Boiler Accessories — What Does an Economiser Do? Assess the statement: “An economiser is used to increase the temperature of saturated steam without raising its pressure.”

Introduction:
Boiler accessories improve plant efficiency by recovering heat from flue gases. Two common devices are the economiser and the superheater. Confusing their roles leads to incorrect system design and poor performance. The statement given confuses these functions.

Given Data / Assumptions:

• Conventional subcritical drum boiler context.
• Economiser placed in the flue gas path upstream of the air preheater and downstream of the evaporator/superheater bank order may vary by design.
• Saturated steam refers to steam at the saturation temperature for its pressure.

Concept / Approach:
An economiser heats feedwater before it enters the boiler drum/evaporator, raising feedwater temperature and reducing fuel required. A superheater, not an economiser, raises the temperature of steam above saturation at essentially the same pressure. Therefore, the statement about an economiser increasing saturated steam temperature is incorrect.

Step-by-Step Solution:
Define economiser duty: raise feedwater temperature using waste heat from flue gases.Define superheater duty: raise steam temperature above saturation at near-constant pressure (superheat).Compare to statement: it describes superheater function, not economiser ⇒ statement is false.

Verification / Alternative check:
P&I diagrams show economiser in the feedwater line; thermal calculations show reduced fuel to reach boiling when feedwater is preheated.

Why Other Options Are Wrong:

• “Correct” or qualifiers involving reheat/subcritical do not change the fundamental device function.

Common Pitfalls:
Using the term “economiser” generically for any heat recovery; always distinguish feedwater heating from steam superheating or reheating.

Final Answer:
Incorrect