Advanced Treatment Technology for Zero Discharge of Desulfurization Wastewater Zero

discharge of desulfurization wastewater is a key step in achieving "full reuse and zero discharge" of wastewater from coal-fired power plants. The core of this process lies in converting the wastewater into reusable water and solid crystalline salts through two main steps: concentration and solidification. Currently, the mainstream processes fall into two main categories: flue gas waste heat utilization and evaporation crystallization.

I. Characteristics of Desulfurization Wastewater

Typical Water Quality Indicators:

Suspended Solids: 10,000-30,000 mg/L (including gypsum particles and ash)

TDS: 30,000-60,000 mg/L

Cl⁻: 8,000-20,000 mg/L (highly corrosive)

Heavy Metals: Trace amounts of Hg, Cd, Pb, As, etc.

COD: <500 mg/L

Treatment Challenges: High suspended solids easily cause clogging; high chloride ion concentration causes strong corrosion; high hardness easily leads to scaling; large fluctuations in water quality.

II. Mainstream Process Routes

Route 1: Flue Gas Waste Heat Evaporation Process (Low investment, low energy consumption)

1. Low-Temperature Flue Gas Concentrator + High-Temperature Flue Gas Bypass Evaporation

Latest Engineering Application in 2026: This process was adopted in the retrofitting of Units 3 and 4 of China Coal Energy Xinjiang Coal Power Chemical Co., Ltd.

Process Flow:

Concentration Section: Low-temperature flue gas at 120-150℃ is drawn from before the air preheater and comes into countercurrent contact with wastewater in the concentration tower, achieving a water evaporation concentration rate of 70-80%.

Consolidation Section: The concentrated liquid is atomized by a high-temperature flue gas (300-350℃) bypass evaporator and instantly dried into a powdery solid.

Product: Mixed salt with a moisture content of <5%, which is collected in an electrostatic precipitator along with the flue gas.

Technical Advantages:

No external heating source required; fully utilizes waste heat from the flue gas, resulting in extremely low operating costs.

Simple system with no rotating equipment, ensuring high reliability.

Miscellaneous salts mixed into fly ash do not affect the comprehensive utilization of ash and slag.

2. Rotary Spray Drying Process

Process: Wastewater is sprayed into 50-100μm droplets by a rotary atomizer, mixed with high-temperature flue gas, and the water evaporates instantly, while salts are dried and precipitated.

Features: Simple process, low investment, but requires high-performance atomizers; suitable for small water volumes <10m³/h.

Route Two: Evaporation Crystallization Process (High Resource Utilization)

MVR/Multi-Effect Evaporation + Salt Separation Crystallization

Suitable for: Water volume >20m³/h, projects with high salt resource value.

Process Chain:

1. Pretreatment: Coagulation and clarification to remove suspended solids, softening and hardening (addition of Na₂CO₃, NaOH)

2. Concentration: MVR or multi-effect evaporation concentrates wastewater to TDS 200,000-250,000mg/L

3. Salt Separation: Nanofiltration membrane separates monovalent/divalent salts.

4. Crystallization: NaCl and Na₂SO₄ product salts are produced by cooling/hot melting crystallization respectively.

Technical Parameters:

Water and Electricity Consumption per Ton: MVR process 15-18kWh (Multi-effect process steam consumption 0.25-0.35t)

Salt Purity: NaCl≥98.5%, Na₂SO₄≥99%

Impurity: <5%

III. Latest Engineering Example

Xinjiang Coal Chemical Energy Plant Project:

Scale: Zero-discharge retrofit of desulfurization wastewater for 2×660MW units

Process: Low-temperature flue gas concentration tower + high-temperature flue gas bypass evaporation

Treatment Capacity: 15m³/h

Emissions: Salt content in fly ash <3%, meeting building material utilization standards

Estimated Commissioning Time: 2026-2027

IV. Technological Development Trends

1. Prioritization of Flue Gas Waste Heat: New units generally reserve flue gas interfaces, and evaporation processes are standard.

2. Intelligent Operation and Maintenance: AI predicts scaling and atomizer wear, automatically adjusting smoke temperature and liquid-to-gas ratio.

3. Coupled Process: Smoke gas concentration + MVR crystallization, balancing low cost and resource utilization.