CFD-investigation of suspension-based pigs in chocolate processing plants

Abstract

In chocolate processing plants, cleaning with water-based cleaning agents is not possible since when in contact with water, sugar and milk powder within the chocolate agglomerate which causes blocking of the plants. Common elastomere-based cleaning pigs pose the risk of contaminating through abrasion and have specific design requirements. Research is now focusing on using highly concentrated sugar-in-oil suspensions as flexible cleaning pigs. The rheology of these suspensions is complex, allowing for various compositions. This study presents a simulative pre-design of these pigs using the volume-of-fluid method, targeting challenging components like L-bow pipes and continuous expansions. Simulations systematically varied the rheological properties of the pig-suspension in terms of the Bingham number ($10^{-3}$–$10^2$) and the Reynolds number ($10^{-4}$–$10^1$). The massflows investigated were $90,180,360\text{kg/h}$. Strong shear-thinning behavior emerged as crucial for creating cohesive pigs with effective cleaning capabilities. No correlation with yield stress was found when the pig was flowable, although values in range $2\text{–}2000\text{Pa}$ were investigated. The tested parameter combinations did not achieve satisfactory contour adaptivity for pigs during continuous expansion. The resulting residual soil layers on the walls and the proportion of soil in the outlet mass flow were up to $\text{50}\text{\%}$ lower than in the reference rinsing process.