Britannica
Sources used in this answer
- coal utilization - Carbonization (coke making)
- bituminous coal
- coal utilization - Coking coals
- coal - Coal types and ranks
- coke
- coal utilization - Carbonization processes
- coal utilization - Thermoplastic properties
- coal utilization - Calorific value
- coal utilization - Coal type
- coal - Chemical content and properties
Why are certain bituminous coals best suited for making metallurgical coke?
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coal
Bituminous coal.
Certain bituminous coals are best suited for making metallurgical coke because of their unique thermoplastic properties, which allow them to soften, swell, and resolidify into a hard, porous, carbonaceous solid when heated in the absence of air.123
These coals, often referred to as "coking coals," are typically of the low- and medium-volatile bituminous ranks, generally containing 20 to 32 percent volatile matter. Their suitability is determined by several key factors:2
- Agglomerating Characteristics: These coals "cake" or agglomerate easily, a necessary trait for forming the strong, spongelike structure required for smelting iron ore in blast furnaces.435
- Petrographic Composition: The presence of specific macerals is critical; vitrinite and liptinite groups are considered reactive and contribute to the desired thermoplastic behavior, while inertinite is unreactive.236
- Chemical Purity: Coals with a low sulfur content are preferred to ensure the resulting coke meets the quality standards necessary for metallurgical processes.4
In modern industrial practice, if prime coking coals are unavailable, engineers achieve the necessary properties through the careful blending, crushing, and sometimes preheating of various coal types.2