A boiler is a closed vessel where water or other liquid is heated. The fluid does not boil. (In North America, the term "furnace" is normally used if the reason is never to boil the fluid.) The heated or vaporized liquid exits the boiler for use in various heating or processes applications,[1][2] including water heating, central heating, boiler-based power generation, food preparation, and sanitation. 
 
Materials 
The pressure vessel of the boiler is usually made of steel (or alloy steel), or of wrought iron historically. 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 is often found in superheater sections that won't come in contact with boiling water, and electrically heated stainless steel shell boilers are allowed under the European "Pressure Equipment Directive" for production of steam for sterilizers and disinfectors.[4] 
[url=https://en.wikipedia.org/wiki/Boiler]https://en.wikipedia.org/wiki/Boiler[/url] 
In live steam models, copper or brass is often used since it is easier fabricated in smaller size boilers. 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 steel) are used instead. 
 
For much of the Victorian "age group of vapor", the only materials 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), mentioned 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 transferred towards the utilization of steel, which is more powerful and cheaper, with welded construction, which is quicker and requires less labour. It should be mentioned, however, that wrought iron boilers corrode far slower than their modern-day steel counterparts, and are less vunerable to localized stress-corrosion and pitting. This makes the durability of old wrought-iron boilers considerably more advanced than those of welded steel boilers. 
 
Cast iron might be utilized for the heating vessel of home water heaters. Although such heaters are usually termed "boilers" in a few countries, their purpose is to create hot water usually, not steam, and so they 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 some of several fuels, such as wood, coal, oil, or natural gas. Electric steam boilers use level of resistance- or immersion-type heating elements. Nuclear fission is also used as a heat source for producing steam, either straight (BWR) or, in most cases, in specialised temperature exchangers called "steam generators" (PWR). High temperature recovery vapor generators (HRSGs) use the heat rejected from other procedures such as gas turbine. 
 
Boiler efficiency 
there are two methods to measure the boiler efficiency 1) direct method 2) indirect method 
 
Immediate 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 flow Hg= Enthalpy of saturated steam in k cal/kg Hf =Enthalpy of feed water in kcal/kg q= level of energy use in kg/hr GCV =gross calorific value in kcal/kg like pet coke (8200 kcal/KG) 
 
indirect method -to measure the boiler efficiency in indirect method, we need a subsequent 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 
Configurations 
Boilers can be classified into the following configurations: 
 
Pot boiler or Haycock boiler/Haystack boiler: a primitive "kettle" where a fireplace heats a partially filled water container from below. 18th century Haycock boilers produced and stored large quantities of very low-pressure vapor generally, hardly above that of the atmosphere often. These could burn off wood or frequently, coal. Efficiency was suprisingly low. 
Flued boiler with one or two large flues-an early type or forerunner 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 left above to support the steam (steam space). This is the type of boiler used in nearly all steam locomotives. Heat source is inside a furnace or firebox that needs to be held completely surrounded by 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 path of the hot gases, thus augmenting the heating surface which may be further increased by causing the gases invert direction through another parallel pipe or a bundle of multiple pipes (two-pass or come back flue boiler); additionally the gases may be taken 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 bundle of fire pipes inside the barrel which greatly increases the heating surface in comparison to a single tube and further improves heat transfer. Fire-tube boilers will often have a comparatively low rate of vapor creation, but high vapor storage capacity. Fire-tube boilers burn solid fuels mostly, but are readily adaptable to the people of the gas or liquid variety. 
 
Diagram of a water-tube boiler. 
Water-tube boiler: In this type, tubes filled with drinking water are arranged inside a furnace in several possible configurations. Often the water pipes connect large drums, the low ones containing water and top of the ones steam and water; in other cases, such as a mono-tube boiler, water is circulated with a pump through a succession of coils. This kind gives high steam creation rates generally, but less storage space capacity than the above mentioned. Water pipe boilers can be designed to exploit any temperature source and are generally preferred in high-pressure applications since the high-pressure drinking 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 kind of water-tube boiler in which pipes are close together and drinking water is pumped through them. A flash boiler differs from the kind of mono-tube steam generator in which the pipe is permanently filled up with water. In a flash boiler, the tube is held so hot that the water give food to is quickly flashed into steam and superheated. Flash boilers got some use in cars in the 19th century and this use continued into the early 20th century. . 
 
1950s design vapor locomotive boiler, from a Victorian Railways J class 
Fire-tube boiler with Water-tube firebox. Sometimes the two above types have been combined in the following manner: the firebox contains an assembly of water pipes, called thermic siphons. The gases then pass through a conventional firetube boiler. 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 included inside ensemble iron sections.[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 like the American Culture of Mechanical Engineers (ASME) develop specifications and regulation codes. For example, the ASME Boiler and Pressure Vessel Code is a typical providing an array of guidelines 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 steel shells can rupture, while welded or riveted seams could start poorly, leading to a violent eruption of the pressurized steam. When drinking water is changed into vapor it expands to over 1,000 times its original quantity and moves down steam pipes at over 100 kilometres per hour. Because of this, steam is a superb way of moving energy and temperature around a site from a central boiler house to where it is necessary, but with no right boiler feed water treatment, a steam-raising place are affected from range corrosion and formation. At best, this increases energy costs and can result in poor quality vapor, reduced efficiency, shorter vegetation and unreliable procedure. At worst, it can result in catastrophic reduction and failing of life. Collapsed or dislodged boiler tubes can also squirt scalding-hot steam and smoke from the air intake and firing chute, injuring the firemen who fill the coal in to the fire chamber. Extremely large boilers providing hundreds of horsepower to operate factories can potentially 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 feed water is sent in to the bare boiler then, the small cascade of inbound drinking water instantly boils on connection with the superheated metallic shell and leads to a violent explosion that can't be controlled even by protection vapor valves. Draining of the boiler can also happen if a leak occurs in the vapor supply lines that is larger than the make-up drinking water supply could replace. The Hartford Loop was invented in 1919 by the Hartford Steam Boiler and INSURANCE PROVIDER as a method to assist in preventing this condition from happening, and thereby reduce their insurance statements.[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 steam boilers vaporize the water and additional heat the steam in a superheater then. This provides steam at much higher heat, but can reduce the overall thermal efficiency of the vapor generating plant because the bigger steam temperatures takes a higher flue gas exhaust temp.[citation needed] There are several ways to circumvent this issue, typically by providing an economizer that heats the give food to drinking water, a combustion air heater in the hot flue gas exhaust route, or both. You will find benefits to superheated steam that may, and often will, increase overall efficiency of both steam generation and its own utilization: gains in input temperatures to a turbine should outweigh any cost in additional boiler problem and expense. There could be practical restrictions in using wet vapor also, as entrained condensation droplets will damage turbine blades. 
 
Superheated steam presents unique safety concerns because, if any system component fails and allows steam to escape, the high 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 intense heat and sound from such a leak clearly indicates its presence. 
 
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 path in the boiler furnace. The temp in this area is normally between 1,300 and 1,600 °C (2,372 and 2,912 °F). Some superheaters are radiant type; that is, they absorb warmth by radiation. 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 heat the superheater steam piping and the steam within also. While the temp of the vapor in the superheater goes up, the pressure of the steam will not and the pressure remains exactly like that of the boiler.[9] Almost 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 charged power vegetable. 
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 higher pressure (over 3,200 psi or 22 MPa) that the physical turbulence that characterizes boiling ceases to occur; the fluid is neither water nor gas but a super-critical liquid. There is absolutely no generation of vapor bubbles within water, because the pressure is above the critical pressure point at which vapor bubbles can form. As the liquid expands through the turbine stages, its thermodynamic state drops below the critical point as it does work turning the turbine which turns the power generator from which power is eventually extracted. The fluid at that time may be a mix of vapor and liquid droplets as it goes by into the condenser. This results in slightly less energy use and for that reason less greenhouse gas creation. 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 control the steam pressure in the boiler. Boilers generally have 2 or 3 3 pressuretrols: a manual-reset pressuretrol, which functions as a security by setting the top limit of vapor pressure, the operating pressuretrol, which controls when the boiler fires to keep up pressure, as well as for boilers outfitted with a modulating burner, a modulating pressuretrol which controls the quantity of fire. 
Protection valve: It is utilized to relieve pressure and stop possible explosion of a boiler. 
Water level indications: They show the operator the level of liquid in the boiler, also known as a sight glass, water gauge or drinking water column. 
Bottom blowdown valves: They offer a way for removing solid particulates that condense and rest on underneath of the boiler. As the name suggests, this valve is usually located directly on the bottom of the boiler, and is sometimes opened up to use the pressure in the boiler to drive these particulates out. 
Constant blowdown valve: This allows a small level of water to escape continuously. Its purpose is to prevent the water in the boiler becoming saturated with dissolved salts. Saturation would business lead to foaming and cause drinking water droplets to be transported over with the vapor - a disorder known as priming. Blowdown is also often used to monitor the chemistry of the boiler water. 
Trycock: a type of valve that is often use to manually check a liquid level in a container. Most entirely on a drinking water boiler commonly. 
Flash tank: High-pressure blowdown enters this vessel where in fact the steam can 'flash' safely and become found in a low-pressure system or be vented to atmosphere as the ambient pressure blowdown flows to drain. 
Automatic blowdown/constant heat recovery system: This system allows the boiler to blowdown only once make-up water is moving to the boiler, thereby transferring the maximum amount of heat possible from the blowdown to the makeup water. No flash tank is normally needed as the blowdown discharged is near to the temp of the make-up water. 
Hand holes: They are metal plates installed in openings in "header" to allow for inspections &amp; installation of pipes and inspection of internal surfaces. 
Steam drum internals, some screen, scrubber &amp; cans (cyclone separators). 
Low-water cutoff: It really is a mechanical means (usually a float switch) that is used to turn from the burner or shut down fuel to the boiler to avoid it from jogging once the drinking water moves below a certain point. If a boiler is "dry-fired" (burnt without drinking water in it) it can cause rupture or catastrophic failure. 
Surface blowdown line: It provides a means for removing foam or other light-weight non-condensible substances that have a tendency to float on top of the water inside the boiler. 
Circulating pump: It really is designed to circulate 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 range. This may be suited to the relative aspect of the boiler, below water level just, or to the top of the boiler.[10] 
Top give food to: With this design for feedwater injection, the water is fed to the very best of the boiler. This may 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 pipes or bundles: Some pipes or bundles of tubes in the water drum or the steam drum designed to cool superheated vapor, in order to supply auxiliary equipment that does not need, or may be damaged by, dry vapor. 
Chemical substance injection line: A connection to add chemicals for controlling feedwater pH. 
Steam accessories 
Main vapor stop valve: 
Steam traps: 
Main steam stop/check valve: It is used on multiple boiler installations. 
Combustion accessories 
Gasoline oil system:gasoline 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 plate: