BOC Boiler Systems and Steam 2 — Questions and Answers
Question 1: What is the recommended procedure when a boiler safety relief valve lifts (opens)?
- Immediately reset it manually and continue operation
- Identify and correct the cause of overpressure before resuming operation (Correct answer)
- Increase feedwater flow to compensate for steam loss
- Reduce fuel input only and allow the valve to reseat on its own
Correct answer: Identify and correct the cause of overpressure before resuming operation
A lifting safety valve signals a potentially dangerous overpressure condition; the root cause must be found and corrected before safely resuming boiler operation.
Question 2: In a steam heating system, what is 'two-pipe' piping?
- A system with supply and return piping kept separate (Correct answer)
- A system using two parallel boilers
- A system with two pressure zones
- A system with dual fuel capability
Correct answer: A system with supply and return piping kept separate
A two-pipe steam system uses separate supply and return mains, allowing more precise control and quicker condensate return compared to single-pipe systems.
Question 3: What is 'scale' in a boiler, and what problem does it cause?
- A weight measurement device; it affects fuel metering
- Mineral deposits on heat transfer surfaces; it reduces heat transfer efficiency (Correct answer)
- Corrosion pitting on the fireside; it weakens metal
- Foam on the water surface; it causes carryover
Correct answer: Mineral deposits on heat transfer surfaces; it reduces heat transfer efficiency
Scale is mineral buildup (primarily calcium and magnesium compounds) on waterside surfaces that acts as insulation, reducing heat transfer and potentially causing overheating.
Question 4: What condition is described as 'priming' in a steam boiler?
- The initial startup procedure for a cold boiler
- Violent water surging that carries water droplets into the steam supply (Correct answer)
- The process of treating feedwater with chemicals
- Building pressure before opening the steam header
Correct answer: Violent water surging that carries water droplets into the steam supply
Priming occurs when the boiler water surges violently, entraining water droplets in the steam, which can cause water hammer and damage downstream equipment.
Question 5: What is the purpose of a feedwater economizer in a boiler system?
- To add chemicals to feedwater before it enters the boiler
- To preheat feedwater using waste heat from flue gases (Correct answer)
- To separate impurities from feedwater using gravity
- To store emergency feedwater supply
Correct answer: To preheat feedwater using waste heat from flue gases
An economizer recovers heat from exhaust flue gases to preheat incoming feedwater, improving overall boiler efficiency and reducing fuel consumption.
Question 6: The boiler horsepower (BHP) rating is defined as the evaporation of how many pounds of water per hour from and at 212°F?
- 10 lbs/hr
- 15.65 lbs/hr
- 34.5 lbs/hr (Correct answer)
- 50 lbs/hr
Correct answer: 34.5 lbs/hr
One boiler horsepower equals the evaporation of 34.5 pounds of water per hour from and at 212°F, equivalent to approximately 33,475 BTU/hr.
Question 7: What does 'TDS' stand for in boiler water treatment, and why is it monitored?
- Thermal Distribution System; to track heat losses
- Total Dissolved Solids; to prevent scale and foaming by controlling blowdown (Correct answer)
- Timed Discharge Schedule; to automate blowdown intervals
- Turbine Discharge Steam; to measure steam quality
Correct answer: Total Dissolved Solids; to prevent scale and foaming by controlling blowdown
Total Dissolved Solids (TDS) measures the concentration of minerals and impurities in boiler water; high TDS causes scale, foaming, and carryover, controlled through blowdown.
BOC Boiler Systems and Steam 2
What is the recommended procedure when a boiler safety relief valve lifts (opens)?