FR2563320A1 - Boiler for the combustion of non-bituminous coals - Google Patents

Abstract

The present invention relates to a boiler 1 for the combustion of non-bituminous coals in a furnace 2 comprising, in its front part, at least one projector 3 delivering continuously into the opposite part a given charge of coal, in its bottom part a mechanical grille 20 which receives the coal which is partially burned in the opposite part to that of the projector and returns this coal into the front part of the furnace, characterised in that it comprises under the projector a radiating refractory arch 30 which partially covers the grille. Application to the combustion of non-bituminous coals in boilers with grille and projector.

Description

Boiler for burning lean coals
The present invention relates to a boiler for the combustion of lean coals, that is to say those whose volatile matter content is less than 20% (less than class 4 of the AFNOR standard).

 The burning of lean coals can be done by heating with pulverized coal, but fine grinding of the coal makes this technique less economical.

 Grid and spray boilers are known which use a very economical technique, but these boilers only allow the combustion of coals, the volatile matter content of which is greater than 20%.

The object of the present invention is to widen the technical limits of these boilers by an improvement allowing them to burn lean coals whose volatile content is less than 20% with combustion results similar to those of a pulverized coal boiler
The present invention relates to a boiler for the combustion of lean coals in a fireplace comprising, in its front part at least one sprayer continuously delivering in the opposite part a determined charge of coal, in its lower part a mechanical grid receiving the coal partially burnt in the part opposite to that of the sprayer and bringing this coal back into the front part of the hearth, characterized in that it comprises under the sprayer a radiant refractory vault partially covering the grid.

 Advantageously, the surface of this vault represents 20 to 50% of the total surface of the grid and the slope of this vault is between 0 and 30%.

 The vault can be traversed by air or water circulation.

 I1 is described below, by way of example and with reference to the figure of the accompanying drawing, a boiler according to the invention.

 The single figure represents a boiler 1 comprising a hearth 2.

This hearth is provided on the front wall with a sprayer ion 3 supplied with coal with a particle size close to 40 rom for example, by an extractor-backer device 4 placed under a storage hopper 5, then under the sprayer 3, a nozzle 6 for injecting secondary air and finally, in the opposite rear zone, two nozzles 7 and 9 for injecting secondary air and a nozzle 8 for re-injecting particles.

 All these elements are, of course, known.

 This boiler 1 also comprises, in a known manner, at the outlet of the hearth 2 a superheater 10 placed on the passage of the flue gases which connects a collector 11 and an upper tank 12 itself connected to a lower tank 13 by vertical tubes 14 of an evaporator 15. The hearth 2 is delimited downwards by a horizontal or inclined mechanical grid 20 constituting an endless flesh 21 passing on either side of the boiler and up to under a vault 30 placed below the nozzle 6.

 This conveyor chain is driven by a driving wheel 22, guided by a free wheel 23 and tensioned by a tensioning roller 24. The grid 20 receives the charcoal 25 in the vicinity of the nozzle 7 and transports the latter as far as the vault 30. This charcoal transformed into a bottom 25 ′ is evacuated at the end of the grid by gravity in a duct 26. This refractory vault 30 can be cooled by the circulation of air or water.

 The surface of this vault 3Q represents 20 to 50% of the total surface of the grid and the slope is between 0 and 30S.

 This original arrangement does not exclude the use of conventional and known means to improve the combustion efficiency if necessary: crushing of coal, heating of the combustion air, total reinjection of the soot.

 The combustion operation takes place in the following manner.

 The coal 25 is stored in the hopper 5 then transported by the extractor-backing device 4 and projected continuously using the projector 3.

 Combustion begins during the trajectory above the mechanical grate 20 under the nozzle 7. The mechanical grate 20 then transports the partly burnt coal 25 in a direction opposite to the projectlon and the combustion continues. The carbon then arrives under the refractory vault 30 which improves the combustion by channeling the hot gases towards the coal during or at the start of ignition on the grate.

This vault 30 favors the ignition of carbon particles in suspension leaving the sprayer 3 and constitutes a very hot zone allowing, if necessary, to complete the complete combustion of the last parts of unburnt fuel before their extraction.

 In a known manner, the fumes are channeled to pass obligatorily into the superheater 10 and then pass through the evaporator 15.

Claims (4)

1 / Boiler for the combustion of lean coals in a central hearth provided, in its front part at least one sprayer continuously delivering in the opposite part a determined charge of coal, in its lower part a mechanical grid receiving the partial charcoal burnt in the part opposite to that of the designer and bringing this coal back to the front of the fireplace, characterized in that it spreads under the projector a radiant refractory vault partially covering the grate. 2 / Boiler according to claim 1, characterized in that the surface of the vault represents 20 to 50S of the total surface of the grate. 3 / Boiler according to one of claims 1 to 2, characterized in that the slope of the vault is between 0 and 302. 4 / Boiler according to one of claims 1 to 3, characterized in that the refractory vault is traversed by a circulation of air or water.