Power plants – Combustion products used as motive fluid
Reexamination Certificate
2000-01-13
2002-04-30
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S039190, C060S039550
Reexamination Certificate
active
06378285
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for the rapid startup and rapid increase in output of a gas turbine plant which has at least one compressed-air source, a combustion chamber and a turbine. It further relates to an apparatus for carrying out the method, to a gas turbine plant having a generator and to a combined-cycle power station with such an apparatus.
BACKGROUND OF THE INVENTION
When an increased power demand occurs in an electrical network into which power from various power stations is fed, the output of the available power stations must be increased. The same requirements arise as a result of an unplanned failure on the generator side, but are also conceivable in the case of network faults and the like.
It is obvious that the increase in output of the power stations or their generator units should be possible with as high an output gradient as possible, inter alia for the sake of maintaining the prescribed frequency band of the electrical network.
Such an increase in output may become necessary in any operating state of a respective energy generator, for example when the latter is under part load or full load.
The term “full load” is identical, in this context, to the terms “rated output” or “maximum continuous output”, that is to say an upper output in terms of which the plant is designed for continuous operation. By “part load” is meant, here, an output below the maximum continuous output, and by “overload” is meant an output above the maximum continuous output. The term “maximum output” is used hereafter for the maximum operative output limited in time.
Increases in output are critical, in particular, during network-side peak load times, during which the respective energy generators are already being operated at their maximum continuous output (rated output), and, at the same time, an unplanned event occurs which requires a brief increase in output above the maximum continuous output.
The expression “primary response” is known in this respect, and this relates to an increase in output above the appointed or currently operated actual output of a respective energy generator having a defined output gradient. For example, the increase in output from the actual output to an about 10% higher output required is to take place within 10 seconds.
The holding of an additional output above an actual output is defined by “secondary response”, that is to say, for example, operating with an additional output of, for example, 8% for a period of time of, for example, 30 minutes.
As regards the “primary response” and “secondary response”, therefore, it is useful to know the maximum operable output gradient, the amount of the additional output as a function of the currently operated actual output and the maximum duration for operating the additional output. It should be possible to furnish an additional output from any load point, with the exception of the maximum output.
This means, in general terms, that power stations must have reserves in any form which make it possible, on the one hand, to achieve a rapid increase in output (primary response) and, on the other hand, to hold an additional output for a limited time (secondary response).
Irrespective of the possibilities for increasing the output, where “primary response” requirements are concerned, it is important by suitable means to have the capability of operating as high an output gradient as possible above the maximum continuous output.
So as to have a reserve available for the rapid increase in output, it is known, for example, to operate steam turbines in a steam power station in a throttled-back mode. However, this constantly entails losses (a reduction in the overall efficiency of the power station) and increased wear.
Another known possibility for the rapid provision of additional output in a conventional power station is to cut off regenerative preheaters or to uncouple them from other steam consumers.
Power stations with a constant hot reserve, that is to say energy generators which are constantly in the startup state, are also known. This, again, signifies a permanent employment of fuel, personnel and the like.
Quick-starting plants, for example diesel engines with a generator, in order, for example in accident situations, to ensure a minimal amount of work in operating and regulating a power station, are also known.
Furthermore, hydroelectric power stations and, in particular, pumped storage power stations may also be used as a power reserve, the latter being intended, in particular, for ensuring daytime balancing.
With the exception of gas turbine plants, only the possibilities for throttling back or opening the inlet valves on steam turbines and the possibility of cutting off extractions of steam from steam turbines are suitable for a rapid increase in output along the lines of a “primary response”. The relevant reserves are therefore exclusively corotating reserves (spinning reserves) at rated speed with an existing electrical connection to the network. Plants which first have to be started or run up to speed and are to be synchronized are unsuitable for making contributions to cover in the “primary response” area.
In other plants, the possible temporary extra power load is too small by virtue of the system or, as in the case of pumped storage power stations, use depends, for “primary response” purposes, on the instantaneous operating state, but also on the hydrological situation.
Moreover, keeping power in hand as a hot or cold reserve ties up capital. Throttling, part-load modes, heat-retaining operation and the like have an adverse influence on plant profitability.
As already mentioned, one exception is gas turbine plants which, because of their good dynamic behavior, are already being used today for “primary response” purposes.
In this case, there are basically two possibilities for increasing the output of a gas turbine plant:
1. Increasing the upper process temperature (gas turbine inlet temperature);
2. Increasing the mass flow through the gas turbine.
Increasing the process temperature by an increase in the fueling capacity, that is to say the fuel mass flow, as a means for increasing the output comes up against limits of thermal material and system stress in the form of a maximum permissible temperature. The maximum permissible output gradient during an increase in output comes up against limits of thermal material and system stress in the form of a maximum permissible temperature gradient.
An increase in output by increasing the mass flow through the gas turbine plant may be carried out, apart from the possibilities of regulating the air mass flow in conjunction with the possibilities of regulating the fuel mass flow, by the injection of water, steam or a water/steam mixture.
If, in the case of water or steam injection, the currently operated process temperature cannot be maintained at the gas turbine inlet by a simultaneous increase in the fueling capacity, the increase in output may be accompanied by a loss of efficiency. In an extreme situation, the gas turbine output itself may also decline. To what extent the water or steam injection influences the efficiency of the gas turbine process and the power output depends on the fueling capacity possibilities, on the state of the additional working medium (water or steam) and its temperature, but also on the design features of the gas turbine plant itself.
Water or steam injection involves a relatively cold additional mass flow which, in the case of water, has to be additionally evaporated in the gas turbine plant.
Gas turbine plants are used nowadays for “primary response” purposes or as peak load plants as follows:
1. By increasing the fueling capacity, if appropriate in conjunction with adjustments of the guide vanes on the compressor in order to increase the air mass flow, the gas turbine plant is run up to the maximum permissible temperature or to the maximum continuous output according to the permissible temperature gradient or output gradient.
2. In a second step, additional power is generated, at most until the maximum output i
Blatter Richard
Liebig Erhard
Alstom (Switzerland) LTD
Casaregola Louis J.
LandOfFree
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