A boiler is a closed vessel in which water or other fluid is heated. The fluid will not boil. (In North America, the term "furnace" is generally used if the reason is never to boil the liquid.) The warmed or vaporized liquid exits the boiler for use in various heating or processes applications, including water heating, central heating, boiler-based power generation, cooking, and sanitation.
The pressure vessel of a boiler is usually manufactured from steel (or alloy steel), or historically of wrought iron. Stainless steel, especially of the austenitic types, is not found in wetted parts of boilers credited to corrosion and stress corrosion breaking. However, ferritic stainless is often found in superheater sections that will not come in contact with boiling drinking water, and electrically heated stainless steel shell boilers are allowed under the European "Pressure Equipment Directive" for creation 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 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 of steam", the only materials used for boilermaking was the highest quality of wrought iron, with assembly 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 suitability for high-reliability use in critical applications, such as high-pressure boilers. In the 20th century, design practice shifted towards the use of metal instead, which is stronger and cheaper, with welded structure, which is quicker and requires less labour. It should be observed, however, that wrought iron boilers corrode far slower than their modern-day metal counterparts, and are less vunerable to localized stress-corrosion and pitting. This makes the longevity of old wrought-iron boilers far more advanced than those of welded steel boilers.
Cast iron can be utilized for the heating vessel of local water heaters. Although such heaters are usually termed "boilers" in some countries, their purpose is to produce hot water usually, 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 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 vapor boilers use resistance- or immersion-type heating system elements. Nuclear fission is also used as a heat source for generating steam, either directly (BWR) or, in most cases, in specialised high temperature exchangers called "vapor generators" (PWR). Temperature recovery vapor generators (HRSGs) use heat rejected from other processes such as gas turbine.
there are two methods to measure the boiler efficiency 1) direct method 2) indirect method
Immediate method -direct approach to boiler efficiency test is more useful or even more common
boiler efficiency =Q*((Hg-Hf)/q)*(GCV *100 ) Q =Total vapor circulation Hg= Enthalpy of saturated steam in k cal/kg Hf =Enthalpy of feed drinking water in kcal/kg q= level of energy use in kg/hr GCV =gross calorific value in kcal/kg like pet coke (8200 kcal/KG)
indirect method -to measure the boiler efficiency in indirect method, we need 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:
Pot boiler or Haycock boiler/Haystack boiler: a primitive "kettle" in which a fireplace heats a partially filled drinking water box from below. 18th century Haycock boilers generally produced and stored large amounts of very low-pressure steam, 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 forerunner or type of fire-tube boiler.
Diagram of a fire-tube boiler
Fire-tube boiler: Here, water partially fills a boiler barrel with a little volume left above to accommodate the steam (steam 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 kept completely surrounded by the water in order to keep the temperature 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 can be further increased by making the gases reverse direction through another parallel tube or a lot of money of multiple pipes (two-pass or return flue boiler); additionally 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 pass through a bundle of fire tubes inside the barrel which greatly increases the heating system surface compared to a single pipe and further increases heat transfer. Fire-tube boilers usually have a comparatively low rate of steam creation, but high vapor storage capacity. Fire-tube boilers burn solid fuels mainly, but are readily adaptable to those of the gas or water variety.
Diagram of a water-tube boiler.
Water-tube boiler: In this kind, tubes filled up with drinking water are arranged inside a furnace in a true quantity of possible configurations. The water tubes connect large drums Often, the low ones containing water and the top ones water and steam; in other cases, such as a mono-tube boiler, water is circulated by a pump through a succession of coils. This type provides high steam creation rates generally, but less storage space capacity than the above. Water pipe boilers can be made to exploit any warmth source and are generally preferred in high-pressure applications because the high-pressure drinking water/vapor is included within small size pipes which can withstand the pressure with a thinner wall.
Flash boiler: A flash boiler is a specialized kind of water-tube boiler in which tubes are close together and water is pumped through them. A flash boiler differs from the kind of mono-tube steam generator in which the tube is permanently filled with water. Super fast boiler, the pipe is held so hot that the water give food to is quickly flashed into vapor and superheated. Flash boilers acquired some use in automobiles in the 19th century and this 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 mixed in the following manner: the firebox contains an assembly of water pipes, called thermic siphons. The gases pass through a typical firetube boiler then. Water-tube fireboxes were installed in many Hungarian locomotives, but have met with little success far away.
Sectional boiler. Within 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 Culture of Mechanical Technical engineers (ASME) develop specifications and regulation rules. For instance, the ASME Boiler and Pressure Vessel Code is a standard providing an array of rules and directives to ensure compliance of the boilers and other pressure vessels with protection, design and security standards.
Historically, boilers were a source of many serious injuries and property destruction as a consequence to badly understood engineering principles. Thin and brittle metal shells can rupture, while badly welded or riveted seams could start, resulting in a violent eruption of the pressurized vapor. 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 per hour. Because of this, steam is a great way of moving energy and warmth around a site from a central boiler house to where it is necessary, 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 steam, reduced efficiency, shorter vegetation and unreliable operation. At worst, it can lead to catastrophic reduction and failure of life. Collapsed or dislodged boiler tubes can also spray scalding-hot steam and smoke out of the air intake and firing chute, injuring the firemen who load the coal in to the open fire chamber. Extremely large boilers providing hundreds of horsepower to operate factories can potentially demolish entire buildings.
A boiler that has a loss of give food to drinking water and is permitted to boil dry can be extremely dangerous. If feed drinking water is then sent in to the unfilled boiler, the small cascade of incoming water instantly boils on contact with the superheated metallic shell and leads to a violent explosion that cannot be controlled even by protection 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 source could replace. The Hartford Loop was invented in 1919 by the Hartford Steam Boiler and Insurance Company as a method to help prevent this condition from occurring, and thereby reduce their insurance statements.
Superheated steam boiler
A superheated boiler on the steam locomotive.
Main article: Superheater
Most boilers produce vapor to be used at saturation temperatures; that is, saturated steam. Superheated steam boilers vaporize the water and then further warmth the steam in a superheater. This provides steam at higher heat range, but can decrease the overall thermal efficiency of the vapor generating seed because the higher steam heat requires a higher flue gas exhaust temp. There are several ways to circumvent this issue, typically by providing an economizer that heats the feed water, a combustion air heating unit in the hot flue gas exhaust route, or both. A couple of benefits to superheated vapor that may, and often will, increase overall efficiency of both vapor generation and its own utilization: gains in input heat to a turbine should outweigh any cost in additional boiler complication and expense. There can also be useful limitations in using moist steam, 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 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 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 path in the boiler furnace. The temp 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 heat by radiation. Others are convection type, absorbing heat from a liquid. Some are a mixture of the two types. Through either method, the extreme heat in the flue gas path will also warmth the superheater vapor piping and the vapor within. While the temperatures of the steam in the superheater goes up, the pressure of the steam does not and the pressure remains exactly like that of the boiler. Almost all steam superheater system designs remove droplets entrained in the steam to prevent damage to the turbine blading and associated piping.
Supercritical steam generator
Boiler for a power seed.
Main article: Supercritical steam generator
Supercritical steam generators are generally used for the production of electric power. They operate at supercritical pressure. In contrast to a "subcritical boiler", a supercritical steam generator operates at such a high pressure (over 3,200 psi or 22 MPa) that the physical turbulence that characterizes boiling ceases to occur; the fluid is liquid nor gas but a super-critical fluid neither. There is no generation of vapor bubbles within the water, because the pressure is above the critical pressure point at which steam bubbles can form. As the fluid expands through the turbine levels, its thermodynamic condition drops below the critical point as it does work turning the turbine which changes the electrical generator from which power is ultimately extracted. The liquid at that point may be considered a mix of steam and liquid droplets as it passes in to the condenser. This leads to slightly less gas use and therefore less greenhouse gas creation. The term "boiler" should not 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 regulate the vapor 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 vapor pressure, the operating pressuretrol, which handles when the boiler fires to keep pressure, as well as for boilers outfitted with a modulating burner, a modulating pressuretrol which controls the amount of fire.
Protection valve: It can be used to alleviate pressure and stop possible explosion of the boiler.
Water level indicators: They show the operator the level of liquid in the boiler, known as a sight glass also, water gauge or water column.
Bottom level blowdown valves: They provide a means for removing solid particulates that condense and lie on the bottom of the boiler. As the name implies, 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 enables 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 transported over with the steam - a condition 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 container. Most entirely on a drinking water boiler commonly.
Flash container: High-pressure blowdown enters this vessel where in fact 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 once makeup water is flowing to the boiler, thereby transferring the maximum amount of heat possible from the blowdown to the makeup water. No flash tank is normally needed as the blowdown discharged is near to the temperature of the makeup water.
Hand openings: They are steel plates installed in openings in "header" to permit for inspections & installing pipes and inspection of inner surfaces.
Steam drum internals, some display screen, scrubber & cans (cyclone separators).
Low-water cutoff: It is a mechanical means (usually a float change) that is utilized to turn off the burner or shut off gasoline to the boiler to prevent it from working once the water goes below a certain point. If a boiler is "dry-fired" (burned without drinking water in it) it can cause rupture or catastrophic failure.
Surface blowdown range: It offers a means for removing foam or other light-weight non-condensible substances that have a tendency to float on top of the water inside the boiler.
Circulating pump: It really is made to circulate drinking water back again to the boiler after it has expelled a few of its heat.
Feedwater check valve or clack valve: A non-return stop valve in the feedwater range. This may be installed to the medial side of the boiler, below water level just, or to the top of the boiler.
Top feed: Within this design for feedwater injection, water is fed to the very best of the boiler. This can reduce boiler exhaustion caused by thermal stress. By spraying the feedwater over some trays water is quickly heated and this can reduce limescale.
Desuperheater pipes or bundles: Some pipes or bundles of tubes in the water drum or the vapor drum made to cool superheated steam, in order to provide auxiliary equipment that does not need, or may be damaged by, dry steam.
Chemical substance injection line: A link with add chemicals for controlling feedwater pH.
Main steam stop valve:
Main steam stop/check valve: It is used on multiple boiler installations.
Gas oil system:energy oil heaters
Other essential items
Inspectors test pressure gauge attachment: