(731d) Effective CO2 Utilization Using Coke Oven in Iron Making Process for Sustainability

The CO₂ recycling from exhaust gases in chemical industry has been received attention due to its potential for saving power energy and reducing CO₂ emissions. Among various industries, the iron making industry generates a significant amount of CO₂, contributing to the formation of greenhouse gases. Iron is produced by the reaction of iron oxide and coke, as shown infollowing equation below;

Fe₂O₃, Fe₃O₄ + Coke → Fe + CO₂ (1)

In order to reduce the amount of greenhouse gas in iron making industry, the development of CCU (CO₂ Capture and Utilization) technology specialized for the steel and iron making process is necessary due to difficulty of change in process or raw materials. Here, we demonstrate CO₂ utilization technology using heat and unused carbon at coke oven in iron making industry.

[Methods]

CO₂-rich gas is injected into the hot coke oven. The Boudouard reaction takes place between CO₂ and unused carbon, resulting in the production of CO, which contains heat energy. The increased production of CO gas is utilized as a fuel source to generate power or heat. A conceptual scheme for the Boudouard reaction with CO₂ in the coke oven is shown in upload Image. The Boudouard reaction can be represented by the following equation below;

CO₂ + C(unused carbon) → 2CO (2)

[Results and discussion]

A Coke oven is used to convert coal into coke by heating it to high temperatures (~ 1,200 °C) in an oxygen-free atmosphere. The main products are coke, coke oven gas (COG), and tar, etc. Coke is used to produce iron by reducing iron oxide. COG mainly contains CH₄, CO and H₂ gas and is used as fuel gases to produce power or heat. The tar is usually sticks to the oven wall and then carbonized, turning it into unused carbon. The unused carbon sources are currently released by air-combustion.

To utilize CO₂ in the coke oven, CO₂-rich gas is injected. The Boudouard reaction occurs between heat and CO₂ and unused carbon, generating CO. The produced CO is mixed with the original COG, resulting in increased COG emissions.

As a result of the analysis, the overall COG flow has increased by approximately 10% and the heat capacity has increased by about 7%. This indicates that the amount of COG that can be used as an energy source has increased due to the conversion of injected CO₂ to CO. Ultimately, by reducing the external LNG supply, it was possible to provide energy supply within the steelworks, resulting in cost savings from LNG usage and a reduction in CO₂ emissions. In 2023, the completion of the demo plant demonstrated the effectiveness of utilizing CO₂ through injection into coke.

[Conclusions]

CO₂ utilization technology, specifically designed for the iron making industry, gas been developed using coke oven. The heat within the coke oven serves as the reaction energy for CO₂ reduction, while the unused carbon attached to the coke oven wall acts as the source of CO₂ reduction. The CO₂ injected into the coke oven was converted into CO, a heat gas, through the Boudouard reaction. The completion of demo plant confirmed the result of increasing the total heat capacity of COG by 7%. This can lead to economic benefits by reducing reliance on energy sources such as LNG in the steel industry, as well as environmental benefits by reducing CO₂ emissions.