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.
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 xe2x80x9cfull loadxe2x80x9d is identical, in this context, to the terms xe2x80x9crated outputxe2x80x9d or xe2x80x9cmaximum continuous outputxe2x80x9d, that is to say an upper output in terms of which the plant is designed for continuous operation. By xe2x80x9cpart loadxe2x80x9d is meant, here, an output below the maximum continuous output, and by xe2x80x9coverloadxe2x80x9d is meant an output above the maximum continuous output. The term xe2x80x9cmaximum outputxe2x80x9d 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 xe2x80x9cprimary responsexe2x80x9d 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 xe2x80x9csecondary responsexe2x80x9d, 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 xe2x80x9cprimary responsexe2x80x9d and xe2x80x9csecondary responsexe2x80x9d, 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 xe2x80x9cprimary responsexe2x80x9d 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 xe2x80x9cprimary responsexe2x80x9d. 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 xe2x80x9cprimary responsexe2x80x9d 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 xe2x80x9cprimary responsexe2x80x9d 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 xe2x80x9cprimary responsexe2x80x9d 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 xe2x80x9cprimary responsexe2x80x9d 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 is reached, by water or steam injection in conjunction with an increase in the fueling capacity, with the maximum permissible temperature being maintained.
In view of the conditions for opening up electrical power markets, there is a constant stream of new requirements placed on generating plants, particularly with regard to output flexibility. In gas turbine plants, too, there is therefore the task of seeking new solutions for increasing the maximum operable output gradient in terms of the xe2x80x9cprimary responsexe2x80x9d.
The object of the invention is to provide a method and an apparatus for the more rapid startup and more rapid increase in output of a gas turbine plant, so that as high an output gradient as possible can be operated, without the maximum permissible positive temperature gradient or other maximum permissible mechanical or thermal material stresses being exceeded.
The method according to the invention is characterized in that the fuel mass flow supplied to the combustion chamber and/or the combustion-air mass flow supplied is/are increased and, at the same time, an additional working medium increasing the mass flow flowing through the turbine is supplied.
An increase in the fuel supply alone in order to increase the output leads to an increase in the temperature, in particular in the combustion chamber and in the turbine which, as is known, is restricted in terms of its height and gradient due to the thermal material and system stress.
Only injecting water or steam leads to a drop in the temperature of the components located downstream of the injection point in the direction of flow. Apart from output and efficiency effects which are not positive in all cases, negative temperature gradients also place limits on the injection of an additional working medium of this kind.
The method according to the invention is based on the idea, irrespective of the load state of the gas turbine plant, of employing in combination both operating modes working in opposition in terms of thermal load, in order
to have the capability of operating higher output gradients, along with the same thermal load, or
to lower the thermal load, along with the same output gradients.
By means of this combination, under the same conditions of temperature and output of the gas turbine plant, the fueling capacity and therefore also the mechanical power output can be increased or reduced more rapidly or in a way which takes greater care of the plant.
The actual location of water or steam injection is unimportant for the concept of the invention. There are possibilities for injecting into the region between the compressor outlet and combustion chamber, into the combustion chamber, particularly via the burners themselves, and downstream of the combustion chamber, either directly into the gas mass flow or indirectly via the guide vanes or moving blades, if appropriate also as a mixture with additional cooling air. Advantageously, water or steam injection should take place at a point having no influence on combustion or on flame stability. In general terms, therefore, only the supply of an additional working medium to the gas turbine plant or from the injection point is referred to hereafter.
An apparatus for carrying out the method is distinguished by a compressed-air source, a combustion chamber and a turbine, by a fuel line for supplying a fuel to the combustion chamber and by a working medium line for supplying the additional working medium to the injection point, and by a regulator for controlling the respective mass flow through the fuel line and the working medium line, said regulator storing the value of the maximum permissible positive temperature gradient of the gas turbine plant and controlling the respective mass flow through the fuel line and the working medium line in such a way that the value of the maximum permissible positive temperature gradient of the gas turbine plant is not exceeded.
A combined-cycle power station having a gas turbine plant with a generator and a regulator for controlling the mass flow of the fuel and of the additional working medium in order to limit the positive temperature gradient and the stress on components of the gas turbine plant contains a heat recovery steam generator heated by the waste gas from the gas turbine and a steam turbo set, the additional working medium being cold water, warm water, hot water, saturated water, wet steam, saturated steam or superheated steam branched off from the water/steam circuit of the combined-cycle power station.