Inside the White Dilemma: The Hidden Challenge in Clean Coal Power

Introduction: The "White Dilemma" in Power Plant Environmental Protection

In the environmental protection system of coal-fired power plants, desulfurization wastewater treatment stands as a tricky "white dilemma". To control sulfur dioxide emissions, most plants adopt the limestone-gypsum wet flue gas desulfurization process, which generates wastewater with complex composition and high treatment difficulty—becoming a key bottleneck for environmental compliance and green development. This article explores the nature of this dilemma and the industrial technical paths to overcome it.

Nature of the Dilemma: Origin and Complex Composition of Desulfurization Wastewater

Desulfurization wastewater originates from the limestone-gypsum wet desulfurization process: limestone slurry reacts with flue gas sulfur dioxide to produce recyclable gypsum. During cyclic reactions, fly ash, impurities, and soluble salts accumulate in the slurry; regular discharge and solid-liquid separation yield desulfurization wastewater, dubbed the "white dilemma" for its white gypsum suspended solids.

Its complexity lies in three core challenges: 

1) High salinity, with total dissolved solids (TDS) reaching tens of thousands of mg/L; 

2) High hardness, with high calcium and magnesium ion concentrations that easily form scale and clog equipment; 

3) High toxicity, containing heavy metals (mercury, cadmium, lead, arsenic) and fluoride. These interacting pollutants make conventional treatment ineffective.

Core Treatment Path: Three-Stage Process for Dilemma Resolution

1. Pretreatment: Reducing Burden by Removing Impurities

Pretreatment focuses on removing suspended solids, heavy metals, and partial hardness via "neutralization + coagulation + sedimentation". Lime milk adjusts pH to alkaline, forming insoluble heavy metal hydroxides. Coagulants and flocculants aggregate particles for solid-liquid separation. This step fades the wastewater's "whiteness" and reduces corrosiveness.

2. Advanced Treatment: Tackling Core Salinity Issue

Advanced treatment targets residual high salinity, mainly using membrane separation and evaporation crystallization. Reverse osmosis (RO) is core for membrane separation, utilizing semi-permeable membranes to separate salt and water; ultrafiltration (UF) pre-treatment protects RO membranes. Treated water can be reused in circulating cooling systems.

Evaporation crystallization is suitable for ultra-high salinity wastewater. Heating evaporates water, leaving solid salt slag. Mechanical vapor recompression (MVR) is energy-efficient and mainstream, enabling complete salt separation and zero liquid discharge.

3. Terminal Disposal: Ensuring Compliance and Resource Utilization

Membrane separation concentrate is sent to evaporation crystallization. Solid salt slag is disposed of as hazardous waste if heavy metal-exceeding, or recycled if pure. Treated clear water is reused in production, reducing fresh water consumption.

Industry Trend: Zero Liquid Discharge and Ongoing Challenges

Zero liquid discharge (ZLD) has become mainstream, but faces challenges: high investment/operation costs, and the need to improve salt slag recycling rate. The industry is exploring new technologies, such as efficient heavy metal removers and anti-pollution membranes.

Conclusion: From Pollution Hazard to Reusable Resource

Technological advancements have made the "white dilemma" surmountable. Mature three-stage systems transform desulfurization wastewater from a hazard to a resource, promoting green and low-carbon power industry development. This progress epitomizes coordinated industrial and environmental development, with future technologies promising higher efficiency and economy.