Power plants – Combustion products used as motive fluid – With safety device
Reexamination Certificate
1999-04-08
2001-05-22
Wayner, William (Department: 3744)
Power plants
Combustion products used as motive fluid
With safety device
C062S082000, C165S230000, C236S04400R, C454S121000
Reexamination Certificate
active
06233917
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of controlling the temperature of intake air which is provided from outside air through an air-feed system. The invention also relates to a temperature-control device for carrying out the method and a gas turbine having the temperature-control device.
In many plants, in particular in internal-combustion engines or compressors, an air feed may be necessary for operation. To that end, an air-feed system which provides intake air obtained from outside air is normally provided. Such an air-feed system may include, for example, a number of intake elements as well as filter elements.
In a gas turbine as well, it is necessary to feed intake air to a compressor which is connected upstream of a combustion chamber. To that end, such an air-feed system is normally likewise connected upstream of the compressor. The air drawn in by the air-feed system is generally accelerated when flowing through the air-feed system. In the process, that acceleration may be effected locally on one hand while flowing around or through an obstacle, for example a bird protection grille or a filter. On the other hand, however, an approximately adiabatic acceleration of the drawn-in air also results from a constriction of the cross section of flow along the throughflow path in the air-feed system. That adiabatic acceleration of the drawn-in air is associated with an enthalpy reduction. The enthalpy reduction in turn produces a temperature drop in the drawn-in air. It is established mathematically, for example, that the drawn-in air cools down by about 5° C. during an acceleration of the drawn-in air to a velocity of about 100 m/s, which is normally present at the inlet of the compressor of the gas turbine. Ice may form in the process depending on the state of the outside air, in particular its pressure and temperature. That formation of ice may lead to a reduction in output of the gas turbine, to breakdowns, or even to damage to the gas turbine and is therefore to be avoided.
In order to avoid the formation of ice in the intake air provided by the air-feed system of the gas turbine, it is normal practice to warm up the intake air before it enters the compressor of the gas turbine or at the inlet of the air-feed system. In that case, conventional heating systems or anti-icing systems are used. In such a heating system, the intake air may be heated up by various methods such as, for example, by feeding recirculated hot compressor air, by using a steam-heated heat exchanger or even by using electric heating. Similar systems for preventing the formation of ice in the intake air provided by an air-feed system may also be used in other plants, such as, for example, in internal-combustion engines or compressors.
However, the use of a heating system results in a consumption of thermal energy, which is then no longer available to the gas turbine or the plant. Thus the efficiency of the gas turbine or the plant is reduced by the use of such a heating system.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method of controlling the temperature of intake air provided from outside air through an air-feed system, a temperature-control device for carrying out the method and a gas turbine having the temperature-control device, which overcome the herein afore-mentioned disadvantages of the heretofore-known methods and devices of this general type and with which a formation of ice in the intake air is safely and reliably avoided at an especially low consumption of energy.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of controlling the temperature of intake air provided from outside air passing through an air-feed system, which comprises forming a temperature setpoint from a sum of the dew point of the outside air and an additive margin of safety, and preselecting the temperature setpoint for the intake air. In this case, the temperature of the intake air is matched to the setpoint, for example by heating the intake air.
In this case, the “dew point” of a mixture of water vapor and air at a preselected pressure is defined as that temperature below which precipitation of water or ice starts as a result of condensation or desublimation.
The invention is based on the concept that the thermal energy to be provided in order to avoid the formation of ice can be kept especially low by preselecting an especially low temperature setpoint for the heating of the intake air. In this case, an especially low temperature setpoint, which in addition eliminates the formation of ice in the intake air in a safe and reliable manner, is determined essentially by the dew point, since the formation of ice cannot take place for physical reasons if the dew point is exceeded by the temperature of the intake air.
In accordance with another mode of the invention, the sum of 0° C. and the margin of safety is preselected as the temperature setpoint when the dew point is greater than 0° C. This is done so that the quantity of heat required for preventing the formation of ice and to be provided for heating up the intake air, is kept especially low. This is based on the knowledge that a second physical boundary condition is also necessary for the formation of ice, namely that the temperature of the intake air must be below 0° C. for the formation of ice irrespective of the dew point of the intake air. Therefore, at a temperature of the intake air of more than 0° C., heating is not required in order to safely avoid the formation of ice.
In order to safely avoid the formation of ice, the temperature setpoint is oriented toward the dew point of the outside air and it exceeds the latter by the preset additive margin of safety. In accordance with a further mode of the invention, the formation of ice is reliably avoided when a margin of safety of at least 0° C. and at most 0.5° C. is selected.
The outside-air dew point, which is used as a basis when forming the temperature setpoint, may be determined in various ways. In accordance with an added mode of the invention, the dew point is determined or measured directly.
In accordance with an additional mode of the invention, however, the dew point may also be determined with the aid of the absolute humidity of the outside air or else with the aid of the temperature and the relative humidity of the outside air in an alternative expedient manner.
In accordance with yet another mode of the invention, a characteristics field is used as a basis for determining the dew point, and this characteristics field represents the physical connection between the dew point and the respective parameters used as a basis.
In accordance with yet a further mode of the invention, no control action is performed with respect to the intake air when the temperature of the outside air is less than −5° C. or more than 5° C. or when the relative humidity of the outside air is less than 80%. This is based on the knowledge that, as a physical boundary condition for the formation of ice in the intake air, the outside air must have a temperature of at least −5° C. and at most 5° C. and a relative humidity of at least 80%.
The dew point of the outside air depends on its pressure. In accordance with yet an added mode of the invention, the air pressure of the outside air is additionally determined and is used as an additional basis when determining the dew point. This mode is especially reliable even in the event of air-pressure fluctuations of the outside air. This may be effected, for example, with the aid of a characteristics field provided for this purpose. At the same time, the effect of the geodetic height on the air pressure of the outside air may also be taken into account.
With the objects of the invention in view there is also provided a temperature-control device for intake air provided from outside air passing through an air-feed system, the temperature-control device comprising a measuring system for determining the dew point of outside air; and a con
Bahr Siegfried
Pfuff Thomas
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
Wayner William
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