Retrofitting Legal Pasteurization in an Existing Evaporator – What to Keep in Mind

Retrofitting Legal Pasteurization in an Existing Evaporator – What to Keep in MindIn the dairy industry, pasteurization is crucial to processing milk and milk products for human consumption. The pasteurization process is named after French scientist Louis Pasteur who discovered that by applying heat to milk, it would destroy harmful pathogens that grow in milk as it ages. Pasteurization helps improve the shelf life of milk products as well as make them safer for human consumption.

A lot of dairy plants in the United States have evaporators to produce concentrates that date back to the ’60s and ’70s when milk processing really took off. However, there are a lot of plants that do not have legal pasteurization systems incorporated into their existing evaporators. This prevents these plants from being able to produce Grade-A product and risks the growth of unwanted pathogens in the finished product, depending on heat treatment upstream of the evaporator system.  When looking to retrofit legal pasteurization in an existing evaporator system, it is important to consider the following:

Properly Designed Equipment

It may seem straight forward, but you want to ensure that your evaporator is designed for legal pasteurization. Meaning, a facility that has bought an industrial secondhand evaporator and plans to produce pasteurized products will more than likely not meet the minimum internal weld radii, surface roughness, and other specifications needed for manufacturing Grade A milk products. A USDA inspection of your existing evaporator system may be required to verify the condition of your equipment.

Flow Restrictions

There are different types of Pasteurization methods. The most common in the USA is known as High-Temperature Short Time Pasteurization (HTST). This means heating the product to a minimum of 161°F for at least 15 seconds. This is done typically by heating with a plate heat exchanger or shell and tube heat exchanger followed by a holding section downstream. Due to this time requirement, there is an official High Flow and a Low-Temperature Cut-off value that is assigned to a particular pasteurization system.

The High Flow Cut-Off is determined during the initial tests that are run on the system when being commissioned. This can affect your current evaporator system’s performance if it is much different from the current rate your evaporator is being run at. If the value is much lower than your current feed rate, then you can potentially be “starving” your evaporator, which can lead to an increase in fouling, which can lead to higher delta T’s between evaporator effects and less finished product in the long run.

System Flow Diverts

For HTST Pasteurization, the system will divert flow for different reasons. A few of them are as follows:

  • Flow into the evaporator surpasses the High Flow Cut-Off value.
  • The minimum temperature requirement (161°F for HTST) is not maintained through the holding section.
  • Flow into the evaporator is less than the Low Flow Cut-Off value (also assigned to the system during commissioning).
  • Loss of signal with the magnetic flow meter or temperature probe.

When the flow is being diverted from the evaporator, the system is being “starved” of liquid. This can create issues as heat is still being fed into the system, but there are no means for heat transfer as there is no liquid present in the tubes. Sure, it is possible to cut-off steam to the system, but that would be sacrificing energy within the system. Other means of accounting for flow diverts for HTST systems include:

  • Recirculate flow back into each evaporator effect during the flow diverts. However, be wary of this as if milk products are recirculated for extended periods of time, the chance of protein denaturing is significantly increased, and longer, uncontrolled residence times can cause bacteriological growth.
  • Install an emergency water system. This will allow water to be brought in after the flow divert valves and will prevent the evaporators from being “starved.” However, this can become quite costly as we must bring in pasteurized quality water into the system if this method is desired. UV Disinfection systems for PMO-compliant Pasteurized Equivalent Water can cost over $100k.

Advantages of Integrated Legal Pasteurization Systems

Integrated legal pasteurization systems in an evaporator have multiple advantages as opposed to stand-alone HTST systems. For instance, heating the product through the evaporator system and then running it through the evaporator is more energy-efficient than using a stand-alone HTST system. An additional benefit of doing this is that there is less heat stress on the product. With a stand-alone HTST system, the product would have to be brought up to legal pasteurization temperature. Then, it would sit in a storage tank until it is ready to be processed through the evaporator. Most evaporators take in product at around the legal pasteurization temperature, so by running the product through an integrated legal pasteurization system, in essence, you are crossing two ‘Ts’ with one stroke of the pen.

Although retrofitting a legal pasteurization system in an existing evaporator will require some capital, it is less a lower investment cost than a stand-alone system. In comparison to a stand-alone HTST system, for example, we would need everything but the additional storage tank and additional equipment for measuring the tank.

GLM Hydro is experienced with different pasteurization systems for the dairy industry. If you are looking to retrofit a legal pasteurization system into your evaporator, give us a call to see how we can help you and answer any questions that you may have!


Aaron Amorim
Calcium Fouling in Barometric Leg of a Direct-Contact Condensor

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