Questions & Answers on Ash handling system

1.What is Ash?

Ash is the remaining product of solid or liquid fuel after burning

2.What are the various components of Ash?

Ash has following components

  • Silica (SiO2)
  • Alumina (AlO3)
  • Iron Oxide (Fe2O3)
  • Sodium Oxide (Na2O)
  • Potassium Oxide (K2O)
  • Calcium Oxide (CaO2)
  • Magnesia (MgO)

3.Which fuel has more ash Liquid, solid or Gaseous fuel?

Solid, Liquid & Gaseous fuels are having more ash consecutively

4.What are the various types of ash produced in Boilers?

Bottom ash & Fly ash are generated in Boilers

5.Which ash is more in quantity?

Generally Fly ash is more around 70-80% & bottom ash is around 20-30%

6.What do you mean by Fly ash?

Ash which is carried out by flue gas is called fly ash.

7.What can fly ash could cause in downstream system of The Boiler?

  • If ash is more, it creates following problems in downstream of the Boiler
  • Improper heat transfer in Super heaters, economizers & APH
  • Erosion of pressure parts & flue gas ducts
  • If there is low velocity, ash deposits in ducts, APH ESP etc

8.Which type of Ash removal is more dangerous & why?

  • Bottom ash removal is more dangerous, because;
  • Bottom Ash is at higher temperature
  • Ash is high Abrasive & Corrosive in Nature
  • When it comes in contact with water high hot fumes are formed
  • Risk of frequent clinker formation

9.What are the different devices or systems used to separate Fly ash from flue gas before letting it into atmosphere?

  • Electrostatic Precipitator
  • Bag filter (Fabric separators)
  • Wet scrubber
  • Inertial separators (Settling chamber, Baffle chambers, Cyclone separator)
  • Fabric hybrid filter

10.Briefly explain the Fabric Separator type bag filters

In this system, fabric bags are used to filter the flue gas to separate the dust. Dust laden gases enter the bag house and passes through fabric bags which act as filter.The bags are woven with material nylon, fiber glass etc. Each bag is externally supported by steel/metal cage. The bag filter house is provided with an explosion vent to avoid explosion during abnormal operation conditions.

Further, the bag filter house consists of hoppers & ash handling system to remove fly ash separated in bag filters.

In bag filters, the dust collects at the outer surface of the bag since flue gas flow from out side to inside of the bag.

Mechanism of dust collection:

Gravity: Due to gravitational force & sudden lower velocity large sized dust/ash particles fall down into hopper due to Gravitational force.

Inertial collection: Due to inertial, heavy dust particles strike the bag filters placed in the flue gas path & fall down into the hopper, since they do not change their flow direction due to inertia.

Interception: Due to the fine mesh or size of the bag filters, dust or ash particles cannot cross the filters. Instead they hit filters & fall down into the hopper.

Electrostatic effect: Electrostatic force between dust particles & bag filter causes the dust to capture.

11.How do you remove dust particles from Bag filters?

  • Mechanical Shaker
  • Reverse air
  • Reverse Jet

12.What are the various materials of composition (MOC) of Bag filters?

Sl No.

Bag filter material

Operating temperature (0C)

1

Nylon

85-90

2

Polyester

130-140

3

Polyphenylene  sulphide or Ryton

180-190

4

Fibre glass

250-260

5

Fibre glass fabric coated with PTFE

250-260

13.What are the various factors considered for selection of Bag filters?

  • Flue gas temperature
  • Moisture level in flue gas
  • Dust or ash particles size
  • O2% in flue gas
  • Flue gas velocity
  • Dust or ash particles abrasiveness
  • Air to cloth ratio

14.What are the main functions of Ash handling system?

  • To remove the ash from Boiler furnace & other various ash discharge points
  • To convey this ash to nearby storage area like ash silo
  • Ash disposing

15.What are the various types of Ash handling systems used in Boilers?

Mechanical ash handling system: In this system chain, belt & screw conveyors are used to convey the ash from various ash termination points to ash silo.









Pneumatic ash handling system:











Pneumatic ash handling system is used widely in most of the Power plants. High pressure air is used to convey the ash to the suitable location.

16.What are the various types of Pneumatic ash handling systems used in Boilers/power plants?

  • Lean phase ash handling system
  • Medium phase
  • Dense phase

17.Why dense phase ash handling system is used in almost all Boilers Ash handling plant?

Because it has less air consumption due to volumetric ration of air & ash is more. Sometimes instead of pressurized air vacuum system is used to convey the ash.

Briefly explain the dense phase Ash handling system

In this system, Ash conveying system is placed just below the ash hopper. This system consists of Main ash hopper

  • Surge hopper with electromagnetic or Mechanical vibrators
  • Knife edge gate valve
  • SS expansion bellow
  • Dome valve assembly & operating mechanism
  • Ash & air conveying valves, solenoid valves
  • Pressure switches & limit switches
  • Conveying pipelines

If the temperature of the ash is more (Economiser & APH) surge hopper is made with water jacket for continuous circulation of water.

The system can be operated from local & remote in probe mode or timer mode.

Calculation part:

1. A Boiler is consuming 72 TPH an imported coal having ash % 8, calculate the total ash generated in a complete month. Assume there is no stoppages or load fluctuation

Total coal consumed in a month = 72 X 24 X 30 = 51840 MT

Total ash generated in a month = 51840 X 8 / 100 = 4147.2 MT

2. A boiler consumes 7 TPH of coal, calculate the total fly ash generated in a day if coal has 35% ash.

Total ash generated = 7 X 24 X 35 / 100 = 58.8 MT

We know that, fly ash is around 80% of total ash.

So total fly ash generated is 58.8 X 80 / 100 = 47.04 MT

3. A Boiler generates 20 MT of ash in a day, calculate total coal consumed in a day if coal has 5% of ash in it

Total ash generated =20 MT/day

Ash % in coal = 5%

Therefore total coal consumed = 20  / 5% = 400 MT

 

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Questions & Answers on steam Blowing



1.What is the purpose of steam blowing?

The purpose of the steam blowing is to remove any foreign materials from steam piping & super heater coils after completion of erection work.

2.What will happen if steam blowing is not done after erection or repair of Boiler?

If steam blowing is not done, considerable damage will happen to the steam lines & other end user applications like steam turbine, process heat exchangers due to scale, debris & other foreign materials present in the newly erected pipe lines/coils.

3.What is the basis behind steam blowing?

The basis behind the steam blowing is to create momentum equal to or preferably greater than that during normal operation. This will blow out all the debris from the steam lines

4.What are the two different methods of steam blowing?

Puff method & continuous method. In puff method thermal shock is created & in continuous steam blowing, constant steam purge is maintained

5.What are the requirements for steam blowing for newly erected Boilers?

  1. Steam blowing area is corned off & notice board or caution board should be displayed
  2. Ensure Boiler hydraulic test, alkali boil out & passivation procedures are completed before steam blowing
  3. All the temporary supports used during erection should be removed
  4. Steam pipe lines & valves used for steam blowing line should be equal to the maximum size of permanent pipe.
  5. Sharp elbows, bends & tees should be avoided in steam blowing pipe line to avoid more pressure drop
  6. Temporary pipe lines used for blowing should be well supported to withstand reaction forces created during steam blowing.
  7. Steam blowing line should be terminated outside the Turbine hall or process
  8. Sufficient allowance should be given to steam blowing line for thermal expansion
  9. Ensure steam line supports & hangers are erected & set properly
  10. Ensure control valves, steam nozzles & NRV flops are not installed during steam blowing
  11. Initially steam blowing is done at lower mass flow

6.What is the time gap between two steam blows?

For an un insulated steam pipe line blowing can be done at every 1 hr. And for insulated steam pile line the gap between two blows should be 3–4 hours

7.Which materials are used for target plates?

Aluminum & stain less steel

8.How do you decide the steam is clear after blowing?

 If there are only two or less than two recognizable impressions found on per square centimeter of target plate, then the target plate is said to be clean.

For Target Plate Made of Aluminum:

The piping considered clean if there are not more than 3 (Three) pitting of 0.5 mm to 1mm dia. in center area of 25 mm X 25 mm and shall not have any deformed edges. Besides this there shall be no pitting in the rim zone. Pitting below 0.5 mm may be ignored.

For Target Plate Made of Stainless Steel:

 The piping is considered clean if there are not more than five pitting of 0.1 mm dia to 0.5 mm dia. in center area of 50 mm X 50 mm & shall not have any deformed edges. Pitting below 0.1 mm may be ignored 

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Standard operating procedure of CHP & Dust extraction system

 

SOP FOR CHP START UP

  • Ensure trained CHP operator & helper are available
  • Ensure adequate illumination is available
  • Ensure Operator has walky-talky for proper communication with control room
  • Have field round on entire CHP & ensure all conveyors are empty & no any foreign materials on belt.
  • Ensure no any maintenance or inspections are going on by other department
  • Ensure all interlocks & local hooters are healthy
  • Ensure shuttle conveyor discharge chute is at required position to discharge the coal
  • Ensure Coal crusher twin gate is opening is as per our requirement 
  • Give clearance to control room for starting CHP
  • Initially start Dust extraction system
  • Then follow the starting sequence of shuttle conveyor & then preceding all conveyors as per system interlocks
  • Ensure OBMS & magnetic separator are inline
  • After ensuring all the coal handling system is healthy, then fill the grizzly hopper & start vibro-feeder (Do not start vibro-feeders if hopper is empty)
  • If coal is dusty, keep ON water sprinklers
  • Ensure coal belt weight is within limit by frequently communicating with control room
  • During CHP running, have the field rounds for running inspections like coal spillage, gear box/motor abnormal sounds etc

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SOP FOR CHP SHUTDOWN

  • Ensure coal bunker is 90%
  • Stop coal feeding
  • Keep OFF water sprinkler system
  • Ensure coal belt conveyors are empty & there is no any coal on belts, vibro screen & crusher
  • Stop CHP as per sequence & wait for 10 minutes then stop  dust extraction system
  • Have field round & ensure no any coal saturation & no any abnormal observations
  • Carryout house keeping
  • Note down abnormalities observed during operation & take into the shift in charges & maintenance team

 SOP Dust Extraction system

Pre checks:

  • Ensure, operators supervising the DE system & coal handling are well trained
  •  Ensure proper communication of operator with control room
  •  Ensure coal handling, coal feeding system & DE systems are free from coal & other foreign materials Ensure there is a proper housekeeping near coal crusher, vibro screen & DE system
  •  Ensure all interlocks & protections systems of conveyors are healthy
  • Ensure sprinklers systems provided on coal belt conveyors are healthy & can be used on immediate use Ensure coal dust collecting pipes are jam free i,e free from large size coal particles  
  • Ensure temperature gauge fitted at DE silo is showing normal temperature

Start up Operation:

  • Start coal belt conveyors as per SOP, initially conveyors after DE systems shall be started first
  • Then start RAV & vibrators, ensure both are working normal
  • Then start air compressor & ensure bag filters purging SOVs are operating sequentially with preset operating & cycle time
  • Start air blower & adjust suction damper, initially suction damper is kept 50% to avoid the sucking of larger sized coal particles
  • Then set individual dust suction dampers of dust collecting pipes from crusher, vibro screen, and conveyor to 30-50% maximum.
  •  After coal feeding, check the dust expelling from chimney, if it is more, then control the blower inlet damper.
  • Allow to stabilize the system Operation checks:
  • Ensure RAV is running continuously
  • Ensure electromagnetic vibrator fitted on bag filter housing hopper is working as per timer set
  • Ensure bag filter housing temperature is normal

 Pre Shutdown & shutdown checks / activities:

  • After shutdown of DE system following safety checks & activities to be carried out
  •  After stopping the coal feeding, keep ‘ON’ DE system for at least 10-15 minutes to ensure bag filters & housing are free from dust & coal particles
  • After ensure there is no more coal falling from RAV & no dust in chimney shutdown the system safely after shutdown, ensure the dust collecting pipes are jam free
  •  Carryout the water washing of coal crusher house & coal belts (near crusher & DE system)
  • During shutdown have a routine field rounds over crusher house, DE system & ensure temperature inside the bag filter housing is normal.

 Questions & Answers on Ash handling system

80-Interview questions & answers for fresher Mechanical Engineers











1.What do you mean by Statics?

It is the branch of Engineering Mechanics which deals with the forces & their effects, while acting upon a bodies at rest

2.What do you mean by Dynamics?

It is the branch of Engineering Mechanics which deals with the forces & their effects, while acting upon a bodies in motion

3.What are the types of Dynamics?

Kinetics: Branch of science which deals with bodies in motion due to applied forces

Kinematics: Branch of science which deals with bodies in motion without considering the applied forces

4.Define the term ‘Force’

It is an agent which produces or tends to produce, destroy or tends to destroy the motion of the body.

5.What is meant by Resultant of Force?

It is a single force which produces the same effect of all the forces acting on a body

6.What does Lami’s Theorem says?

It states that if three coplanar forces acting at a point be in equilibrium, then each force is proportional to sine of the angle between other two forces

7. What do you mean by couple?

The two equal & opposite forces, whose lines of action are different

8. What do you mean by Centre of Gravity (CG)?

The point through which the whole mass of the body acts irrespective of the position of the body is called as CG

9. Define Moment of inertia

It is the moment of moment or second moment of mass or area of a body

10. Define the term ‘Friction’

A force acting in the opposite direction to the motion of the body is called friction force

11. What are the types of friction?

Static friction: Friction experienced by a body, when it is under rest

Dynamic friction: Friction experienced by a body, when it is in motion

Dynamic frictions are classified into sliding friction & Rolling friction

12.What do you mean by coefficient of Friction?

It is the ratio of Limiting friction to the normal reaction friction

13. Define Newton’s three laws of motion

1st Law: It states that everybody continues in the state of rest or of uniform motion, in a straight line, unless it is acted upon by some extent force

2nd law: It states that rate of change of momentum is directly proportional to the impressed force & takes place in the same direction, in which the force acts.

3rd Law: Action & reactions are equal & opposite

14. How do you calculate moment of Inertia?

M = Mass X Velocity

15. How do you calculate the angular velocity of a body if it is rotating at speed N?

Angular velocity  = 2N/60……Rad/sec

16. How do you calculate the linear velocity of a body if it is rotating at speed N & having diameter D?

Linear velocity V = N / 60….m/sec

17. What do you mean by Amplitude?

It is the maximum displacement of a body from its mean position

18. How do you define the work?

When a force of F acts on a Body & the bodyundergoes displacement x in the direction of the Force, then the work is said to be done

Work, W = Force F X Displacement x

19. How do you define the term Power?

Power is rate of doing work

20.What is meant by Energy?

Energy is the capacity to do work, expressed in J or calories

21. What do you mean by Potential energy?

Energy possessed by a body by virtue of its position.

A body kept at height ‘h’ & having mass ‘m’ has potential energy E = mgh (g = 9.81 m/sec)

22. What do you mean by Kinetic energy?

Energy possessed by a body by virtue of its mass & velocity

E= mv2/2

23. What is meant by strain energy?

It is the potential energy stored in an elastic body when deformed

24. Convert 1 kg of Force into Newton

1 kg = 9.81 N

25. What is reversible Machine?

Machine having efficiency < 50% are called Reversible machines

26. How do you calculate the velocity of freely falling body?

V = SQRT(2gh)

27. What do you mean by retardation?

Retardation is the negative acceleration

28. Does a freely falling body possesses weight?

No

29. The force applied on a body of mass 10 Kg to produce an acceleration 2 m/s2 is…….

F = ma = 10 X 2 = 20 kg m/s2 = 20 N

30. What do you mean by Stress?

Stress is force per unit area, Stress = Force / A

31. Define the strain?

The deformation of a body per unit length is called strain

32. What are the units of stress & strain?

Stress N/mm2 or MPa & Strain: Unit less

What is meant by Young’s Modulus?

Young’s Modulus = Stress / Strain

33. What is Poisson’s Ratio?

The ratio of lateral strain to linear strain is called Poisson’s ratio

34. What are the thick and thin cylinders?

Thick Cylinder: Cylinder thickness is greater than 1/15 to 1/10 of its diameter.

Thin Cylinder: Cylinder thickness is less than 1/15 to 1/10 of its diameter

35. What are the different types of Beams used in construction?

Cantilever beam

Simply supported beam

Overhanging beam

Fixed beam

 Continuous beam

36. What are the different types of loading?

Concentrated or point load

Uniformly distributed load

Uniformly varying load

37. What do you mean by spring?

A spring is a device whose function is to start when loaded and to recover its original shape when the load is removed.

38. What are the different types of stresses developed in cylinder?

Circumferential stress or hoop stress & Longitudinal stress

What do you mean by strut?

It is structural member, subjected to an axial compressive force is called strut. It may be horizontal or inclined or even vertical.

39. Write a short note on properties of materials used in engineering of power plant.

Strength: Ability to resist externally applied forces.

Stiffness: Ability to resist deformation under stress.

Elasticity: Ability of materials to regain its original shape after deformation when the external forces are removed.

Plasticity: Ability of a material which retains deformation produced under load permanently.

Ductility: Property of metal to become a wire/thin plate after applying external forces.

Brittleness: Breaking property of material after applying a little or more load.

Malleability: Property of a material to enable it to roll or hammer it into thin sheets.

Toughness: Ability to resist fracture due to high impact load.

Resilience: Ability to absorb energy & to resist impact load.

Creep: Ability of a metal to undergo permanent deformation under constant stress under high temperatures.

Fatigue: Ability to resist repeated stress.

Hardness: Resistance to wear, scratch deformation

40. What do you mean by column?

It is vertical structural member, subjected to axial compressive force.

41. What are short and long columns?

The columns which have lengths less than 8 times of their diameter are called short columns. And columns which have lengths greater than 8 times of their diameter are called short columns

42. What is meant by continuous beam?

A beam supported on more than two supports

43. What is meant by truss?

A truss is a structure that consists of two-force members only, where the members are organized so that the assemblage as a whole behaves as a single object. A two-force member is a structural component where force is applied to only two points

44. Define the term ultimate stress

It is the ratio of ultimate load to the original cross sectional area

45. Is Hooks law holds good for Elastic limit?

Yes

46. State the Young’s law?

It is the ratio of linear stress to linear strain

47. Define the term density?

Density is the mass per unit volume of a liquid at standard pressure & temperature. It is expressed in kg/m3.

48. Define the term specific volume

Volume per unit mass is called as specific volume

49. What do you mean by Specific gravity?

It is defined as the ratio of specific heat of liquid to the specific weight of pure water at standard temperature (4 Deg C).

50. What do you mean by Viscosity?

It is the property of liquid which resists flow of one layer of liquid over another

51. What are the two types of viscosity?

Kinematic viscosity & Dynamic Viscosity

52. What is meant by surface tension?

It is the property of a liquid which enables it to resist tensile stress

53. What does Pascal’s law state?

The intensity of the pressure at any point in a fluid at rest is same in all directions

54. What do you mean by absolute pressure?

It is the sum of Atmospheric pressure & Gauge pressure

55. What do you mean by Buoyancy?

It is the tendency of a liquid to uplift an immersed body, because of the upward thrust of the liquid.

56. What are the different types of fluid flow?

Uniform flow, on uniform flow, Streamline flow, Turbulent flow, Steady flow, unsteady flow, compressible flow, incompressible flow, rotation flow, irrotational flow etc

57. What do you mean by Ideal fluid?

Fluid which has no viscosity

58. What do you mean by real fluid?

Fluid which has viscosity

59. What do you mean by Reynolds’s number?

It is the ratio of Inertia force to the Viscous force

60. What do you mean by Mach number?

It is the ratio of velocity of fluid in an undistributed stream to the velocity of sound wave

61. Define the term Thermodynamics

It is the branch of Engineering science which deals with the energies possessed by gases & vapors

62. What are the different types of Thermodynamics system?

Closed system

Open system

Isolated system

63. State the Zeorth law of thermodynamics

The law states that, when two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other.

64. State the first law of Thermodynamics

Energy can neither be created nor be destroyed, however it can be transformed from one form to another

65. State Charles law, Boyle’s law & Gay-Lussa law

Charles law: The volume of a given mass of perfect gas is directly proportional to absolute temperature, when the absolute pressure remains constant

Boyle’s law: The absolute pressure of gas is inversely proportional to the volume of gas at constant temperature

Gay-Lussac law: The absolute pressure of a given mass of a perfect gas varies directly as its absolute temperature, when the volume remains constant

66. Define the specific heat of a substance

It is the amount of heat required to raise the temperature of its unit mass by 1 deg C

67. What are the different types of Thermodynamic processes?

Isochoric process-Constant volume process

Isobaric process-Constant pressure process

Hyperbolic process

Isothermal process-Constant temperature process

Adiabatic process

68. What are the various types of solid fuels used in power plants?

Coal, wood, bagasse, briquettes etc

69. What are the various types of gaseous fuels used in power plants?

Natural gas, biogas

70. What are the various types of liquid fuels used in power plants?

Diesel, HSD, furnace oil, spent wash etc

71. Define the term calorific value of a fuel

Amount of heat released on complete combustion of 1 kg of fuel

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Questions & Answers on Ash handling system

1.What is Ash? Ash is the remaining product of solid or liquid fuel after burning 2.What are the various components of Ash? Ash has fo...

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