The need to separate powder based Food Ingredients occurs in many industries, from the dairy
to chocolate making
and from beverages
to starches and yeasts
. Processes needing separation include drying (spray, flash), milling and mixing.
of Food Ingredients can be quite challenging, especially for finer particles. That is particularly evident in Spray Drying.
is commonly used to design and produce a variety of powders, many of those quite valuable and sensitive, such as Demineralized Whey
or Whey Protein Concentrate.
Usual spray drying arrangements (with or without integrated fluid bed) include process cyclones
and a final dedusting system
(Bag Filter, WESp, Wet Scrubber High Efficiency Cyclones).
The process cyclones serve the purpose of separating and collecting the dried powder originated in the spray drying chamber. The fraction of product escaping to the final dedusting system is a waste (WESP, Wet Scrubber) or not considered as first grade product (Bag Filter), and thus seen as losses. The underlying reasons are contamination with filter fibers, product cross contamination and risk of heat degradation.
The preferred way
to recover these sensitive and expensive products is with cyclone collectors due to their direct and sanitary powder capture, not only for the first stage but also for the final stage. Unlike bag filters or wet scrubbers, cyclones avoid filter or product contamination and product cross contamination.
However, for fine powders with a median diameter in volume (MVD) of less than 5µm, losses due to low cyclone efficiency can rise to more than 25%. They represent a high cost.
Even for a few applications where the losses may not be so costly (less expensive products), they are not environmentally and socially responsible
, with waste or side stream management being an additional problem to tackle in the final stage dedusting.
The options for these final dedusting systems
have different advantages, drawbacks, investment and operational costs, as follows:
|Regular Cyclones and Multicyclones | Problem: Low Efficiency
+ Low cost, easy to operate and clean. Allow for quick stops and product rotation.
- Low efficiency for small particles (<10μm) leading to non-compliance with emission limits. Regular cyclones available on the market are not an option for emission control.
|Bag & Ceramic Filters | Problem: O&M costs
+ Bag filters are very efficient (> 99.9 %) and guarantee compliance with a wide range of emission limits.
- Demanding in terms of temperature conditions: product can easily stick to the bags if temperature drops.
- CIPable and sanitary bag houses are expensive and maintenance is labour and time consuming.
- For sensitive products such as infant nutrition, lactose or gluten free, etc, product recovered from the bag house may not be considered first grade because of the risk of fiber or cross contamination.
|Wet Venturi Scubbers and WESPs | Problem: Secondary Pollution
+ Can work well for a variety of operating conditions.
- No product recovery possible from a wet scrubber.
- Secondary pollution of water is an operational added problem requiring a water treatment facility.
In short, for the first stage of separation
, clients need
the highest possible performance in the process cyclones
since this is where first grade product is captured. For the final stage dedusting
, a wet based system shall be avoided and, if possible, the fines recovered in a high efficiency cyclone system.
include very high efficiency process cyclones to maximize yield. ACS final stage cyclones are also a real alternative to other police filters depending on the required emission limits and particle size of the product (<20mg/Nm3
is achievable), thereby maximizing yield of the whole production line.