تاريخ النشر: 27 نوفمبر 2017
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A boiler is a closed vessel where drinking water or other fluid is heated. The fluid will not boil. (In North America, the term "furnace" is generally used if the reason is not to boil the liquid.) The warmed or vaporized fluid exits the boiler for use in a variety of procedures or heating system applications,[1 - [2 - including water heating, central heating system, boiler-based power generation, food preparation, and sanitation.
The pressure vessel of a boiler is usually manufactured from steel (or alloy steel), or of wrought iron historically. Stainless steel, of the austenitic types especially, is not found in wetted elements of boilers credited to corrosion and stress corrosion breaking.[3 - However, ferritic stainless steel is often found in superheater sections that won't be exposed to boiling water, and electrically heated stainless shell boilers are allowed under the Western 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 since it is more easily fabricated in smaller size boilers. Historically, copper was often used for fireboxes (especially for vapor 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 of vapor", the only material used for boilermaking was the best quality of wrought iron, with set up by rivetting. This iron was often extracted 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 instead transferred towards the use of metal, which is more powerful and cheaper, with welded structure, which is quicker and requires less labour. It should be observed, however, that wrought iron boilers corrode much slower than their modern-day steel counterparts, and are less vunerable to localized pitting and stress-corrosion. This makes the durability of older wrought-iron boilers much more advanced than those of welded steel boilers.
Cast iron may be used 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 steam 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 resistance- or immersion-type heating elements. Nuclear fission is also used as a heat source for producing steam, either straight (BWR) or, generally, in specialised temperature exchangers called "vapor generators" (PWR). Temperature recovery steam generators (HRSGs) use heat rejected from other procedures such as gas turbine.
there are two solutions to gauge the boiler efficiency 1) direct method 2) indirect method
Direct method -immediate method of boiler efficiency test is more functional 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 give food to drinking 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 are in need of a subsequent parameter like
Ultimate analysis of fuel (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 gasoline 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" where a open fire heats a partially filled water box from below. 18th century Haycock boilers produced and stored large amounts of very low-pressure vapor generally, barely above that of the atmosphere often. These could burn wood or frequently, coal. Efficiency was very low.
Flued boiler with a couple of large flues-an early forerunner or type of fire-tube boiler.
Diagram of the fire-tube boiler
Fire-tube boiler: Here, water partially fills a boiler barrel with a little volume left above to accommodate the steam (vapor space). This is the kind of boiler used in nearly all steam locomotives. Heat source is in the furnace or firebox that has to be kept completely surrounded by the water in order to keep the heat of the heating 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 surface which may be further increased by causing the gases invert direction through a second parallel pipe or a bundle of multiple tubes (two-pass or come back flue boiler); additionally the gases may be taken along the edges and then under the boiler through flues (3-pass boiler). In case of a locomotive-type boiler, a boiler barrel stretches from the firebox and the hot gases pass through a bundle of fire pipes inside the barrel which greatly increases the heating surface in comparison to a single pipe and further increases heat transfer. Fire-tube boilers will often have a comparatively low rate of steam production, but high steam storage capacity. Fire-tube boilers mainly burn solid fuels, but are readily adaptable to those of the gas or liquid variety.
Diagram of a water-tube boiler.
Water-tube boiler: In this kind, pipes filled up with drinking water are arranged inside a furnace in a true quantity of possible configurations. Often the drinking water pipes connect large drums, the low ones containing water and top of the ones water and steam; in other cases, like a mono-tube boiler, drinking water is circulated with a pump through a succession of coils. This kind generally gives high steam creation rates, but less storage space capacity than the above mentioned. Water pipe boilers can be made to exploit any heat source and are generally preferred in high-pressure applications since the high-pressure drinking water/steam 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 in which tubes are close together and water is pumped through them. A flash boiler differs from the type of mono-tube steam generator in which the tube is permanently filled with water. In a flash boiler, the tube is kept 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 vapor locomotive boiler, from a Victorian Railways J class
Fire-tube boiler with Water-tube firebox. Sometimes both above types have been mixed in the next manner: the firebox includes an set up 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 in other countries.
Sectional boiler. In a cast iron sectional boiler, sometimes called a "pork chop boiler" the water is contained inside cast iron areas.[citation needed - These areas 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 Culture of Mechanical Designers (ASME) develop criteria and regulation rules. For instance, 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 basic safety, security and design standards.[5 -
Historically, boilers were a way to obtain many serious injuries and property destruction due to badly understood engineering principles. Thin and brittle metal shells can rupture, while badly welded or riveted seams could open up, leading to a violent eruption of the pressurized steam. When 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 great way of moving energy and warmth around a niche site from a central boiler house to where it is needed, but with no right boiler feed water treatment, a steam-raising seed are affected from scale corrosion and formation. At best, this increases energy costs and can lead to poor quality vapor, reduced efficiency, shorter vegetation and unreliable operation. At worst, it can result in catastrophic reduction and failing of life. Collapsed or dislodged boiler pipes can also squirt 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 can potentially 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 sent in to the bare boiler then, the small cascade of incoming drinking water instantly boils on connection with the superheated metal shell and leads to a violent explosion that cannot be managed even by basic safety vapor valves. Draining of the boiler can also happen if a leak occurs in the vapor source lines that is larger than the make-up water supply could replace. The Hartford Loop was invented in 1919 by the Hartford Steam Boiler and INSURANCE PROVIDER as a method to help prevent this problem from taking place, and therefore reduce their insurance promises.[7 - [8 -
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 vapor boilers vaporize the water and then further high temperature the steam in a superheater. This provides steam at much higher temp, but can decrease the overall thermal efficiency of the vapor generating place because the bigger vapor temperature takes a higher flue gas exhaust heat.[citation needed - There are several 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. You can find benefits to superheated steam that may, and will often, increase overall efficiency of both vapor generation and its own utilization: gains in input temperature to a turbine should outweigh any cost in additional boiler problem and expense. There could be useful restrictions 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 temperature and pressure can cause serious, instantaneous harm to anyone in its path. Since the escaping steam will 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 vapor piping is directed through the flue gas path in the boiler furnace. The temperatures 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 high temperature by radiation. Others are convection type, absorbing heat from a fluid. 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 heat of the steam in the superheater rises, the pressure of the steam will not and the pressure remains exactly like that of the boiler.[9 - Virtually 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. 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 no era of vapor bubbles within the water, because the pressure is above the critical pressure point of which vapor bubbles can develop. As the liquid expands through the turbine levels, its thermodynamic condition drops below the critical point as it can work turning the turbine which converts the electrical generator from which power is ultimately extracted. The liquid at that time may be 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 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 control the steam pressure in the boiler. Boilers generally have 2 or 3 3 pressuretrols: a manual-reset pressuretrol, which functions as a safety by setting the upper limit of steam pressure, the operating pressuretrol, which handles when the boiler fires to maintain pressure, and for boilers outfitted with a modulating burner, a modulating pressuretrol which controls the quantity of fire.
Security valve: It is used to relieve pressure and stop possible explosion of the boiler.
Water level indications: They show the operator the amount of liquid in the boiler, known as a view cup 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 indicates, this valve is located straight on underneath of the boiler usually, and is occasionally opened to use the pressure in the boiler to push these particulates out.
Constant 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 water droplets to be transported over with the vapor - a condition known as priming. Blowdown is often used to monitor the chemistry of the boiler water also.
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 tank: High-pressure blowdown enters this vessel where in fact the vapor can 'flash' safely and be used in a low-pressure system or be vented to atmosphere as the ambient pressure blowdown flows 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 utmost 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 temperatures of the make-up water.
Hand holes: They may be steel plates installed in openings in "header" to allow for inspections & installation of tubes and inspection of internal surfaces.
Vapor drum internals, a series of display, scrubber & cans (cyclone separators).
Low-water cutoff: It really is a mechanical means (usually a float switch) that can be used to turn from the burner or shut off energy to the boiler to avoid it from working once the drinking water goes 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 series: It offers a way for removing foam or other light-weight non-condensible chemicals that tend to float on top of water inside the boiler.
Circulating pump: It really is made to circulate drinking 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 collection. This may be suited to the relative aspect of the boiler, just below water level, or to the top of the boiler.[10 -
Top give food to: Within this design for feedwater injection, the water is fed to the very best of the boiler. This may reduce boiler exhaustion triggered by thermal stress. By spraying the feedwater over some trays the water is quickly warmed and this can reduce limescale.
Desuperheater tubes or bundles: A series of tubes or bundles of tubes in water drum or the vapor drum designed to cool superheated vapor, in order to provide auxiliary equipment that does 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 vapor stop/check valve: It is used on multiple boiler installations.
Gas oil system:gasoline oil heaters
Other essential items
Inspectors test pressure gauge attachment: