The latest "Emission Standards for Air Pollutants from Coal-fired Power Plants" has technical requirements for magnesium hydroxide desulfurization
I. Emission limits and system design logic
The "Emission Standards for Air Pollutants from Coal-fired Power Plants" (GB13223-2025) implemented in 2025 tightens the sulfur dioxide emission concentration limit to 20mg/Nm³ (key areas) and 35mg/Nm³ (non-key areas), which is more than 50% higher than the 2011 version of the standard5. This adjustment forces magnesium hydroxide desulfurization technology to transform from traditional extensive mode to refined and efficient mode. Taking a power plant in Liaoning as an example, under the condition of inlet SO₂ concentration of 1500mg/Nm³, it is necessary to achieve desulfurization efficiency ≥98.5% by optimizing slurry circulation volume (liquid-gas ratio ≥8L/m³) and improving magnesium oxide activity (H2O reaction rate ≥0.8g/s) and other technical means to meet the requirements of the new standard4.
The new standard also strengthens the control of by-products: magnesium sulfate crystal products must meet the indicators of MgO residue ≤3%, heavy metal leaching concentration ≤1mg/L, etc., promoting magnesium desulfurization from "end-of-pipe treatment" to "resource recycling" mode48.
2. Mandatory specifications for corrosion protection of slurry pipelines
Magnesium desulfurization slurry pipelines must withstand three corrosion threats: Cl⁻ electrochemical corrosion (concentration>20000ppm), particulate wear (solid content 20%-30%), and magnesium sulfate crystal expansion stress. The new standard includes the corrosion resistance of pipeline materials into mandatory clauses for the first time:
Main slurry delivery pipeline:
When the solid content is greater than 25% or Cl⁻ is greater than 30000ppm, silicon carbide coated glass fiber reinforced plastic pipes (surface hardness ≥ 2200HV) or super duplex steel 2507 (PREN value > 40) shall be mandatory;
Interlocking ceramic patches (Al₂O₃ content ≥ 95%) shall be installed at vulnerable parts such as elbows and reducers, and the wear rate shall be ≤ 0.1mm/year86.
Agent addition pipeline:
Within the pH fluctuation range of magnesium hydroxide slurry (5.5-6.5), it is recommended to use β-crystalline modified polypropylene pipes (temperature resistance ≥ 95℃), and flange connections shall be fully covered with butyl rubber lining to prevent crevice corrosion7.
A coastal power plant renovation case shows that after using silicon carbide coated pipelines, the annual corrosion rate dropped from 1.2mm to 0.05mm, and the maintenance cycle was extended from 8 months to 5 years8.
3. Technical upgrade of the core modules of the process package
To meet the requirements of the new standard, the magnesium hydroxide desulfurization system needs to integrate four major innovative modules:
1. Preparation of high-activity magnesium oxide
The segmented temperature-controlled calcination process (850℃ pre-calcination + 1200℃ activation) is adopted to increase the specific surface area of magnesium oxide from 15m²/g to 45m²/g, and the hydration reaction rate is increased by 3 times;
Nano-scale calcium aluminate is added as a crystal nucleus inducer, and the slurry supersaturation is reduced from 1.15 to 1.05, suppressing the risk of pipeline crystallization blockage4.
2. Intelligent oxidation control
Equipped with an online pH/ORP sensor, the aeration volume (0.6-1.2m³/min·m³ slurry) is adjusted in real time, and the magnesium sulfite oxidation rate is stable ≥98%;
Introducing ozone synergistic oxidation technology, under the condition of Cl⁻＞50000ppm, the oxidation efficiency fluctuation range is narrowed from ±10% to ±2%39.
3. Utilization of thermal energy gradient
Using flue gas waste heat (140-160℃) to drive the four-effect countercurrent evaporator, the steam consumption of magnesium sulfate crystallization is reduced from 1.5t/t product to 0.8t/t;
The final effect mother liquor (45-50℃) is reused for desulfurization tower water replenishment, and the annual water saving rate reaches 30%210.
4. Digital operation and maintenance system
Based on the digital twin model to simulate the flow field distribution in the tower, dynamically optimize the spray layer opening and circulation pump frequency, the measured energy consumption of a certain project of Beijing Energy is reduced by 18%;
The blockchain traceability system realizes the carbon footprint tracking of the entire life cycle from magnesium oxide raw materials to magnesium sulfate products, meeting the EU CBAM carbon tariff requirements54.
IV. Hard indicators for resource utilization of by-products
The new standard clearly requires that magnesium sulfate products must meet the national standard for magnesium sulfate for agricultural use (GB/T 26521-2024):
Main component (MgSO₄·7H₂O) ≥99.2%;
Water insoluble matter ≤0.5%;
Heavy metals (in terms of Pb) ≤10mg/kg.
To achieve this goal, it is necessary to adopt:
Nanofiltration-melt crystallization co-production process: impurity ions are intercepted by a 200nm pore size nanofiltration membrane, combined with gradient cooling crystallization (50℃→30℃), the product purity is increased from 95% to 99.5%38;
Biological-based scale inhibitor: polysaccharides extracted from seaweed ｒｅｐｌａｃｅ traditional chemical scale inhibitors, prevent evaporator scaling, and avoid the introduction of exogenous heavy metals10.
A steel plant transformation case in Tangshan shows that after adopting the above process, the added value of magnesium sulfate products increased by 40%, and the annual resource utilization income exceeded 50 million yuan4.
V. New provisions for supervision and acceptance
Online monitoring enhancement:
CEMS system needs to add Mg²+ concentration monitoring module, and data should be uploaded to the platform of the Ministry of Ecology and Environment in real time;
The error range of slurry density meter is tightened from ±5% to ±2%, and third-party calibration is mandatory every quarter27.
Full life cycle assessment:
A carbon footprint report is required for project acceptance, covering equipment manufacturing, reagent transportation, power consumption and other links, and carbon emissions per ton of SO₂ treatment shall not exceed 80kg510;
The pipeline material needs to provide a 10-year corrosion resistance guarantee, the peeling strength of the rubber lining layer is ≥8N/mm, and the ceramic patch shedding rate is ≤1%/year68.
When the "tightening curse" of the new standard collides fiercely with the "technical evolution" of magnesium hydroxide desulfurization, this change has gone beyond simple environmental compliance and evolved into a system revolution covering material science, thermodynamic optimization and digital twins. From the high-activity magnesium oxide calcining furnace in Liaoning to the intelligent crystallization workshop in Tangshan, every gram of magnesium sulfate that meets the standards interprets the deep logic of the "dual carbon" goals - only by using technological innovation as a spear and system integration as a shield can we find the optimal solution for high-quality development on the balance between environmental protection and efficiency.