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- Model Boilers and Boilermaking
- Model Boilers and Boilermaking
- some basic direction regarding boiler making
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Model Boilers and Boilermaking
A boiler is a closed vessel in which fluid generally water is heated. The fluid does not necessarily boil. In a fossil fuel power plant using a steam cycle for power generation, the primary heat source will be combustion of coal , oil , or natural gas. In some cases byproduct fuel such as the carbon monoxide rich offgasses of a coke battery can be burned to heat a boiler; biofuels such as bagasse , where economically available, can also be used.
In a nuclear power plant, boilers called steam generators are heated by the heat produced by nuclear fission. Where a large volume of hot gas is available from some process, a heat recovery steam generator or recovery boiler can use the heat to produce steam, with little or no extra fuel consumed; such a configuration is common in a combined cycle power plant where a gas turbine and a steam boiler are used.
In all cases the combustion product waste gases are separate from the working fluid of the steam cycle, making these systems examples of external combustion engines. The pressure vessel of a boiler is usually made of steel or alloy steel , or historically of wrought iron.
Stainless steel , especially of the austenitic types, is not used in wetted parts of boilers due to corrosion and stress corrosion cracking. 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 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 riveting. This iron was often obtained from specialist ironworks , such as those in the Cleator Moor UK area, noted for the high quality of their rolled plate , which was especially suitable for use in critical applications such as high-pressure boilers. In the 20th century, design practice moved towards the use of steel, with welded construction, which is stronger and cheaper, and can be fabricated more quickly and with less labour.
Wrought iron boilers corrode far more slowly than their modern-day steel counterparts, and are less susceptible to localized pitting and stress-corrosion. That makes the longevity of older wrought-iron boilers far superior to that of welded steel boilers. 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 boiling. The brittleness of cast iron makes it impractical for high-pressure steam boilers. The source of heat for a boiler is combustion of any of several 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 , either directly BWR or, in most cases, in specialised heat exchangers called "steam generators" PWR. Heat recovery steam generators HRSGs use the heat rejected from other processes such as gas turbine. To define and secure boilers safely, some professional specialized organizations such as the American Society of Mechanical Engineers ASME develop standards and regulation codes.
For instance, the ASME Boiler and Pressure Vessel Code is a standard providing a wide range of rules and directives to ensure compliance of the boilers and other pressure vessels with safety, security and design standards. 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. Because of this, steam is an efficient method of moving energy and heat around a site from a central boiler house to where it is needed, but without the right boiler feedwater 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 unreliable operation. At worst, it can lead to catastrophic failure and loss of life. Collapsed or dislodged boiler tubes can also spray scalding-hot steam and smoke out of the air intake and firing chute, injuring the firemen who load the coal into the fire chamber.
Extremely large boilers providing hundreds of horsepower to operate factories can potentially 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 can also happen if a leak occurs in the steam supply lines that is larger than the make-up water supply could replace. The Hartford Loop was invented in by the Hartford Steam Boiler Inspection and Insurance Company as a method to help prevent this condition from occurring, and thereby reduce their insurance claims. When water is boiled the result is saturated steam , also referred to as "wet steam.
Saturated steam is useful for many purposes, such as cooking , heating and sanitation , but is not desirable when steam is expected to convey energy to machinery, such as a ship's propulsion system or the "motion" of a steam locomotive. The water entrained in the steam may damage turbine blades or in the case of a reciprocating steam engine , may cause serious mechanical damage due to hydrostatic lock. Superheated steam boilers evaporate the water and then further heat the steam in a superheater , causing the discharged steam temperature to be substantially above the boiling temperature at the boiler's operating pressure.
As the resulting " dry steam " is much hotter than needed to stay in the vaporous state it will not contain any significant unevaporated water. Also, higher steam pressure will be possible than with saturated steam, enabling the steam to carry more energy.
Although superheating adds more energy to the steam in the form of heat there is no effect on pressure, which is determined by the rate at which steam is drawn from the boiler and the pressure settings of the safety valves. However, the overall energy efficiency of the steam plant the combination of boiler, superheater, piping and machinery generally will be improved enough to more than offset the increased fuel consumption. 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, an area in which the temperature is typically between 1, and 1, degrees Celsius 2, and 2, degrees Fahrenheit. Some superheaters are radiant type, which as the name suggests, 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. The design of any superheated steam plant presents several engineering challenges due to the high working temperatures and pressures. One consideration is the introduction of feedwater to the boiler. The pump used to charge the boiler must be able to overcome the boiler's operating pressure, else water will not flow.
As a superheated boiler is usually operated at high pressure, the corresponding feedwater pressure must be even higher, demanding a more robust pump design. Another consideration is safety. High pressure, superheated steam can be extremely dangerous if it unintentionally escapes. To give the reader some perspective, the steam plants used in many U.
In the event of a major rupture of the system, an ever-present hazard in a warship during combat , the enormous energy release of escaping superheated steam, expanding to more than times its confined volume, would be equivalent to a cataclysmic explosion, whose effects would be exacerbated by the steam release occurring in a confined space, such as a ship's engine room.
Also, small leaks that are not visible at the point of leakage could be lethal if an individual were to step into the escaping steam's path. Hence designers endeavor to give the steam-handling components of the system as much strength as possible to maintain integrity. Special methods of coupling steam pipes together are used to prevent leaks, with very high pressure systems employing welded joints to avoided leakage problems with threaded or gasketed connections.
Supercritical steam generators are frequently used for the production of electric power. They operate at supercritical pressure. There is no generation of steam bubbles within the water, because the pressure is above the critical pressure point at which steam bubbles can form. As the fluid expands through the turbine stages, its thermodynamic state drops below the critical point as it does work turning the turbine which turns the electrical generator from which power is ultimately extracted.
The fluid at that point may be a mix of steam and liquid droplets as it passes into the condenser. This results in slightly less fuel use and therefore less greenhouse gas production. The term "boiler" should not be used for a supercritical pressure steam generator, as no "boiling" occurs in this device. A fuel -heated boiler must provide air to oxidize its fuel.
Early boilers provided this stream of air, or draught , through the natural action of convection in a chimney connected to the exhaust of the combustion chamber. Since the heated flue gas is less dense than the ambient air surrounding the boiler, the flue gas rises in the chimney, pulling denser, fresh air into the combustion chamber. Most modern boilers depend on mechanical draught 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 reliable and economical. Types of draught can also be divided into induced draught , where exhaust gases are pulled out of the boiler; forced draught , where fresh air is pushed into the boiler; and balanced draught , where both effects are employed.
Natural draught through the use of a chimney is a type of induced draught; mechanical draught can be induced, forced or balanced. There are two types of mechanical induced draught. The first is through use of a steam jet. The steam jet oriented in the direction of flue gas flow induces flue gases 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 second 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. Mechanical forced draught is provided by means of a fan forcing air into the combustion chamber. 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 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. From Wikipedia, the free encyclopedia. This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. September Learn how and when to remove this template message. See also: Boiler design.
See also: Boiler explosion. Main article: Superheater. Main article: Supercritical steam generator. Main article: Draft boiler.
Model Boilers and Boilermaking
The following articles are NOT plans for building a model boiler. There are no drawings or engineered specifications posted on these pages for a reason. These articles only serve as a record of my experience in building a vertical boiler. Thank you Posted on March 28, Hello again folks!!!
A boiler is a closed vessel in which fluid generally water is heated. The fluid does not necessarily boil. In a fossil fuel power plant using a steam cycle for power generation, the primary heat source will be combustion of coal , oil , or natural gas. In some cases byproduct fuel such as the carbon monoxide rich offgasses of a coke battery can be burned to heat a boiler; biofuels such as bagasse , where economically available, can also be used. In a nuclear power plant, boilers called steam generators are heated by the heat produced by nuclear fission. Where a large volume of hot gas is available from some process, a heat recovery steam generator or recovery boiler can use the heat to produce steam, with little or no extra fuel consumed; such a configuration is common in a combined cycle power plant where a gas turbine and a steam boiler are used. In all cases the combustion product waste gases are separate from the working fluid of the steam cycle, making these systems examples of external combustion engines.
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some basic direction regarding boiler making
Althoqh an essential part of every wr-. Views 3 Downloads 0 File size 13MB. Pearce, mentioned above, Henry Greenty, and Jamas Crebbin.
It is more than 60 years since the late E. This book is in the nature of an attempt somewhat to expand the original book, and so far as possible to bring the subject up-to-date. I have endeavoured to provide such information and statistical data, as will enable any intelligent model engineer to design a boiler to meet his own particular requirements, with a reasonable assurance that it will do the job for which it has been designed successfully and efficiently. Model boilers are, to a large extent, the Cinderellas of model engineering.
Pearce, mentioned above, Henry Greenty, and Jamas Crebbin. HarriL is, in his own right, another of the great model engineers, who wi:i be classed amongst the famous names of the past by future modehers. Uf such is the making of a tradition!
It would undoubtedly be an era of refined evil for as long as it lasted. I was pretty sure he was in the business. For a moment the bed seemed astoundingly empty.
По-видимому, ее работу прочел не только научный руководитель, потому что вскоре последовал телефонный звонок, а затем по почте ей доставили авиационный билет от АНБ. Все, кто имел отношение к криптографии, знали, что о АНБ собраны лучшие криптографические умы нашей планеты. Каждую весну, когда частные фирмы начинают охоту за талантливой молодежью, соблазняя ее неприлично высокими окладами и фондовыми опционами в придачу, АНБ внимательно наблюдает за этим, выделяет наиболее подходящих и удваивает предлагаемую сумму. АНБ покупает все, что ему требуется. Дрожа от нетерпения, Сьюзан вылетела в Вашингтон.