EP0191254B1 - Furnace grate provided with elements which permit a better control of the primary air supply - Google Patents

Description

The present invention relates to a hearth grate intended to support the combustible mass in an oven, in particular for the incineration of waste. The present invention also relates to the individual elements which constitute this grid.

Fuel grids are known which are generally of the type comprising a plurality of individual elements which are identical to each other. These grids are generally inclined, so that the combustible mass discharged at one of their ends progresses along the slope. To do this, and also so as to obtain a good distribution of the combustible mass along the grid, a mixing of this mass is generally necessary.

This mixing is generally carried out by a movement of the individual grid elements which move relative to one another. Asperities, or a particular arrangement (in staircase, for example) allow the elements to modify the surface of the grid according to their respective movements. Brewing is thus achieved.

Such a grid is described in particular in document FR-A-1 567 605 (J. Martin).

In other embodiments, the elements are arranged to supply air to the combustible mass. Reference may be made in particular to patent FR-A-1 006 739 describing an air communication system being established between adjacent elements during their relative longitudinal displacements.

The main problem with the incineration of products such as waste resides in the release of sulphides, which tend to create deposits due to their lower melting point than that of their oxidation product. In addition, they mainly contribute to making the environment extremely corrosive, which tends to create longevity problems for the entire incineration plant. It is thus important to promote the transformation of these sulphides (CaS, Na ₂ S, FeS in particular) into sulphates or corresponding solid oxides and to this end adjust the combustion conditions by ensuring as regular and total combustion as possible.

The support grid elements are therefore generally provided with orifices allowing the primary air blown below the grid to supply the combustion with oxygen.

Such grid elements are known from document DE-U-6 905 562 (C. PETERS AG).

However, the grids made of elements pierced with orifices in very large numbers do not allow good control of the quantity of primary air supplied.

This is important because the excess of primary air is no more favorable for good combustion than its defect.

The document FR-A-2301 163 describes a cooling and combustion grate plate, in particular for an advancing grate, rectangular in plan and having two faces, upper and lower substantially equidistant, a front face carrying a support rim provided for rest on the upper face of an element upstream on the grid, and orifices forming nozzles for blown air leaving from the lower face to open into the upper face near the front face. In addition, longitudinal ribs projecting from the underside constitute, with the orifices, in longitudinal slots, nozzles which narrow upwards. It is clear that the air comes out of the slots normally on the upper face, that is to say in a direction closer to a vertical than a horizontal.

The problem which arises is the blocking of the air intake orifices by the deposition of the sulphides themselves, or by elements which are not yet burnt from the combustible mass. This randomly changes the oxygen supply, which affects combustion.

A second problem which arises is that created by the lifting of the mobile elements, which can intervene by the accidental insertion between two elements of a waste. The lifting of an element has two effects: it disrupts the oxygen supply, and it allows an element to penetrate under the grid, possibly in the primary air supply means. The increase in the weight of each element made it possible to obviate this drawback, but other problems, in particular of construction, would then arise.

Another problem which also arises is that of the abnormal heating of the elements: in the event of blockage of the orifices allowing the passage of air through an element, the latter heats up abnormally, with all the consequences involved: rapid deterioration and / or excessive expansion leading to seizure with neighboring elements.

Another difficulty comes from the excessive quantity of fly ash that can be produced, causing rapid fouling of the parts of the incineration plant located above the hearth.

The object of the present invention is to remedy these drawbacks by proposing a new hearth grid.

The invention proposes for this purpose a hearth grate intended to support a combustible mass during its combustion, in particular in a garbage incineration plant, generally inclined longitudinally downhill from an upstream end where the combustible mass is brought up to '' at a downstream end, this grid consisting of a plurality of elements arranged contiguously in alternately fixed and mobile transverse rows, each element being rectangular in plan and having two substantially equidistant faces which will be called res pectively upper and lower face by reference to their arrangement in the grid, a front face turned upstream and starting from a support rim intended to rest on the upper face of the element immediately upstream in the grid, orifices forming nozzles for blown air leaving the lower face to open into the upper face near the front face, grid characterized in that the element comprises in its upper face a transverse protuberance flush with the front face, which is connected to the upper face by a dorsal face facing downstream of the grid, the orifices all opening into this dorsal face with their axis directed downstream in ascending, the slope of this axis being closer to a horizontal than vertical.

• - Le mouvement de va-et-vient relatif des rangées transversales implique le même mouvement aux protubérances frontales, qui procurent ainsi un brassage et un retournement permanent des déchets.
• - La disposition sur la face dorsale des orifices évite que, lors du brassage des déchets, ceux-ci ne viennent obturer les orifices.

In this way, several advantages are combined to ensure the best possible conditions for waste combustion:

• - The relative back-and-forth movement of the transverse rows involves the same movement at the front protrusions, which thus provide permanent mixing and turning of the waste.
• - The arrangement on the dorsal side of the orifices prevents that, during the mixing of the waste, it does not come to close the orifices.

Thus, the circulation of air between from below to the top of the grid is ensured without the stirring of the combustible mass coming to alter it.

In this way, the combustion conditions provide increased efficiency, which makes it possible to reduce the relative speed of movement of the rows and therefore the wear of the grate.

According to another aspect of the invention, the orifices are the only means of air communication between the bottom and the top of the grid. Thus, it is possible to determine the quantity of primary air supplied to the combustible mass in order to achieve the best combustion conditions.

According to another aspect of the invention, all the elements of the same transverse row are integral and contiguous by their sides.

This makes it possible to prevent the lifting of an individual element thanks to the total mass of an entire row thus secured.

Other characteristics and advantages of the invention will emerge from the description which follows concerning a preferred embodiment of the invention shown by way of example in the appended drawings in which.

Figure 1 is a perspective view, partially broken away, of a grid element according to the invention.

Figure 2 is a longitudinal sectional view of a grid element according to the invention.

Figures 3 and 4 are side elevational views of a grid according to the invention, the movable rows being in the high or low position respectively.

Figure 5 is a perspective view of a grid according to the invention from which several elements have been removed.

The individual element represented by FIGS. 1 and 2 under the reference number 10 consists of a part of generally rectangular shape in plan, comprising a front part constituted by a so-called frontal protuberance 11 projecting from the upper face, and having a forward inclined face 12 called the front face, a flat top 14, and a rear inclined face 13, called the dorsal face.

This protuberance, of constant cross section, extends over the entire width of the element 10.

Following this frontal protuberance, towards the rear, the element has a flat part 19 on the top. A transverse groove 17 is formed under the element near its rear edge, and parallel to it.

A bearing edge 15 is formed by the thickness of the wall of the element, at its anterior end formed by a projection downwards from the front face 12.

This projection being substantially normal to the general plane of the element 10, the bearing edge is substantially parallel to this plane.

The thickness of the element is constant in the exemplary embodiment illustrated. The protuberance of the upper face therefore corresponds to a hollow in the lower face, also comprising a front face, a dorsal face and a bottom connecting these two faces. Two side cheeks 16, substantially flat and projecting from the underside, border the element. These cheeks are pierced with openings 18 situated directly above the flat top 14 of the protuberance 11.

These two openings 18 are symmetrical with respect to a median longitudinal plane of the element 10, and allow the passage of a rod 18 'which secures, in the grid, adjacent elements (Fig. 5).

Three calibrated orifices 20 pierce the wall forming the dorsal face 13 of the protuberance 11, in a direction substantially normal to the latter.

FIGS. 3 and 4 illustrate a hearth grid according to the invention produced from elements 10.

In general, the grid has an end A called upstream, corresponding to the supply of waste constituting the combustible mass, and an opposite end B, said downstream, located at a lower level.

In practice, arranged in the grid, the so-called front parts of each element are turned upstream, and the so-called back parts are turned downstream.

The grid consists of two parts, one fixed, the other mobile.

The movable part comprises a frame-forming structure consisting of two parallel uprights 25 interconnected by at least two spacers such as 26. The uprights 25 rest on inclined planes 29, by means of rollers 28. These rollers are mounted on axes integral with the uprights 25, allowing them to roll on the inclined planes which correspond to them. My tants 25 have, at regular intervals, bosses 22 projecting from their upper part. On these bosses are fixed support cross members 21A with T section lying on the side.

The fixed part comprises a structure made up of support crosspieces 21 B similar to and parallel to the crosspieces 21 A. The support crosspieces 21 B are fixed by oblique bars 21C secured to the body of the hearth.

The elements 10 come to bear on the support crosspieces 21 A, 21 B by their rear grooves 17, and on the upper face of the preceding element by the support flange 15. The elements 10 are thus arranged contiguously in rows parallel, each row resting simultaneously on a support cross member 21A or 21 B and on the previous row, in the manner of tiles.

The first row is supported on a fixed support cross member 21 B on the one hand, and on a structural support 21 provided for this purpose in the body of the hearth, on the other hand.

A drive cylinder 30 is fixed to the front spacer 26, making it possible to move the frame-forming structure of the movable part in a reciprocating movement according to the direction and the amplitude of movement determined by the inclined planes 29 The amplitude of these movements is limited by the stops 31 which are provided with the inclined planes 29. The mobile structure being integral with the rows of elements 10 which it supports, the whole of the mobile part moves according to the movement of back and forth controlled by cylinder 30.

The grid is bordered laterally (FIG. 5) by two housings 34 of U section which cover the rollers 28 and the inclined planes 29. The lateral edges of these housings are joined with the cheeks 16 of the elements 10 immediately adjacent. These casings 34 are made up of a succession of jumpers 32 resting on a spar 33. A grid can also be made up of several sets of rows of elements 10, each set being separated from the adjacent set by a casing 34.

The purpose of these housings is to avoid uncontrolled air communication between the underside and the top of the grille.

When the waste is discharged so as to fall on the first rows of elements of the grid, the back-and-forth movement of the movable rows resting on the fixed rows sets said waste into motion. The front protrusions 11, by this back-and-forth movement, effect mixing of the mass of waste, which is put into combustion. The inclination of the grid causes them to progress slowly, by gravity, along it, from upstream to downstream.

The joining by the rod 18 ′ of the adjacent elements in a row prevents the individual lifting of an element due to a possible insertion of a waste: each element being joined, such an insertion would imply the lifting of the whole row, which its weight prohibited.

The faces 13 inclined towards the rear of the protrusions 11 are due to the inclination of the grid, in a position making an angle of about 15 ° relative to the vertical. This has the effect of preventing waste or combustion products from sticking together on said faces. Thus, the orifices 20 remain free from any blockage.

These orifices, being directly in contact with the mass of waste, allow a local supply of primary air, necessary for good combustion. The primary air is supplied by a blower located under the grid. The elements 10 being contiguous, the primary air is caused to pass only through the orifices 20, which makes it possible to control both the flow rate and the orientation of the orifices 20 determines that of the primary air jets which come to through the gate. This orientation of about 15 ° with respect to the horizontal is important in that the air jets tend to volatilize ash which, if these jets are directed in a direction closer to the vertical, tend to rise and foul the superior structures of the hearth: The orientation of these jets therefore makes it possible to avoid this drawback.

The advantages obtained thanks to the invention allow a reduction in the phenomenon of volatilization of incandescent ashes and therefore consecutive deposits on the upper structure of the hearth, on the one hand, and better combustion obtained thanks to a regular supply of primary air, and therefore a better yield and a reduction in corrosion due to sulphides, on the other hand.

In addition, an improvement in combustion makes it possible to reduce the speed at which the combustible mass is stirred, and therefore the elements slide over one another. This reduces wear.

Other alternative embodiments can also be produced without departing from the scope of the invention. For example, the rows of attached individual elements could be replaced by single elements, produced in sections, each element extending over a more or less significant part, or even the entire width of the grid.

Claims (11)

1. Furnace grate which is intended for supporting a combustible mass during its combustion, notably in an installation for incinerating rubbish, and which is, overall, longitudinally downwardly sloping from an upstream end (A) to where the combustible mass is brought, to a downstream end (B), this grate being constituted by a plurality of elements which are arranged contiguously in transversal rows which are alternately fixed and mobile, each element being of rectangular plan and having two substantially equidistant faces which will be referred to respectively as upper face (19) and lower, with reference to their arrangement in the grate, a frontal face (12) turned towards the upstream direction and starting from a support shoulder (15) provided for resting on the upper face of the element immediately upstream in the grate, orifices (20) forming nozzles for blown air starting from the lower face so as to open into the upper face (19) in proximity to the frontal face (12), grate characterised in that the element (10) comprises, in its upper face (19), a transversal protuberance (11) flush with the frontal face (12), which is joined to the upper face (19) by a dorsal face (13) turned towards the downstream direction (B) of the grate, the orifices (20) all opening into this dorsal face (13) with their axis directed towards the downstream direction as they rise, the slope of this axis being nearer to a horizontal than to a vertical.

2. Grate according to claim 1, characterised in that the axes of the orifices (20), which form nozzles, are parallel in relation to one another and substantially perpendicular to the dorsal face (13).

3. Grate according to one of the claims 1 and 2, characterised in that the axes of the orifices (20) form, with the horizontal, an angle of about 15°.

4. Grate accordling to any one of the claims 1 to 3, characterised in that the elements (10) comprise interlocking means (18, 18') capable of interlocking the elements of a row.

5. Grate according to any one of the claims 1 to 4, characterised in that the elements (10) comprise lateral cheeks (16) capable of contiguously coupling-together a row.

6. Grate according to claims 4 and 5 jointly, characterised in that the lateral cheeks (16) comprise orifices (18) which are symmetrical in relation to a longitudinal median plane of the element (10), a shank (18') being engaged in the orifices (18) of the elements of a row.

7. Grate according to any one of the claims 1 to 6, characterised in that each element (10) has a transversal groove arranged in the lower face in proximity to the downstream end of the element, and which engages on support crossbars of rows which are alternately fixed (216), and mobile (21 A).

8. Grate according to claim 7, characterised in that the mobile crossbars (21A) are fixed on a frame (25, 26) which is capable of having a longitudinal to and fro movement imparted to it.

9. Grate according to claim 8, characterised in that the frame (25, 26) is provided with rollers (28) rolling on ramps (29).

10. Grate according to any one of the claims 1 to 9, characterised in that the support shoulder (15) of each element (10) is capable of resting on the upper face (19) of the element immediately upstream, in substantially tight sealed manner.

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