🔍 Key Concepts

• water circulation paths in a modern water-tube boiler • difference between downcomers, risers, and feedwater lines • location and function of the mud drum in a boiler

💭 Think About

• Think about where the water in a water-tube boiler moves when it is cooler and denser versus when it is hotter and lighter. • Ask yourself: are downcomers carrying water toward the main heating area or away from it? • Consider which component in the answer choices is actually involved with steam versus water circulation.

✅ Before You Answer

• Make sure you know what part of the boiler the downcomers physically connect to at the bottom. • Verify which system actually handles feedwater preheating—is that done by downcomers or by another piece of equipment? • Check which option relates to gas/soot side cleaning, which is separate from the boiler’s internal water circulation system.