Boiler Auxiliaries, Pumps, Fans, and Instrumentation
Core concepts
Know the roles of feedwater pumps (centrifugal, positive displacement), forced and induced draft fans, air preheaters, economizers, and sootblowers. Understand pump curves, NPSH, cavitation, and fan laws (flow ∝ speed, head ∝ speed², power ∝ speed³). Learn instrument basics: transmitters, RTDs, thermocouples, flow elements, and level devices.
Traps
Questions often mix up fan laws, or apply them to variable-pitch fans incorrectly. Watch for cavitation described as "vibration only" - it also reduces head and damages impellers. Distinguish NPSHa from NPSHr. Also beware of economizer and air preheater functions being swapped.
Worked example
A fan running at 900 rpm delivers 30,000 cfm and 20 hp. Doubling speed to 1,800 rpm gives ~60,000 cfm and ~160 hp (2³ = 8× power). Rule of thumb: power rises with the cube of speed, so small speed reductions yield large energy savings.