Furnaces – Refuse incinerator – Refuse suspended in or supported by a fluid medium
Patent
1991-10-10
1993-01-05
Fox, John C.
Furnaces
Refuse incinerator
Refuse suspended in or supported by a fluid medium
110259, 122 4D, F23J 300
Patent
active
051760894
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a power plant with combustion of a fuel at a pressure exceeding the atmospheric pressure in a fluidized bed of particulate material in a combustor placed inside a pressure vessel and surrounded by compressed combustion air in the space between the pressure vessel and the bed vessel, a so-called PFBC power plant. PFBC are the initial letters of the English expression Pressurized Fluidized Bed Combustion.
BACKGROUND ART AND THE TECHNICAL PROBLEM
Combustors with combustion of a fuel, usually coal, in a fluidized bed are advantageously constructed with a so-called open bottom consisting of parallel air distributing tubes for combustion air to a combustion space above the bottom and with one or--in large combustors--several funnel-shaped ash chambers below the air distributing bottom tubes. Residual products, residues from the fuel and consumed bed material absorbent, pass in gaps between the air distributing tubes to the ash chamber or ash chambers. The gaps between the tubes should be of such a size that slag lumps formed during normal operation may pass freely through the gaps so as not to disturb the combustion. It is desirable that the downwardly-directed flow to the ash chamber is evenly distributed over the cross section of the combustor. To obtain a small overall height and a uniform material flow, therefore, large combustors are formed with a plurality of ash chambers with a rectangular cross section nearest the combustor bottom. The ash chambers may have the shape of a pyramid turned upside down, or of a funnel of rectangular cross section which changes into a circular cross section so that its lowermost part has the shape of a cone. A power plant with a combustor of this kind is described in greater detail in European patent application A1 289 974.
Between the ash chambers and the surrounding space in the pressure vessel, the pressure difference may amount to about 1 bar, which means that they are subjected to great forces. Since the temperature is high also in the ash chamber, especially in the uppermost part, the ash chamber walls have been constructed as cooled panel walls which are traversed by cooling water to attain a satisfactory strength. Constructing the ash chambers with water-cooled panel walls in a combustor with a plurality of ash chambers complicates the design and entails high costs of manufacture and erection.
SUMMARY OF THE INVENTION
The present invention aims to simplify and render less expensive the ash chamber section of the combustor. According to the invention, the combustor is designed with a plurality of ash chambers which are all or in groups enclosed in spaces which are separated from the space between the combustor and the pressure vessel. In this way the ash chamber walls will not be subjected to forces caused by a pressure difference between the ash chamber and the surroundings. By providing pressure equalizing openings in the ash chamber walls, pressure equalization is achieved between the ash chamber and the surrounding space when the operating pressure of the plant changes upon variations of the load.
The ash chamber walls only support the load from the bed material and residual products from the combustor and sufficient strength may be imparted to them also at a relatively high wall temperature. Therefore, they do not have to be designed as cooled walls, which entails a simple design and a low cost. The pressure difference between the ash chamber and the space between the combustor and the pressure vessel is absorbed by the walls around the space which surrounds the ash chamber. These are plane and simple to manufacture even if designed, as water-cooled, panel walls. The forces acting on the walls are absorbed partly as bending stresses in the walls and partly by supports connecting the walls to each other and/or by supports connecting the walls to a framework.
Other characteristics of the invention will be clear from the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in greater det
REFERENCES:
patent: 4227488 (1980-10-01), Stewart et al.
patent: 4628834 (1986-12-01), McKelvie
patent: 4655147 (1987-04-01), Brannstrom et al.
ABB Stal AB
Fox John C.
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