High-Concentration Brine Evaporator for Coal Chemical Industry

The high-concentration brine evaporator for coal chemical industry is a core piece of equipment for treating high-salt wastewater generated in processes such as coal-to-gas, coal-to-oil, and coal-to-olefins. It is mainly used for zero wastewater discharge (ZLD) and resource recovery. Here is a summary of the key technical points:

I. Application Scenarios and Water Quality Characteristics

Typical Water Quality Indicators:

TDS (Total Dissolved Solids): 60,000-120,000 mg/L (i.e., 6-12%)

Cl⁻ Concentration: >30,000 mg/L (highly corrosive)

COD: <500 mg/L (requires pretreatment)

Salt Components: Mainly NaCl, Na₂SO₄, small amounts of Ca²⁺, Mg²⁺, and trace heavy metals

Treatment Challenges: High salinity, high corrosivity, easy scaling, organic matter interfering with crystallization

II. Mainstream Technology Types

1. Multi-Effect Evaporator (MED)

Configuration: Five-effect counter-current evaporator is the most common, increasing steam utilization by 50%

Steam Consumption per Ton of Water: 0.25-0.35t (60% energy saving compared to traditional processes)

Evaporation Temperature: First effect 110- 120℃, final effect 45-50℃ (vacuum operation)

2. MVR (Mechanical Vapor Recompression) Evaporator

Percentage: Penetration rate in the coal chemical industry reached 35% by 2025

Energy Consumption: 15-18 kWh of electricity consumed per ton of water treated, energy consumption reduced by 50%-70% compared to traditional processes

Water Production Ratio: 1 kg of steam can evaporate 6 kg of water (with heat pump technology)

3. Combined Process

Nanofiltration Salt Separation + Evaporation Crystallization:

Principle: Nanofiltration membrane selectively retains divalent salts (Na₂SO₄), producing water mainly composed of NaCl, achieving salt separation.

Effect: Sodium chloride and sodium sulfate purity >99%, impurity salt rate <5%, hazardous waste disposal cost reduced by 70%

Crystallized Salt Production: 0.8-1.2 t/m³ wastewater

III. Core Process Features

1. Anti-scaling Design

Tube-type Falling Film Evaporator: Combined with online cleaning system 1. System, Continuous Operation Cycle > 2000 hours

Pretreatment: Ozone catalytic oxidation removes COD, preventing organic matter from interfering with crystallization.

Material Selection: Heat exchange tubes are made of titanium or duplex stainless steel; equipment lifespan > 10 years.

2. Energy Cascade Utilization

Secondary Steam Recirculation: Utilizing heat pump technology to compress and reuse the secondary steam from the final effect, achieving heat energy recycling.

Condensate Recovery: Over 90% of the water can be reused in the production system.

3. Intelligent Control

PLC/DCS System: Real-time monitoring of parameters such as temperature, pressure, liquid level, and concentration; automatic adjustment of steam and feed rates.

Anti-clogging Warning: Monitoring scaling conditions through differential pressure to trigger the cleaning program.

IV. Typical Cases

Case 1: A Million-Ton Coal-to-Olefins Project

Scale: 80 m³/h (10,800 m³/d)

Inlet Water: TDS 85,000 m³ g/L, Cl⁻42,000mg/L

Process: HERO concentration + ozone oxidation + TVR evaporation + freeze/hot melt crystallization

Results: Annual wastewater reduction of 690,000 m³

Recovery of 98,000 tons/year of industrial salt (NaCl purity 98.8-99.2%, Na₂SO₄ purity 99.5-99.7%)

Operating cost reduced to 12 yuan/m³

Case 2: Sodium chloride wastewater from a coal chemical plant

Process: Triple-effect vacuum forced circulation evaporation crystallization

Features: Utilizes heat pump technology to recycle secondary steam, achieving energy cascade utilization

Results: Crystallized salt is sold as an industrial raw material, achieving "zero emissions"

V. Selection Recommendations

Preferred: For large-scale projects such as coal-to-olefins and coal-to-gas, it is recommended to adopt a nanofiltration salt separation + MVR evaporation crystallization combination process to achieve salt resource utilization and achieve the best overall benefits.