Fuel selection for steam boilers (general practice in thermal engineering): Which fuel is most commonly used in steam boilers for power and process applications?

Introduction / Context:
Industrial and utility steam boilers require a fuel that ignites reliably, burns steadily, and delivers high calorific value with manageable ash and handling properties. Among solid fuels, different ranks of coal and their coking tendency influence suitability for boiler firing versus metallurgical applications.

Given Data / Assumptions:

• Conventional grate, stoker, or pulverized-fuel fired steam boilers.
• Need for steady flame, good grindability (for PF systems), and non-sluggish ash behavior.
• Typical industry practice rather than niche or waste-to-energy cases.

Concept / Approach:
Coking (agglomerating) coals soften and become plastic, then resolidify to form coke when heated without air. This property is advantageous for coke ovens, not for boiler furnaces where agglomeration can cause clinker formation and unstable combustion. Non-coking bituminous coal, with good volatile matter and high heating value, provides rapid ignition and stable flames without problematic caking, making it the workhorse fuel for many boilers worldwide.

Step-by-Step Solution:

Verification / Alternative check:
Standard boiler-firing handbooks and utility practice list non-coking bituminous (and sometimes sub-bituminous) as the predominant solid fuel classes for steam generation, with pulverized-coal systems specifically optimized for such ranks.

Why Other Options Are Wrong:

• Brown coal: High moisture and low calorific value; special handling and drying needed.
• Peat: Very low grade and rarely used for industrial boilers.
• Coking bituminous coal: Preferred for metallurgical coke, not boilers, due to caking.

Common Pitfalls:
Assuming “higher rank is always better” without considering coking behavior; ignoring furnace design constraints and slagging/ash fusion temperature issues.

Final Answer:
non-coking bituminous coal