Core Process Flow of Flue Gas Desulfurization and Denitrification Production Units
Flue gas desulfurization and denitrification are core components of industrial waste gas treatment, widely used in industries such as thermal power, steel, chemical, and metallurgy. They effectively remove sulfur dioxide (SO₂) and nitrogen oxides (NOx) from flue gas, preventing environmental pollution such as acid rain and smog, while simultaneously enabling resource recovery and utilization. Tianli has deep expertise in the field of industrial waste gas treatment, developing complete sets of standardized flue gas desulfurization and denitrification production equipment, combined with comprehensive exhaust gas treatment and resource recovery systems. Leveraging advanced technology and intelligent control, we provide customers with efficient, low-consumption, environmentally friendly, and intelligent waste gas treatment solutions, helping them to achieve environmental protection and resource recycling.
I. Properties of Core Materials
Industrial flue gas (raw materials): SO₂ concentration varies by industry—approximately 500~2000 mg/m³ for thermal power plants, approximately 800~3000 mg/m³ for steel & iron sintering machines, and can reach 3%~10% in smelting flue gas. NOx concentration is generally 200~800 mg/m³, and it also contains impurities such as dust and heavy metals. The flue gas is grayish-white or yellowish-brown with pungent odor, and it requires emission treatment before discharge.
Reaction reagents include vanadium-based denitrification catalyst (SCR denitrification core), slaked lime or limestone (desulfurization absorbent), and ammonia (denitrification reducing agent). The catalyst needs to be replaced regularly, and ammonia is volatile, flammable, and explosive, requiring strict control.
Byproducts: desulfurization byproducts are gypsum (wet process) or dry desulfurization ash (dry/semi-dry process), which can be used in the building materials industry; SCR denitrification products are harmless nitrogen and water. Some high-concentration SO₂ flue gas can be recovered to produce sulfuric acid, realizing resource utilization.
II. Core Process Flow Introduction
Tianli offers two mainstream technical routes for different flue gas operating conditions: the dry desulfurization + SCR denitrification combined process (suitable for thermal power and steel sintering) and high-concentration SO₂ to sulfuric acid + SCR denitrification process (suitable for smelting and sulfuric acid tail gas). The following focuses on the most widely used dry desulfurization + SCR denitrification combined process.
1. Flue gas pretreatment
（280~380℃）。
Industrial flue gas is sent to the pretreatment system by induced draft fan where the dust, heavy metals and other impurities are removed by electrostatic precipitator (outlet dust concentration ≤10mg/m³) to prevent clogging of desulfurization and denitrification equipment and to avoid affecting catalyst activity. The flue gas then enters heat exchanger or heating device to adjust the temperature to the optimal reaction window for SCR denitrification (280~380℃).
2. Dry/semi-dry desulfurization (pre-desulfurization)
The pretreated flue gas enters circulating fluidized bed (CFB) dry desulfurization tower or semi-dry desulfurization reactor. Using hydrated lime (Ca(OH)₂) as the absorbent, it is thoroughly mixed with the flue gas under humidification conditions. SO₂ reacts with Ca(OH)₂ to produce calcium sulfite (CaSO₃) and calcium sulfate (CaSO₄), achieving highly efficient desulfurization. The desulfurization efficiency can reach over 95%, and the outlet SO₂ concentration can be stably controlled below 35 mg/m³. The desulfurized flue gas is then separated from the desulfurization ash by cyclone (partially returned to the tower for recycling) before entering the next stage.
3. SCR denitrification process
The desulfurized flue gas (containing low concentration of SO₂) enters the SCR denitrification reactor. Under the action of a vanadium-tungsten-titanium catalyst, the injected ammonia (NH₃) undergoes a selective catalytic reduction reaction with nitrogen oxides (NOx) to generate harmless nitrogen (N₂) and water (H₂O). The denitrification efficiency is ≥95%, and the outlet NOx concentration can be stably controlled below 50 mg/m³.
4. Exhaust emissions standard
The clean flue gas, after desulfurization and denitrification treatment, is discharged into the stack through induced draft fan. The emission indicators can be stably achieved as follows: SO₂≤35mg/m³, NOx≤50mg/m³, and particulate matter≤10mg/m³, meeting the national ultra-low emission requirements.
5. By-product treatment and resource recycling
Desulfurization byproducts (desulfurization ash/gypsum), after dehydration and drying, can be sold as cement retarder, gypsum board raw material, or road construction material. Waste denitrification catalysts (vanadium-based) are hazardous waste and should be disposed of by qualified units in accordance with national regulations. For high-concentration SO₂ flue gas scenarios such as smelting, a conversion and absorption system can be configured: after purification, the flue gas enters the converter, where SO₂ is oxidized to SO₃ under the action of a vanadium catalyst, and then absorbed by 98.3% concentrated sulfuric acid to produce industrial-grade sulfuric acid, achieving sulfur resource recovery and utilization.
III. Core Technical Advantages
1. Energy efficiency advantage
Waste heat recovery system is adopted to preheat the flue gas entering the SCR reactor by reducing auxiliary fuel consumption. The CFB dry desulfurization system has low resistance (approximately 1500~2000Pa), and the fan energy consumption is reduced by about 20% compared to the wet process. Overall energy consumption is reduced by more than 20% compared to traditional processes, significantly reducing the enterprise treatment and operation costs.
2. Environmental advantages
The entire production process is closed-loop, with flue gas undergoing dual treatment to meet emission standards and preventing the leakage of harmful gases. The dry/semi-dry process generates no desulfurization wastewater, completely solving the environmental problem of wastewater treatment in wet desulfurization processes. Desulfurization byproducts can be recycled and used in the building materials industry, and dead catalysts are disposed of in a standardized manner, achieving clean production throughout the entire process.
3. Product advantages
The recovered byproducts are of stable quality: dry desulfurization ash can be used as road construction material or cement admixture; the high-concentration SO₂ sulfuric acid production process can produce 98% industrial-grade sulfuric acid, meeting the GB/T 534 standard. The desulfurization and denitrification effects are stable, and emission indicators are far superior to national standards, helping enterprises pass environmental performance ratings.
4. Control advantage
Equipped with fully automated DCS intelligent control system, it monitors key parameters such as flue gas flow rate, SO₂/NOx concentration, reaction temperature, and ammonia slip in real time, achieving precise control throughout the entire process. It features automatic alarm, interlock protection, and emergency shutdown functions, and it can be operated remotely. By reducing manual intervention, it can ensure long-term stable and safe operation of the unit with uniform treatment effects.
5. Advantages in corrosion resistance and long-term operation
Dry desulfurization processes produce flue gas in dry state, resulting in significantly lower equipment corrosion compared to wet processes. Pre-desulfurization before SCR (Self-Repairing Catalyst) effectively prevents the formation of ammonium bisulfate (ABS), extending catalyst lifespan to 3-5 years. The main body of the equipment is constructed of weather-resistant steel or lined with corrosion-resistant materials, allowing for over 8000 hours of annual operation.