SUBMITTED BY:AMIT VERMAROLL NO.: 0603540154B.TECH {MECHANICAL ENGINEERING}Babu Banarsi Das Institute of Technology, GHAZIABAD

Acknowledgement

I express my sincere gratitude to the management of “RAJGHAT POWER HOUSE” for providing me with the opportunity to undergo training in this esteemed organization.

I take the prerogative to express my gratitude Mr. Sanjeev Malik (Manager BLR) for his valuable suggestion and guidance through my training period.

I also take the opportunity to thanks Mr. Deepak Batra (A.M. TG), Mr. Staindera Sharma(A.M. TG), Mr. Ajay Kumar (A.M. AHP), Mr. Harpal Singh (A.M. BLR) for diligent guidance without which the project would not have been success.

I special thanks to Mr. Ashok Kumar Jha (Manager Operation shift) and Swati Upadhyay (Assistant manager HR) for sharing their experience and provide their support in technical matters.

I also acknowledge the entire staff of RAJGHATPOWER HOUSE for making brief stay in the power plant a memorable.

Preface With day to day advantage of new technology the older machinery are being replaced by new machinery. Now it has not been the work of semi skilled persons. It has opened a new horizon for degree holder engineers. But to do the job properly a suitable training is needed.

The knowledge of entire system is must for an engineer to do the trouble shooting in the quickest possible way so that the production does not get effected.

So for engineering the industrial training is playing a vital role in developing the practical knowledge. The industrial training is not merely an academic requirement but a professional necessity too.

With the increasing demand and utilization of electricity an mechanical and electrical engineer should be well versed or at least must be familiar with the generation of electricity, at the same time must be capable for fault detection.

It is thus the responsibility of a mechanical engineer to deal with the sophistication and make the maximum possible utilization.

INTRODUCTION

IPGCL - INDRAPRASTHA POWER GENERATION Co. ltd.

PPCL – PRAGATI POWER CO. LTD.

IPGCL & PPCL are the companies which produces electricity in Delhi. Under IPGCL 3 power station are in operation to supply electricity and under ppcl one power station is in operation continuously.

DESCRIPTIONGeneration of electricity in Delhi started with a 2 MW diesel set in 1903. The main function of IPGCL and PPCL is generation of electricity for Delhi. IPGCL generates electricity by its 3 power stations and PPCL having only one power station. IPGCL and PPCL produce electricity by using coal and gas.

IPGCL - INDRAPRASTHA POWER GENERATION Co. Ltd.

THERE ARE 3 POWER STATION ARE IN OPERATION:

I.P. STATION RAJGHAT POWER HOUSE GAS TURBINE POWER STATION

PPCL - PRAGATI POWER Co. Ltd.

THERE IS 1 POWER STATION IS IN OPERATION:

PRAGATI POWER STATION

Motto of IPGCL

&

PPCL

“TO PRODUCE AND SUPPLY ELECTRICITY CONTINUOUSLY.”

BRIEF DESCRIPTION

OF

INDRAPRASTHA POWER GENERATION

Co. Ltd.

&

PRAGATI POWER Co. Ltd.

IPGCL-INDRAPRASTHA POWER GENERATION Co. Ltd.

IPGCL produces electricity by its 3 power stations.

I.P. STATION

The present available capacity of this Station is 247.5 MW was installed and commissioned in 1968. Since it is a coal based station, Deshaled coal having ash contents less then 34% is being procured from NCL, Bina. New ESPs have been commissioned recently on all the units at a total cost of Rs.35 crores approx. to restrict the particulate emission below 50mg/NM3.

RAJGHAT POWER HOUSE

Two Units of 67.5 MW were installed in 1989-90 at Rajghat Power House as Replacement of old Units and the present generation capacity of this Station is 135 MW. Both the units are performing well. Additional ESPs are being fitted to bring down the SPM level from 150 mg/NM3 to 50 mg/NM3.

GAS TURBINE POWER STATION

It has installed capacity of 282 MW. Due to gas restriction only 4 gas turbines and 2 steam turbines are generally in operation. Two gas turbines along with one steam turbine are kept on liquid fuel to meet any emergency.

Six Gas Turbine Units of 30 MW each was commissioned in 1985-86 to meet the electricity demand in peak hours and were operating on liquid fuel. In 1990 the Gas Turbines were converted to operate on natural gas.

POWER KNOWN AS “RIVER OF MODERN LIFE”

Life depends on energy. Energy is a source that can neither be destroyed nor negated. It merely changes its form and shape. When captured, energy generates power. Since the discovery of fire, man, has constantly been on the run for more and more useful forms of energy. In today’s times, the most commonly used and useful form of energy is power. Power is the driving force behind life in modern times. From generating light to electricity, power is the vital fluid that runs in the stream of our life. Unfortunately this river of the life often runs dry. Not because nature does not have enough energy to produce power. It runs dry due to man’s negligence in handling and distributing energy.

As a result of the power sector reforms in Delhi, the National Capital is now being served by two of the

best electric utilities in India, BSES and TATA Power. They will take some time to achieve desired objectives. However, one thing is certain. With economic viability the power situation in Delhi will only get better with every passing year, thus reversing the legacy of deteriorating service that we had seen in past.

STATUS OF POWER DEMAND AND GROWTH OF ELECTRICITY GENERATION IN

INDIA

The Power demand in the Capital City is increasing with the growth of population as well as living standard and commercialization. The main sources of electricity generation in India are hydro-power plants, thermal power plants based on coal and nuclear fuels. Diesel generation is also used to feed isolated localities. Natural gas has been also used in Gujarat and Assam where this source is available to a limited extent.

The unrestricted power demand in the summer of year 2000 was 3000 MW and increasing every year @ 6 to 7%. In 2005-2006, it is expected to be 4078 MW and by 2009-10 it will reach 5075 MW. Erstwhile DVB's own generation from RPH, I.P. Station and Gas Turbine Power Station had been around 350-400 MW and Badarpur has

been supplying 600-700 MW and the balance was met from the Northern Grid and other sources. To bridge the gap between demand and supply and to give reliable supply to the Capital City, Delhi Govt. had set up 330 MW Pragati Power Project on fast track basis.

As mentioned in the magazine “India today” the demand rate of electricity of India is 12.5% per year and our growth rate is 5.5%. so till 2015 we will face a major problem of shortage of electricity.

IPGCL & PPCL STATIONS AT A GLANCE

I.P. STATION+RAJGHAT POWER STATION+GAS TURBINE POWER STATION

&

PRAGATI POWER STATION

REPORT IS BASED ON

THERMAL POWER PLANT

OF

RAJGHAT POWER STATION

SINGLE UNIT OF IPGCL

RAJGHAT POWER STATION Rajghat power station is one of important power house for producing electricity & supplied electricity continuously. The rajghat power house is a thermal power station which is located on the eastern side of Delhi & behind Mahatma Gandhi Samadhi towards Yamuna River.

It is one of single unit of IPGCL. The rajghat power house produces electricity by its installed capacity of 135 MW. the power house produces electricity by its two Units of 67.5 MW each were installed in 1989-90 at Rajghat Power House as Replacement of old Units and the present generation capacity of this Station is 135 MW. the units are performing well. Additional ESPs are being fitted to bring down the SPM level from 150 mg/NM3 to 50 mg/NM3.

As we discussed about the capacity of rajghat power house and we know it’s a thermal power plant , it uses coal which is supplied by the NCL , BINA. The main source of water for the rajghat power house is Yamuna river and rajghat power station is beneficial for the area are north and central area of Delhi where It supply the electricity continuously.

THERMAL POWER PLANT

Some question arises in our mind when we discussing “thermal power plant”:

What is thermal power plant?

How does it produce electricity?

Which type of work it need for producing the electricity?

Is it beneficial power plant or not?

THERMAL POWER PLANTThermal power plant is a coal based power plant which is based on the “RANKINE CYCLE”.

Thermal power plant Layout and Operation:

The above diagram is the lay out of a simplified thermal power plant. The above diagram shows the simplest arrangement of Coal fired (Thermal) power plant. Main parts of the plant are:-

1. Coal conveyor 2. Stoker 3. Pulverizer 4. Boiler 5. Coal ash 6. Air preheater

7. Electrostatic precipitator 8. Smoke stack 9. Turbine 10. Condenser 11.

Transformers 12. Cooling towers 13. Generator 14. High - voltage power lines

BASIC OPERATION OF THERMAL POWER PLANT:

A thermal power plant basically works on Rankine cycle.

COAL CONVEYOR: This is a belt type of arrangement. With this coal is transported from coal storage place in power plant to the place near by boiler.

STOKER: The coal which is brought near by boiler has to put in boiler furnace for combustion. This stoker is a mechanical device for feeding coal to a furnace.

PULVERIZER: The coal is put in the boiler after pulverization. For this pulverizer is used. A pulverizer is a device for grinding coal for combustion in a furnace in a power plant.

BOILER: Now that pulverized coal is put in boiler furnace. Boiler is an enclosed vessel in which water is heated and circulated until the water is turned in to steam at the required pressure.

SUPERHEATER: Most of the modern boilers are having super heater and reheater arrangement.

REHEATER: Some of the heat of superheated steam is used to rotate the turbine where it loses some of its energy. Reheater is also steam boiler component in which heat is added to this intermediate-pressure steam, which has given up some of its energy in expansion through the high-pressure turbine.

CONDENSER: Steam after rotating steam turbine comes to condenser. Condenser refers here to the shell and tube heat exchanger (or surface condenser) installed at the outlet of every steam turbine in Thermal power stations of utility companies generally.

COOLING TOWER: The condensate (water) formed in the condense after condensation is initially at high temperature. This hot water is passed to cooling towers. It is a tower- or building-like device in which atmospheric air (the heat receiver) circulates in direct or indirect contact with warmer water (the heat source) and the water is thereby cooled (see illustration).

ECONOMISER: Flue gases coming out of the boiler carry lot of heat. Function of economizer is to recover some of the heat from the heat carried away in the flue gases up the chimney and utilize for heating the feed water to the boiler. It is placed in the passage of flue gases in between the exit from the boiler and the entry to the chimney.

AIR PREHEATER: The remaining heat of flue gases is utilized by air preheater.It is a device used in steam boilers to transfer heat from the flue gases to the combustion air before the air enters the furnace. Also

known as air heater; air-heating system. It is not shown in the lay out. But it is kept at a place near by where the air enters in to the boiler.

ELECTROSTATIC PRECIPITATOR: It is a device which removes dust or other finely divided particles from flue gases by charging the particles inductively with an electric field, then attracting them to highly charged collector plates. Also known as precipitator.

SMOKE STACK: A chimney is a system for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. They are typically almost vertical to ensure that the hot gases flow smoothly, drawing air into the combustion through the chimney effect (also known as the stack effect).

GENERATOR: An alternator is an electromechanical device that converts mechanical energy to alternating current electrical energy.

TRANSFORMER: It is a device that transfers electric energy from one alternating-current circuit to one or more other circuits, either increasing (stepping up) or reducing (stepping down) the voltage.

A SYSTEMATIC DIAGRAM OF POWER PLANT

The above diagram helps us to study the operation of a coal based power plant also known as thermal power plant. The power plant operates on rankine cycle which continuously converts heat into work, in which a working fluid repeatedly performs a succession of processes.

THERMODYNAMIC CYCLE OF THERMAL POWER PLANT The thermal power plant is basically based on the “simple rankine cycle”.

SIMPLE RANKINE CYCLE:

The theoretical basic cycle for the simple steam turbine power plant is the rankine cycle which is closed one. The modern power plant uses the rankine cycle, modified to include superheating, regenerative feed water heating and reheating.

The rankine cycle is a thermodynamic cycle which converts heat into work. The heat is supplied externally to a closed loop, which usually uses water as the working fluid.

DESCRIPTION OF RANKINE CYCLE: A simple layout and processes of the rankine cycle.

A rankine cycle needs four main parts for operating the cycle i.e. water feed pump, boiler, turbine and condenser.

A rankine cycle describes a model of the operation of steam heat engine is found in power generation plant. Common heat sources for power plants using the rankine cycle are coal, natural gas, oil, nuclear energy.

The rankine cycle is sometimes referred to as a practical carnot cycle when an efficient turbine is used. The main difference is that a pump is used to pressurize liquid instead of gas. This requires about 100 times less energy than that compressing a gas in a compressor (as in the “CARNOT CYCLE”).

The efficiency of a rankine cycle is usually limited by the working fluid. Without the pressure going super critical the temperature range cycle can operate over is quite small, turbine entry temp are typically 565˚C [the creep limit of stainless steel] and condenser temperature are around 30˚C. this gives a theoretical carnot efficiency of around 63% compared with an actual efficiency of 42% for a modern coal-fired power station. This low turbine entry temperature is why the rankine cycle is often used as a bottoming cycle in combined cycle gas turbine power stations.

The working fluid in s rankine cycle follows a closed loop and is re-used constantly. The water vapour often seen billowing from power station is generated by the cooling systems and represents the waste heat that could not be converted to useful work. While many substances could be used in the rankine cycle, water is usually the fluid of choice due to its favorable properties such as nontoxic,

unreactive chemistry , abundance and low cost as well as its thermodynamic properties.

The thermodynamic processes define by the T-S diagrams:

T-S diagram of carnot cycle:

T-S diagram of rankine cycle:

PROCESSES OF RANKINE CYCLE:T-S diagram of a typical rankine cycle operating between pressure limit of 0.06 bar to 50 bar.

The rankine cycle is an ideal reversible cycle for steam power plants corresponding to carnot cycle. There are four processes in the rankine cycle, each changing the state of the working fluid. These states are identified by number in the diagram to the right.

PROCESS 1-2 : Pumping of feed water to the boiler from pressure, Pb to pressure P1. The compression process is reversible adiabatic .

PROCESS 2-3 : Conversion of feed water in to the steam at constant pressure equal to the boiler pressure P1. The heat supplied by external heat source to become a dry saturated vapour.

PROCESS 3-4 : Reversible adiabatic expansion of steam in the turbine from boiler pressure P1 to back pressure Pb. This decrease the temperature and pressure of the vapour and some condensation may occur.

PROCESS 4-1 : The wet vapour then enters a condenser where it is cooled at a constant pressure and temperature to become a saturated liquid. The pressure and temperature of the condenser is fixed by the temperature of the cooling coils as the fluid is undergoing a phase change.

In an ideal rankine cycle the pump and turbine work would be isentropic i.e. the pump and turbine would generate no entropy and hence maximize the net work output.

THE RANKINE CYCLE WITH REGENERATION:

Modification of rankine cycle needed to improve the efficiency of rankine cycle by using the some additional components. Improving cycle efficiency almost always involves making a cycle more like a carnot cycle operating between the high and low temperature limits.

The carnot cycle is maximally efficient in parts, because it receives all of its heat addition at the same temperature, which is the highest temperature in the cycle. Similarly, it rejects all of its heat at the same low temperature. The T-S diagram below details the working of a carnot cycle operating between the same temperature limits as in rankine cycle. Most cycle don’t have all of their heat addition or rejection at one temperature.

REGENERATION RANKINE CYCLE

HOW REGENERATION WORKS??? The idea behind regeneration is that we split the turbine in to high pressure and low pressure stages and

do the same for the pump. Then, we can divert some of the heat in the fluid as it leaves the high pressure turbine and add it to the cool fluid leaving the low pressure pump, thereby sending fluid with a higher temperature to the heater. We’ll look as this in more detail in a minute, but now we know enough to construct the rankine cycle with regeneration.

T-S diagram of rankine cycle with regeneration:

BRIEF INTRODUCTION TO COAL BASED POWER

PLANT: A coal based power plant is that in which the coal is supplied from the coal storage to the boiler through the coal handling plant. The atmosphere air is feed to the boiler through an air preheater where air is heated by the flue gases coming out as a waste heat. The heated air enters the boiler and thus increases the efficiency. As a result of combustion of water supplied in the boiler at desired pressure gets converted into steam and ash and flue gases are formed. The ash is removed by ash handling and disposal system whereas the flue gases passes through the preheater, dust collector and finally chimney to the atmosphere.

The steam so generated passes through the super heater tubes and gets converted in to superheated steam. This superheated steam enters to the turbine through the steam stop valve (SSV) and governer valve (GV). The stop valve is used for starting and stopping the turbine whereas the governer valves maintain the speed of the turbine sensibly constant irrespective of the load. Alternator converts the mechanical energy produced by the turbine in to electrical energy produced by the turbine in to electrical energy which is fed to the transformer, circuit breaker and finally to bus bar.

The exhaust steam from the turbine is condensed in the condenser. Due to the exchange of heat With cooling water condenser is equipped with a vaccum pump to extract any air which may be present due to leakage through joints and gases released upon condensation. The condensate is extracted by a condensate extraction pump and lead to L.P. feed heater where feed water is heated with steam bled in the turbine. The heated feed water is pumped back to the boiler through H.P. feed heater.

The cooling water is supplied to the condenser by a circulating water pump through a closed circuit. The heated water is cooled in a cooling tower. Some quantity of cooling water in the form of water vapour carried away by the air hence makeup cooling water to the condenser supplied from the river to a filter. If the source of cooling water is an ocean, then there is a need of desalination plant. If the source of cooling water is river then the cooling tower can be dispensed with and the hot water is led to the river as the case may be like an open system.

Due to leakage of the steam from the turbine some quantity of steam gets lost. Hence makeup water well treated through a water treatment plant is generally added up in the well of condenser.

The major systems of power plant are:

COAL HANDLING SYSTEMSTEAM GENERATION SYSTEMPOST COMBUSTION CLEANUP SYSTEM

POWER CONVERSION SYSTEMCIRCULATING COOLING WATER SYSTEM

The subsystems of thermal power plant are:

STEAM CIRCUIT (CLOSED)COOLING WATER CIRCUIT (CLOSED OR OPEN)COOLING AIR CIRCUIT (OPEN)COMBUSTION GAS CIRCUIT (OPEN)

FUNDAMENTALS PARTSOF

A STEAM POWER PLANT

There is only four fundamental parts of steam power plant but operating and to get the more efficiency by the power plant we add some components.

FUNDAMENTAL PARTS:

BOILER STEAM TURBINE CONDENSER FEED PUMP

There are many other elements such as coal handling unit, cooling tower, feed water heaters, ash handling system etc.

BOILER Steam generator or a boiler is a closed pressure vessel used for generation of steam under pressure. A boiler is usually made of steel in which the chemical energy of fuel is converted by combustion in to heat and this heat energy of products of combustion is transferred to water so as to produce steam.

When steam is used in power generation, it is generated at high pressure and in large quantities due to high efficiency requirements. The design of such boiler is quite intricate and it depends upon the type of fuel used and its capacity. In a boiler, the working fluid i.e. water receives heat due to combustion of fuel and is converted into steam at constant pressure. Its efficiency is around 90%.

A boiler is a device for generating steam, which

consists of two principal parts: the furnace, which

provides heat, usually by burning a fuel, and the boiler

proper , a device in which the heat changes water into

steam. The steam or hot fluid is then recirculated out of

the boiler for use in various processes in heating.

WATER TUBE BOILER

Here in rajghat power house water tube boiler is

used for generating the steam. In these boilers water is

inside the tubes and hot gases are outside the tubes.

They consist of drums and tubes. The boiler receives the

feed water, which consists of varying proportion of

recovered condensed water (return water) and fresh

water, which has been purified in varying degrees (make

up water). The make-up water is usually natural water

either in its raw state, or treated by some process before

use. Feed-water composition therefore depends on the

quality of the make-up water and the amount of

condensate returned to the boiler. The steam, which

escapes from the boiler, frequently contains liquid

droplets and gases. The water remaining in liquid form at

the bottom of the boiler picks up all the foreign matter

from the water that was converted to steam. The

impurities must be blown down by the discharge of some

of the water from the boiler to the drains. The permissible

percentage of blown down at a plant is strictly limited by

running costs and initial outlay. The tendency is to reduce

this percentage to a very small figure.

BOILER OPERATION:

The boiler is a rectangular furnace about 50 ft on a side

and 130 ft tall. Its walls are made of a web of high

pressure steel pressure tubes about 2.3 inches in

diameter.

Pulverized coal is air blown into the furnace from fuel nozzle at the four corners and it rapidly burns, forming a large fire ball at the centre. The thermal radiation of the fire ball heats the water that circulates through the boiler tubes near the boiler perimeter. The water circulation rate in the boiler is three to four times the throughput and is typically driven by pumps. As the water in the boiler circulates it absorbs heat and changes into steam at 700˚F (370˚C) and 3200 psi (22.1 Mpa). It is separated from the water inside a drum at the top of the furnace. The saturated steam is introduced into superheat pendant tubes that hang in the hottest part of the combustion gases as they exit the furnace. Here the steam is superheated to 1000˚F (540˚C) to prepare it for the turbine.

Proper treatment of boiler feed water is an important part of operating and maintaining a boiler system. As steam is produced, dissolved solids become concentrated and form deposits inside the boiler. This leads to poor heat transfer and reduces the efficiency of the boiler.

STEAM TURBINE A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884. It has almost completely replaced the reciprocating piston steam engine (invented by Thomas Newcomen and greatly improved by James Watt) primarily because of its greater thermal efficiency and higher power-to-weight ratio. Because the turbine generates rotary motion, it is particularly suited to be used to drive an electrical generator – about 80% of all electricity generation in the world is by use of steam turbines. The steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency through the use of multiple stages in the expansion of the steam, which results in a closer approach to the ideal reversible process.

History of steam turbine The first device that may be classified as a reaction steam turbine was little more than a toy, the classic Aeolipile, described in the 1st century by Hero of Alexandria in Roman Egypt. More than a thousand years later, the first impact steam turbine with practical applications was invented in 1551 by Taqi al-Din in Ottoman Egypt, who described it as a prime mover for rotating a spit. Similar smoke jacks were later described by John Wilkins in 1648 and Samuel Pepys in 1660. Another steam turbine device was created by Italian Giovanni Branca in 1629.The modern steam turbine was invented in 1884 by the Englishman Sir Charles Parsons, whose first model was connected to a dynamo that generated 7.5 kW of electricity.

Types of steam turbineSteam turbines are made in a variety of sizes ranging from small 1 hp (0.75 kW) units (rare) used as mechanical

drives for pumps, compressors and other shaft driven equipment, to 2,000,000 hp (1,500,000 kW) turbines used to generate electricity. There are several classifications for modern steam turbines like impulse or reaction type turbine.

Impulse Turbines An impulse turbine has fixed nozzles that orient the steam flow into high speed jets. These jets contain significant kinetic energy, which the rotor blades, shaped like buckets, convert into shaft rotation as the steam jet changes direction. A pressure drop occurs across only the stationary blades, with a net increase in steam velocity across the stage. As the steam flows through the nozzle its pressure falls from steam chest pressure to condenser pressure (or atmosphere pressure). Due to this relatively higher ratio of expansion of steam in the nozzle the steam leaves the nozzle with a very high velocity. The steam leaving the moving blades is a large portion of the maximum velocity of the steam when leaving the nozzle. The loss of energy due to this higher exit velocity is commonly called the "carry over velocity" or "leaving loss".

Reaction TurbinesIn the reaction turbine, the rotor blades themselves are arranged to form convergent nozzles. This type of turbine makes use of the reaction force produced as the steam accelerates through the nozzles formed by the rotor.

Steam is directed onto the rotor by the fixed vanes of the stator. It leaves the stator as a jet that fills the entire circumference of the rotor. The steam then changes direction and increases its speed relative to the speed of the blades. A pressure drop occurs across both the stator and the rotor, with steam accelerating through the stator and decelerating through the rotor, with no net change in steam velocity across the stage but with a decrease in both pressure and temperature, reflecting the work performed in the driving of the rotor.

Steam Supply and Exhaust Conditions

These types include condensing, noncondensing, reheat, extraction and induction.

Noncondensing or backpressure turbines are most widely used for process steam applications. The exhaust pressure is controlled by a regulating valve to suit the needs of the process steam pressure. These are commonly found at refineries, district heating units, pulp and paper plants, and desalination facilities where large amounts of low pressure process steam are available. Condensing turbines are most commonly found in electrical power plants. These turbines exhaust steam in a partially condensed state, typically of a quality near 90%, at a pressure well below atmospheric to a condenser. Reheat turbines are also used almost exclusively in electrical power plants. In a reheat turbine, steam flow exits from a high pressure section of the turbine and is returned to the boiler where additional superheat is added. The steam then goes back into an intermediate pressure section of the turbine and continues its expansion. Extracting type turbines are common in all applications. In an extracting type turbine, steam is released from various stages of the turbine, and used for industrial process needs or sent to boiler feedwater heaters to improve overall cycle efficiency. Extraction flows may be controlled with a valve, or left uncontrolled. Induction turbines introduce low pressure steam at an intermediate stage to produce additional power.

Casing or Shaft Arrangements These arrangements include single casing, tandem compound and cross compound turbines. Single

casing units are the most basic style where a single casing and shaft are coupled to a generator. Tandem compound are used where two or more casings are directly coupled together to drive a single generator. A cross compound turbine arrangement features two or more shafts not in line driving two or more generators that often operate at different speeds. A cross compound turbine is typically used for many large applications.

Principle of Operation and Design

An ideal steam turbine is considered to be an isentropic process, or constant entropy process, in which the entropy of the steam entering the turbine is equal to

the entropy of the steam leaving the turbine. No steam turbine is truly “isentropic”, however, with typical isentropic efficiencies ranging from 20%-90% based on the application of the turbine. The interior of a turbine comprises several sets of blades, or “buckets” as they are more commonly referred to. One set of stationary blades is connected to the casing and one set of rotating

blades is connected to the shaft. The sets intermesh with certain minimum clearances, with the size and configuration of sets varying to efficiently exploit the expansion of steam at each stage.

Turbine Efficiency To maximize turbine efficiency, the steam is expanded, generating work, in a number of stages. These stages are characterized by how the energy is extracted from them and are known as impulse or reaction turbines. Most modern steam turbines are a combination of the reaction and impulse design. Typically, higher pressure sections are impulse type and lower pressure

stages are reaction type. Operation and Maintenance When warming up a steam turbine for use, the main steam stop valves (after the boiler) have a bypass line to allow superheated steam to slowly bypass the valve and proceed to heat up the lines in the system along with the steam turbine. Also a turning gear is

engaged when there is no steam to the turbine to slowly rotate the turbine to ensure even heating to prevent uneven expansion. After first rotating the turbine by the turning gear, allowing time for the rotor to assume a straight plane (no bowing), then the turning gear is disengaged and steam is admitted to the turbine, first to the astern blades then to the ahead blades slowly rotating the turbine at 10 to 15 RPM to slowly warm the turbine.

Problems with turbines are now rare and maintenance requirements are relatively small. Any imbalance of the rotor can lead to vibration, which in extreme cases can lead to a blade letting go and punching straight through the casing. It is, however, essential that the turbine be turned with dry steam. If water gets into the steam and is blasted onto the blades (moisture carryover) rapid impingement and erosion of the blades can occur, possibly leading to imbalance and catastrophic failure. Also, water entering the blades will likely result in the destruction of the thrust bearing for the turbine shaft. To prevent this, along with controls and baffles in the boilers to ensure high quality steam, condensate drains are installed in the steam piping leading to the turbine.

Speed regulation The control of a turbine with a governor is essential, as turbines need to be run up slowly, to prevent damage while some type

applications (such as the generation of alternating current electricity) require precise speed control. Uncontrolled acceleration of the turbine rotor can lead to an overspeed trip, which causes the nozzle valves that control the flow of steam to the turbine to close. If this fails then the turbine may continue accelerating until it breaks apart, often spectacularly. Turbines are expensive to make, requiring precision manufacture and special quality materials.

Direct drive Electrical power stations use large steam turbines driving electric generators to produce most (about 80%) of the world's electricity. Most of these centralised stations are of two types: fossil fuel power plants and nuclear power plants. The turbines used for electric power generation are most often directly coupled to their generators. As the generators must rotate at constant synchronous speeds according to the frequency of the electric power system, the most common speeds are 3000 r/min for 50 Hz systems, and 3600 r/min for 60 Hz systems. In installations with high steam output, as may be found in nuclear power stations, the generator sets may be arranged to operate at half these speeds, but with four-pole generators.

CONDENSER

A condenser is a device or unit used to condense a substance from its gaseous to its liquid state, typically by cooling it. In so doing, the latent heat is given up by the substance, and will transfer to the condenser coolant. Condensers are typically heat exchangers which have various designs and come in many sizes ranging from rather small (hand-held) to very large industrial-scale units used in plant processes. For example, a refrigerator uses a condenser to get rid of heat extracted from the interior of the unit to the outside air. Condensers are used in air conditioning, industrial chemical processes such as distillation, steam power plants and other heat-exchange systems.

The function of the condenser is to condense

exhaust steam from the steam turbine by rejecting the

heat of vaporisation to the cooling water passing through

the condenser. The temperature of the condensate

determines the pressure in the steam/condensate side of

the condenser. This pressure is called the turbine

backpressure and is usually a vacuum. Decreasing the

condensate temperature will result in a lowering of the

turbine backpressure. Note: Within limits, decreasing the

turbine backpressure will increase the thermal efficiency

of the turbine.

Condenser and cooling system The condensers and cooling systems involved in condensing the exhaust steam from a steam turbine and transferring the waste heat away from the power station.

Types of Cooling SystemsThe type of cooling system used is therefore heavily influenced by the location of the plant and on the availability of water suitable for cooling purposes. The selection process is also influenced by the cooling system's environmental impacts.

Open Cycle Cooling Systems Open cycle cooling systems may be used for plants sited beside large water bodies such as the sea, lakes or large rivers that have the ability to dissipate the waste heat from the steam cycle. In the open system, water pumped from intakes on one side of the power plant passes through the condensers and is discharged at a point remote from the intake (to prevent recycling of the warm water discharge).

Open systems typically have high flow rates and relatively low temperature rises to limit the rise in temperature in the receiving waters. A typical 350 MW unit would have a flow of some 15000 to 20000 L/s.

Open Cycle with Helper Cooling Tower

In this system, cooling towers are installed on the discharge from open systems in order to remove part of the waste heat, so that the load on the receiving waters is contained within pre set limits. Systems with helper cooling towers are common in Germany and France where cooling supplies are drawn from the large rivers. The helper towers are used in the warmer summer periods to limit the temperature of the discharged cooling water, usually to less than 30˚C.

Closed Cycle Wet Cooling Systems In closed cycle wet cooling systems, the waste energy that is rejected by the turbine is transferred to the cooling water system via the condenser. The waste heat in the cooling water is then discharged to the atmosphere by the cooling tower. In the cooling tower, heat is removed from the falling water and transferred to the rising air by the evaporative cooling process. The falling water is broken up into droplets or films by the extended surfaces of the tower 'fill'. This 'fill' in the later Queensland towers is manufactured from plastic. Some of the warm water,

typically 1 to 1.5% of the cooling water flow, is transferred to the rising air, and this is visible in the plume of water vapour above towers in times of high humidity. The evaporation rates of the Queensland 350 MW cooling systems are typically 1.8 liters of water per kWh of power generated.

Closed Cycle Dry Cooling Systems Dry cooling systems are used where there is insufficient water, or where the water is too expensive to be used in an evaporative system. Dry cooling systems are the least used systems as they have a much higher capital cost, higher operating temperatures, and lower efficiency than wet cooling systems. In the dry cooling system, heat transfer is by air to finned tubes. The

minimum temperature that can be theoretically provided is that of the dry air, which can be regularly over 30º C and up to 40º C on typical summer afternoons in Queensland. Compare this to wet cooling towers, which cool towards the wet bulb temperature, which is typically 20º C on summer afternoons. The steam condensing pressures and temperatures of a dry cooled unit are significantly higher than a wet cooled unit, due to the low transfer rates of dry cooling and operation at the dry bulb temperature.

There are two basic types of dry cooling systems:

The direct dry cooling system. The indirect dry cooling system.

Environmental Effects of Cooling Systems:

All the heat transferred from the exhaust steam to the cooling system eventually finds its way into the earth's atmosphere.In the once-through cooling water system, heat is removed from the steam turbine and transferred to the source body of water. The heat is then gradually transferred to the atmosphere by evaporation, convection and radiation. However, this waste heat transfer process may negatively affect the body of water buy increasing the temperature of the water. In a re-circulating cooling system, the cooling water carries waste heat removed from the steam turbine exhaust to the cooling tower, which rejects the heat directly to the atmosphere. Because of this direct path to the atmosphere, surrounding water bodies typically do not

suffer adverse thermal effects. Some water is discharged from the cooling water system to maintain the concentration of chemicals in the cooling water below licensed limits. This water is often discharged to surrounding watercourses.

FEED WATER PUMPThe hydraulic machines which convert the mechanical energy into the hydraulic energy are called as PUMP. The hydraulic energy is in the form of pressure energy. The pumps are classified in two parts:

1. RECIPROCATING PUMPS

2. CENTRIFUGAL PUMPSThe feed water is also of centrifugal type pumps. The main functions of these type pumps are to feed the water coming out from the condenser to the boiler at the desired pressure. It is either motor or turbine driven. It consumes about 2-2.5% of the power output.

Feed water heatersA feed water heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feed water reduces the irreversibility involved in steam generation and therefore improves the thermodynamic efficiency of the system.[4] This reduces plant operating costs and also helps to avoid thermal shock to the boiler metal when the feed water is introduced back into the steam cycle.

In a steam power plant (usually modeled as a modified Rankine cycle), feed water heaters allow the feedwater to be brought up to the saturation temperature very gradually. This minimizes the inevitable irreversibilities associated with heat transfer to the working fluid (water).

Cycle discussion and explanation

It should be noted that the energy used to heat the feed water is usually derived from steam extracted between the stages of the steam turbine. Therefore, the steam that would be used to perform expansion work in the turbine (and therefore generate power) is not utilized for that purpose. The percentage of the total cycle steam mass flow used for the feed water heater is termed the extraction fraction and must be carefully optimized for maximum power plant thermal efficiency since increasing this fraction causes a decrease in turbine power output.

Feed water heaters can also be open and closed heat exchangers. An open feed water heater is merely a direct-contact heat exchanger in which extracted steam is allowed to mix with the feed water. This kind of heater will normally require a feed pump at both the feed inlet and outlet since the pressure in the heater is between the boiler pressure and the condenser pressure. A deaerator is a special case of the open feed water heater which is specifically designed to remove non-condensable gases from the feed water.

Closed feed water heaters are typically shell and tube heat exchangers where the feed water passes throughout the tubes and is heated by turbine extraction steam. These do not require separate pumps before and after the heater to boost the feed water to the pressure of the extracted steam as with an open heater. However, the extracted steam (which is most likely almost fully condensed after heating the feed water) must then be throttled to the condenser pressure, an isenthalpic

process that results in some entropy gain with a slight penalty on overall cycle efficiency.

Many power plants incorporate a number of feed water heaters and may use both open and closed components.

Feed water heaters are used in both fossil- and nuclear-fueled power plants. Smaller versions have also been installed on steam locomotives, portable engines and stationary engines. An economiser serves a similar purpose to a feed water heater, but is technically different. Instead of using actual cycle steam for heating, it uses the lowest-temperature flue gas from the furnace (and therefore does not apply to nuclear plants) to heat the water before it enters the boiler proper. This allows for the heat transfer between the furnace and the feed water to occur across a smaller average temperature gradient (for the steam generator as a whole). System efficiency is therefore further increased when viewed with respect to actual energy content of the fuel.

COAL HANDLING PLANT

Coal handing plant is the one most important part of the boiler plant. The handling problem of coal in the boiler plant is major problem because for the generation of boiler there are only two raw materials required. One is water and the second is coal. To handle the large amount of handle in a very small and continuing time, we required a plant which is suit according to our need. In the coal handling plant coal from the coal wagons is unloaded in coal handling plant and this coal is send to the raw coal bunkers with the help of belt conveyers.

COAL MILL The coal is conveying by the help of coal

conveyers. The large amount or large sized storage

container situated at the top of the main plant building.

The main part of the coal mill is pulverization.

COAL PUVERIZING AND FIRING

SYSTEM Raw coal is fed through a central coal inlet at the top of the pulverizer and falls by gravity to the rotating

grinding table, mixing with classifier rejects returned for re-grinding. Centrifugal action forces the coal outward to the grinding ring where it is pulverized between the ring and three grinding rollers. Grinding load, transmitted from the tension rods through the loading frame to the roller assemblies, holds the rollers in contact with the grinding ring. The rollers adjust vertically as the depth of the coal load increases or decreases. A nozzle ring on the outside perimeter of the grinding ring feeds primary air to the pulverizer. Pyrites and tramp metal fall through the nozzle ring openings to be scraped into a rejects hopper. A stream of low-velocity air carries the particles of pulverized coal upward where they enter the classifier inlet vanes. Fine particles travel to the burners in the primary air stream, but the larger, heavier particles are returned to the grinding zone for further pulverization. Most efficient way to utilizing coal for steam generation is to burn it in the pulverized form. Pulverized coal fire is a method where the crushed coal generally reduced to a fineness such that 70 – 80% passes through a 200 mesh sieve is carried forward by air through pipes directly to burners or storage bus from where it is passed to burners and discharge into combustion chamber. The mixture of coal and air ignites and burns in suspension condition for pulverizing the coal equipments and system would be required with highly availability.

The major equipments in a pulverizing plant are: PULVERIZER FEEDER

PULVERIZER

LOW SPEED MEDIUM SPEED HIGH SPEEDMILLS 10-20rpm MILLS 30-120rpm MILLS >700rpm

PULVERIZER COAL FIRING SYSTEMThere are basically two system of pulverized coal firing in use:

1. In direct firing system2. Direct firing system

RAW COAL FEEDER

Feeders can be divided in two types:1. Volumetric feeder2. Gravimetric feeder

BOWL MILL

Bowl mill is provide to crush the coal from sized

clinkers to powdered from for better ignition of the coal

inside the furnace. Coal is transported to the bowl mills

by coal feeder. The coal is pulverized in the bowl mill

where it is ground to a powder form of the order of 200

meshes. The mill consists of a round metallic table on

which coal particles fall. This table is rotated with the help

of a motor. These are three large rollers, which are

spaced 120˚ apart.

When there is no coal, these rollers do not rotate

but when coal is fed to the table it packs up between

roller and the table and this force the roller to rotate. Coal

is crushed by the crushing action between rollers and the

rotating table.

ASH HANDLING PLANT Ash handling system is always designed to handle bottom ash from steam generating units and fly ash from ESP, economizer, air peheater and stack hopper for disposal to ash disposal area and storing to fly ash storage silo. A steam generating unit [for Rajghat power house] of 67.5 MW set would require about 60.2 tonnes of coal per hour at MCR with worst coal and the ash handling system is designed for the same. Ash collected in bottom ash hopper in a shift of 8 hours will be emptied through clinker grinder and jet pump. The fly ash collected at various fly ash hoppers will be extracted sequentially by creating vaccum in fly ash lines. Alternatively provision has been made to collect 100% dry fly ash of both the units in storage silos for commercial use.BOTTOM ASH REMOVAL SYSTEMThe bottom ash removal system of each unit consists of a water impounded single ‘V’ type ash hopper with the following major accessories.

1. Seal trough to allow the boiler expands downward while maintaining a gas seal.

2. Poke hole3. Sluice hole4. Sluice gate5. Sluice gate enclosure fitted with access door6. Normal water level overflow weir.

FLY ASH REMOVAL SYSTEM

Two types of fly ash removal system has been envisaged out of which one type will be working for wet disposal system and alternatively other type will be working for dry disposal system.

A. fly ash disposal system

B. fly ash dry disposal system

ELECTROSTATIC PRECIPITATOR The principal components of an electrostatic precipitator (ESP) are two sets of electrodes insulated from each other. The first set is composed of rows of electrically grounded vertical parallel plates called the collection electrodes, between which the dust-laden gas flows. The second set of electrodes consists of wires called discharge or emitting electrodes that are centrally located between each pair of parallel plates. The wires carry a unidirectional negatively charged high-voltage (between 20-100KV) current from an external DC source. The applied high voltage generates a unidirectional, non uniform electrical field whose magnitude is greatest near the discharge electrodes. When that voltage is high enough, a blue luminous glow called a corona, is produced around them. Electrical forces in the corona accelerate the free electrons present in the gas so that they ionize the gas molecules, thus forming more electrons and positive gas ions. The new electrons create again more free electrons and ions which results in a chain reaction.

The positive ions travel to the negatively charged wire electrodes. The electrons follow the electrical field towards the grounded electrodes. But their velocity decreases as they move away from the corona region around the wire electrodes towards the grounded plates. Gas molecules capture the low velocity electrons and become negative ions. As these ions move to the collecting electrodes, they collide with fly ash particles in the gas stream and give them negative charge and the strength of the electric field.When the particles collect on the grounded plates, they lose their charge on the ground. The electrical resistivity of the particles however, causes only partial discharging and the retained charge tends to hold the particles to the plates. High resistivity causes retention of most of the charge, which increases the forces holding the particles to the plate and makes removal more difficult. This can be rectified either by operating at high gas temperature

or by super imposing during operation under high-resistivity conditions.

Collected particulates matter must be removed from the collecting plates on a regular schedule to ensure efficient collector operation. Removal is usually accomplished by a mechanical hammer scarping system. The vibration knocks the particulate matter off the collect in plates and into a hopper at the bottom of the precipitator.

BOILER DRAUGHT Draught means the force needed to draw. With regard to the boilers the requirements is to provide an adequate supply of air to the furnace grate to maintain the proper combustion of fuel, to the resulting gases from

the system and to discharge these flue gases from the chimney to the surroundings.It is of two types:

1. NATURAL OR CHIMNEY DRAUGHT2. ARTIFICIAL DRAUGHT

Most boilers now depend on mechanical draught equipment rather than natural draught. This is because natural draught is subjected to outside air conditions and temperature of flue gases leaving the furnace, as well as the chimney height. All these factors make proper draught hard to attain and therefore make mechanical draught much more economical.There are three types of mechanical draught:

I. INDUCED DRAUGHT

II. FORCED DRAUGHT

III. BALANCED DRAUGHT

ECONOMIZER

An economizer is a heat transfer device used for heating the feed water with the help of hot flue gases before leaving the chimney. It helps in improving the efficiency of the power plants.Economizer is consisting of large number of vertical tubes, made of cast iron, joined with horizontal pipes. The cold feed water is pumped into horizontal pipe through a stop valve. The hot flue gases from boiler pass over the vertical tubes and these gases transfer the heat to cold water rising in these tubes. Finally the hot feed water is supplied to the boiler from stop valve. At the other end of pipe, a safety valve is mounted to guard by the system against the increased pressure. A blow-off-cock is mounted at the end of horizontal pipe to remove any mud or sediments of feed water. Any soot formation on the tubes will effect greatly the coefficient of thermal conductivity, consequently the rate of heat transfer is reduced. This reduced the efficiency of the economizer. In to remove the deposits of the soot from vertical pipes each pipe is provide with a scrapper. In boiler, economizer are heat exchange devices that heat fluids, usually water up to bur=t not normally beyond the boiling point of that fluid. Economizers are so named because they can make use of the enthalpy in fluid stream that are hot but not hot enough to b used in a boiler, thereby recovering more useful enthalpy ang=d improving the boiler’s efficiency.

They are a device fitted to the boiler which saves energy by using the exhaust gases from the boiler to preheat the cold water used the fill the feed water.

AIR PREHEATER An air preheater or air heater is a general term to describe any device designed to heat air before another process with the primary objective of increasing the thermal efficiency of the process. They may be used alone or to replace a recuperative heat system or to replace a steam coil.The combustion air preheaters used in large boilers found in thermal power stations producing electric power from e.g. fossil fuels, biomasses or waste.

The purpose of the air preheater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat lost in the flue gas. As a consequence, the flue gases are also sent to the flue gas stack (or chimney) at a lower temperature, allowing simplified design of the ducting and the flue gas stack. It also allows control over the temperature of gases leaving the stack types.

There are two types of air preheaters for use in steam generators in thermal power stations: One is a tubular type built into the boiler flue gas ducting, and the other is a regenerative air preheater. These may be arranged so the gas flows horizontally or vertically across the axis of rotation

TABULAR TYPE

Tubular preheaters consist of straight tube bundles which pass through the outlet ducting of the boiler and open at each end outside of the ducting. Inside the ducting, the hot furnace gases pass around the preheater tubes, transferring heat from the exhaust gas to the air inside the preheater. Ambient air is forced by a fan through ducting at one end of the preheater tubes and at other end the heated air from inside of the tubes emerges into another set of ducting, which carries it to the boiler furnace for combustion.

REGENERATIVE AIR PREHEATER TYPE

There are two types of regenerative air preheaters: the rotating-plate regenerative air preheaters (RAPH) and the stationary-plate regenerative air preheaters (Rothemuhle).

Rotating-plate regenerative air preheater Typical Rotating-plate Regenerative Air Preheater (Bi-

sector type)

The rotating-plate design (RAPH) consists of a central rotating-plate element installed within a casing that is divided into two (bi-sector type), three (tri-sector type) or four (quad-sector type) sectors containing seals around the element. The seals allow the element to rotate through all the sectors, but keep gas leakage between sectors to a minimum while providing separate gas air and flue gas paths through each sector.

SUPER HEATERS The function of super heater is to increase the temperature of steam above its saturation temperature. Basically, a super heater is a heat transfer device using a set of tubes in which the wet steam flows and takes up the heat from the hot flow flue gases passing over the steam pipe and during the process the wet steam is converted in to super heated steam.

The super heated tubes are made of steel tubes in the ‘U’ shape which are connected to two main headers. The action of super heater is as follows:

The one stop valve is closed and the other two stop valves are in open position. The wet steam from boiler flows in to right and header via a stop valve. After super heating of steam in the tubes it flows into the left hand header, from where it is withdrawn through the stop valve.

If super heated steam is not needed, the stop valves are closed and the wet steam is directly taken out by the other valve.

The superheating of steam can be controlled by controlling the quantity of flow of flue gases by operating the dampers manually.

As the steam is conditioned by the drying equipment inside the drum, It is piped from on the upper drum area in to an elaborate set up of tubing in different areas of the boiler. The areas are known a super heater and reheater. The steam vapour picks up energy and its temperature is now superheated above the saturation temperature. The superheated steam is then piped through the main steam lines to the valves of the high pressure turbine.

DEAERATORThe presence of dissolved gases like oxygen and carbon dioxide in water makes the water corrosive, as they react with the metal to from iron oxide. The solubility of these

gases in water decreases with increase in temperature and becomes zero at the boiling or saturation temperature. These gases are removed in the deaerator where feed water is heated to saturation temperature by the steam extracted from the turbine. Feed water, after passing through a heat exchanger called vent condenser, is sprayed from top so as to expose large surface area, and the bled steam from the turbine is fed from bottom. By contact the steam condenses and the feed water is heated to the saturation temperature. Dissolved oxygen and carbon dioxide gases get released from water and leave along with some vapour, which is condensed back in the vent condense r and the gases are vented out.

FIG: DEAERATOR

To neutralize the effect of residual dissolved carbon dioxide and oxygen gases in water, hydrazine [N2H4] is injected in suitable calculated does into the feed water at the suction of the boiler feed pump.

A deaerator is a device that is widely used for the removal of air and other dissolved gases from the feed water to steam generating boilers. In particular, dissolved oxygen in boiler feed waters will cause serious corrosion damage in steam systems by attaching to the walls of metal piping and other metallic equipment and forming oxides (rust). It also combines with any dissolved carbon dioxide to form carbonic acid that causes further corrosion. Most deaerators are designed to remove oxygen down to levels of 7 ppb by weight (0.0005 cm³/L) or less.

There are two basic types of deaerators, the tray-type and the spray-type:The tray-type (also called the cascade-type) includes a vertical domed deaeration section mounted on top of a horizontal cylindrical vessel which serves as the deaerated boiler feedwater storage tank.

The spray-type consists only of a horizontal (or vertical) cylindrical vessel which serves as both the deaeration section and the boiler feed water storage tank.

Mode of operation of steam turbine: Since it is a steam jet and no more a water jet who meets the turbine now, the laws of thermodynamics are to be observed now. The modern steam turbine is an action turbine (no reaction turbine), i.e. the steam jet meets from a being certain nozzle the freely turning impeller. There's a high pressure in front of the turbine, while behind it a low pressure is maintained, so there's a pressure gradient: Steam shoots through the turbine to the rear end. It delivers kinetic energy to the impeller and cools down thereby: The pressure sinks. "Steam"

Steam turbines are operated today of course no longer with normal water vapour only, but depending on the field of application also with other materials, e.g. with freons). Steam is produced in a steam boiler, which is heated in power stations by the burn of coal or gas or by atomic energy. Steam doesn't escape then, but after the passage through the turbine it is condensed in a condensor and then pushed back into the steam boiler again by a pump. This has the advantage that for example in nuclear power stations work- and cooling water is clearly separated.

Multi-Level steam turbines:

In modern steam turbines not only one impeller is

propelled, but several being in a series. Between them idlers are situated, which don't turn. The gas changes its direction passing an idler, in order to perform optimally work again in the next impeller. Turbines with several impellers are called multi-level. The principle was developed 1883 by Parsons. As you know, with the cooling gas expands. Therefore it is to be paid attention when building steam turbines to a further problem: With the number of passed impellers also the volume increases, which leads to a larger diameter of the impellers. Because of that, multi-level turbines are always conical.

Coupling of several turbines: In power stations today, different types of turbines are used in a series, e.g. one high pressure -, two medium- and four low pressure turbines. This coupling leads to an excellent efficiency (over 40%), which is even better than the efficiency of large diesel engines. This characteristic and the relatively favorable production make the steam turbine competitionless in power stations. Coupled with a generator and fired by an atomic reactor, they produce enormously much electric current. The strongest steam turbines achieve today performances of more than 1000 megawatts.

TURBINE PROTECTIVE DEVICES: These devices are those which protect the turbine from getting damage during an abnormal working condition or malfunctioning.

POSSIBLE HAZARDS:

During the operation of the steam turbine, many damage are likely to be encountered are as follows:

1. OVERSPEEDING2. OILFAILURE3. THRUST BEARING FAILURE4. VACCUM FAILURE5. BOILER PRIMING6. EXCESSIVE VIBRATION7. EXCESSIVE TEMPERATURE DIFFERENTIALS

LUBRICATING SYSTEM It is the one of the most important system of steam turbine. It is the life line of the bearing. Two purposes are saved by the lubricating oil. These are as follows:

KEEP MOVING PARTS APARTREDUCE FRICTIONTRANSFER HEATCARRY AWAY CONTAMINANTS & DEBRISTRANSMIT POWERPROTECT AGAINST WEARPREVENT CORROSIONSTOP THE RISK OF SMOKE AND FIRE OF OBJECTS

The main elements of lubrication system are:

i. OIL PUMPSii. OIL RELIEF VALVEiii. OIL COOLERS iv. OIL TANKS, STAINERS AND FILTERv. OIL

TURBO GENERATOR The 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, two low pressure turbines and the generator. As the steam moves through the system

and loses pressure and temperature energy it expands in volume, requiring increasing diameter and longer blades at each succeeding stage to extract the remaining energy. The entire rotating mass may be over 200 tons and 100 ft (30 m) long. It is so heavy that it must be kept turning slowly even when shutdown (at 3 rpm) so that the shaft will not bow even slightly and become unbalanced. This is so important that it is one of four functions of blackout emergency power batteries on site. There are emergency lighting, communication, station alarms and turbo generator lube oil.

Super heated steam from the boiler is delivered through 14-16 inch (350-400 mm) diameter piping to the high pressure turbine where it falls in pressure to 600 psi (4 MPa) and to 600˚F (315˚C) through the stage. It exits via 24-26 inch (600-650 mm) diameter cold reheat lines and passes back into the boiler where the steam is reheated in special reheat pendant tubes back to 1000˚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 turbine and finally exits to the condenser.

The generator 30 ft (9 m) long and 12 ft (3.7 m) diameter, contains a stationary stator and a spinning rotor, each containing miles of heavy copper conductor- no permanent magnets here. In operation it generates up to 21000 amps at 24000 volts AC (504 MW) as it spins at either 3000 or 3600 rpm, synchronized to the power grid. The rotor spins in a sealed chamber cooled with hydrogen gas, selected because it has the highest known heat transfer

coefficient of any gas and for its low viscosity which reduces wind age losses. This system requires special handling during startup, with air in the chamber first displaced by carbon dioxide before filling with hydrogen does not mix with oxygen in the air.

TURBO GENERATOR

The power grid frequency is 60 Hz across north America and 50 Hz in Europe, Oceania, Asia and some parts of Africa.

The electricity flows to a distribution yard where transformer step the voltage up to 115,230,500 or 765 KV AC as needed for transmission to its destination.

The turbine shaft usually rotates at 3000rpm. This speed is determined by the frequency of the electrical system used in this country and is the speed at which a 2 pole generator must be driven to generate alternating current at a frequency of 50 cycles/sec. when as much as energy as possible have been extracted from the steam it is exhausted directly to the condenser. This runs the length of the low pressure part of the turbine and may be beneath on either side of it. The condenser consist of a large vessel containing 20000 tubes each about 25 mm in diameter cold water from the river, estuary, sea or cooling tower is circulated through these tubes and as the steam from the turbine passes round them it is rapidly condensed in to water condensate. Because water has a much smaller comparative volume than steam, a vaccum is created in the condenser. This allows the steam to reduce down to pressure below that of the normal atmosphere and more energy can be utilized.

WATER TREATMENT PLANTINTRODUCTION In the power plant, the objective of water treatment plant is to produce boiler feed water so that there shall be

a. No scale formation causing resistance to passage of heat and burning of tube,

b. No corrosion andc. No priming or foaming problems.

This will ensure that the steam generated shall be clean and the boiler plant will provide trouble free uninterrupted service. This chapter details the system for production of such water in a power plant.

As the types of boiler are not alike their working pressure and operating conditions vary and so do the types and methods of water treatment. Water treatment plants used in thermal power plants are designed to process the raw water to water with vary

low in dissolved solids known as “demineralized water”. No doubt, this plant has to be engineered very carefully keeping in view the type of raw water to the thermal plant, its treatment costs and overall economics.

Actually, the type of demineralization process chosen for a power station depends on three main factors:

1. The quality of the raw water2. The degree of deionization i.e. treated water

quality3. Selectivity of resins.

The fig. shows a schematic diagram of water treatment process which is generally made up of two sections:

Pretreatment section Demineralization section

PRETREATMENT PLANT: Pretreatment plant removes the suspended solids such as clay, slit, organic, and inorganic matter, plants and other microscopic organism. The turbidity may be taken as of two types of suspended solids in water. Firstly, the separable solids and secondly, the non-separable solids (colloids). The coarse components such as sand, silt etc. can be removed from water by the simple sedimentation. Finer particles however, will not settle in any reasonable time and must be flocculated to produce the large particles which are settling able. Long term ability to remain suspended in water basically a function of both size and specific gravity. The settling rate of the colloidal and finely divided suspended matter is so

slow that removing them from water by plain sedimentation is tanks having ordinary dimensions are impossible. Settling velocity of finely divided and colloidal particles under gravity also is so small that ordinary sedimentation is not possible. It is necessary, therefore, to use procedure which agglomerates the small particles in to larger aggregates, which have practical settling velocities.

The term “coagulation” and “flocculation” have been used indiscriminately to describe process of turbidity removal. “Coagulation” means to bring together the suspended particles. The process describes the effect produced by the addition of a chemical ALg (SP^)g to a colloidal dispersion resulting in particle destabilization by a reduction of force tending to keep particles apart. Rapid mixing is important at this stage to obtain uniform dispersion of the chemical and to increase opportunity for particles to particle contact. This operation is done by flash mixer in the clariflocculator. Second stage of formation of settle able particles from destabilized colloidal sized particles is termed a “flocculation”. Here coagulated particles grow in size by attaching to each other. In contrast to coagulation where thr primary force is electrostatic or inter-ionic. “Flocculation” occurs by chemical bridging. Flocculation is obtained by gentle and prolonged mixing which converts the submicroscopic coagulated particle in to discete, visible and suspended particles. At this stage particles are large enough to settle rapidly under the influence of

gravity and may be removed. If pretreatment of the water is not done efficiently then consequences are as follows:

SiOg may escape with water which will increase the anion loading.

Organic matter may escape which may cause organic fouling in the anion exchanger beds. In the pre-treatment plant chlorine addition provision is normally made to combat organic contamination.

Cation loading may unnecessary increase due to addition of Ca(OH)g in excess of calculated amount for raising the pH of water for maximum floe formation and also AKOrDg may precipitate out. If less than calculated amount of Ca(OH), is added ,proper pH flocculation will not be obtained and silica escape to demineralization section will occur, thereby increasing load on anion bed.

DEMINERALISATION:This filter water is now used for demineralising purpose and is fed to cation exchanger bed, but enroute being first dechlorinated, which is either done by passing through activated carbon filter or injecting along the flow of water, an equivalent amount of sodium sulphite through some stroke pumps. The residual chlorine which is maintained in clarification plant to remove organic

matter from raw water is now detrimental to cation resin and must be eliminated before its entry to this bed.

Normally, the typical scheme of demineralization upto the mark against average surface water is three bed systems with a provision of removing gaseous carbon dioxide from water before feeding to anion exchanger. Now, let us see, what happens actually in each bed when water is passed from one to another.

Resins, which are built on synthetic matrix of a styrene divinely benzene copolymer, are manufactured in such a way that these have the ability to exchange one ion for another, hold it temporarily in chemical combination and give it to a strong electrolytic solution. Suitable treatment is given to them in such a way that a particular resin absorbs only a particular group of ions. Resins when absorbing and releasing cationic portion of dissolved salts, is called cation exchanger resin and when removing anionic portion is called anion exchanger resin.

The present trend is of employing strongly acidic exchanger resin and strongly basic anion exchanger resin in a DM plant of modern thermal power plant. We may see that the chemically active group in a cationic resin Sox-H (normally represented by RH) and in an anionic resin the active group is either tertiary amine or quaternary ammonium group (normally the resin is represented by ROH). The reaction of exchange may be further represented as below:

CATION RESIN:

RH + Na R Na +H2SO4

K K HCl

Ca CaHNO3

Mg Mg

ANION RESIN:

ROH + H2SO4 RSO4 + H2O

HCl Cl

HNO3 NO3

Recharging the exhausted form of resins i.e. regeneration employing 5% of acid / alkali as below:

CATION RESIN:

R K + H Cl R H + NaCl

K K Cl2

Ca Ca Cl2

Mg Cl2

ANION RESIN:

R SO4 + NaOH ROH + Na2SO4

Cl NaCl

NO3 Na NO3

As seen above the water from the ex-cation contains carbonic acid also sufficiently, which is very weak acid difficult to be removed by strongly basic anion resin and causing hindrance to remove silicate ions from the bed. It is therefore a usual practice to remove carbonic acid before it is led to anion exchanger bed. The ex-cation water is trickled in fine streams from top of a tall tower packed with ranching rings and compressed air is passed from the bottom. Carbonic acid break into CO^ and water mechanically (Henry’s law) with the carbon dioxide escaping in to the atmosphere. The water is accumulated in suitable storage tank below the tower, called degassed water dump, from where the same is led to anion exchanger bed, using acid resistant pump.

The ex-anion water is fed to the mixed bed exchanger containing both cationic resin and anionic resin. This bed not only takes care of sodium slip from cation but also silica slip from anion exchanger very effectively. The final output from the mixed bed is extra- ordinarily pure water having less than 0.2 /mho conductivity, H 7.0 and silica contest less than 0.02 ppm. Any deviation from the above quality means that the resins in mixed bed are exhausted and need regeneration, regeneration of mixed bed first calls for suitable back washing and settling, so that the two types of resins are separated from each other. Lighter anion resin rises to the top and the heavier cation resin settles to the bottom. Both the resins are then

regenerated separately with alkali and acid, rinsed to the desired value and air mixed, to mix the resin again thoroughly. It is then put to final rinsing till the desired quality is obtained.

It may be mentioned here that there are two types of strongly basic anion exchanger. Type ll resins are slightly less basic than Type l, but have higher regeneration efficiency than Type l. again as Type ll resins are unable to remove silica effectively, Type l resins also have to be used for the purpose. As such, the general condition so far prevailing in India is to employ Type ll resin in anion exchanger’s bed and Type l resin in mixed bed. It is also a general convention to regenerate the above two resins under through fare system i.e. the caustic soda entering in to mixed bed for regeneration, of Type l anion resin, is utilized to regenerate Type ll resin in cation exchanger bed. The concept of utilizing the above resin and mode of regeneration is now a days being switched over from the economy to a more higher cost so as to have more stringent quqlity control of the final demineralized water.