Detailed process model description for the Pasteurization demo

Model specification

Introduction

Intended audience

The present document is oriented to:

• Model developers

• Model users

• System Integrators.

Scope

The scope of the present document is to describe the capabilities of the Pasteurization demo, for the process modeling of continuous (i.e. flash) pasteurization processes.

Prerequisites

• basic knowledge of process engineering and / or of food processing.

• know about the different roles involved with the lifecycle of solutions developed using the LIBPF^® enabling technology, see LIBPF^® Technology Introduction

Pasteurization kernel

In LIBPF^® one kernel can support many process models, each as a different flowsheet type.

All the process models supported by a kernel share the same list of components and can use all LIBPF^® embedded types plus the custom types registered by the kernel itself.

Type list

The Pasteurization kernel registers the following process models, based on the built-in LIBPF^® FlowSheet type:

Component list

The fluids to be processed are broken down in their constituents and represented as a mixture of basic food components.

The components are defined using built-in LIBPF^® basic types.

More precisely the Pasteurization kernel defines the following component list (click on the component type to jump to the reference documentation for the component):

Process description and scheme

The pasteurization process is designed to reduce the bacterial load of edible fluids such as milk, milk products, beer, wine, fruit and vegetable juices, ice cream mix etc..

The continuous (i.e. flash) pasteurization actually consists in keeping the fluid at a defined hot temperature for a defined short time. Temperature and time must be carefully balanced to prevent the thermal wear of the food and, at the same time, to kill as much as possible pathogenic microbes.

For this purpose, the fluid must be pumped, quickly heated to the desired temperature and held to that temperature using a pipe of proper length. After that the fluid must be quickly cooled at a temperature which can be suitable for storage. It is possible to recover part of the heat by pre-heating of the inlet fluid using the hot treated fluid.

The following process flow diagram should clarify the process.

The cold fluid to be processed (S01) enters the cold side of the REC recuperator heat exchanger, where it recovers energy from the hot pasteurized fluid S05.

The pre-heated fluid S02 is pumped via PUMP through the HEATER heat exchanger, which rapidly brings it to the required temperature. The resulting hot fluid S04 is held at this temperature for the required time in a long pipe HOLD.

The hot pasteurized fluid S05 recovers heat with the cold feed in the hot side of the REC recuperator heat exchanger.

The warm fluid S06 is rapidly cooled at the storage temperature in the COOLER heat exchanger.

Stream list

The streams are defined using built-in LIBPF^® basic types.

Click on the type to jump to the reference documentation for the stream.

Unit list

The unit operations are defined using built-in LIBPF^® basic types.

Click on the type to jump to the reference documentation for the unit operation.

Model options

Continuous pasteurization processes may be operated with different combinations of hot temperature and holding time.

These condition are usully defined by technical regulations.

For this reason the model can get an input string option (processType) which adjusts temperature and holding time.

The feedType string option is available to choose a predefined composition for the fluid to be processed.

processType option

The process type option sets predefined temperature and holding time for the process.

feedType option

The feed type option sets the composition of the fluid to be processed to certain predefined values.

Model parameters

Inputs

At the top-level of the flowsheet object hierarchy there are the following input parameters:

• coolT: Cooling temperature for the storage of the pasteurized fluid

• highT: Hot temperature for pasteurization (Available only if processType is “user”)

• holdTime: Time to keep fluid to designed hot temperature (Available only if processType is “user”)

• dTexchangeLL: Delta T approach for liq-liq exchanger (used to specify the REC cold side temperature increase);

• feed: Feedstock fluid mass flow

• press: Fluid outlet relative pressure

• hs: Design speed in the holding pipe (used to calculate the pipe diameter)

There are also available other input variables inside the unit operations and streams:

Results

At the top-level of the flowsheet object hierarchy there are the following results:

• Qin: Thermal power input (duty of the HEATER)

• Qout: Thermal power output (duty of the COOLER)

• Win: Work power input (PUMP electrical consumption)

• Acooler: Cooler exchange surface

• Aheater: Heater exchange surface

• Arecuperator: Recuperator exchange surface

• highT: Hot temperature for pasteurization (Available as output if processType is not “user”)

• holdTime: Time to keep fluid to designed hot temperature (Available as output if processType is not “user”)

There are also available other results inside the unit operations and streams:

Stream table results:

References

Pasteurization demo

• Demo home

• Demo C++ source code repository on gitlab

• System Integrator tutorial for access to the Pasteurization model via the LIBPF^® RESTful Model User API

• Model Developer step-by-step tutorial for the creation of the Pasteurization example

LIBPF^® technology

• LIBPF^® Technology Introduction

• LIBPF^® SDK Developer manual

• LIBPF^® SDK C++ reference manual

• LIBPF^® Model User API documentation