间歇提馏塔的操作

A stripping batch distillation column is preferred when the amount of the light component in the feed is small and the products are to be recovered at high purity. The operation modes of a batch stripping are believed to be the same as those of a rectifier. However, the control system of a stripper is different. In this paper, we explore three different control methods with Hysys (Hyprotech Ltd. 1997) for a batch stripper. The main difference is the control scheme for reboiler liquid level: (a) controlled by reflux flow; (b) controlled by reboiler heat duty; (c)controlled by bottom product flow. The main characteristics of operating a batch stripper with different control scheme are presented in this paper. Guidelines are provided for the startup of a batch stripper, the effects of some control tuning parameters on the column performance are discussed.     

Iterated belief change in the situation calculus

John McCarthy's situation calculus has left an enduring mark on artificial intelligence research. This simple yet elegant formalism for modelling and reasoning about dynamic systems is still in common use more than forty years since it was first proposed. The ability to reason about action and change has long been considered a necessary component for any intelligent system. The situation calculus and its numerous extensions as well as the many competing proposals that it has inspired deal with this problem to some extent. In this paper, we offer a new approach to belief change associated with performing actions that addresses some of the shortcomings of these approaches. In particular, our approach is based on a well-developed theory of action in the situation calculus extended to deal with belief. Moreover, by augmenting this approach with a notion of plausibility over situations, our account handles nested belief, belief introspection, mistaken belief, and handles belief revision and belief update together with iterated belief change.     

Automatic system for identifying and categorizing temporal relations in natural language

Nowadays, the automatic processing of digitalized documents is crucial to cope with the increasing amount of information available. This issue is addressed from the natural language processing (NLP) research field. One of the tasks required for many NLP applications is temporal information processing. It involves the automatic extraction and interpretation of temporal expressions, events, and their relations. Specifically, the identification and the categorization of temporal relations are the most complex subtasks yet to solve, judging from the results reported in the latest international evaluation exercise. Temporal relation identification has been addressed by very few approaches, and the current categorization approaches are still not a definitive solution. This paper presents a system that approaches temporal relation identification and categorization. The former is approached with a knowledge‐driven strategy and the later with data‐driven strategy based on different machine‐learning techniques. Our proposal has been empirically evaluated over the currently available English data sets annotated with temporal information (TimeBank and AQUAINT) in a 10‐fold cross‐validated experiment. The results obtained support that the presented approach achieves a high performance. It improves the baseline F1 by 46% and outperforms the state of the art. © 2012 Wiley Periodicals, Inc.     

Development of a control algorithm for air‐scour reduction in membrane bioreactors for wastewater treatment

BACKGROUND: Membrane bioreactors are used in an increasing number of wastewater treatment facilities because of their compactness and efficiency in solid‐liquid separation, but energy requirements are still higher than other competitive technologies such as conventional activated sludge. RESULTS: In this paper the development of an air‐scour control algorithm based on short‐term and long‐term membrane permeability evolution is presented. An open loop calibration and partial validation was carried out in a semi‐industrial scale pilot plant where manual changes in air‐scour flow had been previously carried out. The control system was successfully tested in closed loop in an industrial scale pilot plant, defining a maximum daily air‐scour decrease or increase of 6% of the air‐scour recommended by membranes suppliers. An average air‐scour saving of 13% and a maximum of 20%, calculated in terms of air flow saved, were achieved during the validation test without any apparent long‐term effect on membrane permeability. CONCLUSION: It was proven that the air‐scour control system is an important tool capable of reducing operational costs in MBR systems. Copyright © 2011 Society of Chemical Industry     

Environmental-barrier coating ceramics for resistance against attack by molten calcia-magnesia-aluminosilicate (CMAS) glass: Part II, β-Yb2Si2O7 and β-Sc2Si2O7

The high-temperature (1500?°C) interactions of two promising dense, polycrystalline EBC ceramics, β-Yb₂Si₂O₇ and β-Sc₂Si₂O₇, with a calcia-magnesia-aluminosilicate (CMAS) glass have been explored as part of a model study. Unlike YAlO₃ and γ-Y₂Si₂O₇ in the accompanying Part I paper, little or no reaction is found between the Y-free EBC ceramics and the CMAS. In the case of β-Yb₂Si₂O₇, a small amount of reaction-crystallization product Yb-Ca-Si apatite solid solution (ss) forms, whereas none is detected in the case of β-Sc₂Si₂O₇. The CMAS glass penetrates into the grain boundaries of both EBC ceramics, and they both suffer from a new type of ‘blister’ cracking damage. This is attributed to the through-thickness dilatation-gradient caused by the slow grain-boundary-penetration of the CMAS glass. The success of a ‘blister’-damage-mitigation approach is demonstrated, where 1?vol% CMAS glass is mixed into the β-Yb₂Si₂O₇ powder prior to sintering. The CMAS-glass phase at the grain boundaries promotes rapid CMAS-glass penetration, thereby avoiding the dilatation-gradient.     

Digital architecture for a piecewise-linear arbitrary-waveform generator

In this paper a digital architecture for generating piecewise-linear arbitrary waveforms is presented. The proposed design is able to generate a piecewise-linear periodic signal by only using a minimum number of input data (breakpoints). The generator circuit implements a hybrid scheme which takes advantage of two methods: the purely piecewise-linear interpolation and the lookup-table structure. From the piecewise-linear method exploits the characteristic of a reduced memory requirement as well as the capability of automatically construct a waveform by repetitive (iterative) function evaluations. From lookup-table makes use of the simplicity in hardware implementation and the higher processing speed. In order to verify the performance of this proposal, three piecewise-linear waveforms have been successfully implemented in a ATMEGA32 microcontroller. Experimental results show a fast execution speed and a reduced memory demand in the proposed circuit realization.     

Reactor core isolation cooling system analysis of the Fukushima Daiichi Unit 2 accident with RELAP/ScdapSIM

The reactor core isolation cooling (RCIC) system is an auxiliary system of a boiling water reactor (BWR) that provides makeup water in the case of a severe accident. During the Fukushima accident, the extended operation of the RCIC had a large influence on the accident progression and delayed the core meltdown by almost 70 h. During the Fukushima accident, the water level in the reactor pressure vessel (RPV) was assumed to rise enough to flood the main steam line (MSL), which caused the water to move through the RCIC steam turbine and reduce the overall system water injection capability. A RELAP/ScdapSIM analysis was carried out by using RCIC nodalization to reproduce the Fukushima accident and evaluate the impact of the RCIC system on the accident progression. A coefficient based on the critical flow model was included in the RELAP/ScdapSIM source code to reproduce the degradation suffered by the turbine due to the presence of water. Although highly simplified, the analysis demonstrated the RCIC system's feedback capability, which allows the RCIC to control the plant conditions for a long period of time without any human interaction.     

Automatic voltage regulators siting in distribution systems considering hourly demand

This paper presents an approach for the best site determination of automatic voltage regulators in distribution systems taking into account hourly variations of demand. A unique objective function is defined considering losses and voltage drop indices through the weighting coefficients method and then optimized using genetic algorithms. The evaluation of the objective function is done through a Newton Raphson load flow, allowing the optimal tap position determination. To consider the variability of demand, multiple hourly deterministic optimization processes are applied considering the daily load profiles of each node. Results of the application of the proposed approach over a test system and a real distribution feeder are presented.