Boilers, Steam Systems and Thermal Distribution
Core concepts
Understand combustion efficiency, thermal efficiency, and fuel-to-steam efficiency, and the role of excess air and stack temperature. Know the three heat losses: dry flue gas, moisture/ latent, and radiation/convection. Candidates should understand blowdown (surface and bottom), feedwater treatment, deaerators, steam traps (thermodynamic, thermostatic, float-and-thermostatic), condensate return, and flash steam.
Distribution and traps
Steam and hot water distribution losses come from uninsulated piping, failed steam traps, leaks, and improper pressure control. A common trap is assuming higher boiler pressure improves efficiency - it usually increases losses. Another trap is confusing blowdown with makeup water; blowdown controls dissolved solids and wastes energy, while excessive makeup indicates leaks or condensate loss. Questions may ask about stack economizers - they recover sensible heat but must stay above acid dew point to avoid corrosion. Also watch for confusion between gross and net calorific value.
Worked example
A boiler produces 20,000 lb/h of steam. If 10% of steam traps fail open and each passes condensate equivalent to 2% of output, losses can approach 2,000 lb/h of steam. At roughly 1,000 Btu per pound of steam, that is 2 million Btu/h; over 6,000 hours that is 12 billion Btu, or about 12,000 MMBtu per year - a substantial fuel cost.
Practical guidance
Conduct regular trap surveys, tune combustion quarterly, recover condensate, insulate piping and valves, and monitor stack temperature trends as an efficiency indicator.