Coking technology is the core process for producing coke and chemical by‑products through high‑temperature carbonization of coal. Its technical difficulties involve multiple links including raw material treatment, process control, environmental protection and equipment maintenance. The main difficulties of coking technology are analyzed as follows:
1. Selection and Pretreatment of Raw Coal
Coal type adaptability: Different coal types vary greatly in caking property, volatile matter, sulfur content and ash content. Scientific coal blending is required to guarantee coke quality. High‑quality coking coal with low sulfur and low ash is becoming increasingly scarce. It is a major challenge to reduce costs by coal‑blending technologies such as adding non‑caking coal or binders.
Pretreatment uniformity: The crushing particle size and mixing uniformity of coal directly affect the structural stability of coke. Uneven pretreatment may easily result in insufficient coke strength or increased cracks.
2. Coking Process Control
Temperature uniformity: The temperature distribution of the coke oven heating system must be strictly controlled within ±20℃; otherwise, local over‑heating or under‑carbonized coke will occur. Conventional coke ovens suffer from low temperature at side ovens and high temperature in the central zone.
Pressure management: A large amount of coal gas (H₂, CH₄, etc.) is generated during carbonization. Pressure fluctuation inside the oven may cause gas leakage or explosion risks, so the pressure of the collecting main shall be precisely regulated.
Coking time optimization: Too short coking time reduces coke maturity, while excessively long coking time cuts down production efficiency. It is essential to balance coke quality and production capacity.
3. Coke Quality Control
High‑strength coke production: The metallurgical industry sets strict standards for coke cold strength and hot strength (CSR, CRI). Performance can be improved through coal quality optimization, additives (e.g. pitch, petroleum coke) or process improvements such as Coke Dry Quenching (CDQ).
Sulfur and ash control: Sulfur and ash from raw coal get enriched in coke and impair blast furnace performance. Their content shall be lowered by means of coal blending, chemical desulfurization or post‑treatment technologies.
4. Challenges in Environmental Protection
Waste gas treatment:Flue gas emission: Coke‑oven flue gas contains pollutants including SO₂, NOₓ and benzo(a)pyrene. Technologies such as SCR/SNCR denitrification and wet desulfurization are adopted, yet with high operating costs.VOCs leakage: Volatile Organic Compounds (VOCs) escape during coal charging, coke pushing and coke quenching, which demands closed‑loop operation and negative‑pressure recovery systems.
Wastewater treatment: Coking wastewater contains highly toxic substances such as phenol, cyanide and ammonia‑nitrogen. Multi‑stage treatment including ammonia distillation, biodegradation and advanced oxidation is required, while it remains difficult to meet discharge standards.
Solid waste utilization: Hazardous wastes such as tar sludge and acid tar need resource‑oriented utilization (e.g. being blended into coal feed for oven recycling), yet relevant technologies are not fully mature.
5. Durability of Equipment and Materials
Coke oven service life: Traditional coke ovens (e.g. 6‑meter top‑charging coke ovens) operate long‑term under high temperature (1300℃). Refractory materials on oven walls are prone to erosion and cracking, leading to high maintenance costs. It is necessary to improve the thermal shock resistance and chemical corrosion resistance of silica bricks.
Sealing and leakage prevention: Thermal deformation causes sealing failure on oven doors, ascension pipes, bridge pipes and other components. High‑temperature resistant elastic materials and intelligent monitoring systems need to be developed.
Automation level: Conventional coking heavily relies on manual work. Intelligent control such as heating optimization models and robot temperature measurement has not been widely applied, restricting energy efficiency and operational safety.
6. Resource and Energy Efficiency
By‑product recovery: Coke‑Oven Gas (COG) requires high‑efficiency purification (desulfurization, naphthalene removal) for hydrogen production or power generation. Deep processing of coal tar for high‑value‑added chemical extraction is in urgent need of technical upgrading.
Waste heat recovery: Sensible heat of red‑hot coke, accounting for 35% of coking energy consumption, can be recovered for power generation via CDQ. However, huge equipment investment limits its popularization among medium‑ and small‑sized coking plants.
7. Policy and Cost Pressures
Tougher environmental regulations: Under China's "Dual‑Carbon" goals, ultra‑low‑emission renovation (e.g. particulate matter ≤10 mg/m³) requires heavy capital input, and some outdated production capacities are facing phase‑out.
Economic balance: Clean production and equipment upgrading bring higher costs. Benefits shall be enhanced through large‑scale production and industrial chain extension such as coking‑chemical‑hydrogen co‑generation.
Technology Development Trends
Green coking: Promote clean coking technologies such as heat‑recovery coke ovens and negative‑pressure coal charging, as well as coking coupled with hydrogen metallurgy.
Intelligent upgrading: Apply big data and AI to optimize coal blending, heating control and fault prediction.
Circular economy: Adopt the multi‑generation mode integrating coking, chemical industry and energy to realize full resource utilization, such as hydrogen production from coke‑oven gas and CO₂ capture.
Breakthroughs in coking technology call for interdisciplinary collaboration combining material science, automation and environmental‑protection technologies, so as to achieve low‑carbon and intelligent transformation while guaranteeing coke quality. In the future, the industry will keep evolving toward high efficiency, cleanness and high added value.