Boilers are classified into different types based on their working pressure and temperature, fuel type, draft method, size and capacity, and whether they condense the water vapor in the combustion gases. Boilers are also sometimes described by their key components, such as heat exchanger materials or tube design.
Two primary types of boilers include Fire- tube and Water- tube boilers. In a Fire-tube boiler, hot gases of combustion flow through a series of tubes surrounded by water. Alternatively, in a water – tube boiler, water flows in the inside of the tubes and the hot gases from combustion flow around the outside of the tubes.
Fire tube boilers are more commonly available for low pressure steam or hot water applications, and are available in sizes ranging from 500,000 to 75,000,000 BTU input. Water-tube boilers are primarily used in higher pressure steam applications and are used extensively for comfort heating applications. They typically range in size from 500,000 to more than 20,000,000 BTU input.
Cast iron sectional boilers are another type of boiler commonly used in commercial space heating applications. These types of boilers don’t use tubes. Instead, they’re built up from cast iron sections that have water and combustion gas passages. The iron castings are bolted together, similar to an old steam radiator. The sections are sealed together by gaskets. They’re available for producing steam or hot water, and are available in sizes ranging from 35,000 to 14,000,000 BTU input.
Cast iron sectional boilers are advantageous because they can be assembled on site, allowing them to be transported through doors and smaller openings. Their main disadvantage is that because the sections are sealed together with gaskets, they are prone to leakage as the gaskets age and are attacked by boiler treatment chemicals.
Some of the well- known Boilers are:–
- Babcock & Wilcox boiler
- Cochran boiler – A vertical boiler with horizontal fire-tubes.
- Cornish boiler – A large horizontal stationary boiler with a single flue.
- La Mont boiler – A forced-water-circulation boiler. They are often used as marine heat-recovery boilers. It was also used, unsuccessfully, for an experimental steam locomotive in East Germany in the 1950s.
- Lancashire boiler – A development of the Cornish boiler, with two flues.