The advantages of the sterilization by direct steam injection into the retort

There are multiple alternatives for sterilizing food in retorts, although they all have in common the use of steam generated by a boiler. The ways in which the retort uses the steam and the advantages and disadvantages of this are the subject of this post.

Specifically, we are going to focus this analysis between two alternatives:

  1. Direct Steam Injection. The heating of the containers is done by steam injected directly into the retort chamber through perforated pipes, for a uniform temperature distribution throughout the vessel.
  2. Indirect Steam Injection. The heating of the containers is carried out by means of a shower (spray o rain) of superheated water. The heating is done in an external heat exchanger.

At Surdry we provide our best advice, but we adapt to customer preferences by offering both technologies with the best solutions for the safest and most efficient use.

Direct Steam Injection

Direct steam injection into a retort has been the first of the technologies developed and it continues to be the most widely used today. The reason is the reliability it brings when it comes to the repeatability of the process variables.

Typical Steam and Water Spray diagram (SWS). Steam is injected directly into the vessel through stream no. 11

We could say that:

Direct steam injection = better food safety

Deviations in any of the two essential variables, temperature and treatment time, can compromise the level of sterility.

Direct steam injection into a Surdry retort is done through perforated pipes. The uniform rate of heating will depend solely on the flow of steam supplied through the perforated pipes. The steam itself ensures that the perforations are well maintained without reducing their diameter, exerting a self-cleaning or natural CIP process.

Indirect Steam Injection

This technology is proposed on the basis of the following two arguments:

  • The steam does not enter the retort chamber and the risk of contamination of the containers due to possible dragging of the steam pipes is eliminated.
  • The steam that condensates in the exchanger is free from organics carry-over, and can be reused.
Indirect heating system. The steam is injected into a plate exchanger, external to the retort, while the process water is being recirculated through a pump.

However, these advantages go against food safety for easy-to-understand heat transfer reasons:

  • Temperature, as an essential variable. The greater efficiency of the transfer and uniformity of the distribution of temperature in the steam atmosphere with respect to the water shower. The injection of steam helps to eliminate air that is a bad thermal conductor.
  • Time, as an essential variable. The fouling of the heat exchanger directly affects the heat transfer and hence the heating time of the water.

Condensated steam recovering

With few exceptions, indirect steam retorts have a single heat exchanger, both to heat the shower water with steam and to cool it later with water from another external source. Given the large volume of water required to cool the retort, the industry is rarely allowed to use demineralized water for this purpose. Instead, mains water is used, water recovered from cisterns or pools, with or without passing through an evaporative cooling tower. A very common and very detrimental case for cleaning the heat exchanger is the use of groundwater.

The deposit of scale on the exchanger plates dangerously slows down the processing time and makes it difficult and more expensive to recover the condensate to the boiler, since it requires demineralized water to prevent its deterioration.

At Surdry we have developed a system that allows the recovery of the condensate generated by the steam injected directly into the retort. In this way, we can make the process more energy-efficient, without a detriment to food safety provided by direct steam injection.

Surdry’s Energy Recovery System

Do you want to explore how to recover the energy in your SWS retorts system? Contact us.

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