Over the years, we have helped develop a number of blast freezing systems. Most of these, known as “superblasts” (as in supercharge), originated from developments at Cassco, Harrisonburg, Virginia, in the early 1980’s. They were refined later at Wiscold (to then-CEO George Sayres’ credit), and have “evolved” substantially in many other facilities since. Traditional blast freezers had used air unit evaporator fans as the vehicle for “moving” air through palletized boxed product. This method had two major disadvantages:
• The first was the lack of definitive air flow and direction.
• The second was the air unit evaporator gradually collects moisture (ice) and eventually “blocks off” the air passing through the evaporator unit, substantially decreasing air quantities that are needed for good heat transfer.
The superblast overcame these two deficiencies in providing auxiliary fans for uniform and continuous air flow through the product (even though the air unit evaporators go through their cyclic process of collecting moisture and defrosting). Another primary advantage has been the ability to freeze bulk product (60 to 70 lbs. boxes) in a two-day rotation, where before three-day rotations had been required. This means a substantial reduction in “real estate,” as well as “quicker” (typically 30 hours) turn around of products.
The other major advantage is the ability to use higher-temperature air (-15°F to -20°F), as opposed to -30°F to -40°F air. The effect of this is a substantial reduction in compressor horsepower (as much as one-third reduction in total power consumption by the compressor).
The later generations of superblasts also are now using computers to provide multiple air flow quantities, depending on the stage of freezing which may be occurring (removal of latent versus removal of final sensible heat in the product as the product temperature moves from freezing point to 0° F). The ability to stage fans further improves efficiency while still maintaining optimum compressor horsepower. Staging of the air velocities by choosing a combination of air unit fan speeds and multiple motors, with or without booster or assist fans, has become standard procedure on the recently designed superblast freezers.
There have been several attempts to freeze product in 24 hours, or even 12 hours. Although some product, such as whole birds or Cornish hens, have been frozen in 16 hours, products in 60 to 70 lb. boxes (poly bags) would normally require a two-day rotation in superblast freezers (this also allows for loading and unloading). Some of the larger blast cells have 60 to 90 pallets, which may require several truckloads of product to load and unload. It may be noteworthy, that, when needed, superblast temperatures can be lowered (to -35°F) and provide 30-hour rotation, i.e. poultry products.
We hope this information will be helpful to you in considering blast freezing requirements and your needs in the future. You may want to seriously question anyone who claims the ability to freeze 60 and 70 lb. boxes (in poly bags) in a 24-hour rotation, at least determine operating cost, blast temperatures, and power (from an investment viewpoint). If we can help in the design of these, please feel free to call Henry B. (Hank) Bonar, II at (904) 389-6700.
Engineering