Process and apparatus for continuous dry removal of bottom ash

Abstract

Provided is a process to continuously dry remove ash from the bottom of steam boilers by discharging the ash on a high temperature resistant conveyer which is enclosed in a tight sealed envelope. Also is provided an apparatus for accomplishing this which has a steel conveyer belt constructed to withstand high temperatures and enclosed in a sealed steel box connected to the bottom of the boiler so that the conveyer continuously receives and discharges ash from the boiler.

Description

The present invention relates to a process for continuous dry removal of bottom ash as well as to the relevant apparatus for carrying out said process.

Coal used in steam production that a condition in which the material slides back in the inclined stretches. Thus these plates 1 have the load bearing function, while the driving function is effected by a high strength steel wired belt 2. Each plate 1 is individually fixed to belt 2 by bolts 8 with relevant nut 10, which however may be replaced by rivets or other equivalent fastners, which are connected to crosspieces 9 suitably inserted in the links of said wired belt 2. This open system allows free expansion of plates 1 in any direction when temperature changes, so as to avoid permanent set.

The steel wired belt 2 is friction actuated by a cylindrical driving drum 7 and it is tensioned by a jockey drum 13 on which a tensioning device is acting, said device being not illustrated in greater detail as it is well known in the conveyor technique. This driving system, based on friction and tension, also allows that also the wired belt 2 way to undergo free expansion in any direction, so as to avoid permanent set.

The load bearing run of the belt is supported by smooth rollers 3, while the lower return run is supported by cast iron or steel wheels 4. Shafts 14 of smooth rollers 3 protrude outside a steel containing box 15, which is applied at the boiler bottom, so that ash is falling on the conveyor belt enclosed therein and said shafts 14 may be supported outside the hot environment by bearings 16, thus arranged in a cool area and supported by specially designed supports 5. Between shafts 14 and the corresponding holes 17 made in the box 15, there are heat resistant seals 6, preventing air entrance and gas passage, but allowing shafts 14 to slide because of expansion. A guide and adjustment pin 18 protrudes from a hole made in support 5 and provided with a sealing gasket 19.

As illustrated in FIGS. 1 and 2, a cyclically operated valve 60 is located downstream of (that is, below) the area of ash discharge from the boiler, between the load bearing run and the return run of belt 2. Valve 60 may be operated to deliver air to the boiler countercurrently to the direction of ash discharge from the boiler.

It is of course to be understood that the foregoing detailed description was merely given as a non limiting example and therefore many modifications, additions, substitutions and/or variations may be resorted to the apparatus and process of the present invention, which was described in its particular embodiment for steam producing boilers in thermoelectric power plants, but obviously having a much broader range of application, which may be of interest in all those plants where there is the problem of discharging heavy and hot ash, without departing however from spirit and scope of the invention, as it is better defined in the appended claims.

Claims

1. A system for continuously removing bottom ash from a fire bed fired boiler, said system comprising a first and flexible conveyor belt made of high temperature resistant material trained over a drive drum with a friction fit therebetween, a plurality of overlapping load bearing plates loosely joined to said conveyor belt for bearing the weight of a load deposited on said belt, whereby temperature caused expansion and contraction of said conveyor belt is absorbed by said plates sliding relative to each other in said overlap area, and a tightly sealed envelope means surrounding said conveyor belt in order to retain heat of said fire bed fired boiler while enabling said ash to be conveyed out of a furnace in which said fire bed is located combustion chamber of said fired boiler.

2. The system of claim 1 wherein said conveyor belt is a woven wire belt.

3. The system of claim 2 and means down stream of said conveyor for cyclically discharging ash from said conveyor belt while precluding an

escape of a significant amount of heat from said envelope means. 4. The system of claim 3 and means wherein said downstream means returns 2 including valve means, located in said envelope means, for returning air to said fire bed fired boiler, the returned air passing over said conveyor belt in order to recapture heat from said hot ash, said heat being returned to said fire bed fired boiler when said returning air reaches said furnace in which said fire bed is located combustion chamber.

5. The system of claim 1 and means at fire bed for

continuously depositing hot ash on said conveyor belt. 6. The system of claim 1 wherein said overlapping plates form a trough under said flexible over a load bearing run of said conveyor belt.

. The system of claim 1 wherein said conveyor belt is a woven wire belt and said loosely joined plates are connected to said woven wire belt by bolts or rivets which are free to slide and move within the weave of said

woven wire. 8. The system of claim 7 wherein said woven wire belt includes a plurality of cross pieces slipped into the weave of said woven wire,

said bolts or rivets being joined to said crosspieces. 9. The system of claim 1 and a second including a guide drum, said conveyor belt being trained over said second guide drum, and means for adjusting the a position of said second

guide drum to tension said conveyor belt. 10. The system of claim 1 and including a plurality of rollers for supporting said conveyor belt and said plates, said rollers having ends extending outwardly from said conveyor belt to an area which is much cooler than said ash, and bearing means for supporting the ends of

said rollers. 11. The system of claim 1, wherein the conveyor belt receives the ash discharged from the boiler in a first direction;

and wherein the system further comprises

a cyclically activated valve, located in the envelope means downstream from an area where the ash is received onto the conveyor belt, for controlling entrance of cool air and for delivering the cool air controlled by the valve in a second direction countercurrent with respect to the first direction of ash discharge so that heat yielded to the air by the ash and by combustion of unburnt matter on the conveyor belt is returned into the boiler so as to increase its efficiency.