1

"Success seems to be largely a matter of hanging on after others have let go." - 
William Feather

2

"Failure is only the opportunity to begin again more intelligently." - Henry Ford

3

"If you have no critics, you'll likely have no success." - Malcolm Forbes

4

"In the middle of difficulty, lies opportunity." - Albert Einstein

5

"If you want to be successful, it's just this simple: Know what you are doing, love what you are doing, and believe in what you are doing." - Will Rogers

181

Water ingress into the turbine lube oil is a common problem. Water presence could lead to bacterial and fungal contamination in the oil systems. This contamination appears as a yellow or black material similar to grease. This growth occurs in sediment in the oil system. It is very difficult to remove it from the system. Hence the following precautions are required to be taken:

v  Minimizing the water content in the oil by using an oil purification system. The concentration of water in the oil should be maintained at less than 0.05%.

v  Removing the sludge from the sumps of the oil system regularly.

v  If bacterial or fungal growth occurs, a correct amount of biocide should be added to kill it.

182

What is the function of a turbine gland sealing system?

The two functions of the turbine glands and seals are:

1. To prevent or reduce steam leakage between the rotating and stationary components of the turbines, if the steam pressure is higher than atmospheric.

2. To prevent or reduce air ingress between the rotating and stationary components of the turbines, if the steam pressure is less than atmospheric. The last few stages in the low pressure (LP) turbines are normally under vacuum.

A power loss is associated with steam leakage or air ingress. Thus, the design of glands and seals is optimized to reduce any leakage.

Steam turbines use labyrinth glands to restrict steam and air leakage.

183

Explain the working principle of a labyrinth seal?

Labyrinth seal consists of a ring having a series of machined fins.

The fins form a number of fine annular restrictions. An expansion chamber follows each restriction.

When the steam enters a restriction, the velocity increases and the pressure decreases (conversion of pressure energy into kinetic energy—the first law of thermodynamics).

When the steam enters the expansion chamber, the kinetic energy is converted by turbulence into heat. The pressure is not recovered.

The pressure is progressively reduced when the steam goes through successive restrictions.

The finned ring and the shaft are usually stepped to enhance the conversion of energy.

184

What are the types of Labyrinth seals?

Few types of labyrinth seals are:

a.    Plain labyrinth seal

b.    Stepped labyrinth seal

c.    Double stepped labyrinth seal, and

d.    Vernier labyrinth seal

Few other types of labyrinth seals are:

a.    Axial radial labyrinth seal, and

b.    Spring back labyrinth seal

184

The gland rings are normally made of four or more segments. The gland sealing system supplies steam to seal the turbine shaft glands under all operating conditions. It also extracts leak off steam from the glands.

185

Explain the steam turbine gland sealing system in detail?

The gland sealing system is normally divided into two parts.

One part supplies steam to the glands of the high-pressure (HP) and intermediate-pressure (IP) turbines. The second supplies steam to the glands of the LP turbine.

This is done to accommodate the range of temperatures experienced throughout the turbine.

The gland sealing system has two modes of operation.

The first supplies steam at the outlet conditions of the superheater. This is known as live steam. It is used during start-up, shutdown, and when the unit is operating at low loads.

The second mode of operation involves taking steam from the HP and IP turbine and using it to seal the glands of the LP turbine during normal power operation.

The use of steam from the HP and IP turbines rather than live steam results in increased efficiency.

The changeover from one source of steam to the other is entirely automatic.

A desuperheater is used to lower the temperature of the steam supplied to the glands.

An HP desuperheater controls the temperature of the steam supplied to the glands of HP and IP turbines.

An LP desuperheater controls the temperature of the steam supplied to the glands of the LP turbines.

The glands are normally divided into sections. After each section, the steam is fed back to an appropriate stage in the turbine or to a gland steam condenser.

Thus, energy is returned to the cycle to improve the efficiency.

The HP leak-off steam is normally connected to the IP turbine. Its pressure is maintained at the IP exhaust pressure.

The steam pressure at the packing leak-off point is normally maintained slightly above atmosphere. The steam taken from the leak-off is normally used to seal the gland of the LP turbine.

Since the steam is moving outward in the gland, it prevents air ingress into the turbine and condenser.

At higher loads, the glands of the HP/IP turbines are self-sealing. Excess steam from these glands enters the LP desuperheater to seal the glands of the LP turbines.

Two strainers are used to prevent impurities from entering the glands. The first is used for the HP/IP system. The second is used for the LP system. These strainers are installed after the desuperheater.

186

Explain the concept of reversibility in a thermodynamic process?

Mr. Sadi Carnot introduced the concept of reversibility and laid the foundations for the second law of thermodynamics.

A reversible process, also called an ideal process, can reverse itself exactly by following the same path it took in the first place. Thus, it restores to the system or the surroundings the same heat and work previously exchanged.

In reality, there are no ideal (reversible) processes. i.e. all real processes are irreversible.

However, the degree of irreversibility varies between processes.

There are many sources of irreversibility in nature. The most important ones are friction, heat transfer, throttling, and mixing.

Mechanical friction is one in which mechanical work is dissipated into a heating effect. One example would be a shaft rotating in a bearing. It is not possible to add the same heat to the bearing to cause rotation of the shaft.

An example of fluid friction is when the fluid expands through the turbine, undergoing internal friction. This friction results in the dissipation of part of its energy into heating itself at the expense of useful work. The fluid then does less work and exhausts at a higher temperature.

The more irreversible the process, the more heating effect and the less the work.

Heat transfer in any form cannot reverse itself.

Heat transfer causes a loss of availability because no work is done between the high and low-temperature bodies.

187

What are external and internal irreversibility?

External irreversibility are those that occur across the boundaries of the system. The primary source of external irreversibility in power systems is heat transfer both at the high and low-temperature ends.

Internal irreversibility are those that occur within the boundaries of the system. The primary source of internal irreversibility in power systems is fluid friction in rotary machines, such as turbines, compressors, and pumps.

188

What do you mean by the term ‘cogeneration’?

Cogeneration is the simultaneous generation of electricity and steam (or heat) in a power plant.

Cogeneration is recommended for process industries where steam is also required in addition to electric power, as it can produce electricity more cheaply and more conveniently than a utility.

A Cogeneration plant ensures that the total energy needs (heat and electricity) of the industry are met from within.

189

What are the two main categories of cogeneration cycle?

The two main categories of cogeneration are (1) the topping cycle and (2) the bottoming cycle.

The Topping Cycle:

In this cycle, the primary heat source is used to generate high-enthalpy steam and electricity.

Depending on process requirements, process steam at low enthalpy is taken from any of the following:

v  Extracted from the turbine at an intermediate stage (like feed water heating).

v  Taken from the turbine exhaust. The turbine in this case is called a back-pressure turbine.

Process steam requirements vary widely, between 0.5 and 40 bar.

The Bottoming Cycle:

In this cycle, the primary heat (high enthalpy) is used directly for process requirements [e.g., for a high-temperature cement kiln/ furnace].

The low-enthalpy waste heat is then used to generate electricity at low efficiency.

This cycle has lower combined efficiency than the topping cycle. Thus, it is not very common. Only the topping cycle can provide true savings in primary energy.

190

How is steam energy converted into mechanical work in a steam turbine?

In a steam turbine, high-enthalpy (high pressure and temperature) steam is expanded in the nozzles (stationary blades), where the kinetic energy is increased at the expense of pressure energy (increase in velocity due to decrease in pressure).

The kinetic energy (high velocity) is converted into mechanical energy (rotation of a shaft - increase of torque or speed) by impulse and reaction principles.

1

"Wherever you see a successful business, someone once made a courageous  decision." - Peter F. Drucker

2

"Man is what he believes." - Anton Chekhov

3

"Perseverance is a great element of success." - Henry Wadsworth Longfellow

4

"We are continually faced by great opportunities brilliantly disguised as insoluble problems." - Lee Iococca

5

"What the mind can conceive and believe, the mind can achieve." - Napoleon Hill

1

"The successful person places more attention on doing the right thing rather than

doing things right." - Peter Drucker

2

"The first step towards success in any occupation is to become interested in it." -

Sir William Osler

3

"I have failed over and over again - that is why I succeed." - Michael Jordan

4

"Only those who dare to fail greatly can ever achieve greatly." - Robert F.Kennedy

5

"Do not let what you cannot do interfere with what you can do." - John Wooden

1

"First, say to yourself what you would be, then do what you have to do." - Epictetus

2

"Our lives improve only when we take chances, and the first and most difficult risk we can take is to be honest with ourselves." - Walter Anderson

3

"The secret of success is learning how to use pain and pleasure instead of having pain and pleasure use you. If you do that, you're in control of your life. If you don't, life controls you." - Anthony Robbins

4

"I don't dream at night, I dream all day. I dream for a living." - Steven Spielberg

5

"Hope is the companion of power and the mother of success. For those of us who hope strongest have within us the gift of miracles." - Sydney Bremer

1

"To be a champion, you have to believe in yourself when nobody else will." - 
Sugar Ray Robinson

2

"The real secret to success is enthusiasm." - Walter Chrysler

3

"The future belongs to those who believe in the beauty of their dreams." -

Eleanor Roosevelt

4

"Often the difference between a successful man and a failure is not one's better abilities or ideas, but the courage that one has to bet on his ideas, to take a calculated risk and to act." - Maxwell Maltz

5

"He who has never failed somewhere, that man cannot be great." - Herman Melville

"If you envy successful people, you create a negative force field of attraction that repels you from ever doing the things that you need to do to be successful. If you admire successful people, you create a positive force field of attraction that draws you toward becoming more and more like the kinds of people that you want to be like." - Brian Tracy

1

"An aim in life is the only fortune worth finding, and it is not to be found in foreign lands, but in the heart itself." - Robert Louis Stevenson

2

"You see things and say, 'Why?' But I dream of things that never were and say 'Why not?'" - George Bernard Shaw

3

"A problem is a chance for you to do your best." - Duke Ellington

4

"If you can dream it, you can do it. Your limits are all within yourself." - Brian Tracy

5

"Success demands singleness of purpose." - Vince Lombardi

1

"Success is like a ladder and no one has ever climbed a ladder with their hands in their pockets." - Zig Ziglar

2

"Nothing can stop the man with the right mental attitude from achieving his goal. Nothing on earth can help the man with the wrong mental attitude." - E. Joseph Cossman

3

"I can accept failure but I can't accept not trying." - Michael Jordan

4

"Yesterday I dared to struggle. Today I dare to win." - Bernadette Devlin

5

"It is in your moments of decision that your destiny is shaped." - Anthony Robbins

171

What is the function of Oxidation inhibitors in turbine lube oil?

Oxidation inhibitor stabilizes the rate of oxidation.

It also passivates the metals that act catalytically to increase the rate of oxidation.

Oxidation inhibitors maintain low acidity (neutralization number) in the oil for many years.

172

What is the function of Rust inhibitors in turbine lube oil?

Rust inhibitors protects the carbon-steel surfaces from rusting, when they come in contact with water entrained with the oil.

173

Detergent additives in a lube oil, reduces the rate of high-temperature oxidation, formation of sludge at low temperature, and deposition of contaminants.

174

Viscosity index improvers in a lube oil, reduces the decrease in viscosity with increase in temperature.

175

Antifoaming agents in lube oil, suppresses foaming of aerated oil. They also assist in the release of air from the oil.

176

Explain in brief the principle of operation of a lube oil centrifuge?

An oil centrifuge operates based on the principle that if a mixture is centrifuged, the fluids settle out radially with the fluid having the highest specific gravity outermost.

Dirty oil from the main oil tank is delivered to the purifier.

It passes through a regenerative heater/cooler. It is heated to 75°C. This is the best temperature for centrifugal separation. The oil enters the separator bowl.

Centrifugal force separates the mixture into its different densities.

The clean oil is collected by inverted cones. It is delivered to the clean-oil outlet.

The water and acids are discharged from the separator. The solids accumulate at the bottom of the bowl and are discharged regularly.

The clean hot oil is then returned back to the main oil tank.

The oil flow rate through the purifier is around 10 percent of the total oil inventory per hour.

177

Define Economics?

Economics is the social science that seeks to describe the factors which determine the production, distribution and consumption of goods and services.

178

What is ‘engineering economics’?

Engineering economics, is a subset of economics for application to engineering projects.

Engineers seek solutions to problems, and the economic viability of each potential solution is normally considered along with the technical aspects.

Engineering economics involves formulating, estimating, and evaluating the economic outcomes when alternatives to accomplish a defined purpose are available.

Major areas in engineering economics are:

v  The economics of the management, operation, and growth and profitability of engineering firms;

v  Macro-level engineering economic trends and issues;

v  Engineering product markets and demand influences; and

v  The development, marketing, and financing of new engineering technologies and products.

179

What is Heat transfer & what are the fundamental modes of heat transfer?

Heat transfer describes the exchange of thermal energy, between physical systems depending on the temperature and pressure, by dissipating heat.

The fundamental modes of heat transfer are conduction, convection and radiation.

180

During operation, the total acidity of the turbine lube oil increases. This is caused by the fact that oil oxidizes to organic acids. Thus, the level of acidity in the oil is a good indicator about the condition of the oil. Its need for purification and conditioning will be based on the level of acidity.

1

"Human beings can alter their lives by altering their attitudes of mind." - William James

2

"A man can succeed at almost anything for which he has unlimited enthusiasm." - Charles Schwab

3

"Only those who will risk going too far can possibly find out how far they can go." - T.S. Eliot

4

"Losers visualize the penalties of failure. Winners visualize the rewards of success." - Rob Gilbert

5

"When I was young I observed that nine out of ten things I did were failures, so I did ten times more work." - Bernard Shaw

161

What are the objectives of turbine bearing lubrication?

The objectives of bearing lubrication are as follows:

v To provide a hydrodynamic oil wedge between the bearing and the shaft, to reduce friction.

v To provide an oil flow to maintain the white metal (Babbitt metal) of the bearing below 110°C.

162

What are the sources of heat inside a turbine bearing?

The sources of heat inside the bearing are:

a. Thermal conduction

b. Friction between the oil film, the journal (portion of the shaft inside the bearing), and the white metal of the bearing

c. Turbulence within the oil itself

163

What are Disaster Management Plans (DMPs)?

Planning the response strategies, for meeting the emergencies caused by major accidents/ disasters, prior to their occurrence, are termed as Disaster Management Plans (DMPs).

Disaster Management Plans (DMPs) if put to practice, can reduce vulnerability to hazards and allow the plant workers to cope up with disasters effectively.

DMPs cannot be considered in isolation or act as a substitute for maintaining good safety standards in a plant. The best way to protect against major accidents occurrence is by maintaining very high levels of safety standards.

DMPs does not avert or eliminate the threats, instead it focuses on creating plans to decrease the impact of disasters. Failure to create a plan could lead to damage to assets, human mortality, and lost revenue.

164

What are the five phases generally involved in case of an emergency?

Generally, the following five phases are involved in an emergency:

v  Discovery and Notification: An event with an imminent threat of turning into an accident must first be discovered and the discoverer quickly notifies the same to the plant safety officer.

 

v  Evaluation and Accident Control Initiation: Based on the evaluation of available information, the safety officer makes a rapid assessment of the severity of the likely accident and initiates the best course of action.

 

v  Containment and Counter Measures: Action is first taken to contain and control the accident by eliminating the causes which may lead to the spread of accident. Measures are also taken to minimize the damage to personnel, property and environment.

 

v  Cleanup and Disposal: After the accident is effectively contained and controlled, the cleanup of the site of the accident and safe disposal of waste generated due to the accident are undertaken.

 

v  Documentation: All aspects of accidents, including the way it started and progressed as well as the steps taken to contain and the extent of the damage and injury, are documented for subsequent analysis of accident for prevention in future, damage estimation, insurance recovery and compensation payment.

165

What determines the level of emergency/ disaster?

Severity of accident and its likely impact area will determine the level of emergency and the disaster management plan required for appropriate handling of an emergency.

166

What are the different levels of fire emergency and explain in brief the action needed for each level of emergency?

Emergency levels and the action needed for each level are explained below:

Level 1 Emergency

A local accident with a likely impact only to immediate surroundings of accident site, such as, local fires and limited release of inflammable material.

The impact distance may not be more than 15 m from the site of primary accident and may require evacuation of the building/area where accident occurred and utmost the adjacent building/area.

Level 2 Emergency

A major accident with potential threats to life and property up to 500 m distance requiring the evacuation of all personnel from the threatened area except the emergency response personnel. Larger fires, release of large quantities of inflammable materials belongs to emergency level 2.

Level 3 Emergency

An accident involving a very serious hazard and with likely impact area extending beyond 500 m from the operational area, such as, major fire, very large release of inflammable material. Major fires will usually have the triggering effect resulting in the propagation of explosion. In a level 3 emergency, evacuation of population in villages, if any, adjoining the operational area may sometime become necessary if threatened area extend to populated village area adjoining the site of the primary accident in a direction of maximum impact.

167

What are the special design features considered for piping used in jacking oil and lubricating oil systems against oil leakage and fire hazards?

Special design precautions against oil leakage and fire hazards are taken for piping used in jacking oil and lubricating oil systems.

The oil piping is sized to have a velocity only between 1 and 5 m/s.

An enclosure or a duct is installed around the oil piping at the pump discharge.

The number of pipe joints is minimized by maximizing the length of pipe runs.

All pipe joints are welded class 1 type.

At the exit from the ducted area, a protective pipe is installed around the pressure oil pipe. This is done to contain and detect any oil leakage.

The piping between the pump and the filters is made of mild steel, and stainless-steel piping after the filters to minimize corrosion.

If the air is not vented through the bearings, an automatic air venting of the piping from its highest points to the oil tank is installed.

Air vents to the oil tank are installed on the oil filters. They vent any air that accumulates during operation or maintenance to the oil tank.

168

What is the function of lube oil coolers in the turbine lube oil system, and explain in brief the design features of lube oil coolers?

The function of lube oil coolers (heat exchangers) is to lower the temperature of the oil leaving the turbine bearings, below the acceptable limit.

Redundant coolers are provided to allow maintenance to be performed while the unit is operating.

The normal arrangements are 3 X 50% or 2 X 100% coolers.

The oil coolers are installed vertically.

The water flows through the tube in a two-pass arrangement.

The oil flows on the shell side of the coolers through a series of baffles.

The shells of the coolers are generally made of mild steel and the tubes of titanium.

The tube bundle has a floating tube plate to accommodate thermal expansion.

The heat dissipated by each cooler is around 2 MW.

The oil filters are integral with the cooler shell on some units. An automatic bypass of the oil coolers is normally installed. It allows the oil to bypass the cooler upon an excessive pressure drop across the cooler.

The automatic control system is based on the oil outlet temperature.

169

The steam leaking from the turbine glands represents the main source of contamination for the lubricating oil.

The steam condenses when it comes in contact with the bearing housing. The condensate becomes dispersed through the oil.

The used oil normally contains wear particles, oxides, soluble acids, and sludge. These impurities must be removed from the oil to extend its life and maintain adequate lubrication.

The on-line systems used to these remove impurities include centrifugal separation systems and static oil purifiers.

170

What are the functions of lube oil used in a steam turbine?

The oils used for steam turbines must provide the following functions:

v  Removal of heat generated in the bearing housing

v  Removal of impurities from the bearings

v  Minimization of corrosion and oxidation

The lube oil contains additives for the prevention of oxidation, corrosion, and foaming.

1

"If you don't know where you are going, every road will get you nowhere." - Henry Kissinger

2

"You must have long range goals to keep from being frustrated by short-term failures." - Bob Bales

3

"I would rather attempt something great and fail than attempt to do nothing and succeed." - Robert Schuller

4

"Singleness of purpose is one of the chief essentials for success in life, no matter what may be one's aim." - John D. Rockefeller

5

"A leader has the vision and conviction that a dream can be achieved. He inspired the power and energy to get it done." - Ralph Lauren

151

Water can enter the turbine due to backflow of condensate/ feed water from feed heaters. This can occur upon a load rejection. In this case, the pressure inside the turbines drops to a lower value than the one in the feed heaters. Hence, Check valves (NRVs) are installed on the extraction lines to the feed heaters to prevent this reverse flow.

152

Write short notes on the history and nature of coal?

Coal is a product of nature and time, derived from the decay of ancient trees, bushes, ferns, mosses, vines, and other forms of plant life that flourished millions of years ago in humid, tropical climates.

Time, coupled with pressure, heat, and chemical and bacterial decay, has transformed the plant remains into coal.

ASTM D 388 establishes categories or ranks of coal on the basis of measurable properties that relate to its metamorphism or its degree of transformation while buried.

Coal is heterogeneous. Unlike natural gas or fuel oil, composition or quality of coal can vary significantly depending on the degree of metamorphosis, type of vegetation, location in seam, surrounding materials, etc.

153

What do you mean by a turbine trip?

A turbine trip closes the turbine steam valves and opens the generator circuit breaker.

154

Write short notes on Turbine Over speed trip?

The over speed trip is initiated when the governing system fails to limit the speed rise of the turbine shaft.

It is the final line of defense to prevent a catastrophic failure of the turbine.

Turbine over speed can occur following a load rejection (when the unit becomes disconnected from the grid). It can also occur when the unit is operating in the islanding (unsynchronized) mode. If the governing system fails, higher steam flow can enter the turbine, leading to over speed.

If the over speed becomes excessive (approaching 100 percent), the centrifugal forces acting on the rotating parts become extremely high. The blades will start to rupture and penetrate through the casing.

The manufacturer normally performs an over speed test at 120 percent of the speed. This speed is significantly lower than the design limit at which blade rupture could occur (180 to 200 percent over speed).

The over speed trip is normally set in the range from 110 to 112.5 percent speed.

155

What are the six categories of turbine instrumentation?

The six categories of turbine instrumentation are:

v Supervisory instrumentation

v Efficiency instrumentation

v Auxiliary system instrumentation

v Condition-monitoring instrumentation

v Instrumentation associated with protection and control equipment

v Instrumentation to provide post-incident records

156

What are supervisory instruments?

The supervisory instruments are required continuously to determine the condition of the main rotating and stationary components.

157

Explain the main functions of turbo supervisory instruments in detail.

The main functions of supervisory instruments include the following:

1. To ensure safe operation of the turbine generator within acceptable limits.

2. To provide advanced warning of deterioration in the performance of the turbine generator.

The parameters measured includes the following:

a. Rotor axial position: These measurements provide the relative axial movement of the rotor. They are used to ensure that clearance margins are maintained under all operating conditions.

b. Cylinder expansions: These measurements provide the relative radial movement between the rotors and the stators. They are used to ensure that radial clearance margins are maintained under all operating conditions.

c. Bearing pedestal vibrations: These measurements are taken at each bearing. They continuously monitor the dynamic behavior of the machine.

d. Shaft eccentricity: The radial excursion of the rotor relative to the stationary parts is measured on each rotor. This is done to indicate abnormal or unsafe conditions.

e. Shaft speed: The shaft speed is measured independently of the turbine governor. This measurement is used for operator reference. It is mainly used during run-up.

f. Steam valve positions: The position of each steam valve is measured. These measurements are used as a general reference for the operator. They are used to determine if the load can be increased or for diagnostic purposes.

g. Metal temperature measurement: The temperature of the turbines is measured during normal operation and transient states. The instruments are located in the high pressure (HP) and interceptor steam valve chests, and in the cylinders of the HP and intermediate-pressure (IP) turbines.

h. Thrust bearing wear: These measurements are taken to ensure that the wear of the thrust pads is within acceptable limits. If the wear is higher than the acceptable limit, the turbine generator rotor will move with respect to the stator. This could have disastrous consequences on the machine.

All of the above measured turbo supervisory parameters are displayed continuously for the operator to initiate appropriate action.

158

The turbine bearings must be lubricated to prevent damage that is caused by wear or increased temperatures.

159

It is necessary to lift the turbine generator shaft before starting to turn the shaft. The jacking oil system is used to perform this function.

160

What is a Babbitt metal?

Babbitt metal is an alloy of tin with some copper and antimony.

Babbitt metal is used as a lining material for bearings to reduce friction.