Boiler fittings and accessories
* Safety valve :
It is used to relieve pressure and prevent possible explosion of a boiler.
* Water level indicators :
They show the operator the level of fluid in the boiler , also known as a sight glass , water gauge orwater 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. 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 foe inspections & installation of tubes and inspection of internal surfaces.
* Steam drum internals :
A series of screen , scrubber & cans(cyclone separators).
* Low-water cutoof :
It is a mechanical means (usually a float switch) that is used to turn off the burner of 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 form or other lightweight non-condensible substance that tend to float on top of the water inside the boiler.
* Circulating pump :
It is designed to circulate water back to the boiler after it has expelled some of its heat.
* Feedwater check valve or clack valve :
A non-return stop valve in the feedwater 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 (clack valve) in the feedwater line , mounted on top of the boiler. It is intended to reduce the nuisance of limescale. It does not prevent limescale formation but causes the limescale to be precipitaed 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 design to cool superheated steam. Thus is to supply auxiliary equipment that doesn't need or may be damaged by or dry system.
* Chemical injection line:
A connection to add chemicals for controlling feedwater pH.
Monday, November 29, 2010
Friday, November 19, 2010
Safty
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| What Caused the Boiler Explosion at the Ford Rouge Plant |
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| Boiler Explosion At York Rolling MIlls Kills 9 Men; 20 injured |
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.
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| A boiler explosion would not have caused the forward decks to collapse |
Thursday, November 18, 2010
Configurations
Configurations
Boilers can be classified into the following configurations :
* "Port boilers" or "Haycock boilers" : 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 of most often , coal. Efficiency
was very low.
* Fire-tube boilers. Here , water partially fills a boiler barrel with a small volume left above to accommodate
the steam (steam space). This is the type of boilers 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. The furnace can be situated at one end of
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. 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. A specialized type of water-tube boiler.
1950s design steam locomotive boiler , from a victorian Railways J class
* 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 boilers. Water-tube firebox were installed in many Hungarian
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.
Boilers can be classified into the following configurations :
* "Port boilers" or "Haycock boilers" : 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 of most often , coal. Efficiency
was very low.
* Fire-tube boilers. Here , water partially fills a boiler barrel with a small volume left above to accommodate
the steam (steam space). This is the type of boilers 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. The furnace can be situated at one end of
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. 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. A specialized type of water-tube boiler.
1950s design steam locomotive boiler , from a victorian Railways J class
* 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 boilers. Water-tube firebox were installed in many Hungarian
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.
Fuel
Fuel
The source of heat for a boiler is combustion of any of sevaral fuels , such as wood , coal , oil or natural gas. Electric steam boilers use resistance or immersion-type heating elements. Nuclear fission is also used as a heat source for generating steam. Heat recovery steam generators (HRSGS) use the heat rejected from other processes such as gas turbines.
The source of heat for a boiler is combustion of any of sevaral fuels , such as wood , coal , oil or natural gas. Electric steam boilers use resistance or immersion-type heating elements. Nuclear fission is also used as a heat source for generating steam. Heat recovery steam generators (HRSGS) use the heat rejected from other processes such as gas turbines.
Tuesday, November 16, 2010
Boiler
Materials
The pressure vessel in a boiler is usually made of steel (or alloy steel) , or historically of wrought iron. Stainless steel 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 models , copper or brass is often used because it is more easily fabricated in smaller size boilers. Historically , copper was often used for fireboxes (particularly for steam locomotives) , because of its better formability and higher thermal conductivity ; however , in more recent times , the high price of copper often makes this an uneconomic 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 asembly by rivetting . This iron was often obtained from specialist ironworks , such as at cleartor 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. In the 20th century , design practice instead moved towards the use of steel , which is stronger and cheaper , with welded construction , which is quicker and requires less labour.
Cast Iron 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.
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| 1950s design steam locomotive boiler , from a Victorian Railways J class |
For much of the victorian "age of steam" , the only material used for boilermaking was the highest grade of wrought iron , with asembly by rivetting . This iron was often obtained from specialist ironworks , such as at cleartor 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. In the 20th century , design practice instead moved towards the use of steel , which is stronger and cheaper , with welded construction , which is quicker and requires less labour.
 |
| Diagram of a water-tube boiler |
Cast Iron 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.
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| Diagram of a fire-tube boiler |
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