Gas Treatment——Ammonia Condensation Chlorine Cooling

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Gas Treatment ——Ammonia Condensation, Chlorine Cooling

Application Examples:

Ammonia synthesis (NH₃)
Chlor-alkali industry (Cl₂ cooling)
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Process Role

Ammonia condensation

Converting gaseous ammonia into liquid ammonia (below -33°C).

Chlorine cooling

Lowering the temperature of hot chlorine gas from electrolysis (preventing equipment corrosion).

KDP PHE Selection

Low-temperature suitability:

Special sealing materials (e.g., fluororubber).

Corrosion resistance:

Titanium (resistant to wet chlorine corrosion).

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Detailed Process of KDP Plate Heat Exchangers in Ammonia Condensation

and Chlorine Cooling

Plate heat exchangers are widely used in ammonia condensation and chlorine cooling, two critical processes in the chemical industry. However, due to the differing properties of ammonia and chlorine (e.g., corrosivity, toxicity, phase-change behavior), their process flows and design requirements vary significantly. Below is a detailed breakdown:

1. Ammonia Condensation -Ammonia Synthesis or Refrigeration Systems

Process Flow

Hot gas ammonia inlet:

High-temperature gaseous ammonia (70–120°C, 1–2 MPa) from the synthesis reactor or compressor enters the PHE’s gas channel.

If lubricants or impurities are present, a oil separator is used for pretreatment.

Coolant circulation:

Cooling water (or chilled water) flows countercurrently on the opposite side (typically 20–30°C, depending on cooling tower capacity).

Turbulent flow enhances heat transfer.

Condensation phase change:

Ammonia gas releases latent heat on the plate surface, condensing into liquid ammonia (saturation temperature depends on pressure).

Condensate collects at the bottom outlet and flows to an ammonia storage tank or evaporator (in refrigeration systems).

Non-condensable gas handling:

If gases (e.g., H₂, N₂) are present, a vent valve or purge system is installed at the PHE’s top.

Key Design Parameters

Materials:

Plates: 304/316 stainless steel (resists ammonia but must avoid chloride stress corrosion).

Gaskets: EPDM or NBR (resistant to ammonia swelling).

Plate type:

High-NTU (Number of Transfer Units) plates (e.g., herringbone pattern) for efficient condensation.

Pressure drop control:

Wide gas channels prevent condensate accumulation and excessive pressure drop.

2. Chlorine Cooling -Chlor-Alkali Industry or Chlorine Processing

Process Flow

Hot wet chlorine inlet:

Wet chlorine gas (80–100°C, containing traces of HCl and moisture) from electrolysis enters the PHE.

Pre-drying:

Sulfuric acid scrubbers remove moisture to prevent hydrochloric acid formation.

Primary cooling (indirect heat exchange):

Chlorine passes through titanium or graphite PHEs, cooled to 40–50°C by water.

Safety:

Maintain slight positive pressure (0.1–0.3 MPa) to avoid air ingress (explosive mixtures).

Secondary deep cooling (optional):

For liquefaction, brine (-15 to -10°C) further cools chlorine to below -10°C, partially liquefying it.

Gas-liquid mixture enters a separator; liquid chlorine is stored, while uncondensed gas is recycled.

Emergency handling:

Chlorine leak detectors and NaOH scrubbers neutralize accidental releases.

Key Design Parameters

Materials:

Plates: Titanium or titanium-palladium alloy (resists wet chlorine; stainless steel is prohibited).

Gaskets: PTFE or fluoropolymer (Viton).

Fouling prevention:

Wide-gap plates or chemical cleaning if chlorine contains particulates (e.g., salt mist).

Temperature control:

Coolant outlet temperature must stay above chlorine’s dew point to avoid HCl condensation.

Comparison Summary

ParameterAmmonia CondensationChlorine Cooling
Primary mediumNH3 (gas → liquid)Cl₂ (gas - liquid, optional)
Temperature70-120°C→25-40°C80°C→ -10°C (liquefaction)
PressureMedium (1-2 MPa)Slightly positive (leak prevention)
Materials304/316 SS + EPDM gasketsTitanium + PTFE gaskets
HazardsFlammable, toxicHighly toxic, corrosive
Special designNon-condensable ventingHCI condensation prevention, scrubbers