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A boiler is a closed vessel where water or other liquid is heated. The fluid will not boil. (In THE UNITED STATES, the term "furnace" is normally used if the reason is not to boil the liquid.) The warmed or vaporized liquid exits the boiler for use in a variety of heating system or procedures applications,[1][2] including water heating, central heating, boiler-based power generation, cooking, and sanitation.
Materials
The pressure vessel of the 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 due to corrosion and stress corrosion cracking.[3] However, ferritic stainless is often used in superheater sections that will not be exposed to 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]
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 steam 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 much of the Victorian "age group of steam", the only materials used for boilermaking was the highest grade of wrought iron, with assembly by rivetting. This iron was obtained from specialist ironworks, such as at Cleator Moor (UK), noted 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 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 observed, however, that wrought iron boilers corrode much slower than their modern-day metal counterparts, and are less susceptible to localized stress-corrosion and pitting. This makes the durability of old wrought-iron boilers much superior to those of welded metal boilers.
Cast iron may be used for the heating vessel of domestic water heaters. Although such heaters are usually termed "boilers" in some countries, their purpose will be 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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Energy
The foundation of heat 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 also used as a heat source for producing steam, either straight (BWR) or, in most cases, in specialised warmth exchangers called "steam generators" (PWR). High temperature recovery vapor generators (HRSGs) use 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 useful or more common
boiler efficiency =Q*((Hg-Hf)/q)*(GCV *100 ) Q =Total vapor stream Hg= Enthalpy of saturated steam in k cal/kg Hf =Enthalpy of give food to 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 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 gas 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 water container from below. 18th century Haycock boilers generally produced and stored large volumes of very low-pressure steam, barely above that of the atmosphere often. These could burn off wood or most often, 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 kind of boiler used in all steam locomotives nearly. The heat source is in the furnace or firebox that needs to be kept permanently surrounded by water in order to keep the heat range of the heating system surface below the boiling point. The furnace can be situated at one end of the fire-tube which lengthens the road of the hot gases, thus augmenting the heating system surface which can be further increased by causing the gases reverse direction through a second parallel pipe or a lot of money of multiple tubes (two-pass or return flue boiler); on the other hand the gases may be studied along the sides and then under the boiler through flues (3-pass boiler). In case of a locomotive-type boiler, a boiler barrel extends from the firebox and the hot gases pass through a bundle of fire tubes inside the barrel which greatly escalates the heating surface in comparison to a single pipe and further improves heat transfer. Fire-tube boilers have a comparatively low rate of vapor production usually, but high vapor storage capacity. Fire-tube boilers burn solid fuels mostly, but are readily flexible to those of the liquid or gas variety.
Diagram of a water-tube boiler.
Water-tube boiler: In this kind, tubes filled with drinking water are arranged inside a furnace in a true variety of possible configurations. Water tubes connect large drums Often, the low ones containing water and top of the ones water and steam; in other cases, like a mono-tube boiler, water is circulated by a pump through a succession of coils. This kind generally provides high steam production rates, 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 because the high-pressure drinking water/steam is included within small diameter pipes which can withstand the pressure with a thinner wall.
Flash boiler: A flash boiler is a specialized type of water-tube boiler where tubes are close jointly and 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 held so hot that water feed is quickly flashed into steam and superheated. Flash boilers had some use in automobiles in the 19th century which 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 both 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 ensemble iron sectional boiler, sometimes called a "pork chop boiler" water is included inside cast iron areas.[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 like the American Society of Mechanical Technical engineers (ASME) develop standards and regulation rules. For example, the ASME Boiler and Pressure Vessel Code is a typical providing an array of rules and directives to ensure compliance of the boilers and other pressure vessels with safety, security and design standards.[5]
Historically, boilers were a source of many serious injuries and property destruction as a consequence to badly understood engineering principles. Thin and brittle metal shells can rupture, while poorly welded or riveted seams could open up, resulting in a violent eruption of the pressurized steam. When water is converted to steam it expands to over 1,000 times its original volume and moves down steam pipes at over 100 kilometres per hour. Because of this, steam is a great way of moving energy and warmth around a niche site from a central boiler house to where it is necessary, but without the right boiler give food to water treatment, a steam-raising vegetable are affected from scale development and corrosion. At best, this increases energy costs and can result in poor quality steam, reduced efficiency, shorter vegetation and unreliable procedure. At worst, it can result in catastrophic reduction and failure of life. Collapsed or dislodged boiler tubes can also spray scalding-hot steam and smoke from the air intake and firing chute, injuring the firemen who insert the coal in to the fireplace chamber. Extremely large boilers providing hundreds of horsepower to operate factories could demolish entire buildings.[6]
A boiler that has a loss of give food to drinking water and is permitted to boil dry out can be extremely dangerous. If give food to drinking water is then sent into the clear boiler, the tiny cascade of inbound water instantly boils on connection with the superheated metal shell and leads to a violent explosion that can't 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 drinking water source could replace. The Hartford Loop was invented in 1919 by the Hartford Vapor Boiler and Insurance Company as a method to assist in preventing this problem from happening, and thereby reduce their insurance statements.[7][8]
Superheated steam boiler
A superheated boiler on a steam locomotive.
Main article: Superheater
Most boilers produce vapor to be used at saturation temperatures; that is, saturated steam. Superheated steam boilers vaporize water and additional heat the steam in a superheater then. This provides vapor at higher temperatures, but can decrease the overall thermal efficiency of the vapor generating seed because the higher steam temperatures requires a higher flue gas exhaust heat range.[citation needed] There are several ways to circumvent this problem, typically by giving an economizer that heats the feed drinking water, a combustion air heater in the hot flue gas exhaust route, or both. You can find advantages to superheated vapor that may, and often will, increase overall efficiency of both vapor generation and its utilization: increases in input heat to a turbine should outweigh any cost in additional boiler problem and expense. There may be useful limitations in using wet steam 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 harm to anyone in its path. Since the escaping steam will initially 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 range in this field is between 1 typically,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 heat from a liquid. Some are a combination of the two 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 steam in the superheater increases, the pressure of the vapor 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 avoid damage to the turbine blading and associated piping.
Supercritical steam generator
Boiler for a power seed.
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 higher pressure (over 3,200 psi or 22 MPa) that the physical turbulence that characterizes boiling ceases to occur; the fluid is neither liquid nor gas but a super-critical fluid. There is no era of steam bubbles within the water, because the pressure is above the critical pressure point at which vapor bubbles can develop. As the liquid expands through the turbine phases, its thermodynamic state drops below the critical point as it does work turning the turbine which changes the power generator from which power is ultimately extracted. The fluid at that time may be a mix of steam and liquid droplets as it passes in to the condenser. This results in somewhat less gasoline use and therefore less greenhouse gas production. The word "boiler" shouldn't be used for a supercritical pressure vapor generator, as no "boiling" occurs in this product.
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Accessories
Boiler accessories and fittings
Pressuretrols to control 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 vapor pressure, the working pressuretrol, which controls when the boiler fires to maintain pressure, and for boilers outfitted with a modulating burner, a modulating pressuretrol which handles the quantity of fire.
Basic safety valve: It is used to relieve pressure and prevent possible explosion of the boiler.
Water level indicators: They show the operator the level of liquid in the boiler, also called a view cup, water measure or water column.
Bottom level blowdown valves: They offer a means for removing solid particulates that condense and rest on the bottom of a boiler. As the name indicates, this valve is usually located directly on the bottom of the boiler, and is sometimes opened to use the pressure in the boiler to press these particulates out.
Continuous blowdown valve: This enables a small quantity of water to flee continuously. Its purpose is to avoid 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 steam - an ailment known as priming. Blowdown is often used to monitor the chemistry of the boiler drinking water also.
Trycock: a kind of valve that is often use to manually check a liquid level in a container. Mostly found 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 as 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 makeup water. No flash container is generally needed as the blowdown discharged is close to the heat range of the makeup water.
Hand holes: These are metal plates installed in openings in "header" to permit 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 used to turn from the burner or shut down gasoline to the boiler to avoid it from jogging once the drinking water runs 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 collection: It provides a means for removing foam or other lightweight non-condensible chemicals that tend to float on top of the water inside the boiler.
Circulating pump: It is made to circulate drinking water back to the boiler after they have expelled some of its heat.
Feedwater check valve or clack valve: A non-return stop valve in the feedwater range. This may be fitted to the medial side of the boiler, just below water level, or to the top of the boiler.[10]
Top feed: With this design for feedwater injection, the water is fed to the very best of the boiler. This can reduce boiler exhaustion triggered by thermal stress. By spraying the feedwater over some trays water is quickly heated which can reduce limescale.
Desuperheater pipes or bundles: Some pipes or bundles of tubes in the water drum or the vapor drum designed to cool superheated vapor, in order to provide auxiliary equipment that will 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 steam stop valve:
Steam traps:
Main steam stop/check valve: It can be used on multiple boiler installations.
Combustion accessories
Fuel oil system:fuel oil heaters
Gas system:
Coal system:
Soot blower
Other essential items
Pressure gauges:
Feed pumps:
Fusible plug:
Inspectors test pressure gauge attachment:
Name plate:
Registration dish: |
