Liquid heaters and vaporizers – Miscellaneous
Patent
1992-11-09
1993-11-16
Favors, Edward G.
Liquid heaters and vaporizers
Miscellaneous
122 6A, 12223523, F22B 3100
Patent
active
052613542
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a PFBC power plant. PFBC are the initial letters of the English expression Pressurized Fluidized Bed Combustion. In a PFBC power plant the combustion is performed in a fluidized bed of particulate material, usually mainly consisting of limestone or dolomite which acts as sulphur absorbent. The combustion takes place at a pressure which considerably exceeds the atmospheric pressure. The combustor is suitably enclosed within a pressure vessel and is surrounded by compressed combustion air. The combustion gases are utilized by a gas turbine which drives a compressor, which compresses the combustion air, and a generator. The bed section of the combustor includes tube coils which absorb heat from the bed, cool the bed and generate and superheat steam for a steam turbine which drives a generator.
BACKGROUND ART
Hitherto proposed and designed commercial PFBC power plants are relatively small and have a power of up to about 200 MWe. Rectangular combustors have been used to obtain a geometrically simple construction of the tube system in the bed section of the combustor. A cleaning plane in the form of groups of cyclones for separation of dust from the combustion gases has been provided between the combustor and the surrounding pressure vessel.
The problem involved is that the hitherto proposed and designed PFBC power plants require a pressure vessel with a relatively large diameter in view of the geometrical shape of the combustor. In the first generation PFBC power plants, the advantage of the simple tube laying in rectangular combustors has made up for the additional cost of a larger pressure vessel. When doubling or multiplying the power it is important to increase the ratio between the cross-section areas of the combustor and the pressure vessel.
SUMMARY OF THE INVENTION
According to the invention, the combustor is made as a polygonal prism with at least six side walls. Most suitably, the combustor is made with hexagonal cross section with a bed section with a steam generator consisting of evaporation and superheating tubes, and a freeboard section for reception of the combustion gases from the bed. At its top, the freeboard is connected to at least one substantially vertical duct which conducts the combustion gases to a cleaning plant which is located in a space formed between the duct and the surrounding pressure vessel.
The cleaning plant comprises a number of groups of cyclones connected in series, hot gas filters, or a combination of cyclones and hot gas filters.
The combustor design and the location of the gas cleaning plant permit a considerably better ratio between combustor cross section and pressure vessel cross section. An improvement of the order of magnitude of 20% or more is possible. The reduction of the pressure vessel diameter and the necessary wall thickness of the pressure vessel entails a considerable reduction of weight and cost. Further, the shape of the combustor permits a simpler suspension. Suitably, the combustor is suspended, at its corners, from rods which are attached directly to the pressure vessel or to relatively short beams in the pressure vessel. An additional advantage with the embodiment is that the plane walls of the combustor will be shorter. This reduces the length of surrounding beams which absorb forces caused by the pressure difference between the inside and outside of the combustor. The weight and cost of the frames are reduced.
The vertical duct between the freeboard of the combustor and the cleaning plant entails a favourable outflow and mixture of the combustion gases and combustion of accompanying unburnt fuel. Further, separation of coarse particles may take place in the duct by means of simple separating devices. NOX reduction may take place in the duct by the injection of additives, for example ammonia. The duct may also be utilized as a secondary combustion chamber to increase the gas temperature and hence the gas turbine power.
According to a preferred embodiment of the invention, plane vertical tube discs are a
REFERENCES:
patent: 3530835 (1970-09-01), von Wiesenthal
patent: 4479458 (1984-10-01), Goidich et al.
patent: 4537156 (1985-08-01), Rees
patent: 4760817 (1988-08-01), Jonsson
patent: 4790267 (1988-12-01), Mollenhoff et al.
Jonsson Arne
stman Sven-Olov
ABB Carbon AB
Favors Edward G.
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