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Nội dung: A boiler is a closed vessel where drinking water or other liquid is heated. The liquid will not necessarily boil. (In THE UNITED STATES, the word “furnace” is generally used if the purpose is never to boil the liquid.) The heated or vaporized liquid exits the boiler for use in various heating or procedures applications,[1 – [2 – including drinking water heating, central heating system, boiler-based power era, cooking, 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 elements of boilers credited to corrosion and stress corrosion cracking.[3 – However, ferritic stainless steel is often found in superheater sections that won’t be exposed to boiling water, and electrically heated stainless steel shell boilers are allowed under the Western european “Pressure Equipment Directive” for creation of steam for sterilizers and disinfectors.[4 –
https://en.wikipedia.org/wiki/Boiler – https://en.wikipedia.org/wiki/Boiler
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 vapor 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 materials used for boilermaking was the best 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 utilization of steel instead, which is stronger and cheaper, with welded building, which is quicker and requires less labour. It should be noted, however, that wrought iron boilers corrode significantly slower than their modern-day metal counterparts, and are less vunerable to localized stress-corrosion and pitting. This makes the durability of old wrought-iron boilers considerably more advanced than those of welded metal boilers.

Cast iron might be used for the heating system vessel of local drinking 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 try to avoid boiling. The brittleness of cast iron helps it be impractical for high-pressure vapor boilers.
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Energy
The source of heat for a boiler is combustion of any of several fuels, such as wood, coal, oil, or gas. Electric steam boilers use resistance- or immersion-type heating system elements. Nuclear fission is also used as a heat source for generating steam, either straight (BWR) or, in most cases, in specialised high temperature exchangers called “vapor generators” (PWR). High temperature recovery vapor generators (HRSGs) use the heat rejected from other processes such as gas turbine.

Boiler efficiency
there are two solutions to measure the boiler efficiency 1) direct method 2) indirect method

Immediate method -direct approach to boiler efficiency test is more functional or even more common

boiler efficiency =Q*((Hg-Hf)/q)*(GCV *100 ) Q =Total steam circulation Hg= Enthalpy of saturated vapor in k cal/kg Hf =Enthalpy of feed drinking 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 need 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 fuel in kcal/kg
ash percentage in combustible fuel
GCV of ash in kcal/kg
Configurations
Boilers can be classified into the following configurations:

Pot boiler or Haycock boiler/Haystack boiler: a primitive “kettle” in which a fireplace heats a partially filled 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 suprisingly low.
Flued boiler with one or two large flues-an early type or forerunner of fire-tube boiler.

Diagram of a fire-tube boiler
Fire-tube boiler: Here, water partially fills a boiler barrel with a little volume still left above to accommodate the steam (vapor space). This is the kind of boiler used in almost all steam locomotives. The heat source is inside a furnace or firebox that has to be held permanently surrounded by water in order to keep the temp of the heating surface below the boiling point. The furnace can be situated at one end of the fire-tube which lengthens the path of the hot gases, thus augmenting the heating system surface which may be further increased by causing the gases invert direction through another parallel tube or a bundle of multiple pipes (two-pass or come back flue boiler); additionally the gases may be studied along the sides and then beneath 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 pipes inside the barrel which greatly increases the heating system surface in comparison to a single tube and further boosts heat transfer. Fire-tube boilers have a comparatively low rate of vapor creation usually, but high vapor storage capacity. Fire-tube boilers burn off solid fuels mainly, but are readily adaptable to those of the gas or liquid variety.

Diagram of the water-tube boiler.
Water-tube boiler: In this kind, pipes filled with water are arranged inside a furnace in several possible configurations. Water pipes connect large drums Often, the lower ones including water and the top ones steam and water; in other instances, such as a mono-tube boiler, drinking water is circulated with a pump through a succession of coils. This kind provides high vapor production rates generally, but less storage space capacity than the above. Water pipe boilers can be made to exploit any high temperature source and tend to be 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 kind 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 vapor generator where the pipe is permanently filled up 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 got some use in automobiles in the 19th century and this 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 following manner: the firebox consists of an set up of water pipes, called thermic siphons. The gases go through a typical firetube boiler then. Water-tube fireboxes were installed in many Hungarian locomotives,[citation needed – but have met with little success far away.
Sectional boiler. In a ensemble iron sectional boiler, sometimes called a “pork chop boiler” the water is included inside cast iron sections.[citation needed – These areas are assembled on site to produce the finished boiler.
Safety
See also: Boiler explosion
To define and secure boilers safely, some professional specialized organizations like the American Society of Mechanical Designers (ASME) develop specifications and regulation rules. For example, 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 safety, security and design standards.[5 –

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 welded or riveted seams could open up badly, leading to a violent eruption of the pressurized steam. When drinking water is changed into steam it expands to over 1,000 times its original quantity and travels down vapor pipes at over 100 kilometres each hour. Because of this, steam is a superb 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 give food to water treatment, a steam-raising herb are affected from size corrosion and formation. At best, this raises energy costs and can result in poor quality vapor, reduced efficiency, shorter vegetation and unreliable operation. At worst, it can result in catastrophic reduction and failing of life. Collapsed or dislodged boiler tubes can also aerosol scalding-hot vapor 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 a huge selection of horsepower to operate factories can potentially demolish entire buildings.[6 –

A boiler that has a loss of give food to water and is permitted to boil dry out can be hugely dangerous. If nourish water is sent into the bare boiler then, the tiny cascade of incoming drinking water instantly boils on connection with the superheated steel shell and leads to a violent explosion that cannot be managed even by safety steam valves. Draining of the boiler can also happen if a leak occurs in the vapor source lines that is bigger than the make-up drinking water supply could replace. The Hartford Loop was created in 1919 by the Hartford Vapor Boiler and INSURANCE PROVIDER as a method to help prevent this problem from taking place, and therefore 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 used at saturation temp; that is, saturated vapor. Superheated steam boilers vaporize the water and then further warmth the vapor in a superheater. This provides vapor at much higher temperatures, but can reduce the overall thermal efficiency of the steam generating vegetable because the higher vapor heat takes a higher flue gas exhaust temp.[citation needed – There are many ways to circumvent this problem, by providing an economizer that heats the feed water typically, a combustion air heating unit in the hot flue gas exhaust route, or both. A couple of benefits to superheated vapor that may, and will often, increase overall efficiency of both steam generation and its utilization: gains in input heat range to a turbine should outweigh any cost in additional boiler problem and expense. There may also be useful limitations in using damp steam, as entrained condensation droplets will harm 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 injury 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 presence clearly.

Superheater procedure is similar to that of the coils on an fresh air conditioning unit, although for a different purpose. The vapor piping is directed through the flue gas route in the boiler furnace. The temp 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 rays. Others are convection type, absorbing high temperature from a fluid. Some are a combination of the two types. Through either method, the extreme high temperature in the flue gas route will also heat the superheater vapor piping and the vapor within. While the temperatures of the steam in the superheater rises, the pressure of the vapor does 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 avoid harm to the turbine blading and associated piping.

Supercritical steam generator

Boiler for a charged power place.
Main article: Supercritical steam generator
Supercritical steam generators are used for the production of electric power frequently. 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 that occurs; the liquid is neither liquid nor gas but a super-critical fluid. There is absolutely no era of vapor bubbles within the water, because the pressure is above the critical pressure point at which vapor bubbles can form. As the fluid expands through the turbine phases, its thermodynamic state drops below the critical point as it does work turning the turbine which turns the power generator from which power is eventually extracted. The fluid at that point may be a mix of vapor and liquid droplets as it goes by into the condenser. This results in slightly less gas use and for that reason 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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Accessories
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 security by setting top of the limit of vapor pressure, the working pressuretrol, which controls when the boiler fires to maintain pressure, and for boilers equipped with a modulating burner, a modulating pressuretrol which handles the quantity of fire.
Protection valve: It can be used to alleviate pressure and prevent possible explosion of a boiler.
Water level indicators: They show the operator the amount of liquid in the boiler, known as a sight cup also, water gauge 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 located straight on the bottom of the boiler usually, and is occasionally opened up to use the pressure in the boiler to drive these particulates out.
Continuous blowdown valve: This enables a small level of water to escape continuously. Its purpose is to avoid water in the boiler becoming saturated with dissolved salts. Saturation would lead to foaming and cause drinking water droplets to be carried over with the vapor – a condition known as priming. Blowdown is often used to monitor the chemistry of the boiler drinking water also.
Trycock: a type of valve that is often use to manually check a water level in a tank. Most found on a water boiler commonly.
Flash container: High-pressure blowdown enters this vessel where the steam can ‘flash’ safely and become found in a low-pressure system or be vented to atmosphere as the ambient pressure blowdown flows to drain.
Automatic blowdown/continuous heat recovery system: This system allows the boiler to blowdown only when make-up water is moving 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 temperature of the make-up water.
Hand holes: They are steel plates installed in openings in “header” to allow for inspections & installing pipes and inspection of internal surfaces.
Vapor drum internals, a series of display screen, scrubber & cans (cyclone separators).
Low-water cutoff: It is a mechanical means (usually a float change) that can be used to turn from the burner or shut down energy to the boiler to prevent it from jogging once the drinking water runs below a certain point. If a boiler is “dry-fired” (burned without water in it) it can cause rupture or catastrophic failing.
Surface blowdown series: It provides a way for removing foam or other lightweight non-condensible chemicals that have a tendency to float together with the water inside the boiler.
Circulating pump: It is designed 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 series. This may be installed to the side of the boiler, below water level just, or to the very best of the boiler.[10 –
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 a series of trays water is quickly warmed and this can reduce limescale.
Desuperheater tubes or bundles: A series of pipes or bundles of tubes in the water drum or the vapor drum designed to cool superheated vapor, in order to provide auxiliary equipment that will not need, or may be damaged by, dry out vapor.
Chemical injection line: A link with 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
Fuel oil system:gas oil heaters
Gas system:
Coal system:
Soot blower
Other essential items
Pressure gauges:
Feed pumps:
Fusible plug:
Inspectors test pressure gauge attachment:
Name plate:
Registration dish: