A boiler is a closed vessel where drinking water or other liquid is heated. The fluid will not always boil. (In THE UNITED STATES, the word "furnace" is generally used if the reason is not to boil the fluid.) The heated or vaporized liquid exits the boiler for use in various heating system or processes applications,[1][2] including water heating, central heating system, boiler-based power era, cooking, and sanitation.

The pressure vessel of the boiler is usually made of steel (or alloy steel), or historically of wrought iron. Stainless steel, especially of the austenitic types, is not found in wetted parts of boilers thanks to stress and corrosion corrosion breaking.[3] However, ferritic stainless steel is often found in superheater sections that won't come in contact with boiling water, and electrically heated stainless shell boilers are allowed under the European "Pressure Equipment Directive" for production of steam for sterilizers and disinfectors.[4]
In live steam models, copper or brass is often used because it is more fabricated in smaller size boilers easily. Historically, copper was often used for fireboxes (especially for steam locomotives), due to its better formability and higher thermal conductivity; however, in more recent times, the high price of copper often makes this an uneconomic choice and cheaper substitutes (such as metal) are used instead.

For a lot of the Victorian "age of steam", the only material used for boilermaking was the best grade of wrought iron, with set up by rivetting. This iron was extracted from specialist ironworks, such as at Cleator Moor (UK), observed for the high quality of their rolled plate and its suitability for high-reliability use in critical applications, such as high-pressure boilers. In the 20th century, design practice transferred towards the use of steel instead, which is stronger and cheaper, with welded building, which is quicker and requires less labour. It should be observed, however, that wrought iron boilers corrode significantly slower than their modern-day steel counterparts, and are less susceptible to localized stress-corrosion and pitting. This makes the longevity of older wrought-iron boilers much more advanced than those of welded steel boilers.

Cast iron might be utilized for the heating vessel of domestic water heaters. Although such heaters are usually termed "boilers" in a few countries, their purpose is usually to produce hot water, not steam, and they also run at low pressure and stay away from boiling. The brittleness of cast iron makes it impractical for high-pressure vapor boilers.
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The source of heating for a boiler is combustion of any of several fuels, such as wood, coal, oil, or natural gas. Electric steam boilers use level of resistance- or immersion-type heating system elements. Nuclear fission is used as a heat source for generating steam also, either directly (BWR) or, generally, in specialised heat exchangers called "vapor generators" (PWR). Heat recovery vapor generators (HRSGs) use the heat rejected from other processes such as gas turbine.

Boiler efficiency
there are two solutions to gauge the boiler efficiency 1) direct method 2) indirect method

Immediate method -immediate approach to boiler efficiency test is more useful or even more common

boiler efficiency =Q*((Hg-Hf)/q)*(GCV *100 ) Q =Total vapor movement Hg= Enthalpy of saturated steam in k cal/kg Hf =Enthalpy of feed drinking water in kcal/kg q= level of gas use in kg/hr GCV =gross calorific value in kcal/kg like family pet coke (8200 kcal/KG)

indirect method -to gauge the boiler efficiency in indirect method, we need a following parameter like

Ultimate analysis of energy (H2,S2,S,C moisture constraint, ash constraint)
percentage of O2 or CO2 at flue gas
flue gas temperature at outlet
ambient temperature in deg c and humidity of air in kg/kg
GCV of energy in kcal/kg
ash percentage in combustible fuel
GCV of ash in kcal/kg
Boilers can be classified in to the following configurations:

Container boiler or Haycock boiler/Haystack boiler: a primitive "kettle" in which a fireplace heats a partially filled drinking water box from below. 18th century Haycock boilers generally produced and stored large volumes of very low-pressure steam, hardly above that of the atmosphere often. These could burn off wood or frequently, coal. Efficiency was suprisingly low.
Flued boiler with a couple of large flues-an early forerunner or kind of fire-tube boiler.

Diagram of a fire-tube boiler
Fire-tube boiler: Here, water partially fills a boiler barrel with a small volume still left above to support the vapor (steam space). This is the kind of boiler used in all steam locomotives nearly. Heat source is inside a furnace or firebox that needs to be kept permanently surrounded by the water in order to keep the temperature of the heating surface below the boiling point. The furnace can be situated at one end of a fire-tube which lengthens the path of the hot gases, thus augmenting the heating system surface which can be further increased by causing the gases invert direction through a second parallel pipe or a lot of money of multiple pipes (two-pass or return flue boiler); alternatively the gases may be studied along the sides and then under the boiler through flues (3-move boiler). In case there is a locomotive-type boiler, a boiler barrel expands from the firebox and the hot gases pass through a lot of money of fire pipes inside the barrel which greatly escalates the heating surface compared to a single tube and further enhances heat transfer. Fire-tube boilers have a comparatively low rate of steam production usually, but high steam storage capacity. Fire-tube boilers mainly burn solid fuels, but are readily adaptable to people of the gas or water variety.

Diagram of the water-tube boiler.
Water-tube boiler: In this type, tubes filled up with water are arranged inside a furnace in a true number of possible configurations. Often the drinking water tubes connect large drums, the low ones containing water and the top ones water and steam; in other situations, like a mono-tube boiler, drinking water is circulated with a pump through a succession of coils. This type gives high vapor production rates generally, but less storage capacity than the above. Water pipe boilers can be designed to exploit any heat source and tend to be preferred in high-pressure applications since the high-pressure drinking water/vapor is included within small size pipes which can withstand the pressure with a thinner wall structure.
Flash boiler: A flash boiler is a specialized type of water-tube boiler where tubes are close together and water is pumped through them. A flash boiler differs from the kind of mono-tube steam generator where the pipe is permanently filled with water. Super fast boiler, the pipe is held so hot that the water give food to is quickly flashed into steam and superheated. Flash boilers acquired some use in cars in the 19th century and this use continued into the early 20th century. .

1950s design steam locomotive boiler, from a Victorian Railways J class
Fire-tube boiler with Water-tube firebox. Sometimes the two above types have been mixed in the following manner: the firebox consists of an assembly of water tubes, called thermic siphons. The gases pass through a typical firetube boiler then. Water-tube fireboxes were installed in many Hungarian locomotives,[citation needed] but have fulfilled with little success in other countries.
Sectional boiler. In a solid iron sectional boiler, sometimes called a "pork chop boiler" water is included inside solid iron sections.[citation needed] These areas are assembled on site to create the finished boiler.
See also: Boiler explosion
To define and secure boilers safely, some professional specialized organizations like the American Society of Mechanical Technicians (ASME) develop specifications and regulation codes. For instance, the ASME Boiler and Pressure Vessel Code is a typical providing a wide range of guidelines and directives to ensure compliance of the boilers and other pressure vessels with safety, design and security standards.[5]

Historically, boilers were a way to obtain many serious injuries and property destruction as a consequence to badly understood engineering principles. Thin and brittle metallic shells can rupture, while welded or riveted seams could start badly, leading to a violent eruption of the pressurized steam. When water is converted to steam it expands to over 1,000 times its original quantity and moves down steam pipes at over 100 kilometres each hour. Because of this, steam is a great way of moving energy and temperature around a niche site from a central boiler house to where it is necessary, but without the right boiler feed water treatment, a steam-raising plant will suffer from scale development and corrosion. At best, this raises energy costs and can result in poor quality steam, reduced efficiency, shorter plant life and unreliable procedure. At worst, it can lead to catastrophic failing and lack of life. Collapsed or dislodged boiler pipes can also aerosol scalding-hot steam and smoke out of the air intake and firing chute, injuring the firemen who weight the coal in to the fireplace chamber. Extremely large boilers providing a huge selection of horsepower to use factories could demolish entire structures.[6]

A boiler that has a loss of give food to drinking water and it is permitted to boil dry can be extremely dangerous. If supply drinking water is sent into the unfilled boiler then, the tiny cascade of inbound drinking water instantly boils on contact with the superheated metallic shell and leads to a violent explosion that cannot be controlled even by security steam valves. Draining of the boiler can also happen if a leak occurs in the vapor supply lines that is larger than the make-up water supply could replace. The Hartford Loop was invented in 1919 by the Hartford Steam Boiler and INSURANCE PROVIDER as a strategy to assist in preventing this condition from happening, and thus reduce their insurance promises.[7][8]

Superheated steam boiler

A superheated boiler on the steam locomotive.
Main article: Superheater
Most boilers produce vapor to be used at saturation heat; that is, saturated steam. Superheated vapor boilers vaporize water and then further high temperature the vapor in a superheater. This provides steam at higher heat range, but can decrease the overall thermal efficiency of the vapor generating flower because the higher vapor temperature requires a higher flue gas exhaust temperature.[citation needed] There are several ways to circumvent this problem, by giving an economizer that heats the give food to water typically, a combustion air heating unit in the hot flue gas exhaust path, or both. There are benefits to superheated steam that may, and will often, increase overall efficiency of both steam generation and its utilization: gains in input heat to a turbine should outweigh any cost in additional boiler complication and expense. There may also be useful limitations in using wet vapor, as entrained condensation droplets will harm turbine blades.

Superheated steam presents unique safety concerns because, if any system component fails and allows steam to flee, the ruthless and temperature can cause serious, instantaneous harm to anyone in its path. Since the escaping steam will be completely superheated vapor, detection can be difficult, although the extreme heat and sound from such a leak obviously indicates its presence.

Superheater procedure is similar to that of the coils on an fresh air conditioning unit, although for a different purpose. The steam piping is directed through the flue gas path in the boiler furnace. The temperatures in this field is typically between 1,300 and 1,600 °C (2,372 and 2,912 °F). Some superheaters are glowing type; that is, they absorb heat by rays. Others are convection type, absorbing heat from a fluid. Some are a mixture of both types. Through either method, the extreme heat in the flue gas path will also high temperature the superheater vapor piping and the steam within. While the heat range of the steam in the superheater increases, the pressure of the vapor does not and the pressure remains exactly like that of the boiler.[9] Virtually all steam superheater system designs remove droplets entrained in the steam to prevent harm to the turbine blading and associated piping.

Supercritical steam generator

Boiler for a power seed.
Main article: Supercritical steam generator
Supercritical steam generators are frequently used for the production of electric power. They operate at supercritical pressure. In contrast to a "subcritical boiler", a supercritical steam generator operates at such a high pressure (over 3,200 psi or 22 MPa) that the physical turbulence that characterizes boiling ceases that occurs; the fluid is liquid nor gas but a super-critical fluid neither. There is absolutely no generation of vapor bubbles within water, because the pressure is above the critical pressure point of which steam bubbles can develop. As the fluid expands through the turbine stages, its thermodynamic condition drops below the critical point as it can work turning the turbine which turns the power generator that power is eventually extracted. The fluid at that point may be a mixture of steam and liquid droplets as it passes in to the condenser. This leads to slightly less gasoline use and therefore less greenhouse gas production. The word "boiler" should not be used for a supercritical pressure vapor generator, as no "boiling" occurs in this device.
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Boiler accessories and fittings
Pressuretrols to regulate the vapor pressure in the boiler. Boilers generally have 2 or 3 3 pressuretrols: a manual-reset pressuretrol, which functions as a protection by setting the top limit of steam pressure, the operating pressuretrol, which settings when the boiler fires to keep up pressure, as well as for boilers equipped with a modulating burner, a modulating pressuretrol which controls the amount of fire.
Safety valve: It is utilized to alleviate pressure and prevent possible explosion of the boiler.
Water level indicators: They show the operator the level of fluid in the boiler, also known as a view glass, water gauge or water column.
Bottom level blowdown valves: They provide a way for removing solid particulates that condense and rest on the bottom of a boiler. As the name indicates, this valve is located straight on the bottom of the boiler usually, and is sometimes opened to use the pressure in the boiler to force these particulates out.
Continuous blowdown valve: This enables a small level of water to escape continuously. Its purpose is to avoid water in the boiler becoming saturated with dissolved salts. Saturation would lead to foaming and cause water droplets to be carried over with the vapor - a condition known as priming. Blowdown is also often used to monitor the chemistry of the boiler drinking water.
Trycock: a kind of valve that is often use to manually check a liquid level in a container. Most commonly found on a water boiler.
Flash tank: High-pressure blowdown enters this vessel where the steam can 'flash' safely and be found in a low-pressure system or be vented to atmosphere while the ambient pressure blowdown moves to drain.
Automatic blowdown/continuous heat recovery system: This technique allows the boiler to blowdown only once make-up water is moving to the boiler, thereby transferring the utmost amount of heat possible from the blowdown to the makeup water. No flash container is generally needed as the blowdown discharged is close to the heat of the make-up water.
Hand holes: They may be metal plates installed in openings in "header" to permit for inspections & installing tubes and inspection of inner surfaces.
Steam drum internals, some display, scrubber & cans (cyclone separators).
Low-water cutoff: It really is a mechanical means (usually a float switch) that can be used to turn from the burner or shut down gas to the boiler to prevent it from running once the drinking water moves below a certain point. If a boiler is "dry-fired" (burned without drinking water in it) it can cause rupture or catastrophic failure.
Surface blowdown range: It offers a means for removing foam or other light-weight non-condensible substances that tend to float on top of water inside the boiler.
Circulating pump: It is made to circulate water back again to the boiler after it has expelled some of its heat.
Feedwater check valve or clack valve: A non-return stop valve in the feedwater collection. This may be fitted to the relative side of the boiler, just below the water level, or to the very best of the boiler.[10]
Top feed: With this design for feedwater injection, water is fed to the very best of the boiler. This can reduce boiler exhaustion caused by thermal stress. By spraying the feedwater over some trays the water is quickly heated and this can reduce limescale.
Desuperheater pipes or bundles: A series of pipes or bundles of pipes in the water drum or the vapor drum designed to cool superheated steam, in order to supply auxiliary equipment that does not need, or may be damaged by, dry out steam.
Chemical substance injection line: A connection to add chemicals for controlling feedwater pH.
Steam accessories
Main steam stop valve:
Steam traps:
Main steam stop/check valve: It is utilized on multiple boiler installations.
Combustion accessories
Energy oil system:gas oil heaters
Gas system:
Coal system:
Soot blower
Other essential items
Pressure gauges:
Feed pumps:
Fusible plug:
Inspectors test pressure gauge attachment:
Name dish:
Registration dish: