A boiler is a closed vessel in which 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 liquid.) The heated or vaporized liquid exits the boiler for use in a variety of heating or procedures applications, including water heating, central heating system, boiler-based power era, cooking food, and sanitation.
The pressure vessel of the boiler is usually made of steel (or alloy steel), or historically of wrought iron. Stainless steel, of the austenitic types especially, is not used in wetted elements of boilers thanks to stress and corrosion corrosion cracking. However, ferritic stainless is often found in superheater sections that won't be exposed to boiling drinking water, and electrically heated stainless steel shell boilers are allowed under the European "Pressure Equipment Directive" for production of steam for sterilizers and disinfectors.
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 (especially for steam 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 metal) are used instead.
For a lot of the Victorian "age group of steam", the only materials used for boilermaking was the best grade of wrought iron, with assembly by rivetting. This iron was from specialist ironworks, such as at Cleator Moor (UK), mentioned 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 relocated towards the utilization of steel instead, which is stronger and cheaper, with welded construction, which is quicker and requires less labour. It ought to be mentioned, however, that wrought iron boilers corrode far slower than their modern-day steel counterparts, and are less susceptible to localized pitting and stress-corrosion. This makes the longevity of older wrought-iron boilers considerably more advanced than those of welded metal boilers.
Cast iron might be utilized for the heating system vessel of local water heaters. Although such heaters are usually termed "boilers" in a few countries, their purpose is usually to produce hot water, not steam, and so they run at low pressure and stay away from boiling. The brittleness of cast iron helps it be impractical for high-pressure steam boilers.
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The foundation of heating for a boiler is combustion of any of several fuels, such as wood, coal, oil, or natural gas. Electric vapor boilers use level of resistance- or immersion-type heating system elements. Nuclear fission is utilized as a heat source for producing steam also, either directly (BWR) or, generally, in specialised high temperature exchangers called "vapor generators" (PWR). Heat 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
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 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 pet coke (8200 kcal/KG)
indirect method -to gauge the boiler efficiency in indirect method, we need a following 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 fuel in kcal/kg
ash percentage in combustible fuel
GCV of ash in kcal/kg
Boilers can be classified in to the following configurations:
Pot boiler or Haycock boiler/Haystack boiler: a primitive "kettle" in which a fireplace heats a partially filled drinking 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 still left above to support the vapor (vapor space). This is the kind of boiler used in almost all steam locomotives. Heat source is in the furnace or firebox that has to be held completely surrounded by the water in order to keep the temp 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 invert direction through another parallel pipe or a bundle of multiple tubes (two-pass or return flue boiler); alternatively 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 stretches 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 steam storage capacity. Fire-tube boilers burn solid fuels mostly, but are readily adaptable to those of the gas or liquid variety.
Diagram of the water-tube boiler.
Water-tube boiler: In this kind, tubes filled with water are arranged inside a furnace in several possible configurations. Often the drinking water tubes connect large drums, the lower ones comprising water and the top ones vapor and water; in other instances, such as a mono-tube boiler, water is circulated by a pump through a succession of coils. This kind gives high vapor creation rates generally, but less storage space capacity than the above. Water pipe boilers can be made to exploit any high temperature source and tend to be preferred in high-pressure applications because the high-pressure drinking water/steam 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 in which tubes are close collectively and water is pumped through them. A flash boiler differs from the type of mono-tube steam generator where the tube is permanently filled with water. In a flash boiler, the pipe is kept so hot that the water feed is quickly flashed into steam and superheated. Flash boilers got 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 contains an assembly of water tubes, called thermic siphons. The gases pass through a conventional firetube boiler then. Water-tube fireboxes were installed in many Hungarian locomotives, but have fulfilled with little success far away.
Sectional boiler. Inside a ensemble iron sectional boiler, sometimes called a "pork chop boiler" water is contained inside ensemble iron sections. These areas are assembled on site to create the finished boiler.
See also: Boiler explosion
To define and secure boilers safely, some professional specialized organizations such as the American Culture of Mechanical Technical engineers (ASME) develop criteria and regulation rules. For instance, the ASME Boiler and Pressure Vessel Code is a standard providing an array of guidelines and directives to ensure compliance of the boilers and other pressure vessels with basic safety, security and design standards.
Historically, boilers were a source of 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 vapor. When water is changed into vapor it expands to over 1,000 times its original travels and volume down steam pipes at over 100 kilometres per hour. Because of this, steam is a great way of moving energy and high temperature around a site from a central boiler house to where it is necessary, but without the right boiler feed water treatment, a steam-raising flower are affected from size corrosion and formation. At best, this boosts energy costs and can lead to poor quality steam, reduced efficiency, shorter plant life and unreliable operation. At worst, it can lead to catastrophic failing and loss of life. Collapsed or dislodged boiler tubes can also aerosol scalding-hot vapor and smoke from the air intake and firing chute, injuring the firemen who weight the coal in to the fire chamber. Extremely large boilers providing hundreds of horsepower to operate factories could demolish entire buildings.
A boiler which has a loss of give food to water and it is permitted to boil dry can be hugely dangerous. If supply water is sent in to the vacant boiler then, the small cascade of incoming water instantly boils on connection with the superheated metallic shell and leads to a violent explosion that cannot be managed even by protection vapor valves. Draining of the boiler can also happen if a leak occurs in the steam source lines that is bigger than the make-up drinking water supply could replace. The Hartford Loop was developed in 1919 by the Hartford Steam Boiler and INSURANCE PROVIDER as a method to assist in preventing this problem from taking place, and thus reduce their insurance promises.
Superheated steam boiler
A superheated boiler on the steam locomotive.
Main article: Superheater
Most boilers produce vapor to be utilized at saturation heat range; that is, saturated vapor. Superheated steam boilers vaporize water and additional heat up the steam in a superheater then. This provides vapor at much higher heat, but can reduce the overall thermal efficiency of the vapor generating flower because the bigger steam temp requires a higher flue gas exhaust temperatures. There are many ways to circumvent this problem, by giving an economizer that heats the give food to drinking water typically, a combustion air heating unit in the hot flue gas exhaust route, or both. A couple of benefits to superheated steam that may, and often will, increase overall efficiency of both steam generation and its own utilization: gains in input heat range 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 damage turbine blades.
Superheated steam presents unique safety concerns because, if any operational system component fails and allows steam to flee, the high temperature and pressure 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 intense heat and sound from such a leak obviously 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 field is between 1 typically,300 and 1,600 °C (2,372 and 2,912 °F). Some superheaters are radiant type; that is, they absorb warmth by rays. Others are convection type, absorbing high temperature from a fluid. Some are a mixture 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 temperatures of the vapor in the superheater goes up, the pressure of the vapor does not and the pressure remains the same as that of the boiler. 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 vegetable.
Main article: Supercritical steam generator
Supercritical steam generators are used for the production of electric power 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 fluid. There is no generation of steam bubbles within the water, because the pressure is above the critical pressure point of which steam bubbles can form. 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 power generator that power is eventually extracted. The fluid at that point may be considered a mix of steam and liquid droplets as it passes into the condenser. This results in less fuel use and therefore less greenhouse gas production slightly. The word "boiler" shouldn't be used for a supercritical pressure steam generator, as no "boiling" occurs in this product.
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Boiler fittings and accessories
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 basic safety by setting top of the limit of steam pressure, the operating pressuretrol, which controls when the boiler fires to maintain pressure, and for boilers equipped with a modulating burner, a modulating pressuretrol which controls the quantity of fire.
Safety valve: It is used to alleviate pressure and prevent possible explosion of a boiler.
Water level indications: They show the operator the level of liquid in the boiler, known as a sight cup also, water measure or water column.
Bottom blowdown valves: They offer a means for removing solid particulates that condense and lie on the bottom of a boiler. As the name implies, this valve is located directly on underneath of the boiler usually, and is sometimes opened to use the pressure in the boiler to drive these particulates out.
Continuous 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 lead to foaming and cause water droplets to be transported over with the steam - a disorder 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 container. Mostly entirely on a water boiler.
Flash tank: High-pressure blowdown enters this vessel where the vapor can 'flash' safely and be used in a low-pressure system or be vented to atmosphere while the ambient pressure blowdown moves to drain.
Automatic blowdown/continuous heat recovery system: This technique allows the boiler to blowdown only when 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 tank is normally needed as the blowdown discharged is close to the heat of the makeup water.
Hand openings: They are metal plates installed in openings in "header" to allow for inspections & installing tubes and inspection of internal surfaces.
Steam drum internals, some screen, scrubber & cans (cyclone separators).
Low-water cutoff: It is a mechanical means (usually a float switch) that is utilized to turn from the burner or shut off gasoline to the boiler to prevent it from running once the drinking water moves below a certain point. If a boiler is "dry-fired" (burned without drinking water in it) it can cause rupture or catastrophic failing.
Surface blowdown collection: It provides a way for removing foam or other lightweight non-condensible chemicals that have a tendency to float together with water inside the boiler.
Circulating pump: It is designed to circulate drinking water back 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 series. This can be installed to the side of the boiler, below the water level just, or to the very best of the boiler.
Top give food to: Within this design for feedwater injection, water is fed to the top 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 warmed and this can reduce limescale.
Desuperheater tubes or bundles: A series of tubes or bundles of pipes in water drum or the vapor drum designed to cool superheated steam, in order to supply auxiliary equipment that does not need, or may be damaged by, dry steam.
Chemical substance injection line: A connection to add chemicals for controlling feedwater pH.
Main vapor stop valve:
Main steam stop/check valve: It can be used on multiple boiler installations.
Gas oil system:gasoline oil heaters
Other essential items
Inspectors test pressure measure attachment: