A boiler is a closed vessel where water or other liquid is heated. The fluid will not boil. (In North America, the term "furnace" is generally used if the purpose is not to boil the liquid.) The warmed or vaporized liquid exits the boiler for use in a variety of heating system or processes applications,[1][2] including drinking water heating, central heating system, boiler-based power generation, food preparation, and sanitation.

Materials
The pressure vessel of a 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 credited to corrosion and stress corrosion breaking.[3] However, ferritic stainless steel is often used in superheater sections that will not come in contact with boiling drinking water, and electrically heated stainless shell boilers are allowed under the Western european "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 since it is more fabricated in smaller size boilers easily. Historically, copper was often used for fireboxes (especially 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 metal) are used instead.

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

Cast iron may be used for the heating system vessel of local drinking water heaters. Although such heaters are usually termed "boilers" in some countries, their purpose is usually to produce warm 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 steam boilers.
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Energy
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 resistance- or immersion-type heating system elements. Nuclear fission is utilized as a heat source for generating steam also, either straight (BWR) or, generally, in specialised temperature exchangers called "steam generators" (PWR). Warmth recovery vapor generators (HRSGs) use the heat rejected from other procedures such as gas turbine.

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

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

boiler efficiency =Q*((Hg-Hf)/q)*(GCV *100 ) Q =Total steam flow Hg= Enthalpy of saturated vapor in k cal/kg Hf =Enthalpy of feed drinking water in kcal/kg q= quantity of fuel 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 following parameter like

Ultimate analysis of fuel (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 gas in kcal/kg
ash percentage in combustible fuel
GCV of ash in kcal/kg
Configurations
Boilers can be classified into the following configurations:

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

Diagram of a fire-tube boiler
Fire-tube boiler: Here, water partially fills a boiler barrel with a little volume left above to accommodate the steam (steam space). This is the kind of boiler used in all steam locomotives nearly. The heat source is inside a furnace or firebox that has to be kept completely surrounded by the water in order to keep the temperature of the heating system 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 surface which can be further increased by causing the gases invert direction through a second parallel pipe or a bundle of multiple tubes (two-pass or return flue boiler); additionally 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 go through a lot of money of fire pipes inside the barrel which greatly increases the heating system surface in comparison to a single pipe and further boosts heat transfer. Fire-tube boilers have a comparatively low rate of steam production usually, but high vapor storage capacity. Fire-tube boilers mostly 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 kind, tubes filled up with water are arranged in the furnace in a number of possible configurations. Usually the drinking water tubes connect large drums, the low ones comprising water and top of the ones steam and water; in other instances, like a mono-tube boiler, drinking water is circulated with a pump through a succession of coils. This type provides high steam production rates generally, but less storage space capacity than the above mentioned. Water pipe boilers can be designed to exploit any temperature 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.
Flash boiler: A flash boiler is a specialized type of water-tube boiler where pipes are close collectively and drinking water is pumped through them. A flash boiler differs from the type of mono-tube vapor generator where the pipe is permanently filled up with water. Super fast boiler, the pipe is kept so hot that the water give food to is quickly flashed into vapor and superheated. Flash boilers experienced some use in automobiles in the 19th century and this use continued in to the early 20th century. .

1950s design vapor locomotive boiler, from a Victorian Railways J class
Fire-tube boiler with Water-tube firebox. Sometimes both above types have been combined in the next manner: the firebox consists of an set up of water tubes, called thermic siphons. The gases pass through a conventional firetube boiler then. Water-tube fireboxes were installed in many Hungarian locomotives,[citation needed] but have fulfilled with little success far away.
Sectional boiler. Inside a cast iron sectional boiler, sometimes called a "pork chop boiler" water is contained inside solid iron sections.[citation needed] These sections are assembled on site to create the finished boiler.
Safety
See also: Boiler explosion
To define and secure boilers safely, some professional specialized organizations such as the American Society of Mechanical Technical engineers (ASME) develop specifications and regulation rules. For instance, the ASME Boiler and Pressure Vessel Code is a standard providing an array 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 source of many serious injuries and property destruction due to badly understood engineering principles. Thin and brittle steel shells can rupture, while poorly welded or riveted seams could start, resulting in a violent eruption of the pressurized steam. When drinking water is changed into vapor it expands to over 1,000 times its original volume and travels down steam pipes at over 100 kilometres per hour. Because of this, steam is a superb way of moving energy and warmth around a niche site from a central boiler house to where it is needed, but without the right boiler feed water treatment, a steam-raising seed are affected from range formation and corrosion. At best, this raises energy costs and can lead to poor quality vapor, reduced efficiency, shorter plant life and unreliable procedure. At worst, it can result in catastrophic failure and lack of life. Collapsed or dislodged boiler tubes can also aerosol scalding-hot steam and smoke from the air intake and firing chute, injuring the firemen who load the coal in to the fireplace chamber. Extremely large boilers providing hundreds of horsepower to operate factories could demolish entire buildings.[6]

A boiler which has a loss of feed water and it is permitted to boil dry out can be hugely dangerous. If give food to water is sent into the empty boiler then, the tiny cascade of inbound water instantly boils on contact with the superheated metal shell and leads to a violent explosion that cannot be controlled even by basic safety steam valves. Draining of the boiler can also happen if a leak occurs in the steam supply lines that is bigger than the make-up drinking water supply could replace. The Hartford Loop was developed in 1919 by the Hartford Vapor Boiler and Insurance Company as a method to assist in preventing this problem from happening, and thus reduce their insurance promises.[7][8]

Superheated steam boiler

A superheated boiler on a steam locomotive.
Main article: Superheater
Most boilers produce vapor to be used at saturation temperature; that is, saturated vapor. Superheated steam boilers vaporize water and additional heating the steam in a superheater then. This provides steam at much higher heat range, but can decrease the overall thermal efficiency of the vapor generating seed because the higher steam temperatures requires a higher flue gas exhaust temperatures.[citation needed] There are several ways to circumvent this problem, by providing an economizer that heats the feed water typically, a combustion air heater in the hot flue gas exhaust route, or both. You will find advantages to superheated steam that may, and will often, increase overall efficiency of both vapor generation and its own utilization: benefits in input temp to a turbine should outweigh any cost in additional boiler problem and expense. There could be practical limitations in using wet vapor also, 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 high pressure and temperature can cause serious, instantaneous injury 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 indicates its existence clearly.

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 heat in this area is normally between 1,300 and 1,600 °C (2,372 and 2,912 °F). Some superheaters are glowing type; that is, they absorb heat by radiation. Others are convection type, absorbing high temperature from a liquid. Some are a mixture of both types. Through either method, the extreme temperature in the flue gas route will also heat the superheater vapor piping and the steam within. While the heat 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] Almost 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 generally used for the production of energy. They operate at supercritical pressure. As opposed to a "subcritical boiler", a supercritical vapor 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 liquid is neither liquid nor gas but a super-critical fluid. There is no era of vapor bubbles within the water, because the pressure is above the critical pressure point at which vapor bubbles can develop. As the fluid expands through the turbine phases, its thermodynamic condition drops below the critical point as it does work turning the turbine which changes the electrical generator that power is eventually extracted. The fluid at that time may be considered a mix of vapor and liquid droplets as it goes by into the condenser. This results in less fuel use and for that reason 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 fittings and accessories
Pressuretrols to control the steam 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 steam pressure, the operating pressuretrol, which controls when the boiler fires to keep pressure, and for boilers equipped with a modulating burner, a modulating pressuretrol which controls the amount of fire.
Protection valve: It is utilized to alleviate pressure and prevent possible explosion of a boiler.
Water level indications: They show the operator the level of fluid in the boiler, known as a sight cup also, water measure or drinking water column.
Bottom level blowdown valves: They provide a means for removing solid particulates that condense and lie on the bottom of the boiler. As the name implies, this valve is usually located on the bottom of the boiler, and is occasionally opened to use the pressure in the boiler to drive these particulates out.
Constant blowdown valve: This enables a small level of water to flee 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 carried over with the vapor - a disorder 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. Mostly entirely on a water boiler.
Flash tank: High-pressure blowdown enters this vessel where in fact the vapor can 'flash' safely and become used in a low-pressure system or be vented to atmosphere while the ambient pressure blowdown flows to drain.
Automatic blowdown/constant heat recovery system: This technique allows the boiler to blowdown only once makeup water is flowing to the boiler, thereby transferring the maximum amount of heat possible from the blowdown to the make-up water. No flash container is normally needed as the blowdown discharged is near to the heat range of the make-up water.
Hand openings: They are steel plates installed in openings in "header" to permit for inspections & installation of tubes and inspection of internal surfaces.
Steam drum internals, a series of screen, scrubber & cans (cyclone separators).
Low-water cutoff: It really is a mechanical means (usually a float switch) that is utilized to turn from the burner or shut down gas to the boiler to prevent it from working once the drinking water runs below a certain point. If a boiler is "dry-fired" (burned without water in it) it can cause rupture or catastrophic failure.
Surface blowdown series: It offers a way for removing foam or other light-weight non-condensible substances 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 some of its heat.
Feedwater check valve or clack valve: A non-return stop valve in the feedwater series. This can be fitted to the side of the boiler, below the water level just, or to the top of the boiler.[10]
Top give food to: Within this design for feedwater injection, water is fed to the very best of the boiler. This can reduce boiler exhaustion triggered by thermal stress. By spraying the feedwater over a series of trays the water is quickly heated which can reduce limescale.
Desuperheater tubes or bundles: A series of pipes or bundles of pipes in water drum or the steam drum made to cool superheated vapor, in order to supply auxiliary equipment that does not need, or may be damaged by, dry out steam.
Chemical injection line: A link with add chemicals for controlling feedwater pH.
Steam accessories
Main vapor stop valve:
Steam traps:
Main vapor stop/check valve: It can be used 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 plate: