Application of Plate Heat Exchangers in Fertilizer Production

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Application of Plate Heat Exchangers in Fertilizer Production

Plate heat exchangers (PHEs) are widely used in fertilizer production (e.g., urea, compound fertilizers, ammonium phosphate) for processes such as high-temperature reactions, concentration, cooling, and exhaust gas recovery. Their advantages—high heat transfer efficiency, compact design, and easy maintenance—make them ideal for critical stages in fertilizer manufacturing.

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Typical Applications of KDP PHEs in Fertilizer Production

Cooling of Ammonium Carbamate Solution in Urea Production

Process Background:

In urea synthesis, high-pressure ammonium carbamate solution (containing NH₃, CO₂, and H₂O) must be rapidly cooled from ~180°C to ~90°C to prevent thermal decomposition.

Role of PHE:

Multi-stage cooling: Pre-cooling with low-temperature carbamate solution followed by deep cooling with chilled water.

High heat transfer efficiency required: Large temperature difference (ΔT≈90°C) and high pressure (≥4 MPa).

Example:

A urea plant uses 316L stainless steel PHEs with 0.7mm plate thickness and a design pressure of 4.5 MPa, achieving a cooling capacity of 2000 kW.

Phosphoric Acid Concentration (Wet Process)

Process Background:

Dilute phosphoric acid (~30% P₂O₅) is concentrated to ~50% P₂O₅. PHEs replace shell-and-tube exchangers to reduce scaling.

Role of PHE:

Falling film evaporation: Phosphoric acid forms a thin film on plate surfaces, heated by steam at ~120°C.

Anti-scaling design: Wide-gap plates minimize clogging.

Example:

A phosphate fertilizer plant uses graphite-modified polypropylene (PP) PHEs (resistant to HF corrosion), extending service life by 3× compared to stainless steel.

Exhaust Gas Recovery in Compound Fertilizer Granulation

Process Background:

Granulation exhaust gases (containing NH₃ and dust at ~80°C) require ammonia recovery and dust removal.

Role of PHE:

Integrated condensation and scrubbing: Exhaust gas contacts chilled water in the PHE, dissolving ammonia into aqueous ammonia.

Corrosion resistance: Trace HF and SO₂ in the gas stream.

Example:

Titanium (Gr.1) PHEs with 6mm plate spacing and spray systems achieve >95% ammonia recovery.

Cooling of Ammonium Nitrate Solution

Process Background:

Ammonium nitrate solution (~80°C) must be cooled to ~30°C to prevent explosive crystallization.

Role of PHE:

Precision cooling with small ΔT: Uses chilled water (ΔT≤5°C).

Explosion-proof design: Fully welded PHEs eliminate gasket leakage risks.

Example:

An ammonium nitrate plant uses 254SMO stainless steel fully welded PHEs, resistant to nitric acid corrosion and ATEX-certified.

Key Factors in Plate Selection

Material Selection (Based on Medium Characteristics)

Medium/ConditionRecommended MaterialReason
Urea ammonium carbamate (high pressure, Cl⁻)316L stainless steelResists chloride stress corrosion
Wet-process phosphoric acid (HF, H₂SO₄)Hastelloy C-276/graphite-PPResists HF and sulfuric acid
Ammonium nitrate (oxidizing acid)254SMO stainless steelHigh molybdenum content, nitric acid resistance
Ammonia condensation (trace HF)Titanium (Gr.1/Gr.2)Halide corrosion resistance, lightweight
Compound fertilizer exhaust (high dust)2205 duplex stainless steelWear + chloride corrosion resistance

Plate Design

High viscosity/solid-containing media (e.g., phosphoric acid slurry):

Wide-gap plates ( ≥6mm flow channels) to prevent clogging.

High-pressure applications (e.g., urea synthesis):

Thickened plates (0.6–1.0mm), laser-welded for reinforcement.

Fouling-prone applications:

Detachable PHEs (for mechanical cleaning), polished surfaces (Ra≤0.5μm).

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Sealing and Construction

Gasket selection:

EPDM: For weak acids/alkalis (e.g., ammonia water) below 80°C.

FPM (Viton): For strong acids (HF, HNO₃).

Fully welded construction: For high-pressure/hazardous media (e.g., ammonium nitrate).

KDP Case Studies

Case 1: Concentration Stage in Diammonium Phosphate (DAP) Production

Issue:

Traditional shell-and-tube exchangers scaled heavily, requiring biweekly shutdowns.

Solution:

Titanium plate falling-film evaporator with palladium-coated plates (prevents hydrogen embrittlement).

Design parameters: 120°C, 0.3 MPa, 30% higher concentration efficiency.

Result:

Cleaning intervals extended to 3 months, 15% energy savings.

Case 2: Ammonia Recovery from Compound Fertilizer Exhaust

Original process:

Packed tower absorption, 70% ammonia recovery.

Upgrade:

Titanium PHE + spray system for direct gas-liquid heat exchange.

Plate design: Herringbone corrugation (enhanced turbulence).

Result:

>95% ammonia recovery, compliant emissions.

KDP Maintenance and Optimization

Anti-fouling measures:

Regular CIP cleaning (e.g., 5% HNO₃ for phosphoric acid).

Online ultrasonic descaling (for high solids content).

Corrosion monitoring:

Periodic pitting checks (critical in HF environments).

Safety design:

Ammonium nitrate PHEs must comply with API 521 explosion-proof standards.

Conclusion

Key considerations for PHE selection in fertilizer production:

Corrosivity (material choice depends on HF, H₃PO₄, NH₃, etc.).

Fouling risk (wide-gap plates + removable designs).

Pressure rating (reinforced plates for high-pressure urea stages).

Optimal selection improves energy efficiency and reduces maintenance costs.

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