Inorganic Wastewater Treatment——Neutralization Heat Recovery

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Inorganic Wastewater Treatment —— Neutralization Heat Recovery

Application Examples:

Acid/alkali wastewater neutralization
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Process Role:

Recovering reaction heat from acid/alkali neutralization to preheat feed liquids.

Example: H₂SO₄ + NaOH → Na₂SO₄ + H₂O (exothermic reaction).

KDP PHE Selection:

Anti-fouling design:

Detachable plates for periodic cleaning (scaling/sediment removal).

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Application and Plate Design of KDP Plate Heat Exchangers in Wastewater Treatment: A Detailed Explanation

Plate heat exchangers (PHEs) are widely used in wastewater treatment for heat recovery, high-temperature processing, evaporation, and concentration. Their compact design and high heat transfer efficiency significantly reduce energy consumption. However, due to the complex composition of wastewater (e.g., corrosive substances, suspended solids, and scaling agents), plate materials and system designs must be carefully selected. Below is a detailed analysis.

1. Key Applications in Wastewater Treatment

Waste Heat Recovery

Process Applications:

Recover heat from high-temperature wastewater (e.g., industrial cooling discharge, steam condensate) to preheat clean water or other process fluids.

Typical Cases:

Acidic wastewater (60–80°C) from electroplating plants preheats fresh rinse water, saving over 30% energy.

Preheating black liquor before evaporation in paper mills.

Design Considerations:

Use wide-gap plate designs (e.g., free-flow plates) to prevent clogging by suspended solids.

Prefer corrosion-resistant materials (e.g., titanium, graphite) for acidic wastewater.

2. Thermophilic Anaerobic Digestion

Process Applications:

In sludge digestion, PHEs heat sludge to 50–55°C to accelerate organic decomposition while recovering heat from digested sludge.

Challenges:

Sludge contains solid particles (1–5%) that can deposit between plates.

Hydrogen sulfide (H₂S) and ammonia (NH₃) cause corrosion.

Solutions:

Use detachable PHEs for easy mechanical cleaning.

Select titanium or duplex stainless steel plates (resistant to H₂S).

3. Evaporation & Concentration

Process Applications:

In zero liquid discharge (ZLD) systems, PHEs preheat high-salinity wastewater (e.g., RO brine) before evaporation.

Example:

Coal chemical wastewater exchanges heat with steam in PHEs to improve evaporation efficiency.

Design Considerations:

Anti-scaling measures:PTFE-coated plates or graphite materials.

High-pressure tolerance: Welded PHEs (no gaskets) for steam heating.

4. Temperature Control in Chemical Neutralization

Process Applications:

PHEs regulate temperature (e.g., 25–40°C) during acid/alkali neutralization reactions.

Example:

Heat removal during HCl wastewater neutralization with NaOH.

Plate Material and Design for Wastewater Applications

(1) Plate Material Selection

Wastewater composition varies; material selection depends on corrosivity, suspended solids, temperature, and pressure:

MaterialApplicationsPros & Cons
316L Stainless SteelLow-Cl⁻, neutral-pH wastewater (e.g., municipal sewage)Cost-effective but prone to chloride corrosion.
Titanium (Ti)High-Cl⁻, acidic wastewater (e.g., electroplating effluent, brine)Excellent corrosion resistance; expensive.
Hastelloy C-276Strong acids (H₂SO₄, HCl), H₂S-containing wastewaterSuperior corrosion resistance; very costly.
Graphite CompositeHF or high-salinity wastewaterHF-resistant but brittle; low-pressure only.
254 SMO StainlessHigh-Cl⁻ wastewater (e.g., seawater pretreatment)More cost-effective than titanium but less versatile.

(2) Plate Geometry Design

Wide-Gap Plates

Flow channel spacing ≥5 mm for fibrous or particulate-laden wastewater (e.g., pulp/paper effluent).

Welded PHEs:

Gasket-free, withstands high pressure (≤40 bar) and corrosive gases (e.g., Cl₂, H₂S).

Detachable PHEs:

Allow mechanical cleaning but require periodic gasket replacement (EPDM or FKM).

(3) Surface Treatments

Electropolishing:

Reduces surface roughness (Ra≤0.5 μm) to minimize fouling.

PTFE Coating:

For scaling-prone wastewater (e.g., hard water with Ca²⁺/Mg²⁺).

Challenges and Solutions in Wastewater Treatment

(1) Fouling

Common Deposits:

Calcium carbonate, silicates, organic biofilms.

Solutions:

CIP (Clean-in-Place): Regular acid (HNO₃) or alkali (NaOH) cleaning.

Pulsed Electric Field: Inhibits scale crystallization.

(2) Corrosion

High-Risk Factors:

Chlorides (Cl⁻), H₂S, NH₃, low pH (<2).

Mitigation:

Avoid 316L stainless steel if Cl⁻ >200 ppm.

Use titanium for Cl⁻ or H₂S environments.

(3) Blockage

Prevention:

Install pre-filters (100–500 μm mesh).

Opt for single-pass flow designs (reduces port clogging).

Industry Case Studies

Electroplating Wastewater

Titanium PHEs recover heat from 60°C acidic effluent to preheat plating baths.

Landfill Leachate

Welded PHEs heat concentrate before evaporation (resists NH₃/organic acids).

Petrochemical Wastewater

254 SMO PHEs handle oily, high-salinity streams.

KDP Selection and Maintenance Guidelines

Selection Process:

Analyze wastewater (pH, Cl⁻, solids content).
Define temperature/pressure needs (e.g., evaporation requires high-pressure PHEs).
Choose materials (titanium for corrosion; wide gaps for solids).

Maintenance:

Monitor daily pressure drops (indicates fouling/blockage).
Monthly mechanical (detachable) or chemical (welded) cleaning.

Conclusion

PHEs enhance wastewater treatment efficiency via heat recovery, thermal processing, and evaporation, but designs must adapt to wastewater properties:

Materials

Titanium, Hastelloy, or 254 SMO for corrosion resistance.

Structures

Wide-gap or welded designs for solids/high-pressure tolerance.

Maintenance

Combine CIP and mechanical cleaning.

Properly selected PHEs can reduce treatment costs by >30% while extending equipment lifespan.

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