GB2139603A

GB2139603A - Solid-fuel feed auger

Info

Publication number: GB2139603A
Application number: GB08313139A
Authority: GB
Inventors: William John Holden
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-05-12
Filing date: 1983-05-12
Publication date: 1984-11-14
Also published as: GB8313139D0

Abstract

A solid-fuel boiler system includes a uniformly tapering auger which extends through a fuel bunker, the end thereof which is of least diameter being remote from the boiler and the end thereof which is of greatest diameter being near or nearer to said boiler. The pitch of the helical flight of the tapered auger is less than that of another auger which feeds fuel (e.g. coal) along a feed tube into a retort. <IMAGE>

Description

SPECIFICATION Solid fuel feed auger This invention relates to a solid fuel feed auger.

In published Applications No. 2,093,585A and No. 2,093,960 A, I have disclosed a solid fuel boiler system which includes a coal bunker or tank through which extends a shaft which carries a small diameter helical flight or screw (coal-feed conveyor screw) whose function is to ensure that coal is fed or propelled towards the location at which the coal will be burned; in fact, said conveyor screw acts to urge the coal towards another conveyor screw which is of larger diameter than the firstmentioned one and whose function is to force the coal into a feed tube mounted in the back of the boiler and along said tube to the retort.

Said conveyor screw of larger diameter could be so mounted that only two thirds of one pitch of the screw was exposed (namely, by extending into the bunker or tank), the intention being to ensure that only two thirds of the feed tube would be filled with coal at any time; an alternative to this arrangement would be to expose one half of one pitch of said screw in order to ensure that the feed tube is never more than half full. It was thought that, by so doing, a rough form of metering would be obtained.

Early observations of a working instailation showed that, in reality, something quite different was taking place; the small diameter coalfeed conveyor screw did not urge fuel towards the larger diameter conveyor screw but acted rather like a totally independent auger in its own right. It was noticed that, shortly after the bunker had been freshly filled with fuel, two small depressions would appear above shaded areas A 8 B shown in Fig. 1 of the accompanying diagrammatic drawings, and these depressions would gradually develop into deep pits which eventually exposed both the larger diameter auger and the small diameter auger at the opposite end of the bunker.

After a period of several days it was further noticed that the pit A stabilised whereas the pit B continued to grow in size until its angle of repose had been reached; after this, the pit B began to widen as shown in Stages 1, 2 and 3 etc., until pit B joined pit A.

This in effect proved that coal from area B was actually travelling under the general mass of fuel in the bunker and was combining with coal from area A. It was felt that this arrangement of coal feed was responsible for two unsatisfactory characteristics of the performance of the overall boiler system. The first was the inconsistent feed caused by exhausting fuel from pit A, after which only fuel from pit B would find its way into the boiler and this at a very much reduced rate due to the much smaller diameter of the respective conveyor screw. The second was the build-up of fines caused by the continuous feed of coal from area B underneath the main mass of fuel in the bunker, this action producing a tunnel with walls which are under pressure from the mass of coal from above.Friction between the moving coal from area B and the stationary surrounding coal under pressure causes a degrading of the fuel into dust particles, which are not carried forward by the auger because it is already full of fuel, and so these small particles simply accumulate in the centrai area of the bunker and eventually become so compacted that a fines "Swiss Roll" is produced around the small diameter auger. This "Swiss Roll" eventually becomes so compacted that it begins to grip the small diameter auger and then gradually increases the torque required until a stall condition is reached; alternatively, the "Swiss Roll" collapses as the bunker eventually empties and releases considerable quantities of fines which completely unbalance the combustion.

The solution of this problem at first seemed to be the production of a multi-stepped auger so as to encourage take-up of fuel at several different points along the length of the auger in the hope that this would lead to the dust particles being conveyed with the fuel in a more dispersed way. Such a multi-stepped auger proved, however, to be very difficult to make.

Accordingly, the present invention consists in a solid fuel boiler system which comprises a fuel bunker from which fuel is conveyed by a rotating conveyor screw towards the retort of the boiler, wherein said conveyor screw consists of a shaft which carries a helical flight whose diameter decreases in a uniform manner axially of said shaft, the part of said flight which is of the smallest diameter being at or in the vicinity of that end of the shaft which is farthest from the boiler. Preferably, the pitch of the helical flight of said conveyor screw is less than that of the larger diameter conveyor screw whose function it is to feed the fuel along a feed tube to the boiler retort.

A boiler system according to the present invention has been made and experimental/ evaluation trials thereof have demonstrated that the use of the fully tapered auger extending across the bunker (a) prevented the formation of the pits; (b) prevented the formation of the "Swiss Roll" and therefore avoided the effects thereof; (c) achieved complete and uniform dispersal of all fines and uniform fuel feed along the entire length of the bunker; (d) produced a regular fall rate across the surface of the fuel in a newly-filled bunker; (e) prevented the build-up of torque required to keep the auger rotating; (f) keeping the pitch of the flight of the tapered auger less than that of the larger diameter auger which actually feeds the retort ensures that the final feed tube into the retort is always only lightly filled and that there will be no build-up of fuel in the air interceptor box; this ensures, in turn that there will always be an adequate flow of air into retort.

Figs. 2 and 3 illustrate, diagrammatically, one way of carrying the present invention into effect.

The present invention further consists in any features of novelty, taken singly or in combination, of the embodiment(s) of the invention hereinbefore described with reference to Figs. 2 and 3 of the accompanying drawings.

Claims

1. A solid fuel boiler system which comprises a fuel bunker from which fuel is conveyed by a rotating conveyor screw towards the retort of the boiler, wherein said conveyor screw consists of a shaft which carries a helical flight whose diameter decreases in a uniform manner axially of said shaft, the part of said flight which is of the smallest diameter being at or in the vicinity of that end of the shaft which is farthest from the boiler.

2. A system as claimed in Claim 1, wherein the boiler includes a retort into which the fuel to be burned is fed by another conveyor screw which is located in a feed tube, and wherein the pitch of the helical flight of the first-mentioned conveyor screw is less than that of said other conveying screw.

3. A system as claimed in Claim wherein the tapered conveyor screw is connected at a location which is downstream of the bunker and upstream of the retort, to a conveyor screw position which is of substantially the same diameter as said other conveyor screw, the pitch Ou the helical flight of said conveyor screw portion being less than that of the helical flight of said other conveyor screw.

4. A system as claimed in Claim 2, wherein the pitch of the helical flight of the first-mentioned conveyor screw is two and one half inches (635 mm) and wherein that of the other conveyor screw is three inches (762 mm).

5. A system as claimed in Claim 3, wherein the pitch of the helical flight of the first-mentioned conveyor screw and that of said conveyor screw portion is two and one half inches (635 mm) and wherein the pitch of the helical flight of said other conveyor screw is three inches (762 mm).

6. A system as claimed in Claim 3 or Claim 5, wherein the downstream end of the conveyor screw portion is connected by a coupling means to the upstream end of said other conveyor screw in the vicinity of an air interceptor means.

7. A solid-fuel boiler system constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in Figs. 2 and 3 of the accompanying diagrammatic drawing.

8. Any features of novelty, taken singly or in combination, of the embodiments of the invention hereinbefore described with reference to the accompanying diagrammatic drawing.