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How is coal converted into metallurgical coke?
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coal utilization
Cross-regenerative coke oven. (A) Cross section, showing the alternating arrangement of flue walls and ovens; (B) longitudinal section, showing (left) a series of combustion flues in a single flue wall and (right) part of a long, slotlike oven.
The conversion of coal into metallurgical coke, a process known as carbonization, involves heating specific types of bituminous coal to high temperatures in the absence of air.12
The Coking Process
- Preparation: Because prime coking coals are increasingly scarce, modern plants use elaborate preparation methods. This involves selecting, crushing, and blending various coals—often mixing high-volatile and low-volatile varieties—to achieve the desired properties. Drying or preheating the coal charge can also improve efficiency.3
- Heating: The prepared coal is loaded into large, mechanized coke ovens, which are arranged in batteries. When heated without air, the coal undergoes a transformation: it first softens into a plastic mass, decomposes, and then resolidifies into a hard, porous solid known as coke.435
- Finishing: After a coking period of approximately 15 hours, the red-hot coke is pushed from the oven and transferred to a quenching station. It is cooled either with water or by using circulating inert gases, a method known as dry quenching.4
The resulting product is a carbon-rich residue used primarily in blast furnaces to smelt iron.12