FIELD OF THE INVENTION
The invention generally relates to Gas Turbines operating on 'high Hydrogen fuel
gas'. More particularly, the invention relates to a High pressure Nitrogen supply
system for blocking and purging of a fuel system of the Gas turbine.
BACKGROUND OF THE INVENTION
Gas Turbines are operated on various types of gaseous and liquid fuels
depending on the availability and requirement. The fuels can have variations with
respect to their calorific values, flash points, viscosity, presence of corrosive
elements, ash contents etc. The gas turbines also have the need for higher
safety features to be built-in to safeguard against hazards.
A Gas Turbine has the capability to operate on more than one fuel. Accordingly,
many Gas Turbines are designed to operate on various gaseous fuels including
liquid fuels to meet the objective of fuel flexibility.
Gas Turbines handling fuel gases with greater than 5% hydrogen (H) content on
3 percent by volume basis are referred to as 'high Hydrogen fuel gases', thus
requiring additional safety features to be built in. Due to low ignition temperature
of Hydrogen, it is necessary to separate high Hydrogen fuel gas from any other
combustion source for the safe operation of the Gas Turbine. Further, the Gas
Turbines designed to operate on 'high Hydrogen fuel gas' need a safe liquid fuel
system as a startup fuel, as it is not safe to start a Gas Turbine on 'high
Hydrogen fuel gas'. The gas turbine is chariged over to gas fuel wode only after
the safe starting.

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A Gas Turbine when designed to operate on a fuel gas with liquid fuel as an
alternate fuel, the Gas combustion system of the turbine wW have individual and
separate sets of fuel nozzle for the gas fuel and for the liquid fuel. When the Gas
Turbine is operating on the liquid fuel, the gas fuel nozzles will be purged with
discharge hot air of the Gas Turbine compressor, to prevent choking of the gas
fuel nozzles.
Thus, a gas Turbine designed to operate on 'high Hydrogen fuel gas' with "liquid
fuel' as start-up/alternate fuel, requires an inert gas purging device to separate
'hvgh hydrogen fuel gas' from the compressor discharge hot air, a combustion
source, for the safe operation of the gas turbine,
Nitrogen being an inert gas is generally used for the purpose of the purging
system.
Requirement of Nitrogen under various operating conditions of Gas
Turbine:
The fuel gas system for a typical Gas Turbine designed to operate on a 'high
Hydrogen fuel gas' with liquid fuei as an start-up/aiternate fuel is described
her£inbelow.
Atieast a first pair of valves is provided in gas turbine ‘high Hydrogen fuel gas
line to act as the fuel control valve in the 'high Hydrogen fuei gas' of the Gas
Turbine.

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Similarly, a second pair of valves is provided in the Gas Turbine compressor
discharge air line for purging gas fuel nozzles In the combustion system of the
gas Turbine.
A High Pressure Nitrogen purge device blocks and purges the system as
described herein below to avoid mixing of 'high Hydrogen fuel gas' and 'hot
compressor discharge airOperating method
(i) When the gas Turbine is operating on gas fuel mode, the second pair
of valves in compressor discharge air purge air lines, are in closed
position and Nitrogen gas is continuously purged through a cavity
between these valves. The Nitrogen is purged at a pressure higher
than the fuel gas pressure including the compressor air discharge
pressure. This ensures that only inert gas can leak into the gas line
including the compressor discharge air fine, thus avoiding any leakage
of fuel gss into the compressor discharge purge air line and vice versa.
The flow rate of Nitrogen for the continuous purge as above, for a
typical Gss Turbine is 12 SM3/Hr and Nitrogen to be supplied at Gas
Turbine flange at a pressure of 30+/-1 Kg/Cm2 (g).
(ii) When the Gas Turbine is operating on startup/alternate liquid fuel
mode, the first pair of vatves in the high fuel gas. line are in closed
position and Nitrogen gas is continuously purged through the cavity
between these valves. The Nitrogen is purged at a pressure higher

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than the fuel gas pressure Including the compressor air discharge
pressure. This ensures that only inert gas can leak into the gas line
including the compressor discharge air line, thus avoiding any leakage of
the fuel gas into the compressor discharge purge air line and vice versa.
The flow rate of Nitrogen for the continuous purging as above, for a
typical Gas Turbine is 12 sM3 /Hr and Nitrogen to be supplied at gas
Turbine flange at a pressure of 30+/- 1 Kg/Cm2 (g).
Whenever the Gas Turbine changes over from gas fuel mode to liquid
fuel mode, that is, the entrapped fuel gas downstream of the first pair
of valves need to be purged with Nitrogen for a pre-determined time,
before change over, to ensure that entrapped fuel gas will not contact
the compressor discharge hot air, when the compressor discharge air
will not contact the fuel gas, when the compressor discharge air is
introduced into this area after the Gas Turbine is changed over to
liquid fuel mode.
The flow rate of Nitrogen for the intermittent purge as above, for a
typical Gas Turbine is 6000 SM3/Hr for a duration of one minute, ie.f
total quantity required for this intermittent purge is 100 5M5. and
Nitrogen to be supplied at Gas Turbine flange at a pressure of 30+/- l
Kg/Cm2 (g).
Similarly, whenever the Gas Turbine changes over from liquid fuel
mode to gas fuel mode, the entrapped compressor discharge hot air

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downstream of the second pair of valves need to be purged with
Nitrogen gas for a pre-determined time, before change over to ensure
that entrapped compressor discharge air with not contact the fuel gas,
when fuel gas is introduced into this area, after the Gas Turbine has
changed over to gas fuel mode.
The flow rate of Nitrogen for the intermittent purge as above, for a
typical Gas Turbine is 6000 SM/Hrfor a duration of one minute, ie.,
total quantity required for this intermittent purge is 100 SM3 and
Nitrogen to be supplied at gas Turbine flange at a pressure of 30+/- 1
Kg/Cm2 (g).
Analysis of High Pressure Requirement;
From the sbove, the requirement of Nitrogen for Blocking and purging of a
typical Gas Turbine fuel system can be analyzed as under.
a) Continuous requirement for purge white
Gas Turbine is on 'high Hydrogen fuel
gas' (of) on start-up/altemate'Liquid fuel' : 12 SM3/Hr.
b) Intermittent requirement for purge before
transfer from high Hydrogen fuel gas mode'
to start-up/alternate 'liquid fuel' mode and
vice verse : 100 SM3 in one rninute

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c) Pressure required at Gas Turbine Flange for
above requirements : 30± 1 KG/CM1 (g).
d) The trips (or) fuel transfers of Gas turbine are expected to be in-frequent
and for all practical purpose one trip / transfer per week can be
considered.
Further, the gas Turbine shall always be started on start-up / alternate liquid fuel
mode.
In other words, in case of trip of gas Turbine on "high hydrogen fuel gas", the
system shall have intermittent purge with Nitrogen as per parameters indicated
at sl. no.(D) and (c) above, before re-starting on start-up/alternate 'liquid fuel'.
e) When the Gas Turbine trips while operating on 'high Hydrogen fuel gas',
300 SM3 of Nitrogen is required for re-starting the Gas Turbine on start-
up/alternate 'liquid fuel' and subsequent change over to 'high Hydrogen
gas fuel' mode as given below:
Nitrogen required for:
Purge on trip of gas Turbine on 'high Hydrogen
gas fuel' mode : 100 SM3
Re-Start of gas Turbine on liquid fuel : 0 SM3

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Before changeover of Gas Turbine from start-up/
alternate'liquid fuel' mode to "high Hydrogea fuet
gas' mode : 100 SM3
Reserve for intermittent purge for trip of gas
Turbine after change over to 'high Hydrogen fuel
mode' : 100 SM3
Total : 300 SM3
f) Minimum capacity of 200 SM3 of Nitrogen to be ensured for safe change
over of gas Turbine from start-up/alternate "liquid fuel' mode to "high
Hydrogen fuel gas' mode, as given below:
Nitrogen required For:
Before Changeover of gas Turbine from start-up/alternate
liquid fuel' mods to 'high Hydrogen fuel gas' mode: : 100 SM3
Reserve for intermittent purge for trip of Gas Turbine
after change over to 'high hydrogen fuel mode' : 100 SM3
Total : 200 SM3
The Gas Turbine Control system ensures that the required purge quantity of
Nitrogen is drawn from Nitrogen supply system, by suitable opening/cSosing of
solenoid valves of on-base system, as and when required.

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According to the prior art, for the Nitrogen supply for blocking and purging of the
fuel system of the Gas Turbine, following parameters are considered;
g) the Nitrogen supply system for blocking and purging of the fuel system of
the Gas Turbine needs special requirements as below:
i) The Nitrogen gas is required at a pressure of 30 Kg/Cm2 (g),
In all plants, Nitrogen is normally available at a pressure of 2 - 7 Kg /Cm2 (g)
only. Conventionally, air is compressed in a compressor and Nitrogen is
generated from the compressed air through molecular sieve adsorption
technology. Nitrogen can not be generated from air as per above conventional
method, at a pressure beyond 14Kg/Cm2 (g) as the adsorbing media will crush
at higher pressures.
Hence, Nitrogen st 30 kg/Cm2 (g) as required for the purging of the gas Turbine
need to be obtained by boosting the Nitrogen generated In the conventional
method using 9 booster compressor, Nitrogen, generated in a conventional
method being bone-dry type, it calls for special seals [NOBRAC/Eq,] to avoid
damage to the compressor cylinder
(ii) The continuous requirement of Nitrogen for purgmg is only in the order of 12
SM3/Hr. whereas, Intermittent requirement during change over of fuels/ trip of
gas Turbine on lhigh Hydrogen gas fuel', is at a very high rate of 6000 M3/Hr,

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(iii) Intermittent requirement is expected to be once in a week for all practical
considerations. A minimum Nitrogen quantity of 300 SM3 shall be available, for
restarting the Gas Turbine on start-up/alternate 'liquid fuel' ancf subsequent
change over to high Hydrogen gas fuel', when the Gas Turbine trips while
operating on 'high Hydrogen fuel gas' mode. This quantity of Nitrogen is needed
in a short time.
Hence, the Nitrogen supply system shall have a storage provision of 300 SM3 to
meet the above short time requirement.
(iv) Unless otherwise it is ensured that 200 SM3 of Nitrogen is available, change
over of the Gas Turbine from start-up/alternate 'liquid fuel' mode to high
Hydrogen fuel gas' mode, shall not be initiated.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a high-pressure nitrogen
supply system adaptable to gas turbines operating on high hydrogen fuel gas for
blocking and purging the fuel device of the turbine.
Another object of the invention is to propose a high-pressure nitrogen supply
system adaptable to gas turbines operating on high hydrogen fuel gas for
blocking and purging the fuel device of the turbine, which is capable of
separating high hydrogen fuel gas from hot air discharged by the compressor of
the turbine plant.

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A further object of the invention is to propose a high-pressure nitrogen supply
system adaptable to gas turbines operating on high hydrogen fuel gas for
blocking and purging the fuel device of the turbine, which eliminates the
possibility of the entrapped compressor discharge hot air / fuel gas contacting
the fuei gas compressor discharge introduced in a fuef change - over mode of
the turbine.
SUMMARY OF THE INVENTION
Accordingly, there is provided a high-pressure nitrogen supply system adaptable
to gas turbine plants operating on high hydrogen fuel gas for blocking and
purging the fuel device of the turbine, the system corn prising; atleast two
nitrogen booster compressors for boosting the pressure of nitrogen being
suppled from the plant; a plurality of nitrogen receivers (2) inter-connected to
each other and further being operably attached to the booster compressors, the
receivers acting as a buffer storage between the compressors and the gas
turbine so as to compensate s capacity imbalance generating during operation of
the plant; a pressure control device for regulating the pressure of nitrogen in
correspondence with a pre-set pressure at which nitrogen being supplied from
said receivers (2) to the gas turbine; and a piping circuit provided with
instrumentation for monitoring safe operation of the system.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 is schematic diagram of a continuous Nitrogen blocking and purging
system in 3 typical Gas Turbine while operating on 'high hydrogen fuel gas.'

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Fig. 2 is schematic diagram of a continuous Nitrogen blocking and purging
system in a typical Gas turbine while operating on start-up/a Item ate 'liquid fuel'.
Fig. 3 is schematic diagram illustrating an intermittent Nitrogen purge process for
a typical gas Turbine, before change over from 'high Hydrogen gas fuel' mode to
'start-up/alternate liquid fuel' mode and vice verse.
Fig - 4 is schematic diagram of a - High pressure Nitrogen supply system for
blocking and purging of fuel system, for a typical Gas Turbine - operating on
'high Hydrogen fuel gas', according to the present invention.
DETAILED DESCRIPTION A PREFERRED EMBODIMENT OF THE
INVENTION
Fig. - 4 is a schematic diagram of a High pressure Nitrogen supply system - for
blocking and purging of fuel system for a typical Gas Turbine - operating on high
Hydrogen fuel gas.
The system has been developed in a comprehensive way, taking into
consideration of requirements of a typical Gas Turbine including the special
requirements associated with the type of selected device features.
The high-pressure Nitrogen Supply system comprises :-
- atieast two Nitrogen Booster compressors (1);
- a plurality of Nitrogen Receivers (2);

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- a Pressure control device (3)
- Interconnecting piping circuit wit instrumentation; and
- A Control device.
The function and detailed description of above components is described
hereinbelow:-
1.0.0 Atleast two Nitrogen Booster compressors (1)
1.1.0 Function
In the plant, Nitrogen is normally available at a pressure of 2- 7 Kg/Cm2(g) The
Nitrogen Booster Compressor Boosts the nitrogen pressure from 2-7 Kg/Cm"1
(g) to 31 Kg/Cm2(g) to 45 kg/Cm2 (g) as required by the process,
1.2.0. Components Description
Atleast two water cooled reciprocating compressors (l) are selected. The second
compressor will ensure continuity of operation in case of failure of the first
compressor.
As the compressors handle bone dry Nitrogen, the compressor seals are selected
from those produced of special materials namely NOBRAC / Equivalent to ensure
that there is no damage to compressor cylinder due to low lubricity of bone dry
nitrogen.

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The compressor there after boosts the Nitrogen from a pressure of 2 - 7 Kg/Cm2
(g) upto the receiver pressure. When the pressure in the receiver reaches around
40 to 45 Kg/Cm2 (g), the compressor is stopped. The compressor is restarted
when receiver pressure comes down to 37 to 39 Kg/Cm3 (g).
The capacity of the compressor has been selected in 5uch a way that the time
period between start and stop of the compressor is within permissible limits to
prevent over heating of the compressor motor.
Accordingly, a compressor with a capacity between 40 to 60 SM3/Hv at suction
pressure of Nitrogen as 2 Kg/Crrr2 (g) is selected.
Being a positive displacement compressor, the actual swept volume of the
compressor remains same, accordingly, the Nitrogen Booster compressor will
deliver 40 to 60 SM3/Hr with Nitrogen pressure at suction of compressor as 2
Kg/Cm2 (g) and deiiver 100 to 150 SM3/Hr of nitrogen wfth Nitrogen pressure at
Suction of compressor as 1 Kg/Cm'* {g).
Time between stsrt-stop of the compressor with Norm a! continuous consumption
of Nitrogen by Gas Turbine (12 SM3/Hr) and compressor suction pressure of
Nitrogen as 2 Kg/Cm2 (g) is about: 1 Hour Same is about 25 to 35 minutes with
compressor suction pressure of nitrogen as 7 Kg/cm2 (g). These time periods are
well above the permissible time periods between successive start-stops of the
compressor.
2.0.0 A plurality of Nitrogen Receivers (2)

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2,1.0 Function :
The function of the Nitrogen Receivers (2) Is to act as a buffer storage between
the compressor and the Gas Turbine such that imbalance in the compressor
capacity and the Gas Turbine requirement can be compensated. Further, the
receivers will act as a reservoir for maximum intermittent short time Nitrogen
Requirement of 300 SM3.
2.2.0 Components Description:
Atleast three receivers (2) each of 12M3 to 18M3 actual volumes are provided.
The Nitrogen receivers operate between a pressure of 31 Kg/Cm2 (g) to 45
Kg/Cm3 (g). The Mechanical design pressure of the receivers is 55 Kg/Cm7 (g).
Three receivers (2) have been considered instead of providing a single common
receiver of 36 to 54M3, as the thickness of plates required for a 54 M3 receiver is
much higher than 40 mm which are not readily available in the market.
All the three receivers (2) are interconnected such that all the receivers can be
operated at the same pressure.
Normally the receivers (2) operate between a pressure of 37 Kg/Cm2 (g) and 45
Kg/Cm2 (g) meeting the normal Nitrogen consumption of the gas turbine. At the
receiver pressure of 50 Kg/Cm' (g) the nitrogen Booster compressor will start
and at the receiver pressure of 30 Kg/Cm2 (g) the Nitrogen Booster compressor
will stop.

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In addition, each or the receivers will provide intermittent Nitrogen requirement
of 100 SM3 of the Gas Turbine by expanding further from 37 Kg/Cm2 (g) to 31
Kg/Cm2 (g). That isr all the three receivers (2) together have a storage capacity
of 300 SM3 which is the maximum intermittent Nitrogen requirement by the Gas
Turbine.
Time taken by the compressor (1) for filing the receivers from 25 Kg/Cm2 (g) to
45 Kg/Cm2 (g) after consumption of 300 SM3 Nitrogen is 1 Va to 2 1/2 Hours with
Nitrogen pressure at suction of the compressor (1) at 7 Kg/Cm2 (g) and same is
4 to 6 Hours with Nitrogen pressure at suction of compressor at 2 Kg/Cm2 (g).
This is considered adequate as the intermittent requirement is expected only
once In a week.
2.3.0 A Pressure Control device (3)
2.3.1 Function
The function of the pressure control device (3) is to regulate the Nitrogen supply
pressure between 30± 1 Kg/Cm2 (g) as required by the Gas Turbine from the
receiver pressure of 31 Kg/Cm2 (g) to 45 Kg/Cm2 (g),
2,4.0. Components Description:
Atleast a first pair of self actuating type-pressure control valves (PCVOIA and
PCVOIB) have been provided for regulating the Nitrogen pressure while the gas
Turbine is consuming normal Nitrogen continuous requirement of 12 SM/Hr.

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A second parr of self actuating type pressure control valves (PCV-02A and PCV-
02B) have been provided for regulating the Nitrogen pressure while Gas Turbine
is consurming intermittent Nitrogen requirement of 6,000 SM3/Hr.
The set points of said control valves are staggered within an allowable variation
of Nitrogen pressure at inlet of the Gas Turbine [+/- 1 Kg/Cm2] ie., a variation of
2 Kg/Cm2 in such a way that the set point decreases in the order of PCV-01 A to
PCV-01 B to PCV-02 A to PCV-02 B.
Such a setting of the first and the second pair of pressure control valves ensures
that when the Gas Turbine requires lower flow range of 12 SM3/Hr, PCV-01 A
only will operate. In case of failure of the PCV-01 A, the PCV-01 B automatically
comes into operation.
Similarly, rn case of high flow requirement of the Gas Turbine of 6,000 SM3/Hr,
the PCV-02 A automatically comes into operation. In case of failure of the PCV-
02 A, the PCV-02 B automatically tomes into operation,
2,5.0 Interconnecting Piping circuit with Instrumentation:
23.2. Function:
All the required interconnecting piping and instruments like safely valves on
receivers, gauges and transmitters are provided as indicated in Fig. 04 for
monitoring, and safe operation of the system.

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2,6.0. Control device
2.3,3. Function:
All the operations like start /stop of the compressor are controlled via a control
panel mounted in the control room. The panel can be a dedicated PLC/relay
based panel (or) the DCS of the plant. The system has been provided with
required electrical protection means including provision for monitoring the field
instruments to achieve the safe operation of the system.

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WE CLAIM
1- A high-pressure nitrogen supply system adaptable to gas turbine plants
operating on high hydrogen fuel gas for blocking and purging the fuel device of
the turbine, the system comprising:
- atteast two nitrogen booster compressors (1) for boosting the
pressure of nitrogen being supplied from the plant;
- a plurality of nitrogen receivers (2) inter-connected to each other
and further being operably attached to the booster compressors
(1), the receivers (2) acting as a buffer storage between the
compressors (1) and the gas turbine so as to compensate a
capacity Imbalance generating during operation of the plant; and
acting as a reservoir for max inn urn intermittent short-time nitrogen
requirement;
- a pressure control device (3) for regulating the pressure of nitrogen
in correspondence with a pre-set pressure at which nitrogen being
supplied from said receivers (2) to the gas turbine; and
- a piping circuit provided with instrumentation for monitoring safe
operation of the system.
2. The system as claimed in claim 1, wherein the compressors (1) are water-
cooled reciprocating type compressors having seals made of NOBRAC or
equivalent material.

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3- The system as claimed in claim 1, wherein the pressure control device (3)
comprises a first pair of actuating type pressure control valve (PO/-01A, PCV-
01B), and a second pair of' actuating type pressure control valve (PCV-02A, PCV-
02B).
4. The system as claimed in claim l or 3, wherein the set-points of the control
valves are selected such that the set-points of each valve is staggered, and
wherein the set pressure in the control valves decrease in the order of from First
one (PCV-01A) of the first pair to the second one (PCV-01B) of the first pair, and
from the first one (PCV-02A) of the second pair to the second one (PCV-02B) of
the second pair,
5. A high-pressure nitrogen supply system adaptable to gas turbine plants
operating on high hydrogen fuel gas for blocking and purging the fuel device of
the turbine as substantially described herein with reference to the accompanying
drawings.

This invention relates to a Gas Turbines designed to operate on ‘high Hydrogen
fuel gas’ with liquid fuel as start-up/alternate fuel require Nitrogen blocking and
purging for safe operation of the Gas Turbine. The Nitrogen for this purpose is
required at high pressure, with wide variation in the flow rate and further
requires storage to meet short time intermittent requirement.