Detailed Application and Process of Plate Heat Exchangers in Milk and Dairy

Detailed Application and Process of Plate Heat Exchangers in Milk and Dairy

Plate heat exchangers (PHEs) are essential equipment in the dairy industry, widely used for pasteurization, UHT sterilization, preheating, cooling, and standardization. Their high heat transfer efficiency, hygienic design, and easy cleaning make them ideal for dairy processing.

Key Applications of KDP in Milk Processing

（1）Pasteurization：

Purpose

Eliminate pathogens (e.g., Salmonella, Listeria) and extend shelf life (7–14 days under refrigeration).

Process Flow

Preheating (Regeneration):

Cold milk (4°C) enters the regeneration section of the PHE, exchanging heat with pasteurized hot milk (72°C), warming to 50–60°C (85–90% heat recovery).

Heating:

Preheated milk moves to the heating section, where hot water (72–75°C) or steam raises it to pasteurization temperature (HTST: 72°C/15 sec; LTLT: 63°C/30 min).

Holding:

Milk flows through a holding tube to ensure proper sterilization time.

Cooling:

Pasteurized milk is first cooled by incoming cold milk (regenerative cooling), then further chilled to below 4°C using ice water.

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KDP PHE Design Considerations

Plate type

Chevron corrugation (high thermal efficiency).

Temperature control

±0.5°C accuracy to avoid protein denaturation.

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（2）UHT Sterilization (Ultra High Temperature Processing)：

Purpose

Achieve commercial sterility (ambient shelf life: 6–12 months).

Process Flow

Preheating (to 70–80°C):

Regenerative heat exchange.

High-Temperature Heating (135–150°C/2–5 sec):

Indirect heating: PHE uses pressurized hot water or steam.

Direct steam injection: Some systems combine PHE for subsequent cooling.

Flash Cooling (to 80°C):

Removes added steam moisture.

Aseptic Cooling (to 25°C):

Uses sterile chilled water in the PHE.

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KDP PHE Design Considerations

Multi-stage design:

Preheating → high-temperature heating → cooling.

Pressure resistance:

Titanium plates (for high-temperature and corrosive resistance).

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（3）Milk Standardization：

Purpose

Adjust fat content (e.g., whole milk: 3.5%; skim milk: 0.1%).

Process Flow

Preheat milk to 50–60°C (improves separation efficiency).
Separate fat via centrifugal separator.
Blend skim milk and cream to desired ratio, followed by PHE reheating/cooling.
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（4）Yogurt Processing：

KDP PHE Role

Precise temperature control during heating/cooling to protect starter cultures.

Key Steps

Milk Preheating (to 40–45°C):

Facilitates homogenization and culture inoculation.

Homogenization:

Breaks fat globules to prevent creaming.

Heat Treatment (90–95°C/5 min):

Kills contaminants for pure fermentation.

Cooling (to 43°C):

Inoculate with lactic acid bacteria.

Fermentation (42°C/4–6 hr):

Conducted in fermentation tanks.

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KDP Plate Material Selection and Hygiene Requirements

(1) Plate Materials

Milk and dairy products are mildly corrosive but contain chlorides and organic acids (e.g., lactic acid), requiring corrosion-resistant materials:

MaterialApplicationPros & Cons
316L Stainless SteelPasteurization, UHT (neutral pH milk)Cost-effective, machinable, but sensitive to high chloride levels.
Titanium (Ti)UHT high-temperature section, acidic whey processingExcellent corrosion resistance, but expensive.
HastelloyHigh-salt whey or specialty milkSuperior corrosion resistance, high cost.

(2) Gasket Materials

EPDM (Ethylene Propylene Diene Monomer)

Withstands high temperatures (≤150°C), resistant to acids/alkalis; widely used in pasteurization/UHT.

NBR (Nitrile Rubber)

Oil-resistant, suitable for high-fat products (e.g., cream, cheese).

FKM (Fluorocarbon Rubber)

Resists extreme temperatures and chemicals, ideal for aggressive CIP cleaning.

(3) Hygienic Design Standards

Surface roughness:

Ra ≤ 0.8 μm (mirror polish) to prevent microbial adhesion.

Dead-leg-free design:

Wide-gap plates or open corner ports for CIP compatibility.

Certifications:

3-A Sanitary Standards (U.S. dairy equipment).

EHEDG (European Hygienic Engineering & Design Group).

FDA (Food-contact material compliance).

Cleaning and Maintenance (CIP Systems)

Post-processing, PHEs must be thoroughly cleaned to prevent biofilm and protein fouling:

Water rinse

Removes milk residues.

Alkaline wash (1–2% NaOH, 70–80°C)

Degrades fats/proteins.

Acid wash (0.5–1% HNO₃, 60–70°C)

Dissolves mineral deposits (e.g., calcium scale).

Final water rinse

Ensures no chemical residues.

Maintenance Tips:

Daily CIP cycles; weekly gasket inspections.
Periodic disassembly to check plate fouling/corrosion.

Industry Case Studies

Tetra Pak

Uses titanium PHEs in UHT milk lines for high-temperature sterilization.

Mengniu/Yili

316L stainless steel PHEs for pasteurization and standardization.

Cheese Plants

Hastelloy PHEs for high-salt whey processing.

Conclusion

PHEs play a pivotal role in dairy processing for heating, cooling, and sterilization. Selection criteria include:

Process requirements (pasteurization, UHT, yogurt fermentation).
Material corrosion resistance (316L, titanium, Hastelloy).
Hygienic standards (3-A, EHEDG, FDA).
Cleaning protocols (CIP systems, anti-fouling design).

With optimal configuration, PHEs enhance energy efficiency, safety, and product quality in dairy production.

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