Boiler Repairs Winchmore Hill, N21, Boiler Breakdown Emergency Service
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le 07/11/2017 à 21:46 Citer ce message
A boiler is a closed vessel in which water or other liquid is heated. The fluid does not boil. (In North America, the word "furnace" is generally used if the purpose is never to boil the liquid.) The warmed or vaporized fluid exits the boiler for use in a variety of processes or heating applications,[1][2] including drinking water heating, central heating, boiler-based power generation, food preparation, and sanitation.
Materials
The pressure vessel of a boiler is usually made of steel (or alloy steel), or of wrought iron historically. Stainless steel, especially of the austenitic types, is not found in wetted parts of boilers due to stress and corrosion corrosion breaking.[3] However, ferritic stainless steel is often used in superheater sections that won't be exposed to boiling water, and electrically heated stainless steel 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
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 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 steel) are used instead.
For a lot of the Victorian "age group of vapor", the only material used for boilermaking was the highest grade of wrought iron, with assembly by rivetting. This iron was often extracted from specialist ironworks, such as at Cleator Moor (UK), mentioned 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 steel instead, which is stronger and cheaper, with welded building, which is quicker and requires less labour. It should be mentioned, however, that wrought iron boilers corrode considerably slower than their modern-day metal counterparts, and are less susceptible 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 drinking water heaters. Although such heaters are usually termed "boilers" in some countries, their purpose is usually to produce hot 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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Energy
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 elements. Nuclear fission is also used as a heat source for producing steam, either directly (BWR) or, in most cases, in specialised warmth exchangers called "vapor generators" (PWR). Temperature recovery vapor generators (HRSGs) use the heat rejected from other procedures such as gas turbine.
Boiler efficiency
there are two methods to gauge the boiler efficiency 1) direct method 2) indirect method
Direct method -immediate method of boiler efficiency test is more useful 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 feed water in kcal/kg q= level 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 are in need of a following 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 fuel in kcal/kg
ash percentage in combustible fuel
GCV of ash in kcal/kg
Configurations
Boilers can be classified in to the following configurations:
Container 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 steam, often hardly above that of the atmosphere. These could burn off wood or frequently, coal. Efficiency was very low.
Flued boiler with one or two large flues-an early type or forerunner 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 support the steam (vapor space). This is the kind of boiler used in all steam locomotives nearly. The heat source is in the furnace or firebox that has to be held completely surrounded by water in order to maintain the heat range of the heating system 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 may be further increased by causing the gases reverse direction through another parallel pipe or a bundle of multiple tubes (two-pass or come back flue boiler); additionally the gases may be studied along the edges and then under 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 pass through a lot of money of fire tubes inside the barrel which greatly increases the heating surface compared to a single tube and further improves heat transfer. Fire-tube boilers will often have a comparatively low rate of vapor creation, but high vapor storage capacity. Fire-tube boilers mostly burn off solid fuels, but are readily adaptable to the people of the gas or liquid variety.
Diagram of the water-tube boiler.
Water-tube boiler: In this kind, tubes filled up with drinking water are arranged inside a furnace in several possible configurations. Usually the water tubes connect large drums, the lower ones including drinking water and the upper ones vapor and drinking water; in other instances, such as a mono-tube boiler, water is circulated with a pump through a succession of coils. This kind generally gives high steam creation rates, but less storage capacity than the above. Water pipe boilers can be made to exploit any temperature source and are generally preferred in high-pressure applications since the high-pressure drinking water/vapor 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 pipes are close collectively and drinking water is pumped through them. A flash boiler differs from the kind of mono-tube steam generator where the pipe 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 experienced some use in automobiles in the 19th century which use continued into the early 20th century. .
1950s design steam 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 contains 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,[citation needed] but have met with little success in other countries.
Sectional boiler. Within a ensemble iron sectional boiler, sometimes called a "pork chop boiler" the water is contained inside solid iron areas.[citation needed] These areas are assembled on site to create the finished boiler.
Safety
See also: Boiler explosion
To define and secure boilers safely, some professional specialized organizations such as the American Culture of Mechanical Technicians (ASME) develop specifications and regulation rules. For example, the ASME Boiler and Pressure Vessel Code is a standard providing a wide range of guidelines and directives to ensure compliance of the boilers and other pressure vessels with safety, security and design 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 poorly, leading to a violent eruption of the pressurized vapor. 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, steam is a great way of moving energy and heat around a site from a central boiler house to where it is needed, but with no right boiler give food to water treatment, a steam-raising plant will suffer from range corrosion and formation. At best, this boosts energy costs and can lead to poor quality steam, reduced efficiency, shorter vegetation and unreliable operation. At worst, it can result in catastrophic loss and failure of life. Collapsed or dislodged boiler pipes can also squirt scalding-hot steam and smoke out of the air intake and firing chute, injuring the firemen who load the coal in to the fire chamber. Extremely large boilers providing hundreds of horsepower to operate factories could demolish entire buildings.[6]
A boiler which has a loss of feed drinking water and is permitted to boil dry out can be hugely dangerous. If give food to water is then sent in to the unfilled boiler, the small cascade of inbound drinking water instantly boils on contact with the superheated steel 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 steam source lines that is bigger than the make-up water source could replace. The Hartford Loop was developed in 1919 by the Hartford Vapor Boiler and Insurance Company as a strategy to help prevent this condition from taking place, and thus 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 temperature; that is, saturated vapor. Superheated vapor boilers vaporize the water and then further heat the vapor 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 heat takes a higher flue gas exhaust heat range.[citation needed] There are many ways to circumvent this issue, typically by providing an economizer that heats the give food to drinking water, a combustion air heating unit in the hot flue gas exhaust path, or both. A couple of benefits to superheated vapor that may, and will often, increase overall efficiency of both vapor generation and its utilization: gains in input temp to a turbine should outweigh any cost in additional boiler problem and expense. There could be useful limitations in using damp vapor also, 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 indicates its presence clearly.
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 heat in this field is normally between 1,300 and 1,600 °C (2,372 and 2,912 °F). Some superheaters are glowing type; that is, they absorb temperature by radiation. Others are convection type, absorbing warmth from a liquid. Some are a combination of both 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 temperatures of the vapor in the superheater rises, the pressure of the steam will not and the pressure remains the same as that of the boiler.[9] Virtually 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 charged power plant.
Main article: Supercritical steam generator
Supercritical steam generators are used for the production of energy frequently. They operate at supercritical pressure. As opposed 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 that occurs; the fluid is neither liquid nor gas but a super-critical fluid. There is absolutely no generation of steam bubbles within the water, because the pressure is above the critical pressure point at which vapor bubbles can form. As the liquid expands through the turbine stages, its thermodynamic condition drops below the critical point as it can work turning the turbine which converts the power generator from which power is ultimately extracted. The liquid at that point may be a mix of steam and liquid droplets as it passes in to the condenser. This leads to less fuel use and therefore less greenhouse gas production slightly. The term "boiler" should not be used for a supercritical pressure steam generator, as no "boiling" occurs in this device.
Boiler Repairs Winchmore Hill, N21, Boiler Breakdown Emergency Service Boiler Repairs Winchmore Hill, N21, Boiler Breakdown Emergency Service...
Accessories
Boiler fittings and accessories
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 security by setting the top limit of vapor pressure, the operating pressuretrol, which settings when the boiler fires to keep up pressure, as well as for boilers equipped with a modulating burner, a modulating pressuretrol which controls the quantity of fire.
Security valve: It is utilized to alleviate pressure and prevent possible explosion of the boiler.
Water level indicators: They show the operator the level of fluid in the boiler, also called a sight glass, water measure or water column.
Bottom blowdown valves: They offer a means for removing solid particulates that condense and rest on the bottom of the boiler. As the name implies, this valve is situated directly on the bottom of the boiler usually, and is sometimes opened 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 avoid 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 - an ailment known as priming. Blowdown is also often used to monitor the chemistry of the boiler water.
Trycock: a type of valve that is often use to manually check a water level in a tank. Most commonly found on a water boiler.
Flash tank: High-pressure blowdown enters this vessel where in fact the steam can 'flash' safely and become used 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 technique allows the boiler to blowdown only when make-up water is moving 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 close to the temperatures of the makeup water.
Hand holes: These are steel plates installed in openings in "header" to allow for inspections & installing tubes and inspection of internal surfaces.
Vapor drum internals, some display, 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 fuel to the boiler to avoid it from running 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 failing.
Surface blowdown collection: It provides a means for removing foam or other light-weight non-condensible substances that tend to float together with water inside the boiler.
Circulating pump: It is made to circulate water back 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 can be fitted to the relative side of the boiler, just below the water level, or to the top of the boiler.[10]
Top feed: With this design for feedwater injection, the water is fed to the top of the boiler. This can reduce boiler fatigue 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 the water drum or the steam drum designed to cool superheated vapor, in order to provide auxiliary equipment that will not need, or may be damaged by, dry vapor.
Chemical injection line: A connection to add chemicals for controlling feedwater pH.
Steam accessories
Main vapor stop valve:
Steam traps:
Main steam stop/check valve: It is utilized on multiple boiler installations.
Combustion accessories
Gasoline oil system:gas oil heaters
Gas system:
Coal system:
Soot blower
Other essential items
Pressure gauges:
Feed pumps:
Fusible plug:
Inspectors test pressure measure attachment:
Name dish:
Registration dish:
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