In which way do fire tube and water tube boilers differ in the position of gases and water?

Fire tube: gases inside tubes, water outside; water tube: water inside tubes, gases outside

Fire tube: water inside tubes, gases outside; water tube: gases inside tubes

Both have hot gases inside the tubes

Both have water inside the tubes

Which boiler type is suited to high pressure (up to 100 bar and above) and large capacity?

Neither; both are limited to about 25 bar

Why is the explosion risk of a fire tube boiler more serious than that of a water tube boiler?

It holds a large volume of water in the shell

It operates at much higher pressure

Which boiler can tolerate poorer feed water?

Neither tolerates any impurities

Practice · 6 marks

Fire tube versus water tube boilers

Short answer

In fire-tube boilers, hot gases flow through tubes surrounded by water; they produce low-to-medium pressure steam slowly, e.g., Lancashire, Cochran. In water-tube boilers, water flows inside tubes with hot gases outside; they deliver high-pressure steam quickly and are more compact, e.g., Babcock and Wilcox, Stirling.

Differentiate between fire tube boilers and water tube boilers, giving two examples of each.

In a fire tube boiler the hot flue gases pass through tubes surrounded by water. In a water tube boiler water flows inside the tubes and the hot gases pass outside them.

Point	Fire tube boiler	Water tube boiler
Hot gases	Inside the tubes	Outside the tubes
Water	Outside the tubes, in the shell	Inside the tubes
Steam pressure	Low to medium, up to about 25 bar	High, up to 100 bar and above
Steam capacity	Limited, up to about 10 t/h	Large, up to several hundred t/h
Steam raising	Slow, large water content	Quick, small water content
Explosion risk	Serious, large water volume	Less serious, small drum and tubes
Floor space for same output	More	Less
Cost and transport	Cheaper, simple, easy to install	Costlier, erected at site
Water quality	Tolerates poor feed water	Needs well-treated water
Response to load change	Poor	Good
Cleaning and inspection	Easy internally	Tubes are cleaned individually, harder

Examples: Fire tube: Lancashire, Cornish, Cochran, locomotive boiler. Water tube: Babcock and Wilcox, Stirling, Yarrow.

✓ Answer checked by Claude Opus 5.5 (high effort)

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