How a boiler works: Overview & History
A boiler is a pressure vessel that is designed to generate heat, produce steam or cool gases. Typically built as a rectangular or cylindrical tube, the vessel is closed at both ends and is fully insulated. Fuels such as wood, coal, oil, or natural gas power the device, making it possible for pressures of 30 bar and more to be created inside. In general, boilers are welded from thick steel plates with applications varying from hot water boilers to waste heat boilers and biomass boilers.
An industrial boiler works in a very similar way to our household heating boilers but on a significantly larger scale. The system heats or evaporates the water inside it by transferring
heat energy to water, before transporting it to the desired area via a pipe system. The cooled water or the condensed steam then returns to the boiler to be heated again and flue gases are discharged into the atmosphere. Any loss of water must be compensated by treated fresh water in order to avoid corrosion.
The first steam boiler was developed in the eighteenth century and since then many variations have been developed, including:
Haycock and Pot Boilers:
The Haycock boiler produced and stored large volumes of very low-pressure steam. In principle, they were based on a ‘steam-kettle’ design where a heat source (usually a fire) heats a partially filled water container from underneath. The heat transfer efficiency of these types of boilers was generally very low.
This is the type of tube boiler that is commonly found in steam trains. It is partially filled with water and has a void above the water surface to accommodate the steam. The heat source powering the boiler is situated inside a firebox or furnace and it is important that this firebox kept immersed in water to maintain the temperature of the heating surface below boiling point. The fire tube boilers are classified as single tube and multi-tube boilers.
A water-tube boiler circulates water through tubes that are exposed to the source of heat – as opposed to the more usual procedure of the tubes carrying hot gases through the water. They can be powered by different sources of heat and are often used in high-pressure steam applications as they’re able to withstand higher pressure.