A boiler is a closed vessel where water or other fluid is heated. The fluid will not boil. (In THE UNITED STATES, the term "furnace" is generally used if the reason is never to boil the liquid.) The warmed or vaporized fluid exits the boiler for use in a variety of heating or procedures applications, including drinking water heating, central heating, boiler-based power generation, cooking food, and sanitation.
The pressure vessel of the boiler is usually manufactured from steel (or alloy steel), or of wrought iron historically. Stainless steel, especially of the austenitic types, is not found in wetted parts 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 shell boilers are allowed under the Western european "Pressure Equipment Directive" for production of steam for sterilizers and disinfectors.
In live steam models, copper or brass is often used since it is more fabricated in smaller size boilers easily. Historically, copper was often used for fireboxes (especially for vapor locomotives), due to 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 a lot of the Victorian "age of steam", the only material used for boilermaking was the highest quality 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 suitability for high-reliability use in critical applications, such as high-pressure boilers. In the 20th century, design practice shifted towards the utilization of metal instead, which is more powerful and cheaper, with welded building, which is quicker and requires less labour. It should be mentioned, however, that wrought iron boilers corrode significantly slower than their modern-day steel counterparts, and are less susceptible to localized stress-corrosion and pitting. This makes the durability of older wrought-iron boilers significantly superior to those of welded metal boilers.
Cast iron might be used for the heating system vessel of home 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 try to avoid boiling. The brittleness of cast iron makes it impractical for high-pressure steam boilers.
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The source of heat for a boiler is combustion of some of several fuels, such as wood, coal, oil, or gas. Electric steam boilers use resistance- or immersion-type heating elements. Nuclear fission is also used as a heat source for producing steam, either directly (BWR) or, generally, in specialised warmth exchangers called "vapor generators" (PWR). High temperature recovery vapor generators (HRSGs) use the heat rejected from other procedures such as gas turbine.
there are two methods to measure the boiler efficiency 1) direct method 2) indirect method
Direct method -immediate approach to boiler efficiency test is more usable or more common
boiler efficiency =Q*((Hg-Hf)/q)*(GCV *100 ) Q =Total steam flow Hg= Enthalpy of saturated steam in k cal/kg Hf =Enthalpy of feed drinking water in kcal/kg q= quantity 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 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:
Pot boiler or Haycock boiler/Haystack boiler: a primitive "kettle" in which a open fire heats a partially filled water container 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 most often, 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, drinking water partially fills a boiler barrel with a small volume still left above to support the vapor (steam space). This is the kind of boiler used in nearly all steam locomotives. The heat source is inside a furnace or firebox that has to be kept completely surrounded by the water in order to keep up the heat range 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 may be further increased by making the gases invert direction through another 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 under the boiler through flues (3-move 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 in comparison to a single pipe and further enhances heat transfer. Fire-tube boilers have a comparatively low rate of vapor creation usually, but high steam storage capacity. Fire-tube boilers burn solid fuels mainly, but are easily flexible to people of the liquid or gas variety.
Diagram of a water-tube boiler.
Water-tube boiler: In this kind, tubes filled up with water are arranged in the furnace in a true variety of possible configurations. The water pipes connect large drums Often, the low ones formulated with drinking water and the top ones steam and water; in other situations, like a mono-tube boiler, drinking 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. Water pipe boilers can be made to exploit any temperature source and tend to be preferred in high-pressure applications because the high-pressure water/steam is included within small size 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 collectively and water is pumped through them. A flash boiler differs from the kind of mono-tube vapor generator in which the pipe is permanently filled 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 cars 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 following manner: the firebox consists of an set up of water tubes, called thermic siphons. The gases then pass through a typical firetube boiler. Water-tube fireboxes were installed in many Hungarian locomotives, but have met with little success far away.
Sectional boiler. In a solid iron sectional boiler, sometimes called a "pork chop boiler" water is included inside cast iron sections. These sections are assembled on site to generate the finished boiler.
See also: Boiler explosion
To define and secure boilers safely, some professional specialized organizations such as the American Society of Mechanical Technicians (ASME) develop criteria and regulation rules. For instance, the ASME Boiler and Pressure Vessel Code is a typical providing a wide range of rules and directives to ensure compliance of the boilers and other pressure vessels with security, 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 open up poorly, resulting in a violent eruption of the pressurized steam. When water is converted to vapor it expands to over 1,000 times its original volume and moves down vapor pipes at over 100 kilometres per hour. Because of this, vapor is a great way of moving energy and high temperature around a site from a central boiler house to where it is needed, but without the right boiler feed water treatment, a steam-raising place are affected from scale corrosion and formation. At best, this raises energy costs and can lead to 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 pipes can also spray scalding-hot steam and smoke out of the air intake and firing chute, injuring the firemen who fill the coal in to the fire chamber. Extremely large boilers providing hundreds of horsepower to use factories could demolish entire buildings.
A boiler that has a loss of give food to water and it is permitted to boil dry can be hugely dangerous. If give food to water is sent in to the empty boiler then, the tiny cascade of incoming water instantly boils on connection with the superheated steel shell and leads to a violent explosion that can't be managed even by security 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 water supply could replace. The Hartford Loop was created in 1919 by the Hartford Steam Boiler and Insurance Company as a strategy to help prevent this condition from taking place, and therefore reduce their insurance claims.
Superheated steam boiler
A superheated boiler on a steam locomotive.
Main article: Superheater
Most boilers produce steam to be utilized at saturation temperatures; that is, saturated vapor. Superheated steam boilers vaporize the water and then further warmth the vapor in a superheater. This provides steam at higher temperature, but can reduce the overall thermal efficiency of the steam generating place because the bigger steam temperatures requires a higher flue gas exhaust heat range. There are several ways to circumvent this problem, typically by providing an economizer that heats the feed drinking water, a combustion air heater in the hot flue gas exhaust route, or both. You will find advantages to superheated vapor that may, and will often, increase overall efficiency of both steam 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 restrictions in using wet 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 flee, the ruthless and temperature can cause serious, instantaneous harm to anyone in its path. Since the escaping steam will at first be completely superheated vapor, detection can be difficult, although the extreme heat and sound from such a leak indicates its existence clearly.
Superheater operation 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 route in the boiler furnace. The temperatures in this area is typically between 1,300 and 1,600 °C (2,372 and 2,912 °F). Some superheaters are glowing type; that is, they absorb warmth by radiation. 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 temperature of the vapor in the superheater goes up, the pressure of the steam does not and the pressure remains exactly like that of the boiler. Virtually all steam superheater system designs remove droplets entrained in the steam to prevent harm 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 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 liquid nor gas but a super-critical fluid neither. There is absolutely no generation of steam 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 phases, its thermodynamic state drops below the critical point as it does work turning the turbine which converts the electrical generator that power is eventually extracted. The fluid at that point may be considered a mixture of vapor and liquid droplets as it goes by into the condenser. This leads to less fuel use and for that reason less greenhouse gas production slightly. The term "boiler" shouldn't be used for a supercritical pressure vapor 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 two or three 3 pressuretrols: a manual-reset pressuretrol, which functions as a protection by setting the upper limit of steam pressure, the working pressuretrol, which settings when the boiler fires to keep pressure, and for boilers outfitted with a modulating burner, a modulating pressuretrol which controls the amount of fire.
Security valve: It is used to alleviate pressure and prevent possible explosion of the boiler.
Water level signals: They show the operator the level of fluid in the boiler, known as a sight glass also, water measure or drinking water column.
Bottom blowdown valves: They provide a way for removing solid particulates that condense and lie on underneath of a boiler. As the name indicates, this valve is located straight on the bottom of the boiler usually, and is sometimes opened up to use the pressure in the boiler to press these particulates out.
Continuous blowdown valve: This allows a small level of water to flee continuously. Its purpose is to prevent water in the boiler becoming saturated with dissolved salts. Saturation would lead to foaming and cause water droplets to be carried over with the steam - an ailment 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 found on a drinking water boiler.
Flash container: High-pressure blowdown enters this vessel where the steam can 'flash' safely and become 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 once 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 close to the heat range of the makeup water.
Hand openings: They are steel plates installed in openings in "header" to permit for inspections & installation of pipes and inspection of internal 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 used to turn from the burner or shut off gasoline to the boiler to prevent it from jogging once the drinking water moves below a certain point. If a boiler is "dry-fired" (burnt without water in it) it can cause rupture or catastrophic failing.
Surface blowdown collection: It offers a way 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 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 range. This may be fitted to the side of the boiler, just below the water level, or to the top of the boiler.
Top feed: With this design for feedwater injection, water is fed to the very best of the boiler. This may reduce boiler fatigue triggered by thermal stress. By spraying the feedwater over a series of trays the water is quickly heated and this can reduce limescale.
Desuperheater tubes or bundles: Some pipes or bundles of pipes in the water drum or the steam drum designed to cool superheated vapor, in order to provide auxiliary equipment that does not need, or may be damaged by, dry vapor.
Chemical substance injection line: A connection to add chemicals for controlling feedwater pH.
Main vapor stop valve:
Main vapor stop/check valve: It is utilized on multiple boiler installations.
Gas oil system:fuel oil heaters
Other essential items
Inspectors test pressure measure attachment: