POSCO Group does its best to develop technologies that contribute to safety and carbon neutrality. We introduce POSCO Group’s excellent new technologies to create a better world! This part introduces POSCO’s Water Curtain Denitrification Technology, which reduces nitrogen oxide (NOx) emissions caused by the external air infiltration during the scarfing process and helps ensure smooth and stable operations.
Unlike other combustion equipment, scarfing machines used in the scarfing process are open systems that are always exposed to the external environment (air). During high-pressure injections of NG and oxygen, the pressure difference naturally causes external air to flow into the area around the flame. At this time, if the nitrogen in the air oxidizes under high-temperature conditions, nitrogen oxides are produced. Nitrogen oxides undergo chemical reactions with water vapor, ozone, and other substances, becoming a major cause of air pollution by generating fine particles.
POSCO developed the Water Curtain denitrification technology to improve the operational environment by addressing the shortcomings of existing denitrification equipment used on-site and fundamentally preventing the emission of air pollutants caused by external air infiltration during the scarfing process. This technology works on a principle of forming a barrier of water streams positioned as close as possible to the flame generated by the scarfing machine. This minimizes external air inflow, thereby preventing the emission of air pollutants such as nitrogen oxides. This technology significantly reduces the emission of air pollutants caused by external air infiltration without affecting the quality of the slabs. Additionally, it has achieved substantial savings in annual operating costs compared to conventional denitrification equipment.
As environmental issues become increasingly severe worldwide, countries are strengthening environmental regulations to reduce air pollutants emitted from industrial operations. In line with this trend, the Environment and By-Product Group Air Quality Management Section, the Steelmaking Department Slab Finishing Plant, and the Plate Rolling Department Continuous Casting Plant 3 at Gwangyang Works have been exploring the application of denitrification technologies to reduce nitrogen oxide emissions caused by external air infiltration during the scarfing process.
SCR* and SNCR** denitrification technologies have previously been introduced at more than 100 operational sites across Pohang and Gwangyang Works. However, as these technologies are effective only within specific temperature ranges, their application in the scarfing process—characterized by intermittent operations with run times of less than five minutes—has been challenging due to the difficulty in maintaining consistent temperatures. Furthermore, with wet denitrification systems, which use chemically treated water, there were additional challenges, particularly in managing wastewater, resulting in high treatment costs.
*SCR (Selective Catalytic Reduction): A technology that reduces nitrogen oxides to nitrogen and water by injecting a reducing agent (urea solution) into the exhaust gas and reacting it with a catalyst.
**SNCR (Selective Non-Catalytic Reduction): A technology that decomposes nitrogen oxides into nitrogen and water by directly injecting ammonia or urea solution into the exhaust gas at high temperatures without a catalyst.
In response to these limitations, the Environment and Byproduct Group at Gwangyang Works listened to the various challenges faced by on-site workers handling denitrification equipment. Together with RIST, they revisited existing strategies to explore more effective ways to reduce emissions.. With the active support of the plants, they established the goal of developing a denitrification technology that would be both easy to operate on site and very effective in reducing nitrogen oxide emissions. This initiative ultimately led to the start of full-scale development efforts.
Through repeated testing, establish the optimal technology roadmap
The initial step was to evaluate whether the water curtain denitrification technology could be effectively applied to the actual scarfing process with on-site trials. The team explored various installation options in collaboration with the on-site denitrification system operators. Once the installation method was finalized, they proceeded with installing spray nozzles for testing. Given the nature of the technology, which requires large volumes of water to be used in a short period, the water supply infrastructure was insufficient. To overcome this, temporary water tanks and pumps were set up at the test site so that the team could repeatedly store water and establish an optimal testing environment.
If the water particles forming the water curtain are too small, they fail to block external air and are instead drawn into the dust collector hood located at the rear of the scarfing machine, preventing the intended air pollutant reduction effect. In the early tests, the particle size was too small, resulting in repeated trial and error. However, after adjusting the spray pressure and nozzle design multiple times, the team successfully optimized the particle size to effectively block external air, and the technology was successfully validated.
Optimize the installation location of the plant to fully implement it on site
After successfully completing the tests, the team faced a new challenge in determining the optimal location for installing the spray equipment. The core of the technology lies in spraying water as close to the flame as possible. However, the differing conditions at each plant, coupled with variations even among similar scarfing machines, made it challenging to standardize installation criteria. Additionally, the intense strength of the flames made it difficult to monitor in real time whether the flame surface was being adequately shielded during operations. To resolve this, the team conducted repeated checks on nitrogen oxide levels and slab surface quality after each operation. Through this process, they were able to pinpoint the most effective installation positions for each plant.
The construction of new traditional wet denitrification systems required a considerable total investment of KRW 48.1 billion, along with annual operating costs of KRW 7 – 8 billion, including wastewater treatment expenses. The water curtain technology requires a total investment of KRW 2.7 billion and annual operating costs of KRW 390 million. Compared to traditional wet denitrification systems, this results in a cost reduction of KRW 45.4 billion in investment and approximately KRW 7.5 billion in annual operating costs.
Furthermore, the technology enables stable process operations in compliance with environmental regulations, allowing on-site facilities to operate without the burden of improvement orders or operational stoppages. By fundamentally eliminating nitrogen oxides and yellow plume generated during the process, it has significantly minimized external complaints, highlighting the importance of this technological development.
Currently, four scarfing machines at Gwangyang Works are equipped with the water curtain denitrification system. In August, a field evaluation was conducted at Pohang Works to assess the feasibility of installation. POSCO plans to continuously refine and enhance this technology to further improve environmental management standards at operational sites. Through this approach, POSCO plans to proactively respond to future tightening of environmental regulations by effectively utilizing this technology in the right places. We look forward to POSCO’s water curtain denitrification technology being effectively utilized at even more operational sites in the future!
