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Babcock and Wilcox water tube boiler

Short answer

It has a horizontal drum and inclined water tubes connected by uptake and downtake headers. Hot gases from the furnace pass across the tubes; water circulates naturally—heated water rises to the drum, steam separates. Advantages over Lancashire: higher pressure and capacity, quicker steaming, less floor space, better efficiency, and easier tube replacement.

Explain with a neat sketch the construction and working of a Babcock and Wilcox water tube boiler. State its advantages over a Lancashire boiler.

The Babcock and Wilcox (B&W) boiler is a horizontal-drum, longitudinal, inclined water tube boiler with natural circulation, used for high-pressure steam.

Construction

  • A horizontal steam and water drum at the top, about half filled with water.
  • A bank of water tubes inclined at about 15 degrees to the horizontal, joined at the front to an uptake header and at the rear to a downtake header.
  • Headers connect to the drum by short vertical tubes.
  • A mud box at the lowest point collects sediment; a furnace with grate below the tubes; baffles direct the gas across the tubes; a superheater is fitted in the gas path.
        steam outlet
           |   _____________
   ______ [  / steam drum   \ ]______
  |uptake|  \_______________/ |down- |
  |header|      water         |take  |
  |      | \\ \\ \\ \\ \\ \\ |header|
  |      |  inclined tubes   |      |
  |______| baffle   baffle   |______|
        FURNACE (grate)   mud box

Working

  1. Hot gases from the grate rise, cross the tubes upward and downward between baffles (three passes) and leave to the chimney.
  2. Water in the tubes heats up, becomes lighter and rises through the uptake header into the drum. Cooler, denser water falls through the downtake header, giving natural circulation.
  3. Steam separates in the drum and passes through the superheater to the main stop valve.
  4. Feed water enters the drum; sludge settles in the mud box and is blown down.

Advantages over Lancashire boiler

  • Higher pressure (up to about 40 bar) and larger capacity.
  • Quick steam raising because of small water content.
  • Occupies less floor space and can be extended by adding tubes.
  • Flexible to load changes and gives higher efficiency.
  • Any tube can be replaced easily; the sections can be transported separately.

✓ Answer checked by Claude Opus 5.5 (high effort)

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