Auxiliary marine boilers are used to produce steam for a variety of purposes onboard a ship. The most common use for auxiliary boilers is to generate electricity, but they can also be used for propulsion, heating, and other purposes.
There are two main types of auxiliary marine boilers: fire-tube boilers and water-tube boilers.
Fire-tube boilers are the most common type of boiler used on ships, and they work by circulating hot gases through a series of tubes. Water-tube boilers are less common, but they are more efficient than fire-tube boilers and can be used for high-pressure applications.
Foaming In Auxiliary Boilers
It is the formation of a thick layer of steam bubbles on the surface of the water inside the boiler as a result of:
- Impurity concentration is high.
- Because of the animal or vegetable fats in feed water that are carried over from the oil heaters.
- TDS levels of dissolved and suspended solids rise.
- The water level has risen.
Surface or scum blowdown should be performed on a regular basis to expel any floating impurities from the boiler to prevent foaming, and no lube oil should be allowed to enter the boiler.
What Is Boiler Parts Priming And How To Prevent It
It is a condition in which large amounts of water are carried into the steam line along with the steam. It is the result of:
- Foaming excessively
- Inadequate amount of steam space
- By a sudden rush of steam, such as when the steam stop valve is abruptly opened.
To avoid priming, never keep the water level too high. Slowly turn on the steam stop valve.
What steps do you take in the event of foaming and priming?
- Scum blow down
- Lower the boiler’s fire rate.
- Examine whether the boiler chemicals used are excessive.
- Determine the source of contamination.
- In the event of improper priming, the boiler may have to be removed from service and shut down.
Note: Auxiliary boilers must be chemically cleaned if they are contaminated with oil.
What is the procedure for cooling down the boiler?
- Switch the fuel oil burning system from HO to DO and then turn it off.
- Close the feed check valve after stopping the feed.
- Allow the boiler to cool before draining it.
- If there isn’t enough time, reduce the boiler pressure to 3 to 4 bar.
- Close the main steam stop valve.
- Open the blow down valve first, then the ship side valve.
- When the boiler is empty, it will make a banging noise.
- Close the boiler blowdown valve as well as the ship side valve.
- Then, using easing gear, release the steam pressure through safety v/v.
- When the pressure is released, open the air vents and allow the boiler to cool.
Boiler Parts Opening Up and Inspection Procedure
After ensuring that there is no vacuum in it, proceed as follows:
- Slacken the dog holding nuts but do not remove them until the joint has been broken.
- Take out the nuts and dogs and close the door.
- After warning personnel to stay clear of the top door, the bottom door can be removed.
- Allow for adequate ventilation before entering. Allow no naked light near the boiler.
- Prior to cleaning, a preliminary internal inspection is performed to check for scale deposits and any special points.
- Place guards over manhole landings to prevent damage and plug orifice to blow down valves to prevent choke.
- Cleaning and internal work were completed.
- When all work has been completed, a thorough internal examination must be performed.
- All openings are clear, and the water level gauge connection is free of deposits.
- All internal pipes and fittings have been properly replaced and securely fastened.
- Remove the orifice plug from the blow down valve.
- Manhole doors and landings are inspected to ensure that they are clean and undamaged.
- Manhole doors should be replaced with new joints.
- All boiler mountings should be operational. Open the air vent cock and fill the boiler to the proper level.
What is the procedure for starting the boiler from a cold state?
To avoid thermal stress, the boiler is fired from a cold state to a normal working pressure state very slowly.
- Check that the boiler blowdown valve is closed.
- Close the main steam stop v/v.
- Open the air vent cocks.
- Open the feed check valve and pump up to ¼ gauge glass level.
- Start the forced draft fan with dampers properly open to purge the furnace and combustion space of any foul gas.
- After closing the recirculating valve, turn on the burner.
- Normally, the fire should burn for 5 minutes and then be extinguished for 15 minutes. This process is repeated until steam appears.
- When steam escapes from the air vent, the air vent is closed (at 1 to 2 bar pressure).
- Slowly increase the working pressure. (Allow the fire to burn for 30 minutes, then extinguish it for 10 minutes.)
- Drain the steam line when the steam pressure reaches working pressure. (In order to avoid water hammer)
- The main steam stop valve slowly opens (crack opening)
What should you do if the gauge glass shows a low water level?
- Water may be added to the boiler if the water level has not yet dropped completely out of the sight glass.
- If water completely disappears from the sight glass, check another sight glass; if both disappear, do not add water until the boiler is cool enough to prevent any potential damage from rapid cooling of the overheated plate.
- The fire must be put out immediately.
- The primary steam shut-off valve must be closed.
- Cool and blow down the boiler.
- Check for leaks, take the drum outside, identify the source of the problem, and make the necessary repairs.
- After the boiler has cooled, inspect it for any potential damage.
- Water slowly fills up after repair and returns to normal operation.
- If no damage occurred, slowly inject water into the boiler and restart it.
What are the causes of a low water level in the gauge glass?
- One gauge glass is faulty.
- Cracked and leaking boiler tube
- The feed water regulator is stuck.
- Feed water pump failure (Air in feed water line or pump)
- Level controller failure
- The amount of steam consumed is excessive.
What exactly is caustic embrittlement and how to avoid it?
- A crystalline fracture has occurred. It’s caused by a high concentration of caustic soda and a stressed material. The stress corrosion cracks follow the material’s grain or crystal boundaries and fail.
- Caustic embrittlement is prevented with sodium sulphate or sodium nitrate.
- It is commonly found in high-stress areas of boilers. Tube and tube plate connections, riveted heads, seams, and boiler mountings are examples.
Auxiliary marine boilers are an important part of a ship’s machinery, and they must be operated and maintained properly to ensure safe and efficient operation. Boiler operators must be trained in the proper operation of the boiler type they are using, and they must follow all safety procedures. Regular maintenance and inspection of auxiliary marine boilers are essential to prevent accidents and ensure that they are operating at peak efficiency.