Fault Monitoring Based on the VLSW-MADF Test and DLPPCA for Multimodal Processes.

Actual industrial processes often exhibit multimodal characteristics, and their data exhibit complex features, such as being dynamic, nonlinear, multimodal, and strongly coupled. Although many modeling approaches for process fault monitoring have been proposed in academia, due to the complexity of industrial data, challenges remain. Based on the concept of multimodal modeling, this paper proposes a multimodal process monitoring method based on the variable-length sliding window-mean augmented Dickey-Fuller (VLSW-MADF) test and dynamic locality-preserving principal component analysis (DLPPCA). In the offline stage, considering the fluctuation characteristics of data, the trend variables of data are extracted and input into VLSW-MADF for modal identification, and different modalities are modeled separately using DLPPCA. In the online monitoring phase, the previous moment's historical modal information is fully utilized, and modal identification is performed only when necessary to reduce computational cost. Finally, the proposed method is validated to be accurate and effective for modal identification, modeling, and online monitoring of multimodal processes in TE simulation and actual plant data. The proposed method improves the fault detection rate of multimodal process fault monitoring by about 14% compared to the classical DPCA method.

Impact of Physico-Chemical Heterogeneity on Arsenic Sorption and Reactive Transport under Water Extraction.

Heterogeneity in physical and chemical properties is a common characteristic in a subsurface environment. This study investigated the effect of physico-chemical heterogeneity on arsenic (As) sorption and reactive transport under water extraction in a layered system with preferential flow paths. A flume experiment was performed to derive the spatio-temporal data of As reactive transport. The results indicated that the heterogeneous system significantly accelerated downward (vertical direction) As migration as a coupled effect of physical and chemical heterogeneity that led to fast As transport with low As sorption along the preferential flow paths. The results also indicated that such a heterogeneity effect was driven by water extraction that enhanced the downward groundwater flow along the preferential flow paths. Numerical simulations were performed by matching the experimental results to provide insights into the dominant processes controlling the As migration in the heterogeneous systems. The simulation results highlighted the importance of the kinetic oxidation of mineral-bonded Fe(II) to Fe(III) in the clay matrix that dynamically increased As sorption affinity and retarded As reactive transport. A coupled model of reactive transport along the preferential flow paths, sorption-retarded diffusion from the preferential flow paths into the clay matrixes, and reactions that change sorption affinity in the matrix was required to describe the As reactive transport systems with physico-chemical heterogeneities. The results have strong implications for understanding and modeling As downward migration from shallow to deep aquifers under groundwater pumping conditions in field systems with inherent heterogeneity.

Coupled dynamics of As-containing ferrihydrite transformation and As desorption/re-adsorption in presence of sulfide.

This study investigated the coupled dynamics of the redox transformation of arsenic-containing ferrihydrite, and arsenate desorption and re-adsorption in presence of sulfide. Batch experiments, various microscopic and spectroscopic analyses collectively revealed that electrons from sulfide competitively transferred to ferrihydrite and no arsenate was reduced. The reductive dissolution of ferrihydrite by sulfide led to the quick formation of FeS that competitively decreased the availability of sulfide for its subsequent reduction of ferrihydrite. The quick formation of FeS was followed by a relatively slow transformation of ferrihydrite to magnetite and other Fe(II)-Fe(III) minerals that were primarily bound to the residual ferrihydrite surfaces. As a result of the preservation of As-containing ferrihydrite and surface covering by the secondary minerals, the majority (> 90%)of sorbed arsenate resided in the solid phase, and <10% of arsenate participated in the desorption process during the ferrihydrite dissolution and transformation. The desorption of arsenate was fast, and followed by the kinetic re-adsorption. The rate and extent of the re-adsorption was consistent with the dynamic transformation of the secondary minerals and their sorption affinity toward As. The results have a strong implication to understanding of As concentration changes during the redox transformation of As-containing minerals in groundwater systems.