Power plants – Motive fluid energized by externally applied heat – Process of power production or system operation
Reexamination Certificate
2000-05-10
2001-10-16
Nguyen, Hoang (Department: 3748)
Power plants
Motive fluid energized by externally applied heat
Process of power production or system operation
C060S646000, C060S657000
Reexamination Certificate
active
06301895
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention lies in the field of power generation. The invention relates to a method for closed-loop output control of a steam power plant with a turbo-generator set having a steam turbine and a generator. In operation, the plant water is injected into or upstream of a superheater heating surface. The invention also relates to a steam power plant for carrying out the method.
A closed-loop output control of a steam power plant and such a plant are disclosed, for example, in published French patent application No. 2 381 172.
Reliable power supply in an electric power supply system presupposes careful balancing between the generation of electrical power by a number of power units and the tapping of the electrical power by a number of consumers in an electricity distribution network. If the generation and tapping of the electrical power are equal, the system frequency, which is an important parameter in an electricity network, is constant. The nominal value of the system frequency is, for example, 50 Hz in the European interconnected network. A frequency deviation that occurs, for example, due to the failure of a power unit and to the connection or disconnection of a consumer, can be regarded as a measure of an increase or decrease in the generator output.
Along with the correction of frequency deviations within a power supply system, a further task is maintenance of a prescribed interchange power at coupling points to subnetworks from which the distribution network (interconnected network or separate network) is assembled. One requirement is, therefore, the availability of a fast increase in the output of a power unit within seconds. A possible response reserve requirement, for example, can be a sudden load increase of approximately 3 to 5% (measured with respect to the full load of the power supply system) within 30 seconds. However, the plant disclosed in French application 23 81 172 is neither configured nor suitable for providing such a fast output reserve.
Pages 18 to 23 of the publication “VGB Kraftwerkstechnik”, Issue Jan. 1, 1980, describes possibilities for fast closed-loop output control and frequency back-up control. While a plurality of possibilities of intervention exists that can be carried out simultaneously or alternatively for a fast change in output in the range of seconds (seconds reserve), it is also necessary to change the supply of fuel for a permanent change in the output of a power unit. Therefore, for the purpose of bridging delay times within the first seconds in a fossil-fired steam power plant, it is usual for control valves, held in advance in a throttled position of the steam turbine, to be opened and thereby to activate and discharge available steam accumulators virtually without delay. Such an operation mode of the steam power plant in the throttled state leads, however, to a high proper heat consumption, and is, thus, economical only to a qualified extent.
In addition to an increase in output due to the throttling cancellation of control valves of the steam turbine, it is also possible to shut down feed heaters that are provided in the water-steam circuit of the steam turbine and are heated by extraction steam from the steam turbine. A condensate flow guided simultaneously through the low-pressure feed heater can be stopped within a few seconds and increased again. A measure for fast closed-loop output control in fossil-fired power units by shutting down the feed heaters accompanied by stoppage of condensate is also described, for example, in German Patent DE 33 04 292 C2.
It is conventional to use a governing system to subject the fast seconds reserve to closed-loop and/or open-loop control, in other words, to closed-loop control of the loading of steam flows to regenerative feed heaters and/or heating condensers as well as of the process steam and the condensate in the water-steam circuit of the steam turbine of a power unit.
For fast closed-loop output control, that is to say, activating the seconds reserve, the steam supply to the feed heaters is throttled, throttling the process steam and/or throttling the condensate. In such a case, desired setting values for control valves at the turbine bleed points, and for regulating units for setting condensate, are formed to produce a required extra generator output. However, a configuration of a steam turbine suitable for such purpose is disadvantageous because the configuration is relatively complicated. The closed-loop control mechanism is complex and, therefore, vulnerable, resulting in a system that is reliable for fast closed-loop output control only to a qualified extent.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for closed-loop output control of a steam power plant that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that ensures reliable fast closed-loop output control with a particularly low outlay. In addition, an object is to provide a steam power plant that is particularly suitable for carrying out the method.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for closed-loop output control of a steam power plant having a turbo-generator set with a steam turbine, a superheater heating surface and a generator, including injecting plant water into or upstream of a superheater heating surface when the steam power plant is in operation, and setting an extra generator output in a range of approximately 3 to 5% of a full load of the power plant within a reaction time of up to approximately 30 seconds by increasing a water injection rate.
The invention proceeds from the consideration that the expensive activation of steam accumulators in the water-steam circuit of the steam turbine should be dispensed with for reliable fast closed-loop output control in conjunction with a particularly low outlay with regard to the components used. By dispensing with the activation of steam accumulators, it is possible to achieve a relatively fast increase in the output of the steam turbine by a short-term increase in the steam mass flow to be fed to the steam turbine.
Such an increase is performed by additionally injecting water into or upstream of the superheater heating surface.
The additional injection of water into the region of the superheater heating surface has the effect of generating an additional steam flow, which effects an increase in the output of the steam turbine even after a short time. The increase in the water injection rate decreases the steam temperature in the superheater heating surface. The decrease in the steam temperature leads to an increase in the temperature difference between the superheater heating surface and the steam, which is decisive for the level of the heat transfer. As such, accumulator heat can be extracted from the superheater heating surface and, in addition, more heat can be extracted from the flue gas, resulting in a temporary increase of the heat transferred in the steam generator onto the superheater heating surface.
For the purpose of setting the extra generator output, the water injection rate into a high-pressure superheater and/or a reheater is expediently increased.
In order to avoid an undesired decline in the output of the steam turbine, it is expedient that at the latest after a waiting time of approximately one minute, calculated from the increase in the water injection rate, the desired value for the temperature of the steam flowing out from the superheater heating surface is lowered by a prescribable amount. Specifically, it is now understood that the steam temperature in the superheater heating surface drops because of the increased water injection rate after approximately 60 seconds, and, for temperature-controlled closed-loop control, such a drop could lead to a reduction in the water injection rate, and, thus, to a decline in the output of the steam turbine. The drop is reliably avoided given a well-timed reduction in the desire
Kallina Günter
Kral Rudolf
Wittchow Eberhard
Greenberg Laurence A.
Lerner Herbert L.
Nguyen Hoang
Siemens Aktiengesellschaft
Stemer Werner H.
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