A boiler is a closed vessel in which water or other fluid is heated. Poland (Polska officially the Republic of Poland A pressure vessel is a closed container designed to hold gases or liquids at a Pressure different from the ambient Pressure. Water is a common Chemical substance that is essential for the survival of all known forms of Life. FLUID ( F ast L ight '''U'''ser '''I'''nterface D esigner is a graphical editor that is used to produce FLTK Source code The heated or vaporized fluid exits the boiler for use in various processes or heating applications. ^[1][2]

Contents 1 Overview 1.1 Application 1.2 Materials 1.3 Fuel 1.4 Configurations 2 Superheated steam boilers 3 Supercritical steam generators 3.1 History of supercritical steam generation 4 Hydronic boilers 5 Accessories 5.1 Boiler fittings and accessories 5.2 Steam accessories 5.3 Combustion accessories 5.4 Other essential items 6 Controlling draft 7 See also 8 References

Overview

Application

Boilers have many applications. They can be used in stationary applications to provide heat, hot water, or steam for domestic use, or in generators and they can be used in mobile applications to provide steam for locomotion in applications such as trains, ships, and boats. Using a boiler is a way to transfer stored energy from the fuel source to the water in the boiler, and then finally to the point of end use. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός

Materials

Construction of boilers is mainly in steel, stainless steel, and wrought iron. Carbon steel, also called plain carbon steel, is Steel where the main alloying constituent is Carbon. In Metallurgy, stainless steel is defined as a Steel Alloy with a minimum of 11 QtubIronPillarJPG|thumb|right| Iron pillar at Delhi India containing 98% wrought iron]] Wrought iron is commercially pure Iron. In live steam models, copper or brass is often used. Live steam is Steam under pressure obtained by heating water in a Boiler. Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 Brass is any Alloy of Copper and Zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties Historically copper was often used for fireboxes (particularly for steam locomotives), because of its better thermal conductivity. A steam locomotive is a Locomotive powered by Steam. The term usually refers to its use on Railways but can also refer to a "road locomotive" The price of copper now makes this impractical.

Cast iron is used for domestic water heaters. Cast iron usually refers to grey cast iron, but identifies a large group of Ferrous Alloys which solidify with a Eutectic. Although these are usually termed "boilers", their purpose is 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 steam pressure vessels.

For much of the Victorian "age of steam", the only material for boilermaking was the highest grade of wrought iron, with assembly by rivetting. This iron was often obtained from specialist ironworks, such as Cleator Moor (UK), noted for the high quality of their rolled plate and its suitability for high reliability use in critical applications, such as high pressure boilers. 20th century practice moved towards steel and welding.

Fuel

The source of heat for a boiler is combustion of any of several fuels, such as wood, coal, oil, or natural gas. Combustion or burning is a complex sequence of Exothermic chemical reactions between a Fuel and an Oxidant accompanied by the production of Fuel is any material that is burned or altered in order to obtain energy Wood is hard fibrous lignified structural tissue produced as secondary Xylem in the stems of Woody plants notably trees but also shrubs Petroleum ( L petroleum, from Greek πετρέλαιον, lit Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, Electric steam boilers use resistance or immersion type heating elements. Electric steam boilers are used to generate steam for process purposes in many locations e Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is Nuclear fission is also used as a heat source for generating steam. Nuclear fission is the splitting of the nucleus of an atom into parts (lighter nuclei) often producing Free neutrons and other smaller nuclei which may Uses A Steam engine uses the expansion of steam in order to drive a Piston or Turbine to perform Mechanical work. Heat recovery steam generators (HRSGs) use the heat rejected from other processes such as gas turbines. A heat recovery steam generator or HRSG is a Heat exchanger that recovers heat from a hot gas stream A gas turbine, also called a combustion turbine, is a rotary Engine that extracts energy from a flow of Combustion gas

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. A fire-tube boiler is a type of boiler in which hot gases from the fire pass through one or more tubes within the boiler Here, water partially fills a boiler barrel with a small volume left above to accommodate the steam (steam space). 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. The boiling point of a liquid 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. A water-tube boiler is a type of boiler in which water circulates in tubes heated externally by the fire 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; 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 including nuclear fission and are generally preferred in high pressure applications since the high pressure water/steam is contained within narrow pipes which can withstand the pressure with a thinner wall.
• 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 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 syphons. The gases then pass through a conventional firetube boiler. Water-tube fireboxes were installed in many Hungarian locomotives, but have met with little success in other countries. Hungary (Magyarország 'mɔɟɔrorsaːg) officially in English the Republic of Hungary ( Magyar Köztársaság, literally Magyar (Hungarian Republic
• 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.

Superheated steam boilers

Main article: Superheater

Most boilers heat water until it boils, and then the steam is used at saturation temperature (i. See Superheating for the physics process A superheater is a device in a Steam engine that heats the steam generated by the The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid e. , saturated steam). Superheated steam boilers boil the water and then further heat the steam in a superheater. This provides steam at much higher temperature, and can decrease the overall thermal efficiency of the steam plant due to the fact that the higher steam temperature requires a higher flue gas exhaust temperature. However, there are advantages to superheated steam. For example, useful heat can be extracted from the steam without causing condensation, which could damage piping and turbine blades.

Superheated steam presents unique safety concerns because, if there is a leak in the steam piping, steam at such high pressure/temperature can cause serious, instantaneous harm to anyone entering its flow. Since the escaping steam will initially be completely superheated vapor, it is not easy to see the leak, although the intense heat and sound from such a leak clearly indicates its presence.

The superheater works like coils on an air conditioning unit, however to a different end. The steam piping (with steam flowing through it) is directed through the flue gas path in the boiler furnace. This area typically is between 1300-1600 degrees Celsius (2500-3000 degrees Fahrenheit). Some superheaters are radiant type (absorb heat by radiation), others are convection type (absorb heat via a fluid i. e. gas) and some are a combination of the two. So whether by convection or radiation the extreme heat in the boiler furnace/flue gas path will also heat the superheater steam piping and the steam within as well. It is important to note that while the temperature of the steam in the superheater is raised, the pressure of the steam is not: the turbine or moving pistons offer a "continuously expanding space" and the pressure remains the same as that of the boiler. ^[3]The process of superheating steam is most importantly designed to remove all droplets entrained in the steam to prevent damage to the turbine blading and/or associated piping.

Supercritical steam generators

Supercritical steam generators (also known as Benson boilers) are frequently used for the production of electric power. A supercritical fluid is any substance at a Temperature and Pressure above its Thermodynamic critical point. They operate at "supercritical pressure". In contrast to a "subcritical boiler", a supercritical steam generator operates at such a high pressure (over 3200 PSI, 22 MPa, 220 bar) that actual boiling ceases to occur, and the boiler has no 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 the high pressure turbine and enters the generator's condenser. This is more efficient, resulting in slightly less fuel use and therefore less greenhouse gas production. Greenhouse gases are gaseous constituents of the atmosphere bothnatural and anthropogenic that absorb and emit radiation at specific wavelengths within the spectrum of thermal infrared The term "boiler" should not be used for a supercritical pressure steam generator, as no "boiling" actually occurs in this device.

History of supercritical steam generation

Contemporary supercritical steam generators are sometimes referred as Benson boilers. In 1922, Mark Benson was granted a patent for a boiler designed to convert water into steam at high pressure.

Safety was the main concern behind Benson’s concept. Earlier steam generators were designed for relatively low pressures of up to about 100 bar, corresponding to the state of the art in steam turbine development at the time. One of their distinguishing technical characteristics was the riveted drum. These drums were used to separate water and steam, and were often the source of boiler explosions, usually with catastrophic consequences. However, the drum can be completely eliminated if the evaporation process is avoided altogether. This happens when water is heated at a pressure above the critical pressure and then expanded to dry steam at subcritical pressure. A throttle valve located downstream of the evaporator can be used for this purpose.

As development of Benson technology continued, boiler design soon moved away from the original concept introduced by Mark Benson. In 1929, a test boiler that had been built in 1927 began operating in the thermal power plant at Gartenfeld in Berlin for the first time in subcritical mode with a fully open throttle valve. Berlin is the capital city and one of sixteen states of Germany. The second Benson boiler began operation in 1930 without a pressurizing valve at pressures between 40 and 180 bar at the Berlin cable factory. This application represented the birth of the modern variable-pressure Benson boiler. After that development, the original patent was no longer used. The Benson boiler name, however, was retained.

Two current innovations have a good chance of winning acceptance in the competitive market for once-through steam generators:

• A new type of heat-recovery steam generator based on the Benson boiler, which has operated successfully at the Cottam combined-cycle power plant in the central part of England,
• The vertical tubing in the combustion chamber walls of coal-fired steam generators which combines the operating advantages of the Benson system with the design advantages of the drum-type boiler. England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland Construction of a first reference plant, the Yaomeng power plant in China, commenced in 2001. China ( Wade-Giles ( Mandarin) Chung¹kuo² is a cultural region, an ancient Civilization, and depending on perspective a National

Hydronic boilers

Hydronic boilers are used in generating heat typically for residential uses. They are the typical power plant for central heating systems fitted to houses in northern Europe (where they are commonly combined with domestic water heating), as opposed to the forced-air furnaces or wood burning stoves more common in North America. For the Grand Central Records albums see Central Heating (Grand Central album and Central Heating 2. A Forced-air or Warm air Heating system is one which uses Air as its Heat transfer medium 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 radiators, baseboard heaters or through the floors. Radiators and convectors are types of Heat exchangers designed to transfer Thermal energy from one medium to another for the purpose of cooling Radiators and convectors are types of Heat exchangers designed to transfer Thermal energy from one medium to another for the purpose of cooling 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 is currently the most economical and therefore the usual choice. Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, The fluid is in an enclosed system and circulated throughout by means of a motorized pump. For information on Wikipedia project-related discussions see WikipediaVillage pump. Most new systems are fitted with condensing boilers for greater efficiency. A condensing boiler is a water heating device designed to recover Energy normally discharged to the Atmosphere through the flue The name can be a misnomer in that, except for systems using steam radiators, the water in a properly functioning hydronic boiler never actually boils. These boilers are referred to as condensing boilers because they condense the water vapor in the flue gases to capture the latent heat of vaporization of the water produced during combustion. A condensing boiler is a water heating device designed to recover Energy normally discharged to the Atmosphere through the flue Flue gas is Gas that exits to the atmosphere via a Flue, which is a pipe or channel for conveying exhaust gases from a fireplace oven Furnace, Boiler In Thermochemistry, latent heat is the amount of Energy in the form of Heat released or absorbed by a substance during a change of phase

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 systems (although initial installation can be more expensive, because of the cost of the copper and aluminum). A Forced-air or Warm air Heating system is one which uses Air as its Heat transfer medium
• 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. Convection in the most general terms refers to the movement of molecules within Fluids (i Air has much lower thermal conductivity and higher specific heat than copper; however, convection results in faster heat loss of air compared to copper. In Physics, thermal conductivity, k is the property of a material that indicates its ability to conduct Heat. Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the Temperature of a unit quantity See also thermal mass. )
• They do not dry out the interior air as much.
• 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. A Forced-air or Warm air Heating system is one which uses Air as its Heat transfer medium

Accessories

Boiler fittings and accessories

• Safety valve: used to relieve pressure and prevent possible explosion of a boiler
• Water level indicators: to show the operator the level of fluid in the boiler, a water gauge or water column is provided
• Bottom blowdown valves provide a means for removing solid particulates that condense and lay on the bottom of a boiler. 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 Boiler explosions are catastrophic failures of Boilers As seen today boiler explosions are of two kinds 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 Condensation is the change of the physical state of aggregation (or simply state of matter from gaseous phase into liquid phase 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.
• Hand holes are steel plates installed in openings in the boiler shell to allow for inspections of the interior of the boiler.
• Low- water cutoff 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 catastophic failure.
• Surface blowdown line 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 is designed to circulate water back to the boiler after it has expelled some of its heat. For information on Wikipedia project-related discussions see WikipediaVillage pump.
• Feedwater check valve or clack valve: a nonreturn stop valve in the feedwater line. A check valve, clack valve, non-return valve or one-way valve is a Mechanical device, a Valve, which normally allows Fluid This may be fitted to the side of the boiler, just below the water level, or to the top of the boiler. A top-mounted check valve is called a top feed and is intended to reduce the nuisance of 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.

Steam accessories

• Main steam stop valve
• Steam traps
• Main steam stop/Check valve used on multiple boiler installations

Combustion accessories

• Fuel oil system
• Gas system
• Coal system
• Automatic combustion systems

Other essential items

• Pressure gauges
• Feed pumps
• Fusible plug
• Inspectors test pressure gauge attachment
• Name plate
• Registration plate

Controlling draft

Most boilers now depend on mechanical draft equipment rather than natural draft. A steam trap is a device used to discharge condensate and non condensable gases while not permitting the escape of live Steam. Many techniques have been developed for the measurement of Pressure and Vacuum. A fusible plug is a threaded metal plug usually made out of Bronze, Brass, or Gunmetal. This is because natural draft 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 draft hard to attain and therefore make mechanical draft equipment much more economical.

There are three types of mechanical draft:

• Induced draft: 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 more dense 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 draft 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 draft fan (ID fan) which sucks flue gases out of the furnace and up the stack. Almost all induced draft furnaces have a negative pressure.

• Forced draft: Draft 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 draft furnaces usually have a positive pressure.

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

See also

• Btu
• Boiler feed water deaerator
• Electric water boiler (for drinking water)
• External combustion engine
• Firebox (used by railway locomotives)
• Fossil fuel power plant
• Furnace
• Geothermal power plant
• Heating
• Heat-only boiler station
• Heat recovery steam generator
• Hot water reset
• Hydronics
• Power plant and Power station
• Pulverized coal-fired boiler
• Radiator
• Steam generator (nuclear power)
• Thermal power station
• Thermoelectric
• Thermostat
• Water heater

References

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