Sterilization with heat integration

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GENERAL INFORMATION

Most times it is used the Plate Heat Exchanger. Depending on the size of the particles, tubular heat exchangers are used instead. A holding coil is attached to the HE. Helical heat exchangers design (tubular HE) are used also in many applications.

The most efficient process is the direct sterilization (steam direct sterilization) that consist in mixing steam with the product. Used for sensitive products wich have to be treated with short heating-holding times and high temperatures.


TECHNOLOGY DESCRIPTION, TECHNIQUES AND METHODS

Plate Heat Exchangers

Plate heat exchangers are systems that separates two air flows with solid elements (plates). The heat exchange occurs through the plates, which can be built with fins to maximize the contact surface and increase the exchange efficiency. Depending on the flows direction the system will be parallel flows or countercurrent flows. The plate heat exchanger efficiency is around 75% [1].


Plate and Plate-Fin heat exchangers.jpg

Illustration 1: Plate and Plate-Fin heat exchangers [2]


Tubular heat exchangers

Tubular heat exchangers are systems that uses the natural convection as the physical phenomenon for the air movement. Tubular heat exchangers are built as a duct with a liquid layer inside. In one side of the duct, a heat flow passes through the exchangers, and heats up the walls of the duct and the liquid inside. The liquid evaporates and starts to move inside the duct. In the other side of the duct, a cold flow passes through the exchanger. In this side, the vapour that have moved on from the hot side get cold, transferring its heat to the exchanger duct walls, and it condensates. This way the tubular heat exchanger heats up the initially cold air.


Tubular heatexchanger.jpg

Illustration 1: Tubular heat exchanger [3]


The air-air heat exchangers have the inconvenience of the air ducts, much bigger than the water or liquid ones have to be placed side by side, and this imposes physical limitations. These heat exchangers, with the desiccant wheel exception, do not recover latent heat.

The liquid-liquid heat exchangers do not need such a big place as the air-air heat exchangers. The liquid ducts are narrower and losses are lower. The auxiliary consumption is also lower.


CHANGES IN PROCESS

The installation of a heat exchanger does not implies a change in the process, because the main aim of the measure is to harness wasted fluid (and wasted energy) and pre-heat or pre-cool an incoming fluid to the process. Therefore, process can be kept identical, and the heat exchangers affects the fluid in an early stage and when it already has came out from the process.


ENERGY SAVINGS POTENTIALS

CHANGES IN THE ENERGY DISTRIBUTION SYSTEM

REFERENCES

[1] Fundamentals of Heating Systems. ASHRAE

[2] Fundamentals of Heating Systems. ASHRAE

[3] Fundamentals of Heating Systems. ASHRAE


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