Scraped Surface Heat Exchanger Technology in Crystallization

If the mixture is allowed to stand in static conditions, crystals will continue to grow in a rapid solidification phase and a strong, solid mass will result. If, however, the cooled mixture is moved to a secondary processing unit which agitates the product and adds shear to the mixture, the crystals will be kept small and be prevented from growing together into a solid mass, creating a more fluid result. A pin rotor machine can be used for this purpose and the amount of agitation applied during solidification can be varied to get the right crystal size, texture, and final product characteristics required.

Fats and Sugars

SSHEs are widely used to crystallize products containing fats or sugars which react differently in the process. Fondants, for example, crystallize very quickly. Bakery sandwich or cookie creams have firm, poor flowing properties and require a machine which can handle the associated high pressure and high motor shaft torque. The production of low trans- and saturated-fat bakery filling creams, however, also requires care within the process such as distributing gas in the mixture. These creams tend to get too soft if gas is distributed into the mixture at the end of the process with a mixing unit.

Having the right configuration of SSHE means that the gas can be added at the crystallization stage to achieve ideal homogenization while protecting the structure of the crystallized oils and creating the desired consistency of the filling cream for its application. Shortenings and margarines require rapid cooling to avoid separation of the mixture and, as the crystals form, temperature and agitation can influence the resulting product characteristics. SSHEs can be used across all these applications and more but it is important to completely understand all aspects of the process to get the highest product qualities.

A continuous crystallization process in a SSHE not only maximizes production capacity but also minimizes operator intervention and facilitates repeatable, consistent quality results. The quality of the crystallization process largely depends upon the time taken to lower the temperature to the point crystallization occurs, as well as the amount of agitation of the crystals during formation. Faster cooling and more vigorous agitation generally result in the desired smaller crystal sizes within the mixture, giving smooth end product results.

Mathis is a process technical manager for SPX Flow Technology. His 30-year career has primarily focused on sanitary SSHE heat transfer applications. Reach him at [email protected].