Boiler Design, Construction, and Thermodynamics
Core concepts
A candidate must be fluent in heat transfer paths (radiation in the furnace, convection in the tube banks, conduction through tube walls), the steam cycle, and the relationship between pressure, saturation temperature, and enthalpy. Know the difference between sensible heat, latent heat, and superheat, and how a T-s or h-s diagram shows them. Understand drum internals, waterwall and riser/downcomer circulation, natural versus forced circulation, and why circulation ratio matters. Familiarize yourself with pressure-part materials (SA-516 plate, SA-210 tubing) and design temperatures.
Traps in questions
Watch for questions that confuse gauge and absolute pressure, or that ask for enthalpy at a stated pressure without specifying saturated liquid versus saturated vapor. Distinguish design pressure from operating pressure and MAWP. Circulation questions often hinge on whether the boiler is natural or controlled circulation. Also beware of "efficiency" ambiguity: combustion efficiency, thermal efficiency, and fuel-to-steam efficiency are not interchangeable.
Worked example
A boiler produces 50,000 lb/h of saturated steam at 250 psig from feedwater at 220°F. At 250 psig, hg ≈ 1,201 Btu/lb and hf at 220°F ≈ 188 Btu/lb. Heat absorbed ≈ 50,000 × (1,201 − 188) = 50,650,000 Btu/h. If fuel input is 65,000,000 Btu/h, fuel-to-steam efficiency ≈ 50.65/65 ≈ 78%. Rule of thumb: roughly 1,000 Btu is needed to evaporate one pound of water from typical feedwater temperatures, so 1 boiler horsepower ≈ 34.5 lb/h of steam.