The efficient coordinated operation of wet electric demister and desulfurization and denitrification equipment is the key link to achieve deep treatment of multiple pollutants in industrial flue gas. This synergistic mechanism not only involves the complementarity of equipment functions, but also requires systematic optimization in process design, parameter matching and control system. From the overall process of flue gas treatment, desulfurization equipment (such as wet desulfurization tower), denitrification equipment (such as SCR/SNCR) and wet electric demister are usually arranged in series or parallel, each of which plays a role in specific pollutants, but through reasonable process connection, a complete chain from gaseous pollutant removal to liquid/solid particle capture can be formed, and synergistic efficiency can be achieved at the same time.
At the process layout level, the coordinated operation of wet electric demister and desulfurization equipment is particularly critical. Wet desulfurization tower is usually used as the front-end equipment of flue gas treatment, responsible for removing SO₂ and reducing the flue gas temperature, but a large amount of "wet smoke plume" carrying gypsum slurry droplets, soluble salts (such as CaSO₄) and heavy metal ions will be generated during the desulfurization process. At this time, the wet electric demister is arranged at the outlet of the desulfurization tower, and its high-voltage electric field can be used to charge and capture droplets, effectively removing fine particulate matter (PM2.5), aerosols and heavy metals in the flue gas after desulfurization. The key to the synergy between the two is to control the flue gas velocity (usually ≤3m/s) and droplet size (≥1μm) at the outlet of the desulfurization tower, so as to avoid uneven air flow distribution in the electric demister due to excessive flow rate, or droplets with too small a particle size that are difficult to be effectively captured by the electric field. At the same time, the layout of the spray layer in the desulfurization tower needs to match the plate spacing of the electric demister. For example, using a high-efficiency demister (such as a ridge demister) as a pre-treatment can reduce large-size droplets entering the electric demister, reduce equipment load and improve fine particle capture efficiency.
The coordinated operation with the denitrification equipment needs to pay attention to the relationship between ammonia escape and fine particle generation. Taking SCR denitrification as an example, if the catalyst activity decreases or the ammonia injection amount is improperly controlled, the ammonia escape will increase (>3ppm). The escaped NH₃ is easy to react with SO₃ in the flue gas to form ammonium bisulfate (NH₄HSO₄) or ammonium sulfate [(NH₄)₂SO₄]. These substances are easy to condense into aerosols in low temperature environments and become an important source of PM2.5. The wet electric demister can effectively capture such submicron particles through charged condensation. At the same time, its wet environment can dissolve part of the gaseous NH₃, reducing the risk of corrosion of downstream equipment. In order to achieve collaborative optimization, it is necessary to set up a precise ammonia injection control algorithm in the denitrification system (such as feedforward-feedback control based on flue gas flow and NOx concentration) to control the ammonia escape at a low level. At the same time, a temperature monitoring point is set at the entrance of the electric demister to avoid the condensation of ammonium bisulfate on the plate surface due to too low flue gas temperature (such as <50℃), which affects the electric field performance.
The linkage design of the control system is the core link to achieve efficient collaboration. By establishing a multi-device data sharing platform, the pH value, liquid-gas ratio of the desulfurization tower, the ammonia escape rate and reaction temperature of the denitrification system, and the electric field voltage, current, flushing cycle and other parameters of the electrostatic demister are included in a unified monitoring system, and the operating status of each device can be adjusted in real time. For example, when the pH value of the desulfurization tower slurry decreases (indicating a decrease in desulfurization efficiency), the system automatically increases the supply of limestone slurry and simultaneously increases the operating voltage of the electrostatic demister to cope with the increase in droplet concentration caused by fluctuations in desulfurization efficiency; when the ammonia escape rate of the denitrification system is detected to be abnormal, the enhanced operating mode of the electrostatic demister (such as short-term pulse voltage increase) is immediately triggered to enhance the capture of ammonium salt aerosols. In addition, the prediction model based on machine learning can identify equipment abnormalities in advance, such as predicting the scaling trend of the electrostatic demister plate by analyzing historical data, automatically adjusting the flushing frequency, avoiding electric field failure caused by scaling, and reducing water waste.
The synergy between equipment materials and anti-corrosion design directly affects the long-term stable operation of the system. The strong acidic environment (pH=3~5) in the desulfurization tower and the wet flue gas environment in the electrostatic precipitator place strict requirements on the equipment materials. For example, the spray layer of the desulfurization tower usually uses bidirectional stainless steel (such as 2205) or glass fiber reinforced plastic (FRP), while the electrode plate and spray pipe of the electrostatic precipitator can use titanium alloy (Ti), nickel-based alloy (such as C-276) or conductive anti-corrosion coating (such as graphene modified resin) to resist the erosion of corrosive ions such as Cl⁻ and SO₄²⁻. At the process connection (such as the flue between the desulfurization tower and the electrostatic precipitator), an anti-corrosion lining (such as rubber lining) must be installed and the flow field design must be optimized to reduce local corrosion caused by flue gas retention. At the same time, the flushing water of the electrostatic precipitator needs to control the Cl⁻ concentration (usually <200ppm) to avoid the use of hard water to cause plate scaling, and the desulfurization wastewater can be used as a flushing water source after treatment to achieve water resource recycling and further improve the system's synergistic economy.
In terms of the synergistic removal of multiple pollutants, wet electric demister can form a complementary effect with desulfurization and denitrification equipment. For example, the desulfurization tower has a high removal efficiency for Hg²⁺ (oxidized mercury), but has limited removal capacity for Hg⁰ (elemental mercury), while the electrostatic demister can oxidize Hg⁰ to Hg²⁺ through the oxidant (such as ClO₂, H₂O₂) in the spray liquid, and remove it with the droplet capture; the denitrification equipment mainly targets NOx, but the electrostatic demister's dissolution and absorption of NO₂ can assist in reducing the concentration of nitrogen oxides. In addition, the droplets captured by the electrostatic demister contain a large amount of heavy metal ions (such as Pb, Cd) and soluble salts, and the subsequent wastewater treatment system can realize the resource recovery of pollutants (such as gypsum dehydration and heavy metal extraction), further improving the environmental protection benefits.
In actual applications, the flue gas characteristics of different industries are significantly different, and targeted synergistic solutions need to be designed. For example, in the flue gas treatment of sintering machine heads in the steel industry, the dust concentration of the flue gas is high and the SO₂ concentration fluctuates greatly. The combined process of "bag filter + wet desulfurization tower + wet electric demister" can be used to use the bag filter to remove coarse particles first and reduce the load of the electric demister; in the sulfuric acid device of the chemical industry, the flue gas contains a high concentration of SO₃ and is easy to form acid mist. The electric demister can be combined with a condensing heat exchanger to condense SO₃ into sulfuric acid droplets through condensation, and then efficiently capture them using the electric field. Optimizing the flue design between each device through simulation (such as CFD flow field analysis) to ensure uniform flue gas flow rate (deviation ≤±10%) and reasonable pressure loss (total pressure drop <2000Pa) is a key technical means to maximize the efficiency of coordinated operation.
The efficient coordinated operation of wet electric demister and desulfurization and denitrification equipment is essentially to build an integrated multi-pollutant treatment system through process integration, parameter coupling and system intelligent control. This process not only requires solving the problems of physical connection and functional complementarity between equipment, but also requires full chain optimization from the dimensions of material corrosion protection, data linkage, resource circulation, etc., to ultimately achieve a balance between flue gas treatment efficiency, energy consumption control and economy. With the continuous improvement of environmental protection standards, collaborative control strategies based on digital technologies (such as industrial Internet and digital twins) will become an important direction for future development, promoting industrial flue gas treatment towards intelligence and low carbonization.
