Steam infusion heat exchanger

Direct heating involves direct contact between the food and the heating medium by steam injection or steam infusion.

Steam injection introduced steam into the product of an injection chamber as product is pumped through the chamber, while steam infusion introduces product through a steam-filled infusion chamber.

A steam infusion heat exchanger provides a direct contact between steam and the product. A product in liquid state is pumped to the top of the heat exchanger and then allowed to flow in thin sheets in the heating chamber.

It is heated to 142 – 146 ° C in 0.3 seconds and is held for 3 seconds in a holding tube before flash cooling in a vacuum chamber to 65 -70 ° C.

The flash cooler has dual purposes. First, it reduces the sterilization temperature in a very short time and second, it removes water from the product.

The viscosity of the liquid determines the size of the spreader. Products containing particulates, such as diced vegetables, meat chunks and rice can be handled by specially designed spreaders.

High rates of heat transfer are archived when steam contacts tiny droplets of the food. The temperature of the product rises rapidly due to steam condensation.

Steam infusion has advantages over injection methods because the liquid does not contact hotter surfaces and burning-on is therefore reduced.
Steam infusion heat exchanger

Steam injection

Direct exchangers are based on mixing of heating steam with the liquid food product resulting in very fast heat transfer rate. Steam injection and steam infusion are each used to intimately combine the product with potable steam.

In steam injection, the steam is injected into the fluid food through small hole. A typical example is the production of UHT milk by direct steam injection.

Milk is pre-heated to 75 ° C and then brought into contact with saturated steam, resulting in almost instantaneous heating of the UHT temperature. The milk plus the injected water come in the expansion vacuum vessel, where the added water of the steam injection is removed through condensation in the following condenser.

Control of the pressure in this system is needed for two reasons. First, this is to ensure that the correct amount of water is driven off, and second, that any undesirable volatile odors that may have developed during the injection process are removed.

The advantages of direct steam injection are their quick and accurate temperature control (within less than 1 ° C), the restricted pressure drop under normal flow rates (less than 0.14 bar) and their relatively low noise during operation (less than 80 dB).
Steam injection