A boiler is a closed vessel where water or other fluid is heated. The fluid does not boil. (In THE UNITED STATES, the word "furnace" is normally used if the purpose is never to boil the fluid.) The warmed or vaporized liquid exits the boiler for use in a variety of heating system or procedures applications, including water heating, central heating system, boiler-based power era, cooking, and sanitation.
The pressure vessel of the boiler is usually made of steel (or alloy steel), or of wrought iron historically. Stainless steel, especially of the austenitic types, is not used in wetted elements of boilers thanks to stress and corrosion corrosion breaking. However, ferritic stainless steel is often found in superheater sections that won't come in contact with boiling 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 easier fabricated in smaller size boilers. Historically, copper was often used for fireboxes (particularly for steam 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 group of steam", the only materials used for boilermaking was the best quality of wrought iron, with assembly by rivetting. This iron was obtained from specialist ironworks, such as at Cleator Moor (UK), noted 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 transferred towards the use of metal instead, which is more powerful and cheaper, with welded construction, which is quicker and requires less labour. It should be observed, however, that wrought iron boilers corrode significantly slower than their modern-day metal counterparts, and are less susceptible to localized pitting and stress-corrosion. This makes the longevity of older wrought-iron boilers much superior to those of welded steel boilers.
Cast iron might be utilized for the heating vessel of domestic water heaters. Although such heaters are usually termed "boilers" in some countries, their purpose will be to produce hot water, not steam, and they also 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 source of heating for a boiler is combustion of some 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 used as a heat source for producing steam also, either straight (BWR) or, in most cases, in specialised heat exchangers called "steam generators" (PWR). High temperature recovery steam generators (HRSGs) use the heat rejected from other procedures such as gas turbine.
there are two solutions to measure the boiler efficiency 1) direct method 2) indirect method
Immediate method -direct method of boiler efficiency test is more useful or even more common
boiler efficiency =Q*((Hg-Hf)/q)*(GCV *100 ) Q =Total steam flow Hg= Enthalpy of saturated vapor in k cal/kg Hf =Enthalpy of give food to drinking water in kcal/kg q= quantity of fuel 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 following 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 gas 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" where a fireplace heats a partially filled drinking water container from below. 18th century Haycock boilers generally produced and stored large quantities of very low-pressure vapor, barely above that of the atmosphere often. These could burn off 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 the fire-tube boiler
Fire-tube boiler: Here, drinking water partially fills a boiler barrel with a small volume remaining above to accommodate the steam (steam space). This is the kind of boiler used in nearly all steam locomotives. The heat source is in the furnace or firebox that has to be kept permanently surrounded by the water in order to maintain 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 system surface which can be further increased by causing the gases reverse direction through another parallel tube or a bundle of multiple pipes (two-pass or return flue boiler); alternatively the gases may be studied along the sides and then beneath the boiler through flues (3-move boiler). In case of a locomotive-type boiler, a boiler barrel expands from the firebox and the hot gases pass through a bundle of fire pipes inside the barrel which greatly increases the heating system surface in comparison to a single tube and further enhances heat transfer. Fire-tube boilers will often have a comparatively low rate of steam production, but high steam storage capacity. Fire-tube boilers mostly burn solid fuels, but are readily adaptable 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 inside a furnace in a true variety of possible configurations. The water pipes connect large drums Often, the low ones containing water and the upper ones water and steam; in other situations, such as a mono-tube boiler, water is circulated with a pump through a succession of coils. This type generally provides high vapor production rates, but less storage space capacity than the above mentioned. Water pipe boilers can be designed to exploit any warmth source and tend to be preferred in high-pressure applications because the high-pressure water/steam is contained 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 pipes are close jointly and drinking 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 held so hot that water feed is quickly flashed into vapor and superheated. Flash boilers experienced 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 the two above types have been combined in the next manner: the firebox includes an assembly of water pipes, called thermic siphons. The gases then pass through a typical firetube boiler. Water-tube fireboxes were installed in many Hungarian locomotives, but have fulfilled with little success in other countries.
Sectional boiler. Within a ensemble iron sectional boiler, sometimes called a "pork chop boiler" water is contained inside cast iron sections. These sections are assembled on site to make the finished boiler.
See also: Boiler explosion
To define and secure boilers safely, some professional specialized organizations such as the American Society of Mechanical Designers (ASME) develop standards and regulation codes. For example, 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 basic safety, security and design standards.
Historically, boilers were a source of many serious injuries and property destruction as a consequence to poorly understood engineering principles. Thin and brittle metal shells can rupture, while poorly welded or riveted seams could open up, resulting in a violent eruption of the pressurized steam. When water is changed into 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 heat around a niche site from a central boiler house to where it is necessary, but without the right boiler feed water treatment, a steam-raising herb are affected from scale formation and corrosion. At best, this increases energy costs and can result in poor quality vapor, reduced efficiency, shorter vegetation and unreliable operation. At worst, it can lead to catastrophic reduction and failing 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 insert the coal into the fire chamber. Extremely large boilers providing hundreds of horsepower to use factories can potentially demolish entire buildings.
A boiler which has a loss of feed drinking water and is permitted to boil dry can be extremely dangerous. If supply water is sent in to the vacant boiler then, the tiny cascade of incoming water instantly boils on connection with the superheated steel 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 supply lines that is bigger 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 assist in preventing this condition from happening, and thus reduce their insurance statements.
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 steam boilers vaporize water and additional heat the steam in a superheater then. This provides vapor at higher heat range, but can decrease the overall thermal efficiency of the vapor generating plant because the higher vapor temperature requires a higher flue gas exhaust heat. There are many ways to circumvent this problem, typically by giving an economizer that heats the give food to water, a combustion air heating unit in the hot flue gas exhaust path, or both. You can find advantages to superheated vapor that may, and often will, increase overall efficiency of both vapor generation and its utilization: increases in input temperatures to a turbine should outweigh any cost in additional boiler complication and expense. There may also be practical limitations in using damp 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 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 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 vapor piping is directed through the flue gas route in the boiler furnace. The heat 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 warmth by radiation. Others are convection type, absorbing heat from a liquid. 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 range of the steam in the superheater rises, the pressure of the vapor will 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 charged power seed.
Main article: Supercritical steam generator
Supercritical steam generators are generally used for the production of energy. They operate at supercritical pressure. In contrast to a "subcritical boiler", a supercritical vapor generator operates at such a higher pressure (over 3,200 psi or 22 MPa) that the physical turbulence that characterizes boiling ceases to occur; the liquid is neither liquid nor gas but a super-critical fluid. There is no era of steam bubbles within water, because the pressure is above the critical pressure point at which steam bubbles can develop. 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 eventually extracted. The fluid at that time may be a mix of steam and liquid droplets as it passes in to the condenser. This leads to somewhat less energy use and therefore less greenhouse gas production. The word "boiler" shouldn't be used for a supercritical pressure vapor generator, as no "boiling" occurs in this product.
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Boiler fittings and accessories
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 basic safety by setting the top limit of steam pressure, the working pressuretrol, which controls 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.
Security valve: It is used to alleviate pressure and stop possible explosion of a boiler.
Water level signals: They show the operator the amount of fluid in the boiler, also called a sight glass, water gauge or water column.
Bottom level blowdown valves: They offer a way for removing solid particulates that condense and rest on the bottom of the boiler. As the name indicates, this valve is located straight on underneath of the boiler usually, and is occasionally opened up 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 drinking water droplets to be carried over with the steam - a disorder 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 water level in a container. Most entirely on a water boiler commonly.
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 once makeup water is moving to the boiler, thereby transferring the utmost amount of heat possible from the blowdown to the makeup water. No flash tank is generally needed as the blowdown discharged is near to the temperature of the make-up water.
Hand openings: These are steel plates installed in openings in "header" to permit for inspections & installing tubes and inspection of inner surfaces.
Vapor drum internals, some screen, scrubber & cans (cyclone separators).
Low-water cutoff: It is a mechanical means (usually a float switch) that can be used to turn off the burner or shut off gas to the boiler to avoid it from working once the water runs below a certain point. If a boiler is "dry-fired" (burned without 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 chemicals that have a tendency to float on top of the water inside the boiler.
Circulating pump: It is made 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 line. This may be installed to the side of the boiler, just below water level, or to the very best of the boiler.
Top give food to: With this design for feedwater injection, water is fed to the very best of the boiler. This can reduce boiler fatigue triggered by thermal stress. By spraying the feedwater over some trays the water is quickly heated which can reduce limescale.
Desuperheater pipes or bundles: Some tubes or bundles of tubes in the water drum or the vapor drum made to cool superheated vapor, in order to provide auxiliary equipment that does not need, or may be damaged by, dry out steam.
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.
Gasoline oil system:fuel oil heaters
Other essential items
Inspectors test pressure measure attachment: