presentation on one month summer training on working of electrostatic precipitator at NTPC Dadri

1. Presentation on one month summer
training at NTPC Dadri
Presented by :
Raghav Dagar
MSCE-596-2K16
Working of Electrostatic Precipitator at
NTPC Dadri

2. OVERVIEW OF NTPC
NTPC is a company incorporated under the Companies Act 1956. The
headquarters of the company is situated at New Delhi.
NTPC is India’s largest energy producing company from coal and gas. It was
established in 1975 to increase the power production of the country. Beside of
fossil fuels, it is now emphasizing on producing electricity via hydro, nuclear
and renewable sources of energy. The total installed capacity of the company
is 51,635 MW with 20 coal based, 7 gas based stations, 1 Hydro based station
and 1 Wind based station. NTPC has been operating its plants at high efficiency
levels. Although the company has 17.73% of the total national capacity yet it
contributes 24% of total power generation due to its focus on high efficiency.

3. NTPC Dadri At A Glance
NTPC Dadri Gets
Coal from Piparwar mines, Jharkhand
Gas from GAIL Hajira-Bijapur-
Jagdishpur (HBJ) pipeline
Water from Upper Ganges Canal
NTPC Dadri Distributes To
NCR, U.P, Uttrakhand,
Rajasthan, Delhi, Punjab,
Haryana, Himachal Pradesh,
J&K, Chandigarh & Indian
Railways
Commissioned
In 1991, NTPC Dadri has
three types of Thermal
Power Stations- Coal
based, Gas-fired and Solar.
Responsible
For providing power to
NCR. Hence named
National Capital Power
Station (NCPS)
Capacity
Coal - 820 MW
Gas - 817 MW
Solar - 005 MW
Total - 2642 MW

4. Sources of Air Pollution at Thermal Power plant :
• Unloading of coal from wagons.
• Storage of coal at temporary yards.
• Crusher house and mill.
• Furnace and stack.
• Storage and management of fly ash
and bottom ash.
Air Pollutants at thermal power plant:
• Particulate matter(fly ash and soot)
• Sulfur oxides
• Nitrogen oxides
• CO2, CO, Hg and others

5. Water
Sprinklers
Water sprinklers are installed at coal unloading area, coal
transporting conveyer belts, temporary yards, ash dikes and ash
mounds. These water sprinklers prevent the dust from coal by
making it wet.
Coal unloading area
Coal transporting conveyer belts
Temporary coal yard Ash dike

6. Fabric filter Centrifugal collectors
Wet collectors Electrostatic precipitator
Other methods of
pollution control
used in thermal
power plant

7. Emission Standards
Existing emission standards:
Power generation capacity PM Emission
• Less than 210MW 350 mg/Nm3
• 210MW or more 150 mg/Nm3
New Emission standards:- dated 07.12.2015
 TPPs (units) installed before 31.12.2003
• PM 100 mg/Nm3
• SO2 600 mg/Nm3 (<500MW)
200 mg/Nm3 (≥500MW)
• NOx 600 mg/Nm3
• Mercury 0.03 mg/Nm3
 TPPs (units) installed after 01.01.2004 upto 31.12.2016
• PM 50 mg/Nm3
• SO2 600 mg/Nm3 (<500MW)
200 mg/Nm3 (≥500MW)
• NOx 300 mg/Nm3
• Mercury 0.03 mg/Nm3
 TPPs (units) to be installed from 01.01.2017
• PM 30 mg/Nm3
• SO2 100 mg/Nm3
• NOx 100 mg/Nm3
• Mercury 0.03 mg/Nm3

8. Electrostatic precipitator
History
The first use of Corona Discharge
to remove particles from an
aerosol was done by Hohlfeld in
1824. In 1907 Frederick Gardner
Cottrell, a professor of chemistry
at university of California applied
for a patent on a device for charging
particles and then collecting them
through electrostatic attraction—
the first ESP.
Introduction
An electrostatic precipitator (ESP) is a filtration device that removes fine
particles like dust and smoke, from flowing gas using the force of an
induced electrostatic charge minimally impending the flow of gases
through the unit.

9. Cntd…
Principle of ESP
Electrostatic precipitation is a method of dust collection that uses electrostatic
forces and consists of discharge wires and collecting plate. A high voltage is applied
to the discharge wires to form an electric field between the wires and the
collecting plate, and also ionizes the gas around the discharge wires to supply ions.
When the gas that contains an aerosol flows between the collecting plate and
discharge wires, the aerosol particles in the gas are charged by the ions. The
Coulomb force caused by the electric field causes the charged particles to be
collected on the collecting plates, and the gas is purified.
Components of ESP
• Electrodes
• 440 V 50 Hz AC supply
• High voltage transformers
• Rectifiers
• Insulators
• Hooper

10. Working of ESP

11. Corona Discharge : Free electron
generation
• Around the discharge electrode,
electric field is generated due
to DC terminal arrangement.
The applied voltage in discharge
electrode is increased until it
produces a corona discharge,
which can be seen as a luminous
blue glow around discharge electrodes.
• Due to corona discharge formation,
free electrons are emitted with high
velocity from discharge electrodes.

12. Ionization of gas molecules
• As the electrons leave the strong
electrical field area around the
discharge electrode, they start
slowing down. Now they're in the
inter-electrode area where they
are still repulsed by the discharge
electrode but to a lesser extent.
There are also gases molecules in
the inter-electrode region, but instead
of violently colliding with them, the
electrons kind of bump up to them and
are captured. This imparts a negative
charge to the gas molecules, creating
negative gas ions. This time, because the ions are negative, they too want to move in the direction opposite the
strong negative field.
• Now we have ionization of gas molecules happening near the discharge electrode and in the inter-electrode
area, but with a big difference. The ions near the discharge electrode are positive and remain in that area. The
ions in the middle area are negative and move away, along the path of invisible electric field lines, toward the
collection electrode.

13. Particle mechanism
• Particles are charged by negative gas ions moving toward the collection
plate by one of these two mechanisms: field charging or diffusion
charging. In field charging, particles capture negatively charged gas ions as
the ions move toward the grounded collection plate. Diffusion charging, as
its name implies, depends on the random motion of the gas ions to charge
particles.

14. Particle collection and removal
• When a charged particle reaches the grounded collection electrode, the charge on
the particle is only partially discharged. The charge is slowly leaked to the
grounded collection plate. A portion of the charge is retained and contributes to
the inter-molecular adhesive and cohesive forces that hold the particles onto the
plates.
• Adhesive forces cause the particles to physically hold on to each other because of
their dissimilar surfaces. Newly arrived particles are held to the collected particles
by cohesive forces; particles are attracted and held to each other molecularly. The
dust layer is allowed to build up on the plate to a desired thickness and then the
particle removal cycle is initiated.
• Dust that has accumulated to a certain thickness on the collection electrode is
removed by one of two processes, depending on the type of collection electrode.
Collection electrodes in precipitators can be either plates or tubes, with plates
being more common.
• Tubes are usually cleaned by water sprays, while plates can be cleaned either by
water sprays or a process called rapping. Rapping is a process whereby deposited,
dry particles are dislodged from the collection plates by sending mechanical
impulses, or vibrations, to the plates. Precipitator plates are rapped periodically
while maintaining the continuous flue-gas cleaning process.

15. Types of Electrostatic Precipitator
 On the basis of structure and design
• Tubular
• Plate
 On the basis of method of charging
• Single stage
• Double stage
 On the basis of temperature of operation
• Hot-side
• Cold-side
 On the basis of removal of particles from collection surface
• Wet
• Dry

16. Tubular and plate
• Tubular precipitators consist of cylindrical collection electrodes (tubes) with discharge
electrodes (wires) located in the center of the cylinder. Dirty gas flows into the tubes,
where the particles are charged. The charged particles are then collected on the inside
walls of the tubes. Collected dust and/or liquid is removed by washing the tubes with
water sprays located directly above the tubes.
• Plate ESPs have wire, rigid-frame, or plate discharge electrodes. Dirty gas flows into a
chamber consisting of a series of discharge electrodes that are equally spaced along
the center line between adjacent collection plates. Charged particles are collected on
the plates as dust, which is periodically removed by rapping or water sprays.
Tubular type ESP
Plate type ESP

17. Single stage and Two stage
• A single-stage (b) precipitator uses high voltage to charge the particles,
which are then collected within the same chamber on collection
surfaces of opposite charge.
• In a Two-stage(a) precipitator, particles are charged by low voltage in
one chamber, and then collected by oppositely charged surfaces in a
second chamber.

18. Hot-side and Cold-side
• A Hot-side precipitator is located before the combustion air pre-heater in a
boiler. The flue gas temperature for hot-side precipitators is in the range of
320 to 420°C.The use of hot-side precipitators helps reduce corrosion and
hopper plugging.
• Cold-side ESPs have been used where the flue gas temperature is relatively
low ( ≤204°C) and can be used to remove fly ash from boilers that burn high
sulfur coal and also can effectively remove fly ash from boilers burning low-
sulfur coal with the addition of conditioning agents.

19. Wet and Dry
• Wet ESPs are used where the potential for explosion is high or when dust is very
sticky, corrosive, or has very high resistivity. In a circular-plate wet ESP, the circular
collection plates are sprayed with liquid continuously. The liquid provides the
electrical ground for attracting the particles and for removing them from the plates.
• Most electrostatic precipitators are operated Dry and use rappers to remove the
collected particulate matter. The term dry is used because particles are charged and
collected in a dry state and are removed by rapping as opposed to water washing
which is used with wet ESPs.
Wet type ESP
Dry type ESP

20. Scenario at NTPC Dadri
• At NTPC Dadri Plant 4 units of 210MW each (from 1991-94) and 2 units of
490MW each (in 2010) were installed.
• At coal unloading area water sprinkles are installed near the wagon
unloading track to prevent the dust flow in the air during the unloading
and transportation of coal.
• Temporary coal yards also have a line of water sprinklers to spray water on
coal heaps if required.
• As it was commissioned in 1991 it follows the existing emission limits but
it measures the emission of SO2, CO2, NOx, etc for determining its
efficiency.
• The plant performed excellent for the management of fly ash as during the
last year it disposed 205% of the fly ash.
• The all four units of plant have 24 ESPs each connected to 4 ducts which is
further connected to a common outlet in stack.
• All 24 ESpss in a unit are connected to furnace from where flue gas is
entered.

21. Cntd…
• ESPs of Dadri plant are of Plate, Dry, Hot and Two staged type ESPs.
• Id fans are there to create air pressure to carry the flue gas.
• The particulate matter deposit on the walls of electrostatic precipitator is
removed by the on and off action of hammer on the walls.
• Stack height of the plant is 225m and the sampling is done at a height of
110m to analyze continuous emission monitoring system which also
collects samples at intervals.
• Temperature of flue gas is maintained above 150˚C existing from stack
because SO will condense at low temperatures
• Real time emission data of 10th and 11th July of Dadri Plant
NOx SOx PM
10.07.2017 413.49 1020.68 42.11
11.07.2017 421.33 977.29 35.09
all emissions (on average of all stacks) are in milligram per
normal meter cube taken from NTPC Dadri