Hierarchical design of decentralized control structures for the Tennessee Eastman Process

In this work, the systematic approach to a plant-wide control design developed in a previous work by the authors [Antelo, L. T., Otero-Muras, I., Banga, J. R, & Alonso, A. A. (2007). A systematic approach to plant-wide control based on thermodynamics. Computers & and Chemical Engineering, 31(7), 677–691] is applied to derive robust decentralized controllers in the challenging benchmark of the Tennessee Eastman Process (TEP). The hierarchical control design is based on the link between thermodynamics and passivity theory as well as on the fundamentals of process networks. First, the TEP process network is decomposed into abstract mass and energy inventory networks. It is over these subnetworks where conceptual inventory control loops are developed to guarantee the convergence of the mass and energy inventories to a given compact region defined by constant inventories. Thermodynamics gives us a function (the entropy) which has a definite curvature (concavity) over these compact regions of the state space. This function can then be employed on these regions to derive natural storage or function candidates which can be used in designing controllers for stabilizing the network. The last step in the systematic control design procedure will be the realization of the controllers using the available degrees of freedom of the process. The inventory control laws will be obtained as a composition of control loops implemented over the real manipulated variables (degrees of freedom).     

Flank milling model for tool path programming of turbine blisks and compressors

In this paper, a methodology for complex surface machining based on cutting forces prediction is presented. The work is focused on blade finishing operations. The cutting forces model developed can be applied to three axis and five axis milling cases. For three-axis cases, the chip thickness is calculated according to traditional analytical methods. On the contrary, for five-axis cases the chip thickness is obtained from a geometric method developed in the paper. The cutting forces values can be calculated for the complete toolpath, but the presented model can also provide the programmer information about the cutting forces in a single point of the toolpath. The cutting force model is integrated in the CAM software in order to provide an extra tool that helps the programmer to decide which the optimal milling strategy is, based on the minimum cutting forces. In the last section, results of a case study based on impeller and blisk blades flank milling are discussed. Model predicted forces and real measured forces of flank milling operations are compared for model validation. Applying this methodology, cutting forces can be taken into account as a decisive criterion for optimal tool path selection.     

A novel approach to the chemical stabilization of gamma-irradiated ultrahigh molecular weight polyethylene using arc-discharge multi-walled carbon nanotubes

A complete study was made of the stabilization of gamma-irradiated ultrahigh molecular weight polyethylene (UHMWPE) using arc-discharge multi-walled carbon nanotubes (MWCNTs) as inhibitors of the oxidative process. MWCNTs were efficiently incorporated into the polymer matrix by ball milling and thermo-compression processes at concentrations up to 5 wt% and subsequently gamma irradiated at 90 kGy. Raman spectroscopy demonstrated the generation of radicals on the walls of the MWCNTs and that the G/D ratio was altered by their generation. The same spectra showed interactions between the polymer chains as a series of shifts are observed in the UHMWPE bands. The effect of the MWCNTs as inhibitors for the oxidative process of the UHMWPE was evaluated by means of Electron Spin Resonance (ESR) and Fourier Transformed Infrared Spectroscopy (FTIR). ESR detection of the radiation-induced radicals proved the radical scavenger behaviour of MWCNTs. FTIR measurements were performed to ascertain the influence of the irradiation and of the accelerated ageing protocol in the oxidation index of the polymer and the composites. The results pointed to the positive contribution of the MWCNTs in increasing the oxidative stability of the composite when compared to pure UHMWPE. A comparison is made between composites obtained using MWCNTs produced by the carbon vapour deposition and arc-discharge methods.     

Magnetization and Magnetoresistance First-Order-Reversal-Curves Analysis in Spin Valves

This work describes the study on the magnetization reversal for two different spin valves: the first one is characterized by in-plane magnetic anisotropy, and the second by a perpendicular anisotropy. Magnetoresistance-first-order-reversal-curve analysis was used in order to map the magnetoresistance of each valve as a function of the coercive fields and the interaction fields of the particles in the layers. For the valve with in-plane anisotropy, it was possible to identify an exchange-spring behavior in the pinned layer induced by the contact with the AF layer, and mean-field effects produced by interparticle interactions. Also, it was determined that the rotation of the magnetization of the pinned layer cannot happen by coherent rotation. For the second valve, it was possible to identify the distribution of coercivities and interaction fields of each layer, as a function the different magnetic orientations that they may have.     

A Stochastic Approach for Simulating Human Behaviour During Evacuation Process in Passenger Trains

In this paper we present a stochastic approach for modelling passenger performances during evacuation process in passenger trains. The paper is divided into two parts. The first part describes the identification of variables and data collection. This process allows obtaining statistical samples of predefined random variables (personal responses, non-emergency actions, walking speeds, etc.). Then, statistical methods to determine the input and outputs for a stochastic analysis are proposed. In the second part, results from EvacTrain^®, a stochastic model for passenger trains, were compared with other evacuation models and an announced evacuation drill. Results suggest that predicted evacuation times can be strongly dependent on the activities of individuals whose actions interrupt the continuous movement of other passengers within the aisle and the time spent by each passenger to negotiate the train steps. The advantages of using a stochastic approach for modelling passenger behaviours are discussed.     

Kalman filtered MR temperature imaging for laser induced thermal therapies

The feasibility of using a stochastic form of Pennes bioheat model within a 3-D finite element based Kalman filter (KF) algorithm is critically evaluated for the ability to provide temperature field estimates in the event of magnetic resonance temperature imaging (MRTI) data loss during laser induced thermal therapy (LITT). The ability to recover missing MRTI data was analyzed by systematically removing spatiotemporal information from a clinical MR-guided LITT procedure in human brain and comparing predictions in these regions to the original measurements. Performance was quantitatively evaluated in terms of a dimensionless L(2) (RMS) norm of the temperature error weighted by acquisition uncertainty. During periods of no data corruption, observed error histories demonstrate that the Kalman algorithm does not alter the high quality temperature measurement provided by MR thermal imaging. The KF-MRTI implementation considered is seen to predict the bioheat transfer with RMS error < 4 for a short period of time, ?t < 10 s, until the data corruption subsides. In its present form, the KF-MRTI method currently fails to compensate for consecutive for consecutive time periods of data loss ?t > 10 sec.     

Near infrared reflectance spectroscopy and multivariate analysis to monitor reaction products during biodiesel production

In agreement with the principles of green chemistry, near infrared spectroscopy (NIRS) allows multi-component analysis in a fast and nondestructive way, without requiring complex pre-treatments, being a safe, clean and energy saving technique. In this work, a preliminary study to develop near infrared calibration models to predict methyl esters (ME) yield, monoglycerides (MG), diglycerides (DG), triglycerides (TG), free glycerol (FG) and total glycerol (TotalG) content in biodiesel has been carried out. These parameters are considered key factors to determine biofuel quality, its commercialization and to study and monitor the transesterification reaction. For this purpose, samples of biodiesel produced from three different vegetable oils (maize oil, sunflower oil and olive–pomace oil) were analyzed following the EN14103 and EN14105 European standards as reference methods. NIRS calibration equations were validated with a group of validation samples. The mean spectra showed that the main variability on biodiesel NIR spectra occurred around 1700 and 2300 nm. Moreover, the principal components analysis (PCA) applied to the spectra revealed the grouping of samples according to the type of oils used for biodiesel production. The standard deviation of the prediction (cross validation) errors (RMSEP_CV) of the calibration models and the standard deviation error (RMSEP) of the validation set resulted similar to the measurement errors (intra lab SEL_r) and repeatability (inter lab SEL_R) of each analyte. Results confirm the accuracy of the developed NIRS models for determination of glycerides content and methyl esters yield in biodiesel.     

Novel Uncatalyzed Synthesis and Characterization of Diacetone Diperoxide

A novel method used to synthesize diacetone diperoxide (DADP) from acetone and hydrogen peroxide without the presence of a catalytic agent is presented. Previously reported syntheses used toluenesulfonic and m‐sulfonic acid as catalyst. DADP was prepared with a purity of 99.99 %. The melting point range (128.5–134.5 °C) is consistent with reported values. The success of the reported procedure depends on controlling the ratio between acetone and hydrogen peroxide as well as the temperature of the reaction mixture. The purified crystalline DADP samples were characterized using NMR, Raman, and IR spectroscopy, differential scanning calorimetry, gas chromatography and open atmosphere chemical ionization mass spectrometry (DART™). The structure was compared to the well‐known cyclic trimer triacetone triperoxide (TATP). The proposed synthetic scheme can be useful for preparing small amounts of the cyclic organic peroxide for characterization and fundamental studies and for formulation of gas chromatography, high performance liquid chromatography, and mass spectrometry standards.     

Prehydrolysis ofEucalyptus wood with dilute sulphuric acid: operation at atmospheric pressure

MilledEucalyptus globulus wood samples were subjected to acid hydrolysis using H₂SO₄ as catalyst. The reactions were carried out in a stirred, reflux-operated batch reactor. The effects of both catalyst concentration (in the range 3.5–10%) and hydrolysis time (0–11 h) on the concentration of arabinose, glucose, xylose, acetic acid and furfural were studied. The kinetics of xylan hydrolysis followed general trends similar to those described in earlier studies. Almost quantitative xylose recovery was achieved after 11 h of reaction time in experiments with 10% H₂SO₄. The furfural concentrations were low (0–0.44 g/L) in all the cases studied. Additional aspects relative to the selectivity of the prehydrolysis are discussed.     

Carbon‐Supported CoSe2 Nanoparticles for Oxygen Reduction Reaction in Acid Medium

Carbon‐supported CoSe₂ nanoparticles, as non‐precious metal cathodic catalyst, were prepared via the in situ surfactant‐free method with the conventional heating. Structural and electrochemical properties of the obtained 20 wt.‐% CoSe₂/C nanoparticles were investigated by means of powder X‐ray diffraction (PXRD), differential thermal gravimetric analysis (DTA‐DTG) and rotating disc electrode (RDE) techniques. CoSe₂ nanoparticles have two kinds of crystal structure after heat treatment under nitrogen at different temperature: orthorhombic at 250 and 300 °C; cubic at 400 and 430 °C. The latter structure has higher oxygen reduction activity than the former in 0.5 M H₂SO₄. CoSe₂/C nanoparticles after heat treatment from 250 to 430 °C, have an onset potential from 0.78 to 0.81 V versus the reference hydrogen electrode (RHE) in O₂‐saturated 0.5 M H₂SO₄ at 25 °C. 20 wt.‐% CoSe₂/C nanoparticles, after heat treatment at 300 °C, promote ca. 3.5 electrons, per oxygen molecule, transferred during the oxygen reduction process. They have an oxidation wave centred at 0.96 V versus RHE and display higher methanol tolerance as compared to 20 wt.‐% Pt/C (E‐TEK).