Combustion chamber sizing in industrial furnaces: The required size (volume) of a furnace combustion chamber primarily depends on which factors?

Introduction / Context:
Combustion chamber sizing is vital to ensure complete combustion, proper flame development, acceptable residence time, and uniform heat flux to the load. Undersized chambers risk flame impingement and CO formation; oversized chambers can be inefficient and costly.

Given Data / Assumptions:

• We consider a conventional fired furnace or process heater.
• Fuel type, preheat, and mixing arrangements are design variables.
• Target emissions and completeness of combustion are to be satisfied.

Concept / Approach:
Key drivers include: (i) heat release rate (kW per unit volume) which sets necessary volume for safe flame development; (ii) preheating fuel/air accelerates kinetics and can reduce required volume; (iii) efficient mixing ensures rapid, uniform combustion, affecting required residence time and thus chamber size.

Step-by-Step Solution:
Relate heat release rate to chamber volume: higher rates generally need larger volume or advanced burners.Account for preheat: hotter reactants shorten ignition delay and reaction time, permitting more compact chambers.Assess mixing: good mixing reduces unburned pockets and stabilizes shorter flames.Hence all three factors jointly determine sizing → choose “All (a), (b) and (c)”.

Verification / Alternative check:
Burner and heater design guidelines tie allowable heat release (per m^3), reactant preheat, and mixing intensity to the recommended firebox volume, confirming the combined influence.

Why Other Options Are Wrong:
Any single factor alone is insufficient; real designs balance all three.Refractory thickness affects durability/heat loss, not primary chamber volume sizing.

Common Pitfalls:
Overlooking the impact of high air preheat: it can significantly reduce required volume but increases NOx potential, so designs must also address emissions control.

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