Application of low-purity magnesium hydroxide (85%) in industrial desulfurization: the balance point between cost and efficiency
In the field of high-sulfur flue gas treatment such as thermal power and steel, the choice of desulfurizer is directly related to environmental protection and economic efficiency. Although high-purity magnesium hydroxide (≥95%) has excellent performance, its high cost makes many companies reluctant to use it. Magnesium hydroxide with a purity of 85% is opening up the market with the advantage of reducing the processing cost by 40%** per ton through process optimization and resource integration. This article will deeply analyze its technical feasibility, economic model and industrial practice, and explore the optimal solution for cost and efficiency.
1. The "counterattack" of low-purity magnesium hydroxide: from industrial by-product to desulfurization main force
1. Raw material source and cost advantage
85% purity magnesium hydroxide mainly comes from magnesite calcination by-products or seawater magnesium extraction process, and its raw material cost is only 60% of high-purity products. Take Haicheng, Liaoning as an example. Relying on rich magnesite resources, the local area produces more than 2 million tons of low-purity magnesium hydroxide annually, with a stable ex-factory price of 800-1000 yuan/ton, while the price of high-purity products is generally above 1500 yuan/ton.
2. The "double-edged sword effect" of impurity components
The impurities such as CaO (5%-8%) and SiO₂ (3%-5%) contained in low-purity products may affect the reaction activity, but can also be transformed into advantages through process design:
CaO synergistic desulfurization: CaSO₃/CaSO₄ is generated in the slurry to enhance the stability of precipitation;
SiO₂ anti-scaling: a silicate protective layer is formed on the inner wall of the pipeline, and the scaling rate is reduced by 30%.
Case measurement (a coking plant):
The use of 85% pure magnesium hydroxide to treat flue gas containing 3500mg/Nm³ of sulfur has a desulfurization efficiency of 92%, and the treatment cost per ton is only 28 yuan, which is 37% lower than the limestone method.
2. Three major process breakthroughs for efficiency improvement
1. Gradient activation modification technology
Selectively dissolve impurities through acid leaching (pH=3-4) to expose the active sites of magnesium hydroxide:
Acid concentration control: 5% dilute sulfuric acid treatment, CaO dissolution rate>90%, Mg(OH)₂ loss rate<5%;
Specific surface area improvement: After modification, the specific surface area of the material increased from 15m²/g to 80m²/g, and the SO₂ adsorption capacity increased from 0.8g/g to 1.6g/g.
Industrial verification:
After the transformation of a steel plant in Tangshan, the desulfurization efficiency increased from 85% to 93%, and the reagent consumption was reduced by 25%.
2. Multi-stage cyclone reaction tower design
In order to solve the problem of slow reaction rate of low-purity materials, the equipment structure is innovated:
Three-stage cyclone plate: gas-liquid contact time is extended from 8 seconds to 15 seconds, and mass transfer efficiency is increased by 50%;
Two-way spray system: upper countercurrent spray (atomization particle size 100μm) captures free SO₂, and lower downstream spray (particle size 300μm) strengthens liquid phase reaction.
Operation data:
In the application of a 600MW unit in a power plant, the outlet SO₂ concentration is stable below 25mg/Nm³, the liquid-gas ratio is reduced from 8L/m³ to 5L/m³, and 1.8 million kWh of electricity is saved annually.
3. Resource utilization of impurities
Convert CaSO₄ and SiO₂ in desulfurization slag into building materials:
Gypsum board production: CaSO₄ purity> 90%, directly used in gypsum board manufacturing, 20% lower cost than natural gypsum;
Microsilica powder extraction: SiO₂ is recovered through flotation process, with a purity of 98% and a selling price of over 2,000 yuan/ton.
Economic benefit calculation:
Processing 100,000 tons of SO₂/year can produce 150,000 tons of gypsum and 12,000 tons of microsilica powder as by-products, generating annual revenue of over 30 million yuan.
3. Cost and efficiency balance model
Indicator High-purity magnesium hydroxide (95%) Low-purity magnesium hydroxide (85%) Optimization range
Desulfurizer unit price 1500 yuan/ton 900 yuan/ton ↓40%
SO₂ consumption per ton 0.5 tons 0.65 tons ↑30%
Desulfurization efficiency 97% 92% ↓5%
By-product income 800 yuan/ton SO₂ 1100 yuan/ton SO₂ ↑37.5%
Comprehensive processing cost 320 yuan/ton SO₂ 190 yuan/ton SO₂ ↓41%
Key conclusion:
Although the unit consumption of low-purity products increased by 30%, its low price advantage and by-product value-added reduced the comprehensive cost by more than 40%, and still met the national ultra-low emission standards (SO₂＜35mg/Nm³).
IV. Industrialization practice: from pilot to scale
1. Application benchmark in the coking industry
A coking group in Shanxi: Using 85% pure magnesium hydroxide to treat flue gas containing 2800mg/Nm³ of sulfur, the construction cost is 25% lower than that of the limestone method, and the annual operating cost is saved by 5.4 million yuan;
Byproduct path: Desulfurization slag is used for backfilling in the mining area, reducing the cost of solid waste disposal by 80 yuan/ton.
2. Transformation of steel sintering machine
A steel plant in Handan: In the treatment of flue gas from the sintering machine head, low-purity magnesium hydroxide is used in combination with activated coke, the desulfurization efficiency reaches 94%, and the environmental protection cost per ton of steel is reduced by 18%;
Intelligent control system: By dynamically adjusting the slurry pH value (5.5-6.5) through online monitoring of SO₂ concentration, the reagent utilization rate is increased by 20%.
3. Breakthrough of small and medium-sized boilers
Zhejiang Textile Park: 20 10t/h coal-fired boilers are converted to low-purity magnesium hydroxide for desulfurization, the initial investment is reduced by 40%, and the transformation cost is recovered within 3 years.
V. Challenges and Countermeasures: Cracking the "Life and Death Line" of Low-Purity Applications
1. Impurity Fluctuation Control
Raw Material Premixing Technology: Mix different batches of low-purity magnesium hydroxide to ensure that the CaO content is stable at 6%±1%;
Real-time Monitoring System: Use XRF online analyzer to detect the raw material composition every 30 minutes and adjust the process parameters in a linked manner.
2. Equipment Corrosion Resistance Upgrade
Silicon Carbide Coating: Spray 2mm silicon carbide on the slurry circulation pump and the inner wall of the pipeline, and the acid and alkali resistance life is extended to 8 years;
Low-cost alternative: Glass fiber reinforced plastic (FRP) material replaces 316L stainless steel, reducing the cost by 50%, suitable for small and medium-sized projects.
3. Policy and Standard Adaptation
Local Standard Guidance: Hebei, Shandong and other places have issued the "Technical Specifications for Desulfurization of Low-Purity Magnesium Hydroxide", clarifying the application scenarios and process requirements;
Environmental Protection Tax Preferential: For enterprises that use industrial solid waste to prepare desulfurizers, 30% of the environmental protection tax will be exempted.
Low-purity magnesium hydroxide has successfully broken the inherent perception of "high purity = high efficiency" through process innovation and resource integration. Its large-scale application in coking, steel and other industries has proved that under the premise of meeting environmental protection standards, by optimizing reaction conditions and tapping the value of by-products, the economic goal of a ton of processing cost less than 200 yuan can be achieved. With the advancement of the "dual carbon" policy, this plan may become the first choice for small and medium-sized high-sulfur emission enterprises - after all, between survival and development, finding a balance between cost and efficiency is the pragmatic way for enterprises to achieve green transformation.