Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
2002-07-18
2004-01-06
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
C415S114000
Reexamination Certificate
active
06672075
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to turbines, and more particularly to gas turbines with a liquid cooling system encapsulated into the turbine rotor.
The present invention further relates to a liquid cooling system which includes a tank containing a cooling liquid and a coolant pump coupled to the tank for forced recirculation of the coolant liquid along the channels formed in the rotor shaft and through the rotor disks and blades of the turbine, and wherein the coolant pump is actuated as a result of relative motion of the stator with regard to the rotor of the turbine.
The present invention also relates to a turbine liquid cooling system which includes a heat exchanger positioned in a compressor section of the turbine, either in a compressor drum, or at the end of the compressor section, or the combination thereof, and wherein, being positioned at the end of the compressor section, the heat exchanger may use the blade thereof or the blade of the compressor for cooling purposes.
BACKGROUND OF THE INVENTION
As known to those skilled in the art, a gas turbine is a heat engine that converts a portion of the fuel energy into work by using gas as the working medium which commonly delivers its mechanical output through a rotating shaft. In the typical gas turbine, the sequence of thermodynamic processes consists basically of compression, addition of heat in a combustor, and expansion through a turbine. This basic operation of the gas turbine may be modified through the addition of heat exchangers and multiple components for reasons of efficiency, power output, and operating characteristics. In order to achieve an overall performance of the turbine, each process is carried out in the engine by a specialized component.
As shown in
FIG. 1A
, a typical turbine
1
includes: a rotor
2
having a rotating shaft
3
with disks
4
and blades
5
, attached thereto, a stator
6
, as well as a combustor
7
, and a compressor
8
.
In operation, air for the combustion chamber
7
is forced into the turbine by the compressor
8
. In the combustor
7
, fuel is mixed with the compressed air and is burned. Heat energy, thus released, is converted by the turbine into rotary energy.
High emission temperature of the combustion product generally necessitates excess air to cool the combustion product to the allowable turbine inlet design temperature. To improve efficiency, heat exchangers may be added to the gas turbine exhaust to recover heat energy and return heat to the working medium after compression and prior to heat combustion.
Two basic types of compressors are used in gas turbines, namely, axial and centrifugal. In a few special cases, a combination type known as a mixed wheel, which is partially centrifugal and partially axially, is used.
Combustors, sometimes referred to as combustion chambers, for gas turbines take a wide variety of shapes and forms. All contain nozzles to meter the fuel to the gas stream and to atomize or break up the fuel stream for efficient combustion. In addition to being designed to burn the fuel efficiency, the combustors also uniformly mix excess air with the products of combustion to maintain a turbine at a uniform lower temperature. The combustor brings the gas to a controlled uniform temperature with a minimum of impurities and a minimum loss of pressure.
The turbine itself includes the rotor
2
with turbine disks
4
and blades
5
thereon, and a stopper. Two types of gas turbine disks are generally used, namely, radial-in-flow and axial-flow. Small gas turbines usually use a radial flow disk, while for larger volume flows, axial turbine disks are used almost exclusively. Although some of the turbines are of the simple impulse type, most high performance turbines are neither pure impulse nor pure reaction. The high performance turbines are normally designed for varying amounts of reaction and impulse to the optimum performance.
Gas turbines are typically provided with subsystems of control and fuel regulation. The primary function of the subsystem that supplies and controls the fuel is to provide clean fuel, free of vapor, at a rate appropriate to engine operation conditions. These conditions may vary rapidly and over a wide range. As a consequence, fuel controls for gas turbines are, in effect, special purpose computers employing mechanical, hydraulic, or electronic means, with all three in combination being frequently used.
All gas turbines employ some kind of cooling to various extent and use a liquid or gas coolant to reduce the temperature of the metal parts. The cooling system varies from the simplest form where only first stage disk cooling is involved to the more complex systems where the complete turbine (rotor, stator and blades) is cooled. Two basic types of heat exchangers are used in gas turbines, namely, gas-to-gas and gas-to-liquid. An example of the gas-to-gas type is the regenerator which transfers heat from the turbine to the air leaving the compressor. The regenerator must withstand rapid large temperature changes and must have low-pressure drop. Intercoolers, which are used between stages of compression are generally air-to-liquid units. They reduce the work of compression and the final compressor discharge temperature. When used with a regenerator, they increase both the capacity and efficiency of a gas turbine of a given size.
The thermal efficiency of gas turbines is critically dependent on the temperature of burnt gases at the turbine inlet. The higher temperature generally results in a higher efficiency. Stochiometric combustion would provide maximum efficiency, however in the absence of an internal cooling system, turbine blades cannot tolerate gas temperatures that exceed 1300 K. For this temperature, the thermal efficiency of turbine engine is only 52%. Conventional air-cooling techniques of turbine blades allow inlet temperatures of about 1500 K on current operating engines yielding thermal efficiency gains of about 4%. Newer designs, that incorporate advanced air-cooling methods allows inlet temperatures of 1750-1800 K, with a thermal efficiency gain of about 3.5% compared to current operating engines. This temperature is near the limit allowed by air-cooling systems.
Turbine blades may be cooled with air taken from the compressor or by liquid. Cooling systems with air are easier to design but have a relatively low heat transfer capacity and reduce the efficiency of the engine. Some cooling systems with liquid rely on thermal gradients to promote re-circulation from the tip to the root of turbine blades. In these cases, the flow and cooling of liquid are restricted. For optimum results, cooling systems with liquid (shown in
FIG. 1B
) should use a pump
9
to recirculate the coolant
10
contained in coolant tank
11
and a heat exchanger
12
to cool the liquid. In the past, designers have tried to locate the pump
9
on the engine stator
6
and, therefore were unable to avoid high coolant losses through seals
13
′ and
13
″ since it has been found to be impossible to reliably seal the stator-rotor interface.
The Carnot cycle provides the theoretical limit for the thermal efficiency of any heat engine. This limit, &eegr;
Carnot
, is given by
η
carnot
=
1
-
T
L
T
H
(
1
)
where T
L
is the absolute temperature of the low-temperature reservoir, and T
H
is the absolute temperature of the high-temperature reservoir.
For gas turbine engines, maximum thermal efficiency,
η
1
(
max
)
=
1
-
T
1
*
T
3
*
(
2
)
where T
1
* and T
3
* are the total temperature at compressor and turbine inlet, respectively. Therefore, increasing the temperature at the turbine inlet is the most advantageous method for improving the efficiency and power of gas turbine engines. Simultaneously, the specific weight and frontal area of the engine decrease. The improvement of these two performance parameters is especially important for aeroengines.
The design of turbine engines has been continuously perfected for many years. Newer engines have been designed which are more powerful and more efficient as the need has arisen.
Brasoveanu Dan
Sandu Constantin
Casaregola Louis J.
Rosenberg , Klein & Lee
University of Maryland
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