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A boiler is a closed vessel in which drinking water or other liquid is heated. The fluid does not always boil. (In North America, the term "furnace" is generally used if the purpose is never to boil the liquid.) The warmed 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, food preparation, and sanitation.

Materials
The pressure vessel of a boiler is usually manufactured from steel (or alloy steel), or of wrought iron historically. Stainless steel, especially of the austenitic types, is not found in wetted parts of boilers due to corrosion and stress corrosion breaking.[3 - However, ferritic stainless is often found in superheater sections that won't be exposed to boiling drinking water, and electrically heated stainless steel shell boilers are allowed under the European "Pressure Equipment Directive" for production 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 because it is more fabricated in smaller size boilers easily. Historically, copper was often used for fireboxes (especially for vapor locomotives), due to its better formability and higher thermal conductivity; however, in newer times, the high price of copper often makes this an uneconomic choice and cheaper substitutes (such as metal) are used instead.

For a lot of the Victorian "age of vapor", the only materials used for boilermaking was the best quality of wrought iron, with set up by rivetting. This iron was from specialist ironworks, such as at Cleator Moor (UK), mentioned for the high quality of their rolled plate and its own suitability for high-reliability use in critical applications, such as high-pressure boilers. In the 20th century, design practice instead moved towards the use of steel, which is more powerful and cheaper, with welded structure, which is quicker and requires less labour. It should be observed, however, that wrought iron boilers corrode much slower than their modern-day metal counterparts, and are less susceptible to localized stress-corrosion and pitting. This makes the longevity of old wrought-iron boilers considerably superior to those of welded steel boilers.

Cast iron might be utilized for the heating vessel of home water heaters. Although such heaters are usually termed "boilers" in some countries, their purpose is to create hot water usually, not steam, and they also run at low pressure and stay away from boiling. The brittleness of cast iron makes it impractical for high-pressure steam boilers.
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Energy
The source of heating for a boiler is combustion of some of several fuels, such as wood, coal, oil, or natural gas. Electric vapor boilers use level of resistance- or immersion-type heating system elements. Nuclear fission is used as a heat source for producing steam also, either directly (BWR) or, in most cases, in specialised high temperature exchangers called "steam generators" (PWR). Heat recovery steam generators (HRSGs) use heat rejected from other procedures such as gas turbine.

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

Immediate method -immediate method of boiler efficiency test is more useful or more common

boiler efficiency =Q*((Hg-Hf)/q)*(GCV *100 ) Q =Total steam flow Hg= Enthalpy of saturated vapor in k cal/kg Hf =Enthalpy of feed drinking water in kcal/kg q= level of energy use in kg/hr GCV =gross calorific value in kcal/kg like family pet coke (8200 kcal/KG)

indirect method -to measure the boiler efficiency in indirect method, we need a following 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 gas in kcal/kg
ash percentage in combustible fuel
GCV of ash in kcal/kg
Configurations
Boilers can be classified into the following configurations:

Container boiler or Haycock boiler/Haystack boiler: a primitive "kettle" where a open fire heats a partially filled drinking water container from below. 18th century Haycock boilers generally produced and stored large quantities of very low-pressure vapor, hardly above that of the atmosphere often. These could burn wood or frequently, coal. Efficiency was suprisingly low.
Flued boiler with a couple of large flues-an early type or forerunner of fire-tube boiler.

Diagram of a fire-tube boiler
Fire-tube boiler: Here, drinking water partially fills a boiler barrel with a small volume left above to support 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 needs to be kept permanently surrounded by the water in order to keep the heat range of the heating system 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 can be further increased by causing the gases reverse direction through a second parallel tube or a bundle of multiple pipes (two-pass or come back flue boiler); alternatively the gases may be studied along the sides and then beneath the boiler through flues (3-move boiler). In case of a locomotive-type boiler, a boiler barrel expands from the firebox and the hot gases pass through a bundle of fire tubes inside the barrel which greatly increases the heating surface in comparison to a single tube and further improves heat transfer. Fire-tube boilers will often have a comparatively low rate of vapor production, but high vapor storage capacity. Fire-tube boilers burn off solid fuels mostly, but are easily adaptable to those of the liquid or gas variety.

Diagram of the water-tube boiler.
Water-tube boiler: In this kind, pipes filled up with water are arranged in the furnace in several possible configurations. Often the drinking water pipes connect large drums, the lower ones containing water and the top ones water and steam; in other situations, like a mono-tube boiler, water is circulated by a pump through a succession of coils. This kind provides high vapor production rates generally, but less storage capacity than the above. Water tube boilers can be made to exploit any temperature source and tend to be preferred in high-pressure applications because the high-pressure drinking water/vapor is included within small size pipes which can withstand the pressure with a thinner wall.
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 steam generator where the pipe is permanently filled with water. In a flash boiler, the tube is kept so hot that water give food to is quickly flashed into steam and superheated. Flash boilers got some use in cars in the 19th century and this use continued into the early 20th century. .

1950s design vapor 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 then pass through a conventional firetube boiler. Water-tube fireboxes were installed in many Hungarian locomotives,[citation needed - but have fulfilled with little success far away.
Sectional boiler. Within a ensemble iron sectional boiler, sometimes called a "pork chop boiler" the water is contained inside solid iron sections.[citation needed - These sections are assembled on site to create the finished boiler.
Safety
See also: Boiler explosion
To define and secure boilers safely, some professional specialized organizations like the American Society of Mechanical Technical engineers (ASME) develop standards and regulation codes. For example, the ASME Boiler and Pressure Vessel Code is a standard providing an array of guidelines and directives to ensure compliance of the boilers and other pressure vessels with protection, security and design standards.[5 -

Historically, boilers were a way to obtain many serious injuries and property destruction as a consequence to badly understood engineering principles. Thin and brittle metallic shells can rupture, while poorly welded or riveted seams could start, leading to a violent eruption of the pressurized steam. When water is changed into steam it expands to over 1,000 times its original quantity and travels down steam pipes at over 100 kilometres per hour. Because of this, vapor 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 give food to water treatment, a steam-raising vegetable will suffer from scale corrosion and formation. At best, this boosts energy costs and can result in poor quality vapor, reduced efficiency, shorter plant life and unreliable procedure. At worst, it can lead to catastrophic loss and failure of life. Collapsed or dislodged boiler pipes can also spray 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 hundreds of horsepower to operate factories can potentially demolish entire buildings.[6 -

A boiler that has a loss of feed drinking water and is permitted to boil dry can be extremely dangerous. If feed water is then sent in to the empty boiler, the tiny cascade of inbound drinking water instantly boils on contact with the superheated steel shell and leads to a violent explosion that can't be controlled even by basic 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 water supply could replace. The Hartford Loop was developed in 1919 by the Hartford Steam Boiler and INSURANCE PROVIDER as a strategy to help prevent this condition from taking place, and thereby reduce their insurance claims.[7 - [8 -

Superheated steam boiler

A superheated boiler on a steam locomotive.
Main article: Superheater
Most boilers produce vapor to be used at saturation temperatures; that is, saturated vapor. Superheated steam boilers vaporize the water and additional heating the steam in a superheater then. This provides vapor at much higher temp, but can reduce the overall thermal efficiency of the steam generating vegetable because the higher steam heat range takes a higher flue gas exhaust temp.[citation needed - There are many ways to circumvent this issue, typically by giving an economizer that heats the feed drinking water, a combustion air heater in the hot flue gas exhaust route, or both. You can find advantages to superheated vapor that may, and will often, increase overall efficiency of both vapor generation and its utilization: benefits in input heat to a turbine should outweigh any cost in additional boiler complication and expense. There can also be useful limitations in using wet vapor, as entrained condensation droplets will harm turbine blades.

Superheated steam presents unique safety concerns because, if any operational system component fails and allows steam to flee, the ruthless and temperature can cause serious, instantaneous harm to anyone in its path. Since the escaping steam will at first be completely superheated vapor, detection can be difficult, although the intense heat and sound from such a leak indicates its presence clearly.

Superheater operation is similar to that of the coils on an fresh air conditioning unit, although for a different purpose. The steam piping is directed through the flue gas route in the boiler furnace. The temperatures in this field is typically between 1,300 and 1,600 °C (2,372 and 2,912 °F). Some superheaters are radiant type; that is, they absorb heat by radiation. Others are convection type, absorbing high temperature from a fluid. Some are a combination of the two types. Through either method, the extreme heat in the flue gas path will heat the superheater steam piping and the steam within also. While the heat of the steam in the superheater rises, the pressure of the steam will 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 damage to the turbine blading and associated piping.

Supercritical steam generator

Boiler for a power plant.
Main article: Supercritical steam generator
Supercritical steam generators are frequently used for the production of energy. They operate at supercritical pressure. In contrast to a "subcritical boiler", a supercritical steam generator operates at such a high pressure (over 3,200 psi or 22 MPa) that the physical turbulence that characterizes boiling ceases to occur; the fluid is liquid nor gas but a super-critical fluid neither. There is absolutely no era of vapor bubbles within water, because the pressure is above the critical pressure point at which vapor bubbles can develop. As the fluid expands through the turbine phases, its thermodynamic state drops below the critical point as it can work turning the turbine which converts the electrical generator that power is eventually extracted. The liquid at that point may be a mixture of steam and liquid droplets as it goes by in to the condenser. This results in somewhat less energy use and for that reason less greenhouse gas production. The term "boiler" should not be used for a supercritical pressure steam generator, as no "boiling" occurs in this device.
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Accessories
Boiler accessories and fittings
Pressuretrols to regulate the steam pressure in the boiler. Boilers generally have two or three 3 pressuretrols: a manual-reset pressuretrol, which functions as a protection by setting the upper limit of vapor pressure, the working pressuretrol, which controls when the boiler fires to keep up pressure, as well as for boilers equipped with a modulating burner, a modulating pressuretrol which handles the amount of fire.
Safety valve: It is utilized to relieve pressure and stop possible explosion of a boiler.
Water level indications: They show the operator the amount of fluid in the boiler, also called a sight cup, water gauge or drinking water column.
Bottom level blowdown valves: They provide a means for removing solid particulates that condense and rest on the bottom of the boiler. As the name implies, this valve is located directly on the bottom of the boiler usually, and is sometimes opened to use the pressure in the boiler to drive these particulates out.
Constant blowdown valve: This allows a small quantity of water to escape continuously. Its purpose is to avoid the water in the boiler becoming saturated with dissolved salts. Saturation would business lead to foaming and cause water droplets to be carried over with the vapor - an ailment 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 liquid level in a container. Mostly entirely on a water boiler.
Flash container: High-pressure blowdown enters this vessel where in fact the steam can 'flash' safely and be found in a low-pressure system or be vented to atmosphere while the ambient pressure blowdown moves to drain.
Automatic blowdown/continuous heat recovery system: This system allows the boiler to blowdown only once make-up water is moving to the boiler, thereby transferring the maximum amount of heat possible from the blowdown to the makeup water. No flash tank is normally needed as the blowdown discharged is close to the temperatures of the makeup water.
Hand openings: They are metal plates installed in openings in "header" to permit for inspections & installing tubes and inspection of internal surfaces.
Steam drum internals, some display screen, scrubber & cans (cyclone separators).
Low-water cutoff: It really is a mechanical means (usually a float change) that is utilized to turn from the burner or shut off energy to the boiler to avoid it from working once the drinking water goes below a certain point. If a boiler is "dry-fired" (burned without drinking 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 substances that tend to float together with the water inside the boiler.
Circulating pump: It really is designed to circulate water back again to the boiler after it has expelled a few of its heat.
Feedwater check valve or clack valve: A non-return stop valve in the feedwater line. This may be installed to the side of the boiler, below water level just, or to the top of the boiler.[10 -
Top give food to: Within this design for feedwater injection, water is fed to the very best of the boiler. This can reduce boiler fatigue caused by thermal stress. By spraying the feedwater over some trays the water is quickly warmed and this can reduce limescale.
Desuperheater pipes or bundles: Some tubes or bundles of tubes in water drum or the vapor drum made to cool superheated vapor, in order to provide auxiliary equipment that does not need, or may be damaged by, dry 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 can be used on multiple boiler installations.
Combustion accessories
Gas oil system:gasoline oil heaters
Gas system:
Coal system:
Soot blower
Other essential items
Pressure gauges:
Feed pumps:
Fusible plug:
Inspectors test pressure gauge attachment:
Name dish:
Registration plate: