We all know that boilers generate steam for heating and processing loads on our ships. But do you recognize these different types of boilers and their applications?
1. The Water-tube Boiler
Babcock & Wilcox water-tube boiler, circa 1889
Water-tube boilers are boilers that have water being warmed inside the tubes and hot gases surrounding them. ‘Water-tube’ (as opposed to ‘fire-tube’) is a generic categorization of boilers that work in this manner.
Why this matters: Water-tube boilers can handle higher pressures of up to 5,000 psig and can produce up to several million pounds-per-hour of steam. This means that water-tube boilers can be used for applications that require large amounts of steam and high pressures.
2. The Main Propulsion Boiler
The Main Propulsion Boiler: Source
Main propulsion boilers provide steam for propulsion turbines on a ship, propelling the ship through water by allowing for gear reduction, shafting and propeller movement.
Main propulsion boilers are usually ‘D-type’ boilers, a type of water-tube boiler that is named as such because of the positions of the drums and side header, which form the letter ‘D’.
3. The Auxiliary Boiler
Auxiliary boilers on ships, both large and small, are boilers that supply steam for essential purposes other than main propulsion, such as XYZ, ABC, EFG.
Auxiliary Boiler: Source
Large auxiliary boilers used for marine purposes are usually top-fired ‘D’-type boilers.
D-type water-tube boilers by Babcock & Wilcox can be designed for a steam capacity of 10,000 to 300,000 lbs/hr, pressures from 250 to 1,250 psig, and a maximum temperature of 850F (for gas fired units). ‘D-type’ boilers are uncontrolled superheat boilers as the steam produced must go through a superheater.
4. The Waste Heat Boiler
Waste heat boilers are part of a vessel’s Waste Heat Recovery System (WHRS), using waste heat from exhaust gases from a vessel’s engine to heat and generate steam for a variety of purposes such as heating the cargo and accommodation areas. Most waste heat boilers are water-tube designs.
A welder works in the waste heat boiler No. 3 area aboard the destroyer HAYLER (DD-997) in the USA, circa 1981. WHRS have been in existence for some time and have quickly gained popularity.
Why this matters: Although costs have to be set aside for installing WHRS, they have been in existence for a while now and maximising the system’s efficiency can lead to vast reductions in a ship’s fuel consumption. This has become a popular type of boiler amongst ship owners, given the marine industry’s move in recent years towards being more eco-friendly.
5. The Composite Boiler
Composite boilers are composed of exhaust gas economizers and oil-fired boilers. This type of boiler is usually used alongside diesel machinery. Composite boilers are considered small auxiliary boilers, generating steam for auxiliary purposes.
Why this matters: Composite boilers can be a cost-effective solution for smaller vessels as they can reduce pumping needs and save space by combining oil-fire systems with exhaust gas ones.
About the author
Michael Brecker is the President of Instruments & Controls, Inc. (ICI) and the co-founder of GIANTECH Industries. He specializes in the design, manufacture, repair and installation of diesel engine automation and monitoring systems, boiler burner management systems, combustion control systems, inert gas generator systems, and control valve repairs for both marine and land-based industries. His expertise in boilers has earned him a reputable position, making him one of the leading opinion makers in the industry.