Gas turbine cycle

In a humid air gas turbine cycle the compressed air is humidified prior to introduction to the combustor. Compressed air before humidification is used to cool the first turbine stage rotor blades. Humidified air is used to cool the first turbine stage stationary vanes.

DESCRIPTION 
Technical Field 
The invention relates to gas turbine vane and blade cooling, and in 
particular, to such cooling in a humid air gas turbine cycle. 
Background of the Invention 
A humid air turbine cycle is described in U.S. Pat. No. 4,829,763. 
Compressor exhaust from a gas turbine engine compressor is humidified by 
direct contact with a water supply. The humidified air is used in a gas 
turbine combustor as the combustion supporting air. This humidified air is 
first preheated by turbine exhaust products. 
Feed water to the humidifier is preheated by using the feed water for 
interstage compressor cooling and for further gas turbine exhaust product 
cooling. Occasionally this feed water is also used for precooling the 
compressor exhaust. 
In conventional, or simple cycle gas turbine engines, turbine component 
cooling is accomplished by bleeding air from the high pressure compressor 
and delivering metered amounts to the cooling passages within turbine 
seals, cavities and airfoils. This process maintains material temperatures 
within limits commensurate with desired part lives. The amount of cooling 
air required for each part is a function of the desired metal temperature, 
the pressure and temperature of the coolant, the effectiveness of the 
cooling scheme in each part and the temperature of the flow path gas. 
For a given flow path temperature, turbine cooling flow can be reduced by 
increasing the effectiveness of the cooling scheme, by using a material 
which permits a higher allowable metal temperature, or by reducing the 
temperature of the coolant. Generally, turbine cooling has a detrimental 
effect on cycle performance. On the other hand turbine cooling allows a 
significant increase in the gas turbine inlet temperature. The cycle 
benefits from the high inlet temperature, overwhelms the penalties of the 
cooling bleed. The favorable trade between high gas path temperature and 
air cooling of hot section parts has improved the gas turbine over recent 
years. 
A basic requirement for any cooling scheme is for the cooling air to have a 
higher pressure than the gas path fluid at the point of injection. The 
turbine cooling air exits the cooling part once it has performed its 
cooling function and enters the primary gas path. The outflowing air from 
the cooled part prevents ingestion of hot gas within the cooling passages 
of the part. The outflowing air can form a cooling zone on the exposed 
metal which further enhances cooling effectiveness and protection of the 
part. Allowing the cooling flows to reenter the gas path adds working 
fluid to the expansion process through the downstream portion of the 
turbine. 
Cooling air for the initial turbine stages must generally come from the 
high compressor discharge, or more conveniently, from the burner diffuser. 
At this engine station the highest pressure air in the system is found. 
Because of the pressure loss taken by the main stream gas the combustion 
process and the reduction in gas path static pressure because of 
acceleration in the turbine, diffuser bleed air has ample pressure to cool 
the first stage vanes and blades and still enter the gas path. Diffuser 
air is, however, the hottest cooling source in the system and is also the 
most expensive air in the system in terms of energy spent to compress the 
coolant. 
For turbine parts downstream of the first stages, gas stream pressure drops 
significantly. For these parts we may provide the cooling from lower 
pressure compressor sources. Such cooling does not form a part of the 
present invention but is used in conjunction therewith. 
SUMMARY OF THE INVENTION 
As in the conventional humid air gas turbine cycle, air is compressed to a 
predetermined level to form compressed air. This air is humidified to form 
a gaseous medium which is delivered to the combustor. This humidified air 
is the combustion supporting air for the burning of fuel in the combustor. 
The first stage vanes located upstream of the turbine rotor are cooled by 
passing a portion of the gaseous medium which has been humidified through 
the vanes and then to the primary gas flow path. The first stage turbine 
blades on the other hand are cooled by the compressed air which has not 
yet been humidified with this air then passing into the primary gas 
stream. 
The gaseous medium for cooling the first stage vanes may be preheated prior 
to the cooling operation by passing this medium in heat exchange relation 
with the turbine exhaust products. 
The use of the humidified air for cooling the first stage vanes requires 
more flow than the compressed air per se, because of the high temperature 
of the mix. However, this entire coolant flow passes through the entire 
turbine so that power generation is achieved with the entire flow. Cooling 
of the first stage blade on the other hand uses only the air without the 
vapor being added, thereby avoiding bypass of excessive amounts of coolant 
around the first stage blades which would cause a loss in power generation 
.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, the fuel supply to combustor 10 comes from gasifier 12 
where fuel 14 and air 16 is supplied. After quench tank 18 the gas passes 
through precooler 20 to disulfurizer 22. This low BTU gas is then supplied 
to combustor 10. 
Low pressure compressor 24 discharges air at 72 Psia and 448.degree. F. 
through intercooler 26 to the high pressure compressor 28. The discharge 
of compressed air at 541 Psia and 608.degree. F. from the high pressure 
compressor passes through line 29 to humidifier or saturator 30. It then 
passes at 522 Psia and 388.degree. F. to heat exchanger 42. At 512 Psia 
and 831.degree. F. it passes through line 32 to a diffuser area 34 where 
it is used as combustion supporting air in the combustor 10. 
First stage stationary vanes 36 experience the full temperature of the gas 
leaving the combustor. First stage turbine blades 38 located on the rotor 
experience the temperature of the gases leaving the first stage vanes 36. 
Gas turbine exhaust products at a temperature of 900.degree. F. pass from 
the turbine exhaust products 40 through heat exchanger 42. Heat from the 
exhaust gas is thereby transferred to the incoming humid air passing 
through line 32. 
Turbine exhaust gases may be further cooled in heat exchanger 44 where they 
pass in heat exchange relationship with incoming feed water which is being 
supplied to humidifier 30. 
Makeup water 46 is heated in passing through intercooler 26. A portion of 
this is further heated in heat exchanger 20 passing through line 48 to the 
humidifier 30. Another portion is heated in the heat exchanger 44 passing 
through line 50 to the humidifier 30. 
A shaft connected generator 52 generates electric power. 
A portion of the compressor exhaust air before humidification which is 
directed to line 29 passes through line 54, passing through the first 
stage blades 38 for cooling of the blades. A portion of the humidified air 
passing through line 32 is schematically shown as passing through line 56 
for the cooling of first stage vanes 36. 
FIG. 2 is a section of a portion of the turbine illustrating a means of 
conducting the cooling flows to the vane and blades. The humidified air or 
gaseous medium 56 being supplied to the combustor area accessing the zone 
58 surrounding the combustor. It may then be passed directly to the 
interior of first stage vanes 36 through any desired cooling path, with 
outlet flow 60 passing from the vanes in a manner to achieve film cooling 
of the vanes. 
Flow through line 54 may pass into a portion of the stator assembly where 
it is transferred through a tangential outboard injection connection 61 
into a rotating zone 62 of the rotor. It is then directed upwardly through 
roots 64 of first stage blades 38. The air passes through the blades in a 
selected cooling path with the outflow 66 being directed for film cooling 
of the blades. 
For discussion purposes the source of cooling fluid is indicated as A or C. 
A is the unhumidified compressed air directed into line 29 from the high 
pressure compressor outlet. Flow C is the humidified air which is being 
directed to the combustion chamber. 
The coolant for the first stage vane 36 is selected as flow C which is the 
humidified air. This coolant after it discharges from the vanes passes 
through the entire turbine and therefore is available for power 
generation. The flow contains not only 33.7 pounds per second of air but 
also 16.3 pounds per second of vapor for a total flow of 50.0 pounds per 
second. This is a higher flow than would be required if only air were 
being supplied since this is at a higher temperature level than the air 
from A. The excess flow is not a detriment however because of the complete 
power recovery. 
The first stage blade on the other hand does not use the humidified air. 
The cooling fluid for the first stage blade is from source A prior to 
humidification. This results in a lower flow of air which is preferred 
since this coolant bypasses the first stage of turbine insofar as power 
generation is concerned. 
Table 1 shows comparative values of various possibilities of cooling of the 
vanes and blades from these two sources. In the first column is listed the 
present scheme with the vane flow from source C and the blade flow from 
source A. The lowest heat rate is achieved and accordingly the highest in 
efficiency. The power is amongst the highest, and the permitted combustion 
temperature for a fixed 2507.degree. F. inlet temperature is the highest 
at 2539.degree. F. 
The flow to the vanes and blades is shown as air, vapor, and total. 
The use of a coolant from either A or C which is available adjacent the gas 
turbine engine has advantages over other sources throughout the power 
plant cycle. Blockage of any of these lines is minimized as well as 
breakage. 
TABLE 1 
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Vane Flow Source C A A C 
Blade Flow Source A C A C 
Heat Rate BTU/KWHr 8526 8587 8559 8548 
Net. Eff. BTU/KWHr 40.0 39.7 37.9 39.9 
Power % 210 207 213 205 
Combustor Temp. 
.degree.F. 2539 2500 2500 2535 
Flow to Vane 
Lb/sec Air 33.7 43.1 43.1 34.5 
Lb/sec Vapor 
16.3 0 0 15.6 
Lb/sec Total 
50.0 43.1 43.1 50.1 
Flow to Blade 
Lb/sec Air 19.4 15.2 19.4 15.8 
Lb/sec Vapor 
0 7.9 0 7.2 
Lb/sec Total 
19.4 23.1 19.4 23.0 
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