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eoow oral prep > Boilers > Flashcards

Boilers Flashcards

1
Q

What is the difference between a safety valve and a relief valve?

A

A safety valve must be able to reduce the pressure within a vessel while still working at full capacity. This is done suddenly.

A relief valve has a proportional opening to maintain optimal pressure.

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2
Q

How many safety valves must be fitted to a boiler?

A

2.

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3
Q

Boiler water tests?

A

pH, nitrites, chlorides, p-alkalinity, DEHA, phosphates

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4
Q

Boiler cut offs/ trips

A

-Emergency stop activated
-Low-low level
-High-high level
-No flame detected
-Low fuel pressure
-boiler door swung open
-High steam pressure (burner cuts off)
-Low combustion air pressure
-Low atomising steam pressure

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5
Q

Boiler alarms other than trips/ cut offs

A

-low water level
-High water level
-Low steam pressure
-Low feed water pressure (standby feed pump will auto start)
-Low fuel oil pressure (standby feed pump will start)
-low fuel oil temperature
-high fuel oil temperature

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6
Q

pH level in boiler

A

9-5-11.5pH ideally

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7
Q

Chloride level

A

Low as possible - 50 ppm max

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8
Q

Cause of high chlorides?

A

-Sea water from evaporator feed, possible salometer error, sea water not being evaporated etc
-Leak from steam condenser - can occur when steam dump not in use

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9
Q

What to do if chlorides are too high?

A

Blow down boiler

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10
Q

How to blow down boiler?

A

-Check blowdown is possible regarding MARPOL Annex V, reg 1.12
-Open overboard valve
-Open blowdown valve (non-return closest to boiler)
-Open valve between boiler and overboard (middle) is used to regulate blowdown rate
-Close valves in reverse order

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11
Q

What is P-alkalinity?

A

Number of inorganic carbons inside the boiler causing alkalinity
Can be increased using UNITOR treatment (auto treat, etc)

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12
Q

Phosphate levels?

A

20-50ppm

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13
Q

How does phosphate occur in the boiler?

A

Reactions with calcium impurities within the water.
Sits at the bottom of the boiler and can be discharged via blow down

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14
Q

Nitrite level?

A

700-2400ppm

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15
Q

Safety valve lifting point?

A

Should begin to lift at 103% working load as per SOLAS II-1

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16
Q

What is the usual pressure found within a boiler?

A

Between 5 and 25 bar.

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17
Q

What is the difference between a water tube and fire tube boiler?

A

Fire tube
- Burner is ignited in a tubing system where the exhaust gas flows around to heat up the water that has filled the exterior of the boiler.

Water tube
- Water flows through tubing where it is heated up by the flame on the outside.
- The steam drum collects the boiling water and steam is released.

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18
Q

What is a boiler mounting?

A

Something affixed to a boiler in a manner so that it cannot be isolated and is always subject to full boiler pressure.
- Required to be tested by class at each boiler survey.
- Up to 8 years old, surveyed every 2 years.
- Over 8 years old, surveyed every year.

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19
Q

Examples of boiler mountings.

A
  • Safety valves.
  • Gauge glass and isolation valves.
  • Any root valves for pressure gauges.
  • Main steam stop valve.
  • Auxiliary steam stop valve.
  • Air vent.
  • Blow down valve.
  • High/low level alarms.
  • Feed check valve.
  • Chemical dosing points.
  • Sampling valves.
  • Drain valves.
  • Inspection hatches.
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20
Q

Boiler start-up after long shut-down period.

A

1) Ensure all heating surfaces are clean and furnace is in good condition.
2) The furnace bottom and burner wind box are clean of oil and other debris.
3) All safety valves are free and in good condition.
4) All manholes are tightened, blow-off and drain valves are closed and root valves for all instruments and controls connected are open.
5) Open the vent valve of the combined water/steam drum.
6) Fill the boiler with water until about 25-50mm of water appears in the gauge glass. (This allows for expansion and increase in level after firing.
7) Selected feed water pump should be in manual and stopped when level is reached.
8) Start the boiler burner on MDO.
9) Steam pressure should be raised slowly to reduce stress and use 5 minutes on flame, 15 off for an hour. Should aim for 6 bar after 1.5 hours.
10) When enough steam is available and HFO reaches temperature, switch the boiler to HFO and keep increasing pressure until the nominal.
11) Switch to auto mode.

21
Q

Alarms and shutdowns on the boiler.

A
  • Low water level alarm.
  • High water level alarm.
  • Fuel supply shut off at low water level.
  • Feed pump stopped at high water level.
  • Flame failure.
  • High and low steam pressure alarms.
  • Burner shut down if purge air low pressure, overload combustion air fan and burner motor and burner swing out.
22
Q

Normal start-up of the boiler.

A

1) Check all lights are functional.
2) Check if the water level is within acceptable limits with one feed pump in operation and the other in standby.
3) Do the same with the fuel pumps.
4) Turn the switch to AUTO position where the start-up sequence will occur.

23
Q

How to operate an EGB from cold.

A

1) Ensure all valves between EGB and boiler are fully open.
2) Ensure all instrumentation is reading correctly.
3) Start the circulation pump.
4) When full circulation conditions have been established in the economiser and the temperature is at the correct level, the generator engine may be started.
5) As steam is generated in the economiser, a steam/water mixture will return to the boiler and separate out.
6) Set to automatic.

24
Q

How is the feed rate regulated on the boiler?

A

Regulating valve after feed pumps based on boiler water level.

25
Q

What is the purpose of an EGB?

A

As up to 25% of the output of engine is wasted as hot exhaust gas, this is a heat recovery system that can be used to heat water into steam for services.

26
Q

How often should economisers be cleaned and how?

A

Soot blown at least 3 times daily and water washed once a month.

Soot blowing should also be carried out following periods of slow running, an increase in power or when shutting down the engine.

27
Q

When should the EGB circulation pumps be running?

A

In advance of the engine starting and not stopped for at least 2-3 hours after the main engine has been shut down. Some manufacturers recommend 12 hours.

28
Q

Why are the safety valves on economisers different to on the boiler?

A

The EGB safety valve setting is higher than the boiler drum’s setting because the circulating pump is drawing water from the boiler drum and supplying to the economiser and as such the pressure in the economiser is greater than the boiler steam pressure.

29
Q

What safety items are present on an EGB?

A

1) Safety valve
2) Vent valve
3) Drain valve
4) Outlet water temperature gauge
5) Auto-bleed valve - supplied with an actuator switch attached to the boiler feed water regulating valve.

30
Q

Why might electronically controlled fuel injection reduce the chances of economiser fire?

A

Running at low loads leaves a low turbocharger efficiency with a lower air-fuel ratio leading to higher exhaust gas temperatures.

Electronic control allows for higher injection pressure and selective fuel injector cut-off which reduces carbon deposits and fouling on EGB and turbocharger.

31
Q

What is the required HFO viscosity at the fuel pump?

A

13-17 cSt

32
Q

How to start-up the boiler from the cold condition?

A

1) Close the blow down valve.
2) Shut the main steam stop valve.
3) Open the air vent cocks.
4) Open the feed check valve and pump up to 1/4 of gauge glass level.
5) Start forced draft fan with dampers to purge combustion space.
6) Light the burner after closing the recirculating valve.
7) Allow the boiler to burn for 5 minutes and stop for 15 minutes. Continue until steam is present.
8) When steam comes out of the air vent (1-2 bar) close it.
9) Rise up to working pressure slowly. (start for 30 stop for 10).
10) When pressure reached drain the steam line to avoid water hammer.
11) Slowly open the main steam stop valve to reduce steam hammer.

33
Q

How to shut down the boiler for maintenance?

A

1) Change fuel over to DO and stop the burner.
2) Stop the feed pumps and close the feed check valve.
3) Shut the main steam stop valve.
4) Open the overboard valve and then the blow down valve.
5) Banging noise will appear when boiler is empty.
6) Close the boiler blow down valve and ship side valve.
7) Release the steam pressure with the easing gear.
8) When pressure is released, open the air vent and allow the boiler to cool down.

34
Q

How to isolate the boiler for maintenance?

A

1) Prepare a risk assessment for entry.
2) Prepare a PTW.
3) Isolate fuel supply, isolate power supply to burner and lock out tag out.
4) Open up doors, ensuring area is clearly marked with tape.
5) Ventilate the space for a minimum of 24 hours and confirm using a gas monitor the atmosphere is safe.
6) Get an authorised person to sign off on the works within a given time limit.

35
Q

What is boiler foaming?

A

Formation of thick layers of steam bubbles on the top of the water surface inside the boiler due to:
1) High concentration of impurities.
2) Fats an oils from oil heaters.
3) Increase in level of dissolved & suspended solid TDS level.
4) Increase in water level.

36
Q

How can you prevent boiler foaming?

A

Surface or scum blow down done frequently to expel floating impurities.

37
Q

What is boiler priming?

A

Large amounts of water are carried along with the steam into the steam line caused by:
1) Excessive foaming.
2) Improper amount of steam space.
3) Sudden rush of steam when main stop valve is suddenly opened.

38
Q

How to prevent boiler priming?

A

1) Never keep water level too high.
2) Open main steam stop valve slowly.

39
Q

What action to be taken in the event of boiler foaming or priming?

A

1) Scum blow down.
2) Reduce boiler fire rate.
3) Check whether chemicals are added in excess.
4) Detect source of contamination.
5) In case of bad priming take the boiler out of service.

40
Q

What are the effects of foaming?

A

1) Cannot accurately tell the boiler water level.
2) Reduced efficiency of heat exchangers.
3) Improper heating of consumers.

41
Q

What are the effects of priming?

A

1) Reduction in boiler efficiency.
2) Increase in maintenance costs.
3) Lower lifespan of parts.

42
Q

What is steam hammer?

A

Releasing steam onto cold pipes condenses some of the steam and shrinks, creating a vacuum and a runaway situation.

43
Q

What is water hammer?

A

The result of a pressure surge when water is made to change direction or stop abruptly.

44
Q

What should the boiler pH be, how would you test and how would you treat?

A

9.5-11.5

pH indicating strips.

Alkalinity control - boiler
Condensate control - hotwell

45
Q

What does phosphate do, how would you test, what level should it be at and how would you treat?

A

Reacts with calcium in the water allowing it to settle at the bottom for blow down.

Take a control and measured sample, add a phosphate indicator tablet to 1 and compare against the other.

20-50ppm

Hardness control.

46
Q

What does hydrazine do, how do you test, what levels should be maintained and what do you add to treat it?

A

Reacts with dissolved oxygen to form hydrogen and water.

Same steps as phosphate.

0.1-0.2ppm

Oxygen control

47
Q

What does chlorine show, how is it tested, what level should be maintained and how is it treated?

A

Sea water ingress.

Dissolve tablets until it goes from yellow to brown.

Maximum 50ppm.

Replacement of water and stopping of sea water leak.

48
Q

What does P&M alkalinity show, how is it tested and how is it treated?

A

Amount of inorganic compounds in the boiler and therefore its alkalinity.

Adding pills until a change in colour.

Alkalinity control.

49
Q

How would you blow down a boiler gauge glass?

A

1) Close the steam and water cocks and slowly open the drain valve. Prove valve sealing.
2) Slowly open steam valve and check for discharge out of the drain, then close.
3) Slowly open the water valve and check for discharge out of the drain, then close.
4) Close the drain valve.
5) Open water valve slowly until fully open.
6) When the water valve is fully open, open the steam valve slowly.
7) Water level in gauge glass should settle to the level in the boiler.

eoow oral prep (29 decks)

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