FIELD OF INVENTION
The present invention generally relates to a cooling system for gas turbine
generator in combined cycle Power Plants. More particularly, the invention
relates to a dual cooling water system capable of additionally cooling hot air in
the generator with atmospheric air in winters and with water in summers.
BACKGROUND OF THE INVENTION
Forced Cooling Water device is known to be used in the cooling of hot air in the
gas turbine generators in Combined cycle power plants. The air inside the
generator cools the windings on the rotor as well as those of the stator, the hot
air being cooled with DM water which is supplied inside the generator coolers by
several pumps. The DM water used for cooling the hot air is further cooled by at
least one fin-fan cooler having the fins exposed to the atmosphere. In summers
when the atmospheric temperature rises, and the difference between the water
and the atmospheric temperature decreases the hot air is not effectively cooled
inside the generator.
As described hereinabove, the existing device for cooling i.e. Forced Cooling
water device uses DM water as a coolant for cooling hot air and needs Fin fan
Coolers for cooling the water for generation of power. The prior art device has
limitations in summers as the ambient temperature rises and this restricts the
power output of the generator thereby decreasing efficiency of the plant.
The existing forced cooling water device however, fulfils the following
requirements:

Delivering cooling water to generator coolers.
Transferring heat from water coolers to the air cooler system.
Maintaining cooling water temperature and pressure within
allowable values.
The existing device is generally a closed cooling loop cycle type system. It
consists of :
Forced cooling water (circulating) pumps.
DM water make-up pumps
Fin-fan coolers
Expansion tank -1
Expansion tank - 2 (with butyl rubber balloon)
Carbon steel piping and valves
The existing forced cooling device is operable during start-up, normal operation
and blank start of the gas turbine. The operation and configuration of the prior
art device includes:
At least two forced cooling water pumps, the first pump running continuously
and the second pump starts automatically upon the differential pressure between
the discharge and suction falling below a specified value. A pressure switch
provided at the suction end of the two pumps also calls for the pumps tripping
on 'low suction pressure'. Water is supplied through a header line to the
generator coolers which after cooling the generator, caused to enter the fin-fan
cooler located outside the GT where the hot water is cooled.

Cooled water from the fin fan air cooler is returned back to the suction end of
the cooling water pumps which makes the system closed. The cold water is again
supplied to the generator coolers to repeat the cycle.
An expansion tank-2 (with butyl rubber ballon) is disposed at the suction end of
the cooling water pumps. The expansions tank-2 maintains the system pressure,
and provides a volume control.
The existing forced cooling water device is operated with demineralised water.
Accordingly the expansion tank-1 is filled with demineralised water. To maintain
the make-up pressure, DM make-up pumps are provided. The first of the two
pumps continuously runs and a first constant pressure regulator is provided to
maintain a constant pressure for make up. When the DM plant is operated, the
make up is maintained in an expansion tank-1 by a float valve provided in the
expansion tank-1.
A second constant pressure regulator maintains a constant pressure at the
suction end of the forced cooling water pumps. In case, the pressure in the
expansion tank drops, demineralised water is fed via a filling nozzle
automatically.
To avoid over pressure, a safety relief valve on the suction end of the forced
cooling water pumps is provided.
The pumps and the expansion tanks are located outside the Gas Turbine
Building.

The fin fan air coolers are located on the structure of the forced cooling water air
cooler disposed outside the gas turbine building.
A NaOH-dosing unit is provided for feeding dilute NaOH liquid into the system for
control of water pH value, so as to avoid corrosion to carbon steel piping system.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a dual cooling water
system capable of cooling hot air in the generator with atmospheric air in winters
and with water in summers which provides enhanced output.
Another object of the present invention is to propose a dual cooling water
system capable of cooling hot air in the generator with atmospheric air in
winters and with water in summers which increases the efficiency of the
generator vis-a-vis the plant.
SUMMARY OF THE INVENTION
Accordingly, there is provided a dual cooling water system adaptable to power
plants having at least one generator air cooler, for cooling hot air in the
generator air cooler with atmospheric air in winters and with water in summers,
the system comprising; a forced cooling water device imputed to the at least one
generator air cooler and having at least two forced cooling pumps, a first of the
two pumps runs continuously, the second forced cooling water pump
automatically commences operation, when the differential pressure between the
suction and the discharge of the generator falls below a specified value;

A fin fan cooler disposed in the cooling water circuit of the generator which
transfers the heat from the hot water coming out of the at least one generator
air cooler to the atmosphere; atleast one plate-type heat exchanger for cooling
water supplied from a cooling water sump; and two cooling water being pumps
disposed in the circuit; characterized in that the system is configured to :
activate the second forced cooling pump to allow flow of water in
the winter seasons via the fin-fan cooler, and
deactivate the second forced cooling pump to allow flow of water in
the summer seasons being directed via the plate-type heat
exchanger.
According to the invention, the air to be cooled is passed through the generator
air coolers where it is cooled sufficiently with DM water (about a temperature of
40 - 45°C). The DM water is then cooled with Fin Fan Coolers having fins
exposed to the atmosphere. In summers when the differential temperature
between the ambient and that of the DM water reduces the air inside the
generator cannot be effectively cooled thereby the windings of the stator of the
generator is not properly cooled. This phenomenon restricts the maximum
output from the generator.

The inventive system uses plate type heat exchangers and water from the
Cooling water Sump for efficient cooling of the DM water even at lower
differentials which enhances the output from the machine because of sufficient
heat absorption from the air inside the generator. Alternatively, the hot air can
be cooled with DM water with the help of Fin fan Coolers. Accordingly, the
inventive cooling system adapts plate type heat exchangers for cooling water in
case of low temperature differential, and fin coolers in case of high temperature
differential to improve efficiency of the machine.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 - a single line diagram of a forced cooling water device for gas turbine
generator in a combined cycle power plant according to prior art.
Fig.2 - a single line diagram of a dual cooling water system according to the
invention.
DETAILED DESCRIPTION OF A PREFERED EMBODIMENT OF THE
PRESENT INVENTION.
As shown in figure 1, a forced cooling device, comprises two forced cooling
pumps (2), one of the two pumps runs continuously, the second pump
automatically starts when the differential pressure between the suction and
discharge of the generator falls below a specified value.

Firstly, forced cooling water is pumped into generator air cooler (1). After cooling
the generator air, the water is passed through a fin-fan cooler (3). The fin fan
cooler (3) transfers heat from hot water to the atmosphere. The forced cooling
water pumps are operated with demineralised (DM) water for which a DM-plant
with 'make-up' pumps are provided. Further, at least two expansion tanks are
provided for the DM-plant (not shown). Associated controls and piping are
provided to operate the system.
The dual cooling water system of the invention as shown in Fig. -2, is enabled to
adapt a forced water cooling device of Fig. -1. The system is generally operable
when the ambient temperature rises in summers, so as to limit the temperature
where, the temperature differential between the ambient and the cooled water
starts decreasing. The system comprises apart from the forced cooling water
device, atleast one plate type heat exchanger (5) which cools the water from the
cooling water sump (6) of the main power station. Two cooling water pumps (7)
having foot-valves are disposed in the cooling water circuit. A self-cleaning
strainer (8) is disposed between the cooling water pumps (7) and the heat
exchanger (5).
The dual cooling water system works on the principle of heat transfer from Hot
air inside the generator to DM water flowing in the tubes of the generator air
Coolers (1). The forced cooling water is pumped to the generator air coolers (1)
and the Fin Fan Coolers (3). The fin fan coolers (3) transfer heat from the hot
water to the atmosphere. In summers, when the ambient temperature is at its
peak, the differential between the hot water from the generator air coolers (1)
and the atmosphere is less and thus the cooling is not effective.

However, with the plate type heat exchangers (5) installed, the hot water from
the generator air coolers (1) is passed through these heat exchangers (5) and
effective cooling is achieved even at low differential between the primary and
secondary cooling water of the heat exchangers (5). The device is dual in the
sense that it gives two options for cooling the hot water, the first being by the
atmosphere through the fin fan coolers (3) and the second through the plate
type heat exchangers (5). The flow of the water is controlled with necessary
valves and fittings. In winters the first option of cooling through the fin fan
coolers (3) can be employed. This can be done by auto cut-in and auto-cut-out
with the cold air temperature in the generator.

WE CLAIM
1. A dual cooling water system adaptable to power plants having at least
one generator air cooler for cooling hot air in the generator air cooler
(1) with atmospheric air in winters and with water in summers, the
system comprising :
a forced cooling water device imputed to the at least one generator
air cooler (1), and having at least two forced cooling pumps (2), a
first of the two forced cooling (2) pumps runs continuously, the
second forced cooling pump automatically commences operation
when the differential pressure between the suction and discharge
of the generator falls below a specified value;
a fin fan cooler (3) disposed in the cooling water circuit of the
generator which transfers the heat from the hot water coming out
of the at least one generator air cooler (1) to the atmosphere;
atleast one plate-type heat exchanger (5) for cooling water being
supplied from a cooling water sump (6); and
two cooling water pumps (7) disposed in the circuit;
characterized in that the forced cooling water device is configured
to:-
activate the second forced cooling pump to allow flow of water in
the winter seasons via the fin fan cooler (3) and

deactivate the second forced cooling pump and allow flow of water
in the summer seasons being directed via the plate-type heat
exchanger (5).
2. The system as claimed in claim 1, comprising a self-cleaning strainer
(8) disposed between the cooling water pumps (7) and the heat
exchanger (5).
3. The system as claimed in claim 1, wherein the forced cooling water
device is operated with demineralised water (DM-water) for which at
least one DM make up-plant with expansion tanks including associated
controls are provided.
4. A dual cooling water system adaptable to power plants having at least
one generator air cooler for cooling hot air in the generator air cooler
with atmospheric air in winters and with water in summers as
substantially described herein with reference to the accompanying
drawings.

ABSTRACT

TITLE "A DUAL COOLING WATER SYSTEM
ADAPTABLE TO POWER PLANTS"
A dual cooling water system adaptable to power plants having at least one
generator air cooler for cooling hot air in the generator air cooler (1) with
atmospheric air in winters and with water in summers, the system comprising
a forced cooling water device imputed to the at least one generator air cooler
(1), and having at least two forced cooling pumps (2), a first of the two
forced cooling (2) pumps runs continuously, the second forced cooling pump
automatically commences operation when the differential pressure between
the suction and discharge of the generator falls below a specified value; a fin
fan cooler (3) disposed in the cooling water circuit of the generator which
transfers the heat from the hot water coming out of the at least one
generator air cooler (1) to the atmosphere; atleast one plate-type heat
exchanger (5) for cooling water being supplied from a cooling water sump
(6); and two cooling water pumps (7) disposed in the circuit; characterized in
that the forced cooling water device is configured to activate the second
forced cooling pump to allow flow of water in the winter seasons via the fin
fan cooler (3) and deactivate the second forced cooling pump and allow flow
of water in the summer seasons being directed via the plate-type heat
exchanger (5).