A boiler or steam generator (thermal Power Plant) is a device use to create steam by applying heat energy to water. Although the definitions are somewhat flexible, it can be said that older steam generators were commonly termed boilers. And worked at low to medium pressure (7–2,000 kPa or 1–290 psi) but, at pressures above this, it is more usual to speak of a steam generator.
A boiler or steam generator (thermal Power Plant) is use wherever a source of steam is required. The form and size depends on the application: mobile steam engines such as steam locomotives, portable engines and steam-powered road vehicles typically use a smaller boiler that forms an integral part of the vehicle. stationary steam engines, industrial installations and power stations will usually have a larger separate steam generating facility connected to the point-of-use by piping. A notable exception is the steam-power fire less locomotive, where separately-generate steam is transfer to a receiver (tank) on the locomotive.
The next stage in the process is to boil water and make steam. The goal is to make the heat flow as completely as possible from the heat source to the water. The water is confine in a restrict space heat by the fire. The steam produced has lower density than the water and therefore will accumulate at the highest level in the vessel; its temperature will remain at boiling point and will only increase as pressure increases. Steam in this state (in equilibrium with the liquid water which is being evaporate within the boiler) is name “saturate steam”.
For example, saturated steam at atmospheric pressure boils at 100 °C (212 °F). Saturated steam taken from the boiler may contain entrained water droplets, however a well designed boiler will supply virtually “dry” saturated steam, with very little entrained water. Continued heating of the saturated steam will bring the steam to a “super heated” state, where the steam is heated to a temperature above the saturation temperature, and no liquid water can exist under this condition. Most reciprocating steam engines of the 19th century used saturated steam, however modern steam power plants universally use super heated steam which allows higher steam cycle efficiency.
Water Tube Boiler
Another way to rapidly produce steam is to feed the water under pressure into a tube or tubes surrounded by the combustion gases. The earliest example of this was develop by Goldsworthy Gurney in the late 1820s for use in steam road carriages. This boiler was ultra-compact and light in weight and this arrangement has since become the norm for marine and stationary applications. The tubes frequently have a large number of bends and sometimes fins to maximize the surface area.
This type of boiler is generally prefer in high pressure applications since the high pressure water/steam is contain within narrow pipes which can contain the pressure with a thinner wall. It can however be susceptible to damage by vibration in surface transport appliances. In a cast iron sectional boiler, sometimes call a “pork chop boiler” the water is contain inside cast iron sections. These sections are mechanically assemble on site to create the finished boiler.