WO1995006845A1

WO1995006845A1 - Method for combustion of solid fuels and grate comprising superposed flat elements

Info

Publication number: WO1995006845A1
Application number: PCT/SE1994/000799
Authority: WO
Inventors: Mats KARLSTRÖM
Original assignee: RK ENERGI AB
Current assignee: RK ENERGI AB
Priority date: 1993-09-01
Filing date: 1994-08-31
Publication date: 1995-03-09
Anticipated expiration: 1996-03-01
Also published as: EP0714495A1; AU7627394A; SE9302820D0

Abstract

This invention relates to a method of gasification/combustion of a solid fuel in a furnace by means of a grate device comprising a plurality of grate means, positioned on different levels, which device is intended to be positioned at the bottom portion of the furnace. According to the invention the method is characterized by the combination of the following steps: the solid fuel is fed out onto the outside of the grate device so that the fuel forms a layer on the same; primary air is brought up through the grate device (1), the primary air during the passage from one grate means to a superposed grate means (3-6) hitting against the underside of this grate means, whereby the pressure fall of the primary air becomes great; the primary air is evenly and effectively distributed out to the fuel on the outside of the grate device (1), the primary air being allowed to stream outwards from each grate means (3-6) with a low velocity. The invention also relates to a grate device which is usable for carrying out the method.

Description

Method for combustion of solid fuels and grate comprising superposed flat elements.

This invention relates to a method of gasification/combustion of a solid fuel in a furnace by means of a grate device comprising a plurality of grate means, positioned on different levels, which device is intended to be positioned at the bottom portion of the furnace. The invention also relates to a grate device which is usable for carrying out the method.

Grate devices for furnaces in which a solid fuel is intended to be gasified/burnt up are previously known in the market. The drawback of the known devices is that they do not give a complete gasification/combustion of the fuel.

This grate device, in contrast to the known grate devices, gives an extremely effective gasification/combustion of the fuel. This has been made possible by the fact that the grate device has the features which appear from the claims.

A preferred embodiment of the invention shall be described more closely below with reference to the accompanying drawings, where Fig 1 shows a schematic sketch of a furnace in which the new grate device is intended to be used, Fig 2 shows the grate device, seen from above, Fig 3 shows the grate device, seen from the side and divided into grate means, and Fig 4-12 show the grate means being integral parts of the grate device.

Referring to fig 1 is shown there a schematic sketch of the new grate device 1 positioned on the bottom portion of a furnace 2. The grate device 1 has a plurality of grate means 3-7 which have an essentially round design with mutually different diameters. These grate means are intended to be superposed in relation to each other, the means being positioned in that way that the diameter is reduced in the direction upwards. Due to that fact the grate device 1 gets a design which is sloping downwards, seen from the upper, central portion of the grate device. The grate device 1 has a hole 8 in its central portion, which hole goes through the device and through which hole the solid fuel is intended to be fed in the direction from below and upwards. Due to the sloping design of the outside of the grate device, the fuel will slide down along the device and accordingly form a layer, which is of relatively uniform thickness, on the outside of the grate device.

According to this embodiment the grate device 1 comprises five different grate means 3-7, each of the four uppermost grate means comprising two rings, an upperring A and an underring B. The lowermost grate means 7 comprises only one ring and has a design which is similar to the design of the upperrings 4A, 5A and 6A. All upperrings 3A-7 (see for instance fig 12) are designed as an essentially circular plate in which has been made an essentially circular recess 9. Due to that fact there is created an area 10, comprising material, between the periphery 11 of the the plate and the periphery 12 of the hole 9, i.e. the inner edge portion of the area 10. In this area of the upperrings 4A-7 (see fig 12) has been made a great number of holes 13, which go through the upperrings and have an essentially regular placing around the rings. The function of the holes 13 is to lead primary air up through the grate device so that the gasification/combustion of the fuel can proceed in an effective way. The uppermost upperring 3 A has not these holes going through the ring but has in similiarity with the remaining rings the central hole 9, which goes through the ring. As is apparent from figs 8, 9 the upperrings 5A, 6A are provided with two holes 13A, B, which are positioned close to each other. These two upperrings can be turned some degrees during operation, whereby the primary air only goes up through the one hole 13A, B. Due to that fact the hole area of the primary air can be reduced with up to 30%.

As has been mentioned previoulsy each grate means 3-6 comprises an underring B, which accordingly is positioned under respective upperring A. Respective underring 3B - 6B has a very special design, which is apparent from the drawings. Each underring has two main purposes: Partly it shall distribute the primary air hitting the underside of the superposed upperring, partly it shall make possible a passage of primary air up through the grate device. For this purpose each underring 3B - 6B (see particularly fig 11) has a periphery 14 which is like the periphery of a gear-wheel but with that difference that the "points of the gear-wheel" 15 has a rounded design in this case. Between the "points of the gear-wheels" 15 there is a space 16 with delimitation walls 17, 18. The purpose of these delimitation walls is to distribute the primary air hitting against the underside of the superposed upperring towards the fuel lying on the outside of the grate device 1 with a low velocity which does not exceed 4 m/s. Due to this fact the gasification/combustion of the fuel is made more effective. This new construction where the primary air passing the holes 13A, B, in for instance the upperring 6A, hits against the underside of the upperring 5 A has the consequence that the pressure fall of the primary air becomes great. This great pressure fall, which ought to exceed 400 pascal, is a condition that the air reaching the fuel hearth becomes uniformly distributed. As has been mentioned previously, there is a central hole 8 going through the grate device 1. This means that each grate means 3-7 has a central hole 19 and so has also the underring 6B (see fig 11). Due to that fact there is an area 20, comprising material, between the perephery 14 of the underring 6B and the periphery of the hole 19. The inner edge portion 21 of this area 20, i.e. the peripheral portion of the hole has a reversed gear- wheel-like design with rounded points 22, i.e. the "points of the gear-wheel" 22 are directed towards the center of the underring 6B. Each recess 22 which exists between two adjacent "points" 22 is positioned in that way that it is essentially right before the "point of the gear-wheel" 15 at the outer, peripheral portion of the underring 6B. Furthermore, each recess 23 has essentially straight delimitation edges 24, 25. The purpose of the recesses 23 of the underrings 4B-6B is to create a space for the streaming of the primary air from below and upwards in the grate device 1. Due to that fact the fuel on the entire outside of the grate device gets a good supply of primary air. The underring 3B which is that one of the underrings, which is intended to be positioned on the top of the device, is different regarding the design from the remaining underrings 4B-6B. Thus, the inner edge portion 21 of the area 20, provided with material, of this underring has essentially circular form.

The grate device functions in the following way. In this connection is presumed that the grate device is positioned at the bottom portion of a furnace and that primary air is supplied to the grate device from below.

Primary air is supplied towards the underside of the grate means 7, which is provided with a great number of holes 13 round the means. These holes have such a placing that the recesses 16 between the "points" 15 of the peripheral portion 14 of the underring 6B can be positioned essentially straightly above the holes 13 of the grate means 7. This means that primary air which is forced upwards through these holes hits against the underside of the upperring 6A, and is distributed out into the fuel hearth on the outside of the grate device 1 by means of the delimitation walls 17, 18 of the recesses 16 of the underring 6B.

The recesses 23 at the inner edge portion 21 of the area 20 of the underring 6B have such a design and are so arranged that when applying the upperring 6A on this underring, the holes 13A, B of the upperring 6A end up essentially straightly above the recesses 23. This means that the primary air being forced up through the centrally positioned hole of the grate device 1 streams through the recesses 23 of the underring 6B, through the holes 13 of the upperring 6A, through the recesses 16 of the underring 5B and hits against the underside of the upperring 5A and is then distributed out into the fuel hearth in a similar way as has been described previously by means of the delimitation walls 17, 18 of the recesses 16 of the underring 5B. By turning for instance the upperring 6A some degrees, the one hole 13A, B gets out of position in relation to the recess 16 of the superposed underring 5B. Due to that fact, as has been mentioned previously, the hole area for the primary air streaming upwards can be strongly reduced. This fact makes great variations regarding the power output possible. Thus, it is possible with this new invention to vary the power output from a maximum value to a value being under 10% of the maximum value. This is of course a great advantage from an economic point of view. In a similar way the primary air will be distributed out to the fuel hearth on the levels lying above.

It should be clear for everyone that this invention makes possible an extremely good distribution of primary air into the fuel hearth along the outside of the entire grate device 1. The invention is of course not limited to the mentioned embodiment but can be modified within the scope of the following claims. Thus, it is not necessary to feed the fuel to the grate device from below, but the fuel should be able to be fed to the grate device from above. The grate device can of course have another design than the shown one. For instance, it could be designed in that way that it rises in steps. Furthermore, it is not necessary that the grate means are made circular but they could have another design.

Claims

1. A method of gasification/combustion of a solid fuel in a furnace by means of a grate device comprising a plurality of grate means, positioned on different levels, which device is intended to be positioned at the bottom portion of the furnace, c h a r a c t e r- i z e d by the combination of the following steps:

- The solid fuel is fed out onto the outside of the grate device so that the fuel forms a layer on the same;

- Primary air is brought up through the grate device (1), the primary air during the passage from one grate means (4-7) to a superposed grate means (3-6) hitting against the underside of this grate means, whereby the pressure fall of the primary air becomes great;

- The primary air is evenly and effectively distributed out to the fuel on the outside of the grate device (1), the primary air being allowed to stream outwards from each grate means (3-6) with a low velocity.

2. A grate device usable for carrying out the method according to claim 1 and intended for a furnace in which a solid fuel is intended to be gasified/burnt up, the grate device being intended to be positioned at the bottom portion of the furnace, and the fuel being intended to be fed to the outside of the grate device, where it forms a relatively uniform layer, c h a r a c t e r i z e d by the combination of the following features: - The grate device (1) comprises a plurality of plate-like grate means (3-7) of different sizes, which are superposed in relation to each other;

- Each grate means (3-6) except the lowermost one comprises an upper part (A) and an underpart (B);

- The lowermost grate means (7) and the upper part (A) of each grate means (4-6) except the uppermost one have a great number of holes (13), which go through the grate means and have a regular placing on the means/the upper part;

- Each underpart (3B-6B) has a space (16) with delimitation walls (17, 18) at its peripheral part, which space is open outwards;

- The upperparts (A) and the underparts (B) are arranged in that way that when cooperating the holes (13) of one upper part (A) in an underlying grate means (4A-7) are positioned under the spaces (16) of the underpart (B) of the superposed grate means (3-6) so that the primary air streaming upwards through the holes (13) of the upper part (A) of the underlying grate means (4-7) can pass the space (16) of the underpart (B) of the superposed grate means (3-6) and hit against the underside of the upper part of the mentioned grate means (3-6) in order then to be distributed out to the outside of the grate device at this level by means of the delimitation walls (17, 18) of the mentioned space

(16).

3. A grate device according to claim 2, the grate device having a central hole, which goes through the device and extends essentially vertically through the device, and the grate means having an essentially circular design, characterized in that each underring (3B-6B) has a periphery (14) which is like the periphery of a gear-wheel, but with rounded "points of gear-wheels" (15), the spaces (16) with the delimitation walls (17, 18) being positioned between the "points of the gear-wheels" (15).

4. A grate device according to claim 3, each grate means (3-7) having a central hole (19), and each underring (4B-6B) having an area (20), comprising material, between the periphery (14) of the underring and the periphery of the hole (19), i.e. the inner edge portion of the area (20), characterized in that the inner edge portion (21) of the area has a reversed gear-wheel-like design with rounded "points of gear-wheels" (22), i.e. that the points (22) are directed towards the center of the underring (B), and that between two adjacent "points of gear-wheels" (22) there is a recess (23) with essentially straight delimitation edges (24, 25).

5. A grate device according to claim 4, characterized in that the upperring (A) and the underring (B) of each grate means (4-6) are so arranged, that in a normal position the holes (13) of the upperring (A) are positioned essentially straightly above the recesses (23) of the underring (B).

6. A grate device according to claim 4 or 5, the grate means (5, 6) comprising two holes (13A, B) which are positioned close to each other around the entire means, characterized in that the grate means (5, 6) from the normal position is turnable one or some degrees, whereby the one of the two holes (13A, B) is covered by the "point of the gear-wheel" (15) of the superposed grate means (4, 5).