Dr. NARLA TATA RAO THERMAL POWER

STATION

POWER PLANT FAMILIARIZATION -2016

INDUSTRIAL IN-PLANT TRAINING REPORT

COURSE CO-ORDINATOR

MR. GOPI KRISHNA

SUBMITTED BY: BATCH-8

ACKNOWLEDGEMENT

We wish to extend our profund and sincere thanks to VTPS management as without their support, this training have been a distinct dream.

We also acknowledged to the corporation authority of Vijayawada Thermal Power Station for their permission to visit the plant and their support. Specially we are very much thankful to the All-chief engineers for all detailed information they have provided about the working and other components of the power plants.

INDEX

SERIAL NO.

NAME OF CHAPTERS

1. Abstract2. Introduction

3. Purpose of visit4. Details of TPS5. Block Diagram of TPS6. Working of VTPS7. Equipments required in VTPS8. Generator9. Transformer10. Switchyard11. Control Room12. Cooling

13. Advantages &disadvantages14. Conclusion15. Reference

ABSTRACT

Thermal Power

A thermal power station is a power plant in which heat energy is converted to electric power. Water is heated, turns into steam and spins a steam turbine which drives a generator. After it passes through the turbine, the steam is condensed and recycled to where it was heated; this is known as a Rankine cycle.There are different types of thermal power plant in India based on fuel used to generate the steam such as coal, gas, diesel, etc. About 75% of electricity consumed in India is generated by thermal power plants.

Coal

More than 51% of India’s commercial energy demand is met through the country’s vast and massive coal reserves. A coal based thermal power plant converts the chemical energy of coal into electrical energy. This is done by raising steam in boiler, expanding it through turbine and coupling the turbines to generators which converts mechanical energy into three phase AC electrical energy.

Introduction

Andhra Pradesh Power Generation Corporation Limited is power generating organization in Andhra Pradesh. It undertakes operation and maintenance of the power plants and also setting up new power projects alongside upgrading the project's capacity..

The total installed capacity of APGENCO, after the formation of TSGenCo is 4559.6 MW comprising 2810 MW Thermal, 1747.6 MW Hydro and 2 MW Wind power stations. The Power Plants of APGENCO include thermal, hydel and wind based plants.

The performance of APGenCo thermal power stations in terms of reliability, availability and maintainability is one of the best in India.

A] Thermal projects

Dr Narla Tata Rao Thermal Rayalaseema Thermal Power Station

Power Station

2] Hydel projects

Srisailam dam Tungabhadra dam

Sr. No. Project Installed Capacity (MW) Total (MW)

1 Chettipeta Mini Hydel 2 x 0.5 1

2 Donkarayi PH 1 x 25 25

3 Hampi Dam PH 4 x 9(AP Share – 28.8)

28.8

4 Lower Sileru PH 4 x 115 460

5 Machkund PH 3 x 17 + 3 x 23 84

Sl. No.

Project Capacity(installed / under construction)

(MW)

Total (installed) (MW)

1 Dr. Narla Tata Rao TPS

6×210 + 1×500 (Stage IV) 1760

2 Rayalaseema TPP 5×210 + 1×600 (Stage IV, Unit-6 under construction)

1050

Overall capacity 3410.00 2810.00

Sr. No. Project Installed Capacity (MW) Total (MW)

(AP Share – 84)

6 Nagarjuna Sagar RCPH 3 x 30 90

7 Penna Ahobilam PH 2 x 10 20

8 Srisailam RBPH 7 x 110 770

9 Tungabhadra Dam PH 4 x 9(AP Share – 28.8)

28.8

10 Upper Sileru PH 4 x 60 240

Overall capacity 1747.6

3] Non-conventional units

Sl. No. Project Inst.Capacity (MW) Total (MW)

1 Ramagiri Wind Mills 10 x 0.2 2.0

Overall capacity 2.0

Dr. Narla Tata Rao Thermal Power Station is also known Vijayawada Thermal Power Plant. It was developed under 4 stages, with the project cost of Rs 193 Crores and Rs 511 Crores respectively. Again with an

investment of RS 840 Crores 2 units were commissioned under III Stage. The seventh unit of 500 MW was commissioned in 2009. The station stood first in country during 94-95, 95-96, 96-97, 97-98 and 2001-02 by achieving the highest plant load factor. The station has received many prestigious awards from various organizations.

Purpose of Visit

The main reason to visit the power plant was to understand and get complete knowledge about practical overview of energy generation plant. Since we are to study the theoretical working and details about various thermal plants in our syllabus, this visit helped us to correlate between the various equipments and parameters used in actual power generation technique with the one given in books.

WORKING OF THERMAL POWER PLANT

The thermal power station converts heat energy of coal into electrical energy. The coal handling plant supplies coal to the boiler. The ash formed in the boiler is disposed of by ash handling plant. Air is taken from atmosphere by primary and forced draft fans and thus air is heated in preheated before fed to the boiler. The flue gases pass through the re-heater, superheater, and economizer, air preheater and electrostatic precipitator before being discharged to the atmosphere through chimney. The boiler vaporizes water into wet steam which is further heated in super heater and fed to the high pressure turbine. After expanding the steam is reheated again in the boiler and fed to the intermediate pressure turbine. The exhaust steam from low pressure turbine is condensed by condenser as shown in fig and condensate along with the makeup water is passed through economizer before being fed to the boiler. In this way electrical energy is produced by rotating turbine using steam which is coupled to the alternator of required rating.

UNITS in Dr. NTTPS

The total installed capacity of VTPS is 1760 MW. This TPS consist of 6 units of 210MW and 1 unit of 500MW. It is having reserved unit of one 500MW which is commissioned in 2016 but not yet in working. We have visited and given all the information about these 6 units of 210MW. Some comparisons of parameters between 500MW and 210MW details were also given to us. As soon as we entered there this we noticed the greenery of campus as around 1, 34,000 trees were planted during erection of this plant.

Coal handling Plant (CHP)

In a coal based thermal power plant, the initial process in the power generation is “Coal Handling”.

Plant was designed for bituminous coal (70% from Talcher mines and 30% is imported from Singapore and Indonesia). Bituminous is second best, hardest form of coal. Such coals may contain ash, moisture and volatile material, and hence there is a need for pulverisation. The firing systems also differ for different grades of coal.

The huge amount of coal is usually supplied through railways. A railway siding line is taken into the power station and the coal is delivered in the storage yard. The coal is unloaded from the point of delivery by means of wagon tippler. It is rack and pinion type. The motor used for tippling is a slip ring induction motor. The coal is taken from the unloading site to bunker by belt conveyors.

The transfer points or junction towers are used to transfer coal to the next belt.

The belt further elevates the coal to the transfer point and it reaches the crusher through belt. In the crusher a high-speed 3- phase induction motor is used to crush the coal to a size of 20mm so as to be suitable for milling system. Coal rises from crusher house and reaches the bunker by passing through transfer point.

1. Pulveriser: Pulverization is a mechanical process for grinding of different types of material. For example, they are used to pulverize coal for combustion in steam generating furnaces of thermal power plants. There are various types of mills such as ball and Tube mills, Ring and ball mills, demolition. The pulveriser reduces the coal size to 74 micron which is then sent to the boiler through the secondary air.

2. Dryers: They are used in order to remove moisture from coal

mainly wetted during transport. As the presence of moisture will result in fall in efficiency due to incomplete combustion and also result in CO emission.3. Magnetic separators: Coal which is brought may contain iron

particles. This iron particle may result in wear and tear. The iron particles may include bolts, nuts wire fish plates, etc so this is unwanted and removed with the help of magnetic separators which are usually placed above the conveyer belts.

Stacker-Reclaimer

BoilerThe water-tube boiler is about 65 feet tall. Its walls are made of a web of high pressure steel tubes.

Pulverized coal is air-blown into the furnace through burners located at the four corners and it is ignited to rapidly burn, forming a large fireball at the centre(tangential firing). The thermal radiation of the fireball heats the water that circulates through the boiler tubes near the boiler perimeter. As the water in the boiler circulates it absorbs heat and changes into wet steam. It is separated from the water inside a drum at the top of the furnace by turbo separators. The saturated steam is introduced into superheater that hangs in the hottest part of the flue gases as they exit the furnace. Here the steam is superheated to 540 °C to prepare it for the turbine.

Boiler auxiliaries are used to increase the efficiency of its working. They are-

A] Economizer: It is located in the boiler. It is there to improve the efficiency of boiler by extracting heat from flue gases to heat water and send it to the boiler drum.

Advantages of economizer include:

1. Fuel economy: - Used to save fuel and to increase efficiency of boiler plant.

2. As the feed water is pre heated in the economizer and enter boiler tube at elevated temperature, it reduces thermal stresses.

3. Optimum usage of heat of the flue gases.

B] Superheater: It super heats the wet steam from the drum to dry super-saturated steam which then drives the HP turbine.

Advantages:1. Increases the efficiency2. Protects the turbine blades from corrosion.3. Optimum usage of heat from flue gases.

C] Re-heater: it reheats the steam from the HP turbine before sending it to the IP turbine. Advantages:

1. Increases the efficiency2. Protects the turbine blades from corrosion.3. Optimum usage of heat from flue gases.

ECONOMISER

Steam TurbineThe turbine generator consists of a series of steam turbines interconnected to each other and a generator on a common shaft. There is a high pressure turbine at one end, followed by an intermediate pressure turbine, a low pressure turbine, and the generator. As steam moves through the system and loses pressure and thermal energy it expands in volume, requiring increasing diameter and longer blades at each succeeding stage to extract the remaining energy. It is so heavy that it must be kept turning slowly even when shut down (at 3 rpm) so that the shaft will not bend even slightly and become unbalanced. This is so important that it is one of only six functions of blackout emergency power batteries on site. Other functions are emergency lighting, communication, station alarms, generator hydrogen seal system, and turbo-generator lube oil.

Superheated steam from the boiler is delivered to the high pressure turbine where it falls in pressure to 39kg/sq.cm and to 320 °C in temperature through the stage. It exits cold reheat lines and passes back into the boiler where the steam is reheated in special re-heater tubes back to 1,000 °F (540 °C). The hot reheat steam is conducted to the intermediate pressure turbine where it falls in both temperature and pressure and exits directly to the long-bladed low pressure turbines and finally exits to the condenser.

CondenserThe condenser condenses the steam from the exhaust of the turbine into liquid to allow it to be pumped. If the condenser can be made cooler, the pressure of the exhaust steam is reduced and efficiency of the cycle increases. The function of condenser is

1. To provide lowest economic heat rejection temperature for steam.

2. To convert exhaust steam to water for reserve thus saving on feed water requirements.

3. To introduce make up water.

The heat absorbed by the circulating cooling water in the condenser tubes must also be removed to maintain the ability of the water to cool as it circulates. This is done by pumping the warm water from the condenser that reduce the temperature of the water by evaporation, by about 11 to 17 °C (20 to 30 °F)—expelling waste heat to the atmosphere.

1] Ejectors: From the condenser the water then goes to the main air ejector through the condensate extraction pump to extract non condensing gases. Then the water is then sent to the low pressure heaters which are 2 in number and is then sent to deaerator.

2] Deaerator: Its function is to remove dissolved non-condensable gases and to heat boiler feed water.

3] Boiler Feed Pump: It is provided for pumping feed water to economiser. There is also a feed water storage tank to store the water when not needed

GeneratorThe generator voltage for modern utility-connected generators ranges from 11 kV in smaller units to 22 kV in larger units. The generator high-voltage leads are normally large aluminium channels because of their high current as compared to the cables used in smaller machines. They are enclosed in well-grounded aluminium bus ducts and are supported on suitable insulators. The generator high-voltage leads are connected to step-up transformers for connecting to a high-voltage electrical substation (usually in the range of 115 kV to 765 kV) for further transmission by the local power grid.

The necessary protection and metering devices are included for the high-voltage leads. Thus, the steam turbine generator and the transformer form one unit. Smaller units may share a common generator step-up transformer with individual circuit breakers to connect the generators to a common bus.

GENERATOR AUXILARIES: The generator in the 210 MW generates a voltage of 15.75kV of which the auxiliaries in the plant take about 6.6 kV through the unit auxiliary transformers.

There is also a station transformer which takes power from the grid directly in case of emergencies. The station transformers are designed to be able to withstand the entire unit auxiliary’s requirements.

Ash handling plantSlag and ash falling from the furnace are temporarily stored in the bottom ash silo. They are then sent to the ash pond using a hydro ejector. Alternatively, they are sent back to the bottom ash silo to be recycled after going through a submerged drag chain conveyor or dry ash extraction conveyor.

Bottom Ash Hopper System utilizing Hydro-ejector’s Dry Ash Extraction System.

For the Fly Ash Handling for power plants, pneumatic conveyor system have world-widely been applied (ESP, Bag Filter, Etc.). The fly ash handling system transports the ashes pneumatically with the compressed air from blower or air compressor through it.

Ash Disposal System: The bottom ash, coarse ash and fly ash lead to the common slurry sump. Wet ash can be used by cement industries and extra wet ash is disposed in ash ponds which on filling are converted into parks.

Control RoomThe control room, in case of remote control, houses all the necessary measuring instructions for each panel or alternator and feeder, synchronizing gear, protective gear, automatic voltage regulator, communication arrangement etc.

Types of Control panel

Fuel gas panel Combustion Panel

Primary Air and coal panel Steam panel(boiler) Feed Water panel Condensate & cooling water panel Turbo-supervisory panel

Switch yardEHV Substation at VTPS:1) 220 kV Switchyard2) A) 220 /132 kV SS; B)132 kV SS3) 400 kV Switchyard

The 220 kV switchgear comprises of the following equipment:.1) C.T’s and P.T’s2) ISOLATOR3) CIRCUIT BREAKER4) LIGHTNING ARRESTOR5) CVT6) Wave trap (included in PLCC)7) BUS BARS8) Bus coupler

Tasks of the switchyard: Protection of transmission system Controlling the exchange of power Maintain the system frequency within targeted limits Determination of power transfer through transmission lines Fault analysis and subsequent improvements Communication

SWITCH YARD

Advantages and Disadvantages of thermal power stations : Advantages:

1. Economical for low initial cost other than any generating plant.2. Land required less than hydro power plant. 3. Since coal is main fuel and its cost is quite cheap than petrol or

diesel so generation cost is economical.4. These are having easier maintenance.5. Thermal power plant can be installed in any location where

transportation and bulk of water are available.

Disadvantages:

1. The running cost for a thermal power station is comparatively high due to fuel maintenance etc.

2. Large amount of smoke causes air pollution. The thermal power station is responsible for global warming.

3. Overall efficiency of thermal power plant is low like 30%.

Conclusion:After visiting this power station I came to know about the practical generation process of electrical energy. I understood the function of various components in thermal power station, there importance, there arrangements and precaution to be used for the safety in the power plants. This experience gave us good exposure to the industries- tied branches of engineering. This visit to VTPS was an exciting experience, since the hard work of APGENCO and mutual cooperation of their staff and workers is really appreciable. I would like to thank our staff members for arranging this quality visit.

REFERENCES:1. www.apgenco.gov.in2. Google, Wikipedia3. Course material on Power plant familiarization-

APGenCo