A boiler is a closed vessel in which water or other fluid is heated. The fluid will not boil. (In North America, the word "furnace" is normally used if the purpose is never to boil the fluid.) The warmed or vaporized fluid exits the boiler for use in various heating system or processes applications,[1][2] including drinking water heating, central heating, boiler-based power era, food preparation, and sanitation.

Materials
The pressure vessel of a boiler is usually manufactured from steel (or alloy steel), or historically of wrought iron. Stainless steel, especially of the austenitic types, is not used in wetted parts of boilers thanks to stress and corrosion corrosion breaking.[3] However, ferritic stainless is often found in superheater sections that won't be exposed to boiling drinking water, and electrically heated stainless steel shell boilers are allowed under the Western "Pressure Equipment Directive" for creation of steam for sterilizers and disinfectors.[4]
https://en.wikipedia.org/wiki/Boiler
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 (particularly for vapor locomotives), due to its better formability and higher thermal conductivity; however, in newer times, the high price of copper often makes this an uneconomic choice and cheaper substitutes (such as steel) are used instead.

For much of the Victorian "age of vapor", the only material used for boilermaking was the highest quality of wrought iron, with set up by rivetting. This iron was from specialist ironworks, such as at Cleator Moor (UK), mentioned 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 instead shifted towards the use of steel, 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 vunerable to localized pitting and stress-corrosion. This makes the longevity of older wrought-iron boilers far superior to those of welded steel boilers.

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

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

Direct method -immediate approach to boiler efficiency test is more functional 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 measure the boiler efficiency in indirect method, we need a subsequent parameter like

Ultimate analysis of gasoline (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 gasoline in kcal/kg
ash percentage in combustible fuel
GCV of ash in kcal/kg
Configurations
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 pot from below. 18th century Haycock boilers generally produced and stored large volumes of very low-pressure vapor, barely above that of the atmosphere often. These could burn off wood or frequently, coal. Efficiency was very low.
Flued boiler with a couple of large flues-an early forerunner or type of fire-tube boiler.

Diagram of the fire-tube boiler
Fire-tube boiler: Here, drinking water partially fills a boiler barrel with a little volume remaining above to accommodate the vapor (vapor space). This is the kind of boiler used in all steam locomotives nearly. Heat source is inside a furnace or firebox that has to be held permanently surrounded by the water in order to maintain 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 road of the hot gases, thus augmenting the heating system surface which can be further increased by making the gases reverse direction through a second parallel tube or a lot of money of multiple tubes (two-pass or come back flue boiler); alternatively the gases may be taken along the edges and then beneath the boiler through flues (3-pass boiler). In case there is a locomotive-type boiler, a boiler barrel stretches from the firebox and the hot gases pass through a bundle of fire tubes inside the barrel which greatly increases the heating surface in comparison to a single tube and further enhances heat transfer. Fire-tube boilers usually have a comparatively low rate of vapor creation, but high vapor storage capacity. Fire-tube boilers burn off solid fuels mostly, but are easily flexible to those of the liquid or gas variety.

Diagram of the water-tube boiler.
Water-tube boiler: In this kind, tubes filled up with water are arranged in the furnace in a true amount of possible configurations. The water pipes connect large drums Often, the lower ones including drinking water and the upper ones steam and drinking water; in other instances, such as a mono-tube boiler, water is circulated with a pump through a succession of coils. This kind generally gives high vapor creation rates, but less storage space capacity than the above mentioned. Water pipe boilers can be designed to exploit any warmth source and tend to be preferred in high-pressure applications since the high-pressure water/steam is contained within small diameter pipes which can withstand the pressure with a thinner wall structure.
Flash boiler: A flash boiler is a specialized type of water-tube boiler in which tubes are close collectively and water is pumped through them. A flash boiler differs from the kind of mono-tube steam generator where the tube is permanently filled up with water. In a flash boiler, the pipe is held so hot that water give food to is quickly flashed into vapor and superheated. Flash boilers had some use in automobiles in the 19th century and this use continued in to 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 includes 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 far away.
Sectional boiler. Within a cast iron sectional boiler, sometimes called a "pork chop boiler" the water is contained inside solid iron areas.[citation needed] These sections are assembled on site to make the finished boiler.
Safety
See also: Boiler explosion
To define and secure boilers safely, some professional specialized organizations such as the American Culture of Mechanical Engineers (ASME) develop requirements and regulation codes. For example, the ASME Boiler and Pressure Vessel Code is a typical providing a wide range of rules and directives to ensure compliance of the boilers and other pressure vessels with protection, security and design 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 poorly welded or riveted seams could start, leading to a violent eruption of the pressurized vapor. When water is changed into vapor it expands to over 1,000 times its original travels and volume down steam pipes at over 100 kilometres per hour. Because of this, steam is a superb way of moving energy and warmth around a site from a central boiler house to where it is necessary, but with no right boiler give food to water treatment, a steam-raising seed are affected from level formation and corrosion. At best, this raises energy costs and can result in poor quality vapor, reduced efficiency, shorter vegetation and unreliable operation. At worst, it can result in catastrophic failure and loss of life. Collapsed or dislodged boiler tubes can also aerosol scalding-hot vapor and smoke from the air intake and firing chute, injuring the firemen who insert the coal into the open fire chamber. Extremely large boilers providing a huge selection of horsepower to use factories can potentially demolish entire buildings.[6]

A boiler that has a loss of feed drinking water and is permitted to boil dry out can be hugely dangerous. If feed drinking water is sent in to the empty boiler then, the tiny cascade of inbound drinking water instantly boils on connection with the superheated metallic shell and leads to a violent explosion that cannot be managed even by safety vapor valves. Draining of the boiler can also happen if a leak occurs in the vapor source lines that is bigger than the make-up drinking water source 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 taking place, and thereby reduce their insurance statements.[7][8]

Superheated steam boiler

A superheated boiler on the steam locomotive.
Main article: Superheater
Most boilers produce steam to be used at saturation temperature; that is, saturated vapor. Superheated vapor boilers vaporize water and then further high temperature the steam in a superheater. This provides steam at much higher heat, but can decrease the overall thermal efficiency of the vapor generating seed because the bigger steam temp takes a higher flue gas exhaust heat range.[citation needed] There are several ways to circumvent this issue, by providing an economizer that heats the give food to drinking 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 often will, increase overall efficiency of both vapor generation and its own utilization: gains in input temp to a turbine should outweigh any cost in additional boiler complication and expense. There could be useful restrictions in using damp steam also, as entrained condensation droplets will damage turbine blades.

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

Superheater procedure is similar to that of the coils on an air conditioning unit, although for a different purpose. The steam piping is directed through the flue gas route in the boiler furnace. The heat in this area is between 1 typically,300 and 1,600 °C (2,372 and 2,912 °F). Some superheaters are glowing type; that is, they absorb temperature by radiation. Others are convection type, absorbing high temperature from a liquid. Some are a combination of both types. Through either method, the extreme heat in the flue gas path will heat the superheater steam piping and the steam within also. While the temperature of the steam in the superheater goes up, the pressure of the steam will not and the pressure remains the same as that of the boiler.[9] Virtually all steam superheater system designs remove droplets entrained in the steam to prevent damage to the turbine blading and associated piping.

Supercritical steam generator

Boiler for a power herb.
Main article: Supercritical steam generator
Supercritical steam generators are used for the production of energy frequently. 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 steam 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 changes the power generator that power is ultimately extracted. The liquid at that point may be considered a mixture of vapor and liquid droplets as it passes into the condenser. This leads to less fuel use and therefore less greenhouse gas production slightly. The term "boiler" shouldn't be used for a supercritical pressure steam generator, as no "boiling" occurs in this product.
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Accessories
Boiler accessories and fittings
Pressuretrols to regulate the vapor pressure in the boiler. Boilers generally have two or three 3 pressuretrols: a manual-reset pressuretrol, which functions as a safety by setting the top limit of vapor pressure, the operating pressuretrol, which controls when the boiler fires to keep pressure, as well as for boilers outfitted with a modulating burner, a modulating pressuretrol which controls the quantity of fire.
Basic safety valve: It can be used to relieve pressure and prevent possible explosion of a boiler.
Water level indications: They show the operator the amount of fluid in the boiler, known as a sight glass also, water gauge or water column.
Bottom level blowdown valves: They offer a way for removing solid particulates that condense and rest on underneath of a boiler. As the name implies, this valve is usually located on underneath of the boiler, and is occasionally opened up to use the pressure in the boiler to push these particulates out.
Continuous blowdown valve: This enables a small quantity of water to escape continuously. Its purpose is to prevent the water in the boiler becoming saturated with dissolved salts. Saturation would lead to foaming and cause water droplets to be transported over with the steam - an ailment 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 water level in a tank. Mostly found on a drinking water boiler.
Flash tank: High-pressure blowdown enters this vessel where in fact the vapor can 'flash' safely and become found in a low-pressure system or be vented to atmosphere as the ambient pressure blowdown moves to drain.
Automatic blowdown/continuous heat recovery system: This system allows the boiler to blowdown only once make-up water is flowing to the boiler, thereby transferring the utmost amount of heat possible from the blowdown to the make-up water. No flash tank is normally needed as the blowdown discharged is close to the temperatures of the makeup water.
Hand holes: These are metal plates installed in openings in "header" to permit for inspections & installation of tubes and inspection of inner surfaces.
Vapor drum internals, some screen, scrubber & cans (cyclone separators).
Low-water cutoff: It really is a mechanical means (usually a float switch) that is used to turn off the burner or shut down gas to the boiler to prevent it from jogging once the drinking water runs 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 provides a means for removing foam or other light-weight non-condensible chemicals that tend to float on top of water inside the boiler.
Circulating pump: It really is made to circulate drinking water back to the boiler after it has expelled a few of its heat.
Feedwater check valve or clack valve: A non-return stop valve in the feedwater range. This may be installed to the medial side of the boiler, just below the water level, or to the very best of the boiler.[10]
Top give food to: With this design for feedwater injection, water is fed to the very best of the boiler. This can reduce boiler fatigue triggered by thermal stress. By spraying the feedwater over some trays water is quickly warmed which can reduce limescale.
Desuperheater pipes or bundles: Some pipes or bundles of tubes in water drum or the vapor drum designed to cool superheated steam, in order to provide 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 vapor stop valve:
Steam traps:
Main vapor stop/check valve: It is utilized on multiple boiler installations.
Combustion accessories
Energy oil system:fuel oil heaters
Gas system:
Coal system:
Soot blower
Other essential items
Pressure gauges:
Feed pumps:
Fusible plug:
Inspectors test pressure measure attachment:
Name dish:
Registration dish: