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Use of Boiler in Ships
Boiler is an device used to produce steam either for main propulsion or for auxiliary machines. Boiler is basically a closed liquid-containing vessel that produces steam on application of heat. This vessel is made with suitable high-quality material and equipped with different equipment and safety devices to serve our purpose.
Auxiliary boilers are most commonly found on-board ship and are used to generate superheated steam with the help of device super heater. These superheated steam are used to rotate the turbines which in turn is used to produce electricity and power generation. Exhausted steams (lower temperature and pressure) from the turbines are sent to:-
- Galley for heating water.
- Accommodation for heat exchanger domestic purposes.
- On deck for tank cleaning in oil tankers.
- In lube oil purifier.
- Earlier it was also used in windlass for Anchoring. Finally, steam is sent to auxiliary condenser where it is cooled and used as boiler feed water.
What is boiler cleaning?
Unwanted deposits and impurities deposited on the inner walls of boiler and on tubes and various surfaces of boiler needs to be cleaned and removed. Carbon and particle deposits like water scale (calcium carbonate) and other are removed from the boiler mostly by two methods:-
- Chemical cleaning.
- Scrubber and brush cleaning.
- Soot deposit is cleaned with 10% soda solution water washing with the help of water hose.
Note- For minimal particle deposit, fresh water should be feeded instead of heavy-water into the boiler.
- If the burner is functioning properly and regular maintenance is carried out soot deposits inside oil fired boiler would be minimal.
- Refractories are covered with plastic so that they don’t get wet, otherwise due to sudden cooling and heating on lighting the burner, the refractory may crack resulting in damaging the equipment.
Why is it important to clean boiler in ship?
Like any machine/ equipment boiler also need cleaning for its smooth functioning and operating at maximum efficiency for as long as possible. It improves boiler heat rate and reduced tube failure and improve stability of boiler.
- According to US department of energy for a 450000 million BTU industrial boiler producing 150 psi steam, cost $3.6 million a year and a mere 0.03125 mm scale increased cost by 2% i.e. $72,000 per year extra.
- Insufficient blow-down will caise sludge deposit at the bottom of boiler.
- If hard deposits are not removed, over heating takes place of boiler plate and material-damage can happen.
Procedure and Remarks for Boiler Inspection:-
- Shut off the boiler and allow it to cool down to room temperature. The boiler should not be depressurised by cold feed water as the stress induced by too rapid cooling will cause damage.
- Empty the boiler and close all valves present.
- Remove the manhole hatches on the boiler and enter the boiler. Inspection for cracks and scale deposit must be carried. Necessary steps must be takes for anything that may pose a threat.
- Check the function of the high steam pressure switch by lowering the set point or by raising the steam pressure. The burner must stop automatically.
- The furnace should be inspected at least twice in 3 years to check on cracks in the refractory and soot deposits are in normal limits in the boiler.
- The exhaust gas section should be inspected at least twice a year. It is ensured that all the exhaust system parts are undamaged and soot deposit are within normal limits.
The inside of boiler water side must be carefully inspected at least twice a year. The deposit of water scales and hard deposits of CaCO3 are inspected. Higher the deposit, more is risk of overheating, lower the efficiency and it may even lead to material failure.
How much does it cost?
So far, we understood that boilers are robust and of great use on board ship. They are used for generation of steam which is fundamental requirement for any machine available. The overall cost of ownership of an equipment include its price, its fuel consumption and the maintenance and servicing cost. Chemical cleaning of boiler can set you back by $50,000- $150,000 depending on the size and type if boiler.