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Editor's Note:

Since 2018, the company has established a dedicated team focused long-term on the R&D of this waste gas treatment equipment, building several core technologies with independent intellectual property rights. The products currently hold two invention patents and five utility model patents. The first- and second-generation DS Combustion Purification technology products have been applied in 14 units, of which nine are in normal operation and five are under construction.

The following article is sourced from and authored by the Chinese Society for Metals.

From October 15 to 17, 2025, the Chinese Society for Metals held the "2025 National Seminar on Key Technologies for Green and Low-Carbon Metallurgical Sintering" in Tianjin. The conference theme was low-cost intelligent sintering and high-efficiency energy saving, pollution reduction, and carbon mitigation. In-depth exchanges and discussions were held on cost reduction and efficiency improvement in sintering and pelletizing, green and low-carbon technologies, pollution and carbon reduction technologies, and CO recovery and treatment technologies. The conference secretariat will organize, review, and subsequently report on the relevant technologies presented.

1 Background

As a pillar of the national basic industry, the iron and steel industry entails substantial energy consumption and emissions of pollutants such as carbon monoxide, VOCs, and nitrogen oxides. These pollutants originate mainly from sintering machine head flue gas, primary steelmaking flue gas, coke oven stack emissions, and CDQ (coke dry quenching) exhaust, causing serious environmental damage and posing a significant threat to human health.

With the advancement of the national "dual carbon" strategy and the continuous tightening of environmental policies, the iron and steel industry faces unprecedented environmental pressure. Meanwhile, carbon monoxide, as a combustible gas, is both a pollutant and a potential energy carrier; how to achieve its efficient treatment and energy recovery has become a focus for steel enterprises. Ningbo Taiji Environmental Protection began R&D in 2018 and pioneered the DS Combustion Purification Heat Recovery System, which achieves integrated deep oxidative removal of CO and VOCs through high-efficiency combustion, coupled with a denitrification function, to synergistically purify multiple pollutants within a single system. The system also innovatively integrates a heat recovery unit that effectively recovers and reuses the heat released during pollutant decomposition, markedly reducing overall operating energy consumption and enabling enterprises to make a transformative leap from "single treatment" to "synergistic purification" and from "high energy consumer" to "energy-saving pioneer."

2 Existing Problems and Treatment Difficulties

Waste gas treatment in the iron and steel industry faces multiple challenges arising mainly from the characteristics of the pollutants and the limitations of existing technologies: (1) Large concentration fluctuations: in steel production, different production stages and operating conditions cause wide fluctuations in waste gas concentration and flow. Taking the sintering process as an example, CO concentration generally fluctuates within 5,000–10,000 mg/m³, and NOx concentration varies between 200 and 400 mg/m³; this instability makes stable operation difficult for conventional treatment technologies. (2) Coexistence of complex components: steel flue gas contains multiple pollutants; in addition to VOCs, CO, and NOx, it also contains sulfur dioxide, dioxins, heavy metals, and other pollutants, which produce mutual interference that affects the stable operation and treatment efficiency of the equipment. (3) High energy consumption: SCR catalytic denitrification operates at 210–350°C and requires additional heating for low-temperature flue gas (90–150°C), increasing energy consumption. An independent SCR system consumes large amounts of natural gas, blast furnace gas, or electricity to heat the flue gas, resulting in extremely high operating costs. (4) Difficult system coordination: when multiple treatment facilities operate in parallel, coordinated control between systems is difficult, easily causing secondary pollution or mutual interference between equipment.

3 Technical Route

3.1 DS Combustion Purification Heat Recovery System Coupled with SCR Denitrification

The DS Combustion Purification Heat Recovery System coupled with SCR denitrification comprises Indirect Heat Recovery Module I, Regenerative Heat Recovery Module II, the Combustion Purification Module, and the SCR Denitrification Module, as shown below.

Figure 1 Process principle diagram

The process route is as follows: dust-removed flue gas passes sequentially through the indirect heat exchange module and the regenerative module to recover heat and raise temperature, then is fully combusted in the combustion-purification module at approximately 850°C, removing CO and VOCs while generating heat. The high-temperature flue gas after combustion again passes through the regenerative module, which transfers heat to the newly entering low-temperature flue gas to recover heat. Where heat is in surplus, a waste heat boiler can be installed to recover heat as steam or electricity. Once the flue gas temperature reaches 280–350°C, it enters the SCR denitrification module to remove NOx. After denitrification, the flue gas passes through the indirect heat exchange module again; after its temperature drops below 180°C to recover further heat, the purified flue gas, with CO, VOCs, and NOx removed, is discharged.

Through the regenerative heat recovery module and periodic switching of airflow direction, the system achieves efficient heat recovery with a heat recovery efficiency of over 95%. The inlet-to-outlet temperature difference of the entire flue gas system is only 40°C or even lower, meaning that only a very low CO concentration is required for the system to operate on self-generated heat without supplementary fuel, achieving energy saving and emission reduction.

4 Technical Advantages

Process innovation: The indirect heat exchange module, regenerative module, combustion-purification module, and SCR denitrification module are integrated organically. The combustion-purification module efficiently removes CO and VOCs, while the heat released by flue gas combustion is recovered to raise the temperature for SCR denitrification to remove NOx. Surplus heat can be used to generate steam or electricity, and the discharged high-temperature flue gas passes again through the regenerative and indirect heat exchange modules to recover heat, achieving synergistic removal of multiple pollutants and waste heat recycling. The overall system heat recovery efficiency reaches over 95%; above a certain CO concentration, the system can operate on self-generated heat without auxiliary fuel. Meanwhile, the discharged high-temperature flue gas provides the suitable reaction temperature for SCR denitrification, eliminating the energy consumed by separate SCR heating and realizing cascade energy utilization. Compared with conventional treatment technologies, the system reduces operating energy consumption by 30%–50%, with marked energy-saving and economic benefits.

Key reversing equipment — auxiliary gas-seal hard-seal lift valve: By combining a high-temperature-resistant main hard seal with an auxiliary dynamic gas-curtain seal, zero leakage is achieved, solving the leakage problem of conventional valves under high-temperature, highly corrosive conditions. The CO and VOCs removal rate can exceed 99%, markedly improving the reliability and environmental performance of the DS Combustion Purification system.

Multi-stage split-flow technology combining guide vane arrays with perforated partition plates: adjusts airflow direction and distribution to improve furnace temperature uniformity and flue gas treatment performance. The CFD flow field simulation model is continuously refined based on on-site measurement feedback to optimize flow field design.

Precise, intelligent control of the flue gas treatment system through regenerative temperature control and raw flue gas parameter regulation: the DS Combustion Purification Heat Recovery System features multiple control loops, including combustion-purification module temperature control, post-combustion flue gas temperature control, and raw flue gas combustible gas concentration control, offering a high degree of automation with high safety and reliability.

High-temperature oxidation technology with stable system and strong adaptability: it can treat flue gas with wide concentration fluctuations and complex composition. The regenerator can operate stably for 5–8 years, or even more than 10 years, with an investment payback period of 2–4 years; unlike catalytic oxidation of CO, which requires catalyst replacement every 1–2 years.

Energy recovery, green and low-carbon: while purifying flue gas and reducing carbon, the system can export surplus heat for process preheating, steam, or power generation, further unlocking energy-saving potential and reducing the enterprise's overall carbon emissions. It achieves ultra-low emissions and supports circular economy development.

5 Economic Analysis

An economic analysis is presented using a steel plant's 230 m² sintering machine with an air volume of 145×10⁴ Nm³/h as an example.

The specific process flow is as follows: flue gas from the cold-side outlet of the indirect heat exchanger (GGH) is introduced into the DS Combustion Purification Heat Recovery System for purification and heating, fully utilizing the heat from high-temperature CO oxidation in the flue gas to sustain operation and meet the temperature required for SCR denitrification, replacing the original direct-fired hot-air heater in the existing flue. Surplus heat can be sent to a waste heat boiler to generate steam for power generation. Flue gas (87°C) — GGH cold side (180°C) — DS Combustion Purification Heat Recovery System (850°C) — SCR (210°C) — GGH hot side (114°C) — booster fan — stack discharge.

Energy saving and emission reduction calculations: based on a 230 m² sintering machine, 145×10⁴ Nm³/h, and a CO concentration of 10,000 mg/m³.

At this CO concentration, the system reaches self-balance and operates normally without consuming additional blast furnace gas. Surplus heat is used to produce steam or generate electricity, with estimated steam output of about 17 tons/hour and annual benefit of 14 million yuan. Had the original system used a direct-fired furnace for heating, it would have consumed an additional 12,000 m³/h of blast furnace gas; this now saves 9.5 million yuan per year. Taking environmental carbon-reduction tax benefits into account and deducting operating costs, the estimated annual benefit is about 48 million yuan; after accounting for equipment investment and maintenance, the estimated payback period is about 2–3 years, with significant economic and social benefits.

6 Technology R&D and Engineering Cases

Since 2018, the company has established a dedicated team focused long-term on the R&D of this waste gas treatment equipment, building several core technologies with independent intellectual property rights. The products currently hold two invention patents and five utility model patents. The first- and second-generation DS Combustion Purification technology products have been deployed at enterprises such as High Energy Environment and Lanxi Zili Environmental Protection. To date, 14 units have been applied: nine in normal operation and five under construction, with a cumulative total treatment air volume exceeding 1.1 million Nm³/h, giving the company extensive experience in design, manufacturing, installation and commissioning, and after-sales service.

6.1 Case 1: Full-flue-gas treatment of a deep dryer in the smelting industry, air volume 40,000 Nm³/h

6.2 Case 2: Roasting furnace flue gas denitrification and CO/VOCs treatment project in the smelting industry, air volume 45,000 Nm³/h

6.3 Case 3: Roasting furnace and smelting furnace flue gas treatment in the smelting industry, air volume 45,000 Nm³/h

6.4 Case 4: Full-flue-gas treatment of a deep dryer in the smelting industry, air volume 150,000 Nm³/h

6.5 Case 5: Full-flue-gas treatment of a deep dryer in the smelting industry, air volume 45,000 Nm³/h

6.6 Case 6: Drying furnace flue gas desulfurization and CO/VOCs treatment project, air volume 45,000 Nm³/h