Stripping phase model for steam pressure filtration in combination with a water insoluble pore liquid
Introduction
Steam pressure filtration is an integrated process of mechanical-thermal dewatering and thermal drying (Peuker and Stahl, 2001). The primary aim of steam pressure filtration is the separation of mother liquid and solids by using steam. The process promises less energy consumption compared to the combination of conventional filtration and drying processes, and additionally provides the washing of a filter cake.
The potential of steam pressure filtration could also be used to separate solids from volatile organic compounds (VOC) (Peuker, 2003), whereby a complete purification of the solids is often necessary for reasons of product purity or compliance of impurity limits. Conventional separation processes reach their limits when the treated solids are poorly wettable for water (Burisch and Peuker, 2016, Wilkens and Peuker, 2012, Peuker, 2018).
In steam pressure filtration steam is applied to the saturated filter cake in both process phases of mechanical-thermal displacement of the pore liquid and thermal drying of the remaining bridge and adhesive liquid after steam breakthrough (Gerl, 1999). The mechanical-thermal displacement of the pore liquid generally results in lower residual VOC loads of the solids compared to conventional filter cake deliquoring (Esser and Peuker, 2020, Peuker, 2003, Peuker, 2005). However, a second process phase occurs subsequent to the steam breakthrough in which the steam evaporates and transports the VOC out of the filter cake.
Esser & Peuker experimentally investigated steam pressure filtration in combination with a water insoluble mother liquid and already showed the promising characteristics, i.e. the occurrence of a stripping phase (Esser and Peuker, 2020, Esser and Peuker, 2020). This article introduces a numerical model to describe the stripping and drying phase during steam pressure filtration. The differential model is evaluated by experimental results and a parameter study shows the functional relationships between the influencing parameters. Hence, this model also works as a prediction tool facilitating the process and plant design for steam pressure filtration.
Section snippets
Fundamentals
Several authors already explained the theoretical fundamentals of steam pressure filtration (Peuker and Stahl, 2001, Peuker, 2002, Bott et al., 2002, Peuker and Stahl, 2001, Peuker and Stahl, 2001, Peuker and Stahl, 2001, Ruf et al., 2000, Peuker and Stahl, 1999, Ruf, 1998, Gerl and Stahl, 1998, Gerl and Stahl, 1997, GERL and STAHL, 1996, Bott and Langeloh, 1996, Korger and Stahl, 1993) whereas Esser and Peuker showed experimental results for steam pressure filtration in combination with VOC as
Stripping phase model
The following numerical model is developed to describe the kinetics of the stripping and drying phase of steam pressure filtration after the vapour breakthrough (Peuker and Stahl, 2002) and to predict the attainable separation or rather stripping results. The model makes use of the theory of steam distillation on the one hand and on the other hand, it takes advantage of well-known model equations of the conventional filter cake dewatering and steam pressure filtration with a single-phase liquid
Methods and materials
The validity of the model needs to be proved by experimental investigations of steam pressure filtration in combination with a water insoluble mother liquid. The experimental setup, the implementation of the experiments and the used materials are already described in detail by Esser and Peuker (Esser and Peuker, 2020, Esser and Peuker, 2020). The solid materials are SiLibeads® 0–20 µm representing a spherical model system and Celite®512, known for its high specific surface area.
The wetting
Results and discussion
The generated model allows both a temporal and spatial resolution of the filter cake composition. However, the evaluation uses the integral model, in which the filter cake is viewed as a single layer, since the experimental determination of the filter cake composition in horizontal layers is not possible.
Fig. 5 shows the comparison of the stripping kinetics of experiment and model for the material system SiLiBeads® 0–20 µm & toluene. Three filter cake samples were analysed by gas chromatography
Conclusions and outlook
This work introduced a numerical model for the stripping and drying phase during steam pressure filtration in combination with a water insoluble volatile pore liquid based on mechanical and thermodynamic equations. The developed model results in a linear decrease of the VOC load during the stripping phase and furthermore reveals a complete separation of the filter cake. The findings were evaluated by the experimentally determined stripping and drying kinetics and showed a good accordance.
CRediT authorship contribution statement
S. Esser: Conceptualization, Methodology, Software, Data curation, Writing – original draft, Visualization, Investigation, Validation. U.A. Peuker: Supervision, Writing – review & editing, Project administration, Funding acquisition.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
Parts of the presented results (IGF 19305 BR: steam pressure filtration in combination with a water insoluble liquid as mother liquid) have been supported via AiF within the programme for promoting Industrial Collective Research (IGF) of the German Ministry of Economic Affairs and Energy (BMWi), based on a resolution of the German Parliament. A further gratitude goes to Dr. Ralph Dohrn from Bayer AG, who provides the material data of the used liquids evaluated by the company.
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