Thermal Power Plant Training Report at DSTPS

A COMPLETE OVERVIEW TO ALL THE WOKING OPERATIONS.

1. || A THERMAL POWER PLANT MANUAL ||


DURGAPUR STEEL THERMAL POWER STATION
Owned by DVC (Damodar Valley Corporation)
Located at, Andal, Durgapur, Paschim Barddhaman, West Bengal

Prepared by
Arghya Das & team
Undergraduate student of Techno Main Salt Lake, Kolkata pursuing a Bachelor of
Technology in the Mechanical Engineering Department

Supported by
DVC, DSTPS, Central and State Government (West Bengal, Bihar, and Jharkhand)
This report summarizes the findings of our study on how a steel thermal power plant
operates, its various components, and their working. We gathered information from
engineers and employees and feedback from surveys in order to prepare this report.
Our content is based on practical knowledge. We would like to thank everyone who
contributed to this project, including our mentors and survey respondents.

2. ACKNOWLEDGEMENT

On this great occasion of accomplishment of our report on the Thermal Power Plant,
we would like to sincerely express our gratitude to Mr. Shiwa Nand Singh (Chief
Engineer) and Miss Rashi Agarwal (HR) OF DVC, DSTPS, who has supported us
through the completion of this report. Further, we would like to deeply appreciate the
Junior Engineers, Senior Engineers, Site Visiting Officers, Staff Members, CRPF &
CISF Officers, and Workers for guiding and mentoring us throughout the training
period.
We would also be thankful to the Training & placement officer of our college, Mr.
Dipon Mitra, and guiding professor, Dr. Aditi Mazumder of Techno Main Salt
Lake, for guiding us and supporting us throughout the process of enrolment in this
vocational training.
Finally, as one of the team members, I appreciate all my group members’ support
and coordination. The team participation provided a broader and more innovative
way to present the whole analysis in the form of a report. Moreover, the creativity
and coordination of all the members have led to the completion of this report. With
this reciprocated attitude and equal participation, I hope we will achieve more in our
future endeavors.
Project
Coordinator
Mr. Shiwa Nand Singh
Team
Coordinator
Mr. Shankar Kumar Yadav
Mentor Mr. Niles Biswas (Divisional Engineer)
Team
Members
Akshita Singh
Kalyan Baidya
Ashutosh Mandal
Adrija Roy
Arghya Das
Dattatreya Sekhar Das
Deepika Choudhary
Trainer
Associates
Mr. S. Yadav & Mr. Abhijeet Dey (Water Package)
Mr. Manish Kumar & Biswajit Kar (Coal Mill & Coal Handling
Plant)
Mr. Arvind Kumar Yadav (Boiler)
Mr. Gautam Kumar (Pump)
Mr. S Toppo & Mr. Rajeev Kumar (Ash Handling Plant)
Mr. Manish Jain & Dinesh Kumar Bayen (Turbine)

3. CONTENTS

Serial Number Topic
1 Thermal Power Plant Profile
2 About DSTPS
3 Safety
4 Rankine Cycle
5 Modified Rankine Cycle
6 Practices/ Technologies Equipped in DSTPS
7 Water Package
8 Coal Handling Plant
9 Coal Mill
10 Boiler
11 Turbine
12 Cooling Tower
13 Ash Handling Plant
14 Conclusion

4. THERMAL POWER PLANT PROFILE

Thermal power plants can be classified on the basis of the fuel used for power
generation. On the basis of fuel used, thermal power plants may be classified as:
 Coal-based thermal power plants
 Gas-based thermal power plants
 Oil-based thermal power plants
Coal-Based Thermal Power Plant
A coal-fired power station produces heat by burning coal in a steam boiler. The
steam drives a steam turbine, this steam turbine is coupled with a generator which in
turn produces electricity. The waste products of combustion include ash, sulfur
dioxide, nitrogen oxides, and carbon dioxide.
Gas-Based Thermal Power Plant
In this type, natural gas is fired in a gas turbine which acts as the prime mover. The
gas turbine is coupled with a generator to produce electricity. The exhaust gases
from the gas turbine are at a very high temperature which can further be utilized for
process heating or electricity production through a Heat Recovery Steam Generator
(HRSG) and a steam turbine. It may, however, be noted that gas being a cleaner fuel
produces less Greenhouse Gas (GHG) emissions compared to Coal Based Power
Plants. Further, with less availability of natural gas and higher cost of generation
being a cause of concern, gas-based power plants operate intermittently and at low
capacities, depending on the requirements. Under such circumstances, it would be
inappropriate to consider any productivity or performance improvement options.
Hence, gas-based power plants are not covered in this report.
Oil-Based Power Plant
In the case of oil-based power plants, oil is combusted in a steam generator to
generate steam and this steam is used to drive a steam turbine to produce
electricity. In some other types of oil-based power plants, oil is used as fuel to run
turbines or engines which act as prime movers and coupled with generators,
produce electricity. 15 Oil-based power plants are very few in number and at remote
locations, which are operated only in emergencies. Hence, the oil-based power
plants are also not included in this report.

Productivity and Performance Indicators
The assessment of the productivity and performance of a thermal power plant could
be carried out by monitoring various parameters. The major parameters that highlight
the actual performance of thermal power plants are as follows.

5.  Heat Rate (Indicator of Fuel Consumption per unit of Power Generation)
 Plant Load Factor (PLF)
 Auxiliary Power Consumption (Internal Consumption)
 Generation Efficiency
 Greenhouse Gases (GHG) Emissions
Heat Rate
It is the measure of the performance of a power plant which signifies the amount of
thermal energy consumed for the production of one unit of electricity. Heat rate
is expressed in kcals per KWH. The lower the heat rate of a thermal power plant, the
better the performance.
Plant Load Factor (PLF)
PLF is the ratio between the actual energy generated by the plant to the
maximum possible energy that can be generated with the plant working at its rated
power for a particular duration of time. A higher plant load factor signifies better
utilization of capacity and hence, better performance of a thermal power plant.
Auxiliary Power Consumption (Internal Consumption)
APC is the amount of energy consumed within the plant for the normal operation of
a power plant. For the production of electricity, power plants operate various
auxiliaries and consume electricity which is a part of the gross energy produced by
the plant. The net energy exported by a plant is the energy available after accounting
for APC. Lower APC signifies the better performance of a power plant.
Generation Efficiency
The generation efficiency of a thermal power plant signifies its performance in terms
of energy supplied that got converted into useful work (electricity). It is the ratio of the
energy produced by the plant to the energy supplied to the plant. The remaining
energy is usually lost to the environment as heat. This is expressed in percentage
and the higher the efficiency of a power plant, the better the performance.
Greenhouse Gas (GHG) Emission
Every thermal power plant consumes fossil fuels for the generation of electricity in
the form of coal or natural gas. As the combustion of these fuels takes place it
results in the generation of CO2, Sulphur Oxides (SOx), and Nitrogen Oxides (NOx)
which are GHG and contribute to global warming. The amount of GHGs emitted for
the production of every unit of electricity differs from plant to plant and is dependent
on its performance. High GHG emission for the generation of a unit of electricity
shows the poor performance of a plant as compared to a plant that is generating the
same amount of electricity with a lesser amount of GHG emissions, for a given fuel.

6. ABOUT DURGAPUR STEEL THERMAL
POWER STATION (DSTPS)

Damodar Valley Corporation (DVC) is a Government-owned power generator that
operates in the Damodar River area of West Bengal and Jharkhand handles the
Damodar Valley Project, it is the first multipurpose river valley project of
independent India. Meghnad Saha an Indian Astrophysicist is the former chief
architect of river planning in India, he prepared the original plan for the Damodar
Valley Project. The corporation operates both thermal power stations and hydel
power stations under the ownership of the Ministry of Power, Government of India.
The headquarter of DVC is in the Kolkata city of West Bengal, India.
Durgapur Steel Thermal Power Station, commonly known as DSTPS is a Coal-
based Thermal Power Plant located in Durgapur city in Paschim Bardhaman district
in the Indian state of West Bengal. The power plant is operated by the Damodar
Valley Corporation (DVC). It has an installed capacity of 1,000 megawatts.

The project is currently owned by Damodar Valley with a stake of 100%. It is a
Steam Turbine Power Plant that is used for Baseload. The project got commissioned
in May 2012. Contractors Involved: BHEL (Bharat Heavy Electricals Limited) was
selected to render EPC services for the coal-fired power project.

Unit Number Generating Capacity Commissioned On Status
1 500 MW 2012 May Running
2 500 MW 2013 March Running

7. SAFETY
“THE FIRST PRIORITY”

The thermal power plant is a large electricity generation industry. It consists of a
number of processes to generate electricity by use of fossil fuel. It also consists of
several major equipment and operations involved in its process. The purpose of
hazard identification and risk assessment in thermal power plants is to identify
physical, chemical, biological and environmental hazards in the plant, analyze the
event sequences leading to those hazards and calculate the frequency and
consequences of hazardous events. Then the risk level is assigned to each hazard
for identifying required corrective action to minimize the risk or eliminate the
hazard. In the present scenario for any industry to be successful it should meet not
only the production requirements but also maintain the safety standards for all
concerned. The coal fired thermal power plant is susceptible to a wide range of
hazards in its various operational areas. Hazard identification and risk assessment is
a systematic approach to protect the health and minimize danger to life, property and
environment.
10 Rules for Workplace Safety
1. You are responsible for your own safety and for the safety of others.
2. All accidents are preventable.
3. Do not take shortcuts. Always follow the rules.
4. If you are not trained, don’t do it.
5. Use the right tools and equipment and use them in the right way.
6. Assess the risks before you approach your work.
7. Never wear loose clothes or slippery footwear.
8. Do not indulge in horseplay while at work.
9. Practice good housekeeping.
10. Always wear PPEs. Helmets should be tightened and covered shoes are
mandatory.

HAZARDS IDENTIFICATION AND RISK
ASSESSMENT
Methodology
Hazard identification and risk assessment is a combination of deterministic,
probabilistic and quantitative methods. The deterministic methods take into
consideration the products, the equipment, and the quantification of the various
targets such as people, environment, and equipment. The probabilistic methods are
based on the probability or frequency of hazardous situation apparitions or on the

8. occurrence of potential accidents. The quantitative methods analyse various data
numerically. The five steps of hazard identification and risk assessment are:
Step1: System Description: Define the system and their subsystem and
operations.
Step2: Hazard Identification: Defining and describing a hazard, including its
physical characteristics, magnitude and severity, causative factors, and locations or
areas affected.
Step3: Risk Analysis: Analyse the Probability, frequency or likelihood of the
potential losses associated with a hazard.
Step4: Risk Rating: Risk Classification Screening Table is formed and the value of
hazard or calculated risk class gives the required action to be taken.
Step5: Resolve the Risk: corrective action recommended preventing, reducing or
transferring the risks, by short- and long-term planning.

Risk Classification screening table
S.
No.
Hazard Description Corrective Action
1. Coal Handling Plant Hazard
A Fire in coal storage Regular inspection, water
spray, isolation from ignition
sources
B Coal dust explosion in coal conveyor bunker Proper ventilation, spark
proof electrical equipment
C Rail line and other transport line accidents Speed limit on plant area
D Fall from the height during work on conveyer
belt, conveyer control room etc
Safety belt, safety net
should provide, training
2. D.M. Hazard
A Fire hazard Fire extinguisher, eliminate
the possible ignition source
B Chemical burn by Spillage of sulphuric acid
and caustic soda lye during unloading,
overflow, Damage on storage tank or pipe
line
Wash rinse exposed area,
training, maintenance,
proper supervision

9. C High noise level Ear plug, ear muff should be
provided
3. Boiler Hazard
A Explosion in boiler due to over pressure and
temperature
Continuous monitoring,
maintenance
B Burn injury due to hot water and hot steam
pipeline leakage
Inspection, maintenance
C Catches on the moving part of the machinery
like F. D. fans or motors
Proper fencing on the
moving part of turbine
4. Generator and Turbine Hazard
A Explosion in turbine due to cooling system
failure
Regular inspection,
maintenance
B Fire on cooling oil Proper storage, isolation
from the ignition sources
C Damage on generator due to lack of
lubrication in coupling shaft
Regular inspection,
maintenance
D High noise level Ear plug, ear muff should be
provided
5. Switch Yard Hazard
A Fire on transformer Regular inspection,
maintenance
B Electric shock and electric burn routine work,
maintenance or inspection of electrical panels
in switch yard
Training, PPEs should be
provided
C Slip, trip and from the height during routine
work, maintenance on switchyard
Safety belt, safety harness
should be provided, training
Other Hazards
A Control room fire hazard Fire extinguisher, eliminate
the over heating
B Eye irritation and respiratory problem from
the exposure of ammonia leakage from
storage tank or pipeline
Wash rinse exposed area,
maintenance

10. RANKINE CYCLE

What is Rankine Cycle?
William John Macquorn Rankine, a Scottish Engineer, continued his study and
developed a complete theory of the heat engines along with the steam engine during
1859. The Rankine cycle was named after him honouring his contribution to this
subject.

The Rankine cycle is an ideal thermodynamic cycle involving a constant pressure
heat engine which converts heat into mechanical work. The heat is supplied
externally in this cycle in a closed loop, which uses either water or any other organic
fluids (Pentane or Toluene) as a working fluid.
The Rankine cycle is a theoretical cycle on which the power plants work. This cycle,
which is the basic principle of Steam turbines, is also known as a modified Carnot
cycle. The Carnot cycle is a thermodynamic cycle that has maximum efficiency. The
drawbacks of the Carnot engine like its difficulty to operate practically or to work with
superheated steam are overcome by this cycle.
Components of the Rankine Cycle
 Pump: They can be centrifugal pumps in industrial applications. Water as
saturated liquid enters the pump and is compressed.
 Boiler: Boilers are generally heat exchangers as in thermal power plants. The
compressed liquid enters the boiler to be converted to superheated steam.
 Turbines: Turbines or steam turbines are machines that use pressurised
steam to produce mechanical work. The superheated steam entering the
turbine expands and rotates the shaft to produce work which generates
electricity.
 Condenser: Condenser has a set of tubes with a cooling medium surrounding
it. The cooling medium may be air or water depending upon the placement of

11. the power plant. Steam, in a saturated liquid-vapor state, is condensed at
constant pressure and the heat is rejected to a cooling medium.
Working Principle of Rankine Cycle
The study of components in the cycle helps us understand that the cycle operates in
a closed loop where the working fluid is reused. Let us consider the Rankine cycle P-
v and T-s diagrams with the h-s diagram to understand the working.



A typical Rankine cycle has four thermodynamic processes which are explained
below referring to all the diagrams. Let us assume that the cycle is operating at
temperatures ranging from 0 °C to 400 °C.
 Process 1-2: The working fluid (saturated liquid) entering the pump, is
pumped from a low to high pressure. This is also known as isentropic
compression. The input energy is needed at this stage.
 Process 2-3: Liquid at a high pressure entering the boiler is heated by an
external heat source at a constant pressure. The liquid is converted to dry
saturated steam by constant pressure heat addition in the boiler.
 Process 3-4: The dry saturated steam from the boiler expands as it enters the
turbine. It is also known as isentropic expansion. Due to this, the
temperature and pressure of the steam decrease.
 Process 4-1: The wet vapour entering the condenser at this stage is
condensed at a constant pressure. It is then converted to saturated liquid.
This process is also known as constant pressure heat rejection in the
condenser. This saturated liquid is again circulated back to the pump, and the
cycle continues. The heat rejected or the exhaust heat after the final stage is
represented as Qout.

12. MODIFIED RANKINE CYCLE

In steam engine plants the steam is not expanded down to condenser pressure. It is
released at a higher pressure and then there is a pressure drop at constant volume
down to condenser pressure. This early release causes a reduction in efficiency
because the work for the cycle is reduced while the heat supplied per cycle remains
the same.
This cycle is known as Modified Rankine cycle. The reason for the early release is
that at the lower pressure the specific volume of steam is high. In order to
accommodate such rapidly expanding steam, large cylinder volume is necessary and
the extra work obtained is very small.


Advantages of Modified Rankine Cycle
The modified Rankine cycle provides number of advantages as shown below:
 The toe of a Rankine cycle has been cut off which results in minor reduction in
work and the fuel consumption is slightly increased.
 This saves high initial cost.
 The length of engine cylinder is reduced.
 The weight of the engine is drastically reduced with minor loss of power.
 The power to weight ratio of engine is increased.
 This results in high fuel economy.

13. PRACTICES/TECHNOLOGIES
EQUIPPED IN DSTPS

Coal Based Thermal Power Plant
The figure given below shows the schematic diagram of a thermal power plant. In
coal thermal power plants, the steam is produced in high pressure in the steam
boiler due to burning of fuel (pulverized coal) in boiler furnaces. This steam is further
superheated in a super heater. This superheated steam then enters into the
turbine and rotates the turbine blades. The turbine is mechanically so coupled
with alternator that its rotor will rotate with the rotation of turbine blades to produce
electricity.

The basic components of the thermal power station are:
 Water Package
 Coal Handling Plant
 Boiler
 Steam turbine
 Generator/Alternator
 Condenser
 Boiler feed pump
 Forced or induced draft fan system
 Ash Handling Plant

14. WATER PACKAGE

The working fluid of this power plant is water. As the name suggests Damodar
Valley Corporation (DVC), its main source is the Damodar River. From the river
through a raw water intake pump the water is pumped into huge open reservoirs.
There are two reservoirs in DVC. As per requirement water from the reservoir is sent
through a net for primary filtration, to a pump house. There are three pumps
operating in the raw water pump house.
1. PTP-DM Water Pump [Pre-Treatment Plant De-Mineralized Water Pump] (x2)
[A & B]
2. PTP-CW Pump [Pre-Treatment Plant Cooling Water Pump] (x3) [A, B, C]
3. Ash makeup pump (x2) [A & B]
No pre-treatment of water is required for the part of ash handling.
Water is first pumped up to the cascade aerator by PTP-CW Pump and PTP-DM
Water pump. In total there are 2 Cascade aerators, one for DM water plant and the
other for cooling water (e.g., service water, cooling water, portable water, flushing
water, etc…). Cascade aerator is an open head structure with a large surface area
where the inlet pipe is kept vertical and is located at the bottom centre of the
structure. Water with huge pressure energy flows in the aerator as a result the
surface area of water also increases. This water with a large surface area comes
in contact with air and the dissolved unwanted gasses are removed. The other
function is to increase the oxygen content of water. This process also removes CO2,
thus corrosive characteristics of water are also reduced. This whole process is called
aeration. Before moving to the next stage, chlorine is added to the water to kill
bacteria and it is known as pre-chlorination.

15. Then water is moved to the Reactor Clarifier (Clariflocculator) through a pipe. There
are 4 reactor clarifiers in total. Two for the DM water plant and the other two for
cooling water. A Clariflocculator is the combination of a ‘Clarifier’ and a
‘Flocculator’. A clarifier is used to remove solid particulates or suspended particles
from a liquid, in this case, water, and Flocculator is used to form larger clusters or
flocks by combining smaller particulates. The process is known as flocculation.
Here, Alum is used as the flocculant.

First, Alum is mixed in water at a particular amount by using an agitator separately
and the required amount of alum solution is provided in the agitator of the
Clariflocculator. The agitator is located at the centre of the Clariflocculator.
Water from the cascade aerator goes through a pipe to the bottom of the agitator.
This agitator is used to mix chlorinated water and alum solution thoroughly. Now
due to flocculation large heavy chunks of solid particles settle down and form sludge.
The centre portion of the Clariflocculator is 1m deeper than the circumferential depth,
as a result all the sludge has a tendency to move towards the centre. By using a
scrapper this sludge is brought towards the centre and then discharged through a
sludge discharge pipe.
Now the top layer of water has minimum impurities with respect to its depth.

Cooling Water
In case of cooling water, the top layer is overflown into a number of launders (inlet
channels) which has numerous holes present. This clarified water then flows
through two outlet channels into a reservoir. Above which there are numerous
pumps that supply water wherever and whenever needed.

16. There are seven types of pumps in total. They are:
1. Recycled Makeup Pump
2. Portable water feed Pump
3. Flushing Water feed pump
4. CW makeup pump
5. HVAC Pump (Heating Ventilation and Air Conditioning Pump)
6. APH wash pump (Air Preheater Wash Pump)
7. Service water pump
Drinking water is obtained by passing water through a dual media filter by using
portable water feed pump.
Demineralised Water
In case of Demineralised DM water, the top layer is overflown around the
circumference of the Clariflocculator to a Sand bed Gravity Filter, through a channel.
Water flows through the centre channel and overflows from both sides. This structure
is made symmetric so as to maintain equal water level on both the sides. Due to
gravity, water slowly makes its way down this sand filter and due to different grain
sizes, we get filtered water at the bottom tank. This water is stored in a reservoir and
is supplied when required in the DM plant.
For both the types of water, post chlorination is done.

17. DM Water Treatment Plant
The working fluid i.e., water, which is converted into steam and used to spin the
turbine must not contain any other contaminants or minerals. To do so water is
treated in the DM water plant to obtain pure H2O.
First, water goes into an Activated Carbon Filter (ACF) where Anthracite Coal
powder is used. Activated carbon arrests residual chlorine and volatile organic
compounds from water by adsorption. Turbidity of water decreases after passing
through ACF.
After that it goes in Strong Acid Cation (SAC) Exchanger where H2SO4 is used as
the strong acid that removes most of the cations present in water. The inner wall is
coated with cation exchange resins where the impure cations are adsorbed and H
+
ions are released. After that the water is passed through a de-gasifier blower, for
removal of carbonate ions by forming carbon dioxide gas. Here water is poured from
top and air is blown from bottom. As a result, Carbonic acid present in water
dissociates into H2O and CO2. This CO2 can then be released into the air.

After that, a Strong Basic Anion (SBA) Exchanger removes all the anions present
in water in a very similar manner. Here the chemical used is Caustic Soda (NaOH)
and an anion exchange resin adsorbs most of the impure anions and will release
OH
-
ions.
After this stage we almost obtain pure H2O from the two ions that are released in the
SBA and SAC but just to make sure that there are no more impure ions present in
the water, it is passed through a Mixed Bed Exchanger (MBE), where both types of
resins are present i.e., both cation exchange resin and anion exchange resin.
Finally, this water is passed through the Ultra Filtration (UF) Membrane where all
the colloidal silica that is present is trapped and removed from the water. This pure
H2O that we get is stored in DM Water Storage Tank. There are two tanks of
capacity 2400 m
3
in DSTPS.

18. COAL HANDLING PLANT (CHP)

We got our working fluid and now we need the fuel, which is to be burnt, to provide
necessary energy to water and convert it into steam. Coal is used as the fuel due
to the following reasons:
1. High heat release rate
2. Coal is a solid fuel and thus burning rate will be slower
3. It is cheaper than most of the other fuels
4. Easily available and present in abundant quantity
There are mainly two types of coal. One having a higher calorific value and the
other having a lower calorific value, in simple words we have good-quality coal
anbad-qualityty coal. Both types of coal are supplied in CHP. Both types are staked
in the stacker area. Coal is supplied from the stacker as per requirement in the
boiler. Generally, both types are mixed and sent to boiler. Huge amounts of coal are
bought by rail and discharged in coal handling plant. In DSTPS coal supplied is three
thousand tons in four coaches when required. Two types of wagon transports coal to
coal handling plant:
1. BOBR Wagon (Bogie Open Bottom Rapid Discharge Hopper Wagon)
2. Box-type Wagon
BOBR wagon has an open-bottom system. There are consecutive holes present in
between rail tracks where these wagons stand and the bottom part of the wagon
opens, as a result, the coal is dumped in the hole. There are track hoppers present
underground where the coal is collected. Some amount of coal clusters around the
circumference of the hole, which are manually fed into holes by an excavator.

Coal is unloaded from Box type wagons with the help of a wagon tippler. Tippler is
used for emptying the loaded wagons by tippling them. It has three jaw-like
structures which hold the wagon firmly, then lifts and flip it.

19. From the hopper this coal is fed in the apron feeder (conveyor belt) by using a
paddle feeder. Paddle feeder has blades of large surface area that scraps an
amount of coal and feeds it in the apron feeder when required. The speed of paddle
feeder will determine how much coal is fed in the apron feeder. The conveyor belt
has a width of 1400mm and can carry 900 tons of coal per hour.

Now this coal travels through the apron feeder under a suspended magnetic
separator, where ferromagnetic substances are separated from the coal. This
suspended magnet is an electromagnet. Big chunks of rocks are separated
manually by a line of workers.

20. This coal is fed in Roller Screening to separate smaller chunks from bigger chunks of
coal. These big chunks are then fed into a crusher where coal is crushed into smaller
pieces of required size. Usually, 20mm diameter.

There is an inline magnetic separator above the crusher. This coal is then sent into a
reversible belt feeder. This conveyor belt can transport coal in two directions.
Normally it will carry the coal and store it in stacker, and in reverse it will supply the
coal in bunker. Stacker reclaimer is used to stack huge amounts of coal in the stack
zone.

21. COAL MILL

Coal mills play a critical role in the coal-fired power generation process by
providing the necessary coal and air mixture for efficient combustion. Bowl coal mill,
also known as pulveriser or pulverizing mill, is a device used to grind coal into a fine
powder for combustion in the steam-generating furnaces of thermal power plants.
This steam is used to drive a turbine, which in turn generates electricity. The coal mill
plays a crucial role in this process by grinding the coal into a powder of the
desired fineness.
The purpose of the pulveriser is to increase the efficiency of coal combustion in
the boiler and to provide the necessary coal-air mixture for efficient and complete
combustion.
A bowl mill consists of a rotating bowl or cylindrical vessel that holds the coal and the
grinding elements i.e., grinding rolls or grinding balls within it. The coal is fed into the
mill through a central inlet pipe and falls onto the rotating grinding table. As the bowl
rotates, the coal gets crushed. The pulverized coal is then blown into the furnace
through the combustion air ducts.
The main operations of a coal mill are as follows:
 Coal Feeding: The coal from the coal storage area is fed into the mill through
a central inlet pipe. The coal is then dropped onto the rotating grinding table.
 Grinding: As the bowl or table rotates, the coal is crushed and ground by the
grinding rollers, which are mounted on a rotating shaft. The rollers exert
pressure on the coal against the grinding ring or bowl, pulverizing it into a fine
powder.
 Drying and Transporting: Hot primary air is blown into the mill through the
bottom of the bowl. This air dries the coal and transports the pulverized coal
particles upward to the classifier.
 Classification: The pulverized coal and the primary air enter the classifier,
which separates the fine coal particles from the coarse ones. The fine coal
particles are directed to the furnace for combustion, while the coarse particles
are returned to the grinding zone for further grinding.
 Drying: In addition to grinding, the bowl mill also performs a drying function.
The hot air used for the classification and transportation of coal also serves to
dry the coal. This helps to remove moisture and improve the combustion
efficiency of the coal.
 Coal Discharge: The pulverized coal, now classified and dried, is discharged
from the mill through a coal outlet located at the bottom of the mill. It is then
transported to the burners in the furnace for combustion.

22. The main components of a bowl coal mill include:
 Bunker: a storage container or compartment where coal is stored before it is
fed into the mill for grinding and pulverization. The coal bunker is typically
located adjacent to or near the mill and is designed to hold a certain quantity
of coal to ensure a continuous and controlled supply to the mill.
 Coal Feeder: A coal feeder, also known as a coal conveyor or coal feeder
belt, is a device used to transport coal from a coal bunker or storage area to a
coal mill for grinding and pulverization. The primary function of a coal feeder is
to provide a continuous and controlled supply of coal to the coal mill. It
ensures that the mill receives a consistent flow of coal, which is necessary for
efficient combustion and stable operation.
The coal feeder typically consists of the following components:

23.  Conveyor Belt: The coal feeder employs a conveyor belt to transport
the coal. The belt is usually made of rubber or similar material and is
designed to withstand the abrasive nature of coal.
 Drive Mechanism: The drive mechanism powers the conveyor belt
and controls its speed. It may consist of an electric motor, gearbox, and
associated components. The drive mechanism ensures a controlled
and regulated flow of coal.
 Classifier Assembly: The classifier assembly is responsible for
classifying the pulverized coal particles based on their size. It is
typically located above the grinding zone. The assembly includes a
classifier cone that separates the fine particles from the coarse
particles. The fine particles are collected and sent to the burners, while
the coarse particles are returned to the grinding zone for further
grinding.
 Mill Housing: The mill housing is a sturdy enclosure that houses the
grinding components and other internal parts of the bowl coal mill. It
provides support and protection for the mill internals and helps to
contain the coal dust generated during the grinding process.
 Drive System: The drive system of a bowl coal mill consists of a
motor, gearbox, and associated components that provide the power
and control the rotational speed of the grinding bowl or table and the
grinding rollers. The drive system is designed to handle the high loads
and torque required for grinding coal.
 Grinding Bowl: The grinding bowl or table is a horizontally rotating
bowl or table where the coal is crushed and pulverized. It is typically
made of cast steel or cast iron and has a smooth and circular inner
surface. The coal is fed onto the bowl or table, and the grinding rollers
press against it to grind the coal into a fine powder.
 Grinding Rollers: The three grinding rollers are cylindrical or conical-
shaped components that are mounted on a shaft and rotate around the
bowl or table. They exert pressure on the coal as the bowl or table
rotates, crushing and grinding it.
 Spring Assemblies: Spring assemblies are used to apply pressure on
the grinding rollers against the grinding table or bowl. They help
maintain the required grinding force and ensure proper grinding
efficiency.
 Air System: The air system of a bowl coal mill includes a primary air
fan, a secondary air fan, and a system of ducts and dampers. The
primary air fan supplies the primary air required for the drying and
transportation of coal. The secondary air fan provides the combustion
air needed for coal combustion in the furnace.
 Coal Discharge System: The mill side assembly also includes
components related to coal discharge, such as a coal outlet or
discharge chute, which allows the pulverized coal to exit the mill and be
transported to the burners or storage.
 Air Preheater: The APH is a heat exchanger located downstream of
the coal mill, typically in a coal-fired power plant or industrial boiler. The
primary purpose of the APH is to preheat the combustion air before it
enters the furnace.

24. Specifications of Coal Mill
 Mill Base Capacity: 657 T/hr
 Spring Rate: 5359 kg
 Spring per Load: 9500 kg
 Mill Outlet Temperature: 70-80°C
 Fineness: 70% passing (200 mesh)
 Motor Speed: 980 rpm

25. BOILER

A Boiler is an enclosed Pressure Vessel in which water is converted into steam by
gaining heat from the source that is from coal powders supplied in the furnace. Boiler
is basically a steam generator in the thermal plant. In the thermal power plant, it
accumulates the steam and build up a pressure to feed it in the turbine and convert
thermal energy to mechanical energy by rotating the shaft. The generator which is
connected to convert the mechanical energy into electrical energy.

There are different types of boilers that are used in industries, based on tube
content, there are two types of boilers namely,
 Fire Tube Boiler
 Water Tube Boiler

In DSTPS, the boiler used is Pulverized Coal Fired Boiler. This type of boiler is
basically Water Tube Boiler.


Specifications of Pulverized Coal Fired Boiler
 Diameter: 21882mm
 Inside Temperature: Around 1200°C
 Pressure: 180kg/cm²

Construction

It is hanging by tiered or sling grader. It is just supported with the bottom hopper
and the gap between boiler and bottom hopper is 10mm. It is filled with water. This
gap is provided because of the expansion of the boiler (Trap seal). There are 4

26. corners in a boiler and each corner has 8 coal pipes which are coming from eight
individual mills.



A boiler consists of different accessories which are those devices used to increase
the performance and efficiencies of the boiler. Those are as follows:

 Pressure Relief Valve: A safety device that automatically releases excess
pressure to prevent the boiler from exploding.
 Water Level Indicator: It indicates the water level inside the boiler and helps
ensure proper water levels for safe and efficient operation.
 Blowdown Vessels: Used to remove impurities and sediment from the boiler
water by periodically discharging a portion of the water.
 Combustion Air Preheater: A device that heats the combustion air before it
enters the boiler, improving efficiency by utilizing waste heat.
 Economizer: Economizer in the boiler system is an extremely important part.
A boilers economizer is a heat exchanger that uses the heat from flue gases
to preheat boiler feedwater. This reduces the amount of fuel needed to heat
the water, which can save energy and money. Economizers are typically
installed in steam boilers, but they can also be used in hot water boilers. The
water which gets heated already to some extent goes to the steam drum
through the economizer.
 Steam Drum: The steam drum level is an essential component of a boiler,
particularly in water tube boilers. It is a cylindrical vessel located at the upper
part of the boiler where water and steam are separated. There are different
operations including steam water separation, steam storage, level control,
pressure control, blow down, etc. It helps ensure the production of dry and
high-quality steam while maintaining the proper water level and pressure in
the boiler system.

27.  Feed Water pump: A feedwater pump is a crucial component in a boiler
system that is responsible for supplying water to the boiler at the required
pressure and flow rate. The main function is to deliver feedwater from a water
source, such as a condensate tank or a deaerator, to the boiler. The
feedwater pump takes water from a water source, which can be a condensate
tank, deaerator, or other water treatment equipment. This water is typically
treated to remove impurities and improve its quality before being supplied to
the boiler.
The feedwater pump delivers water at a specific flow rate to match the
demand of the boiler. The flow rate is determined based on the steam
generation rate and the design specifications of the boiler.
There are various types of feedwater pumps used in boiler systems, including
centrifugal pumps and positive displacement pumps. Centrifugal pumps are
commonly used due to their high flow rates and relatively simple design.
Positive displacement pumps, such as reciprocating pumps or rotary pumps
are used in certain applications such as high pressure or precise flow control.
 Bottom Ring Header & Z Panel: the water comes to this part using the feed
pump. This part is situated at the bottom of the furnace. There are two risers
connected to the drummer.
 Furnace: Furnaces heat air and distribute the heated air through the house
using ducts. Boilers heat water and provide either hot water or steam for
heating. Steam is distributed via pipes to steam radiators, and hot water can
be distributed via baseboard radiators or radiant floor systems or can heat air
via a coil. Steam boilers operate at a higher temperature than hot water
boilers, and are inherently less efficient; however, high-efficiency versions of
all types of furnaces and boilers are currently available.
 Secondary Air Control Discharge (SADC): The secondary Air Damper
control is to regulate the velocity and distribution of the secondary air in a
tangentially fired furnace to control its combustion and controlling the effective
openings of a secondary air nozzle as an orifice in the regulation of the
secondary air supplied to the nozzle to affect the desired velocity and
distribution of the secondary air from the nozzle.
 Fuel Input: The process begins with the input of fuel, such as natural gas, oil,
coal, or biomass, into the boiler's combustion chamber.
 Combustion: The fuel is ignited, and the combustion process begins. Heat is
generated, raising the temperature of the boiler's heat transfer surfaces.
 Heat Transfer: The heat generated from combustion is transferred to the
boiler's water-filled tubes or heat exchanger. These tubes carry the hot gases
from the combustion chamber, allowing the heat to transfer to the water,
which surrounds the tubes.
 Steam Generation: As the heat is transferred to the water, it causes the
water to boil and generate steam. The steam produced is typically saturated
steam, which means it contains no moisture.
 Steam Distribution: The generated steam is then directed out of the boiler to
the steam distribution system, which can include pipelines, valves, and control
devices. This system carries the steam to various applications, such as power
generation, heating, or industrial processes.
 Air Preheater (APH): An air preheater is a device commonly used in boiler
systems to increase the temperature of the combustion air before it enters the

28. boiler. It improves the overall efficiency of the boiler by utilizing waste heat
from the flue gases.
The main purpose of an air preheater is to preheat the combustion air before
it enters the boiler's combustion chamber. By increasing the air temperature, it
reduces the amount of heat energy required to raise the temperature of the air
to the desired combustion temperature.
These are typically installed in the flue gas path of the boiler. They use the
waste heat from the flue gases, which are hot gases produced during the
combustion process. The preheater transfers heat from the flue gases to the
incoming combustion air, maximizing energy efficiency.
 Super Heater: A superheater is a device used in boiler systems to further
increase the temperature of saturated steam generated in the boiler. It plays a
crucial role in improving the overall efficiency and performance of the steam
power plant or industrial process. The temperature of the steam rises to
around 540 Degree centigrade. The superheated steam then enters the HP
turbine and then its temperature becomes low and it is sent to cold reheater.
The primary superheater is the first heater that is passed by steam after the
steam comes out of the steam drum. After the steam is heated on the super
primary heater, eating steam will be passed onto the secondary superheater
to be heated again.
 ID Fan: An ID fan, short for Induced Draft fan, is an essential component in a
boiler system. It plays a crucial role in maintaining proper combustion
conditions and ensuring the efficient operation of the boiler.
The main purpose of an ID fan is to create a negative pressure or suction in
the boiler's combustion chamber and flue gas system. It draws flue gases out
of the boiler and creates a draft, facilitating the flow of combustion gases
through the boiler and out of the exhaust stack. The ID fan is responsible for
supplying combustion air to the boiler system. It draws in fresh air from the
environment and delivers it to the combustion chamber, supporting the
combustion process. In addition to supplying combustion air, the ID fan also
facilitates the exhaust of flue gases from the boiler. It creates a negative
pressure inside the boiler and flue gas system, ensuring the proper flow of
combustion gases through the boiler and exhaust stack.
 FD Fan: An FD fan, also known as a Forced Draft fan or Primary Air fan, is an
integral component in a boiler system. It is responsible for supplying the
necessary combustion air to the boiler, creating positive pressure, and aiding
the combustion process. Here are some key points about the FD fan. The
primary purpose of an FD fan is to provide a pressurized flow of air into the
boiler's combustion chamber. It supplies the combustion air required for the
efficient burning of fuel in the boiler.

The FD fan draws in atmospheric air and delivers it to the combustion
chamber of the boiler. Along with supplying combustion air, the FD fan assists
in venting the flue gases produced during the combustion process. It creates
positive pressure in the flue gas system, aiding the flow of combustion gases
through the boiler and exhaust stack. The efficient operation of the FD fan is
critical for overall energy efficiency in the boiler system. By supplying the
proper amount of combustion air, it helps optimize fuel combustion, improve
heat transfer efficiency, and minimize heat losses.

29. TURBINE

A steam turbine is a machine that extracts thermal energy from pressurized
steam and uses it to do mechanical work on a rotating output shaft. It is a form
of heat engine that derives much of its improvement in thermodynamic efficiency
from the use of multiple stages in the expansion of the steam, which results in a
closer approach to the ideal reversible expansion process.
As the turbine generates rotary motion, it can be coupled to a generator to harness
its motion into electricity. Such turbogenerators are the core of thermal power
stations which can be fuelled by fossil-fuels, nuclear fuels, geothermal, or solar
energy. About 75% of all electricity generation in India is done through thermal
power plants.
Basically, turbines are of two types: impulse turbines and reaction turbines. The
impulse turbine is the simplest type of turbine. It consists of a group of nozzles
followed by a row of blades. The gas is expanded in the nozzle, converting the high
thermal energy into kinetic energy. But in reaction turbine pressure drop happens in
every fixed blade and a particular amount of thermal energy is converted into kinetic
energy and the remaining is transmitted to the next fixed blade arrangement for
conversion.
Here, Impulse Turbine is used in three different pressure stages, which are
 HP Turbine (High-Pressure Turbine)
 IP Turbine (Intermediate Pressure Turbine)
 LP Turbine (Low-Pressure Turbine)
All three turbines are connected with the same shaft additional with three phase
generators and an exciter. In every turbine superheated or reheated steam expands
at different pressure and temperature.
Firstly, superheated steam (temperature 813K and 120 bar pressure) from the
boiler is transmitted to the High-Pressure Turbine via the main steam tube. During
the inlet section, a series of nozzles is given which expands the superheated steam
and converts the thermal energy into kinetic energy. This high-velocity steam is used
to provide rotary motion to the moving blade which is connected to the rotor and a
fixed blade arrangement after each moving blade is given just for providing direction
to the steam flow so that max enthalpy can be used.
After expansion in the HP Turbine, the pressure of superheated steam is decreased
from 120 bar to 40 bar, then the same superheated steam is sent back to the boiler
to regain the temperature up to 813K (enthalpy increased) at the same pressure (40
bar).
Now the reheated steam is sent back to the intermediate-pressure turbine for further
expansion and then to the low-pressure turbine for final expansion. After the low-
pressure turbine, the expended steam enters the condensation circuit.

30. Structural Analysis
All three, HP, IP and LP turbines are designed in such a way that they can utilize the
max enthalpy of steam and give a common RPM (Rotation per minute) to the shaft
which is around 3000 RPM. generator and exciter both are connected with the same
common shaft by the means of pedestal and supported by seven different types of
bearings (help in damping the weight of the shaft, moving blades and rotors, and at
the same time allow the shaft to rotate freely).
Specification HP turbine IP turbine LP turbine
Type of turbine Impulse Impulse Impulse
No. of blades 17 2 x 12 2x 6
Type of forces
acting on the
turbine blades due
to high velocity of
steam
Rotational force ()
Thrust
Rotational
force ()
Thrust
Rotational
force ()
Thrust
Thrust balancing Not self-balancing due
to unsymmetrical
structure; balanced by
thrust bearings
Self-balancing
(due to
symmetrical
structure)
Self-balancing
(due to
symmetrical
structure)
Bearing HP Front journal
bearing for rotary
motion and common
journal cum thrust
bearing for thrust
balancing
IP rear journal
bearing
LP rea journal
bearing
Pedestal Front Bearing Pedestal
and HP-IP Pedestal
IP-LP Pedestal LP-Generator
pedestal

Three Phase AC Generator
 Specification: 500 kw,3000 RPM, 3 Phase coiling
 Stator: 21000V 16200 A
 Rotor: 340 V 4040 A

Working Principle of AC Generator
AC generator is a machine that converts mechanical energy into electrical energy.
The AC Generator’s input supply is mechanical energy supplied by steam turbines.
The output is an alternating electrical power in the form of alternating voltage and
current.

31. AC generators work on the principle of Faraday’s law of electromagnetic
induction. When the armature rotates between the magnet’s poles upon an axis
perpendicular to the magnetic field, the flux linkage of the armature changes
continuously. Due to this, an emf is induced in the armature. For this current flow
starts which is further transmitted to the transfer and then to the Switchyard via three
phase electrical cable.
Exciter's Working Principle
An excitation system is a means to provide regulated DC current to the field
windings of a generator, to produce an output voltage to the field. The generator is
used to turn mechanical energy from a prime mover into electrical energy for
transmission to customers. The prime mover - which is a steam turbine - controls the
megawatt load of the generator.
The generator’s armature (or stator winding) is stationary and carries the output
power of the generator to the step-up transformer. The generator’s rotor fits into the
centre of the armature and the field winding is attached to the rotor. It carries the
current supplied by the excitation system to excite the generator.
All electrical generators require excitation to create electrical energy. The excitation
system excites the armature by creating a magnetic field on the rotor via a DC
current. The output voltage of the armature varies with the strength of the magnetic
field.
Thus, the excitation system controls the output voltage of the generator by adjusting
the DC current to the generator field winding.

32. COOLING TOWER

The type of cooling tower used in DSTPS IS NDCT (Natural Draft Cooling Tower).
The natural draft cooling tower is an open, direct-contact system. It works using a
heat exchanger, allowing hot water from the system to be cooled through direct
contact with fresh air. To increase the heat transfer surface area (and optimize the
cooling process), hot water is sprayed from nozzles within the tower. This increases
both the temperature and humidity of the air in the tower. The warmer, moister air
moves to the top of the tower, while the cold water is collected at the bottom. The
fresh air supply is located in the bottom of the natural draft cooling tower to take
advantage of the difference in density between the hot air at the top and the
atmospheric air outside the cooling tower.
Principle of the Natural Draft Cooling Tower
Airflow is obtained in natural draft cooling tower systems by way of the chimney
effect of the cooling tower’s actual structure, which uses the natural pressure
difference. Warm and moist air is less dense, which causes it to rise out of the
cooling tower into the atmosphere and draw in the denser fresh air. The difference
between the warm air inside the tower and the cooler air outside creates the perfect
airflow. For sufficient airflow to occur, a specific mathematical formula is used to
calculate the height of the cooling tower to ensure it is almost as large as the density
difference. This means cooling towers using this system tend to be large: around
200 meters tall and 150 meters in width. There is also a significant amount of
water flowing in the towers. The shell itself is typically made from concrete in a
hyperbolic shape. The natural draft cooling tower is the preferred choice for cool and
humid climates and for heavy winter loads.

Hot water that needs cooling in the natural draft cooling tower is pumped in via the
hot water inlet. The inlet is connected to nozzles that spray the water over the fill
material, which provides a large surface area for heat transfer. At the bottom of the
tower, the structure is open to draw in the fresh air, which then flows upward and

33. allows for direct-contact heat transfer between the warm water and the air. The hot
water releases heat after coming into direct contact with the fresh air, and some of
the hot water is evaporated. Cold water is collected at the bottom of the tower.
The warm and moist air is discharged from the top of the tower into the atmosphere.




AVGF (Automatic Valves Gravity Filter)
A part of the cooling water is passed via AVGF. The main function of AVGF is to
decrease the turbidity of the cooling water.


CWPH (Cooling Water Pump House)
Cooling water Pump House collects water from the AVGF and the cooling tower.
Chlorine and Sulphuric acid are dosed for degemination and pH balancing of the
water. The main function of CWPH is to send the cooling water to the condenser.
Also, it sends cooling water to turbine, boilers and auxiliaries for keeping the
machinery cool.

34. ASH HANDLING PLANT

What is Coal Ash?

Coal ash, also referred to as coal combustion residuals or CCRs, is produced
primarily from the burning of coal in coal-fired power plants. After burning of coal,
40% of total coal consumption is converted into ash which needs to be disposed-off
from the thermal power plants.

Ash Handling System

Ash handling systems or Ash handling plants in thermal power plants are used to
cool down the ash to manageable temperature, transfer to a disposal area or storage
which is further utilized in other industries.



The different sections in an AHP are as follows:

 Electrostatic Precipitator: Electrostatic precipitator is also called in the short
form of ESP. It is used to filter dust particles in the flue gas in thermal power
plants. As per government law to avoid air pollution these kinds of
precipitators are widely used. Also, some other power plants are using bag
filter dust collecting systems. Bag filters are used to filter very small particles
typically in micron size. However, compare to bag filter ESP is very
economical.
 Feed/Discharge/Sluice Gate: They are commonly utilized in steam systems.
Thermal expansion in steam lines may also cause valve body distortion,
leading to thermal binding. The flexible gate design accommodates this
expansion by allowing the gate to be flexed as the valve seat is compressed
because of the steam pipeline’s thermal expansion, thereby preventing
thermal binding.

35.  Clinker Grinder or Crusher: Clinker grinders are provided in boilers to grind
large pieces of clinker into small ones so that choking of the exhaust hole may
be avoided,
 Jet Pump: Steam jet thermos-compressors or steam boosters are used to
boost or raise the pressure of low-pressure steam to a pressure intermediate
between this and the pressure of the motive high-pressure steam. These are
useful and economical when the steam balance allows the use of the
necessary pressure levels.
 Dewatering Bin: The first tank, called the dewatering bin, collects and
dewaters bottom ash solids to approximately 15 to 18 percent moisture. The
clarified water is stored in a surge tank and reused during the conveying
cycle. The ash is then unloaded into trucks.
 Transfer Bin: The transfer points are used to transfer coal to the next belt.
The belt elevates the coal to the breaker house. It consists of a rotary
machine, which rotates the coal and separates the light dust from it through
the action of gravity and transfers this dust to the reject bin house through a
belt.
 Storage Bin: A drum is provided in the boiler to collect steam. Here, hot water
and steam are separated with the help of a steam separator. Separated
steam is passing through the superheater. Separated water is going to the
water drum. It stores the water.
 Dry Bottom Ash Conveyor: Hot bottom ash falls onto the DRYCON
conveyor, where it is simultaneously conveyed and cooled, Grabowski
explained. The DRYCON (DRY and CONveyor) technology uses the negative
draft of a pulverized coal-fired boiler to draw ambient air through the
conveyor. This airflow cools the hot ash while supplying about 1% of the
combustion air into the boiler.
 Clinker Cooling Conveyor: The cold air is blown into the material layer from
the lower direction of the bed to cool the hot clinker. The quenched clinker is
then screened. After that, small pieces fell into the conveyor for transportation;
large pieces are crushed into small pieces by the crusher and cooled another
time before entering the conveyor.
 Dry Bottom Ash System: The operations involved in a bottom ash handling
system include the collection, cooling, and crushing of the furnished bottom
ash. After these operations, the ash is collected into a bottom ash bunker. The
ash that drops from the hot boiler is conveyed to a crusher using a conveyor
belt sunk into the water at 60 degrees.
 Slurry Pump: The coal is used as fuel in the thermal power plants for
producing to run thermal power plants, prime movers. 10% to 20% of coal ash
is produced on the daily coal consumption rate. For coal ash disposal it is
mixed with water to form the slurry because slurry is easy to handle and
transport as compared to dry ash.
 Stack: The stack is nothing but a chimney that is used to disperse the hot air
at a great height, emissions & particulate matter are emitted from the various
types of stacks like boilers, flue gas, etc.
 Ash Pond: An ash pond, also called a coal ash basin or surface
impoundment, is an engineered structure used at coal-fired power stations for
the disposal of two types of coal combustion products: bottom ash and fly ash.

36. The pond is used as a landfill to prevent the release of ash into the
atmosphere.
 Telescopic Chute: The main idea behind the telescopic chute system is
discharging the powdered or granular bulk solid through a vertical column by
its own weight and collecting any dust within the same enclosed column
upwards. The varying height between the upper discharge point and lower
loading point is compensated by making the column flexible.

Classification of Ash

Bottom Ash Handling System




Bottom ash is the coarser component of coal ash, comprising about 10 percent of
the waste. Rather than floating into the exhaust stacks, it settles to the bottom of the
power plant’s boiler. Bottom ash is not quite as useful as fly ash, although power
plant owners have tried to develop “beneficial use” options, such as structural fill and
road-base material. This isn’t a good idea, because the bottom ash remains toxic
when recycled.

Dry Handling System

A dry bottom ash handling system contemplates a plurality of hoppers disposed
beneath a solid fuel-fired steam boiler. Each hopper includes angled walls
converging at a generally rectangular opening controlled by a grated door. Air inlets
are provided at intersections between adjacent angled walls to
 facilitate combustion of unburned fuel in the storage hopper, and
 facilitate the flow of ash through the hopper opening.

37. Ash flowing through the hopper opening enters a crusher and is then conveyed via a
vacuum line to a point of disposal including a mobile tank truck that receives heavier
ash particles and allows bypassing of lighter particles to a silo.

Wet Handling System

The free-falling ash from the boiler furnace is collected and stored in a W shaped
water impounded bottom ash hopper provided below the furnace for its periodic
removal twice in a shift of eight hours per unit. The hot ash from the furnace gets
quenched as it enters into the water minimizing the clinker formation. The mixture of
ash and water (slurry) stored in the hopper is discharged through the feed gate to the
clinker grinder to crush the oversize clinkers to 25mm and below.



Fly Ash Handling System



The most voluminous and well-known constituent is fly ash, which makes up more
than half of the coal leftovers. Fly ash particles are the lightest kind of coal ash—so
light that they “fly” up into the exhaust stacks of the power plant. Filters within the
stacks capture about 99 percent of the ash, attracting it with opposing electrical
charges. Fly ash is recyclable. The fine particles bind together and solidify,
especially when mixed with water, making them an ideal ingredient in concrete and
wallboard. The coal ash versions of these products are actually stronger than those
made from virgin materials. The recycling process also renders the toxic materials
within fly ash safe for use.


Applications include cosmetics, toothpaste, kitchen countertops, floor and ceiling
tiles, bowling balls, flotation devices, stucco, utensils, tool handles, picture frames,
auto bodies and boat hulls, cellular concrete, geopolymers, roofing tiles, roofing
granules, decking, fireplace mantles, cinder block, PVC pipe, structural insulated

38. panels, house siding and trim, running tracks, blasting grit, recycled plastic lumber,
utility poles and crossarms, railway sleepers, highway noise barriers, marine pilings,
doors, window frames, scaffolding, sign posts, crypts, columns, railroad ties, vinyl
flooring, paving stones, shower stalls, garage doors, park benches, landscape
timbers, planters, pallet blocks, moulding, mail boxes, artificial reef, binding agent,
paints and under coatings, metal castings, and filler in wood and plastic products.




Boiler Slag/Ash Slurry Disposal System

Finally, there’s boiler slag, the melted form of coal ash that can be found both in the
filters of exhaust stacks and the boiler at the bottom. Even this foul sludge has its
uses. Boiler slag can be included in roofing shingles (a reasonably safe application)
and in structural fill. Slurry formed due to mixing of water and ash is transported to
ash disposal area by using two system:
1. High concentration ash slurry disposal system-Slurry pump is used to
transport ash slurry to ash disposal area via ash slurry transportation pipes.
2. Lean ash slurry disposal system-Slurry transported to a dewatering bin by a
jet pump and carried to an ash dump by truck after dewatering.

Wastewater from the dewatering bin goes into an ash sedimentation tank or an ash
sedimentation pond for the sedimentation of ash particles and water without ash
particles is supplied to a jet pump by an ash handling pump. The ash particles which
settle in the ash sedimentation tank and the water tank are returned to the
dewatering bin by a sludge return pump.

39. CONCLUSION

As an undergraduate student, the training was an excellent opportunity to get to
know the whole system and processes closely to understand how the engineering
study has put these into application in a power plant. The theoretical knowledge and
even the lab works alone would not have provided such a deep understanding of the
practices. To draw an overall conclusion, we believe that the practical experience
that we have gathered during the vocational training period at Durgapur Steel
Thermal Power Station in the two weeks was a rememberable experience, and will
immensely help us in building a bright professional career in our future life. It gave us
a spectrum to visualize and utilize all the gathered theoretical knowledge and put it
into practice.

This vocational training was not only restricted to technical and manual ideas but has
also given a self-realization and hands-on experience in developing personality,
interpersonal relationships with professional executives, staffs and developing
leadership ability in the industry dealing with workers of all categories. Moreover, this
training has also taught me the importance of being punctual, committed, and team
spirit.

We would like to thank everybody who has been a part of this project, without whom
this project would never be completed with such ease.