Utilization Pathways of Coke Oven Gas, Blast Furnace Gas, and Converter Gas

Utilization Pathways of Coke Oven Gas, Blast Furnace Gas, and Converter Gas

In recent years, China’s steel industry has witnessed rapid development, accompanied by continuous progress in metallurgical technologies. As a result, steel plants are generating increasingly abundant by-product gases. Coke oven gas (COG), blast furnace gas (BFG), and converter gas (BOFG) are major secondary energy resources produced during ironmaking and steelmaking. Together, they account for approximately 40% of a steel plant’s overall energy consumption and therefore significantly influence production costs and profitability. Maximizing the recovery and efficient utilization of these gases is essential to reducing operating costs and enhancing the energy-conversion efficiency of steel enterprises.

I. Utilization Pathways of Metallurgical Gases

Due to variations in coal blending, raw-material structure, and process conditions, the calorific values of COG, BFG, and BOFG fluctuate within a controllable range. According to gas-balance and calorific-value optimization principles, the rational utilization of by-product gases can be guided by the following strategies:

1. Blast Furnace Gas (BFG)

BFG should be prioritized for supplying coke ovens, hot blast stoves, boilers, and rolling mills. In the coking process, BFG should replace COG as much as possible, forming an energy-use pattern of “BFG as primary fuel, COG as supplementary fuel.”
The COG displaced from the coking line can then be utilized in combined-cycle gas–steam power generation with an efficiency of up to 45%.

2. Coke Oven Gas (COG)

COG production is relatively stable, with low fluctuation in composition and high calorific value, and contains fewer toxic components. It should therefore be distributed to users with high calorific-value requirements, such as sinter ignition furnaces. It can also be blended with BFG and BOFG for use in rolling-mill reheating furnaces.

High-calorific-value gas helps shorten heating cycles and reduce billet scaling losses.

3. Converter Gas (BOFG)

BOFG should first be used within the steelmaking process itself—for ladle preheating, alloy drying, hot-metal mixers, on-line baking systems, and tundish preheating.

The remaining gas can be supplied to low-pressure boilers or directly to rolling-mill reheating furnaces, and finally to users with less stringent fuel requirements, such as lime kilns and primary mills.

Maximizing BOFG consumption increases its recovery volume and allows for greater substitution of BFG and COG.

Most steel mills primarily use by-product gases as fuel. Owing to its stability and high calorific value, COG is often prioritized by end-users, which frequently leads to shortages. Excess gases are commonly used for conventional power generation, with an energy-conversion efficiency of only about 32%. By adopting ultra-high-pressure turbine units or combined gas–steam cycle technology, power-generation efficiency can be increased to 37–42%.

II. Utilization of Metallurgical Gases in Non-metallurgical Industries

Beyond combustion applications, metallurgical gases—especially COG and BOFG—can serve as important chemical feedstocks. Their downstream pathways include the following:

1. Hydrogen Production

COG naturally contains more than 50% hydrogen, making it an ideal feedstock. Hydrogen is typically produced via pressure swing adsorption (PSA), yielding purity levels above 99.99%.
Major domestic steelworks have built PSA hydrogen-production units, supplying hydrogen mainly for cold-rolling annealing furnaces. Independent coking plants also produce hydrogen for benzene-hydrogenation and coal-tar hydroprocessing, but internal demand remains limited.

Hydrogen fuel cells represent another emerging utilization direction.

2. Synthetic Natural Gas (SNG) Production

Given COG’s high hydrogen and low carbon content, methanation offers an energy-utilization efficiency of up to 80%. After hydrogen separation, the remaining gas contains higher methane and calorific value, further enhancing utilization efficiency.

3. Ammonia Synthesis

The average energy consumption of ammonia synthesis using non-coking coal in China is around 1,554 kgce/t-NH₃. Traditional COG-based ammonia synthesis consumes approximately 1,250 kgce/t-NH₃.
With recent advances, energy consumption can be reduced to 1,142 kgce/t-NH₃.

COG-based ammonia synthesis offers rational resource utilization, lower investment, reduced operating cost, and lower unit product cost—advantages unmatched by coal-gasification routes. Ammonia is used in fertilizer production and other chemical industries; hydrogen in purge gas can also be recovered, making it one of the most efficient hydrogen-production pathways.

4. Carbon Monoxide Production

Vent BFG can be re-utilized through adsorption purification to recover CO and CO₂, reducing carbon emissions. Given BFG’s low CO and high N₂ content—with similar boiling points—specialized PSA adsorbents must be used for effective CO purification.

5. Carbon Dioxide Production

COG and BOFG contain up to 60% syngas components. Mature PSA technology can separate and purify H₂ and CO, while CO₂ is obtained as a by-product during BOFG processing.
Purified CO₂ has broad applications in food processing, agricultural storage, greenhouse CO₂ fertilization, and supercritical extraction.

6. Methanol and Ethanol Production

BOFG contains nearly 80% CO + CO₂. Supplementing BOFG in COG-based oxygen-rich methanol synthesis improves the H₂/CO ratio and increases methanol yield.

For ethanol production, BOFG—after dust and oxygen removal—can directly undergo microbial fermentation regardless of fluctuations in CO concentration or the presence of N₂ and CO₂.

Conclusion

Coke oven gas, blast furnace gas, and converter gas are not only valuable industrial fuels but also important feedstocks for clean-fuel production and chemical synthesis. Maximizing gas recovery and utilization reduces specific energy consumption, lowers emissions, and expands resource-utilization pathways. Through integration with non-steel industries, metallurgical gases can form an industrial ecological chain, increase added value, and support multi-product cogeneration models.

Innovative utilization of metallurgical gases requires abandoning the traditional “burn-on-site” approach and instead upgrading to targeted extraction of valuable components through gas purification and separation technologies.

Peking University Pioneer has specialized in gas purification and separation for over two decades and can efficiently and cost-effectively recover CO, CO₂, H₂, CH₄ and other valuable components from steelmaking gases. This enables downstream gas-chemistry integration and top-gas recycling ironmaking.

Before the introduction of China’s “dual-carbon” (carbon-peaking and carbon-neutrality) goals, metallurgical gas utilization evolved from “waste discharge” to “useful application.” With the dual-carbon strategy in place, the steel industry must further transition from “partial utilization” to “maximum utilization.”

Among these strategies, integrated gas-chemistry (steel–chemical co-production) has been proven as a viable pathway for carbon-fixation and cost-reduction, while top-gas recycling ironmaking represents a highly feasible closed-loop “self-production and self-consumption” model for the future of steel gas utilization.