Performance and Energy Consumption of an Impinging Stream Dryer for High-Moisture Particulate Materials

Abstract

Impinging stream dryers (ISDs) are a novel alternative to flash dryers for high-moisture particulate materials. However, studies on hydrodynamics and heat/mass transfer as well as drying characteristics of an ISD are still limited or incomplete. The effects of various geometric and operating parameters of an ISD on its performance, in particular, are not conclusive. In addition, ISD was tested mainly with model materials that do not represent the real challenge of higher-moisture materials, which tend to be sticky in nature. In this study, modifications were made to an existing coaxial two-impinging stream dryer of Sathapornprasath et al.[ 1 ] to make it more suitable for high-moisture particulate materials. This newly modified dryer was then evaluated for its performance in terms of the volumetric water evaporation rate and volumetric heat transfer coefficient. Soy residue (okara), which is a by-product of a soymilk production process, was used as a test material. Particle mean residence time was also evaluated and the results were used to support and explain the performance data of the dryer. Finally, the specific energy consumption of the dryer was assessed at various geometric and operating conditions. The maximum volumetric water evaporation rate was found to be around 520 kgwater/m3h and the maximum volumetric heat transfer coefficient was around 4,500 W/m3K for the mean particle residence time of approximately 0.97–1.74 s. In terms of the specific energy consumption the lowest specific energy consumption was found to be around 5.6 MJ/kgwater.