Furnaces – Including means to feed solid fuel – Movable grate
Patent
1990-05-14
1991-01-01
Favors, Edward G.
Furnaces
Including means to feed solid fuel
Movable grate
110257, 110286, 198777, 126152B, 126176R, F23H 710
Patent
active
049810901
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an arrangement of the type stated in the preamble of the claim.
In incinerators, especially for refuse and the like, it is important that the pressure drop through the grate is carefully supervised. It is equally important that the distribution of air across the entire grate is as uniform as possible to prevent that a strong through-flow of air occurs at some locations, while at other locations in which the fuel layer is compact, practically no combustion air passes.
In movable grate incinerators, preferably such as described in Swedish patent specifications 315,679, 316,559 and 338,125, the grate is made up of a number of mutually movable and, more precisely, tiltable steps, each step consisting of a number of bars which are laterally interconnected and supported by a common shaft. Each end of such a step is provided with an end plate adapted to be fitted in an opening in the fixed side shields of the grate. To allow relative pivotal movement of the grate steps partly overlapping one another, the front and the rear edges of the step formed by the grate bars extend beyond the associated end plate and closely follow the side shield as the grate steps move. In the prior art design, a space outside the side shield is used as a duct for secondary air which is blown out at the upper edge of the side shield after having cooled the outside of the side shield and the end plates. This amount of secondary air constitutes part of the amount of air which is supplied under the grate as primary combustion air. The cooling efficiency thus depends to some extent on the amount of primary air which is injected.
Since the length of the shaft changes under the action of heat, the end plates and the outermost grate rods are displaced relative to the side shields, for which reason a free space must be left between the outermost grate rods and the side shields and also at the periphery of the end plates so as to prevent mechanical contact with the side shields and ensuing wear, when the shaft expands. However, these free spaces, although small in themselves, interfere with air supply and pressure drop, when the total area of the free spaces along the grate is so large that the intended air flow cannot be maintained. The air takes the easiest way, i.e. when the free spaces are "large" along the edges of the grate surface where also the fuel layer, as a rule, is thinner than in the centre, and consequently the supply of air along the centre part of the grate will be insufficient, when the grate temperature is low. When the grate has become heated, the grate step shafts have expanded and the free spaces have been substantially eliminated.
The invention aims at completely obviating the shortcomings which are caused by the heat expansion and contraction of the grate step shafts and affect the air supply.
The novel features of the invention are stated in the claims.
An embodiment will now be described with reference to the accompanying schematic drawings in which
FIG. 1 is a cross-sectional view of one side wall of the incinerator in parallel with the grate step shaft, and
FIG. 2 shows, partly in section radially through the grate step shaft and on a smaller scale, one side of the incinerator as seen from the inside.
One end of the grate step shaft is designated 1, the shaft being mounted in a manner not described in detail in a grate frame (not shown) by means of a bearing 2 allowing axial movement of the grate shaft. Adjacent the bearing, cup springs are arranged to position the shaft, and a sealing ring enclosing the cup springs. The grate shaft portion 3 extending across the incinerator and radially offset in a crank-like manner relative to the shaft ends 1, carries a number of grate bars 4 forming the grate steps. Adjacent the outermost grate bar 4', an end plate 5 is screwed to the cranked shaft, said end plate following the movement of the grate step. The lower portion of the plate is formed by the flange coupling between the cranked shaft and the centre part.
The side wall of the incinerator is
REFERENCES:
patent: 3581684 (1971-01-01), Nobelius et al.
patent: 4793471 (1988-12-01), Bartels
B & S Miljoteknik A/S
Favors Edward G.
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