Dryer feed solids may hold the key to eliminating problems with efficiency and capacity in food and dairy spray dryers.
UPDATE: We really appreciate engagement with our audience. A colleague suggested a different viewpoint, that the opportunity may be still greater under some circumstances. We have updated our original post to clarify our original message, and will issue a follow-up post in two weeks to explain the additional opportunity.
Once again, we value our reader’s feedback, and if you have any topics you’d like to see us write about, please feel free to drop a note and make a suggestion.
A typical spray dryer has an important function–to convert a concentrated liquid into a free flowing powder. This is accomplished by removing most of the water content via evaporation. The powder can be produced from a variety of milk-based concentrates, with both low and high fat and/or protein content.
To operate your process at a high efficiency, the water removal in the spray dryer needs to be minimized. Only the water that cannot be removed by the upstream evaporator should be removed in the spray dryer. Why? Because an evaporator can do the water removal at no less than double the efficiency.
Furthermore, every spray dryer is limited to a specific water removal rate. To operate your process at maximum powder output, the same spray dryer needs to receive its feedstock at the maximum practical concentration (total solids content). This ideal dryer feed solids level necessarily varies for each product, mostly dictated by the viscosity.
Unfortunately, some facilities are using evaporators that are unable to concentrate to the ideal solids level. The reasons vary from case-to-case, but most of these situations can be remedied. Additionally, many facilities could achieve a higher solids level from the upstream evaporator, but not with consistency, and with frequent “over-shoots.” This lack of control results in the practice of operating at a “comfortable” solids level, sometimes as much as 5% below the ideal solids level. This situation can also be remedied.
When the upstream evaporator is underperforming and feeding the spray dryer low solids (say 45%TS vs. 50%TS), then the spray dryer must handle ~10% additional water removal. When the spray dryer is able to handle this additional load, it will do so at a lower energy efficiency. In the case where the spray dryer is unable to handle the extra water removal, then the system will need to operate at a lower capacity, in other words, less powder will be generated per hour.
For most facilities, the upstream evaporator is responsible for the low solids condition. Current designs have made significant advances with achieving higher concentrations at stable conditions, which can be applied to most existing evaporators. A review of your current conditions can quickly determine the best solution.
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