Power plants – Combustion products used as motive fluid
Reexamination Certificate
2000-07-24
2002-03-19
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S039120, C060S039780
Reexamination Certificate
active
06357217
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of gas turbines. More specifically, the present invention is concerned with a method for the cooling of guide vanes and/or moving blades in the turbine stages of a gas turbine plant, in which a cooling medium, which contains a first fuel, is fed through the interior of the guide vanes and/or moving blades to be cooled and, using a catalyst, undergoes an endothermal chemical process therein in which the first fuel is converted at least partially into a second fuel, and in which the cooling medium containing the second fuel, after flowing out of the guide vanes and/or moving blades, is used as fuel for driving the gas turbine plant.
BACKGROUND OF THE INVENTION
Such a method is known, for example, from the publication U.S. Pat. No. 5,125,793. In the known method, an endothermal fuel for cooling is fed through the cooling ducts of a gas turbine moving blade, which are lined with a catalyst layer, and is simultaneously evaporated therein and decomposed into a plurality of partially combustible components.
Continuing developments in gas turbines make it possible to increase the turbine inlet temperatures to ever higher values, with the result that, in theory, higher efficiencies can be achieved in the basic cyclic process. However, these increases are associated with the following two problems:
1. How can the vanes/blades of the gas turbine, particularly in the entry stages where the gas temperatures exceed 800° C., be cooled effectively without the excessive use of cooling air?
2. How can the ever increasing turbine outlet temperatures of up to 700° C. be handled due to material-related restrictions, the steam temperature in combined cycle plants cannot be superheated to much more than 550° C. It is therefore not possible for the steam generator to utilize all the possible exergy of the turbine exhaust gases.
It has already been proposed in the past (see, for example, U.S. Pat. No. 5,795,130) to cool gas turbine vanes/blades, particularly in combined cycle power stations, by means of steam, instead of by compressed air, in order to increase both the efficiency in the cyclic process and cooling effectiveness. Both the moving blades and the guide vanes are in this case steam-cooled. The steam is extracted from the steam turbine at high pressure and is supplied to it again at lower pressure.
It has also been proposed (U.S. Pat. No. 5,896,738), in an otherwise conventionally cooled gas turbine, to make use, by thermochemical recuperation, of part of the energy contained in the turbine exhaust gases in order to reform a gaseous fuel which is mixed with steam and which is then supplied as fuel to the combustion chamber of the gas turbine. Another proposal (U.S. Pat. No. 5,431,007) relates to a comparable use of a reformed fuel in a steam-cooled gas turbine.
U.S. Pat. No. 5,590,518 proposes, in a gas turbine with thermochemical recuperation, to cool the last turbine stage of the gas turbine by means of the steam/fuel mixture either before reforming (
FIG. 4
) or after reforming (FIG.
3
). Reforming, in this case, is carried out in an external reformer.
Finally, in U.S. Pat. No. 5,125,793 mentioned hereinabove, an endothermal liquid fuel, for example standard kerosene JP7, is used for cooling the vanes/blades of a gas turbine (without the use of steam and without reforming). The fuel is fed through cooling ducts in the vanes/blades, the ducts being coated with a catalyst layer, and is simultaneously evaporated therein and decomposed catalytically into various components, so that the evaporation heat and the energy consumption of the endothermal decomposition reaction are used at the same time for cooling.
The known cooling methods have various disadvantages: in the cooling method with external reforming, an external reformer with corresponding line connections is required, thus entailing a considerable additional outlay in terms of apparatus and space. Cooling by means of an endothermal fuel, such as is described in the last-mentioned publication, is restricted to gas turbine plants which are operated with a special liquid fuel, while the gas turbine plants in combined cycle power stations are normally operated with natural gas (NG).
SUMMARY OF THE INVENTION
The object of the invention, therefore, is to specify a cooling method for gas turbines and a gas turbine plant which avoid the disadvantages of known cooling methods and, in particular, bring about highly effective cooling of the turbine vanes/blades in a space-saving way and at little outlay in terms of apparatus, along with an optimal utilization of the energy employed.
The essence of the invention is to use, at least partially, a reformed fuel for the gas turbine, the endothermal reforming of the steam/fuel mixture (steam methane) taking place catalytically in the vanes/blades to be cooled (cooling ducts) of the gas turbine itself.
A preferred embodiment of the method according to the invention which is distinguished by a particular simplicity includes cooling ducts provided in the interior of the guide vanes and/or moving blades to be cooled. The cooling ducts are delimited by walls covered with a catalyst layer and the cooling medium is fed through the cooling ducts.
Preferably, in this case, the reforming of the methane in the guide vanes and/or moving blades is carried out at temperatures of between 600 and 800° C. and at pressures of between 10 and 30 bar, and a ratio of steam to methane of 3:1 to 4:1 on a molar basis prevails in the cooling medium before inflow into the guide vanes and/or moving blades.
In a further preferred embodiment of the method according to the invention the cooling medium, flows out through corresponding outflow orifices, at least partially, directly into the respective turbine stage of the gas turbine plant after running through the reforming process in the respective guide vane and/or moving blade. The hot gases flowing through the turbine thereby undergo intermediate heating (reheating) which increases the effectiveness thereof.
In an embodiment which is an alternative to the above, the cooling medium, after running is used at least partially as fuel in a combustion chamber of the gas turbine plant after running through the reforming process in the respective guide vane and/or moving blade. Here too, the chemical energy of the reformed fuel is returned into the cyclic process of the gas turbine. In both instances, the thermal energy of the hot turbine exhaust gases is utilized even more effectively as a result of the so-called “chemical recuperation”. At the same time, it is perfectly possible for the reformed cooling medium not to be used exclusively, but as an additive to a further fuel in the combustion chamber of the gas turbine plant.
If the reforming of the fuel in the turbine blades is not complete, it may be advantageous if, according to another preferred embodiment of the invention, in each case, part of the cooling medium, is branched off and is added again to the cooling medium to be reformed after running through the reforming process.
In the gas turbine plant according to the invention for carrying out the method, the gas turbine plant includes one or more turbine stages, in which a multiplicity of guide vanes and/or moving blades are arranged in various vane/blade arrangements. The turbine plant also includes interior cooling ducts having catalytic properties. The cooling ducts are connected to a steam source through a cooling line, and the cooling line has a fuel feed for introducing the first fuel into the cooling line.
In a preferred embodiment of the gas turbine plant according to the invention, the cooling ducts are delimited by walls which are covered with catalyst layers.
The reformed fuel is introduced into the gas turbine either by virtue of the provision of outflow orifices on the guide vanes and/or moving blades cooled by the cooling medium, through which outflow orifices the cooling medium can flow out of the guide vanes and/or moving blades after running through the cooling ducts, or by virtue of the
Alstom (Switzerland Ltd
Casaregola Louis J.
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