FURNACE CHAMBER GRATE FOR BURNERS FUELED WITH PELLETS AND OTHER SOLID FUELS

Abstract

 The object of the present invention is a segmented burner furnace chamber grate whose entire surface is formed by a series of movable grate bars connected using any known method, with inlet ventilation holes, loosely fitted by means of a mounting assembly, positioned one next to another to form sections (sectors), at least two of which are mechanically driven and repeatedly move in a reciprocating fashion.
According to the invention, the grate bars forming the grate (1) are in the form of plates (2a, 2b, 2c ... 2n), each in the shape of a prism or a truncated pyramid with a rectangular base, while one edge of each plate is fitted with a coupling protrusion (tongue) (5), and its parallel edge is fitted with a groove (6) whose shape matches that of the coupling protrusion (tongue) (5) of a neighboring plate (2), thus enabling joining the plates (2a, 2b, 2c ... 2n) in a jigsaw-puzzle fashion, to form rows (R1, R2, R3, R4, .... Rn), and while the other two parallel edges of each plate are smooth and loosely fitted to form longitudinal expansion gaps (7) between plate surfaces.

Description

[0001] The object of the present invention is a furnace chamber grate dedicated for burner fuelled with pellets, agripellets and other similar solid fuels (including fossil fuels), intended for households, public buildings, storage facilities and production halls.

[0002] Pellets and other similar fuels are incinerated on grate plates installed inside burners. In most known pellet burners fixed grates are used, which is somewhat problematic because cleaning a fixed grate involves the stoppage of the entire unit, as the furnace must be cooled down by shutting off fuel supply and increasing fan speed. Once the burner has cooled down, the grate needs to be manually removed and sintered deposit formed during the incineration process need to be manually scrapped off while the grate is outside the boiler. The deposits need to be carefully removed because they block air inlets in the grate and reduce the cubic capacity of the furnace chamber, which could eventually lead to a failure and burner malfunction. After the cleaning operation, it is necessary to reinstall the grate inside the burner and to initiate the start-up sequence. For the above reasons, the designs of newer solid fuel boilers combine a movable and a fixed grate, or only use a movable, usually stepped and at least bipartite grate, perfectly suitable for the combustion of sustainable fuels such as wood chips, shavings and sawdust, wood pellets, straw and hay pellets, or fruit / vegetable production waste. The working principle of a movable grate involves feeding fuel to its upper part, following which the reciprocal movement of the grate gradually transfers fuel towards the lower part of the furnace, which is accompanied by its gradual combustion and drying by means of adequately targeted streams of hot flue gas (the flue gas flow direction being opposite to the fuel transfer direction). By the time fuel reaches the far end of the grate, it is completely incinerated. The design of movable grates makes it possible to remove ash and unburned remains from the furnace.

[0003] The Polish utility model PL067681 (Y1) teaches a burner of a water heating boiler adapted for biomass incineration, an example embodiment of which is shown in Pos. Ia, Pos. Ib, characterized in that a fixed grate in its floor is fitted with longitudinal gaps wherein upright movable grate bars (1) are located, powered by a motor (17) via of a drawbar (14) and a eccentric mechanism (15). The movable grate bars (1) rest on a slide support (18) fitted with rounded surfaces along the entire distance travelled by the grate bars (1) from the eccentric mechanism (15). The supports_[MC1] are located in the front section of a grate housing (20) and on the outer, front side of an insulation tray (22). Furthermore, the movable grate bars (1) have a toothed upper surface, preferably with vertical tooth edges directed towards the burner outlet. The eccentric mechanism (15) is fitted with a sensor for positioning the grate bars (1).

[0004] A fixed grate, (2) and a movable grate (1)_[MC2] is covered with a cover (6) from the top. The upper part of the cover (6) has chamotte ceramic insulation (7). The grate bars (1)and (2) _[MC3]are fitted with the housing (20) that forms an air chamber. Over the entire surface of the trough-shaped fixed grate (2) there are ventilation holes (5). The movable grate bars (1) are connected via the drawbar (14) with the eccentric mechanism (15) powered with the motor (17). At the drawbar (14) end-piece, the eccentric mechanism (15) is fitted with the sensor (16) for positioning the grate bars (1). The eccentric mechanism (15) with the motor (17) and the positioning sensor (16) as well as the support of the drawbar (14) are all located on a supporting platform (19). Combustion air is fed from a fan via an aeration chamber (21) and a blow duct (9) to the air chamber, from where it moves through the ventilation holes (5) to a furnace space (3). The bottom of the air chamber is fitted with an opening cleanout (10), intended for ash removal from the chamber.

[0005] Regular movements of the vertical movable grate bars (1) inside the chamber transfer ashes to the ash chamber. After the furnace cleaning cycle is completed, the movable grate bars (1) go to the working position (so-called home position). When in the home position, the grate bars (1) are located inside gaps in the lower part of the furnace.

[0006] Self-cleaning is one advantage of the burner described above. The furnace grate is cleaned automatically, in accordance with the cleaning frequency set on the movable grate bar positioning sensor. A cleaner furnace ensures enhanced combustion performance, thus improving the boiler's thermal efficiency.

[0007] The description of the utility model W. 123240 teaches a pellet burner grate with stepped and segmented design, as shown in Pos. 2a, Pos. 2b and Pos. 2c, characterized in that the complete burner grate assembly is fitted in a retractable drawer (1) that can be retracted from a burner (12), while individual parts of fixed grate bars (7) are permanently and directly mounted to the retractable drawer (1) on rest supports. Individual segments of movable grate bars (8) are mounted via rest supports to an inner movable drawer (2). The movable drawer (2) is mounted on slide bearings inside the retractable drawer (1). The segments of the fixed and movable grate bars (7, 8) are fitted with ventilation openings on the surface and are attached to the rest supports via H-shaped locks, ensuring clearance in three directions. The front parts of the segments of the grate bars (7, 8) are bent downwards, in an L-shaped fashion.

[0008] A similar pellet burner grate design is known from the description of the utility model W. 123375. The grate, as shown in Pos.3a and Pos. 3b, resembles a drawer (2) in a drawer (1), with a stepped and segmented design. It is alternatingly fitted with fixed grate bars and movable grate bars, installed every other step. The movable grate bars move over fixed bars in a reciprocating motion induced by a mechanical drive (3) housed in the retractable drawer (1) that can be retracted from a burner via a drawbar (4), while individual parts of the fixed grate bars (5) are permanently and directly mounted to the retractable drawer (1) on rest supports. Individual segments of movable grate bars (6) are mounted via rest supports to the inner movable drawer (2). The movable drawer (2) is mounted on slide bearings inside the retractable drawer (1). The front parts of the grate bars (5) and (6) are bent backwards, and the segments of the grate bars (5) and (6) have at least one longitudinal ventilation groove (9) on their horizontal surface, and a downward-bent extension (7) of that surface is fitted with a protruding tongue (8) that matches the opposite groove (9) in lower segments of the grate bars, which expels slag from the groove (9) as it moves over the surface of the fixed grate (5). In addition, the length of the tongue (8) is at least equal to the thickness of the grate bars (5) and (6).

[0009] The Polish application for the invention P. 398958 (A1) teaches a pellet burner with a self-cleaning grate, as shown in Pos. 4a, Pos. 4b and Pos. 4c, characterized in that the lower section of a furnace body (8), underneath a fixed grate (7) is fitted with a movable grate (6) which forms its bottom and which is detachably mounted on pins screwed to a [bogie_[MC4] (9). The bogie (9) is screw-mounted to a toothed bar, which in its turn is connected to a linear actuator (12). The linear actuator (12) is installed on a mounting platform located on the outer side of an air jacket (28), on the projected extension of the toothed bar (23). The lower surface of the furnace body (8) is fitted with front openings the length of which corresponds to a single pitch traveled by the bogie (9) during the furnace cleaning cycle. The front section of the furnace body (8) under the movable grate (6) is fitted with a cleanout (25). The bogie (9) periodically moves in a reciprocating motion along the front openings.

[0010] The burner cleaning cycle involves cooling down the furnace by shutting off fuel supply and increasing fan (13) speed. The next stage involves switching the linear actuator (12) to the toothed bar (23) feeding mode while the movable grate (6) is fully retracted to the back of the burner (open position). When the grate is fully retracted, it is being inserted until a contact sensor (15) detects its correct location (closed position). As the grate is being retracted, combustion residues from the front part of the furnace fall directly to the ash chamber via the cleanout (25) in the burner furnace body (8), while the other residues fall to the bottom of the inner part of the furnace body (8). While the movable grate (6) is being retracted, ash is being scraped from its upper surface by the end wall of the fixed grate. While the movable grate (6) is being inserted, all impurities that fell to the bottom of the furnace body (8) are pushed by the front wall of the movable grate (6) towards the cleanout (25) available in its bottom section.

[0011] The international patent application published as WO96/16306 (also published as PL179002 (B1)) teaches a grate plate design for multi-stage grates dedicated primarily for cooling or other kinds of processing of loose or volumetric materials. Pursuant to that solution, as shown in Pos. 5a, Pos. 5b, Pos. 5c and Pos. 5d, the grate consists of a number of plates, preferably arranged one next to another on a grate conveyor, with each grate plate being fixed to the grate conveyor via a mounting assembly. The mounting assembly (11, 211, 311, 411, 412, 911) features at least one mounting element (12, 212, 412), whose one end (14) on the grate plate side penetrates through an opening (15) in a front wall (3, 203, 403, 503, 903, 903') of the grate plate (2, 202, 302, 402, 502, 602, 902) and is mounted by means of mounting units in the form of a dome cap_[MC5] (16, 216, 416, 916), installed on the mounting element (12, 212, 412), while its opposite end on the grate support / conveyor side (1, 201, 301, 401, 901) is connected to that grate support / conveyor via a hitching element / anchoring means (13, 213) for rigid hitching to the grate support / conveyor (1, 201, 301, 401, 901). Such a design makes it possible to mount or remove grate plates from the top of the grate.

[0012] The purpose of the present invention was to develop a grate for burner furnace chambers, whose working principle would be similar to that of a mechanism known from another technical area and used in transport vehicles (trucks, tippers, dump trailers dedicated for removal of deposits, sludge, loose materials such as scrap metal, sand, gravel, recycled glass, construction waste, animal feed, bran, etc.). While the said mechanism uses the principle of movable grate, in fact it constitutes the so-called walking floor, i.e. a segmented floor made of a series of steel bars (panels, profiles) clustered in groups of a few such bars per row (segment), adapted to make slow reciprocating motions in an alternating fashion, induced by a push-pull action of elements powered with a hydraulic drive. Just as a walking floor facilitates, automates and largely accelerates loading and unloading of goods in transport vehicles, the newly designed grate for burner furnace chambers with a similar working principle could ensure operation-free, self-cleaning furnace chamber by efficiently shredding and automatically removing ash and sinter deposits from the grate. Such deposits build up when fuel is contaminated for instance with sand, fine plastic particles or - in the case of fuels made of laminated furniture boards - with varnish, paint or glue.

[0013] The said objective is met by a segmented furnace chamber grate for pellet burners according to the present invention. Its entire surface is formed by a number of movable grate bars connected by known means, fitted with inlet ventilation holes. The grate bars are loosely mounted by means of a mounting assembly. The grate bars are located side by side, forming identifiable parts (sectors), at least two of which are mechanically driven and repeatedly move in a reciprocating fashion.

[0014] According to the invention, the grate bars that form the grate take the form of plates in the shape of a prism or pyramid with a rectangular base. Each such plate has a coupling protrusion (tongue) on one edge, and a groove on the edge parallel to it, designed to match the coupling protrusion (tongue) of a neighboring plate, for joining the plates in a jigsaw-puzzle fashion. The other two edges of each plate are smooth and loosely fitted so that longitudinal expansion gaps are formed between plate surfaces.

[0015] The plate components of the grate form either a flat surface or an arched concave surface.

[0016] The working cycle of each row of plates is configured mechanically and can be effected in any sequence and at any speed.

[0017] The grate plates are made of a material resistant to very high temperatures (over 500°C).

[0018] The working cycle of each row of plates is configured mechanically and can be effected in any preprogrammed sequence and at any speed, thanks to a reciprocating movement mechanism. The mechanism is installed behind the rear furnace plate and consists of a mechanical drive with a toothed gearing that drives one or more drive shafts with push cams that interact with the distal ends of guide rails, thus moving them to the front and to the back of the burner. The guide rails are connected to the rows of the plates, thus inducing their reciprocating motion.

[0019] One advantage of the burner furnace chamber grate according to the invention is that the furnace chamber grate is cleaned automatically, thus making the combustion chamber operation-free. Thanks to a clean furnace the efficiency of the incineration process is higher because the burner can be used continuously. Monolithic grates, commonly known and used so far, are susceptible to the serious problem of grate cracking caused by operational thermal stress. With the presence of the characteristic grate bars consisting of smaller elements (plates) in the present invention, the grate is modular, as it is divided into a number of smaller surfaces with numerous gaps between them, which not only ensures free movement of the plates in relation to one another, but also effectively neutralizes additional stress and thermal deformation of the grate, thus making the grate more resistant to cracking. Consequently, the grate thickness can also be reduced, which translates into tangible economic gains as less material is required for manufacturing. Depending on the requirements and the type of the device in which the grate according to the invention is to be installed, it is possible to configure the forward and backward motion of individual grate plate rows. It is also possible to control grate movement cycles so that all rows move forward or backward at the same time. The rows can also move forward in an alternating pattern (i.e. plates 1, 3, 5 etc. move forward while plates 2, 4, etc. move backward). Alternatively, some rows can be immobilized (e.g. 2, 4 and 6). Furthermore, the grate can be made in two versions: either flat or concave (arched), which improves combustion efficiency.

[0020] Three embodiments of the present invention are presented in the drawing, showing schematic views of the following:

Fig. 1 - three views (top, side and front) of a single grate plate,

Fig. 2 - three views (top, side and front) of a flat grate,

Fig. 3 - three views (top, side and front) of a concave (arched) grate,

Fig. 4 - side view of the grate;

Fig. 5 - top view of the grate;

Fig. 6 - axonometric front view of the grate,

Fig, 7 - axonometric rear view of the grate,

[0021] The furnace chamber grate for burners fuelled with pellets and other solid fuels according to the present invention has been used in a burner fuelled with pellets, agripellets and wood chips, in which fuel is continuously fed into the furnace chamber in order to sustain the combustion process. The burner is fitted with a steel body constituting a permanent housing with a pellet inlet and a furnace chamber surrounded by a cylindrical, immovable shield permanently fixed to the body. The space between the furnace chamber and the shield forms a semi-annular inlet duct supplying air to the furnace chamber via inlet openings distributed along the shield's circumference. Fig. 2 and Fig. 3 show a simplified view of the grate only, while Fig. 4, Fig. 5, Fig. 6 and Fig. 7 show the furnace chamber with the grate according to the present invention, complete with the driving mechanism.

[0022] The grate shown in Fig. 2 was used in the first embodiment. Another embodiment is presented in Fig. 3, while Figs. 4 to 7 show a third embodiment.

Embodiment 1:

[0023] The grate 1 as shown in Fig. 2 is flat and segmented. Its surface is formed by 30 movable grate bars in the form of plates 2 (2₁, 2₂, 2₃ ... 2₃₀), each in the shape of a low prism with a rectangular base. The surface of each plate is fitted with six inlet ventilation holes 3, supplying air to the furnace space, and one sharp-edged jutting section 4 of a nearly cuboidal shape, the purpose of which is to ensure that the movement of the grill bars more efficiently induces transfer of burning fuel (wood chips). In addition, one of the shorter edges of each plate is fitted with a protrusion (tongue) 5, and its opposite shorter edge is fitted with a groove 6. Both elements serve the purpose of joining the plates in a jigsaw-puzzle fashion, to form rows R1, R2, R3, R4, R5. The other two edges of each plate are smooth and loosely fitted to form longitudinal expansion gaps 7 between plate surfaces. Plate rows R1, R2, R3, R4, R5 are mechanically driven by means of a cam mechanism and a gearing (not shown), inducing cyclical reciprocating movements in the following configuration: when all rows are in the full-forward position, they begin to be retracted one by one (for example in the following sequence: R2, R4, R1, R5, R3). When all row plates are fully retracted, they begin returning to the starting position, and the cyclical reciprocal movement causes the furnace to self-clean. Ashes from solid fuel incineration and impurities in that fuel fall to an ash chamber placed underneath (not shown).

Embodiment 2:

[0024] The grate 1 as shown in Fig. 3 is concave (arched) and segmented. Its surface is formed by 36 movable grate bars in the form of plates 2 (2₁, 2₂, 2₃ ... 2₃₆), each in the shape of a low truncated pyramid with a rectangular base. The surface of each plate 2 is fitted with six inlet ventilation holes 3. In addition, the plates 2 are fitted with coupling elements (not shown) for joining the plates in a jigsaw-puzzle fashion, to form rows R₁, R₂, R₃, R₄, R₅, R₆. The other two edges of each plate are smooth and loosely fitted to form longitudinal expansion gaps 7 between plate surfaces. Plate rows R₁, R₂, R₃, R₄, R₅, R₆ are mechanically driven by means of electric linear actuators (not shown). The rows move cyclically in a reciprocating fashion: rows R₁ and R₆ do not move, while the other rows move as follows: when all of them are in the full-forward position, they begin to be retracted one by one (for example in the following sequence: R2, R4, R5, R3). When all of them are fully retracted, they begin returning to the starting position.

Embodiment 3:

[0025] A burner was built, and its combustion chamber was fitted with a grate 1 according to the present invention. The grate 1 is concave (arched) and segmented. Its surface is formed by 36 movable grate bars in the form of plates 2 (2₁, 2₂, 2₃ ... 2₃₆), each in the shape of a low truncated pyramid with a rectangular base, made of a material resistant to temperatures exceeding 500°C. The surface of each plate 2 is fitted with ten inlet ventilation holes 3, and its upper surface is fitted with a prism-shaped jutting section 4. The shorter edges of the rectangular plates 2 are fitted with coupling elements - a protrusion (tongue) 5 on one edge, and a groove 6 on the opposite edge. The shape of the protrusion 5_[MC6] matches the shape of the groove 6 of a neighboring plate, thus joining the plates in a jigsaw-puzzle fashion, to form rows R₁, R₂, R₃, R₄, R₅, R₆. The longer edges of each plate 2 are smooth and loosely fitted to form longitudinal expansion gaps 7 between rows R made of the plates 2.

[0026] The grate 1 was placed inside a furnace chamber consisting of a bottom section 8 which constitutes an air jacket supplying air to the chamber, and a top section 9 covering approximately two-thirds of the combustion chamber.

[0027] The rear section of the grate 1 is set on the rear furnace plate 10 fitted with a centrally positioned hole 11 used to feed fuel to the combustion chamber, and with air supply holes 12. Behind the rear furnace plate 10 there are driving mechanisms consisting of a drive motor 13, a drive shaft 14 with push cams 15, a toothed gearing 16 of the reciprocating movement mechanism and guide rails 17. The mechanisms are mounted to a left and right mounting wall (18 and 19, respectively) and secured with |cross-bars|_[MC7] 20.

[0028] Individual rows R of the plates 2 of the grate 1 move cyclically in a reciprocating fashion in the following configuration: rows R₁ and R₆ do not move, while the other rows move forward. When rows R₂, R₃, R₄, R₅ are in the full-forward position, they begin to be retracted one by one (for example in the following sequence: R5, R3, R2, R4). When all of them are fully retracted, they begin returning to the starting position.

[0029] In another cycle, while rows R₂ and R₅ are moving forward, rows R₃ and R₄ are being retracted, and vice versa: while rows R₃ and R₄ are moving forward, rows R₂ and R₅ are being retracted.

[0030] In yet another cycle, rows R₁ and R₆, remain immovable, rows R₂ and R₄ move forward, and rows R₃ and R₅ go backward (and vice versa).

[0031] In yet another cycle, all rows (R₂, R₃, R₄ and R) were moving forward and backward at the same time.

[0032] The above examples are not the only possible embodiments of the invention. Further modifications may be introduced primarily to the shape of the plates 2 (2a, 2b, 2c ... 2n), the shape of the jutting section 4, which can just as well take the form of a simple cuboid or the so-called "shark fin", as well as to the shape of the coupling elements, i.e. the coupling protrusion (tongue) 5 and the groove 6.

Key

[0033] 

1

- Grate

2

- Plate

3

- ventilation hole

4

- jutting section

5

- protrusion (tongue)

6

- groove

7

- expansion gap

8

- bottom part of the combustion chamber

9

- top part of the combustion chamber

10

- rear furnace plate

11

- fuel supply opening

12

- air supply hole

13

- drive

14

- drive shaft

15

- cam

16

- toothed gearing

17

- guide rail

18

- right mounting wall

19

- left mounting wall

R₁, R₂, R₃, R₄, R₅, R₆

- rows of furnace chamber plates

Claims

1. A segmented-design burner furnace chamber grate whose entire surface is formed by a series of movable grate bars connected using any known method, with inlet ventilation holes, loosely fitted by means of a mounting assembly, positioned one next to another to form sections (sectors), at least two of which are mechanically driven and repeatedly move in a reciprocating fashion characterized in that grate bars forming the grate (1) are in the form of plates (2_a, 2_b, 2_c ... 2_n), each in the shape of a prism or a truncated pyramid with a rectangular base, while one edge of each plate is fitted with a coupling protrusion (tongue) (5), and its parallel edge is fitted with a groove (6) whose shape matches that of the coupling protrusion (tongue) (5) of a neighboring plate (2), thus enabling joining the plates in a jigsaw-puzzle fashion, to form rows (R1, R2, R3, R4, .... Rn), and while the other two parallel edges of each plate are smooth and loosely fitted to form longitudinal expansion gaps (7) between plate surfaces.

2. The grate according to claim 1 characterized in that its constituent parts in the form of rows (R) of plates (2a, 2b, 2c ... 2n) form a flat surface.

3. The grate according to claim 1 characterized in that its constituent parts in the form of rows (R) of plates (2a, 2b, 2c ... 2n) form a concave (arched) surface.

4. The grate according to claim 1 or 2 or 3 characterized in that the top surface of its plates (2) is fitted with sharp-edged jutting sections (4).

5. The grate according to claim 1 characterized in that the working cycle of its individual rows (R1, R2, R3, R4 ... Rn) of plates (2a, 2b, 2c ... 2n) is mechanically configured by means of a reciprocating movement mechanism positioned behind a rear furnace plate (10).

6. The grate according to claim 5 characterized in that its reciprocating movement mechanism is fitted with a shaft (14) with cams (15) that control guide rails (17) of individual rows (R₁, R₂, ...Rn) of plates (2).

Drawing