GB2080138A

GB2080138A - Fluidizable bed combustion chamber with ash-discharging means

Info

Publication number: GB2080138A
Application number: GB8120412A
Authority: GB
Original assignee: Stal Laval Turbin AB
Current assignee: ABB Stal AB
Priority date: 1980-07-03
Filing date: 1981-07-02
Publication date: 1982-02-03
Also published as: DE3124908A1; SE8004924L

Abstract

A fluidizable bed combustion chamber 1 is provided with an ash- discharging means for the discharge and cooling of ash from the combustion chamber, comprising an ash chamber 7 into which hot ash is fed from the combustion chamber 1 via a tubular member 6. Cooling air is blown into the accumulation of ash that forms in the ash chamber 7, this cooling air being introduced via tube 10 and a perforated plate 9 in the ash chamber. After heat exchange contact with the ash, the air is led to the combustion chamber 1, mainly via a tubular member 11. A tube 14 and a conveyor 15 are provided for conveying cooled ash away from the accumulation of ash in the ash chamber. <IMAGE>

Description

SPECIFICATION Fluidizable bed combustion chamber Technical Field This invention relates to a fluidizable bed combustion chamber which is provided with means for the discharge and cooling of ash from the combustion chamber.

In a fluidizable bed combustion chamber a considerable amount of ash is constantly formed, partly from the fuel consumed in the combustion chamber, and partly in the form of consumed or worn-down bed material. This ash has to be transported away from the combustion chamber, and it is important to utilize the heat content thereof in order to achieve good economy in the combustion chamber. In this respect, it is important not only to extract heat from the ash, but also the calorific value of any remaining fuel, or partially burnt fuel, in the ash.

Disclosure of Invention According to the invention, in a fluidizable bed combustion chamber comprising a shell in which ash is formed during combustion of fuel in the combustion chamber, there is provided an ash-discharging means for discharging said ash from said shell, said ash-discharging means comprising an ash chamber situated below said shell, a first tubular member for conducting ash from said shell into said ash chamber to form an accumulation of ash in said ash chamber, means for conducting cooling air into said ash chamber in heat exchange contact with said accumulation of ash, a second tubular member for conducting a major portion of said cooling air, after its heat exchange contact with said accumulation of ash, to said shell, and means for discharging from said ash chamber cooled ash from said accumulation of ash.

In one embodiment of a fluidizable bed combustion chamber in accordance with the invention said means for conducting cooling air into said ash chamber forms a support for said accumulation of ash. In this case, the means for discharging cooled ash may comprise at least one ash-discharge passageway through said support for leading said cooled ash into a funnel-shaped portion of said ash chamber situated below said support. Any suitable conveying means may be provided for conveying ash away from said funnelshaped portion of the ash chamber: In operation of a combustion chamber in accordance with the invention, it is important that the speed of the cooling air is sufficiently low that the ash does not fluidize in the ash chamber.In this way, cold and hot ash are prevented from being intermixed in the ash chamber, so that an even temperature gradient is obtained up through the accumulation of ash.

Brief Description of Drawing The invention will now be described, by way of example, with reference to the accompanying drawing, the single Figure of which is a schematic sectional view of one embodiment of a fluidizable bed combustion chamber in accordance with the invention.

Description of Preferred Embodiment The Figure shows a fluidizable bed combustion chamber comprising an outer shell 1 and an air chamber 2 at the bottom of the shell 1.

Air is blown into the chamber 2 through a tube 3 and passes up through a perforated plate 4 into a bed 5 of particulate material in the shell 1 at a rate sufficient to fluidize the bed material. Fuel is also blown into the bed 5, and for this purpose the plate 4 is normally provided with a large number of fuel injection nozzles (not shown).

Extending downwardly from the bottom of the combustion chamber is at least one hollow shaft for the discharge of ash from the shell 1, this shaft consisting at its upper end of a relatively narrow ash tube 6 connected to the plate 4. The lower end of the tube 6 is disposed in a wider portion of the shaft which constitutes an ash chamber 7 in which the ash spreads out across a floor formed by two vertically spaced-apart, horizontally disposed plates 8, 9 to form an accumulation of ash in the ash chamber. Through a tube 10 cooling air is passed in between the plates 8 and 9 and up through holes in the upper plate 9.

Because the ash chamber 7 is wide, a considerably volume of cooling air can be passed up through the accumulated ash without the latter lifting or becoming fluidized. As it flows up through the accumulation of ash, the temperature of the cooling air is raised through heat exchange with the hot ash, and, by choosing a suitable volumetric flow rate for the cooling air, such a temperature may be maintained in the upper part of the ash in the ash chamber 7 that combustion of carbonized residues may take place in the upper portion of the accumulated ash. Part of the cooling air passes up through the tube 6. The ash in the tube 6 has such a high temperature that carbonized residues in the ash are burnt to the extent permitted by the oxygen content in the upwardlyflowing air.Only a limited portion of the carbonized residues in the ash remains to be burnt in the ash chamber 7 where there is certain to be an excess of oxygen.

The major part of the cooling air flowing up through the ash in the ash chamber 7 is conducted through a tube 11 directly up into the combustion chamber where it serves as heated secondary air. In this way, there will only be a limited upward air flow in the ash tube 6, allowing the ash to slide down gently through this tube. The upper end of the tube 11 is provided with a cover 1 6 which allows the upwardly flowing air to pass from the tube but prevents ash flowing down the tube into the ash chamber 7.

Between the plates 8 and 9 there are tubes 12 serving as passageways through which the cooled ash from the ash chamber 7 slides down into a funnel-shaped portion 1 3 of the discharge shaft. From the shaft portion 1 3 the ash then passes via a tube 14 to an ash conveyor 1 5 in a known manner. Air injected via tubes 1 7 and 1 8 assists discharge of the ash via the conveyor 1 5.

The above described ash discharge shaft may be employed with a fluidizable bed combustion chamber operating at atmospheric pressure or at super-atmospheric pressure. It is only a matter of choosing a suitable pressure for the cooling air and suitable dimensioning of the walls and other parts of the discharge shaft.

Claims

1. A fluidizable bed combustion chamber comprising a shell in wich ash is formed during combustion of fuel in the combustion chamber, and an ash-discharging means for discharging said ash from said shell, said ashdischarging means comprising an ash chamber situated below said shell, a first tubular member for conducting ash from said shell into said ash chamber to form an accumulation of ash in said ash chamber, means for conducting cooling air into said ash chamber in heat exchange contact with said accumulation of ash, a second tubular member for conducting a major portion of said cooling air, after its heat exchange contact with said accumulation of ash, to said shell, and means for discharging from said ash chamber cooled ash from said accumulation of ash.

2. A combustion chamber according to claim 1, wherein a minor portion of said cooling air is conducted to said shell via said first tubular member.

3. A combustion chamber according to claim 1, wherein said means for conducting cooling air into said ash chamber forms a support for said accumulation of ash.

4. A combustion chamber according to claim 3, wherein said means for discharging cooled ash comprises at least one ash-discharge passageway through said support for leading said cooled ash into a funnel-shaped portion of said ash chamber situated below said support.

5. A combustion chamber according to claim 4, comprising conveying means for conveying ash away from said funnel-shaped portion of said ash chamber.

6. A fluidizable bed combustion chamber constructed and arranged substantially as herein described with reference to, and as illustrated in, the accompanying drawing.