The subject of this invention is a draining and cooling system for gas turbine cushions.
As is known, gas turbines have a compressor, to which outside air is supplied to be brought up to pressure.
The pressurised air passes into a series of combustion chambers, ending with a nozzle, in each of which an injector supplies fuel which mixes with the air to form an air-fuel mixture for burning.
Then, the combusted gases are sent to the turbine which transforms the heat content of the gases which have been combusted in the above-mentioned combustion chamber into mechanical energy available to a user.
Twin-shaft gas turbines have a gas generator and a power turbine with independent shafts which rotate at different speeds.
The power rotor consists of a shaft which, at one end, supports the low pressure turbine discs and at the other end, the load flange.
The hot gases generated in the gas generator must be converted into power available to a user by a low pressure turbine.
The low pressure nozzles accelerate and direct the hot gases towards the rotor blades, transmitting the useful power to the turbine""s shaft.
In order better to understand the technical problems which are involved in the present invention, at this point reference is made to the following state of the art, with particular reference to FIG. 1.
FIG. 1 represents a draining and cooling system for gas turbine cushions, relating to a twin-shaft turbine of the known art, indicated globally by the numeric reference 30.
In this case, the power rotor rests on a pair of cushions, indicated respectively by the numbers 17 and 18.
The heels of the cushions 17 and 18 are fitted onto a rigid support (cushions unit) which is supported by the cushion carrier unit.
It should be noted that in some cases the cushion unit is integral with the cushion carrier unit.
The service pipes 31 and 32 of cushions 17 and 18, through which pass the lubricating oil and the air for pressurisation of the seals on the shaft, are installed in the area adjacent to the load flange.
Each cushion 17 and 18 has at least one oil feed pipe 31, a pipe 60 for the seals barrier air and a drain pipe 32 common to both the lubricating oil and the sealing air containing the oil vapours.
In fact, the oil and barrier air feed and drain area is a xe2x80x9cdifficult environmentxe2x80x9d as it is located inside the drain diffuser 34, the walls of which 33, usually insulated, have areas of very high temperature as a result of the thermal bridges which are created and for which there is no practical means of elimination.
In the event of an oil leak, the insulation may become impregnated with a consequent emission of fumes or flames.
Furthermore, the turbines designed most recently have undergone a transformation as a result of which the connections area is even less accessible and even smaller.
Therefore, lubricating oil and pressurisation air must be supplied, avoiding oil leaks (or leaks of air containing oil vapours in the case of the drain pipes) through the static seals (joints between stator parts).
It is also necessary to try to limit as much as possible the size of the cushions 17 and 18, of the seals and of the units which support the cushions 17 and 18 themselves in particular in the case of small, low-power gas turbines.
Another key aspect to be considered in the draining of oil is the maximum temperature that the oil may reach.
In fact, the lubricating oil must not reach excessively high temperatures, otherwise it deteriorates and loses its own physical capacities and properties.
The turbine""s internal unit, that is the unit which supports the cushions, is made from materials which cannot withstand high temperatures (for example cast iron) in order to limit costs, but it supports the drain diffuser 34 in which flow the gases at high temperature.
Consequently, the internal part of the turbine""s drain unit is covered with a layer of insulation and there is always a cooling system for the unit itself to keep the temperature low.
In general terms, it can, however, be observed that in power turbines the cushion housings are installed in the following ways:
In a first example, separate cushion housings are provided, where each has two end seals as the shaft passes through, and there are pipes which carry the lubricating oil which are usually contained within the drain pipes and pressurisation air pipes.
The two cushion housings are installed in the turbine drain unit with the appropriate provisions to take into account the differential expansions between the cushion housings and the drain unit, maintaining, however, the coaxiality of the shaft with the gas channel.
In a second example, the cushions are installed directly in a common unit, that is the shaft support unit, secured in its turn to the drain unit.
The service pipes are flanged in the area of cushion 18 which is usually a combined supporting and thrust cushion, the oil and pressurisation air feed connection is via pipes inside the unit, and the oil return from cushion 17 is by means of flowing to the bottom of the shaft support unit where it combines with that which drains from cushion 18.
The connection with the drain pipe which carries the oil into the central unit housing is in the area of cushion 18.
A third example of the known art provides three cushions, two support and one thrust, installed directly on the turbine drain unit. In this case the unit is structured to have the capacity to collect the oil drained from the cushions.
The turbine drain unit can be considered to be a combination of the shaft support unit and the drain unit itself, the service fluid connections are located in the area of cushion 18.
Consequently, the purpose of this invention is to create a draining and cooling system for gas turbine cushions which permits a more efficient circulation of the lubricating and cooling oil, to make the design of the pipes more rational, considering the increasingly limited spaces available on the most recently designed turbines.
Another purpose of the invention is that of creating a draining and cooling system for gas turbine cushions which serves to create a suitable cooling effect, that is such as to reduce the internal surface temperature of the turbine""s drain unit and able to avoid a significant and damaging increase in the temperature of the oil itself.
Another purpose of the invention is that of creating a draining and cooling system for gas turbine cushions which offers a high level of efficiency and mechanical reliability, as well as being advantageous on an economic level.
These and other purposes fulfilled by a draining and cooling system for gas turbine cushions, where the above-mentioned gas turbine has a drain it, which consists of two essentially concentric rings connecting to each other by several spokes, where, inside the above-mentioned drain unit, there is a rotor shaft, associated with the cushions, characterised by the fact that the lubricating and cooling oil is fed to the above-mentioned gas turbine drain unit by means of at least a first pipe, located inside one of the above-mentioned spokes, and is drained by means of at least a second pipe, located inside another of the above-mentioned spokes.
In a particular version of this invention, a section of one of the above-mentioned drain pipes is passed inside the gas turbine drain unit.
In accordance with another preferred version of this invention, the lubricating and cooling oil is drained by means of at least a pair of pipes, each of which is located inside one of the spokes, where the above-mentioned pipes are suitably insulated as they pass through an area the temperature of which may be high.
More particularly, the oil feed pipe arrives inside the turbine drain unit and divides into two further pipes which feed the third and fourth cushions of the above-mentioned turbine.
In accordance with another preferred version of this invention, the cushion""s thrust bearing drags the oil at high peripheral speeds and increases its energy level to create an accelerating jet for draining of the oil through at least one of the above-mentioned pipes located inside the spokes.
Further characteristics of the invention are defined in the claims attached to this patent application.
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