Controlling artificial draught in furnaces: A mechanically produced (fan-driven) draught in a fired furnace can be regulated using which of the following methods?

Introduction / Context:
Artificial (mechanical) draught is created by forced-draft and/or induced-draft fans in furnaces, boilers, and kilns to supply combustion air and evacuate flue gases. Effective control of this draught is essential for stable flames, appropriate excess air, and safe operation across varying loads.

Given Data / Assumptions:

• A fan is installed to create or augment draught.
• We consider practical, industry-standard control actions available to operators or control systems.

Concept / Approach:
Fan-based draught can be controlled via multiple levers: (i) speed control (e.g., variable frequency drive) changes fan head and flow; (ii) dampers adjust system resistance and flow distribution; (iii) variable-pitch blades (on suitable fans) alter the fan characteristic and delivered flow/pressure at a given speed.

Step-by-Step Solution:
Identify all legitimate, commonly used mechanisms for regulating flow/pressure.Fan speed, dampers, and pitch change are all established and effective methods.Therefore, “All (a), (b) and (c)” is correct.

Verification / Alternative check:
Fan control strategies in boiler/furnace practice often combine VFD speed control with inlet or outlet dampers to balance multi-zone flows, confirming all three approaches are valid.

Why Other Options Are Wrong:
Single options (a, b, or c) are incomplete; industry uses all of them where available.Grate modifications: relevant only to stoker systems and not a primary draught control for fan-driven systems.

Common Pitfalls:
Believing dampers alone are sufficient. While dampers work, VFD speed control often saves power and stabilizes control—best practice frequently combines methods.

Final Answer:
All (a), (b) and (c)