Home      Discussion      Topics      Dictionary      Almanac
Signup       Login
Boiler

Boiler

Overview

A boiler is a closed vessel
Pressure vessel
A pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.The pressure differential is dangerous and many fatal accidents have occurred in the history of their development and operation. Consequently, their design,...

 in which water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 or other fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....

 is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.

The pressure vessel
Pressure vessel
A pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.The pressure differential is dangerous and many fatal accidents have occurred in the history of their development and operation. Consequently, their design,...

 in a boiler is usually made of steel (or alloy steel), or historically of wrought iron
Wrought iron
thumb|The [[Eiffel tower]] is constructed from [[puddle iron]], a form of wrought ironWrought iron is an iron alloy with a very low carbon...

. Stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

 is virtually prohibited (by the ASME Boiler Code) for use in wetted parts of modern boilers, but is used often in superheater sections that will not be exposed to liquid boiler water.
Discussion
Ask a question about 'Boiler'
Start a new discussion about 'Boiler'
Answer questions from other users
Full Discussion Forum
 
Unanswered Questions
Recent Discussions
Encyclopedia

A boiler is a closed vessel
Pressure vessel
A pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.The pressure differential is dangerous and many fatal accidents have occurred in the history of their development and operation. Consequently, their design,...

 in which water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 or other fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....

 is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.

Materials


The pressure vessel
Pressure vessel
A pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.The pressure differential is dangerous and many fatal accidents have occurred in the history of their development and operation. Consequently, their design,...

 in a boiler is usually made of steel (or alloy steel), or historically of wrought iron
Wrought iron
thumb|The [[Eiffel tower]] is constructed from [[puddle iron]], a form of wrought ironWrought iron is an iron alloy with a very low carbon...

. Stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

 is virtually prohibited (by the ASME Boiler Code) for use in wetted parts of modern boilers, but is used often in superheater sections that will not be exposed to liquid boiler water. In live steam
Live steam
Live steam is steam under pressure, obtained by heating water in a boiler. The steam is used to operate stationary or moving equipment.A live steam machine or device is one powered by steam, but the term is usually reserved for those that are replicas, scale models, toys, or otherwise used for...

 models, copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 or brass
Brass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...

 is often used because it is more easily fabricated in smaller size boilers. Historically, copper was often used for fireboxes (particularly for steam locomotive
Steam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...

s), 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 much of the Victorian "age of steam", the only material used for boilermaking was the highest grade of wrought iron, with assembly by rivet
Rivet
A rivet is a permanent mechanical fastener. Before being installed a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite the head is called the buck-tail. On installation the rivet is placed in a punched or pre-drilled hole, and the tail is upset, or bucked A rivet...

ting. This iron was often obtained from specialist ironworks
Ironworks
An ironworks or iron works is a building or site where iron is smelted and where heavy iron and/or steel products are made. The term is both singular and plural, i.e...

, such as at Cleator Moor
Cleator Moor
Cleator Moor is a small town and civil parish in the English county of Cumbria and within the boundaries of the traditional county of Cumberland....

 (UK), noted for the high quality of their rolled plate
Rolling (metalworking)
In metalworking, rolling is a metal forming process in which metal stock is passed through a pair of rolls. Rolling is classified according to the temperature of the metal rolled. If the temperature of the metal is above its recrystallization temperature, then the process is termed as hot rolling...

 and its suitability for high-reliability use in critical applications, such as high-pressure boilers. In the 20th century, design practice instead moved towards the use of steel, which is stronger and cheaper, with welded
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...

 construction, which is quicker and requires less labour.

Cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...

 may be used for the heating vessel of domestic water heaters. Although such heaters are usually termed "boilers" in some countries, their purpose is usually to produce hot water, not steam, and so they run at low pressure and try to avoid actual boiling. The brittleness of cast iron makes it impractical for high pressure steam boilers.



Fuel


The source of heat for a boiler is combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 of any of several fuel
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...

s, such as wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

, coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

, oil
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

, or natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

. Electric steam boiler
Electric steam boiler
An electric steam boiler is a type of boiler where the steam is generated using electricity, rather than through the combustion of a fuel source. They are used to generate steam for process purposes in many locations, for example laundries, food processing factories and hospitals...

s use resistance-
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...

 or immersion-type heating elements. Nuclear fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...

 is also used as a heat source for generating steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...

. Heat recovery steam generators (HRSGs) use the heat rejected from other processes such as gas turbine
Gas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....

s.

Configurations


Boilers can be classified into the following configurations:
  • "Pot boiler" or "Haycock boiler": a primitive "kettle" where a fire heats a partially-filled water container from below. 18th century Haycock boilers generally produced and stored large volumes of very low-pressure steam, often hardly above that of the atmosphere. These could burn wood or most often, coal. Efficiency was very low.
  • Fire-tube boiler
    Fire-tube boiler
    A fire-tube boiler is a type of boiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water...

    . Here, water partially fills a boiler barrel with a small volume left above to accommodate the steam (steam space). This is the type of boiler used in nearly all steam locomotives. The heat source is inside a furnace or firebox that has to be kept permanently surrounded by the water in order to maintain the temperature of the heating surface just below boiling point
    Boiling point
    The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

    . The furnace can be situated at one end of a fire-tube which lengthens the path of the hot gases, thus augmenting the heating surface which can be further increased by making the gases reverse direction through a second parallel tube or a bundle of multiple tubes (two-pass or return flue boiler); alternatively the gases may be taken along the sides and then beneath the boiler through flues (3-pass boiler). In the case of a locomotive-type boiler, a boiler barrel extends from the firebox and the hot gases pass through a bundle of fire tubes inside the barrel which greatly increase the heating surface compared to a single tube and further improve heat transfer. Fire-tube boilers usually 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 those of the liquid or gas variety.
  • Water-tube boiler
    Water-tube boiler
    A water tube boiler is a type of boiler in which water circulates in tubes heated externally by the fire. Fuel is burned inside the furnace, creating hot gas which heats water in the steam-generating tubes...

    . In this type,the water tubes are arranged inside a furnace in a number of possible configurations: often the water tubes connect large drums, the lower ones containing water and the upper ones, steam and water; in other cases, such as a monotube boiler, water is circulated by a pump through a succession of coils. This type generally gives high steam production rates, but less storage capacity than the above. Water tube boilers can be designed to exploit any heat source and are generally preferred in high pressure applications since the high pressure water/steam is contained within small diameter pipes which can withstand the pressure with a thinner wall.
  • Flash boiler
    Flash boiler
    A flash boiler is a type of water-tube boiler, whose tubes are strong and close together with water pumped through the tubes. The tubes are kept very hot so the water feed is quickly flashed into steam and superheated...

    . A specialized type of water-tube boiler.

  • Fire-tube boiler with Water-tube firebox. Sometimes the two above types have been combined in the following manner: the firebox contains an assembly of water tubes, called thermic siphons. The gases then pass through a conventional firetube boiler. Water-tube fireboxes were installed in many Hungarian
    Hungary
    Hungary , officially the Republic of Hungary , is a landlocked country in Central Europe. It is situated in the Carpathian Basin and is bordered by Slovakia to the north, Ukraine and Romania to the east, Serbia and Croatia to the south, Slovenia to the southwest and Austria to the west. The...

     locomotives, but have met 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 create the finished boiler.

Safety



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 poorly welded or riveted seams could open up, leading to a violent eruption of the pressurized steam. When water is converted to steam it expands in volume over 1,000 times and travels a down a steam pipes at over 100 kilometres/hr. 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 without the right boiler feed water treatment, a steam-raising plant will suffer from scale formation and corrosion. At best, this increases energy costs and can lead to poor quality steam, reduced efficiency, shorter plant life and an operation which is unreliable. At worst, it can lead to catastrophic failure and loss of life. Collapsed or dislodged boiler tubes could also spray scalding-hot steam and smoke out of the air intake and firing chute, injuring the firemen who loaded coal into the fire chamber. Extremely large boilers providing hundreds of horsepower to operate factories could demolish entire buildings.

A boiler that has a loss of feed water and is permitted to boil dry can be extremely dangerous. If feed water is then sent into the empty boiler, the small cascade of incoming water instantly boils on contact with the superheated metal shell and leads to a violent explosion that cannot be controlled even by safety steam valves. Draining of the boiler could also occur if a leak occurred in the steam supply lines that was larger than the make-up water supply 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 claims.

Superheated steam boilers




Most boilers produce steam to be used at saturation temperature; that is, saturated steam. Superheated steam boilers vaporize the water and then further heat the steam in a superheater. This provides steam at much higher temperature, but can decrease the overall thermal efficiency of the steam generating plant because the higher steam temperature requires a higher flue gas exhaust temperature. There are several ways to circumvent this problem, typically by providing an economizer that heats the feed water, a combustion air heater in the hot flue gas exhaust path, or both. There are advantages to superheated steam that may, and often will, increase overall efficiency of both steam generation and its utilisation: gains in input temperature to a turbine should outweigh any cost in additional boiler complication and expense. There may also be practical limitations in using wet steam, as entrained condensation droplets will damage turbine blades.

Superheated steam presents unique safety concerns because, if any 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 clearly indicates its presence.

Superheater operation is similar to that of the coils on an air conditioning unit, although for a different purpose. The steam piping is directed through the flue gas path in the boiler furnace. The temperature in this area is typically between 1300–1600 °C (2,372–2,912 F). Some superheaters are radiant type; that is, they absorb heat by radiation. Others are convection type, absorbing heat from a fluid. Some are a combination of the two types. Through either method, the extreme heat in the flue gas path will also heat the superheater steam piping and the steam within. While the temperature of the steam in the superheater rises, the pressure of the steam does not: the turbine or moving pistons offer a continuously expanding space and the pressure remains the same as 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




Supercritical steam generators are frequently used for the production of electric power
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...

. They operate at supercritical
Supercritical fluid
A supercritical fluid is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist. It can effuse through solids like a gas, and dissolve materials like a liquid...

 pressure. In contrast to a "subcritical boiler", a supercritical steam generator operates at such a high pressure (over 3200 psi (22.06 MPa) or 3200 psi (220.6 bar)) that actual boiling ceases to occur, the boiler has no liquid water - steam separation. There is no generation of steam bubbles within the water, because the pressure is above the critical pressure at which steam bubbles can form. It passes below the critical point as it does work in a high pressure turbine and enters the generator's condenser
Condenser (heat transfer)
In systems involving heat transfer, a condenser is a device or unit used to condense a substance from its gaseous to its liquid state, typically by cooling it. In so doing, the latent heat is given up by the substance, and will transfer to the condenser coolant...

. This results in slightly less fuel use and therefore less greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...

 production. The term "boiler" should not be used for a supercritical pressure steam generator, as no "boiling" actually occurs in this device.

Hydronic boilers


Hydronic boilers are used in generating heat for residential and industrial purposes. They are the typical power plant for central heating
Central heating
A central heating system provides warmth to the whole interior of a building from one point to multiple rooms. When combined with other systems in order to control the building climate, the whole system may be a HVAC system.Central heating differs from local heating in that the heat generation...

 systems fitted to houses in northern Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 (where they are commonly combined with domestic water heating), as opposed to the forced-air
Forced-air
A forced-air system is one which uses air as its heat transfer medium. These systems rely on ductwork, vents, and plenums as means of air distribution, separate from the actual heating and air conditioning systems. The return plenum carries the air from several large return grills to a central...

 furnaces or wood burning stoves more common in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

. The hydronic boiler operates by way of heating water/fluid to a preset temperature (or sometimes in the case of single pipe systems, until it boils and turns to steam) and circulating that fluid throughout the home typically by way of radiator
Radiator
Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in automobiles, buildings, and electronics...

s, baseboard heaters or through the floors. The fluid can be heated by any means...gas, wood, fuel oil, etc., but in built-up areas where piped gas is available, natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 is currently the most economical and therefore the usual choice. The fluid is in an enclosed system and circulated throughout by means of a motorized pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...

. The name "boiler" can be a misnomer in that, except for systems using steam radiators, the water in a properly functioning hydronic boiler never actually boils. Some new systems are fitted with condensing boiler
Condensing boiler
A condensing boiler utilizes the latent heat of water produced from the burning of fuel, in addition to the standard sensible heat, to increase its efficiency.-Principles of work:...

s for greater efficiency. These boilers are referred to as condensing boiler
Condensing boiler
A condensing boiler utilizes the latent heat of water produced from the burning of fuel, in addition to the standard sensible heat, to increase its efficiency.-Principles of work:...

s because the boilers are designed to operate at lower temperatures than typical hydronic boilers. These lower temperatures would typically damage a boiler because it would cause condensation in the flue gases which ultimately form carbonic acid which corrodes the flue and fireside boiler heating surfaces. Condensing boilers solve this problem by routing the carbonic acid down the drain and by making the flue out of stainless steel or PVC. Although condensing boilers are becoming more popular, they are still less common than other types of hydronic boilers because they are more expensive.

Hydronic systems are being used more and more in new construction in North America for several reasons. Among the reasons are:
  • They are more efficient and more economical than forced-air
    Forced-air
    A forced-air system is one which uses air as its heat transfer medium. These systems rely on ductwork, vents, and plenums as means of air distribution, separate from the actual heating and air conditioning systems. The return plenum carries the air from several large return grills to a central...

     systems (although initial installation can be more expensive, because of the cost of the copper and aluminum).
  • The baseboard copper pipes and aluminum fins take up less room and use less metal than the bulky steel ductwork required for forced-air systems.
  • They provide more even, less fluctuating temperatures than forced-air systems. The copper baseboard pipes hold and release heat over a longer period of time than air does, so the furnace does not have to switch off and on as much. (Copper heats mostly through conduction and radiation, whereas forced-air heats mostly through forced convection. Air has much lower thermal conductivity
    Thermal conductivity
    In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

     and volumetric heat capacity
    Volumetric heat capacity
    Volumetric heat capacity , also termed volume-specific heat capacity, describes the ability of a given volume of a substance to store internal energy while undergoing a given temperature change, but without undergoing a phase change...

     than copper, so the conditioned space warms up and cools down more quickly than with hydronic. See also thermal mass.)
  • They tend to not dry out the interior air as much as forced air systems, but this is not always true. When forced air duct systems are air-sealed properly, and have return-air paths back to the furnace (thus reducing pressure differentials and therefore air movement between inside and outside the house), this is not an issue.
  • They do not introduce any dust, allergens, mold, or (in the case of a faulty heat exchanger) combustion byproducts into the living space.


Forced-air heating does have some advantages, however. See forced-air heating.

Boiler fittings and accessories

  • Safety valve
    Relief valve
    The relief valve is a type of valve used to control or limit the pressure in a system or vessel which can build up by a process upset, instrument or equipment failure, or fire....

    :
    It is used to relieve pressure and prevent possible explosion of a boiler
    Boiler explosion
    A boiler explosion is a catastrophic failure of a boiler. As seen today, boiler explosions are of two kinds. One kind is over-pressure in the pressure parts of the steam and water sides. The second kind is explosion in the furnace. Boiler explosions of pressure parts are particularly associated...

    .
  • Water level indicators: They show the operator the level of fluid in the boiler, also known as a sight glass
    Sight glass
    A sight glass or water gauge is a transparent tube through which the operator of a tank or boiler can observe the level of liquid contained within.-Liquid in tanks:...

    , water gauge or water column is provided.
  • Bottom blowdown valves: They provide a means for removing solid particulates that condense and lie on the bottom of a boiler. As the name implies, this valve is usually located directly on the bottom of the boiler, and is occasionally opened to use the pressure in the boiler to push these particulates out.
  • Continuous blowdown valve: This allows a small quantity of water to escape continuously. Its purpose is to prevent the water in the boiler becoming saturated with dissolved salts. Saturation would lead to foaming and cause water droplets to be carried over with the steam - a condition known as priming
    Priming (steam engine)
    Priming is a condition in the boiler of a steam engine in which water is carried over into the steam delivery. It may be caused by impurities in the water, which foams up as it boils, or simply too high a water level...

    . Blowdown is also often used to monitor the chemistry of the boiler water.
  • Flash Tank: High pressure blowdown enters this vessel where the steam can 'flash' safely and be used in a low-pressure system or be vented to atmosphere while the ambient pressure blowdown flows to drain.
  • Automatic Blowdown/Continuous Heat Recovery System: This system allows the boiler to blowdown only when 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 generally needed as the blowdown discharged is close to the temperature of the makeup water.
  • Hand holes: They are steel plates installed in openings in "header" to allow for inspections & installation of tubes and inspection of internal surfaces.
  • Steam drum internals, A series of screen, scrubber & cans (cyclone separators).
  • Low- water cutoff: It is a mechanical means (usually a float switch) that is used to turn off the burner or shut off fuel to the boiler to prevent it from running once the water goes below a certain point. If a boiler is "dry-fired" (burned without water in it) it can cause rupture or catastrophic failure.
  • Surface blowdown line: It provides a means for removing foam or other lightweight non-condensible substances that tend to float on top of the water inside the boiler.
  • Circulating pump
    Pump
    A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...

    :
    It is designed to circulate water back to the boiler after it has expelled some of its heat.
  • Feedwater check valve
    Check valve
    A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid to flow through it in only one direction....

     or clack valve
    : A non-return stop valve in the feedwater
    Boiler feedwater
    Boiler feedwater is water used to supply a boiler to generate steam or hot water. At thermal power stations the feedwater is usually stored, pre-heated and conditioned in a feedwater tank and forwarded into the boiler by a boiler feedwater pump....

     line. This may be fitted to the side of the boiler, just below the water level, or to the top of the boiler.
  • Top feed: A check valve
    Check valve
    A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid to flow through it in only one direction....

     (clack valve) in the feedwater
    Boiler feedwater
    Boiler feedwater is water used to supply a boiler to generate steam or hot water. At thermal power stations the feedwater is usually stored, pre-heated and conditioned in a feedwater tank and forwarded into the boiler by a boiler feedwater pump....

     line, mounted on top of the boiler. It is intended to reduce the nuisance of limescale
    Limescale
    Limescale is the hard, off-white, chalky deposit found in kettles, hot-water boilers and the inside of inadequately maintained hot-water central heating systems...

    . It does not prevent limescale formation but causes the limescale to be precipitated in a powdery form which is easily washed out of the boiler.
  • Desuperheater tubes or bundles: A series of tubes or bundles of tubes in the water drum or the steam drum designed to cool superheated steam. Thus is to supply auxiliary equipment that does not need, or may be damaged by, dry steam.
  • Chemical injection line: A connection to add chemicals for controlling feedwater pH
    PH
    In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

    .

Steam accessories

  • Main steam stop valve:
  • Steam trap
    Steam trap
    A steam trap is a device used to discharge condensate and non condensable gases with a negligible consumption or loss of live steam.Most steam traps are nothing more than automatic valves. They open, close or modulate automatically...

    s:
  • Main steam stop/Check valve: It is used on multiple boiler installations.

Combustion accessories

  • Fuel oil system:
  • Gas system:
  • Coal system:
  • Soot blower
    Soot blower
    A Sootblower is a system for removing the soot that is deposited on the furnace tubes of a boiler during combustion. Various types of soot blowers such as Wall Blowers, Long Retractable Blowers and Air Heater Blowers are used for the cleaning...


Other essential items

  • Pressure gauges
    Pressure measurement
    Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure pressure are called pressure gauges or vacuum gauges....

    :
  • Feed pumps:
  • Fusible plug
    Fusible plug
    A fusible plug is a threaded metal cylinder usually of bronze, brass or gunmetal, with a tapered hole drilled completely through its length. This hole is sealed with a metal of low melting point that flows away if a pre-determined, high temperature is reached...

    :
  • Inspectors test pressure gauge attachment:
  • Name plate:
  • Registration plate:

Controlling draught


Most boilers now depend on mechanical draught equipment rather than natural draught. This is because natural draught is subject to outside air conditions and temperature of flue gases leaving the furnace, as well as the chimney height. All these factors make proper draught hard to attain and therefore make mechanical draught equipment much more economical.

There are three types of mechanical draught:
  • Induced draught: This is obtained one of three ways, the first being the "stack effect" of a heated chimney, in which the flue gas is less dense than the ambient air surrounding the boiler. The denser column of ambient air forces combustion air into and through the boiler. The second method is through use of a steam jet. The steam jet oriented in the direction of flue gas flow induces flue gasses into the stack and allows for a greater flue gas velocity increasing the overall draught in the furnace. This method was common on steam driven locomotives which could not have tall chimneys. The third method is by simply using an induced draught fan (ID fan) which removes flue gases from the furnace and forces the exhaust gas up the stack. Almost all induced draught furnaces operate with a slightly negative pressure.

  • Forced draught: Draught is obtained by forcing air into the furnace by means of a fan (FD fan) and ductwork. Air is often passed through an air heater; which, as the name suggests, heats the air going into the furnace in order to increase the overall efficiency of the boiler. Dampers are used to control the quantity of air admitted to the furnace. Forced draught furnaces usually have a positive pressure.

  • Balanced draught: Balanced draught is obtained through use of both induced and forced draught. This is more common with larger boilers where the flue gases have to travel a long distance through many boiler passes. The induced draught fan works in conjunction with the forced draught fan allowing the furnace pressure to be maintained slightly below atmospheric.

See also


  • Aquastat
    Aquastat
    An aquastat is a device used in hydronic heating systems for controlling water temperature. To prevent the boiler from firing too often, aquastats have a high limit temperature and a low limit. If the thermostat is calling for heat, the boiler will fire until the high limit is reached, then shut off...

  • Boiler design
    Boiler design
    Boiler design is the process of designing of boilers used for various purposes. The main function of boilers is to transfer heat produced by the combustion of fuel to water and ultimately to generate steam. Steam produced in a boiler is used for a variety of purposes including space heating,...

  • British thermal unit (Btu)
    British thermal unit
    The British thermal unit is a traditional unit of energy equal to about 1055 joules. It is approximately the amount of energy needed to heat of water, which is exactly one tenth of a UK gallon or about 0.1198 US gallons, from 39°F to 40°F...

  • Boiler feed water deaerator
    Deaerator
    A deaerator is a device that is widely used for the removal of oxygen and other dissolved gases from the feedwater to steam-generating boilers. In particular, dissolved oxygen in boiler feedwaters will cause serious corrosion damage in steam systems by attaching to the walls of metal piping and...

  • Dealkalization of water
    Dealkalization of water
    The dealkalization of water refers to the removal of alkalinity ions from water. Chloride cycle anion ion exchange dealkalizers remove alkalinity from water....

  • Electric water boiler
    Electric water boiler
    An electric water boiler, also called an electric dispensing pot, electric water heater, electric water urn, is a consumer electronics small appliance used for boiling water and maintaining it at a constant temperature...

     (for drinking water)
  • External combustion engine
    External combustion engine
    An external combustion engine is a heat engine where an working fluid is heated by combustion in an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine, produces motion and usable work...

  • Firebox (used by railway locomotives)
  • Fossil fuel power plant
    Fossil fuel power plant
    A fossil-fuel power station is a power station that burns fossil fuels such as coal, natural gas or petroleum to produce electricity. Central station fossil-fuel power plants are designed on a large scale for continuous operation...

  • Furnace
    Furnace
    A furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...

  • Geothermal power plant
  • Heating
  • Heat-only boiler station
    Heat-only boiler station
    A heat-only boiler station generates thermal energy in the form of hot water for use in district heating applications. Unlike combined heat and power installations which produce thermal energy as a by-product of electricity generation, heat-only boiler stations are dedicated to generating heat.The...

  • Heat recovery steam generator
  • Hot water reset
    Hot water reset
    Hot water reset is an energy-saving automatic control algorithm for hot water boilers that are typically fired with fuel oil or natural gas. A hot water reset control loop measures the outside air temperature; this information is used to estimate demand or heating load as the outdoor temperature...

  • Lancashire boiler
  • Hydronics
    Hydronics
    Hydronics is the use of water as the heat-transfer medium in heating and cooling systems.Some of the oldest and most common examples are steam and hot-water radiators. Historically, in large-scale commercial buildings such as high-rise and campus facilities, a hydronic system may include both a...

  • Power plant and Power station
    Power station
    A power station is an industrial facility for the generation of electric energy....

  • Pulverized coal-fired boiler
    Pulverized coal-fired boiler
    A pulverized coal-fired boiler is an industrial or utility boiler that generates thermal energy by burning pulverized coal that is blown into the firebox....

  • Radiator
    Radiator
    Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in automobiles, buildings, and electronics...

  • Recovery boiler
    Recovery boiler
    Recovery boiler is the part of Kraft process of pulping where chemicals for white liquor are recovered and reformed from black liquor, which contains lignin from previously processed wood. The black liquor is burned, generating heat, which is usually used in the process or in making electricity,...

  • Steam generator (nuclear power)
    Steam generator (nuclear power)
    Steam generators are heat exchangers used to convert water into steam from heat produced in a nuclear reactor core. They are used in pressurized water reactors between the primary and secondary coolant loops....

  • Thermal power station
    Thermal power station
    A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this...

  • Thermoelectric
  • Thermostat
    Thermostat
    A thermostat is the component of a control system which regulates the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. The thermostat does this by switching heating or cooling devices on or off, or regulating the flow of a heat transfer...

  • Water heater


Further reading


  • American Society of Mechanical Engineers
    American Society of Mechanical Engineers
    The American Society of Mechanical Engineers is a professional body, specifically an engineering society, focused on mechanical engineering....

    : ASME Boiler and Pressure Vessel Code, Section I. Updated every 3 years.
  • Association of Water Technologies: Association of Water Technologies (AWT).