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A boiler is a closed vessel where water or other liquid is heated. The liquid does not necessarily boil. (In North America, the word "furnace" is generally used if the reason is never to boil the fluid.) The warmed or vaporized fluid exits the boiler for use in various heating system or processes applications,[1 - [2 - including water heating, central heating, boiler-based power generation, cooking, and sanitation.
The pressure vessel of a boiler is usually made of steel (or alloy steel), or historically of wrought iron. 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 will not come in contact with boiling drinking 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 - 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), because of 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 steel) are used instead.
For a lot of the Victorian "age of vapor", the only materials used for boilermaking was the best grade of wrought iron, with set up by rivetting. This iron was often from specialist ironworks, such as at Cleator Moor (UK), observed 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 moved towards the use of metal 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 metal counterparts, and are less susceptible to localized stress-corrosion and pitting. This makes the durability of older wrought-iron boilers considerably more advanced than those of welded steel boilers.
Cast iron might be used for the heating vessel of local drinking water heaters. Although such heaters are usually termed "boilers" in some countries, their purpose is to create warm water usually, 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 foundation of heating 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 can be used as a heat source for generating steam also, either straight (BWR) or, generally, in specialised high temperature exchangers called "vapor generators" (PWR). Temperature recovery vapor 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 -immediate method of boiler efficiency test is more usable or more common
boiler efficiency =Q*((Hg-Hf)/q)*(GCV *100 ) Q =Total vapor movement Hg= Enthalpy of saturated steam in k cal/kg Hf =Enthalpy of give food to water in kcal/kg q= quantity 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 fuel 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" in which a open fire heats a partially filled water pot from below. 18th century Haycock boilers produced and stored large volumes of very low-pressure steam generally, often barely above that of the atmosphere. These could burn wood or frequently, coal. Efficiency was very low.
Flued boiler with a couple of large flues-an early type or forerunner of fire-tube boiler.
Diagram of a fire-tube boiler
Fire-tube boiler: Here, water partially fills a boiler barrel with a small volume remaining above to accommodate the steam (vapor space). This is the type of boiler used in all steam locomotives nearly. Heat source is inside a furnace or firebox that needs to be held completely surrounded by the water in order to keep the heat range of the heating 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 can be further increased by making the gases reverse direction through a second parallel tube or a bundle of multiple pipes (two-pass or come back flue boiler); on the other hand the gases may be taken along the sides and then beneath the boiler through flues (3-pass boiler). In case there is a locomotive-type boiler, a boiler barrel expands from the firebox and the hot gases go through a bundle of fire tubes inside the barrel which greatly escalates the heating surface compared to a single tube and further increases heat transfer. Fire-tube boilers have a comparatively low rate of steam production usually, but high steam storage capacity. Fire-tube boilers burn solid fuels mainly, but are easily adjustable to people 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. Usually the water tubes connect large drums, the low ones containing water and the upper ones vapor and water; in other situations, like a mono-tube boiler, drinking water is circulated with a pump through a succession of coils. This kind provides high vapor creation rates generally, but less storage capacity than the above mentioned. Water tube boilers can be designed to exploit any warmth source and are generally preferred in high-pressure applications because the high-pressure drinking water/steam 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 pipes are close together and water is pumped through them. A flash boiler differs from the kind of mono-tube steam generator where the tube is permanently filled with water. In a flash boiler, the pipe is held so hot that 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 steam 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 tubes, 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 met with little success far away.
Sectional boiler. Inside a solid 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 create the finished boiler.
See also: Boiler explosion
To define and secure boilers safely, some professional specialized organizations like the American Society of Mechanical Technical engineers (ASME) develop requirements and regulation codes. 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, design and security standards.[5 -
Historically, boilers were a source of many serious injuries and property destruction due to poorly understood engineering principles. Thin and brittle metal shells can rupture, while welded or riveted seams could start badly, resulting in a violent eruption of the pressurized steam. When drinking water is changed into steam it expands to over 1,000 times its original travels and volume down steam pipes at over 100 kilometres each hour. As a result of this, steam is a superb way of moving energy and temperature around a niche site from a central boiler house to where it is needed, but without the right boiler give food to water treatment, a steam-raising seed will suffer from scale formation and corrosion. At best, this increases energy costs and can lead to poor quality vapor, reduced efficiency, shorter plant life and unreliable operation. At worst, it can lead to catastrophic loss and failing of life. Collapsed or dislodged boiler tubes can also squirt scalding-hot steam and smoke out of the air intake and firing chute, injuring the firemen who weight the coal into the fireplace chamber. Extremely large boilers providing hundreds of horsepower to use factories could demolish entire buildings.[6 -
A boiler that has a loss of give food to water and it is permitted to boil dry out can be extremely dangerous. If nourish drinking water is then sent in to the empty boiler, the small cascade of inbound water instantly boils on connection with the superheated metallic shell and leads to a violent explosion that can't be managed even by basic safety 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 developed in 1919 by the Hartford Vapor Boiler and Insurance Company as a method to help prevent this problem from happening, and thus 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 temperature; that is, saturated steam. Superheated vapor boilers vaporize water and then further warmth the vapor in a superheater. This provides steam at much higher temperature, but can decrease the overall thermal efficiency of the steam generating herb because the higher steam temp requires a higher flue gas exhaust temperatures.[citation needed - There are many ways to circumvent this problem, by giving an economizer that heats the give food to water typically, a combustion air heating unit in the hot flue gas exhaust path, or both. You can find advantages to superheated steam that may, and will often, increase overall efficiency of both vapor generation and its utilization: gains in input temperature to a turbine should outweigh any cost in additional boiler complication and expense. There can also be useful limitations in using damp vapor, as entrained condensation droplets will harm turbine blades.
Superheated steam presents unique safety concerns because, if any operational system component fails and allows steam to escape, 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 intense heat and sound from such a leak clearly indicates its presence.
Superheater operation is similar to that of the coils on an 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 between 1 typically,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 warmth from a liquid. 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 heat range of the vapor in the superheater goes up, 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 charged power vegetable.
Main article: Supercritical steam generator
Supercritical steam generators are used for the production of energy 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 that occurs; the fluid is neither liquid 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 phases, its thermodynamic condition drops below the critical point as it can work turning the turbine which turns the power generator from which power is eventually extracted. The liquid at that time may be a mix of vapor and liquid droplets as it passes in to the condenser. This results in less fuel use and for that reason less greenhouse gas production slightly. The word "boiler" should not 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 control the vapor pressure in the boiler. Boilers generally have 2 or 3 3 pressuretrols: a manual-reset pressuretrol, which functions as a protection by setting top of the limit of vapor pressure, the working pressuretrol, which settings when the boiler fires to keep up pressure, as well as for boilers outfitted with a modulating burner, a modulating pressuretrol which settings the amount of fire.
Protection valve: It can be used to alleviate pressure and prevent possible explosion of a boiler.
Water level indications: They show the operator the level of fluid in the boiler, known as a sight cup also, water gauge or water column.
Bottom level blowdown valves: They offer a way for removing solid particulates that condense and lay on the bottom of a boiler. As the name suggests, this valve is usually located on underneath of the boiler, and is occasionally opened to use the pressure in the boiler to force these particulates out.
Constant blowdown valve: This allows a small quantity of water to flee continuously. Its purpose is to prevent water in the boiler becoming saturated with dissolved salts. Saturation would business lead to foaming and cause water droplets to be carried over with the steam - a disorder known as priming. Blowdown is also often used to monitor the chemistry of the boiler drinking water.
Trycock: a kind of valve that is often use to manually check a liquid level in a tank. Most commonly entirely on a drinking water boiler.
Flash container: High-pressure blowdown enters this vessel where the vapor can 'flash' safely and become used in a low-pressure system or be vented to atmosphere while the ambient pressure blowdown flows to drain.
Automatic blowdown/constant heat recovery system: This system allows the boiler to blowdown only once makeup water is moving 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 range of the make-up water.
Hand holes: They may be metal plates installed in openings in "header" to permit for inspections & installation of tubes and inspection of inner surfaces.
Vapor drum internals, a series of screen, scrubber & cans (cyclone separators).
Low-water cutoff: It really is a mechanical means (usually a float switch) that is utilized to turn off the burner or shut off fuel to the boiler to prevent it from jogging once the drinking water runs 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 offers a means for removing foam or other lightweight non-condensible chemicals that have a tendency to float together with the water inside the boiler.
Circulating pump: It is designed to circulate 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, below water level just, or to the very best of the boiler.[10 -
Top feed: In this design for feedwater injection, water is fed to the top of the boiler. This can reduce boiler fatigue caused by thermal stress. By spraying the feedwater over some trays the water is quickly heated which can reduce limescale.
Desuperheater pipes or bundles: A series of tubes or bundles of pipes in water drum or the vapor drum made to cool superheated vapor, in order to supply auxiliary equipment that does not need, or may be damaged by, dry steam.
Chemical injection line: A connection to add chemicals for controlling feedwater pH.
Main steam stop valve:
Main vapor stop/check valve: It is utilized on multiple boiler installations.
Fuel oil system:fuel oil heaters
Other essential items
Inspectors test pressure gauge attachment: