Method and apparatus for cooling the inlet air of gas turbine and internal combustion engine prime movers

A multi-stage method and apparatus for cooling the inlet air of internal combustion engine and gas turbine prime movers associated with various load applications comprising: generating and providing a multi-stage refrigerated cooling system associated with the air inlet of internal combustion engine and gas turbine prime movers which provides thermodynamic efficiencies in accordance with a divided psychrometric inlet air cooling path enthalpy curve; cascading the cooled refrigerant from stage to stage to cool primary or secondary refrigerant from a first cooling stage as a precooling heat transfer coolant to exchange against and subcool subsequent stages of primary or secondary refrigerant for cooling to the desired temperature; energizing power means to drive the prime mover and refrigerant cooling system; and adjusting the power means based on current energy costs to optimize net revenues to produce electricity or useful work from the prime mover application.

BACKGROUND OF THE INVENTION 
1. Field 
This invention pertains to methods for increasing the performance for gas 
turbines and internal combustion (IC) engines. 
Specifically, it relates to a new multi-stage method and apparatus for 
cooling the inlet air of gas turbines and internal combustion engines to 
increase their power output and combustion efficiencies. 
2. State of the Art 
Kohlenberger, U.S. Pat. No. 5,444,971, describes a Method and Apparatus for 
Cooling the Inlet Air of Gas Turbine and Internal Combustion Prime Movers, 
which increases the performance of a gas turbine or internal combustion 
engine by cooling the air inlet to densify the air mass flowing into the 
engine and into the gas turbine compressor blades or engine cylinders. The 
performance benefits are accomplished by the sequential staging of the 
cooling coils in the airstream in serial fashion allowing increased 
refrigeration efficiency. Additional refrigeration efficiencies are gained 
via the cascading from stage to stage of cooled primary or secondary 
refrigerant from the first cooling stage, to subcool directly or 
indirectly the refrigerant for the subsequent stages to sequentially cool 
the air inlet stream entering the compressor. The turbine performance 
increase is limited by the lowest temperature of inlet air provided by the 
interconnected first and second stages (or more if in multiple succeeding 
stages) of compatible primary or secondary refrigerant systems which 
interchange the refrigerant which is fed from stage to stage, directly or 
indirectly. 
Therefore, although the staged single cooled primary or secondary 
refrigerant feed system is workable and economical, maximum performance 
increases are achieved by providing an improved multi-stage constant air 
cooling system method and apparatus for optimizing turbine and engine 
performance which utilizes systems with interchanging refrigerant feeds 
from stage to stage. These multi-stage systems can also be arranged in 
primary/secondary hybrid combinations. This involves the use of primary 
evaporating refrigerant created in a conventional compressor system and 
used in the latter stages of cooling in combination with chilled 
water/brine or well water as a secondary refrigerant chilled in any 
variety of chillers and drivers used in first stages of inlet air cooling. 
Additionally, the secondary refrigerant (chilled water, brine, etc.) could 
be generated in a thermal energy storage mode by making and storing 
chilled water or brine or ice at off-peak low cost energy times for usage 
during peak energy power generation periods where energy costs to produce 
secondary refrigerant are higher. 
The invention described below provides such a system. 
SUMMARY OF THE INVENTION 
The present method and apparatus optimizes the electrical power output 
performance of gas turbine and internal combustion engine prime movers 
which can drive a variety of rotating loads, i.e. pumps, generators, 
compressors, or electrical generator sets. This optimization is 
accomplished by cooling the turbine/engine inlet air which increases its 
mass density and throughput. It comprises: first creating a psychrometric 
inlet air cooling path enthalpy curve beginning with the average ambient 
air temperature entering the turbine/engine and reducing the air 
temperature to the optimum air inlet temperature above the ice point for 
maximum performance. The psychrometric inlet air cooling path enthalpy 
curve is then sectionalized and divided into dedicated multiple cooling 
stages to optimize thermodynamic cooling of the refrigeration cycle 
efficiencies by operating the turbine along the least energy intensive 
segments of the enthalpy curve. 
A multi-stage refrigeration system is then structured and associated with 
the air inlet to provide the multi-stage cooling along with the 
thermodynamic efficiencies in accordance with the divided psychrometric 
turbine inlet air cooling path enthalpy curve. The multi-step cooling 
stage system utilizes primary (direct) or secondary (indirect) cooled 
refrigerant which is circulated to absorb heat from the inlet air and 
transfers the same to a heat sink. Primary (direct) refrigerant is defined 
as one which actually changes state (boils or condenses) directly against 
its heat exchanger coil surface to produce cooling. Secondary (indirect) 
refrigerant is one which does not change state and is first cooled by a 
primary refrigerant and is then recirculated through its heat exchanger 
coil surface to produce cooling by the sensible transfer of heat. The 
inlet air cooling system is structured such that cooled primary or 
secondary refrigerant from the first cooling stage is cascaded from stage 
to stage as a precooling heat transfer coolant to exchange and subcool, 
directly or indirectly, against any subsequent stage of primary or 
secondary refrigerant to incrementally cool the inlet air to the desired 
optimum performance temperature (Currently, the general optimum air inlet 
temperature for maximum turbine performance is the air inlet "ice point", 
32 F.). This technique of cascading the cooled primary or secondary 
refrigerant from stage to stage increases the Carnot thermal transfer 
efficiencies of the process. 
The turbine drive and multi-stage refrigerant cooling system is then 
powered and adjusted to run based on current energy cost inputs to 
optimize the net revenues from prime mover output or electrical sales from 
the turbine generator set. 
In one preferred embodiment for optimizing the power output and performance 
of a turbine, the turbine fuel controls are set at and inlet guide vanes 
positioned in the optimum position for maximum turbine efficiency. The 
staged refrigeration system is then used to control and modulate the inlet 
air temperature to operate the turbine at the optimum temperature to 
optimize turbine performance. 
One variation of a gas turbine inlet air cooling system currently being 
installed in the Upper Midwest, uses well water at 52 F. to cool the inlet 
air for a Solar Saturn Gas Turbine Generator Set. The design inlet air 
temperature is 95 F. and the well water cooling system cools the air to 57 
F. prior to it inlet into the turbine. This cooling effect increases the 
turbine output from 0.97 megawatts to 1.15 megawatts, a 19% increase. 
Further increases in power output are achieved by adding a second stage 
refrigerated coil in hybrid fashion which further cools the inlet air from 
57 F. to 40 F. to provide a further increase of 0.05 megawatts for a total 
output of 1.20 megawatts, or a 24% increase from the 95 F. ambient 
temperature. 
Recent studies of a Westinghouse 501D5 natural gas fired turbine generator 
set associated with a three stage gas turbine inlet air cooling system 
utilizing direct ammonia refrigerant revealed a 13% power output increase 
over that achieved with by an evaporative cooled gas turbine air inlet. In 
addition the heat rate was reduced by 4% at a constant power setting. 
The three stage gas turbine inlet air cooling system consisted of three 
staged cooling coils in series utilizing ammonia (or other) primary 
refrigerant which was pump recirculated to the coils and back to each of 
the three dedicated pump accumulator vessels. The first stage coil cooled 
the air from 105 F. to 71 F. using 61 F. ammonia refrigerant. The second 
stage coil cooled the air from 71 F. to 55 F. using 45 F. ammonia. The 
third cool completed the cooling of the inlet air from 55 F. to 40 F. 
using 30 F. ammonia. Three ammonia compressors take the evaporated 
refrigerant from the three dedicated accumulators and compress it for 
condensing into liquid refrigerant in a common bank of evaporative 
condensers. This high pressure condensed liquid refrigerant then returns 
to the suction accumulators to repeat the heat transfer cycle. The 
refrigerant introduced to the second and third stage coils is precooled by 
the preceding stages and cascaded into the subsequent stages for maximum 
thermodynamic efficiency. 
Lower optimal turbine operating temperatures can be achieved below the 
icing point of the air inlet to further increase gas turbine or internal 
combustion engine performance. In this embodiment, the inlet air is 
pre-cooled below the icing point and then re-heated (warmed) slightly by 
the incoming warm refrigerant or other means to prevent moisture in the 
air from condensing and freezing which could cause damage to the turbine 
blading. This further cooling then provides even more gas turbine output. 
It is theoretically possible to divide the psychrometric turbine inlet 
cooling path enthalpy curve into many (infinite) stages. The optimum 
system would depend on the capital cost and physical space limitations. 
Multiple substantially equal enthalpy stages and corresponding staged 
cooling systems are generally employed. 
To further save energy in a gas turbine inlet air cooled system, if the 
waste heat from the turbine/engine exhaust can be utilized, this can 
become a source of direct absorption refrigeration or steam turbine driven 
compression refrigeration. This use of low grade waste heat provides 
increased prime mover or generator revenues by reducing parasitic 
refrigeration loads. The hybrid combination of waste steam turbine driven 
refrigeration compressors which would condense into steam 
absorber/chillers provides yet another possible technique. Additionally, 
gas turbine generator set output can be enhanced by the reduction of 
parasitic refrigeration energy by using direct gas fired 
absorber/chillers, internal combustion engine or gas turbine refrigeration 
system drivers. 
By thermodynamically controlling the turbine operating parameters, daily 
inlet air temperature fluctuations are avoided. 
This enables the turbine/engine to be operated at a constant temperature 
and pressure. This can result in reduced wear, as well as optimizing the 
electrical output from a turbine generator set or other prime mover 
application. 
In areas where the electric energy revenues are dependent upon the time of 
generation, an algorithm control system based on the computer simulation 
model is generally employed to calculate the hourly costs of the fuel 
energy consumed to generate electric power vs. power sales revenues paid 
for the electricity produced to develop net cost curves. Based on these 
hourly net costs to operate the system, the fuel energy inputs to run the 
turbine generator set are adjusted to optimize net revenues, which may or 
may not correspond to the optimum turbine performance efficiencies. For 
example, instead of simple physical performance optimum energy 
comparisons, a computer program, such as that produced by Kohlenberger 
Associates Consulting Engineers, Inc. entitled "Program for Controlling 
Multi-Temperature Staged Refrigeration Systems", Copyright.COPYRGT. 1992 
by Kohlenberger Associates Consulting Engineers simulated on an Apple 
Macintosh computer, models the thermodynamic efficiencies of a 
sectionalized divided psychrometric turbine inlet air cooling path 
enthalpy curve of the average ambient air temperature turbine performance 
and the optimum air inlet temperature for maximum turbine performance at a 
given temperature and altitude. The program then assigns the hourly price 
of adding refrigerated cooling energy during peak electrical periods to 
reduce turbine fuel costs, while optimizing electrical output. The cost of 
added refrigeration energy to produce the increased electrical benefits at 
a given time is then calculated to generate a net revenue curve. The 
computer program thus calculates the operating parameters to produce 
optimum hourly net revenues so that the turbine generator set can be 
adjusted to generate optimum net revenues. 
The present method and apparatus has resulted in net output increases in 
the turbine/generator set of 20-25% while at the same time reducing fuel 
usage 3 to 5%. These factors combined then increase operating revenues as 
much as 20 to 30 percent over those produced by conventional evaporative 
inlet air cooling systems. These cost savings and revenue increases are 
significant, particularly where employed with large electrical generation 
plants These savings will repay the total cost of refrigerated inlet air 
cooling systems within approximately two to four years.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
FIG. 1 illustrates the increase in turbine performance for a Westinghouse 
501D5 natural gas fired combustion turbine as the turbine inlet air 
temperature is cooled to 40 F. At this point, the optimum power output is 
107% of the turbine performance at the standard 59 F. ISO temperature. 
FIG. 2 illustrates a psychrometric chart showing the turbine inlet air 
cooling path for the three stage method and cooling system more 
particularly described in the schematic flow diagram shown in FIG. 3. This 
psychrometric chart was generated for a three stage coil heat transfer 
system associated with the turbine air inlet as shown in FIG. 5. FIG. 3 
shows a first stage refrigerant coil utilizing ammonia as a refrigerant 
mounted within the air inlet to reduce the inlet air from 105 F. DBT to 71 
F. utilizing ammonia refrigerant at 61 F. The ammonia coolant from the 
first stage cooling coil is cooled and then passed into a second stage 
cooling coil within the air inlet to reduce the temperature from 71 F. to 
55 F. DBT, using 45 F. refrigerant. The third stage cooling coil then 
reduces the airstream from 55 F. to 40 F. using 30 F. refrigerant. 
The schematic flow diagram of a water chiller turbine air inlet 
refrigeration system arrangement is shown in FIG. 4. Cooling coil 1 using 
chilled water as a coolant is mounted upstream of cooling coil 2 within 
the air inlet. A first water chiller 1 is operationally connected with the 
first cooling coil 1. The water coolant from the first cooling coil 1 is 
used to precool the refrigerant in chiller 2. A separate water chilling 
circuit in water chiller no. 2 is used in coil no. 2 to further cool the 
inlet air using water at a lower temperature. Chilled water in the no. 2 
circuit is also used to precool refrigerant in chiller no. 3. Finally, 
water chiller no. 3 is used with coil no. 3 to cool the inlet air to its 
final temperature with the lowest chilled water temperature. This is the 
optimal inlet air temperature; thereby optimizing the performance of the 
turbine driving an electric generator. 
An optional chilled water, ice, or other thermal energy storage tank or 
means may be associated with the water chilling loop to store chilled 
water as coolant feed for the refrigeration system produced during 
off-peak hours when the price paid for electricity is lowest--i.e. the 
turbine generator is operated during off peak hours to produce less 
electricity and more refrigerated coolant. This chilled water or ice in 
storage then cools the inlet air without having the chillers operating 
during the peak power periods, thereby reducing the refrigeration 
parasitic power and increasing the net output of the turbine/generator 
set. 
FIG. 5 illustrates an ammonia refrigeration system, wherein a first stage 
compressor, no. 1, a second compressor, no. 2, and a third stage 
compressor, no. 3, are operably associated with a first stage cooling coil 
1, a second stage cooling coil 2, and a third stage cooling coil 3 to 
stepwise reduce the temperature of the inlet air in a similar fashion to 
that described above. 
FIG. 6 is a plan view of the Westinghouse 501D5 combustion turbine air 
inlet refrigeration system 10. Three cooling coils, 12, 14, 16 are located 
within the turbine air inlet 18, and operably associated with three 
compressors 20, 22, 24. The ammonia coolant of the three cooling coils, 
12, 14, 16 is interconnected as shown with refrigerant lines 26 forming a 
circuit along with three ammonia recirculators 28, 30, 32, and three 
evaporative condensers 34,36,38 to make a complete three stage system for 
cooling the inlet air for the gas turbine generator. The gas turbine 
generator set 40 consists of a simple cycle natural gas fired Westinghouse 
501D5 combustion turbine 42 driving an 80 megawatt electric generator 44. 
A motor/turbine control center 46 controls the ignition and feed of the 
combustion fuel entering the gas turbine 42, as well as the electricity 
required to operate the electrical compressor drives (not shown) to lower 
the temperature of the cooling coils 12,14,16. This motor/turbine control 
center 46 has sensors (not shown) within the air inlet to insure that the 
air entering the turbine cabinet 48 is of constant temperature and 
pressure to optimize the performance of the gas turbine 42. 
Three evaporative condensers 34,36,38 are associated with the refrigeration 
system 10 to dispel heat of compression and condensation within the 
refrigeration cycle. 
A typical refrigeration load profile to cool the inlet air over a 24 hour 
period is shown in FIG. 7. A typical operating cost profile for a three 
stage inlet air cooling system is shown in FIGS. 8 and 9. FIG. 8 is a data 
summary of the performance analysis/comparison of a typical three stage 
inlet air cooling system for a Westinghouse 501D5 Combustion Turbine 
Generator Set. FIG. 9 is a data summary of the operating cost analysis, 
performance, and net increases in electrical revenues for the Westinghouse 
501D5 Combustion Turbine Generator Set three stage inlet air cooling 
system. 
As can be seen from the tables in FIGS. 8 and 9, electrical revenues paid 
for electricity produced generally vary based on the time of day that 
these power deliveries are made. Therefore, a computer (not shown) with a 
revenue/cost algorithm is generally associated with the motor/turbine 
control center 46 to optimize the hourly net energy outputs by producing 
maximum electricity during on-peak electrical pricing periods. If a 
thermal storage system is utilized, stored cooled secondary refrigerant 
produced and stored during off-peak pricing periods is then circulated 
during on-peak electrical pricing periods to optimize the production of 
electricity with minimal refrigerant costs. 
The three stage turbine air inlet refrigeration system thus produces 
significant net revenues by optimizing the performance of the turbine 
generator set 40. 
Although this specification has made reference to the illustrated 
embodiments, it is not intended to restrict the scope of the appended 
claims. The claims themselves recite those features deemed essential to 
the invention.