This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Vor dem Hintergrund der Energiewende wird die aktuelle Forschung zum energieoptimalen, lastflexiblen Betrieb von Luftzerlegungsanlagen beschrieben. Zum einen wird ein realitätsgetreuer, druckgetriebener Ansatz zur dynamischen Simulation vorgestellt. Auf dessen Basis wird ein detailliertes, transientes Simulationsmodell einer realen Luftzerlegungsanlage, ein digitaler Zwilling, erstellt. Exemplarisch werden Simulationen extremer Betriebsszenarien, wie das Anfahren oder Abschalten des Hauptwärmeübertragers, der Trennkolonnen und der gesamten Luftzerlegungsanlage, beschrieben. Zum anderen wird die Lebensdauer des Hauptwärmeübertragers aufgrund der hohen thermischen Wechselbelastung mithilfe eines Prüfstands untersucht. Die aufgenommenen Daten dienen zur Ableitung und Validierung dreidimensionaler Simulationsmodelle.
Air separation units are one of the prime examples for studies on demand side management and (non-)linear model predictive control due to their high power consumption and energy storage potential. These plants separate ambient air into its main components, nitrogen, oxygen, and argon, by means of cryogenic distillation at different pressure levels. Approximately two thirds of the industrially operated air separation units consider the separation of argon either as a value product or for reasons of energy efficiency. However, most of the studies in literature neglect the separation of argon since this requires additional equipment, increases the heat and process integration and, thus, the complexity of process control. In this work, a digital twin of an air separation unit with argon system is used to analyze and to improve load change procedures. Moreover, the potential of applying the digital twin as a soft sensor is demonstrated.
As part of the Energiewende, the current research on energy‐optimized, flexible operation of air separation units is described. A realistic, pressure‐driven approach for dynamic simulation is presented, which is used to provide a detailed, transient simulation model, a digital twin, of an air separation unit. Extreme operation scenarios, such as start‐up and shutdown of the main heat exchanger, the distillation columns or the entire air separation unit, are described. Since the main heat exchanger experiences repeated temperature changes, its lifetime is investigated in a test rig. The gathered data is used to derive and validate detailed, three‐dimensional simulation models.
Fixed-tube-sheet shell-and-tube heat exchangers (FTHEs) are widely used in process plants to enhance energy efficiency and to control temperature levels of unit operations. Even moderate temperature differences between shell and tube bundle of FTHEs can lead to failure mechanisms induced by thermal stress. To avoid equipment failure, design codes require an analysis of the transient response of an FTHE during special operating conditions. This work presents a modularhierarchical approach for the dynamic simulation of FTHEs, which is applied to special operating scenarios such as a loss of tube-side flow, a shell-side steaming-out (cleaning procedure to remove hydrocarbon residues with steam) and a reactor trip (sudden stop of exothermic reaction).
Background
The aim of this study was to investigate the occurrence of postoperative bleeding following dentoalveolar surgery in patients with either continued vitamin K antagonist medication or perioperative bridging using heparin.
Methods
A retrospective study was performed analyzing patients who underwent tooth extraction between 2012 and 2017. Patients were retrospectively allocated into two comparative groups: un-paused vitamin K antagonist medication versus bridging using heparin. A healthy, non-anticoagulated cohort with equivalent surgery served as a control group. Main outcome measures were: the occurrence and frequency of postoperative bleeding, the number of removed teeth, the surgical technique of tooth removal (extraction/osteotomy/combined extraction and osteotomy) and the prothrombin time.
Results
In total, 475 patients were included in the study with 170 patients in the group of un-paused vitamin K antagonist medication VG, 135 patients in the Bridging group BG and 170 patients in the control group CG. Postoperative bleeding was significant: CG versus VG p = 0.004; CG versus BG p < 0.001, BG versus VG p < 0.001. A significant correlation of number of the extracted teeth in the BG (p = 0.014) and no significance in VG (p = 0.298) and CG (p = 0.210) and in the BG versus VG and CG with p < 0.001 in terms of surgical intervention extraction. No difference observed in terms of prothrombin time.
Conclusions
Bridging with heparin increases the risk for bleeding compared to un-paused vitamin K antagonist medication. The perioperative management of anticoagulated patients requires a well-coordinated interdisciplinary teamwork to minimize or at best avoid both: postoperative bleeding and thromboembolic incidences.
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