Boilers & Steam

Question 1

Boiler mountings

Answer 1

• Pressure gauge
• Sample cock
• Blowdown valve
• Scum valve
• Main feed valve
• Aux/emgcy filling feed valve
• 2 safety valves
• 2 gauge glasses
• Vent v/v
• Burner door
• Steam outlet
• Top hatch
• Drain valve
• Level sensors including LLL trip

Question 2

No water in gauge glass

Answer 2

Blowdown other gauge glass, if no water there then E-stop
Inform CE

Investigation:
Check boiler blowdown v/v is closed
Check Auto-regulating feed valve may be stuck - do not open it
Check hotwell level
LL trip has failed
Advise CE on findings

If water is introduced to the hot boiler without cooling first, the tubes will be hot and could crack due to thermal shock and create a steam explosion from the flashing off of the water touching the overheated metal.

Boiler should be vented and allowed to cool naturally before carefully and systematically refilling.

Question 3

Boiler gauge glass blowdown

Answer 3

PPE
Check drain
(Always crack open never just open)
Close steam Close water Open drain
Open water (expect water and water flashing into steam due to pressure drop)
Close water
Open steam (expect steam)
Close steam
Close Drain
Open water till it fills to top and then open steam and it should drop to the true level

Question 4

Boiler blowdown

Answer 4

• PPE
• Obtain ovbd v/v key from CE
• Open ovbd
• Open the blowdown valve
• Use the 2nd valve to throttle
• Throttle at 10 second intervals to avoid reversing the circulation of the boiler
• Close v/vs in opposite order

You must throttle with the 2nd valve to protect the blowdown valve from ‘wiring’ on the valve seat

Question 5

Boiler testing

Answer 5

We can take a boiler sample from the salenomitor cock mounting (sample valve) and allow it to cool to room temperature

Limits
-Hardness: <0.5ppm
-P Alkalinity: 50-300 ppm
-Chlorides: 300ppm max
-Conductivity (Dissolved solids): <700 ųs/cm ppm (microsiemens per cm)
-PH (9.5-11)
-DEHA (Die-thy-lhydroxy-lamine) (residual of oxygen scavenger on drewplex ox) 0.4-0.8ppm
• Hydrate alkalinity (Drewplex AT) 30-65ppm
• Phosphate: (Drewplex AT) 10-80ppm

Question 6

What do we dose the boiler water with?

Answer 6

• Drewplex OX
Contains DEHA (Die-thylhyd-roxylamine) which is an oxygen scavenger, prevents corrosion by forming a stable protective oxide layer on the metal.

• Drewplex AT
Autotreat is used to control alkalinity and phosphates.
It contains phosphates combined with synthetic polymers. The chemical combines itself with the minerals remaining in the water and they fall to the bottom as sludge which is removed via bottom blowdown

• Oxygen can cause pitting and reduced tensile strength on the boiler tubes which could result in tube failure.
• Scale by calcium and magnesium ions can cause bulging that reduces tensile strength and tube failure. It can also create an insulating layer reducing the efficiency of the boiler.

Question 7

What should the temperature be in the hot well and why?

Answer 7

It should be around 90+ degrees but below boiling point
This is so that the process is more efficient in the boiler as it is already close to boiling but also so that the oxygen is displaced

Question 8

How could oil get into the hot well

Answer 8

-Oil may enter the hot well due to a leak from the heating coils in fuel tanks. When the coil is inactive, the steam can condensate and suck oil in due to its change of 1700/1.
-We can remove oil by using absorbent pads or by performing a scum blowdown of the hot well or by using coagulants in the boiler.

Question 9

What would indicate a soot build up in the economiser and how do we soot blow the economiser?

Answer 9

Indication of soot buildup - exhaust gas temp usually drops around 50-100 degrees across the economiser. If this drop is lower/outlet temp higher than usual then this is an indication of soot buildup. The available steam pressure will also drop in the boiler due to there being less heat transfer.

There is a steam pipe in the economiser which has nozzles on it and it can be rotated manually.
Ensure the engine is above 65% load.
Open the drain to check that the line is clear of condensate to prevent water hammering. (Drain goes to bilge)
Then keep the drain cracked open and open steam to this line to clear it out. (Aalborg procedure)
Close the drain
Start the sootblow (it is automatic and blows each section for a preset time)

We release steam through the nozzles on the lances to dislodge soot and the exhaust air to blow it out the funnel
More commonly done at night and usually to be done daily or 1-2 days depending on fuel used and the load

Question 10

How does the economiser work?

Answer 10

Boiler water circulating pumps take suction from the bottom of the boiler. Circ pump Inlet 7 bar and outlet 12 bar
The water then enters the economiser and passes through upwards. At the top , around 80% of it is steam coming out the economiser at around 8-9 bar. (This has to be higher than the boiler working pressure so that the flow of the mixture of water and steam goes to the boiler and not back to economiser. Enter the boiler through a NR valve and steam rises in the drum while the water returns to the bottom.

Question 11

Which safety valves are set higher, economiser or auxiliary boiler?

Answer 11

Economiser because the water circulating is at a higher pressure due to head pressure needed to rise up through the piping to the economiser.

Question 12

Checks on economiser

Answer 12

• Check both safety valves are closed, check drain lines to see if safety valve is passing and to drain any rain water.
• Check temperature difference across the economiser is 50-100 degrees.
If less, then it could indicate that there is an excessive buildup of soot in the economiser which is making the heat transfer less effective due to it creating an insulating layer.
Also, if the outlet temperature is higher than the inlet then this is a strong indication of an economiser fire.

Question 13

How do you know if your safety valve is leaking on the economiser?

Answer 13

Check whether there is steam or steam condensate coming from the drain line but be careful to not mistake this with rainwater which would be coming from the adjacent drain line. (2 drain lines per safety valve)

Question 14

How to refill boiler from cold

Answer 14

Force draft fan on and open the vent v/v to remove gases
Follow manufacturers guidance and/or manual

Question 15

Boiler alarms and trips

Answer 15

• HL
• LL
• LLL
• Flame failure - could be a dirty flame eye
High steam pressure
• Burner not in firing position (door open)
• Force draft fan failure / low combustion air pressure
• Low fuel pressure

Question 16

How to prevent water-hammer in a steam line

Answer 16

Drain the line before introducing steam (or do it while drain is open?)
Crack open always never just open

Question 17

Difference between relief valves and safety valves

Answer 17

Safety valves have an easing gear to allow us to open them manually. They are set at around 3% above the set pressure and it fully opens when this set point is reached to rapidly vent pressure from the system.

Relief valves do not have an easing gear and are set 5-10% above the set pressure. It will open in proportion to the pressure increase

Question 18

What would stop fuel from being supplied to the boiler?

Answer 18

• Flame failure (flame eye dirty)
• High steam pressure
• Low combustion air pressure
• Burner not in firing position
• Low fuel pressure (could be filter)
• Exhaust alarm

Question 19

Difference between blowdown valve & scum valve

Answer 19

• A blowdown valve is at the bottom and is used to replenish big quantities of water/sediment if the water tests are not good
• A scum valve is at the water line and used to blow foaming/scum/oil off the top of the water