Boiler Basics: 18 flashcards
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1. What is the fundamental difference between a fire-tube boiler and a water-tube boiler?
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In a fire-tube boiler, hot gases (from combustion) pass through tubes surrounded by water. In a water-tube boiler, water passes through tubes that are heated externally by hot gases.
2. In a fire-tube boiler, which medium flows inside the tubes?
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Hot combustion gases (flue gases).
3. In a water-tube boiler, which medium flows inside the tubes?
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Water (and sometimes steam-water mixture).
4. What is the typical pressure range for fire-tube boilers?
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Fire-tube boilers are generally limited to lower pressures, typically up to about 250 psi (approx. 17 bar).
5. What is the typical pressure range for water-tube boilers?
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Water-tube boilers can operate at high pressures, often exceeding 1000 psi (approx. 70 bar) and even higher in large utility boilers.
6. Why are fire-tube boilers generally limited to lower pressures?
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Because the large-diameter shell (drum) containing water and steam is subjected to high stress at high pressures, requiring very thick and expensive walls.
7. Why can water-tube boilers achieve higher pressures?
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Because the water tubes have small diameters, which can withstand higher internal pressures with thinner walls, and the large drum is not directly exposed to the hottest gases.
8. Which type of boiler has a larger water volume and thus a higher thermal inertia?
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Fire-tube boilers, because they have a large shell filled with water.
9. Which type of boiler responds more quickly to load changes?
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Water-tube boilers, because they have a smaller water volume and thus lower thermal inertia.
10. What is the primary advantage of fire-tube boilers in terms of design and cost?
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They are simpler in construction, more compact, and generally less expensive for small to medium steam demands.
11. What is a common application for fire-tube boilers?
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Small to medium industrial processes, heating, and small power plants where moderate steam pressure and capacity are sufficient.
12. What is a common application for water-tube boilers?
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Large power plants, high-pressure steam generation, and industrial processes requiring high steam output and rapid load changes.
13. In a fire-tube boiler, what is the purpose of the shell (drum)?
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The shell holds the water and steam, and it contains the fire tubes through which hot gases pass.
14. In a water-tube boiler, what is the role of the steam drum?
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The steam drum separates steam from the water-steam mixture and provides a space for steam to be collected and sent to the superheater or turbine.
15. Which boiler type is more suitable for very high steam capacities (e.g., >100,000 lb/hr)?
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Water-tube boilers, as they can be designed with multiple tubes and larger heat transfer surfaces without excessive shell thickness.
16. What is a major safety concern with fire-tube boilers due to their large water volume?
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If the shell ruptures, a large amount of stored energy (hot water and steam) is released suddenly, causing a violent explosion.
17. What is a major safety concern with water-tube boilers?
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They are more prone to tube failures due to high heat flux and water chemistry issues, but the smaller water volume reduces the severity of a rupture.
18. Which boiler type typically requires more careful water treatment?
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Water-tube boilers, because the small-diameter tubes are more susceptible to scale deposition and overheating, which can lead to tube failure.
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