High Pressure Boilers
High pressure boilers are composed of a series of water-filled tubes inside a rectangular metal tank or enclosure. These machines are used to create power from converting the water into steam through thermal energy and harnessing the steam to power equipment. The pressure within the cavity increases the efficiency and power of the boiler.
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Advantages of High Pressure Boilers
High pressure boilers boast a multitude of advantages. While high pressure boilers can be manufactured to over a story tall, often high pressure boilers are smaller and less bulky than other configurations. They also can be manufactured horizontally which saves space and gives easier access for maintenance. High pressure boilers are more efficient because they are manufactured with better monitoring and furnace conditions. Because of these factors, high pressure boilers can be smaller than other boiler types with a greater output, making them an ideal choice for smaller spaces. The efficiency is also increased by better firing methods and by having a higher rate of heat transfer. Modern high pressure boilers use radiation with conduction and convention to improve heat transfer. The higher rate of heat transfer is also a result of the large number of small diameter tubes which increases the area density. This also contributes to the water flowing at a higher velocity, therefore, scale formation is less likely. Because of these features, high pressure boilers also offer more uniform heating with reduced risk of overheating.
Disadvantages of High Pressure Boilers
High pressure boilers do pose a few disadvantages with improper use. For instance, if water flow is not sufficient the tubes can become overheated. Also, bubbles may form on the inner face of the tube which lowers the heat transfer rate. However, when high pressure boilers are operated smoothly and are well maintained, they prove to be highly efficient and functional.
Design of High Pressure Boilers
To produce steam, heat is generated from burning fuel such as coal, natural gas, petroleum, or biomass. The hot gases heat the tubes that are filled with water through either natural circulation, created by density difference, or by forced circulation, in which water is pushed through the systems with the help of pumps. Forced circulation helps to increase evaporation rates. Natural circulation is limited to a flow up to 120 kilogram-force per square centimeter whereas force circulation can generate pressure up to 210 kilogram-force per square centimeter. The generated steam rises and is channeled out to power separate machinery. The steam that is produced is used to power equipment in a variety of industrial and commercial applications, such as plant processes, turbine driving, hot water supply, and heating systems. Industries such as pharmaceutical processing, medical, thermal power, and industrial laundries, common in healthcare facilities, resorts, and high-end hotels also utilize high pressure boilers for a multitude of reasons.
Classification of Boilers
Boilers are classified as high pressure when they generate steam pressures above 80 bars. The larger the variance between the temperature of the stream while rising and the steam once it leaves the boiler, the higher efficiency achieved. High pressure boilers produce pressures greater than 15 pounds per square inch (PSI). These structures are considerably large in order to accommodate industrial applications, which can require pressures ranging from 250 PSI to up to 1,000 PSI.
Fire and Water Tubes in Industrial Boilers
There are two configurations of tubes used in industrial boilers, fire-tubes and water tubes. High pressure boilers use water-tubes since fire-tubes are not sufficient in regards to pressure or temperature, even if the boiler were larger and burned more fuel. In order for fire-tube boilers to create the same amount of pressure, the system would require thicker walls and bigger tubes but still would not be able to reach high enough temperatures to be considered comparable to water tube boilers. The small diameters of water tube boilers allow more water to be heated faster because of the ratio of surface area and volume. Water tube boilers are also available in larger sizes than fire-tube boilers and water boilers have the ability to recover more quickly.
Regulations for High Pressure Boilers
When first introduced, there were no regulations on high pressure boilers. They were used to power trains and factories and often exploded due to excessive pressure causing deaths and other damages. Explosions were at their highest rate in 1905, with around 400 reported, so in 1915 the American Society of Mechanical Engineers (ASME) composed a set of standards for manufacturers to follow in order to equip companies with reliable boilers. Now, with proper use and maintenance, high pressure boilers are much safer to operate since they are equipped with valves and gauges to help monitor pressure levels and other operations.