This is particularly true for CHP plants, where gas turbines and supplementary firing are used. This type of implementation is shown in Figure Boilers are often the principal steam or hot water generator system used in industrial plant or commercial heating.
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Excess air regulation In actual practice, gas, oil, coal burning and other systems do not do a perfect job of mixing the fuel and air even under the best achievable conditions. Oxygen trim When a measurement of oxygen in the flue gas is available, the combustion control mechanism can be vastly improved since the percentage of oxygen in flue is closely related to the amount of excess air by adding an oxygen trim control module, allowing: Tighter control of excess air to oxygen setpoint for better efficiency Faster return to setpoint following disturbances Tighter control over flue emissions Compliance with emissions standards Easy incorporation of carbon monoxide or opacity override.
- The Control of Boilers.
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Burner modulation Modulating control is a basic improvement in controlling combustion. The advantages of introducing burner modulation in combustion control include: Fuel and air requirements are continuously matched to the combustion demand Steam pressure or hot water temperature is maintained within closer tolerances Greater boiler efficiency Weighted average flue gas temperature is lower. Cross-limiting combustion control is highly effective and can easily provide the following: Optimization of fuel consumption Safer operating conditions by reducing risk of explosion Fast adaptation to variations in fuel and air supplies Satisfaction of the plant demand for steam.
Protection and Control of Boilers
Enhanced cross-limiting Double cross-limiting combustion control is an enhancement to the above. Total heat control In situations where combustion is not the principal heat source and when several factors contribute to the total heat to be generated by a boiler, a control loop can be introduced in order to monitor and manage the generated heat.
Studies have been conducted on combustion rate controllers at steam boilers of the electric power plant. These studies proved the controller's efficiency. 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.
Boilers and Boiler Control Systems (Energy Engineering)
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.
Indirect method : To measure the boiler efficiency in indirect method, we need a following parameter like:. 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.
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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 to over 1, times its original volume and travels down steam pipes at over kilometres per hour. 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 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.