Questions & Answers (Boiler) Part-1

1. What is boiler?

It is a pressure vessel in which the water is heated to evaporate and generate the steam and the unit is so arranged that the generated steam accumulated in it.

2. Types of boiler:

          A. Water Tube Boiler

          B. Fire Tube Boiler.

3.Types of boiler by pressure:

1. Low pressure boiler up to 10 kg/cm².
2. Medium pressure boiler 10 to25 kg/cm².
3. High pressure boiler over  25 kg/cm².

4. Explain the difference between fire tube & water tube boiler.

                          Difference between water tube & fire tube boiler

Water tube boiler	Fire tube boiler
1. Water flows through the tube.	1. Water flows around the outside of the tube.
2. Hot gasses pass around the outside of the tube	2. Hot gas passes through the tube.
3. Lighter in comparison with capacity	3. Robust 8 heavier.
4. High pressure & high capacity	4. Less pressure & less capacity.
5. Complex, cleaning difficult	5. Simple, easy maintenance
6. More efficient	6. Less efficient.
7. Distilled water to be used.	7. Normal water to be used.

5. What are the advantages & disadvantages of water tube boiler?

Advantage of water tube boiler: 

·                     Lighter.

·                     Simple to construction

·                     Safer.

·                     Efficient over 85%, Hence reduce fuel consumption.

·                     Steam can be produced within shorter time.

·                     Greater evaporation rate.

·                     High pressure and temp. steam is produce.

Disadvantage:

           1) Little reserve of water and steam in the boiler, so efficient control of water level is required.

           2) the high rate of heat transfer across those tube walls together with small bores required positive circulation of water.

          3)The small bore tubes demand  pure feed condition to prevent scale formation which could lead to blow and over heating.

          4)The thin tubes give little resistance for corrosion, Cleaning difficult.

6. What are the functions of steam drum?

    (a) steam separation, 

    (b) steam-water circulation and 

    (c) purifying steam.

7. What is the function of super-heater?

Super-heater is used to super heat the steam and get higher thermal Efficiency of the plant.

8. Why large boilers are top supported?

        (a) avoid buckling of furnace walls, 

       (b) allow thermal expansion and 

       (c) reduce thermal loads.

Q. Name of Aux. boiler Mounting & major parts:

1) Main steam stop v/v (non return type)
2) Two safe v/vs.
3) Two gauge glass
4) Air vent cock.
5) Feed check v/v (non return type)
6) Automatic feed water regulator. (Not mounting)
7) Scum blow down v/v.
8) Blow down v/v (non return type).
9) Salinometer cock / sampling cock.
10) Man-hole door.
11) Mud-hole door
12) Pressure gauge connector.
13) Root v/v for level indicator.
14) Root v/v for pressure gauge glass.
15) Circulating p/p suction v/v
16) Soot blower.  (Not mounting)

9. Sketch a vertical auxiliary boiler

Save the images for clear view.  

10. Feed check v/v: (Short Note) 

Pair of non return valves, one main and other auxiliary v/v fitted with stop/close indicator. Double shut off reduces the risk of boiler water leakage into the feed water line and if the feed water line fractures or a joint in the line blows then boiler contents will not be discharged out.

11.Main steam stop v/v: (Short Note) 

Main steam stop v/v is fitted on top of the boiler and connected with the main steam pipe-line. It is usually screw down non return type v/v. Its purpose is to isolate the boiler from the main steam line.

12. Safety v/vs :  (Short Note) 

Safety v/vs are fitted to a boiler to prevent boiler over pressure. At least two safeties must be fitted to a boiler. Safety values should be capable to release all steam, the boiler can produce without raising the pressure by more the 10% over a set valve.

13. Where air vent cock is located and its purpose?

The air vent cock is fitted at the top of the steam space of the boiler.

Its purposes are-

1. To release air from the boiler either filling the boiler water or raising the steam.

2. To allow air to enter in the event of boiler cooling down or blowing down .( to prevent vacuum effect)

14.Boiler safety devices :

1} Safety valves (Two)

2} Low / high water level alarm

3} Too low water level alarm and shut down

4} Water level indicators

5} Pressure gauge

6} Low fuel oil pressure alarm

7} Low / high fuel oil temperature alarm

8} Flame failure alarm

9} Smoke density alarm

10} Easing gear arrangement

11} Air vent

12} Force drought fan stop alarm

13} Low / high steam pressure alarm

15. Why we need to blow down the gauge glass?

Gauge glass blow down is made to know the boiler and gauge glass connection is clear or not. And to give the exact water level in the boiler.

16. Boiler gauge glass blow down procedure:

1} Shut steam and water cocks than open the drain cock.

2} After draining water from the sight glass,if nothing comes out, both steam and water cocks are good in order.

3} Open the steam cock side, blow out the steam.

4} Close the steam cock side, the steam connection is clear.

5} Open the water cock side, blow out the water.

6} Close the water cock side, the water connection is clear.

7} Close the drain cock.

8} Open the water cock, water should then gradually come rise up to the top of the gauge glass.

9} Open the steam cock, the water in the glass should fall to the level of the water in the boiler.

Note: Working position - all cocks handle are in downward position.

17. Why we need to blow down the boiler water?

Boiler blow down is made to reduce the density of salt and to remove the dissolved and suspended solids, also the floating solid impurities in the boiler system.

If these are not removed from the boiler water system, foaming, priming, corrosion will occur in the boiler steam space and feed water system.

18. What check should be carried out on a boiler during watch?

1. Steam pressure & temperature.
2. Boiler water level.
3. Blow down gauge glass.
5. F.O. Pressure and temp.
6. Check the flow gas temp.
7. Check the flame shape.
9. Feed water press and temp.
10. Feed water regulator
11. Check safety level devices.
12. Cascade tank water level and temp.
13. Observation tank check for oil.
14. Condenser sea water outlet temp.
15. Check any leakage of valves.
16. Blow down the boiler
17. Soot blow

19. Alarm fitted in boiler system.

1. Steam press, high / low.
2. Boiler water level high/low.
3. Flame failure
4. High salinity.
5. Fuel temp. high or low

20. Indication of soot blow is done.

1. Shoot will come out through the funnel.
2. If steam is used for soot blowing steam press. Will suddenly comedown.
3. Exhaust back press will reduce.
4. Exhaust gas outlet temp at the uptake (after the EGB) will reduce because of boiler heat transfer.
5. After soot blow is finished within short time steam press will come up.

21. Why do you perform scum blow down and bottom blow down?

Scum blow down ( surface blow down):

To remove accumulated, suspended and floating solids, impurities and also remove dissolved solid concentration, they hinder the formation of steam.

Bottom blow down: 

To remove suspended solids and residual sludge that have settled at the bottom.

If these contaminants are not removed regularly they will build up until they hinder the

circulation patterns.

To be continue................. 

Reference:

1. Bangladesh Marine Academy

2. Hand Notes of Mr. Min Zar Tar

3. Manual Book: AALBORG MISSION OM 1200

4.Marine Engineers' World (Facebook)