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Boiler Repairs Abbey Wood, SE2, Boiler Breakdown Emergency Service
|# 07/11/2017 à 21:55 Jameshaido (site web)|
||A boiler is a closed vessel in which drinking water or other liquid is heated. The fluid will not boil. (In THE UNITED STATES, the term "furnace" is normally used if the purpose is not to boil the liquid.) The heated or vaporized liquid exits the boiler for use in various heating system or procedures applications, including water heating, central heating, boiler-based power generation, cooking food, and sanitation.
The pressure vessel of a 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 due 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 steel shell boilers are allowed under the Western "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 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 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 quality of wrought iron, with assembly by rivetting. This iron was 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 relocated towards the utilization of metal instead, which is more powerful and cheaper, with welded construction, which is quicker and requires less labour. It ought to be noted, however, that wrought iron boilers corrode much slower than their modern-day metal counterparts, and are less susceptible to localized stress-corrosion and pitting. This makes the longevity of old wrought-iron boilers considerably superior to those of welded steel boilers.
Cast iron may be used for the heating system vessel of home water heaters. Although such heaters are usually termed "boilers" in a few countries, their purpose is to produce hot water usually, 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 heat for a boiler is combustion of any 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, generally, in specialised temperature exchangers called "vapor generators" (PWR). Heat recovery vapor 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
Direct method -direct method of boiler efficiency test is more functional 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 water in kcal/kg q= quantity of energy 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 gasoline (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 water box from below. 18th century Haycock boilers generally produced and stored large quantities of very low-pressure steam, barely above that of the atmosphere often. These could burn off wood or most often, coal. Efficiency was suprisingly low.
Flued boiler with one or two large flues-an early forerunner or kind of fire-tube boiler.
Diagram of a fire-tube boiler
Fire-tube boiler: Here, drinking water partially fills a boiler barrel with a little volume remaining above to support the steam (steam space). This is the kind of boiler used in almost 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 temperatures of the heating surface below the boiling point. The furnace can be situated at one end of a fire-tube which lengthens the road of the hot gases, thus augmenting the heating surface which can be further increased by causing the gases invert direction through a second parallel tube or a bundle of multiple tubes (two-pass or come back flue boiler); additionally the gases may be taken along the sides and then beneath the boiler through flues (3-pass boiler). In case there is a locomotive-type boiler, a boiler barrel extends from the firebox and the hot gases pass through a lot of money of fire pipes inside the barrel which greatly escalates the heating system surface in comparison to a single tube and further improves heat transfer. Fire-tube boilers have a comparatively low rate of vapor production usually, but high steam storage capacity. Fire-tube boilers burn solid fuels mainly, but are readily flexible to those of the liquid or gas variety.
Diagram of the water-tube boiler.
Water-tube boiler: In this type, tubes filled with drinking water are arranged in the furnace in a number of possible configurations. Water pipes connect large drums Often, the lower ones containing water and the top ones water and steam; in other instances, like a mono-tube boiler, water is circulated with a pump through a succession of coils. This type generally gives high vapor production rates, but less storage capacity than the above mentioned. Water tube boilers can be made to exploit any warmth source and tend to be preferred in high-pressure applications since the high-pressure water/steam is contained 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 where pipes are close together 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 tube is held so hot that the water feed is quickly flashed into steam and superheated. Flash boilers acquired some use in cars 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 combined in the next manner: the firebox consists of an set up of water pipes, called thermic siphons. The gases then go 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. In a cast iron sectional boiler, sometimes called a "pork chop boiler" the 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 Engineers (ASME) develop standards and regulation rules. For instance, the ASME Boiler and Pressure Vessel Code is a typical providing an array of guidelines and directives to ensure compliance of the boilers and other pressure vessels with basic safety, design and security standards.
Historically, boilers were a way to obtain many serious injuries and property destruction due to poorly understood engineering principles. Thin and brittle steel shells can rupture, while badly welded or riveted seams could start, resulting in a violent eruption of the pressurized steam. When drinking water is converted to vapor 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 temperature around a niche site from a central boiler house to where it is needed, but without the right boiler give food to water treatment, a steam-raising herb will suffer from level corrosion and formation. At best, this increases energy costs and can lead to poor quality vapor, reduced efficiency, shorter vegetation and unreliable procedure. At worst, it can lead to catastrophic failure and lack of life. Collapsed or dislodged boiler pipes can also aerosol scalding-hot vapor 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 a huge selection of horsepower to use factories could demolish entire buildings.
A boiler which has a loss of feed water and is permitted to boil dry can be hugely dangerous. If feed drinking water is then sent into the clear boiler, 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 controlled even by security steam 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 developed in 1919 by the Hartford Steam Boiler and INSURANCE PROVIDER as a strategy to assist in preventing this problem from taking place, and thereby reduce their insurance statements.
Superheated steam boiler
A superheated boiler on the steam locomotive.
Main article: Superheater
Most boilers produce steam to be used at saturation heat; that is, saturated steam. Superheated steam boilers vaporize the water and further heat up the steam in a superheater then. This provides steam at higher temp, but can reduce the overall thermal efficiency of the steam generating place because the higher vapor temp requires a higher flue gas exhaust temperature. There are many ways to circumvent this problem, typically by giving an economizer that heats the feed drinking water, a combustion air heating unit in the hot flue gas exhaust route, or both. A couple of advantages to superheated steam that may, and will often, increase overall efficiency of both steam generation and its utilization: gains in input temp to a turbine should outweigh any cost in additional boiler complication and expense. There may also be useful restrictions in using moist vapor, as entrained condensation droplets will damage turbine blades.
Superheated steam presents unique safety concerns because, if any system component fails and allows steam to flee, the high 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 indicates its existence clearly.
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 path in the boiler furnace. The temperatures in this area is normally between 1,300 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 temperature 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 temp of the steam in the superheater goes up, the pressure of the vapor will not and the pressure remains the same as that of the boiler. Almost 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 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 higher pressure (over 3,200 psi or 22 MPa) that the physical turbulence that characterizes boiling ceases that occurs; the fluid is neither water nor gas but a super-critical liquid. There is no generation of vapor bubbles within the water, because the pressure is above the critical pressure point at which vapor bubbles can develop. As the liquid expands through the turbine levels, its thermodynamic state drops below the critical point as it can work turning the turbine which turns the electrical generator that power is eventually extracted. The fluid at that time may be a mixture of steam and liquid droplets as it goes by in to the condenser. This results in less fuel use and therefore less greenhouse gas production slightly. 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 regulate the steam pressure in the boiler. Boilers generally have two or three 3 pressuretrols: a manual-reset pressuretrol, which functions as a protection by setting the top limit of vapor pressure, the operating pressuretrol, which settings when the boiler fires to keep pressure, and for boilers equipped with a modulating burner, a modulating pressuretrol which settings the quantity of fire.
Protection valve: It can be 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, also known as a view glass, water gauge or drinking water column.
Bottom blowdown valves: They offer a way for removing solid particulates that condense and lay on underneath of a boiler. As the name suggests, this valve is usually located on the bottom of the boiler, and is sometimes opened to use the pressure in the boiler to drive these particulates out.
Constant blowdown valve: This enables a small quantity of water to flee continuously. Its purpose is to prevent the 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 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 water level in a container. Mostly entirely on a water boiler.
Flash container: High-pressure blowdown enters this vessel where in fact the vapor 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/constant heat recovery system: This technique allows the boiler to blowdown only once 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 container is normally needed as the blowdown discharged is near to the temperature of the makeup water.
Hand openings: These are metal plates installed in openings in "header" to allow for inspections & installation of tubes and inspection of inner surfaces.
Steam 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 utilized to turn off the burner or shut down fuel to the boiler to prevent it from jogging once the water moves 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 line: It offers a way for removing foam or other light-weight non-condensible chemicals that tend to float on top of the water inside the boiler.
Circulating pump: It is designed 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 collection. 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, the water is fed to the very best of the boiler. This may reduce boiler exhaustion caused by thermal stress. By spraying the feedwater over a series of trays water is quickly warmed which can reduce limescale.
Desuperheater pipes or bundles: A series of tubes or bundles of pipes in the water drum or the vapor drum made to cool superheated vapor, in order to supply auxiliary equipment that does not need, or may be damaged by, dry steam.
Chemical injection line: A link with add chemicals for controlling feedwater pH.
Main vapor stop valve:
Main steam stop/check valve: It is utilized on multiple boiler installations.
Energy oil system:gas oil heaters
Other essential items
Inspectors test pressure gauge attachment: