A boiler is a closed vessel where water or other fluid is heated. The fluid will not always boil. (In North America, the word "furnace" is generally used if the purpose is never to boil the liquid.) The warmed or vaporized fluid exits the boiler for use in various procedures or heating system applications,[1 - [2 - including drinking water heating, central heating, boiler-based power era, cooking food, and sanitation.
The pressure vessel of a boiler is usually made of steel (or alloy steel), or of wrought iron historically. Stainless steel, of the austenitic types especially, is not found in wetted parts of boilers credited to corrosion and stress corrosion cracking.[3 - However, ferritic stainless steel is often used 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 creation of steam for sterilizers and disinfectors.[4 -
https://en.wikipedia.org/wiki/Boiler - https://en.wikipedia.org/wiki/Boiler
In live steam models, copper or brass is often used because it is easier fabricated in smaller size boilers. Historically, copper was often used for fireboxes (especially 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 group of steam", the only materials used for boilermaking was the highest grade of wrought iron, with assembly by rivetting. This iron was 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 relocated towards the use of metal, which is stronger and cheaper, with welded construction, which is quicker and requires less labour. It should be noted, however, that wrought iron boilers corrode considerably slower than their modern-day metal counterparts, and are less susceptible to localized stress-corrosion and pitting. This makes the longevity of old wrought-iron boilers much more advanced than those of welded metal boilers.
Cast iron can be utilized for the heating vessel of home 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 vapor boilers.
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The source of heating for a boiler is combustion of some of several fuels, such as wood, coal, oil, or gas. Electric steam boilers use level of resistance- or immersion-type heating elements. Nuclear fission is used as a heat source for producing steam also, either straight (BWR) or, in most cases, in specialised heat exchangers called "steam generators" (PWR). Heat recovery steam generators (HRSGs) use heat rejected from other processes such as gas turbine.
there are two methods to gauge the boiler efficiency 1) direct method 2) indirect method
Immediate method -direct approach to boiler efficiency test is more useful or more common
boiler efficiency =Q*((Hg-Hf)/q)*(GCV *100 ) Q =Total vapor flow Hg= Enthalpy of saturated vapor in k cal/kg Hf =Enthalpy of feed drinking water in kcal/kg q= level of gasoline 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 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 energy in kcal/kg
ash percentage in combustible fuel
GCV of ash in kcal/kg
Boilers can be classified into the following configurations:
Container boiler or Haycock boiler/Haystack boiler: a primitive "kettle" where a fireplace heats a partially filled water box 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 wood or most often, coal. Efficiency was very 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, water partially fills a boiler barrel with a little volume remaining above to support the vapor (vapor space). This is the type of boiler used in nearly all steam locomotives. The heat source is in the furnace or firebox that needs to be held permanently surrounded by water in order to maintain the temperatures 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 system surface which can be further increased by making the gases reverse direction through another parallel pipe or a lot of money of multiple tubes (two-pass or come back flue boiler); on the other hand the gases may be studied along the sides 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 compared to a single pipe and further boosts heat transfer. Fire-tube boilers have a comparatively low rate of vapor production usually, but high steam storage capacity. Fire-tube boilers mostly burn solid fuels, but are easily flexible to people of the liquid or gas variety.
Diagram of a water-tube boiler.
Water-tube boiler: In this type, tubes filled up with water are arranged inside a furnace in several possible configurations. Often the drinking water tubes connect large drums, the low ones made up of drinking water and the upper ones steam and water; in other situations, such as a mono-tube boiler, water is circulated by a pump through a succession of coils. This type generally gives high steam production rates, but less storage space capacity than the above mentioned. Water pipe boilers can be made to exploit any temperature source and tend to be preferred in high-pressure applications since the high-pressure drinking water/vapor is contained 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 in which tubes are close collectively and 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 kept so hot that water feed is quickly flashed into steam and superheated. Flash boilers acquired some use in automobiles in the 19th century which 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 consists of an assembly of water pipes, called thermic siphons. The gases then pass through a typical firetube boiler. Water-tube fireboxes were installed in many Hungarian locomotives,[citation needed - but have fulfilled with little success far away.
Sectional boiler. In a cast iron sectional boiler, sometimes called a "pork chop boiler" the water is contained inside cast iron sections.[citation needed - These sections are assembled on site to make the finished boiler.
See also: Boiler explosion
To define and secure boilers safely, some professional specialized organizations like the American Society of Mechanical Technicians (ASME) develop standards and regulation codes. For example, the ASME Boiler and Pressure Vessel Code is a standard 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 steel shells can rupture, while welded or riveted seams could open up badly, leading to a violent eruption of the pressurized steam. When drinking water is converted to steam it expands to over 1,000 times its original travels and volume down steam pipes at over 100 kilometres each hour. Because of this, vapor is a superb way of moving energy and temperature around a site from a central boiler house to where it is needed, but with no right boiler feed water treatment, a steam-raising flower are affected from scale development and corrosion. At best, this boosts energy costs and can lead to poor quality steam, reduced efficiency, shorter vegetation and unreliable operation. At worst, it can result in catastrophic failure and lack of life. Collapsed or dislodged boiler pipes can also aerosol scalding-hot vapor and smoke out of the air intake and firing chute, injuring the firemen who weight the coal in to the fireplace chamber. Extremely large boilers providing hundreds of horsepower to operate factories could demolish entire structures.[6 -
A boiler that has a loss of give food to drinking water and it is permitted to boil dry out can be extremely dangerous. If give food to drinking water is then sent into the empty boiler, the small cascade of incoming drinking water instantly boils on connection with the superheated steel shell and leads to a violent explosion that can't be managed even by protection 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 water supply could replace. The Hartford Loop was developed in 1919 by the Hartford Steam Boiler and Insurance Company as a strategy to help prevent this condition from happening, and therefore 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 utilized at saturation temperature; that is, saturated vapor. Superheated steam boilers vaporize the water and then further temperature the vapor in a superheater. This provides vapor at higher heat, but can reduce the overall thermal efficiency of the steam generating plant because the bigger vapor heat range takes a higher flue gas exhaust temp.[citation needed - There are many 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 path, or both. There are benefits to superheated vapor that may, and often will, increase overall efficiency of both vapor generation and its utilization: increases in input temperatures to a turbine should outweigh any cost in additional boiler problem and expense. There can also be useful restrictions in using moist steam, 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 escape, the high temperature and pressure can cause serious, instantaneous injury to anyone in its path. Since the escaping steam will initially be completely superheated vapor, detection can be difficult, although the intense heat and sound from such a leak clearly indicates its presence.
Superheater operation is similar to that of the coils on an fresh air conditioning unit, although for a different purpose. The vapor 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 heat by radiation. Others are convection type, absorbing temperature from a liquid. Some are a combination of both types. Through either method, the extreme temperature in the flue gas path will also warmth the superheater steam piping and the vapor within. While the temperature of the vapor in the superheater increases, the pressure of the steam does 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 avoid damage 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 energy frequently. 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 fluid is neither water nor gas but a super-critical liquid. There is absolutely no era of vapor bubbles within the water, because the pressure is above the critical pressure point of which steam bubbles can develop. As the liquid expands through the turbine levels, its thermodynamic state drops below the critical point as it does work turning the turbine which changes the power generator from which power is eventually extracted. The fluid at that time may be a mixture of steam and liquid droplets as it passes 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 device.
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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 basic safety by setting the top limit of steam 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 controls the amount of fire.
Basic safety valve: It can be used to alleviate pressure and stop possible explosion of the boiler.
Water level indications: They show the operator the level of liquid in the boiler, known as a view glass also, water gauge or drinking water column.
Bottom level blowdown valves: They provide a way for removing solid particulates that condense and lay on the bottom of a boiler. As the name suggests, 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 press these particulates out.
Constant blowdown valve: This allows 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 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 drinking water.
Trycock: a type of valve that is often use to manually check a water level in a container. Most found on a drinking water boiler commonly.
Flash tank: High-pressure blowdown enters this vessel where 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/constant heat recovery system: This system allows the boiler to blowdown only when 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 generally needed as the blowdown discharged is near to the heat range of the make-up water.
Hand openings: These are metal plates installed in openings in "header" to allow for inspections & installation of pipes and inspection of inner surfaces.
Vapor drum internals, some display 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 gas to the boiler to avoid it from working once the 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 collection: It offers a means 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 water back again 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 series. This may be fitted to the medial side of the boiler, below water level just, or to the very best of the boiler.[10 -
Top give food to: In this design for feedwater injection, the water is fed to the top of the boiler. This may reduce boiler fatigue triggered by thermal stress. By spraying the feedwater over some trays the water is quickly warmed and this can reduce limescale.
Desuperheater pipes or bundles: A series of pipes or bundles of pipes 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 vapor.
Chemical injection line: A connection to add chemicals for controlling feedwater pH.
Main steam stop valve:
Main vapor stop/check valve: It can be used on multiple boiler installations.
Gas oil system:energy oil heaters
Other essential items
Inspectors test pressure measure attachment: