Power plants – Combustion products used as motive fluid
Patent
1993-12-20
1995-04-18
Casaregola, Louis J.
Power plants
Combustion products used as motive fluid
60 39464, 122 4, F02C 326
Patent
active
054067855
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method and a device for maintaining a high gas temperature to a gas turbine in connection with partial-load operation of a PFBC plant, in which gas is fed out from a fluidizable bed in a combustor which also includes tubes for generating steam, the tubes being completely or partially covered by the fluidized bed in dependence on the degree of load.
BACKGROUND OF THE INVENTION
In operation of a PFBC (Pressurized Fluidized Bed Combustion) plant, a varying part of the tubes which are to generate steam for a steam turbine in the plant will be covered by the fluidized bed in dependence on the degree of load. In case of full-load operation, the tubes are completely covered, and in case of partial-load operation they are partially covered. One problem in this connection is that the non-covered tube portions cool the combustion gases which leave the bed at a temperature of about 850.degree. C. A reduced temperature of the gases to the gas turbine entails, among other things, a deteriorated efficiency of the plant, favorable conditions for NO.sub.x reduction, and an increased CO content in the waste gases from the plant.
SUMMARY OF THE INVENTION
The present aims to provide a solution to the above-mentioned problems and other problems associated therewith and is characterized in than hot combustion gases are discharged from outlets located at different levels in the combustor in dependence on the degree of partial load. By discharging combustion gas via outlets at different levels, outlets at lower levels during low-load operation and outlets at higher levels during high-load operation, the cooling of the combustion gases due to the cooling effect of exposed tube is reduced. By means of this device the waste gas temperature can be maintained at the desired, high value.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be exemplified with reference to the accompanying figures, wherein:
FIG. 1 is a view showing the principle of a PFBC power plant according to the present invention;
FIG. 2 is a side view of the same plant;
FIGS. 3 and 4 show features of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1 and 2 show a combustor 1 for a PFBC power plant, wherein the combustor 1 comprises a fluidizable bed 2 of a known kind, see for example, EP108 505. This bed 2 accomodates tubes 3 for cooling the bed 2, which generate steam for steam turbines. In operation of the plant, in case of full load, the tubes 3 are normally fully covered by the fluidized bed 2. The combustion gases leaving the bed 2 to a freeboard 2a above the bed surface, have a high temperature, preferably 850.degree. C. In partial-load operation of the plant, the bed level is lowered, parts of the tubes 3 thus being exposed such that portions of the tubes 3, tube portions 3a, will be located above the surface of the bed 2.
Valve members 4 are arranged at the upper part of the combustion chamber in the combustor 1. For discharging combustion gases, two separate flue gas channels are provided. These consist primarily of a centrally arranged flue gas channel, a central channel 5, which may, and is suitably designed as several channels separated from each other. The central channel 5 is provided with a higher outlet 5a for flue gases from the freeboard 2a, which outlet 5a is located at a higher level in the combustor 1 than the tube portions 3a. Other channels for flue gases, side channels 6, are arranged adjacent to the walls of the combustor 1. These side channels 6 are provided at their lower part with lower outlets 6a for flue gases from the freeboard 2a, which lower outlets 6a are located at a lower level in the combustor 1 than the outlets 5a, namely at the side of the upper tube portions 3a. This means that the flue gases which are forced out from the combustor 1 via the side channels 6 do not pass the tube portions 3a to any major extent and consequently are not cooled by these tube portions 3a.
In full-load operation, the valve members 4 are arranged such that the central chan
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patent: 4896497 (1990-01-01), Pillai
patent: 5022893 (1991-06-01), Abdulally
Andersson Mats
Weatherby John
ABB Carbon AB
Casaregola Louis J.
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