Coking

Coking is the process of heating coal in the absence of air to drive off volatile components, producing coke, a carbon-rich solid used as a fuel and reducing agent in ironmaking. The coal selected is typically a high-volatile, low-ash coking coal, often blended to meet specific quality requirements.

In industrial cokemaking, coal is prepared, blended, and loaded into coke ovens arranged in batteries. The ovens are heated to roughly 1000–1100°C for 12–36 hours. Volatile matter is driven off and collected in a by-product recovery system where coal tar, light oils, ammonium-containing liquor, and combustible gases are processed into marketable by-products. The solid coke remains in the ovens, is pushed out, cooled, and screened to produce coke of specified sizes and strengths.

Two main oven types exist: by-product coke ovens that recover volatile components for chemical processing, and non-recovery or heat-recovery ovens that do not recover byproducts but can be cheaper and produce coke more quickly. The resulting coke is used in blast furnaces to support ironmaking, serving as both fuel and reducing agent, and can also be employed as a fuel in other industries or as a feedstock for chemical processes. By-products and emissions from cokemaking are managed to reduce environmental impact, with modern plants implementing gas cleaning, tar decantation, and sulfur removal.

Coke quality is described by parameters such as Coke Strength after Reaction (CSR) and Coke Reactivity Index (CRI). Other important properties include porosity, ash content, moisture, and particle size distribution, which influence performance in a blast furnace.

Global production centers include China, India, the United States, Australia, and Russia. The industry is closely linked to the supply of high-quality coking coal and to demand for steel, with prices influenced by both coal markets and steel production cycles.