Renovation of old desulfurization towers: Key points of engineering connection for magnesium hydroxide to ｒｅｐｌａｃｅ limestone method
1. Renovation background and pain points
Traditional limestone-gypsum desulfurization systems in old power plants generally have pain points such as efficiency attenuation, high operation and maintenance costs, and difficult disposal of by-products. Taking a northern power plant as an example, after 10 years of operation, its limestone desulfurization system had problems such as desulfurization efficiency dropping below 85%, slurry circulation pump power consumption accounting for more than 20%, and gypsum purity less than 80% leading to unsalable products, which forced the demand for technology iteration. Magnesium hydroxide desulfurization technology has become the preferred solution for the renovation of old desulfurization towers due to its high reactivity, low liquid-gas ratio (only 1/3 of the limestone method) and resource-recyclable by-products.
2. Process adaptation and core transformation path
1. Reconstruction of the internal absorption tower
Spray layer optimization: ｒｅｐｌａｃｅ the original hollow cone nozzle with a titanium alloy solid cone nozzle to improve atomization uniformity and coverage. A power plant renovation case in Jiangsu Province showed that after replacing the nozzle, the desulfurization efficiency increased by 12%, and the liquid-gas ratio dropped from 8L/m³ to 4.5L/m³.
Oxidation zone renovation: The original oxidation fan and aerator were removed, and the natural oxidation of magnesium sulfite was achieved by self-circulation of the desulfurization slurry. A project in Hebei Province increased the oxidation efficiency from 75% to 92% by adding a cyclone stirring device.
Anti-corrosion upgrade: Silicon carbide-epoxy resin composite coating was applied to the tower wall to withstand the corrosion environment of pH 2-12, and the service life was extended to more than 10 years.
2. Pulping system iteration
Raw material supply switching: The limestone powder silo was transformed into a magnesium oxide ton bag storage silo, equipped with a moisture-proof and airtight device. A power plant in Liaoning Province adopted spiral conveying + ultrasonic arch breaking technology to solve the problem of moisture absorption and compaction of magnesium oxide powder.
Maturation process adjustment: A two-stage aging tank was added, and dynamic vortex stirring technology was used to stabilize the concentration of magnesium oxide slurry at 15%-20%, and the aging time was shortened to 30 minutes.
Slurry transportation optimization: ｒｅｐｌａｃｅ the original gypsum slurry pump with a plastic-lined centrifugal pump to avoid blockage caused by magnesium sulfate crystallization, and expand the flow adjustment range to 40%-100%.
3. Reshaping the by-product value chain
Magnesium sulfate purification: Introduce a nanofiltration membrane separation system to remove Cl⁻ (concentration <0.01%) in the slurry and produce battery-grade magnesium sulfate crystals. A renovation project in Shandong increased the price of by-products from 80 yuan/ton to 3,000 yuan/ton.
Zero wastewater discharge: Adopt DTRO membrane concentration + spray drying process to achieve full reuse of desulfurization wastewater, saving more than 500,000 tons of water annually.
3. Intelligent upgrade of control system
Dynamic balance algorithm: Develop a pH-liquid level linkage module based on the DCS system to adjust the magnesium hydroxide dosage and circulation pump frequency in real time. After application in a project in Tangshan, the ammonia escape concentration was stabilized below 2ppm.
Crystallization warning system: Implant a fiber optic sensor in the slurry pipeline to predict the crystallization risk through turbidity changes and automatically trigger the flushing procedure.
Energy efficiency management platform: integrates multi-dimensional data such as current, pressure, and concentration to optimize system energy consumption. After the transformation of a power plant in Zhejiang, the power consumption per ton of SO₂ removed was reduced from 18kWh to 9.6kWh.
IV. Key control points for project connection
1. Utilization of shutdown window period
Phase-based construction: use the unit maintenance period to complete the replacement of tower internals, and simultaneously build pulping and by-product workshops on the periphery. The transformation of the 350MW unit of Shajiao B Power Plant in Guangdong took only 59 days, reducing shutdown losses by more than 20 million yuan.
Modular prefabrication: prefabricate components such as spray layers and demisters in the factory, and control the on-site assembly error within ±3mm.
2. Material compatibility verification
Weld stress test: conduct a 48-hour salt spray test on the joints of the modified titanium steel composite plate to ensure that the corrosion resistance meets the standard.
Slurry adaptation experiment: simulate the slurry reaction kinetics under different SO₂ loads (800-3000mg/m³) in the laboratory to determine the optimal pH control range (6.0-6.5).
3. Smooth transition of operation mode
Dual system parallel: retain the limestone slurry pipeline as an emergency backup, and achieve seamless switching through a three-way valve.
Personnel skill transformation: carry out special training on magnesium desulfurization, focusing on mastering the key points of by-product quality control and membrane separation operation and maintenance.
V. Economic benefits and ecological value
Cost reconstruction: A 1000MW unit transformation case shows that the total investment recovery period is 4.2 years, the annual limestone procurement cost is saved by 18 million yuan, and the by-product income covers 65% of the operating cost.
Carbon emission reduction gain: The magnesium hydroxide method reduces CO₂ emissions by 42% compared with the limestone process, and generates more than 5 million yuan in annual revenue through CCER trading.
Green transformation bonus: meet ultra-low emission standards (SO₂＜35mg/m³), obtain local environmental protection subsidies and green credit support.
VI. Future evolution direction
Hydrogen energy coupling: explore magnesium sulfate electrolysis hydrogen production technology, a pilot project has achieved 62m³ green hydrogen by-product per ton of magnesium sulfate.
Digital twin operation and maintenance: build a three-dimensional model of the desulfurization tower, simulate scaling, corrosion and other faults in real time, and the early warning accuracy rate reaches 92%.
Regional circulation network: connect power plant by-products to salt lake magnesium extraction, desert agriculture and other industries to form a "desulfurization-resource-ecology" closed loop.
When the old limestone desulfurization tower is injected with the technical gene of magnesium hydroxide, an industrial leap from "calcium-based shackles" to "magnesium-based circulation" has been launched. From the titanium alloy flash of the spray layer to the digital large screen in the control room, from unsalable gypsum to high-purity magnesium sulfate, this transformation is not only a replacement of equipment, but also a reconstruction of the energy value chain. Under the pressure of the "dual carbon" goals, only by breaking through with technological innovation and weaving a network with ecological thinking can a new paradigm of green transformation grow within the texture of old facilities.