2.2.1 General Description
The steam generating plant consists of two auxiliary boilers and one exhaust gas boiler. The steam demand of the plant, in port is served by the auxiliary boilers. At sea, steam demand is met by the exhaust gas boiler.
The gas boiler is arranged in the funnel to take waste heat from the main engine exhaust.
An auxiliary boiler may be required at sea in low temperature areas, as well as during reduced power operation of the main engine, such as during manoeuvring or slow steaming on passage. Cargo and tank cleaning operations at sea will also require a boiler to supplement the steam supply.
Auxiliary Boilers
No. of Sets: 2
Maker: Aalborg Ltd
Model: AQ18
Type: Oil fired vertical water tube marine boiler
Evaporation: 25,000 kg/h
Steam Condition: 16 kg/cm2saturated steam.
Fuel Oil: H.F.O up to 700 cSt at 50°C
Safety Valve Setting: 18 kg/cm2
Fuel Oil Consumption: 1,880 kg/h at 100% evaporation
Description
General Construction
The boiler is of a two drum type construction, with one steam drum and one water drum. It also includes a boiler casing, fuel firing equipment, mountings, fittings and other accessories.
The boiler structure is supported with the water drum acting as a supporting basis. The whole boiler construction is designed so as to be able to withstand the rolling and pitching of the ship. Careful consideration is also given to the movement by thermal expansion of the boiler.
Combustion gas leaves the furnace through the deflected tubes at the bottom and passes through the generating bank before leaving the boiler. Efficient circulation in the boiler is achieved because a number of tubes in the coldest part area act as down comers
Furnace
Closely spaced water wall tubes are arranged in a staggered configuration and constitute the furnace side and roof, except for burner opening, rear and front wall. This arrangement increases the heat absorption in the furnace and makes it strong enough to withstand vibration etc.
The side water wall tubes are welded to the water and steam drums with no headers provided. The boiler is downward fired from the roof using a steam assisted pressure jet burner.
Boiler Casing
The furnace of the boiler is made completely gas tight by the adoption of a welded water wall construction. The welded water wall construction is also adopted in the front and rear walls of the rear evaporating tube section where tubes are exposed to the combustion gas.
Insulation is provided on the outer surface of the furnace water walls.
Insulation is applied to the outer surface of the water walls and the outermost surface of the furnace is covered with galvanised steel casing except for the furnace roof and floor.
Steam Drum and Fittings
The steam and water drums are cylindrical with two flat plates on the top and bottom. Due to the internal pressure, the flat plates are mutually connected by vertical solid stays.
A steam separator is provided to completely remove the moisture. This can be dismantled for removal.
The steam drum also has a feedwater internal pipe, surface blow off internal pipe and water sampling pipe.
Operating Procedures
The following steps should be taken before attempting to flash up the boiler: a) All foreign materials to be removed from internal pressure parts. b) Ensure all gas side-heating surfaces are clean and all refractory is
in good condition.
c) The furnace bottom and the burner wind box to be cleaned of oil and other debris.
d) Ensure all personnel are clear.
e) All manhole covers to be securely tightened.
f) Inspect safety valves and see that gags have been removed and easing levers are in good condition.
g) Open root valves for all instruments and controls connected to the boiler.
h) Open the vent valve of the steam drum.
i) Open all pressure gauge valves and ensure that all valves on the pressure gauge piping are open.
j) Check and close all blow-off valves and drain valves.
k) Fill the boiler until water level appears 25 to 50 mm high in the gauge glasses. Allow for swell in level after firing.
l) Check operation of gauge glasses and compare with remote reading instruments.
(Note ! Remote-reading instruments may not be accurate until steam is being generated.)
Raising pressure with no steam available from the other boiler.
a) Set up the fuel system for diesel oil and circulate the fuel until all heavy fuel has been discharged from the fuel lines.
b) Set burner for air atomising, using an air pressure of 4 kg/cm2and fuel pressure of 3 kg/cm2. Purge the furnace with forced draught fan for one minute with vanes fully open.
c) Reduce the air pressure at the windbox to between 10 and 20 mm water and close recirculating valve.
d) Light the burner and adjust air and fuel pressure, to ensure stabilised combustion, using the furnace observation port and smoke indicator.
e) When raising the pressure, keep the burner firing for 5 minutes and out of service for 15 minutes repeatedly at the lowest oil pressure (2.5kg/cm2) for one hour. Again, repeatedly light and shut down the burner to raise pressure as recommended by the manufacturer. A guideline would be to aim for 1kg/cm2after 1.5 hours firing, 5kg/cm2after 2 hours firing and 12 kg/cm2after 2.5 hours firing.
f) When the drum pressure has risen to about 2 kg/cm2, close the drum vent valve.
g) Drain and warm through all steam supply lines to ancillary equipment before putting the boiler on load.
h) Supply steam to the F.O. tank. When the tank is of sufficient temperature to be pumped by the F.O. pump, supply steam to the F.O. heater and prepare to change over from D.O to F.O. Continue circulating F.O. as before.
Raising Pressure with Steam Available from other Boiler.
a) Start forced draught fan, open the inlet vanes and purge the furnace.
b) Start the F.O. burning pump and circulate oil through the heater and burner manifold. Open the recirculating valve and discharge the cold heavy oil in the line.
(At normal sea going condition, the boiler F.O. system will be continually circulating heated F.O.)
c) Reduce the air pressure at the windbox to between 10 and 20 mm water gauge.
d) Close the recirculating valve.
e) Light the burner and adjust air and fuel pressure to ensure stabilised combustion, using the furnace observation port and smoke indicator.
When raising the pressure, keep the burner firing for 5 minutes and out of service for 15 minutes repeatedly at the lowest oil pressure (2.5kg/cm2) for one hour. Again, repeatedly light and shut down the burner to raise pressure as recommended by the manufacturer. A guideline would be to aim for 1kg/cm2 after 1.5 hours firing, 5kg/cm2after 2 hours firing and 12kg/cm2after 2.5 hours firing.
f) When the drum pressure has risen to about 2 kg/cm2, close the drum vent valve.
g) Drain and warm through all steam supply lines to ancillary equipment before putting the boiler on load.
Shutting Down
a) Operate sootblowers before shutting down the boiler whenever possible.
b) Shut down the burner.
c) Continue the operation of the forced draught fan for a short while after shutting down keeping an air pressure of 150mm water gauge at the burner inlet and purge the furnace of combustible gases.
d) Maintain the water level visible at about 50mm in the gauge glass. e) Open the drum vent valve before the boiler reaches atmospheric
pressure.
f) Change the fuel system to diesel oil and circulate back to the tank. (If steam is available from the other boiler or economiser, the boiler F.O. system should remain in use.)
g) When the fuel oil has been purged, shut down the fuel system.
After the boiler has been shut down for 4 hours the forced draught fan may be used to assist cooling down, but to avoid damage to refractory allow the boiler to cool down naturally if possible.
! CAUTION
Do not attempt to cool down the boiler by blowing down and then by filling with cold water.
Shutting Down in an Emergency
Should the boiler trip (when the burner is in use) due to the low low alarm, and the subsequent trip of the fuel oil supply, shut down steam stop valve, feed valve and forced draught fan after purging the furnace.
(Note ! Never attempt to feed water until the boiler has cooled sufficiently.)
Flame Failure
In the event of flame failure, close the oil inlet valve and reduce the air pressure to prevent over cooling the furnace.
Purge the furnace before relighting the burner. Always use the pilot burner for ignition.
(Note ! Never attempt to relight the burner from the hot furnace refractory.)
Taking the Boiler Out of Service.
When taking a boiler out of service, the wet lay up method is preferable, this is because it requires less preparation and can be quickly returned to service. When the boiler is in the cooling down process following shut down, inject into the drum appropriate quantities of boiler chemicals, using the boiler chemical injection device. To ensure adequate protection of the boiler, follow the guidelines given by the chemical supplier.
When the pressure is approaching atmospheric pressure, open the steam drum air vent valve.
When the pressure is off the boiler, supply distilled water until it issues from the vent valve, then close the vent valve.
Put a hydrostatic pressure of 3.5 to 5 kg/cm2on the boiler. Hold this pressure until the boiler has cooled to ambient temperature. Bleed the boiler using the vent valve to be sure all the air is out. Maintain a hydrostatic pressure of 2 to 3.5 kg/cm2on the boiler.
Take a periodic boiler water sample and replenish any spent chemicals. Before returning the boiler to service, drain the boiler to the normal working level and return the chemical content concentration to the normal level by blowing down.
Maintaining Boiler in Warm Condition
At sea the stand-by boiler should be maintained in a warm condition by supplying steam to the heating element in the bottom drum. This is done by closing the heating coil drain valve and opening the inlet and outlet valves. The boiler pressure should be maintained at 0.5 kg/cm2or above. When the heating element is not in use the inlet and outlet valves are closed and the drain left open.
Illustration 2.2.2a Boiler Control Panel
1. Water Level
2. Fuel Oil Temperature Controller 3. Fuel Oil Pressure Controller 4. Atomis ing Steam Pressure 5. High Temperature In Uptake 6. Oil Valves Not In Position 7. High Water Level 8. High Steam Pressure 9. High Oil Temperature
10. Overload Ignition Burner Pump 11. Interlock OK
12. Low Combustion Air Flow 13. Flame Failure
14. Low water Level 15. High Steam Pressure 16. Low Oil Temperature 17. Lance Not In Position 18. Sequence Failure
19. Aut. Stand By Feed Water Pump Started 20. Low Steam Pressure
21. Too Low Water Level 22. Atomising Steam Pressure Low 23. Low Oil Pressure
24. Fuel Oil Stand By Pump Started 25. High Temperature In Preheater 26. A - Meter
27. A - Meter 28. Fuel Oil Pump 1 29. Fuel Oil Pump 2 30. Combustion Air Fan 31. Hour Counter 32. Hour Counter 33. Fuel Oil Pump 1 34. Fuel Oil Pump 2 35. Combustion Air Fan
36. Feed Water Pump 1 St. By - 0 - Man 37. Feed Water Pump 2 St. By - 0 - Man
38. Fuel Oil Pump 1 Mode Selector St. By - 0 - Duty 39. Fuel Oil Pump 2 Mode Selector St. By - 0 - Duty 40. Combustion Air Fan Mode Selector Auto - Man 41. Start/Run
42. Start/Run
43. Fuel Oil Pump 1 Start/Run 44. Fuel Oil Pump 2 Start/Run
45. Combustion Air Fan Run 46. Stop
47. Stop
48. Fuel Oil Pump 1 Stop 49. Fuel Oil Pump 2 Stop 50. Space Heating Combustion Air Fan
1. Combustion Air Flow 2. Fuel Oil Flow 3. Air/Oil Controller 4. Main Steam Pressure
5. Air Flow Setting In Manual 0 - 100% 6. Air/Fuel Ratio Adjustment -50% - +50% 7. Oil Flow Setting In Manual 0 - 100% 8. Oil Flow Totaliser
9. Atomising Steam Valve 10. Ignition On 11. Oil Valve Open 12. Steam Purge Valve 13. Burner Normal Stop 14. Combustion Controller Off 15. Ignition Lance Inserted 16. Heavy Fuel Oil 17. Diesel Oil 18. Burner On
19. Chemical Dosing Unit Oil F. Boiler 20. Emergency Stop
21. Emergency Operating Mode 22. Control Voltage On 23. Reset
24. Lamp Test
25. Auto Manual Burner Mode 26. Soot Blower Start/Run 27. Stop Buzzer 28. Buzzer
1. Steam Dump Controller 2. Water Level
3. High Water Level 4. High Steam Pressure. AQ2 5. Low Water Level 6. Low Steam Pressure. AQ2
7. Chemical Dosing Unit Exh. Gas Boiler 8. Aut. Stand By Feed Water Pump Started 9. A - Meter
10. A - Meter 11. Hour Counter 12. Hour Counter 13. Feed water Pump 1 14. Feed water Pump 2 15. Start/Run 16. Start/Run 17. Stop 18. Stop