GB2034868A

GB2034868A - Boiler combustion chamber

Info

Publication number: GB2034868A
Application number: GB7937010A
Authority: GB
Original assignee: FLSmidth and Co AS
Current assignee: FLSmidth and Co AS
Priority date: 1978-10-27
Filing date: 1979-10-25
Publication date: 1980-06-11
Also published as: JPS5560105A; DK155464C; GB2034868B; JPS6224213U; DK478478A; DK155464B; DE2941713A1

Abstract

A combustion chamber (1) provided with built-in boiler tubes (2) has a bottom (3) which slopes downwardly from side walls of the chamber towards a central inlet (4) for combustion air. An outlet for exit gas and ash particles is provided at the top of the chamber (1). Means (5, 6) are provided for leading fuel and inert, granular material, in use, to the bottom (3) of the chamber. <IMAGE>

Description

SPECIFICATION Whirl chamber boiler plant The invention relates to a steam boiler plant in which the fuel is burnt in suspension in a whirl chamber. It is known to use steam boiler plants in which the combustion of the fuel necessary for the steam generation takes place in a fluid-bed in which the fuel is mixed with an inert, granular material, which does not itself participate in the combustion, but serves to maintain an even distribution of the fuel on the fluid-bed. The heat generated is transferred to for example built-in heat absorbing boiler tubes, and at least part of the oxygen necessary for the combustion is taken from the fluidising air.

It is a disadvantage of fluid-beds that the surface on which the fluidised material rests is rather complex, as it is composed of a number of nozzles through which the fluidising air is blown in. Such nozzles are likely to block up, and it calls for a considerable pressure drop over the nozzles to maintain an even air flow over the entire crosssection of the bed, which implies a substantial loss of power.

In order to overcome these disadvantages a whirl chamber boiler plant is provided which, according to the invention, is characterized by at least one combustion chamber provided with built-in boiler tubes, a bottom sloping downwardly from side walls of the chamber towards a central inlet for combustion air, and an outlet for exit gas and ash particles at the top of the chamber; and means for leading fuel and an inert, granular material, in use, to the bottom of the chamber.

The inert material may be ash which is similar to the kind produced during burning of the fuel.

Upon introduction into the chamber, the fuel and the hot, inert material are mixed intimately, the mixture formed sliding downwards along the sloping bottom towards the air-inlet. Upon contact with the flowing-in combustion,air the fuel starts to burn, the inert material preheating the fuel to its ignition temperature. The exit gases and some of the ash particles leave the combustion chamber at its top, while the remaining ash particles slide down along the walls of the chamber, giving off their heat to the built-in boiler tubes, and along the bottom where they are mixed with fresh fuel before again meeting with blown-in combustion air. Thus a whirl is formed in the combustion chamber, having an upwardly directed flow centrally in the chamber and a downwardly directed flow along the chamber walls.This construction overcomes the problems of the known fluid-bed since the combustion air inlet has a large cross-section which is disinclined to blockup and creates only a small pressure drop.

As the exit gases constantly entrain part of the inert material, it is necessary, in use, continuously to supply fresh inert material. This may be achieved by providing a separator communicating with the combustion chamber outlet, which is arranged to separate part of the hot ash particles from the ash particles/exit gas effluent and to return at least part of the ash particles to the combustion chamber.

If insufficient material is separated in the separator for maintaining the necessary amount of inert material in the combustion chamber, it may be expedient to provide means for returning cold separated ash to the combustion chamber. The cold ash may be ash continuously being separated off before the exit gases pass out through a chimney, or ash stored for this use.

The plant may be equipped with measuring devices for determining the size of the charge in the whirl chamber, so as to decide whether inert material should be returned to the combustion chamber and the amount of such material.

The heat released by the combustion is removed and utilized by means of the built-in boiler tubes, which may be located along the walls of the combustion chamber. The majority of the boiler tubes are preferably substantially vertically oriented. This arrangement of the boiler tubes ensures that they do not interfere with the whirling movement of the inert material, which movement consists of a central, upwardly directed stream in which the inert material is heated while the added fuel is burnt, and a downwardly directed stream along the walls of the combustion chamber, during which movement the inert material gives off its heat to the boiler tubes; eventually, the inert material is mixed with fresh fuel at the bottom of the chamber.

Means may be provided for feeding lime or dolomite to the combustion chamber along with the fuel in order to remove sulphur oxides, the lime supplied being fed separately or mixed with the fuel, and in doses proportional to the sulphur content of the fuel.

A whirl chamber boiler plant according to the invention is illustrated in the accompanying drawing which is a schematic, diagrammatic view.

A combustion chamber 1 is provided with built in boiler tubes 2, serving to conduct away the thermal energy generated during the combustion.

Fuel and an inert, granular material are led to the bottom 3 of the combustion chamber 1, which bottom slopes downwardly towards a central inlet 4 for combustion air indicated by the arrows 1 5.

The drawing diagrammatically shows this by way of an arrow 5 for the fuel, and an arrow 6 for the inert material. An arrow 7 represents a supply of lime for removal of sulphur oxides. The arrows only signify that the respective materials are supplied, and give no indication of the place in the combustion chamber where the supply tubes end.

Thus, in the case of coal firing, the lime addition may happen by adding lime or dolomite in the coal mill so as to feed coal and lime through the same tube.

The added inert material, which in the present example is ash similar to the kind produced during the burning of the fuel, preferably has a temperature above the ignition temperature of the fuel, so that the fuel, which during its supply stage and further passage downwardly along the inclined bottom of the combustion chamber is intimately mixed with the inert material, is evenly distributed and preheated to such a temperature that burning starts upon contact of the fuel with the blown-in combustion air. The combustion takes place in a whirl which moves upwardly, as shown in the drawing, centrally in the combustion chamber 1, and downwardly along the walls of the chamber. The combustion is preferably controlled in such way that hot exit gas at substantially 7000C can be conducted away at the top of the combustion chamber 1.Part of the conductedaway exit gas is led to a cyclone 8, in which entrained ash particles are separated and, through the material outlet 9 of the cyclone, returned to the inert material supply 6. The exit gas from the cyclone 8 is, together with any exit gas which has bypassed the cyclone, in known manner passed from the combustion chamber 1 past an economizer 10 and a preheater for combustion air 1 to an ash separator 12, in which the remaining ash is known manner is separated by means of cyclones and electrofilters. From the ash separator 12 the dedusted exit gas is passed to a chimney 13. Part of the separated dust may, if desired, through a tube marked by an arrow 14, be returned to the combustion chamber 1 as inert material. Thus it is possible, by addition of cold ash, to maintain the requisite amount of inert material in the combustion chamber 1, if the amount of ash separated in the cyclone 8 should prove insufficient. By measuring the pressure drop over the chamber 1 an indication may be seen as to whether the combustion chamber contains the requisite amount of material. The pressure drop measured can thus be used for controlling the amount of ash to be returned to the combustion chamber 1.

In the drawing, the plant comprises one single combustion chamber 1. There may be an upper limit to the size of such a chamber 1 if an expedient gas distribution is to be maintained in the chamber. For large plants use can thus be made of several combustion chambers 1, working in parallel with each other, combustion being controlled separately in each chamber.

Claims

1. A whirl chamber boiler plant, characterized by at least one combustion chamber provided with built-in boiler tubes, a bottom toping downwardly from side walls of the chamber towards a central inlet for combustion air, and an outlet for exit gas and ash particles at the top of the chamber; and means for leading fuel and an inert, granular material, in use, to the bottom of the chamber.

2. A plant according to claim 1, characterized in that the slope of the chamber bottom allows fuel and inert material, in use, to pass under gravity towards the central opening in the chamber bottom where the fuel, which by its contact with hot inert material has reached its ignition temperature, starts burning upon contact with the combustion air.

3. A plant according to claim 1 or claim 2, characterized in that the plant further comprises a separator communicating with the combustion chamber outlet, and which is arranged to separate part of the hot ash particles from the ash particles/exit gas effluent and to return at least part of these to the combustion chamber.

4. A plant according to claim 3, characterized by means for returning, in use, cold separated ash to the combustion chamber.

5. A plant according to any of the preceding claims, characterized by measuring devices for determining the size of the charge in the combustion chamber.

6. A plant according to any of the preceeding claims, characterized in that the boiler tubes are arranged along the walls of the combustion chamber.

7. A plant according to claim 6, wherein the majority of the boiler tubes are substantially vertically oriented.

8. A plant according to any of the preceding claims, characterized in that means are provided for supplying lime or dolomite to the combustion chamber.

9. A plant according to claim 1, substantially as described with reference to the accompanying drawing.

10. A method of operating a whirl chamber boiling plant according to any one of the preceding claims, wherein the inert material supplied to the combustion chamber is ash similar to the kind produced during burning of the fuel.

1 A method according to claim 10, substantially as described with reference to the accompanying drawing.