Separation of fine particles, such as ice crystals, from viscous liquids presents considerable problems for chemical engineers in general and especially for those working on food processing problems. In some cases the development of a desirable product may be blocked due to the lack of an economical separation method. One particularly difficult separation problem is that presented by the need to separate small (100 micron diameter) ice particles from skim milk during the process of freeze concentration of the milk. Separation of the mixture is difficult because the particles are small and the concentrated milk is relatively viscous (>20 cP). In addition, the surface tension between the ice and concentrated milk is low. Also, the ice particles are relatively soft and rinsing with water must be controlled to minimize redilution of the concentrated milk.

In order to solve this problem, a fine particle viscous slurry separator has been developed. The equipment is simple, inexpensive, and could also be used to separate fine particle suspensions similar to the ice/skim milk slurries including crystals formed from a melt, cells or substrate particles from a biological process, or catalyst particles from a product stream.

In the case of the milk, the separation leaves some liquid on the solid particles but, for many applications, including freeze concentration, the separation cost advantages more than offset the value of the lost liquid.

The pilot plant equipment usually operates at a rate controlled by slurry production, approximately 100 pounds of ice per hour. Slurry flows up to 1600 pounds per hour, and as much as 30% ice with solution viscosities above 20 cP, have been successfully separated. Test data for salt solutions, skim milk, and skim milk-simulating (CIMC) ice slurries are available, and other slurries can be tested. At higher production rates productivity of the equipment will improve.

The benefit of this separation method will depend on the method of separation it replaces. One aspect of this process that is different. from many current separation methods is that the maximum practical fraction of the liquid is removed from the solid with minimal dilution. The process will be most advantageous to intermediate value materials produced in amounts of at least 100 pounds per hour. The separation cost will be around $0.01 per pound of dry powder, cheaper than laboratory type equipment, such as centrifuges or conventional filtration.

Patent Status:
U.S. Patent 5,816,057 issued October 6, 1998

Responsible Scientist/Engineer:
Dr. Leland C. Dickey
Eastern Regional Research Center
ARS, USDA
600 East Mermaid Lane
Wyndmoor, PA 19038
(215) 233-6640
e-mail: Leland.Dickey@ars.usda.gov  

Technology Transfer Contact:
Victor (Vic) Chavez
(215) 233-6610
e-mail: vic.chavez@ars.usda.gov