EP0708902A1

EP0708902A1 - Grate

Info

Publication number: EP0708902A1
Application number: EP95918631A
Authority: EP
Inventors: Markku Rantonen
Original assignee: Sermet Oy
Current assignee: Sermet Oy
Priority date: 1994-05-20
Filing date: 1995-05-19
Publication date: 1996-05-01
Anticipated expiration: 2015-05-19
Also published as: CN1083967C; PL312616A1; ATE165149T1; FI95964C; DK0708902T3; RU2138734C1; CN1128560A; WO1995032392A1; DE69502070D1; AU2448995A; DE69502070T2; EE03782B1; EE9600008A; EP0708902B1; FI95964B; FI942350A0

Abstract

The object of the invention is a grate (1) comprising stationary (6) and rotating (7) grate sections. The grate (1) is preferably fitted in a combustion chamber (2) of circular horizontal cross section. According to the invention, the stationary grate section (6) comprises at least two stationary grate frames (61, 62, 63, 64), and the rotating grate section (7) comprises at least one rotating grate frame (71, 72, 73), the grate frames being arranged in a concentric, stepped manner close to one another, partly overlapping one another, so that the innermost grate frame (61) is the uppermost with respect to the other grate frames. The number of grate frames is odd and they are arranged so that every second grate frame is a stationary one and every second one is a rotating grate frame (61, 71, 62, 72, 63, 73, 64). The innermost and outermost grate frames (61, 64) are stationary grate frames. The rotating grate frames (71, 72, 73) are installed eccentrically with respect to the stationary grate frames (61, 62, 63, 64), resulting in a lateral movement with respect to the stationary grate frames being combined with their rotating movement.

Description

GRATE

The object of the invention is a grate according to the introductory part of Claim 1.

The grate is already known from patent publication US-4 437 452, comprising a stationary central grate section and a rotating grate section around it. The stationary grate section is highly conical and the main part of the combustion air is fe'd to the combustion chamber through the stationary grate. Fuel is handled and ashes are removed from the combustion chamber by using a stationary expansion bracket in conjunction with the rotating grate section.

A disadvantage in the grate described above is that both grate sections are relatively large parts, and which are arranged in the combustion chamber by using complicated structures so that the maintenance, especially cleaning, is troublesome and difficult.

The purpose of the invention is to disclose a new grate whose structure is simple, functional, and easy to maintain. The purpose of the invention is, especially, to disclose a grate which can be adapted in different-sized solid fuel combustion chambers, burners, boilers or the like and which is advantageous to manufacture.

The grate according to the invention is characterized in that which is disclosed in the independent Claim.

The grate according to the invention comprises stationary and rotating grate sections, the grate preferably being fitted in a combustion chamber of circular, horizontal cross-section. According to the invention the stationary grate section comprises at least two separate stationary grate frames and the rotating grate section comprises at least one rotating grate frame, which is adapted between the stationary grate frames, the grate stationary frames and the rotating grate frame being in a concentric, stepped relation close to one another, covering each other partly so that the innermost grate frame is the uppermost with respect to the other grate frames, and the rotating grate frame is installed eccentri¬ cally with respect to the stationary grate frames so that a lateral movement is combined with the spinning movement of the rotating grate frame with respect to the stationary grate frames.

An advantage of the invention is that it comprises several grate frames and the rotating motion of the one or several rotating grate frames is eccentric, whereby the fringe areas of the grate frames move with respect to each other not only in a rotating but also in a linear, back and forth movement, whereby the rotating and stationary grate frames, which are in each other's range and at least partly touch each other, remain clean.

In one embodiment of the invention the number of grate frames is odd, i.e., there are at least three of them and they are arranged so that every other grate frame is stationary and every other one rotating. An advantage of this structure is that the grate can be fitted in combustion chambers of different sizes in a desired manner to provide the most advantageous possible handling and combustion of f el.

In another embodiment of the invention the rotating grate frames closest to each other are arranged to rotate in opposite directions. An advantage of this arrangement is the effective cleaning of the grate frames. Using this arrangement, the ash can be effectively removed downwards from one grate frame to another towards the ash box.

In one embodiment of the invention each grate frame is in the form of an essentially flat annular part, a bracket periphery being arranged in the vicinity of the outer edge of the annular part, preferably on the lower surface of the outer edge, exclusive of the outermost grate frame, the bracket periphery comprising brackets inclined essentially downwards and placed at a small distance from each other. Consequently, the grate according to the invention is preferably formed of ovelying grate frames of essentially similar structure, the bracket peripheries of the overlying grate frames resting on, or being at least close to, the upper surface of the next grate frame placed radially outward. An advantage of this application is that the bracket peripheries and the brackets serve as effective ash removal devices and cleaners of the grate frames.

In one embodiment of the invention the brackets of the bracket periphery included in the grate frame form, together with the upper surface of the grate frame following this grate frame radially outward, air openings for the combustion air fed from underneath the grate. An advantage of this application is that the feeding of combustion air from underneath the grate is arranged in a simple and effective manner through the bracket peripheries working as cleaning members.

In another embodiment of the invention the air openings of each rotating grate frame are arranged to open outward from the outer edge of the grate frame, at an obtuse angle with respect to the direction of rotation. In this case the air openings of the grate frames are arranged to open away from the direction of rotation and they are tangentially trailing with respect to the direction of rotation. An advantage of this application is that ashes do not spread through the air openings of the rotating grate frames to the space below the grate. Another advantage is that the brackets on the edges of the air openings are used to effectively plough the stationary grate frames and to move the ashes lying in them to the next grate frame. A further advantage is that the combustion air fed from under the grate is effectively mixed with the fuel to be burned. In one embodiment of the invention each rotating grate frame comprises a chain wheel and a driving device, such as a hydraulic cylinder, which is used to influence the chain wheel and to move the grate frame periodically. An advantage of this application is that each grate frame can be used independently and rotated in thrusts at a desired speed, thus enhancing the cleaning of the grate and the feeding of combustion air.

In another embodiment of the invention the driving device, preferably a hydraulic cylinder, is fitted into an air channel. An advantage of this application is the easy maintenance and the fact that the heat of the grate and the combustion chamber cannot influence the hydraulic cylinder arranged in the air channel. The hydraulic cylinder is effectively cooled using the combustion air fed through the air channel.

In another embodiment of the invention the feeding arrangement of combustion air comprises air channels which are connected to air plenum chambers which are arranged below the grate, preferably in areas defined by the stationary grate frames. Consequently, the stationary grate frames divide the part under the grate into sectors, through which the combustion air is fed to the combustion chamber through the air openings of the grate frames. This arrangement has the advantage that the feeding of combustion air to different grate frames of the grate is divided into a number of different zones, whereby the adjusting of combustion and the power control of the combustion chamber can be realized in a simple and effective way.

The invention is described in the following in detail with reference to the appended drawings, in which:

Fig. 1 shows a vertical cross-section of the combustion chamber, perpendicular to the fuel feeding channel, the grate according to the invention being fitted in the combustion chamber; Fig. 2 shows another cross-section of the combustion chamber of Fig. 1 in the direction of the feeding channel; Fig. 3 shows a horizontal cross-section of the combustion chamber in Fig. 1 so that the grate is viewed from above; and Fig. 4 illustrates a diagrammatic plan of the grate as viewed from above, the actual grate frames being removed from the grate.

Referring to Fig. l, grate 1 according to the invention is fitted in combustion chamber 2 of circular horizontal cross- section, the chamber serving as the front chamber of the boiler in this application. Lower part 2a of combustion chamber 2 is cylindric and its upper part 2b is conical. Conical upper part 2b is connected to smoke duct 3 which is connected to an after-combustion chamber and a boiler (not shown in the figure) for recovering heat from the combustion fuels. Furnace jacket 4 is provided with thermal insulation. Grate 1 is fitted in lower part 2a of combustion chamber 2. Annular ash box 5 surrounds grate 1.

Grate 1 according to the invention comprises stationary and rotating grate sections 6, 7. Stationary grate section 6 comprises several separate stationary grate frames 61, 62, 63, 64 and rotating grate section 7 comprises several separate rotating grate frames 71, 72, 73 which are adapted between the stationary grate frames 61, 62, 63, 64. The number of grate frames 61, 62, 63, 64; 71, 72, 73 is odd; this application comprises a total of seven grate frames. Every second grate frame is rotating grate frame 71, 72, 73 and every other grate frame is stationary grate frame 61, 62, 63, 64. The innermost and outermost grate frames 61, 64 are stationary grate frames.

Fuel feeding channel 8 is arranged to go from outside combustion chamber 2 in a horizontal direction through the middle area of lower part 2a of the combustion chamber, as viewed in Fig. 2. Feeding screw 9 is arranged in feeding channel 8 and it is driven by a driving device, such as electric motor 10. Feeding channel 8 is arranged to connect to feeding hopper 11 whose output aperture 12 is arranged to open into combustion chamber 2 in the middle of grate 1.

Grate sections 6, 7 of grate 1 are arranged around output aperture 12 of feeding hopper 11. Grate frames 61, 62, 63, 64;

71, 72, 73 are essentially flat annular parts. They are arranged around output aperture 12 in a concentric and stepped manner so that the first, i.e., innermost grate frame 61 in the vicinity of output aperture 12 of feeding hopper 11 is the uppermost and the following grate frames 71, 62, 72, 63, 73, 64 are always lower than the preceding frame, as seen in Figs. 1 an 2, for example. The fringe areas of the grate frames partly overlie or overlap one another in each other's vicinity.

Both stationary and rotating grate frames 61, 62, 63; 71, -72, 73 have essentially the same structures, except for outermost grate frame 64. Only their diameters vary, i.e., increase from the innermost grate frame 61 towards the outermost grate frame 64. Each grate frame 61, 62, 63, 64, 71, 72, 73, including the outermost grate frame 64, is formed of sheet-like material, preferably of suitable steel sheet. Grate frame 61, 62, 63, 64, 71, 72, 73 is preferably attached at its inner edge 61a, 62a, 63a, 71a, 72a, 73a to the support structure, and to its outer edge 61b, 62b, 63b, 71b, 72b, 73b, in turn, is arranged bracket periphery 13 which comprises brackets 13a placed at a small distance from each other so that air openings 14 are formed between them (cf. Fig. 3). Outer edge 61b, 62b, 63b, 71b, 72b, 73b of grate frame 61, 62, 63; 71, 72, 73 is slightly downwards curved and said bracket periphery 13 with its brackets 13a is arranged on the lower surface in the vicinity of the outer edge. Outer edges 61b, 71b, 62b, 72b, 63b, 73b of stationary and rotating grate frames 61, 71, 62,

72, 63, 73 which follow each other alternately, as well as brackets 13a of bracket peripheries 13 connected in the vicinity thereof, are always in the vicinity of or rest on the upper surface of the outermost and the lower grate frames 71, 62, 72, 63, 73, 64. Furthermore, grate frames 61, 62, 63, 64, 71, 72, 73 are arranged in the following way with respect to one another: The first stationary grate frame 61 is preferably attached at its inner surface 61a around output aperture 12 of feeding hopper 11 essentially on the same plane. The first rotating grate frame 71, in turn, is attached from the bottom, preferably from near inner edge 71a, to cylindrical support 15; 151. The first rotating grate frame 71 and its support 151 rest on bearing frame 16; 161 in which the support is installed eccentrically. The term eccentric in this context means that rotating grate frame 71 is installed eccentrically with respect to stationary grate frame 61 preceding it. At the same time, it is also installed eccentrically with respect to the following stationary grate frame 62. Stationary grate frames 61, 62, 63, 64 are all preferably installed concentrically with respect to one another and to output aperture 12 of the feeding hopper. However, bearing frame 16; 161 is installed concentrically with respect to an imagined vertical axis via the central point of stationary grate frames 61, 62, 63, 64. Bearing frame 16; 161 is supported rotatably in place, by using both horizontal and vertical rolls 17, 18, on support 19; 191 arranged around feeding hopper 11. Vertical annular flange 16a is provided on the lower surface of bearing frame 16; 161, the horizontal rolls 17 being supported against the annular flange.

Chain wheel 20; 201 is arranged on the outer edge of bearing

• frame 16; 161. Chain wheel 20; 201 is influenced upon by using a driving device, preferably hydraulic cylinder 22; 221 and grate frame 71 is set into motion in thrusts with the aid of bearing frame 16; 161 and support 15; 151. Hydraulic cylinder 22; 221 is arranged in air channel 23; 231. Hydraulic cylinder 22; 221 is attached to a suitable support 24, arranged in the air channel, at its cylinder body 22a (Fig. 4) . Piston 22b of hydraulic cylinder 22; 221, in turn, is connected to operating rod 25 whose other free end is fitted between teeth 21 of chain wheel 20; 201 so that, by suitably driving hydraulic cylinder 22; 221 and by propelling operating rod 25 to and fro, chain wheel 20; 201 can be turned forward one pitch of teeth at a time in a predetermined direction of rotation.

The second stationary grate frame 62 of grate 1 is fitted outside and under the first rotating grate frame 71 so that bracket periphery 13 of this rotating grate frame 71 is in close proximity of the upper surface of second stationary grate frame 62 on the side of inner edge 62a. Second stationary grate frame 62 is preferably supported in place in the lower part of combustion chamber 2 on the side of the lower surface of its inner edge 62a by using support 26; 261 which is preferably cylindrical. At the same time, this cylindric support 26; 261 contains inside it the first air plenum chamber 27 to which the first air channel 23: 231 is connected.

Second rotating grate frame 72 is arranged partly outside and under second stationary grate frame 62 in the same way as first rotating grate frame 71 is arranged with respect to first stationary grate frame 61. Second rotating grate frame 72 is supported eccentrically by second cylindric support 15; 152 in connection with second bearing frame 16; 162 on the same principle as first rotating grate frame 71 is supported in connection with the respective bearing frame 16; 161. Bearing frame 16; 162 is supported rotatably in place on support 19; 192 arranged around support 26; 261 of second stationary grate frame 62 by using both horizontal and vertical rolls 17, 18. Vertical annular flange 16a is provided on the lower surface of bearing frame 16; 162, horizontal rolls 17 being supported against the flange. Second driving device, preferably second hydraulic cylinder 22; 222 is used to influence chain wheel 20; 202 in connection with bearing frame 16; 162 so that rotating grate frame 72 can be moved in thrusts. Second rotating grate frame 72 is arranged to rotate in the opposite direction with respect to the previous, i.e., first rotating grate frame 71. Second hydraulic cylinder 22; 222 is arranged in second air channel 23; 232 in the same way as first hydraulic cylinder 22; 221 related to first rotating grate frame 71 is arranged in first air channel 23; 231.

Third stationary grate frame 63 is arranged outside and under second rotating grate frame 72 in the same way as second stationary grate frame 62 was previously arranged with respect to first rotating grate frame 71. Third stationary grate frame 63 is supported on the lower part of combustion chamber 2, using third support 26; 262 which is preferably cylindric. Support 26; 261 of second stationary grate frame 62 and second cylindric support 26; 262 of third stationary grate frame 63 together circumvent second air plenum chamber 28, to which second air channel 23; 232 is connected.

Third rotating grate frame 73 is arranged outside and under third stationary grate frame 63 in a corresponding way as first and second rotating grate frames 71, 72 were arranged above with respect to corresponding stationary grate frames 61, 62. Third rotating grate frame 73 is supported eccentrically, using third cylindric support 15; 153, in connection with third bearing frame 16; 163 by the same principle as first and second rotating grate frames 71, 72 are supported in connection with the respective bearing frame 16; 161, 162. Bearing frame 16; 163 is supported rotatably in place, using both horizontal and vertical rolls 17, 18, on support 19; 193 arranged around support 26; 262 of third stationary grate frame 63. Vertical annular flange 16a is provided on the lower surface of bearing frame 16; 163, horizontal rolls 17 being supported against the flange. Third driving device, preferably third hydraulic cylinder 22; 223, is used to influence chain wheel 20; 203 in connection with bearing frame 16; 163 so that rotating grate frame 73 can be moved in thrusts. Third rotating grate frame 73 is arranged to rotate in the opposite direction with respect to the previous, i.e., second rotating grate frame 72. Third hydraulic cylinder 22; 223 is arranged in third air channel 23; 233 in the same way as first and second hydraulic cylinders 22; 221, 222 related to first and second rotating grate frames 71, 72 above were arranged in first and second air channels 23; 231, 232.

Fourth stationary grate frame 64 is arranged outside and under third rotating grate frame 73 basically in the same way as is described above in connection with the stationary and rotating grate frames. Fourth stationary grate frame 64 is supported on the lower part of combustion chamber 2 by using fourth support 26; 263 which is preferably cylindrical. Support 26; 262 of third stationary grate frame 63 and second support 26; 263 of fourth stationary grate frame 64 together circumvent third air plenum chamber 29, to which third air channel 23; 233 is connected.

Fourth stationary grate frame 64 is the outermost grate frame and its shape differs to some extent from the other grate frames 61, 62, 63, 71, 72, 73 described. In this application, grate frame 64 is an essentially flat, sheet-like periphery whose upper surface is arranged as a flat surface. There is no bracket periphery 13 on the lower surface of grate frame 64; it is not required here. Between outer edge 64b of grate frame 64 and jacket 4 of combustion chamber 2 there is a slit 30 through which ashes fall down into ash box 5.

Maintenance hatches 31 are arranged in jacket 4 of combustion chamber 2 under the upper surface of grate 1, through which maintenance hatches ash box 5 can be emptied of ashes collected therein. In a corresponding manner, maintenance hatches 32, 33, 34 (Fig. 4) can be arranged in supports 26; 261, 262, 263 of stationary grate frames 62, 63, 64, through which maintenance hatches air plenum chambers 27, 28, 29 can be maintained and cleaned. In addition, air channel 35 is connected to ash box 5, through which combustion air is directed, via the above-described air channels 23; 231, 232, 233 that lead to below grate 1, to combustion chamber 2 via air openings 14 of the grate frames. It should be further noted that air openings 14 of each rotating grate frame 71, 72, 73 are arranged to open outward from outer edge 71b, 72b, 73b of the grate frame, at an obtuse angle ό to the direction of rotation. Brackets 13a of bracket periphery 13, between which air openings 14 are arranged, are thus preferably elongated blades 13 arranged lengthwise along the lower surface of the grate frame, directing the combustion air outward from under grate 1 and ploughing ashes effectively outward from the top of the following grate frame together with the eccentric, lateral movement of the grate frame.

In principle, the combustion chamber and the grate illustrated in the figures function in the following way. Solid fuel, such as peat, is fed along feeding channel 8, using feeding screw 9, to the combustion chamber through feeding hopper 11. From feeding hopper 11 the solid fuel is discharged through output aperture 12 on different sides thereof and spread on grate 1. Combustion air is brought through air channel 35, ash box 5, and slit 30 to combustion chamber 2, and also through air channels 23; 231, 232, 233 underneath grate 1 to below grate frames 61, 62, 63, 71, 72, 73, and further through air openings 14 of the grate frames to the fuel and combustion chamber 2. Owing to the effective combustion air feeding, the fuel burns well in grate 1. Simultaneously with the burning event, rotating grate frames 71, 72, 73 of grate 1 are moved in thrusts using driving devices, such as hydraulic cylinders 22; 221, 222, 223, with the aid of chain wheels 20; 202, 202, 203 one pitch of teeth at a time, as described above. The second one of the rotating grate frames 72 is rotated in direction B, while the first and third rotating grate frames 71, 73 are rotated in opposite direction A. The rotation of grate frames 71, 72, 73 results in that, owing to their eccentric installation, these grate frames also move a small distance to and fro horizontally, whereby bracket peripheries 13 of stationary grate frames 61, 62, 63 wipe the upper surface of rotating grate frames 71, 72, 73 and clean them and, correspondingly, bracket peripheries 13 on the outer edge of rotating grate frames 71, 72, 73 wipe and clean the upper surfaces of the following stationary grate frames 62, 63, 64 underneath and outside.

It should be further noted that the widths of grate frames 61, 62, 63, 63, 71, 72, 73 are relatively small with respect to the diameter of grate 1 and its grate frames, whereby their cleaning is effective in the manner described above. The ashes of the burned fuel are thus removed stepwise from the first stationary grate frame 61 to the first rotating grate frame 71, and so on until the ashes fall through slit 30 into ash box 5. From there the ashes can be removed through maintenance hatch 31 from time to time.

The invention is described above mainly with reference to one of its advantageous embodiments but it is obvious that the invention can be applied in various ways within the inventive idea defined in the appended Claims.

Claims

1. A grate (1) comprising stationary (6) and rotating (7) grate sections, the grate (1) being preferably adapted in a combustion chamber (2) of circular horizontal cross-section, characterized in that the stationary grate section (6) comprises at least two separate stationary grate frames (61, 62, 63, 64) and the rotating grate section (7) comprises at least one rotating grate frame (71, 72, 73), which is adapted between the stationary grate frames and the stationary grate frames and the rotating grate frame being arranged in a concentric manner and stepwise close to one another, partly overlapping one another so that the innermost grate frame (61) is the uppermost with respect to the other grate frames (62, 63, 64, 71, 72, 73) , and the rotating grate frame (71, 72, 73) is installed eccentrically with respect to the stationary grate frames (61, 62, 63, 64), causing a lateral movement with respect to the stationary grate frames to be combined with the rotating movement of the rotating grate frame.

2. A grate according to Claim 1, characterized in that the number of grate frames (61, 62, 63, 64, 71, 72, 73) is odd and they are arranged so that every other grate frame is a stationary one and every other one is a rotating grate frame (61, 71, 62, 72, 63, 73, 64) .

3. A grate according to Claim 2, characterized in that the innermost and the outermost grate frames (61, 64) are stationary grate frames.

4. A grate according to Claim 1, 2 or 3, characterized in that the rotating grate frames (71, 72; 72, 73) closest to one another are arranged to rotate in opposite directions (A, B) .

5. A grate according to any of the preceding Claims, characterized in that each grate frame (61, 62, 63, 71, 72, 73) is a part with an essentially flat annular shape, a bracket periphery (13) being arranged in the vicinity of the outer edge (61b, 62b, 63b, 64b, 71b, 72b, 73b) of the annular part, preferably on the lower surface of the outer edge, except for the outermost grate frame (64) , the bracket periphery comprising brackets (13a) placed at a small distance from each other and essentially inclined downward.

6. A grate according to Claim 5, characterized in that the brackets (13a) of the bracket periphery (13) included in the grate frame (61, 71, 62, 72, 63, 73) together with the upper surface of the next grate frame (61, 71, 62, 72, 63, 73) form air openings (14) for the combustion air fed from underneath the grate (1) .

7. A grate according to Claim 6, characterized in that the air openings (14) of each rotating grate frame (71, 72, 73) are arranged to open outward from the outer edge of the grate frame, at an obtuse angle (0) to the direction of rotation (A,B) .

8. A grate according to any of the preceding Claims, characterized in that each rotating grate frame (71, 72, 73) comprises a chain wheel (20; 201, 202, 203) and a driving device, such as a hydraulic cylinder (22; 221, 222, 223), which is used to influence the chain wheel (20; 201, 202, 203) and to move the grate frame (71, 72, 73) in thrusts.

9. A grate according to Claim 7, characterized in that the driving device, preferably a hydraulic cylinder (22; 221, 222, 223), is fitted in an air channel (23; 231, 232, 233).

10. A grate according to any of the preceding Claims, characterized in that the combustion air feeding system comprises air channels (23; 231, 232, 233) which are connected to air plenum chambers (27, 28, 29) that are arranged under the grate (1) preferably in the areas defined by the stationary grate frames (61, 62, 63, 64) .