Process Intensification Enabling Continuous Manufacturing Processes Using Modular Continuous Vacuum Screw Filter

A novel apparatus concept for integrated, small-scale continuous filtration, washing, and drying is presented. The continuous vacuum screw filter (CVSF) allows obtaining dried and free-flowing product particles from the continuously fed suspension. While the first study presented the CVSF concept in detail and focused on the characterization with respect to the product quality control and solid-phase residence time distribution (RTDS) during sole filtration, the modular extension with washing modules and a vacuum-induced (pre-) drying setup is now presented here. For this purpose, a wash module was designed and implemented. The influence of single-stage and two-stage washing on the particle size distribution (PSD) and RTDS was investigated for the L-alanine/water model system. Single-stage washing increased the particle size of d(90,3) by 120 mu m (+19%) due to a higher agglomeration degree, while using two-stage washing could completely preserve the particulate properties of the inlet suspension. To identify favorable operating conditions for efficient (pre-) drying, the effect of varying throughputs and mean residence times on the residual moisture of the product particles was quantified. High filling degrees (>30%) and increased mean residence times (>11 min), in combination with two-stage washing and efficient vacuum-induced airflow, ensured completely isolated, free-flowing, and almost dry particles with residual moistures of 1% and an entire maintenance of the PSD. Measurements of the RTDS showed a slight broadening due to the wash liquid used, still ensuring a narrow RTDS and thus almost plug-flow-like behavior. In summary, the CVSF offers unique features, such as its modularity and rapid start-up behavior, providing a promising concept for integrated continuous particle isolation from suspensions.