Metallurgical coke is made by heating prepared coal in coke ovens at high temperatures while limiting oxygen. Volatile materials leave the coal and can be collected as gas and liquid byproducts; the solid left behind is carbon-rich coke. Coke making can also release air pollutants at several stages, including oven charging, leaks, pushing, quenching, combustion, and materials handling.
This is the process for metallurgical coke used in ironmaking—not petroleum coke or household charcoal.
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How coal becomes metallurgical coke
Coke plants use batteries of ovens to carbonize prepared coal. In this process, coal is heated without enough oxygen for ordinary combustion. Heat drives off volatile compounds, leaving a solid, carbon-rich material: coke. The U.S. Environmental Protection Agency’s AP-42 technical reference describes high-temperature carbonization above 900°C (1,650°F). Coke is used in blast furnaces to help convert iron ore into iron, which can then be refined into steel.
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As the coal heats, volatile material leaves the oven and enters a collection system in by-product operations. That raw stream contains gases, water vapor, tar, light oils, dust, and other compounds. Cooling and recovery stages condense and separate some of the material. The resulting gas may be conditioned and used as fuel. Equipment and recovery arrangements differ among plants, so not every facility recovers every chemical or uses the same process layout.
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What byproducts come from coke making?
Coke is the solid product; coke-oven gas and the separated liquids are distinct outputs. EPA’s AP-42 reference lists hydrogen, methane, ethylene, carbon monoxide, carbon dioxide, hydrogen sulfide, ammonia, and nitrogen among coke-oven gas components. Liquid products include water, tar, and crude light oil. Recovery plants process condensate and gas to recover coal chemicals and condition gas for fuel use.
EPA’s 2008 AP-42 reference gives an approximate coke-oven gas yield of 338,000 liters per megagram of coal charged, also expressed as about 10,800 standard cubic feet per ton. This is a technical-reference estimate, not a guaranteed yield or a universal measurement for modern plants.
Where emissions can occur
Pollutants can be released at different points in the operation, not only from the oven stack. EPA identifies potential emission sources that include coal unloading and handling, oven charging, leakage at doors, lids and offtakes during coking, pushing, hot-coke quenching, combustion, and crushing, screening, handling and storage of coke.
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsEPA’s AP-42 chapter identifies particulate matter and volatile organic compounds (VOCs), along with sulfur dioxide, nitrogen oxides and carbon monoxide from specified operations. It also identifies hazardous organic pollutants in emissions, including benzene, toluene, xylenes, cyanide compounds, naphthalene, phenol and polycyclic organic matter. These are pollutants the agency associates with coke-making operations; the list does not mean each plant emits every substance at the same level. Actual pollutants and quantities depend on the source, operation, controls and facility.
Compounds recovered from raw coke-oven gas should not be treated as a direct inventory of what reaches ambient air. Recovery systems capture and process some material, while leaks and other discrete operations can still release pollutants.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How U.S. coke-oven rules fit in
In the United States, EPA materials cover coke-oven batteries, pushing, quenching, battery stacks and by-product recovery. The agency’s standards page describes 2024 amendments and states that a final rule dated October 2, 2025, withdrew a July 2025 interim rule that had extended certain compliance deadlines. EPA materials also address subjects such as coke-oven leaks and benzene fenceline monitoring.
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Those summaries do not establish the requirements for every plant or country. Applicable standards, deadlines, permits and compliance duties depend on the facility and jurisdiction; consult current EPA rule materials and the relevant permits for a specific site.
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