Fluidized bed combustion chamber

BACKGROUND OF THE INVENTION

The present invention relates generally to combustion chamber assemblies of the type employed with relatively large gas turbines and the like. In particular, the present invention is directed to a substantially spherically-shaped outer casing enclosing an annular fluidized bed combustion chamber and further enclosing a cleaning assembly adaptable for cleaning heated combustion gases emitted from the fluidized bed prior to contact with the turbine assembly.

Fluidized bed combustion chambers are particularly adaptable for use with large gas turbines, because the fluidized bed assembly can easily be maintained at relatively high temperatures through the use of a variety of fuel sources. While fluidized bed combustion chambers have been used in the prior art, known assemblies have proven less than completely satisfactory in the excessive amount of material required in the construction of the fluidized bed in order to withstand forces generated by the pressurized gas flowing therethrough. Another problem confronting known combustion chambers is the formation of relatively serpentine air flow passages through the combustion chamber whereby the heated combustion gases tend to significantly cool in temperature prior to passage through the turbine assembly. A related problem of such combustion chambers is the tendency to overheat certain portions of the chamber casing via direct contact with the heated combustion gases, which can lead to premature failure of the casing during prolonged use.

As will be discussed in detail hereafter, applicant's invention provides a compact fluidized bed combustion chamber which overcomes the aforestated problems, while also providing an effective device for supplying heated combustion gases for use in large gas turbines and the like, wherein almost any type of fuel can be used within the fluidized bed.

OBJECTS AND SUMMARY OF THE PRESENT INVENTION

An object of the present invention is to provide a combustion chamber including a substantially spherically-shaped outer casing which encloses a substantially annularly-shaped fluidized bed and which further encloses an assembly for cleaning debris, ashes and the like from the heated gases upon exit from the fluidized bed.

A further object of the present invention is to provide a symmetrically-shaped combustion chamber which includes a fluidized bed having a cross-section which is substantially conical in shape.

Another object of the present invention is to provide a combustion chamber wherein the outer casing and the fluidized bed are both supported by a base plate assembly which extends through the casing and is attached to an air distributing box upon which the annular, fluidized bed is mounted.

Each of the above-stated objects is achieved in a preferred embodiment of the present invention, wherein a combustion chamber is constructed with a substantially spherically-shaped outer casing. A double-bottom air distributing box is positioned within the casing, with both the fluidized bed and the cleaning assembly mounted on the box. A base plate assembly entends from the box, through the casing wall and serves to support the casing, fluidized bed and cleaning assembly in a fixed position relative to a support floor or the like.

The fluidized bed is substantially conical in cross-section and spaced from an inner wall of the casing to form an air flow passage therebetween. An output portion of the fluidized bed is connected to an input portion of the cleaning assembly, which in itself makes up no part of the present invention. A valve assembly is positioned in the air distributing box to control the flow rate of a compressed gas, such as air, into the box and fluidized bed mounted thereon.

During operation, compressed air is introduced into the spherical casing and is caused to flow into the air-distributing box. The compressed air then travels into the fluidized bed, where it interacts with the fluid source to create hot combustion gases. The heated combustion gases exit from the fluidized bed and are directed through the cleaning assembly to remove ashes, debris and the like which may be picked up during the combustion process. Finally, the heated combustion gases flow out of the casing and into contact with a gas turbine and the like.

It is noted that either cooling or boiling tubes may be positioned within or above the fluidized bed, making the combustion chamber adaptable for use with combined steam and gas turbine plants. Furthermore, by using substantially radially extending tubes within the annularly-shaped fluidized bed, it is possible to obtain excellent heating symmetry within the combustion chamber.

The present invention will become apparent from a reading of the following specification and claims, together with the accompanying drawings, wherein similar elements are referred to and are indicated by similar reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be best understood with reference to the accompanying drawings, wherein:

FIG. 1 shows a cross-sectional view through a combustion chamber formed in accordance with the present invention; and

FIG. 2 shows a cross-sectional view through a further combustion chamber formed in accordance with the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Referring to the drawings, and FIG. 1 in particular, a cross-section of a fluidized bed combustion chamber is shown. The combustion chamber includes a substantially spherically-shaped outer casing 1, which encloses a substantially annularly-shaped fluidized bed 2. Positioned within fluidized bed 2 is a cleaning assembly designated generally at 3 which includes conventional cleaning devices for separating solid particles of ash and the like from the heated combustion gases existing from fluidized bed 2.

A compressed gas, such as air, enters outer casing 1 through an inlet generally indicated at 4, with the air filling an upper space 6 within outer casing 1. A portion of the air then flows through a cooling gap 7 created between confronting surfaces of annular fluidized bed 2 and spherical casing 1, while a further portion of the air flows through a relatively narrow cooling gap 8 created between confronting surfaces of fluidized bed 2 and cleaning assembly 3. It is to be noted that the different portions of casing 1, bed 2, and cleaning assembly 3 which form gaps 7 and 8 are constructed such that the air tends to maintain a substantially constant speed while flowing through gaps 7 and 8, respectively, which ensures even cooling on both sides of the fluidized bed 2.

Both the fluidized bed 2 and cleaning assembly 3 are mounted on a double-bottom air distributing box 9 which extends substantially between opposite sides of outer casing 1. Box 9 is constructed with a centrally disposed aperture extending through a wall portion facing away from cleaning assembly 3 as shown in FIG. 1. Mounted in the aperture is a valve assembly 5 which can be adjusted to control the amount of air introduced into air distributing box 9. A plurality of separate apertures 10 may be formed through abutting surfaces of box 9 and fluidized bed 2, with the apertures being substantially evenly spaced throughout the abutting surfaces to allow the air to flow from box 9 into fluidized chamber 2. It is also within the scope of the present invention to construct air nozzles between box 9 and fluidized bed 2 similar to the nozzles suggested in German Offenlegungsschrift No. 2,743,030.

A base plate 11 is attached to air distributing box 9 and extends through outer casing 1, with base plate 11 providing the entire support for the combustion chamber assembly. A plurality of apertures 13 have been formed in portions of the base plate 11 located between casing 1 and box 9 to allow the air from gap 7 to enter the combustion chamber. Referring to FIG. 1, it is noted that fluidized bed 2 is formed with a substantially conical cross-sectional shape which significantly reduces the speed of the air flowing through bed 2 to ensure proper heating of the material within bed 2.

The uniquely constructed spherical casing 1, box 9 and base plate 11 ensures that the pressure within the combustion chamber is taken up from the casing 1. This means that the walls of the fluidized bed 2 as well as the walls of the cleaning assembly 3 need only be dimensioned to withstand a conventional drop in pressure which occures during operation. Because fluidized bed 2 and box 9 are directly supported by base plate 11, neither gravitational forces nor thermal expansion forces can interrupt the air flow path formed therebetween.

Returning again to FIG. 1, after the heated combustion gases exit from fluidized bed 2, they are caused to flow through a conventional cleaning assembly 3, wherein the gases are cleaned in a conventional manner which in itself makes up no part of the present invention. The heated and cleaned gases exit from casing 1 through an outlet tube 12 which may be coaxially arranged within inlet 4. To ensure a substantially uniform temperature distribution within the walls of the combustion chamber, insulation 14 is mounted on an outside wall of casing 1, while insulation 15 is mounted on both the inside and outside walls of the fluidized bed 2. As a result, walls of bed 2 and casing 1 will substantially maintain the same temperature as the incoming gas.

FIG. 2 shows a further embodiment of the present invention, wherein a fluidized bed 2 includes an open end portion which is in direct fluid communication with an upper space 6' within casing 1. Outer edge portions of fluidized bed 2 are attached to casing 1 along a line 20, which subdivided the volume within casing 1 into separate chambers. A gas intake aperture 4 extends through casing 1 and is positioned on an opposite side of fluidized bed 2 from space 6'. It is also noted than an outer side portion of fluidized bed 2 is made even more saliently conical in cross-sectional shape as compared to the shape of the fluidized bed 2 disclosed in the preceding embodiment.

Resilient elements 16 have been inserted between base plate 11 and air distributing box 9 to reduce the adverse affect of any thermal stresses which may arise due to the construction of the combustion chamber. A pair of inspection doors 17 and 18 are attached to outer casing 1 and cover apertures formed therethrough.

Compressed air is introduced through inlet 4 and flows through air distributing box 9 and apertures 10 into fluidized bed 2. Because the fluidized bed 2 is open at an upper end thereof, space 6' will be heated by a portion of the gas exiting from bed 2. Therefore, additional insulation 15' has been attached to that inner surface of casing 1 which forms a boundary for space 6'. After the heated combustion gas flows from fluidized bed 2, it passes through cleaning assembly 3 and exits via output tube 12.

A bundle of radially directed cooling tubes 19 may extend through fluidized bed 2 to either heat or cool a gas flowing therethrough. By locating cooling or boiling tubes 19 within or above fluidized bed 2, the combustion chamber is adaptable for use with combined steam-gas-turbine plants. In a preferred embodiment of the present invention, a gas, such as air, having a working pressure of 10 to 15 bar may be employed when the outer casing has a diameter of 10 to 15 m.

The present invention is not intended to be limited to the above-described embodiments, but is to be limited only by the scope of the following claims.