Major Equipment
of Thermal Power Plants
URVISH
Rankine Cycle
The Rankine cycle operates in the
following steps:
•Isobaric Heat Transfer in Boiler
•Isentropic Expansion in Turbine
•Isobaric Heat Rejection in Condenser
•Isentropic Compression in Pumps
Boilers
The Heart
Water tube and Shell Boiler
Shell Boilers
Boilers and Their Types
• Subcritical
• Supercritical
• Ultra-supercritical boilers
Water and Steam
• The critical point of
water occurs at
647.096 K
(373.946 °C;
705.103 °F) and
22.064 megapascals
(3,200.1 psi;
217.75 atm;
220.64 bar).
Subcritical
• A subcritical boiler is a boiler that
produces steam at a pressure that is
lower than the critical pressure of
water or steam
• How does a subcritical boiler work?
• Fuel is combusted to produce hot
gases and flames
• The hot gases and flames pass
through tubes surrounded by water
• The water is heated to produce steam
Subcritical
• Subcritical boilers operates at steam pressures upto 19Mpa.
• There are 2 types-forced and natural boilers. In natural boilers there is
flow from boiler drum to the water walls of the furnace by natural
circulation. The flow is mixed phases both vapour and liquid from and
to the boiler.
• This requires larger tubes and thicker pipes. In forced boilers, there is
a pump called boiler circulation pump, which enables easy flow of
fluid from and to the boiler, thus reducing the need for large tubes.
Supercritical
• Supercritical boilers operates at steam pressures upto 22 Mpa.
• Here the water flows from the economiser to the water tubes, up to the
superheaters to the turbine. There is no boiler drum in this set up.
• This reduces cost and enables to use smaller tubes. During initial stages
when there is water flow, the bcp is in operation. It helps transportation of
liquid into the economiser, until such time when there is only steam flow.
• The term “supercritical” refers to main steam operating conditions, being
above the critical pressure of water (221.5 bar). The significance of the
critical point is the difference in density between steam and water. Above
the critical pressure there is no distinction between steam and water, i.e.
above 221.5 bar, water is a fluid.
Supercritical
• In supercritical cycle, equipment is designed to operate above the
critical pressure of water.
• Supercritical boilers are once-through where in the feedwater enters
the economiser and flows through one path and main steam exits the
circuit.
• Typically current supercritical units operate at 242 bar main steam
pressure, 565ºC main steam temperature and 593ºC reheat steam
temperature.
Comparison to supercritical boilers
• Supercritical boilers operate at pressures above the critical pressure of water
or steam
• Supercritical boilers are more efficient and emit less pollution than subcritical
boilers
• Supercritical boilers are drumless, while subcritical boilers may have drums
Modern subcritical plants with a single reheat operate at efficiencies between
33% and 39%
Boiler design, operation and
maintenance
• Boilers are classified
by their pressure
capacity, design
type, and use.
• The maximum
allowable working
pressure (MAWP) is
the highest
pressure the boiler
can withstand. schematic diagram illustrating the working of a supercritical boiler
Working of a supercritical boiler in a thermal power
plant. The key components include:
1.Feedwater Pump – Pressurizes water above the critical pressure (22.1
MPa).
2.Economizer – Preheats water using flue gases.
3.Boiler Furnace – Burns fuel to generate heat.
4.Superheater – Converts water directly into high-temperature, high-
pressure steam.
5.Turbine – Expands steam to generate mechanical power.
6.Condenser – Converts steam back to water for recirculation.
7.Cooling Tower – Releases excess heat.
Operation
• Start-up involves pre-start checks, warming up the boiler, and firing
the burner.
• Normal operation involves maintaining water levels, monitoring fuel
flow, and adjusting steam flow.
• Shut-down involves gradually reducing the steam load and lowering
the firing rate.
Maintenance
• Low Water Cut-Off (LWCO)
• An automatic reset device that shuts off the boiler when water
drops below a set level
• Auxiliary Low Water Cut-Off (ALWCO)
• A manual reset device that shuts off the boiler when water drops
below a set level
Daily Maintenance
1.Check water level gauge glass, record the pressure gauge and
temperature gauges
2.Check LWCO and ALWCO operation and ensure the burner shuts down
3.Blowdown the water column and gauge glass
4.Turn off burner control switch, observe the response to flame failure
5.Observe operating control and high limit control
6.Perform bottom blowdown to remove sludge and sediment.
7.Observer burner refractory cone, looking for broken chunks or hot spots
Weekly Maintenance
1.Check all linkages on burner controls and the automatic draft
controllers
2.Check air damper on the burner
3.Test valve operation in gas train
4.Check pilot and igniter, look at the condition of the flame
5.Check process of LWCO – blowdown boiler water level through the
drain. Watch gauge glass to see burner cut off before losing sight of
water.
Monthly Maintenance
1.Test limit controls on boiler.
2.Test flame detection controls.
3.Check blowdown for sludging at bottom of boiler.
4.Verify blowdown separator and cooler operation.
5.Check floor drains for proper function.
6.Check boiler fresh air inlet screens.
https://www.rasmech.com/everything-boiler-maintenance/
Annual Maintenance
1.Disassemble and check LWCO and ALWCO for sludge, corrosion or
electrical switch defects.
2.Verify and tune up burners and settings. **We recommend quarterly
tuning by a qualified technician**
3.Inspect fire side for soot or damage and water side for scale or
corrosion & Clean the boiler inside and out.
4.Hydro test boiler for leaks (tube joints and piping).
5.Inspect all refractory for fallen broken chunks.
6.Check gas regulator pressure settings.
7.Replace or re-certify safety valves.
8.Bubble test fuel train safety shut-off valves.
Steam turbine in a thermal power
plan.
• In a thermal power plant, a steam turbine
functions by converting the thermal energy
stored in high-pressure steam into
mechanical energy through a rotating shaft,
which is then used to drive an electrical
generator, effectively generating electricity
from the heat source within the power
plant; essentially, it transforms the heat
energy of steam into usable mechanical
power to produce electricity.
• Types : Impulse and Reaction turbines
Steam Turbines
• Types: Impulse and Reaction
turbines
S.no Impulse Turbine Reaction Turbine
1. In an impulse turbine, the steam flows through the In the reaction turbine, first, the steam flows
nozzle and strike on the moving blades. through the guide mechanism and then flows
through the moving blades.
2. Steam strikes on the buckets with kinetic energy. The steam glides over the moving blades with both
pressure and kinetic energy.
3. During the flow of steam through moving blades, its During the flow of steam through moving blades its
pressure remains constant. pressure reduces.
4. The steam may or may not be admitted to the whole The steam must be admitted over the whole
circumference. circumference.
5. The blades of impulse turbine are symmetrical. The blades of reaction turbine are not symmetrical.
6. While gliding over the blades the relative velocity of In reaction turbine, while gliding over the blades
steam remains constant. the relative velocity of steam increases.
7. For the same power developed, the number of stages For the same power developed, the number of
required is less. stages required is more.
8. The direction of steam flow is radial to the direction The direction of steam flow is radial and axial to the
of turbine wheel. turbine wheel.
9. It requires less maintenance work. It requires more maintenance work.
10. It is suitable for low discharge. It is suitable for medium and high discharge.
Key points about steam turbines in
thermal power plants:
• Steam source:
• High-pressure steam produced in a boiler is directed towards the turbine blades.
• Blade rotation:
• As the steam expands and pushes against the turbine blades, it causes them to
rotate, creating mechanical energy.
• Generator coupling:
• The rotating shaft of the turbine is connected to a generator, which converts the
mechanical energy into electrical power.
• Pressure drop:
• The steam loses pressure as it passes through the turbine stages, eventually
reaching a low pressure state before being condensed.
Gas Turbine Operations (GE MARK 4)
https://www.artisantg.com/info/
GE_Speedtronic_Mark_VI_Manual_20167610475.pdf
https://www.gevernova.com/content/dam/gepower-
new/global/en_US/downloads/gas-new-site/resources/
reference/GEA35311-Mark-VIe-Control-Product-
Description-Brochure-DRAFT.pdf
Condensers
• Role of the condenser in a thermal power plant
• In a thermal power plant, the condenser's primary role is to convert
the low-pressure steam exhausted from the turbine back into liquid
water by cooling it down, thus maintaining a vacuum at the turbine
outlet which maximizes its efficiency and allows for the recycled
water to be reused in the boiler as feedwater; essentially, it completes
the steam cycle by condensing the steam at a low pressure, creating a
vacuum that helps the turbine extract maximum energy from the
steam.
Condensers
• Surface and jet condensers.
condenser
• What is the role of the condenser in a thermal power plant? Explain
with a diagram.
https://www.watco-group.co/surface-condenser-in-thermal-power-plant/
cooling towers
• Types of cooling towers: Natural draft, forced draft, and induced draft
• Significance of cooling towers in maintaining plant efficiency.
Auxiliary Systems
• Coal handling and feeding systems.
• Ash handling systems.
• Water treatment and feedwater systems.
Coal handling and feeding systems.
• Explain how a coal handling system operates in a thermal power
plant.
Ash handling systems.
Water treatment and feedwater
systems.
