crazy engineering: Project on Power Generation Technology in Steam Turbine

A MINI PROJECT ON

STUDY OF POWER GENERATION TECHNOLOGY

IN STEAM TURBINE

A Project Report submitted in the partial fulfillment

Of project based training

V.NAVEEN KUMAR 09A05A0301

Under the esteemed guidance of

B.Gindal Dy GM (ST)

BHEL, HYDERABAD

CONTENTS

1. Abstract

2. Acknowledgement

3. Introduction to BHEL

4. Power generation

4.1 Working principle of steam turbine

5. Thermodynamics of steam turbine

5.1 T-S diagram for steam

6. Classification of steam turbine

6.1 Impulse turbine

6.2 Simple impulse steam turbine

6.3 Reaction turbine

6.4 Simple reaction steam turbine

6.5 Turbine blades

7. Methods of reducing rotor speed

7.1 Velocity compounding

7.2 Pressure compounding

7.3 Pressure-velocity compounding

8. Parts of steam turbine

8.1 Operating and maintenance

8.2 Supply and exhaust conditions

8.3 Advantages and disadvantages of steam turbine

9. Applications of steam turbine

ABSTRACT

Steam turbine is an excellent prime mover to convert heat energy of steam to mechanical energy. Of all heat engines and prime movers the steam turbine is nearest to the ideal and it is widely used in power plants and in all industries where power is needed for process.

In power generation mostly steam turbine is used 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.

Rotor is the heart of the steam turbine and it affects the efficiency of the steam turbine. In this project we have mainly discussed about the working process of a steam turbine. The thermal efficiency of a steam turbine is much higher than that of a steam engine.

ACKNOWLEDGEMENT

We are very thankful to BHEL Ramachandrapuram Unit for permitting and providing all the requisite facilities to carry out this project in the Technology department.

We are extremely grateful to our onsite project guide Sri K.K.NANDA (Dy.General Manager, TOOL ROOM) for his valuable guidance in our project.

We convey our heart full thanks to Sri K. Ajay Kumar (Engineer, Technology/T&C) who was responsible for the entire project to happen.

We would like to thank our Head of the Department K.P.SIREESHA for his full- fledged encouragement in our project.

INTRODUCTION TO BHEL

Bharat Heavy Electricals Limited (BHEL) is the largest Engineering and Manufacturing Enterprise in India in the energy related and infrastructure sector today. BHEL is one of the “NAVARATNA” Companies in India, which has played a leading role in the development of Power Generation and Transmission and is poised to help the country achieve its targeted generation capacity of two lakh megawatts by the end of 11^th plan. In 2010-11, BHEL has amassed the provisional turnover of Rs 43,451 Crs. with an outstanding Order Book of more than Rs.1,64,130 Crs. It has presence in more than sixty countries spanning all the six continents of the world.

The beginning of BHEL can be traced to its roots in the Planning Commission in Feb. 1947 when the Advisory Board of the Commission recommended the need to set up indigenous power equipment manufacturing plant. With the establishment of Heavy Electricals (India) Limited at Bhopal in 1956 under the collaboration of AEI (UK), India laid its foundation for self sufficiency in production of Heavy Electrical Equipments. In the next five years, three more plants were started by Govt. of India at Tiruchy, Hyderabad and Haridwar under a different company known as Bharat Heavy Electricals Limited. In pursuance of the recommendations of the action committee on Public Enterprises, the operations of all the four plants were integrated from July 1972. The BHEL Corporation was formed in January 1974 and HE(I)L, Bhopal was merged with BHEL.

Today BHEL has 15 manufacturing divisions, 4 Power Sector Regional Centres, 4 Overseas offices, 1 Subsidiary and over 100 project sites, service centers etc. BHEL caters to six major lines of business i.e. Power, Industry, Transmission, Transportation, Oil and Electronics. The company has the capabilities for executing power projects from concept to commissioning.

BHEL has acquired certifications to Quality Management Systems (ISO 9001), Environmental Management Systems (ISO 14001) and Occupational Health & Safety Management Systems (OHSAS 18001) and is also well on its journey towards Total Quality Management.

Product profile of BHEL:

1. Gas Turbines

2. Steam Turbines

3. Compressors

4. Turbo Generators

5. Heat Exchangers

6. Pumps

7. Pulverizes

8. Switch Gears

9. Oil Rings

Evolution and growth of BHEL Hyderabad unit:

The Hyderabad Unit of BHEL is located at Ramachandrapuram which is around 30KM from the historic city of Charminar. Foundation Stone of the Plant was laid in 1959 and the production commenced in the year 1965. The Unit was set up mainly to manufacture 60MW and 110MW Steam Turbo generator sets for State Electricity Boards and also 12 MW TG Sets.

From this small beginning, the Ramachandrapuram Unit has been growing steadily in different phases of development and today it caters to a wide spectrum of business in Power, Industry, Transmission, Oil and Gas.

BHEL –the largest Gas Turbine manufacturer in India, with the state-of-art facilities in all areas of Gas Turbine manufacture provide complete engineering in house for meeting specific customer requirement. With over 100 machines and cumulative fired hours of over four million hours. BHEL has supplied gas turbines for variety of applications in India and abroad. BHEL also has the world’s largest experience of firing highly volatile naphtha fuel on heavy duty gas turbines.

Specific features of BHEL:

1. Capability to fire a wide range of gaseous and liquid fuels and a mix of such

fuels ranging from clean fuels like natural gas. Distillate oil, naphtha.

2. Facilities like Black start, fast start and emergency start.

3. Suitable for power generation and mechanical drive applications. Models below

100MW suitable for 50Hz and 60Hz.

4. All machining equipment like generators, compressors etc manufactured in

house. Design of combustion system as per international emission

norms. Machines designed as per major international codes like API etc.

5. Suitable for IGCC applications.

6. Suitable for indoor and outdoor applications.

7. Use of water or steam injection for abatement of NOX emission sand power

Augmentation.

BHEL equipped with precision and sophisticated machine tools like CNC Broaching machine5 Axis Milling Machine and over speed vacuum balancing tunnel offers conversion, modification and up gradation services-through joint venture with Gefor all existing gas turbines. Services are also offered for all field support, retrofits and repairs, inspections and technical consultancy on “operation & maintenance of Gas Turbine Based Power Plants”.

Power generation

In power generation mostly steam turbine is used because of its greater thermal efficiency and high 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. Steam turbine has an ability to utilize high pressure and high temperature steam.

The power generation in a steam turbine is at a uniform rate, therefore necessity to use flywheel is not felt. Much higher speeds and greater range of speed is possible for a a steam turbine. No internal lubrication is required as there are no rubbing parts in the steam turbine. It can utilise high vacuum very advantageously.

Due to the above said salient features, of all heat engines and prime movers the steam turbine is nearest to the ideal and is widely used in power generation.

4.1Working principle of a steam turbine:

The steam turbine is essentially a flow machine in which heat energy in the steam is transferred into kinetic energy and its kinetic energy is utilised to rotate the rotor while steam flows through the turbine. During the flow of steam through the nozzle, the heat energy is converted into kinetic energy. The steam with high velocity enters the turbine blades and suffers a change in direction of motion which gives rise to change of momentum and therefore to a force. This constitutes the driving force of the turbine. This force acting on the blades in the circumferential direction sets up the rotation of the wheels or rotor. As the wheel rotates each one of the blades fixed on the rim of the wheel comes into action of the jet of steam which causes the wheel to rotate continuously.

5. THERMODYNAMICS OF STEAM TURBINE

The steam turbine operates on basic principles of thermodynamics using the part of the Rankin cycle. Superheated vapour (or dry saturated vapour, depending on application) enters the turbine, after it having exited the boiler, at high temperature and high pressure. The high heat/pressure steam is converted into kinetic energy using a nozzle (a fixed nozzle in an impulse type turbine or the fixed blades in a reaction type turbine).

Once the steam has exited the nozzle it is moving at high velocity and is sent to the blades of the turbine. A force is created on the blades due to the pressure of the vapour on the blades causing them to move. A generator or other such device can be placed on the shaft, and the energy that was in the vapour can now be stored and used. The gas exits the turbine as a saturated vapour (or liquid-vapour mix depending on application) at a lower temperature and pressure than it entered with and is sent to the condenser to be cooled. If we look at the first law we can find an equation comparing the rate at which work is developed per unit mass.

5.1 T-S diagram for steam

Rankine cycle with super heat

Process 1-2: The working fluid is pumped from low to high pressure.
Process 2-3: The high pressure liquid enters a boiler where it is heated at constant pressure by an external heat source to become a dry saturated vapour.

Process 3-3': The vapour is superheated.
Process 3-4 and 3'-4': The dry saturated vapour expands through a turbine, generating power. This decreases 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 condensed at a constant pressure to become a saturated liquid.

6.CLASSIFICATION OF STEAM TURBINES

There are several ways in which the steam turbines may be classified. The most important and common division being with respect to the action of the steam, as

Impulse turbine
.Reaction turbine
Combination of impulse and reaction turbine

Figure showing the difference between impulse and reaction turbine

6.1 IMPULSE TURBINE:

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 inlet pressure to the exit pressure (atmospheric pressure, or more usually, the condenser vacuum). Due to this 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 has 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".

The details of simple impulse turbine is shown in the below figure, it consists of set of nozzles and blade ring mounted on a rotor. Steam supplied from the boiler expands through the nozzle to the exit pressure. After the expansion it enters the blades at high velocity, and the blades are shaped such that steam glides over the blades without shock. Due to change in momentum, steam exerts an impulsive force on the blades. This provides driving torque on the rotor of the turbine.

In impulse turbine pressure drops only in the nozzles and remains constant over the moving blades, but velocity of steam decrease as the kinetic energy is absorbed by the moving blades.

6.2 SIMPLE IMPULSE STEAM TURBINE (DE-LAVAL TURBINE)

6.3 REACTION TURBINE:

In 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.

Reaction turbine consists of fixed blades followed by a ring of moving blades. The fixed blades acts as nozzle and allows a relatively small expansion of steam. Further expansion takes place in the moving blades. Thus in the reaction turbine, steam expands continuously and consequently, there is an increase in specific volume as the expansion proceeds, which is expanded by an increase in the size of blades.

As the steam expands through blades relative velocity increases and in the increase of relative velocity is achieved from the enthalpy drop. Due to increase in relative velocity a thrust or reaction force acts on the blades. This reaction force constitutes the driving force.

6.4 SIMPLE REACTION STEAM TURBINE (PARSON’S TURBINE

METHODS OF REDUCING ROTOR SPEED

The following methods are used to reduce the speed of an impulse turbine

1. Velocity compounding

2. Pressure compounding

3. Velocity-pressure compounding

7.1 Velocity compounding:

Steam is expanded through stationary nozzle from the boiler to condensor pressure.So the pressure in the nozzle drops, the kinetic energy of steam increases due to increase in velocity.This energy is absorbed by row of moving blades.The steam flows through fixed blades.The function of these blades is to re direct the steam flow without altering its velocity to the following next row of moving blades where again work is done on them.This method has the advantage of less initial cost, but its efficiency is low.

7.2 Pressure compounding:

Figure shows rings of fixed nozzles incorporated between the rings of moving blades.The steam at boiler pressure enters the first set of nozzles and expands partially.The kinetic energy is absorbed by moving blades.The steam then expands partially in second set of nozzles where pressure again falls and valocity increases,the KE is then absorbed by second ring of moving blades.This is repeated in stage 3 and stem finally leaves the turbine at low velocity and pressure.

7.3 Pressure-Velocity compounding:

This method of compoundin is the combination of two previously discussed methods.The total drop i steam pressure is divided into stages and velocity obtained in each stage is also compounded.The rings of nozzles are fixed at the beginning of each stage and pressure remains conststant during each stage.This method of compounding is used in curits and moore turbine.

PARTS OF STEAM TURBINE

Casing

2. Rotor

3. Casing sealing glands

4. Governor system

5. Oil ring lubrication system

6. Bearing case

7. Steam chest

8. Over speed trip system

Rotor is one of the critical parts of the steam turbine. All the expansion process is done on the rotor in steam turbine.

8.1 OPERATING AND MAINTENENCE

When warming up a steam turbine for use, the main stream 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 - that is, superheated steam with minimal liquid water content. If water gets into the steam and is blasted onto the blades (moisture carryover), rapid impingement and erosion of the blades can occur leading to imbalance and catastrophic failure. Also, water entering the blades will 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.

TYPES

Steam 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

8.2 Supply and exhaust conditions:

These types include condensing, no condensing, reheat, extraction and induction. No condensing or back pressure 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 feed water 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.

8.3Advantages of steam turbine include:

Ability to utilise high pressure and high temperatures
High efficiency.
High rotational speed
High capacity/weight ratio.
Smooth operation.
No internal lubrication.
Oil free exhaust system
Can be built in small or very large units ( upto to 1200 MW)

Disadvantages include:

For low speed application reduction gears are required.
Steam turbine cannot be made reversible.
Efficiency of small steam turbine is poor.

9.APPLICATIONS

To drive large centrifugal pumps, such as feed water pumps at a thermal power plant. A small industrial steam turbine (right) directly linked to a generator (left). This turbine generator set of 1910 produced 250 kW of electrical power. Electrical power stations use large steam turbines driving electric generators to produce most (about 80%) of the world's electricity. The advent of large steam turbines made central-station electricity generation practical, since reciprocating steam engines of large rating became very bulky, and operated at slow speeds. Most central stations are fossil fuel power plants and nuclear power plants; some installations use geothermal steam, or use concentrated solar power (CSP) to create the steam. Steam turbines can also be used directly

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 RPM for 50 Hz systems and 3600 RPM for 60 Hz systems. Since nuclear reactors have lower temperature limits than fossil-fired plants, with lower steam quality, the turbine generator sets may be arranged to operate at half these speeds, but with four-pole generators, to reduce erosion of turbine blades.

9.1 Marine propulsion

In ships, compelling advantages of steam turbines over reciprocating engines are smaller size, lower maintenance, lighter weight, and lower vibration. A steam turbine is only efficient when operating in the thousands of RPM, while the most effective propeller designs are for speeds less than 100 RPM; consequently, precise (thus expensive) reduction gears are usually required, although several ships, such as Turbine, had direct drive from the steam turbine to the propeller shafts. Another alternative is turbo-electric drive, where an electrical generator run by the high-speed turbine is used to run one or more slow-speed electric motors connected to the propeller shafts; precision gear cutting may be a production bottleneck during wartime. The purchase cost is offset by much lower fuel and maintenance requirements and the small size of a turbine when compared to a reciprocating engine having an equivalent power. However, diesel engines are capable of higher efficiencies: propulsion steam turbine cycle efficiencies have yet to break 50%, yet diesel engines routinely exceed 50%, especially in marine applications.

Nuclear-powered ships and submarines use a nuclear reactor to create steam. Nuclear power is often chosen where diesel power would be impractical (as in submarine applications) or the logistics of refuelling pose significant problems (for example, icebreakers). It has been estimated that the reactor fuel for the Royal Navy's Vanguard class submarine is sufficient to last 40 circumnavigations of the globe – potentially sufficient for the vessel's entire service life.

9.2 Locomotives

Main article: Steam turbine locomotive. A steam turbine locomotive engine is a steam locomotive driven by a steam turbine. The main advantages of a steam turbine locomotive are better rotational balance and reduced hammer blow on the track. However, a disadvantage is less flexible power output power so that turbine locomotives were best suited for long-haul operations at a constant output power.