Pasteurizer

Section 01

Scope and Design Intent

This note presents a practical engineering description and calculation basis for a milk pasteurization system using a Tetra Therm Lacta / plate heat exchanger pasteurizer concept, supported by retrieved technical file content.

The design philosophy is based on:

Indirect heating and cooling in heat exchangers.
Use of hot water as the heating medium.
A holding tube / holding cell sized for a defined holding time at a defined flow rate.
Supporting utilities including steam, hot water, cooling water, chilled water / ice water, and CIP supply/return.

Technical reference: This article is informed by established dairy processing principles, including indirect heating and cooling through heat exchangers, hot water as a heating medium, plate heat exchanger separation principles, flow-rate-dependent holding time, and the use of external holding tubes in modern pasteurization systems. Reference: Dairy Processing Handbook, Tetra Pak, pp. 84–86 and 91.

HOMO PROD. IN CIP PR CIP R STEAM CW LYE ACID

The process symbols and equipment references used in this article are presented for engineering clarity and should be reviewed together with the project P&ID, equipment datasheets, and applicable hygienic design requirements.

Section 01-1

Pasteurizer Diagram

Pasteurizer process flow and P&id drawing

Pasteurizer P&id Drawing

Section 02

Product Flow

2.1 General Process Path

A typical milk pasteurizer flow path can be described as follows:

Product inlet

Feed / balance section

Regeneration section of plate heat exchanger

Heating section

Homogenizer, if arranged in this process position

Holding tube

Flow diversion / safety section

Regeneration cooling

Final cooling section

Outlet to downstream process or storage

Important note: The exact sequence of every internal component in the drawing could not be fully reconstructed from the text layer alone. However, the file-backed evidence confirms the presence of product inlet, homogenizer, steam utility, cooling utility, and CIP circuits.

2.2 Functional Sequence

The milk enters the pasteurizer at a relatively low temperature and is first preheated through regeneration, where outgoing hot pasteurized milk transfers heat to incoming cold milk. This reduces steam consumption.

The milk is then brought to final pasteurization temperature in the heating section, using a hot-water circuit on the utility side of the plate heat exchanger.

After reaching the target temperature, the product flows through the holding tube, where it remains for the required minimum residence time.

After the holding period, the product continues through the regeneration and final cooling sections, where it is cooled to the required discharge temperature.

Section 03

Thermal Concept

3.1 Indirect Heating Principle

The correct heating philosophy is:

Steam→ Hot Water Unit→ Hot Water Loop→ Plate Heat Exchanger→ Milk

This means the milk is not directly heated by steam. Instead, steam heats a closed hot-water circuit, hot water flows through the heating side of the plate heat exchanger, milk flows through adjacent channels, and heat passes through the plate wall into the milk.

File-backed basis: “Hot water is used as the heating medium”, “Milk is heated by a heating medium such as low-pressure steam ... or hot water”, “In this method a partition is placed between the product and the heating or cooling medium”, and “In a plate heat exchanger the plate is the partition”.
Source: Dairy processing handbook - Tetra pack.pdf, pages 84–86.

3.2 Engineering Advantages

✓

No Direct Steam Contact

Milk is heated indirectly through plates, not by direct steam injection.

°C

Stable Temperature Control

The hot-water loop gives smoother and more controllable thermal behavior.

Lower Scorching Risk

The system reduces local overheating, fouling, cooked flavor and burning risk.

Section 04

Hot Water Unit

4.1 Function

The hot water unit acts as the thermal interface between the steam system and the product heating section.

Its role is to:

Receive heat from steam.
Transfer that heat to circulating water.
Maintain a stable hot-water supply temperature.
Feed the heating section of the plate heat exchanger.

4.2 Process Logic

The hot-water set generally includes:

Steam Control Valve

Controls the energy input from steam into the hot-water system.

Hot-Water Circulation Pump

Maintains circulation through the heating section of the pasteurizer.

Water Heater / Heat Exchanger

Transfers heat from steam to the closed or controlled water loop.

Temperature & Safety Devices

Includes temperature sensors, control loop, pressure and temperature protection.

4.3 Design Rationale

The use of hot water instead of direct steam-to-product heating is essential in dairy service because milk is sensitive to:

Protein denaturation.
Fouling.
Cooked flavor development.
Hot-spot damage.

Design objective: steam-to-water heat transfer first, followed by water-to-milk heat transfer.

Section 05

Holding Tube Sizing

5.1 Design Principle

The holding tube is designed to ensure that all product passing through the pasteurizer remains at or above the target pasteurization temperature for the required holding time.

File-backed basis: “Accurate control of the flow rate is essential because the holding equipment is dimensioned for a specified holding time at a given flow rate”, “The holding time changes in inverse proportion to the flow rate in the holding cell”, and “External holding cells are used almost exclusively nowadays”.
Source: Dairy processing handbook - Tetra pack.pdf, page 91.

5.2 Engineering Variables

The holding tube length depends on:

Required holding time.
Product flow rate.
Internal diameter of the tube.

5.3 Basic Formula

L = (Q × t) / A

Symbol	Description	Unit
L	Holding tube length	m
Q	Volumetric flow rate	m³/s
t	Holding time	s
A	Tube cross-sectional area	m²

A = πD² / 4 L = (Q × t) / (πD² / 4)

If the flowrate is given in m³/h:

Q = qh / 3600 L = ((qh / 3600) × t) / (πD² / 4)

5.4 Practical Sizing Notes

Tolerance / safety margin.
Actual internal diameter after manufacturing.
Pipeline fittings influence if counted.
Viscosity effects if relevant.
Pump stability.
Flowmeter accuracy.
Minimum legal holding time requirement.
Whether design is based on volumetric flow or mass flow conversion.

5.5 Time–Temperature Context

The handbook confirms that pasteurization performance depends on the combination of time and temperature. Examples visible in the extracted text include:

70°C / 1 s 65°C / 10 s 70°C / 20 s Above 80°C / approx. 5 s

Source: Dairy processing handbook - Tetra pack.pdf, pages 82–83.

Section 06

Steam Demand

6.1 Objective

Steam is used to provide the thermal energy required by the hot water unit, which then heats the milk indirectly.

6.2 Heat Duty for Product

Qprod = ṁmilk × Cp,milk × (Tout − Tin)

Symbol	Description
Qprod	Product heat duty, kW or kJ/h
ṁmilk	Milk mass flow rate
Cp,milk	Specific heat capacity of milk
Tout	Target heating temperature
Tin	Inlet temperature to the heating calculation boundary

6.3 Net Heating Duty with Regeneration

If regeneration is present, the final external heating load is lower than the total temperature rise of the milk.

Qnet = ṁmilk × Cp,milk × (Theating,inlet-to-final − Tpasteurization) Qsteam-side = Qfinal heating + Qlosses

In practical terms, regeneration recovers a portion of the energy, reducing the external load required from steam.

6.4 Steam Consumption Formula

ṁsteam = QHW / λsteam

If sensible cooling / condensate effects are included:

ṁsteam = QHW / (hsteam − hcondensate)

6.5 Practical Notes

Steam demand must include:

Steady-state product load.
Startup heating load.
Hot water loop losses.
Exchanger inefficiency.
Control margin.
Piping heat losses.
Fouling factor over time.

Section 07

Cooling / Chilled Water Demand

7.1 Cooling Philosophy

After heating and holding, the milk is cooled through:

Regeneration against incoming cold milk.
Cooling water section.
Chilled water / ice water section if low final temperature is required.

Utility reference: The utility terminology used in this article is aligned with common process and dairy engineering references, including chilled/ice water, cooling water, steam, and hot water services used around pasteurization and heat-exchange systems. References: Lacta drawing legend, p. 1; Dairy Processing Handbook, Tetra Pak, pp. 84–86.

7.2 Product Cooling Duty

Qcool = ṁmilk × Cp,milk × (Thot − Tcold)

7.3 Utility-Side Calculation

Qcool = ṁu × Cp,u × (Tu,out − Tu,in) ṁu = Qcool / [Cp,u × (Tu,out − Tu,in)]

7.4 Typical Design Split

Regeneration

Major energy recovery by heat exchange between outgoing hot milk and incoming cold milk.

Cooling Water

Used for intermediate cooling where chilled water is not required.

Chilled / Ice Water

Used for final trim cooling to achieve low outlet temperature.

This split minimizes refrigeration or chilled-water demand.

Section 08

CIP Considerations

8.1 File-Backed Utility Cues

CIP PR CIP R LYE ACID

Source: Lacta.pdf, earlier OCR-backed page 2 extraction.

8.2 Functional Meaning

This indicates the pasteurizer is designed for CIP circulation and chemical cleaning with at least:

Alkaline cleaning circuit.
Acid cleaning circuit.
CIP supply / pressure line.
CIP return line.

8.3 Design Expectations

CIP design for the pasteurizer should ensure:

Full wetting of product-contact surfaces.
Sufficient flow velocity in plates, tubes, valves, and holding tube.
Proper drainability.
Chemical compatibility of seals and elastomers.
Thermal resistance of components.
Validated rinse and return routing.

8.4 Key CIP Attention Points

Holding tube.
Homogenizer interface.
Divert valve / product-routing zone.
Dead-leg prevention.
Instrument tee connections.
Balance / feed section, if present.

Section 09

Instrumentation and Control Considerations

Based on the retrieved content, instrument tags such as PC124, PC145, LIC87, LT67, and LSL67 were visible in earlier extraction, indicating that the system includes pressure and level related control / monitoring points.

Source: Lacta.pdf, earlier OCR-backed page 2 extraction.

A professional control philosophy should include at minimum:

Product Temperature Control

Critical temperature measurement at the pasteurization control point.

Flow Control

Flow must be tied to holding time compliance and pasteurization safety.

Hot Water Loop Control

Temperature control through steam valve modulation and water circulation.

Safety Diversion Logic

Non-compliant product should be diverted based on temperature, flow, and utility status.

Alarm and trip handling should cover:

Low temperature.
No flow.
Utility failure.
Abnormal pressure.
Low level where applicable.
CIP mode interlocks.

Section 10

Calculation Template

Below is a compact engineering template suitable for implementation in a calculation sheet.

10.1 Input Data

Product Data

Product: Milk
Flow rate: ṁmilk kg/h or qh m³/h
Density: ρ kg/m³
Specific heat: Cp,milk kJ/kg.K
Inlet temperature: Tin °C
Pasteurization temperature: Tpast °C
Outlet cooling temperature: Tout °C
Holding time: t s

Holding Tube Data

Tube internal diameter: D m

Heating Utility Data

Steam pressure
Steam enthalpy or latent heat
Condensate enthalpy
Hot water inlet/outlet temperatures

Cooling Utility Data

Cooling water inlet/outlet temperatures
Chilled water inlet/outlet temperatures
Utility specific heat

10.2 Holding Tube Length

Q = qh / 3600 A = πD² / 4 L = (Q × t) / A

If product flow is mass flow:

Q = ṁmilk / (ρ × 3600)

10.3 Product Heating Load

Qprod = ṁmilk × Cp,milk × (Tpast − Tin)

If using kg/h and kJ/kg.K, the result is in kJ/h. To convert to kW:

QkW = QkJ/h / 3600

10.4 Steam Consumption

ṁsteam = QHW / λsteam ṁsteam = QHW / (hsteam − hcond)

10.5 Cooling Water / Chilled Water Requirement

Qcool = ṁmilk × Cp,milk × (Thot − Tcold) ṁu = Qcool / [Cp,u × (Tu,out − Tu,in)]

Section 11

Example Calculation Structure

Example Placeholders

Parameter	Value
Milk flow	10,000 kg/h
Milk density	1030 kg/m³
Specific heat	3.9 kJ/kg.K
Inlet milk temperature	4°C
Pasteurization temperature	72°C
Holding time	15 s
Holding tube ID	38 mm = 0.038 m

Step 1: Volumetric Flow

Q = 10000 / (1030 × 3600) = 0.002697 m³/s

Step 2: Tube Area

A = π(0.038)² / 4 = 0.001134 m²

Step 3: Holding Tube Length

L = (0.002697 × 15) / 0.001134 ≈ 35.7 m

L ≈ 36 m

The theoretical holding tube length is about 36 m before applying engineering margin, exact legal design basis, or calibration allowance.

Step 4: Product Heating Duty

Qprod = 10000 × 3.9 × (72 − 4) Qprod = 2,652,000 kJ/h Qprod = 2,652,000 / 3600 ≈ 736.7 kW

Result: Gross heating duty is approximately 736.7 kW before considering regeneration.

Section 12

Final Engineering Summary

The milk pasteurizer should be designed as an indirect plate heat exchanger-based system in which steam heats a hot-water circuit, and hot water transfers heat to milk through the PHE plates.

This arrangement is preferred to avoid direct steam contact with the milk and to minimize burning, fouling, and thermal instability.

The process must include a properly sized external holding tube, with length determined by required holding time, product flow rate, and tube internal diameter. Since holding time is inversely proportional to flow rate, accurate flow control is a critical safety requirement.

Utility design must additionally account for steam demand, hot water loop duty, and cooling/chilled water demand, while the CIP system must cover the full pasteurizer circuit including product sections, holding tube, and utility-associated cleaning paths.

Milk Pasteurizer Engineering Design Basis

This page presents a structured engineering basis for milk pasteurizer design, including indirect heating, hot water circulation, holding tube sizing, steam demand, cooling utility requirements, CIP considerations, and process control logic.