BOE Exam Question Answer | Questions are based on B.O.E. Examination appeared student

BOE Exam Question Answer

 

Question : 1. Location of Fusible plug in boiler.

Answer : Fire-actuated and steam actuated plugs are located at the lowest permissible water level. Normally screwed into rear tube sheet above highest row of tubes.

Question : 2. Construction material of Fugible plug.

Answer : 90%tin,5%lead&5%bismuth(melting point 205*C).

Question : 3. Number of drums in once through Boiler.

Answer : None(Zero).

Question : 4. Compound pressure gauge application in pressure measurement.

Answer : Pressure sensing, Altitude sensing, Flow sensing, Level / depth sensing, Leak testing etc. It measures pressures below and above atmospheric pressures.

Question : 5. Pressure gauge range for hydro in a Boiler of 35KSC and below assuming that feed water is internally treated.

Answer : 0-100KSC

Question : 6. Pressure gauge range for hydro in a Boiler of 35KSC and above, but below 70KSC.

Answer : 0-160KSC.

Question : 7. At what pressure latent heat of vaporization of water is zero.

Answer : At critical pressure(222bar).

Question : 8. Reason for why coal is pulverised w.r.t. combustion.

Answer : To ensure complete combustion of coal (i.e. to create maximum turbulence of mixture of carbon & oxygen molecules) .So that coal particles can expose to maximum oxygen.

Question : 9. IBR welder certificate validity for how many years.

Answer : Two years.

Question : 10. Can we allow a mild steel welder to weld alloy steel.

Answer : No (only IBR welder is to authorized to do welding work in any pressure parts of boiler).

Question : 11. Killed steel composition.

Answer : Killed steel is steel that has been completely deoxidized by the addition of an agent before casting, so that there is practically no evolution of gas during solidification. They are characterized by a high degree of chemical homogeneity and freedom from gas porosity. Usually Killed steel composition is 99.65% Fe,0.25% Carbon,0.1%silica(Killed steel are characterized by freedom from porosity.)

Question : 12. How to adjust blowdown capacity of safety valve.

Answer : By movement of compression screw in clockwise or anti-clock wise direction.

Question : 13. Cast iron properties.

Answer : Cast iron used to make valves , pipes & fittings when pressure do not exceed 13.358Kg/cm2(190psi) and temperature 400*C(204*C).

Question : 14. Effect of superheat on blowdown capacity of safety valve.

Answer : Blowdown capacity increases with amount of superheat.

Question : 15. Effect of increased salinity on blowdown percentage.

Answer : Increases with increment of salinity.

Question : 16. Relation between sensible heat and pressure.

Answer : Sensible heat means heat gaining by any fluid below its corresponding saturation temperature. Corresponding saturation temperature is increasing by increasing the pressure of fluid. Thus sensible heat is increasing by increases in fluid pressure.

Question : 17. Name the process – if a steam is passed through restricted opening or aperture.

Answer : Throttling process

Question : 18. What is throttling process of steam.

Answer : During the throttling process the steam expands from high pressure to lower pressure through a small opening(restricted opening or aperture). The heat transfer and work done are zero. This process is also known as “wire drawing”. During expansion the steam(wet) will start drying up even it may be superheated. During throttling process :

(i) No work is done. (ii) No heat is supplied or rejected. (iii) Total heat remains constant. It is an adiabatic kind of process.

Question : 19. In throttling which parameter is constant.

Answer : Total heat( Enthalpy ) parameters is constant.

Question : 20. 18/8 stainless steel means.

Answer : 18/8 stainless steel means alloying of 18% Chromium & 8% Nickel.

Question : 21. Unit of Power.

Answer : KW, MW, BHP, Joule Note : Power can not have a time domain.

Question : 22. Unit of Energy.

Answer : Kwh, Mwh, MU Note : Energy will always be accompanied with time domain.

Question : 23.Methods of burning the low grade coal.

Answer :  By pulverizing.  By blending with high grade coal.  By mixing with oil.

Question : 24.For static loading, which property is more serious – Brittleness, Ductility.

Answer : Brittleness

Question : 25.For thermodynamic equilibrium what is necessary – Chemical, Mechanical and Thermal.

Answer : Thermal(Zeroth law of thermodynamics is “If each of the two given systems are in thermal equilibrium with a third system, then the two given systems are in thermal equilibrium with each others”).

Question : 26. Range of radiation loss in Lancashire Boiler.

Answer : Exactly it is 4%.

Question : 27.Type of draught used in Lancashire Boiler.

Answer : Natural draft (-ve draft created by stack).

Question : 28.If blowdown is opened by 10%, what about thermal loss %age.

Answer : A 10% blow down in a 15 kg/cm2 boiler results in 3% efficiency loss. Kindly note that Blow down percentage shares a random relationship with thermal loss.

Question : 29.Boiler efficiency of a well maintained Boiler.

Answer : It is depending upon the type of boiler used. It will be in range of 85% to90%.

Question : 30.Downcomer material.

Answer : Usually “SA210 Gr A1” is used for down comer.

Question : 31.Primary Super heater material.

Answer : Usually “SA 213 Gr T22” is used for primary super heater.

Question : 32.Calculation of Shear Stress.

Answer : Shear stress (fs=(16T/Πd3)

Question : 33.Water wall tube welding type.

Answer : TIG welding

Question : 34. Factors affecting circulation ratio in the boiler.

Answer : Operating Pressure, Operating Temperature and the kind of fuel fired into the Boiler.

Question : 35.Fish mouth type tube failure reason.

Answer : Symptoms: Failure results in a ductile rupture of the tube metal and is normally characterized by the classic “fish mouth” opening in the tube where the fracture surface is a thin edge. Causes: Short-term overheat failures are most common during boiler start up. Failures result when the tube metal temperature is extremely elevated from a lack of cooling steam or water flow. A typical example is when superheater tubes have not cleared of condensation during boiler start-up, obstructing steam flow. Tube metal temperatures reach combustion gas temperatures of 1600°F or greater which lead to tube failure. Simply say it is prolonged overheating.

Question : 36.Ideal water condition at Economiser outlet.

Answer : About saturation temperature (It is depending upon the corresponding fluid working pressure).It is just saturated liquid.

Question : 37.Dryness fraction calculation of steam.

Answer : The ratio of the actual mass of dry steam in the given sample of wet steam, to the weight of wet steam containing ,it is called dryness fraction of steam. Dryness fraction (x)=Ms/(Ms+Mv)=Ms/M Where ,Ms=Mass of actual dry steam Mv=Mass of water vapor in suspension. M=Mass of wet vapor steam.

Question : 38.Need for Dearation.

Answer : In de-aeration, dissolved gases, such as oxygen and carbon dioxide, are expelled by preheating the feed water before it enters the boiler. All natural waters contain dissolved gases in solution. Certain gases, such as carbon dioxide and oxygen, greatly increase corrosion. When heated in boiler systems, carbon dioxide (CO2) and oxygen (O2) are released as gases and combine with water (H2O) to form carbonic acid(H2CO3).
Removal of oxygen, carbon dioxide and other non-condensable gases from boiler feed water is vital to boiler equipment longevity as well as safety of operation. Carbonic acid corrodes  metal reducing the life of equipment and piping. It also dissolves iron (Fe) which when returned to the boiler precipitates and causes scaling on the boiler and tubes. This scale not only contributes to reducing the life of the equipment but also increases the amount of energy needed to achieve heat transfer.

Question : 39.Process of mechanical De-aeration.

Answer : Mechanical de-aeration for the removal of these dissolved gases is typically utilized prior to the addition of chemical oxygen scavengers. Mechanical de-aeration is based on Charles’ and Henry’s laws of physics. Simplified, these laws state that removal of oxygen and carbon dioxide can be accomplished by heating the boiler feed water, which reduces the concentration of oxygen and carbon dioxide in the atmosphere surrounding the feed water.
Mechanical de-aeration can be the most economical. They operate at the boiling point of water at the pressure in the deaerator. They can be of vacuum or pressure type.
The vacuum type of de-aerator operates below atmospheric pressure, at about 82 °C, can reduce the oxygen content in water to less than 0.02 mg/litre. Vacuum pumps or steam ejectors are required to maintain the vacuum.
The pressure-type de-aerators operates by allowing steam into the feed water through a
pressure control valve to maintain the desired operating pressure, and hence temperature at a minimum of 105 °C. The steam raises the water temperature causing the release of O2 and CO2 gases that are then vented from the system. This type can reduce the oxygen content to 0.005 mg/litre.

Question : 40. SH material considering MS Temperature>540C.

Answer : Low – alloy steels with 0.5%Mo in combination with 0.5 to 9%Cr are often used at up to about 650°C. The 1Cr-0.5Mo steel is used for piping, cracking-still tubes and boiler tubes at service temperatures up to 510 or 540°C. The similar 1.25Cr-0.5Mo steel is used at up to 590° and has stress-rupture and creep properties comparable to those of the 1Cr-0.5Mo alloy3. Maximum temperature limit for 1Cr-05Mo superheater tube materials is specified at 649°C in allowable stresses table in ASME Boiler Codes for Section I application.

Question : 41.Preheating is required in what kind of Steel.

Answer : Ferrite stainless steels.

Question : 42.For cyclic loading, which property is more serious – Brittleness, Ductility.

Answer : Brittleness

Question : 43.Which factor accounts at maximum in Boiler losses.

Answer : Dry flue gas loss which is depending upon the supplied excess air.

Question : 44.Ideal condition of flue gas at APH outlet.

Answer : Just above dew point temperature (depending upon the sulphur content in fuel).

Question : 45.Purpose of PA Fan in PF system.

Answer : To supply the air into the pulverizer for conveying the pulverized fuel form pulverizer to coal burner.

Question : 46.Efficiency range of a steam operated power station.

Answer : Subcritical : 35-40%, Supercritical : 41 to 45%, CCPP : Above 48%.

Question : 47.Why blow down is required in Boiler.

Answer : Removal of Total dissolved solids (conductivity ,silica, sludge etc.)from boiler water which is responsible for scale formation resulted in terms of failure of boiler tubes.

Question : 48.Effect of Mangnese (Mn) addition in steel.

Answer : It’s hot working properties improves and it’s strength, hardenablility and toughness improves.

Question : 49.Purpose of ORSAT Meter w.r.t. Flue Gas.

Answer : Volumetric analysis of the flue gas. Measuring gas composition(i.e. O2,CO2&CO).

Question : 50.Purpose of Bomb Calorimeter w.r.t. Fuel.

Answer : Measuring calorific value of the Solid fuel.

Question : 51.Which case Boiler efficiency is more – GCV OR NCV.

Answer : NCV is lower value w.r.t. GCV hence Boiler efficiency will be more in case of NCV. GCV means Gross Calorific Value or Higher Heating Value of Coal:
NCV means Net Calorific Value or Lower Heating Value:
NCV (NCV<GCV).

Question : 52.Gas law applies to which kind of steam.

Answer : Superheated steam.

Question : 53.Wet preservation of Boiler .

Answer : It is done for a period of One to Two weeks.Plant which is temporarily taken out of service and required to return to service at short notice should be stored full and have sufficient water available for quick return to service.

Wet Preservation process :

System completely filled with DM water containing 200ppm hydrazine and ammonia is added to raise the pH to 10. Chlorine should below 2ppm. At the time of return to service it is better to drain the water and fill with fresh DM water and stop chemicals, for normal operation.

Question : 54.Bending moment calculation.

Answer : Basic bending equation is given by

M/I = f/y = E/R

Where,

M=Moment of inertia,Y=centriodal distance from axis,E=Modulus of elasticity,f=shear stress,R=Radius of plate.