A boiler is a closed vessel in which drinking water or other fluid is heated. The fluid does not necessarily boil. (In North America, the term "furnace" is generally used if the purpose is never to boil the liquid.) The heated or vaporized liquid exits the boiler for use in various procedures or heating applications, including water heating, central heating, boiler-based power era, food preparation, and sanitation.
The pressure vessel of the boiler is usually manufactured from steel (or alloy steel), or of wrought iron historically. Stainless steel, of the austenitic types especially, is not used in wetted elements of boilers due to stress and corrosion corrosion cracking. However, ferritic stainless is often used in superheater sections that will not come in contact with boiling water, and electrically heated stainless shell boilers are allowed under the Western european "Pressure Equipment Directive" for production of steam for sterilizers and disinfectors.
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 (particularly for vapor locomotives), because of 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 of steam", the only materials used for boilermaking was the highest grade of wrought iron, with set up by rivetting. This iron was extracted 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 structure, which is quicker and requires less labour. It ought to be noted, however, that wrought iron boilers corrode significantly slower than their modern-day metal counterparts, and are less vunerable to localized stress-corrosion and pitting. This makes the longevity of old wrought-iron boilers considerably superior to those of welded metal boilers.
Cast iron might be used for the heating vessel of home drinking water heaters. Although such heaters are usually termed "boilers" in some countries, their purpose is usually to produce warm water, not steam, and so they 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 heat for a boiler is combustion of any of several fuels, such as wood, coal, oil, or natural gas. Electric vapor boilers use resistance- or immersion-type heating elements. Nuclear fission is also used as a heat source for generating steam, either directly (BWR) or, generally, in specialised temperature exchangers called "steam generators" (PWR). Temperature recovery steam generators (HRSGs) use the heat rejected from other procedures such as gas turbine.
there are two methods to gauge the boiler efficiency 1) direct method 2) indirect method
Direct method -direct approach to boiler efficiency test is more usable or even more common
boiler efficiency =Q*((Hg-Hf)/q)*(GCV *100 ) Q =Total steam circulation Hg= Enthalpy of saturated vapor in k cal/kg Hf =Enthalpy of feed water in kcal/kg q= quantity of gas 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 are in need of a subsequent parameter like
Ultimate analysis of gas (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
Boilers can be classified in to the following configurations:
Container 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 produced and stored large amounts of very low-pressure steam generally, barely 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 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 remaining above to support the steam (steam space). This is the kind of boiler used in nearly all steam locomotives. The heat source is in the furnace or firebox that has to be kept permanently surrounded by the water in order to maintain the temperature of the heating system surface below the boiling point. The furnace can be situated at one end of the fire-tube which lengthens the path of the hot gases, thus augmenting the heating system surface which may be further increased by making the gases invert direction through another parallel pipe or a bundle of multiple pipes (two-pass or come back flue boiler); alternatively the gases may be studied along the edges and then beneath the boiler through flues (3-move boiler). In case there is a locomotive-type boiler, a boiler barrel stretches from the firebox and the hot gases pass through a lot of money of fire tubes inside the barrel which greatly increases the heating system surface compared to a single tube and further enhances heat transfer. Fire-tube boilers have a comparatively low rate of steam creation usually, but high vapor storage capacity. Fire-tube boilers burn solid fuels mainly, but are readily adjustable to those of the liquid or gas variety.
Diagram of a water-tube boiler.
Water-tube boiler: In this type, tubes filled up with drinking water are arranged inside a furnace in several possible configurations. Often the drinking water pipes connect large drums, the low ones containing water and the top ones vapor and water; in other cases, such as a mono-tube boiler, water is circulated with a pump through a succession of coils. This type gives high vapor creation rates generally, but less storage space capacity than the above mentioned. Water pipe boilers can be made to exploit any high temperature source and are generally preferred in high-pressure applications since the high-pressure water/vapor is included 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 where tubes are close collectively and drinking water is pumped through them. A flash boiler differs from the kind of mono-tube vapor generator in which the pipe is permanently filled up with water. In a flash boiler, the tube is kept so hot that water give food to is quickly flashed into steam and superheated. Flash boilers got some use in cars in the 19th century which 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 the two above types have been mixed in the following manner: the firebox consists of an set up of water pipes, called thermic siphons. The gases go through a conventional firetube boiler then. Water-tube fireboxes were installed in many Hungarian locomotives, but have fulfilled with little success in other countries.
Sectional boiler. Inside a ensemble iron sectional boiler, sometimes called a "pork chop boiler" water is included inside cast iron areas. These areas are assembled on site to produce the finished boiler.
See also: Boiler explosion
To define and secure boilers safely, some professional specialized organizations like the American Society of Mechanical Engineers (ASME) develop requirements and regulation rules. 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, design and security standards.
Historically, boilers were a way to obtain many serious injuries and property destruction as a consequence to badly understood engineering principles. Thin and brittle metal shells can rupture, while welded or riveted seams could open up poorly, resulting in a violent eruption of the pressurized vapor. When water is converted to vapor it expands to over 1,000 times its original volume and moves down vapor pipes at over 100 kilometres each hour. As a result of this, vapor is a superb way of moving energy and high temperature around a site from a central boiler house to where it is needed, but with no right boiler give food to water treatment, a steam-raising seed will suffer from range corrosion and formation. At best, this raises energy costs and can lead to poor quality vapor, reduced efficiency, shorter vegetation and unreliable procedure. At worst, it can lead to catastrophic loss and failure of life. Collapsed or dislodged boiler tubes can also squirt scalding-hot vapor and smoke out of the air intake and firing chute, injuring the firemen who load the coal into the open fire chamber. Extremely large boilers providing a huge selection of horsepower to use factories can potentially demolish entire buildings.
A boiler which has a loss of feed water and is permitted to boil dry can be extremely dangerous. If give food to water is sent in to the clear boiler then, the small cascade of incoming water instantly boils on contact with the superheated metal shell and leads to a violent explosion that cannot be controlled even by safety steam valves. Draining of the boiler can also happen if a leak occurs in the steam source lines that is larger than the make-up water source could replace. The Hartford Loop was invented in 1919 by the Hartford Vapor Boiler and Insurance Company as a method to help prevent this condition from taking place, and thereby reduce their insurance claims.
Superheated steam boiler
A superheated boiler on a steam locomotive.
Main article: Superheater
Most boilers produce vapor to be utilized at saturation temperature; that is, saturated vapor. Superheated vapor boilers vaporize the water and then further high temperature the steam in a superheater. This provides vapor at higher temperatures, but can reduce the overall thermal efficiency of the steam generating seed because the higher vapor heat range takes a higher flue gas exhaust heat range. There are several ways to circumvent this problem, typically by giving an economizer that heats the feed water, a combustion air heater in the hot flue gas exhaust path, or both. You can find advantages to superheated vapor that may, and often will, increase overall efficiency of both steam generation and its own utilization: gains in input temperature to a turbine should outweigh any cost in additional boiler problem and expense. There may be useful restrictions in using moist steam 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 flee, the ruthless 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 intense heat and sound from such a leak obviously indicates its presence.
Superheater operation 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 temperature in this field is typically between 1,300 and 1,600 °C (2,372 and 2,912 °F). Some superheaters are radiant type; that is, they absorb temperature by rays. Others are convection type, absorbing high temperature from a liquid. 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 heat range of the vapor in the superheater increases, the pressure of the steam will not and the pressure remains exactly like that of the boiler. Virtually all steam superheater system designs remove droplets entrained in the steam to avoid harm to the turbine blading and associated piping.
Supercritical steam generator
Boiler for a charged power plant.
Main article: Supercritical steam generator
Supercritical steam generators are used for the production of electric power 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 no generation of vapor bubbles within the 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 state drops below the critical point as it does work turning the turbine which converts the electrical generator from which power is eventually extracted. The fluid at that point may be considered a mix of vapor and liquid droplets as it goes by in to the condenser. This results in slightly less gasoline use and therefore less greenhouse gas production. The word "boiler" shouldn't be used for a supercritical pressure steam 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 basic safety by setting the upper limit of steam pressure, the working pressuretrol, which handles when the boiler fires to keep pressure, as well as for boilers equipped with a modulating burner, a modulating pressuretrol which settings the quantity of fire.
Safety valve: It can be used to relieve pressure and prevent possible explosion of a boiler.
Water level indicators: They show the operator the level of liquid in the boiler, known as a view glass also, water measure or water column.
Bottom blowdown valves: They offer a means for removing solid particulates that condense and lie on underneath of a boiler. As the name indicates, this valve is situated straight on the bottom of the boiler usually, and is occasionally opened up to use the pressure in the boiler to push these particulates out.
Continuous blowdown valve: This allows a small level of water to escape continuously. Its purpose is to avoid the water in the boiler becoming saturated with dissolved salts. Saturation would lead to foaming and cause drinking water droplets to be carried over with the steam - an ailment known as priming. Blowdown is often used to monitor the chemistry of the boiler drinking water also.
Trycock: a type of valve that is often use to manually check a liquid level in a tank. Mostly entirely on a drinking water boiler.
Flash tank: High-pressure blowdown enters this vessel where the steam 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 technique allows the boiler to blowdown only once make-up 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 temperature of the makeup water.
Hand holes: They may be steel plates installed in openings in "header" to allow for inspections & installing tubes and inspection of inner surfaces.
Vapor drum internals, a series of screen, scrubber & cans (cyclone separators).
Low-water cutoff: It is a mechanical means (usually a float change) that is utilized to turn off the burner or shut down fuel to the boiler to prevent it from jogging once the drinking water moves below a certain point. If a boiler is "dry-fired" (burnt without 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 substances that have a tendency to float together with the water inside the boiler.
Circulating pump: It really is designed to circulate drinking water back again to the boiler after they have expelled a few of its heat.
Feedwater check valve or clack valve: A non-return stop valve in the feedwater line. This may be fitted to the comparative aspect of the boiler, below the water level just, or to the top of the boiler.
Top give food to: Within this design for feedwater injection, the water is fed to the very best of the boiler. This can reduce boiler exhaustion caused by thermal stress. By spraying the feedwater over a series of trays the water is quickly warmed which can reduce limescale.
Desuperheater tubes or bundles: Some tubes or bundles of pipes in water drum or the vapor drum made to cool superheated vapor, in order to provide auxiliary equipment that will not need, or may be damaged by, dry out vapor.
Chemical injection line: A connection to add chemicals for controlling feedwater pH.
Main vapor stop valve:
Main steam stop/check valve: It is used on multiple boiler installations.
Gasoline oil system:gasoline oil heaters
Other essential items
Inspectors test pressure measure attachment: