NTPC was set up in the
central sector in the 1975 in response to widening demand & supply gap with
the main objective of planning, promoting & organizing an integrated
development to thermal power in India. Ever since its inception, NTPC has never
looked back and the corporation is treading steps of success one after the
other. Today NTPC contributes more than 1/ 4th
of the total power generation in India
OVERVIEW
OF NTPC
NTPC KAYAMKULAM
BRIEF DISCRIPTION
Established
in : 1998
Project
Name : Rajiv Gandhi
Combined Cycle Power Project (RGCCPP)
Type
of station : Gas based
combined cycle
Approved
investment : Rs.1189.94 crore
Location : Choolatheruvu
in Alappuzha district of Kerala
Fuel : Naphtha
Fuel
source : BPCL
Water
source : Achankovil river
Gas
turbine output : 2 X 115 MW
Steam
turbine output : 350 MW
Beneficiary
states : Kerala and Tamil Nadu
(with consent of Kerala)
INTRODUCTION TO GAS POWER PLANTS
The development of the
sector in the country, since independence has been predominantly through the
State Electricity Boards. In order to supplement the effects of the states in
accelerating power development and to promote power development on a regional
basis to enable the optimum utilization of energy resources, the Government of India
decided to take up a program of establishment of large hydro and thermal power
stations in the central sector on a regional basis. With this in view, the
Government set up the National Thermal Power Corporation Ltd., in November 1975
with the objective of planning, construction, commissioning, operation and
maintenance of Super Thermal and Gas Based Power projects in the country.
The power plant
consists of gas turbine generating units waste heat recovery boilers, steam
turbo generator, auxiliary electrical and mechanical equipments. The power
generated at this power station is fed over 220 KV AC transmission system and
is distributed to substations at Kundara and Pallam.
The function of a gas
turbine in a combined cycle power plant is to drive a generator which produce
electricity and to provide input heat for the steam cycle. Power for driving
the compressor is also derived from gas turbine.
Combined Cycle to improve
efficiency
Combined cycle power
plant integrates two power conversion cycles namely. Brayton Cycle (Gas
Turbines) and Rankin Cycle (Conventional steam power plant) with the
principal objective of increasing overall plant efficiency.
In the above two cycles
gas turbine exhaust is at a temperature of 500±550 C and in Rankine Cycle heat
is required to generate steam at the temperature of 500-550 C. so, why not use
the gas-turbine exhaust to generate steam in the Rankine cycle and save the
fuel required to heat the water ? Combined Cycle does just the same. The
efficiency of Gas Turbine cycle alone is 30% and the efficiency of Rankine
Cycle is 35%. The overall efficiency of combined cycle comes to 48%.
Black
Start System
To start a gas turbine
in the event of AC-power failure an emergency black start system is provided.
It also helps in safe closing down of the gas turbine and its auxiliaries
following a ‘trip’in the event of grid collapse. The black start system consists
of a separate diesel engine or a gas turbine driven synchronous generator
connected to station switch gear bus. Itcan be operated manually from local or
remote and also itautomatically comes into operation following a black out
condition. Capacity of the black start unit should be such that it can supply
the total auxiliary power required to start a gas turbine from standstill
condition. RGCCPP is provided with diesel generator set for the duty.
How
Does A Combined-Cycle Power Plant Work?
Air Inlet
The
amount of air needed for combustion is drawn though the large air inlet section
where it is
cleaned, cooled and controlled, in order to reduce noise.
cleaned, cooled and controlled, in order to reduce noise.
Turbine-Generators:
The air then enters the gas turbine where it is compressed, mixed with fuel Naptha and ignited,
which causes it to expand. The pressure created from the expansion spins the turbine blades, which
are attached to a shaft and a generator, creating electricity.
Each gas turbine produces 115 megawatts (MW) of electricity.
SIMPLE GAS
TURBINE
Gas turbine
cycle
Heat
at Recovery Steam Generator (HRSG)
The
hot exhaust gas exits the turbine at about 550 degree Celsius and then passes
through the Heat Recovery Steam the HRSG, there are tubes filled with
de-mineralized water. The hot exhaust gas coming from the turbines passes
through these tubes, which act like a radiator, boiling the water inside the
tubes, and turning that water into steam. The gas then exits the power plant
through the exhaust stack at a much cooler 100 degree Celsius, after having
given up most of its heat to the steam process.
This steam is fed to the steam turbine through large pipes.
STEAM TURBINE
The steam turbine is capable of
producing up to 120 MW .It is located on top of the
condenser, from the
cooling turbine
Steam
enters the turbine with temperatures as high as 550degree Celsius and pressure
as strong as 2,200 pounds per square inch. The pressure of the steam is used to
spin turbine blades which is coupled to a generator, producing additional
electricity, about 120 MW per HRSG unit.
After
the steam is spent in the turbine process, the residual steam leaves the
turbine at low
pressure
and low heat, about 100 degree Celsius. This exhaust steam passes into a
condenser, to be turned back into
water.
By
using this ³combined-cycle´ process, two gas turbines and one steam turbine, we can
produce a total of about 350 MW of
electricity.
Transmission of Generated Power
On to the Grid
The Gas Turbine and Steam Turbine generators produce power at 10.5 kV.
The transformers take
the generated 10.5 kV and³transform´ them to 220 kV, which is the
required
voltage needed for transmission to the nearby tower that sends power to the
substation.
A small amount of generation is directed
to auxiliary transformers which transform the generated voltage to a 6.6 kV, so that it may be used
by the plant to power its own pumps, fans and motors.
Gas
Insulated Switchyard(GIS)
The most salient feature of NTPC Kayamkulam is the
GIS, which is the 1st of its kind in India.
GIS is extremely compact compared to other
conventional switchyards.
Unlike
conventional switchyards here the insulation between three phase lines(R,Y,B)
in each
bus bar is provided by SF6 which is a highly inert
gas.
From each transformer, the power passes
underground into the switchyard. The power from all of the generators comes
together there, where it is measured, metered and directed onto the grid.
Condenser
and Cooling Tower
The purpose of the condenser is to turn low energy
steam back into pure water for use in the Heat
Recovery Steam Generator.
The purpose of the
cooling tower is to cool the circulating water that passes through the
condenser. It consists of 8cells with large fans on top, inside the cone-like
stacks, and a basin of
water underneath.
The cool basin water absorbs all of the heat from
the residual steam after being exhausted from
As
the cool water drops into the basin, hot wet air goes out of the stacks.
Normally, hot moist air
mixes with cooler dry air, and typically a water vapor
plume can be formed.
It is the plant where
the purified water to condenser is demineralized. Demineralization is done to prevent
the rusting of condensing chamber and its pipes.
It has the
following 5stages:
Actuated
Carbon Filter (ACF)
Strong
Acid-Cation exchange bed (SAC)
Degasser
tower
Strong
Base Anion exchange bed
Mixed
bed unit (MBU)
Passing through these 5 stages
,purified water is degeneralised and fed to the condenser
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