Continuation to the Technical Q&A posted on 28th March 2015
 
36

 

What is spontaneous combustion or spontaneous ignition?

Spontaneous combustion or spontaneous ignition is a type of combustion which occurs by:

a)  Self-heating (increase in temperature due to exothermic internal reactions), followed by

b)  Thermal runaway (self-heating which rapidly accelerates to high temperatures) and finally,

c)   Ignition.
 

The same can be explained as follows:

 

1.    A substance with a relatively low ignition temperature begins to release heat.

2.    This may occur in several ways, usually oxidation by a little moisture and air, generates heat.

3.    The heat is unable to escape and the temperature of the material rises.

4.    The temperature of the material rises above its ignition point.

5.    Combustion begins if sufficient oxidizer, such as oxygen, and fuel are present to maintain the reaction into thermal run-away.
 

37

 

What is weathering of coal?
 

The chemical  and  physical  properties of coal  can  often undergo  substantial  changes  after  removal  of  the  coal from  its natural  environment or mines.  This phenomenon is known as weathering of coal.
 

Weathering  commences  once  the  coal  is unearthed  and/or  removed  from  the coal seam  unless precautions  are  taken  to prevent  its exposure  to  oxygen  (air)  and changes  in  temperature  and  humidity.
 

Subsequent  reaction  with  oxygen  in air  is  recognized  as  the most  important contributor  to weathering. 
 

The  reaction  of  the coal with  oxygen  occurs readily  at  ambient  temperature,  results  primarily  in oxidation  of  the coal's organic  constituents,  and  leads  to an  increase  in  the  oxygen  content  and  a decrease  in  the  atomic  hydrogen-to-carbon  ratio  of  the coal.
 

Weathering of coal can alter  the  coal's  calorific  value,  beneficiation,  coking,  liquefaction,  and gasification  characteristics. 
  

38

What are all various areas in a power plant where corrosion is being encountered?

v  Waterside/ steam side corrosion of boiler tubes

v  Turbine CF and SCC

v  Oxide particle erosion of turbine

v  Heat exchanger corrosion

v  Fire side corrosion of water wall tubes

v  Generator clip to strand corrosion

v  Copper deposition in turbines

v  Fireside corrosion of SH & RH tubes

v  Corrosion of FGD system

v  Liquid slag corrosion of cyclone boilers

v  Backend dew point corrosion

v  Generator cooling water clogging and purging

v  FAC of steam plant piping

v  Corrosion of service water, circulating water and other water systems

v  Corrosion of structures

v  Corrosion of CHP & AHP equipment, Oil pipes and tanks, electrical equipment etc.

39

What are the various possible sources of water for a thermal power station?

v  River

v  Sea

v  Ponds

v  Lakes

v  Irrigation canals

v  Bore wells

v  Recycled water

v  Reservoirs

v  Recycled effluents

40

What are the various impurities present in water?

v  Bacteria and viruses

v  Other micro-organisms

v  Turbidity

v  Colour

v  Metals

v  Dissolved gases

v  Ammonia

v  Organic matter

v  Pollutants, etc.

41

Various uses of water in thermal power plants?

v  Circulating cooling water

v  Auxiliary cooling water

v  Steam Cycle makeup (DM water)

v  Water for AHP systems

v  Water for coal dust suppression

v  Washing – service water

v  Drinking – potable water

v  Sanitation – toilets

v  Fire water

v  Make up water for HVAC system

v  DM water for chemical preparation, etc.

42

What is the allowable levels of TSS in CW for splash and film fills?

TSS < 300 ppm for cooling tower using splash fills

TSS < 100 ppm for cooling tower using film fills

The above allowable levels are as per EPRI guidelines.

43

Define Maintenance?

Dictionary meaning for Maintenance: “The work of keeping something in proper condition; upkeep.”

Maintenance can be defined as, the action or a set of actions, taken to prevent a device or component from failing (or) to repair the equipment degradation experienced with the operation of the device, to keep it in proper working order. 

Maintenance is performed to keep equipment and systems running efficiently, for at least the design life of the component.

44

What is called a ‘bathtub’ curve in Maintenance?

It denotes the shape of the curve obtained, when the component failure rate of an equipment were to be plotted over time.

 

In the above figure, the Y axis represents the failure rate and the X axis the time. From its shape, the curve can be divided into three distinct periods: infant mortality, useful life, and wear-out periods. 

The initial infant mortality period of bathtub curve is characterized by high failure rate followed by a period of decreasing failure.  Many of the failures associated with this region are linked to poor design, poor installation, or misapplication and inadequate O&M practices in place.

The infant mortality period is followed by a nearly constant failure rate period known as useful life.

The wear-out period is characterized by a rapid increasing failure rate with time.

45

What is an Electrode?

An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit.

An electrode in an electrochemical cell is referred to as either an anode or a cathode.

An electrode may become either the anode or the cathode depending on the voltage applied to the cell.

A bipolar electrode is an electrode that functions as the anode of one cell and the cathode of another cell.

46

What is an Anode?

Anode is an electrode at which electrons leave the cell and where oxidation occurs.

47

What is a Cathode?

Cathode is an electrode at which electrons enter the cell and where reduction occurs.

48

List a few Interpersonal skills.

v  Leadership,

v  Team building,

v  Motivation,

v  Communication,

v  Influencing,

v  Decision making,

v  Political and cultural awareness,

v  Negotiation,

v  Trust building,

v  Conflict management, and

v  Coaching.

49

List a few Intrapersonal skills.

v  Ability to control unexpected emotions like anger and frustration

v  Knowing your own strengths and limitations

v  Self confidence

v  Initiative

v  Taking measured risks

v  Taking responsibility

v  The ability to stay calm and balanced in stressful situations

v  Persistence and perseverance in challenging situations

v  Resilience and ability to bounce back from setbacks

v  The ability to forgive and forget

50

What is an interpersonal skill?

Interpersonal: Existing or occurring between persons.

Interpersonal skills are the skills we use every day to communicate and interact with other people, both individually and in groups. 

Interpersonal skills are also sometimes referred to as: social skills, people skills, soft skills, communication skills or life skills.

People who have worked on developing strong interpersonal skills are usually more successful in both their professional and personal lives.

Employers often seek to hire staff with 'strong interpersonal skills' - they want people who will work well in a team and be able to communicate effectively with colleagues, customers and clients.