Power plants – Combustion products used as motive fluid – With exhaust treatment
Reexamination Certificate
2002-03-26
2004-02-24
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
With exhaust treatment
C060S727000
Reexamination Certificate
active
06694722
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a recuperator in a thermal power installation such as, for example, an air storage power installation, air from a storage cavern being heated by means of hot exhaust gases in the recuperator, which air is supplied to turbines after it has been heated.
BACKGROUND OF THE INVENTION
Recuperators of this type are used for heating air which is intended for driving turbines, the air being heated by heat transfer from the exhaust gases of the turbines. They are employed in thermal power installations such as, for example, air storage power installations.
In air storage installations, the air from a storage cavern is heated. Power installations of this type are, for example, known from the Patent Specification WO 96/01942.
An important function of air storage power installations in the present-day electricity market is their use during peak load periods in which other power installations' electricity demand is not sufficiently covered. Such peak load periods often occur at short notice and, for this reason, it is also necessary for air storage power installations to have the capability of being started up rapidly. This means that they can be started up again to full load from standstill or reduced operation as rapidly as possible.
A typical air storage power installation such as is in operation in Alabama, USA, for example, is shown in FIG.
1
. The power installation
1
comprises a storage cavern
2
, in which air is stored at a certain pressure and a typical temperature of approximately 35° C. and, in addition, a recuperator
3
, a generator G, two turbines with a high-pressure turbine
4
and a low-pressure turbine
5
, upstream of which is respectively connected a high-pressure combustion chamber
6
and a low-pressure combustion chamber
7
. When the power installation is put into operation, the stored air is supplied via the duct
8
to the recuperator
3
. There, it flows through one or a plurality of sectors, each consisting of a pipework system, the stored air being heated to above 300° C. by heat exchange with hot exhaust gases from the low-pressure gas turbine. After it has been heated, the air is supplied via a duct to the turbine group. The hot exhaust gases from the low-pressure turbine
5
are supplied via the duct
9
to the recuperator
3
.
Recuperators of the prior art can also comprise a so-called selective catalytic reduction system (SCR) for the purpose of reducing pollutant exhaust gases such as, for example, NO
x
.
When starting up an air storage power installation, in particular in the case of a cold start after a fairly long outage period, the combustion chambers, the turbines and also the recuperator are, inter alia, started up, temperatures of between 300° C. and 550° C. being attained. During a cold start, it is then necessary to take account of the temperature distribution in the items of equipment in order to ensure risk-free operation. During the outage period of the installation, namely, the temperature distribution in the power installation components mentioned evens out and there is a reduction in their average temperature. During the subsequent start, the thermal load may only be applied gradually to the components because, otherwise, the component details such as the tubes of the recuperator, for example, are subjected to marked transient stresses.
In the recuperator of the prior art, as shown in
FIG. 1
, the heating of the air (relaxation or temperature response) takes place with delay. This is a consequence of the thermal capacity of the recuperator and is strongly marked, particularly in the case of high pressures such as occur in air storage power installations and in the case of high efficiencies. This effect makes the cold start of the high-pressure turbine more difficult and, under certain circumstances, imposes the need for the high-pressure combustion chamber
6
of FIG.
1
. In addition, the delayed temperature response leads to a likewise delayed effective appearance of the selective catalytic reduction (SCR). The limitation to a gradual increase in the thermal load leads to a loss of time when starting up the air storage power installation, which makes it impossible for the installation function of covering peak times to occur at short notice and endangers the economic success of the air storage power installation per se.
SUMMARY OF THE INVENTION
Based on this prior art, the object of the present invention is to create a recuperator for a thermal power installation, which latter can be started up, without loss of time, to full load after an outage period or reduced power operation. In particular, the power installation is to be able to be put into operation—as compared with the prior art—both in a reduced start-up time and without risk, its start-up time being matched as far as possible to that of the turbines or, preferably, markedly bettering this start-up time.
This object is achieved by means of a recuperator according to claim 1 and a method for its operation according to claim 5. Special and preferred embodiments of the invention are given in the sub-claims.
A recuperator for an air storage power installation having at least one turbine such as, for example, a high-pressure turbine and low-pressure turbine, at least one combustion chamber and a generator, has a sector or a plurality of sectors in a recuperator casing, which sectors each exhibit a duct system for the heating of air by heat transfer from hot exhaust gases from a gas turbine, and which recuperator is connected to air supply ducts and transfer ducts to the at least one turbine. According to the invention, the recuperator has one or a plurality of external heat storage devices, which are connected between the sectors of the recuperator. In the case of a single sector in the recuperator, an external heat storage device is connected before and/or after this sector.
During a normal on-load operation, the external heat storage devices have the function of storing heat which is used during an installation outage to keep the individual sectors of the recuperator, together with the combustion chambers and turbines, sufficiently warm so that they do not cool. During the outage period of the installation, the heat storage devices ensure the heat which is necessary for maintaining a temperature distribution in the recuperator and the turbines, which temperature gradients are not larger than the critical temperature gradients which cause critical, transient stresses in the components of the recuperator and the turbines.
The external heat storage devices are expediently arranged outside the recuperator casing.
In a special embodiment of the invention, the one or the plurality of external heat storage devices are provided with water as the thermal heat storage medium or, in the case of higher temperatures, with a solid such as, for example, sand or stone.
In a method of operating the recuperator according to the invention, the external heat storage devices are, during the normal on-load operation of the power installation, brought to the temperature of the recuperator. During an installation outage, the recuperator, the turbines and the combustion chambers are then continuously or discontinuously flooded during a heat retention phase, by which means a temperature distribution is attained and maintained in the recuperator, the temperatures of the various sectors of the recuperator not falling below the temperature of the nearest heat storage device. This ensures that temperature gradients in the recuperator and the turbines remain smaller than a specified critical value.
In a special embodiment of the method according to the invention, the temperature distribution in the recuperator is held in such a way that the difference between the temperatures of the storage media of two adjacently connected heat storage devices remain smaller than the critical temperature with respect to transient stresses.
In one embodiment of the invention, the recuperator is flooded by air or air flows through it.
In one variant of the invention, the rec
Alstom Technology Ltd
Burns Doane Swecker & Mathis L.L.P.
Casaregola Louis J.
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