; and wherein the access door comprises an aperture for air to be drawn by a circulation fan of the wood pellet boiler through the access door, the aperture being in fluid communication with the wood pellet burner assembly, whereby air circulated through the aperture provides combustion air for the combustion pot, cooling air for the housing of the wood pellet burner assembly, and cooling air for the cleaning mechanism and its motor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the accompanying drawings:

(2) FIG. 1 is a perspective schematic view of an exemplary wood pellet boiler in accordance with the invention having an access door to a combustion chamber shown in an opened configuration;

(3) FIG. 2 is a perspective detailed schematic view of the access door of FIG. 1;

(4) FIG. 3 shows the access door of FIG. 2, but with a combustion pot shown removed from the burner assembly;

(5) FIG. 4 shows the access door of FIGS. 2 and 3, but with the burner assembly housing removed;

(6) FIG. 5 is an end elevation of the view of FIG. 4; and

(7) FIGS. 6a, 6b and 6c are further views of an exemplary combustion pot.

DESCRIPTION OF CERTAIN EXAMPLES OF THE INVENTION

(8) Referring initially to FIG. 1, there is shown an exemplary wood pellet boiler 1 in accordance with the invention, the wood pellet boiler comprising a an outer casing 2, a hopper 3, an external flue 4, a fuel feed mechanism (not shown), a combustion chamber 5, an access door 6 leading to the combustion chamber, and a burner assembly 7 mounted to the access door 6. A further door (not shown), forming part of the outer casing 2, may also be provided to conceal access door 6 in use. Access door 6 is hinge mounted to the wood pellet boiler.

(9) As shown in FIG. 2, access door 6 is further provided with a locking handle 62 on its exterior side, one or more locking levers or bolts 63 along one or more side edges, and one or more hinge barrels 64 adapted to cooperate with one or more corresponding hinge barrels provided on a boiler 1 and through which a hinge pin (not shown) extends in use. It will be appreciated that instead of hinge barrels 64 being provided on the door, the door may be attached to a boiler by any suitable means, for example by means of a conventional hinge mechanism having a hinge pin and leafs that are affixed to the door and boiler, respectively.

(10) Conveniently, the wood pellet burner assembly 7 is mounted to the reverse, i.e. interior side, of the access door 6. In this way, the wood pellet burner assembly 7 is movable from and into the combustion chamber 5 when the access door 6 is opened and closed, respectively.

(11) So that combustion of the fuel pellets may occur, access door 6 further comprises an aperture (not shown) to allow airflow through said access door and into the combustion chamber. A grille 61 may be provided to generally cover but not close the aperture, which is in fluid communication with burner assembly 7. A circulation fan (not shown) located within the wood pellet boiler draws ambient air from the exterior side of the access door to the interior of the access door and through the burner assembly 7 and combustion pot 72 as described below. On access door 6 behind grille 61 there is also located a fan (not shown) which operates to supply air to the ignition means associated with the combustion pot. This fan only operates when the ignition means is activated and is glowing.

(12) Referring to FIG. 2, burner assembly 7 which is mounted to access door 6, generally comprises a housing 71 having an upper in use surface 71a adapted to support a removable combustion pot 72. Combustion pot 72 is retained in place on surface 71a by clips 73 or other suitable releasable retaining means. In this way, combustion pot 72 is readily removable by a domestic user for the purpose of cleaning or replacement.

(13) Referring to FIGS. 6a, 6b and 6c, combustion pot 72 comprises a substantially annular member having spaced apart and generally concentric outer 72a and inner walls 72b. Spaced apart outer 72a and inner 72b walls are joined at their respective upper in use ends by a cap member 72c that slopes to direct granular fuel pellets downwardly into a central combustion region bounded by the inner wall 72b of combustion pot 72. Combustion pot 72 is generally hollow in construction. A base plate 72d substantially covers the lower in use end of combustion pot 72 as shown in FIGS. 6b and 6c. The walls 72a, 72b and cap member 72c have a thickness of approximately 2 mm. Base plate 72d has a thickness of approximately 10 mm.

(14) As shown in FIGS. 6b and 6c, in one possible arrangement, the combustion pot 72 further comprises a grate 70a in the form a plurality of spaced apart slots 72e formed in base plate 72d and which extend across the lower in use end of the central combustion region of the combustion pot 72. In this way, adjacent slots 72e define the spaced apart bars 72f of a grate.

(15) Accordingly, the bars 72f of the grate may be integrally formed with, or connected to the combustion pot 72. For example, where the base plate 72d and the combustion pot are of metal (e.g. stainless steel) construction, base plate 72d may be welded to the combustion pot 72. Alternatively, where base plate 72d and the combustion pot are made from a ceramic material, the base plate 72d and the combustion pot 72 may be cast or fused together.

(16) It will be appreciated that in other possible arrangements, the grate may be separate from the combustion pot, i.e. the grate may comprise a separate grate unit, or may comprise a plurality of individual bars which may be arranged in a spaced apart relationship to form a grate. In any case, the grate occupies the space at a lower end of the central combustion region of the combustion pot.

(17) Base plate 72d is further provided with a plurality of apertures 72g which provide openings into the space 70B defined between the spaced apart walls 72a, 72b of combustion pot 72. When the combustion pot is correctly positioned on upper surface 71a of burner assembly housing 71, apertures 72g align with apertures 71b provided on said upper surface 71a as described below. To ensure that apertures 72g of the combustion pot align correctly with apertures 71b of the burner assembly housing, combustion pot 72 is provided with a plurality of locating pins 72h (FIGS. 6a, 6c) which engage with complementary locating holes 71c (FIG. 2) provided on upper surface 71a of burner assembly housing 71.

(18) Apertures 71b of upper surface 71a of burner assembly housing 71 allow air drawn through the access door 6 to travel through housing 71 and via apertures 72g into the space 70B between the spaced apart walls 72a, 72b of combustion pot 72. A plurality of apertures 72j (FIG. 6a) provided in the inner wall 72b and cap member 72c of combustion pot 72 in turn enable air from drawn through the access door that has traveled through the housing 71 to enter the central combustion region of the combustion pot 72 (FIG. 2).

(19) An ignition tube 75 extends from access door 6 to a position proximate the grate. The ignition means delivered via tube 75 instigates the ignition of the pellet fuel delivered to, or residing within, combustion pot 72. A cut out portion or portions 72i (FIG. 6a) formed in or through the walls 72a, 72b of combustion pot 72 enable ignition tube 75 to extend into or proximate the central combustion region of said combustion pot. In this way, the ignition tube 75 can access the grate in use, whether said grate is formed integrally with the combustion pot, or is formed as a separate grate unit, or as a plurality of individual bars supported on the upper surface 71a of burner assembly 7.

(20) With reference to FIG. 4 and FIG. 5, burner assembly 7 is provided with a means to dislodge residual ash and clinker from the grate, the means comprising one or more movable members 76 adapted to move in upwards and downwards reciprocating motion between the bars (not shown) of said grate. Ideally, there are provided a plurality of members 76. Members 76 are substantially planar blade or knife members each having an upper in use end 76a that projects above surface 71a of burner assembly housing 71 as shown in FIGS. 2 and 5. Motion of the or each blade member 76 is affected by a rotatable rod 77 that extends through and engages in a cam-action with a lower in use end of the each blade member 76. Rod 77 is rotated by a motor (not shown) provided within the access door 6. In FIG. 5, dashed lines show the relative position of one or more blade members 76 when raised by rod 77. Upon the upward stroke(s), the upper in use ends 76a of one or more blade members dislodges any ash or clinker which they contact. Conveniently, air drawn through the aperture 60 in the access door as described above not only provides combustion air for the combustion process but also cooling air for the cleaning mechanism and its motor which it passes over and around as it flows through the access door, the burner assembly and onwards to the combustion pot.

(21) With reference to FIG. 3, and the combustion pot 72 as shown in FIGS. 6b and 6c and having a base plate 72d, the upper ends 76a of the respective blade members 76 extend through the slots 72e which define the spaced apart bars 72f of the grate. Air circulating through the burner assembly can pass through said grate into the central combustion region of combustion pot 72.

(22) To ensure that the or each blade member 76 remains in a substantially vertical orientation while being urged upwardly and downwardly by rod 77, the or each blade member comprises respective elongate upper 761 and lower 762 guide slots through which upper 763 and lower guide 764 rods extend. Guide rods 763 and 764 are supported at their respective ends by supports 771, 772 (FIG. 4).

(23) Conveniently, a programmable controller (not shown) is provided so that a cleaning cycle can be performed by the blade members 76 at regular intervals, or upon the detection of a build up of ash or clinker on the grate. It will be appreciated that the cleaning cycle can be performed during operation of the boiler, i.e. when the burner is operating. In addition, such a cleaning cycle may be performed as part of, or in advance of, a burner start-up procedure. Similarly, a cleaning cycle may be performed as part of, or after, a burner shut-down procedure.

(24) Advantageously, blade members 76, rod 77, guide rods 763, 764 and support members 771, 772 are housed substantially within housing 71 of burner assembly 7. In this way, they are cooled by air circulated by the circulation fan which passes through said housing as previously described.

(25) As the burner assembly 7 forms part of the access door 6 of the boiler to which it is mounted, it is easily accessible by a user or technician. To access the various burner components, one need only open the access door 6 whereby said burner components are moved outwardly from the combustion chamber of the wood pellet boiler 1. This obviates the need to remove one or more parts of the outer casing 2 of the boiler, which is often the case with prior art boilers. In turn, this means that a boiler 1 in accordance with the invention, or having an access door 6 in accordance with the invention, can be installed in an enclosed space where access to only one side is possible. Similarly, incorporating the burner assembly 7 with the access door 6 reduces the time to assemble a boiler during manifesting. Still furthermore, a field technician can simply replace a door 6 should one or more parts or functions of the burner fail and cannot be repaired or replaced on site. In this way, the end user can resume use of their boiler with minimal down-time. Furthermore, by locating the grate cleaning mechanism and its motor upon the access door, both the cleaning mechanism and its motor are cooled by air circulating through said access door as it flows through the burner assembly.