Neural network‐based PID gain tuning of chemical plant controller

Plant control systems are now highly automated and are used in many industries. The control performance changes with the passage of time because of deterioration of plant facilities. For this reason, human experts tune the control system to improve overall plant performance. In this study, a PID control system for the oil refining chemical plant process is discussed. In oil refining, thousands of control loops are used in plants in order to keep the product quality at the desired value and to assure the safety of plant operation. Due to the ambiguity of the interference between control loops, it is difficult to estimate the plant dynamical model accurately. Using a neuro emulator and a recurrent neural networks model (RNN model) for emulation and tuning of parameters, a PID gain tuning system for a chemical plant controller is constructed. Numerical experiments using actual plant data demonstrate the effect of the proposed method. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(4): 28–36, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20973     

Liquid flow in impeller region of an unbaffled agitated vessel with an angularly oscillating impeller

The characteristics of a liquid flow were studied in the impeller region of an unbaffled agitated vessel with an angularly oscillating impeller whose unsteady rotation proceeds while periodically reversing its direction at a set angle. The measurement of the velocity of the liquid flow was performed by particle tracking velocimetry (PTV), abreast of that of the torque of the shaft to which the impeller was attached. When a disk turbine impeller with six flat blades was used with variations in operating conditions, such as the frequency and amplitude of impeller angular oscillation, a series of images obtained during one oscillation cycle were analyzed to characterize the internal and discharge streams inside and outside the impeller rotational region. Energy data were inferred on the basis of the circumferential and radial velocities of an internal flow. Results showed that although the total head provided to the liquid by the impeller blades is almost similar, independent of the amplitude of impeller angular oscillation, namely, the acceleration of its movement, the transformation of energy from the pressure head to the velocity head is more efficient at a larger amplitude. In addition, the discharge flow was characterized in terms of volumetric flow rates calculated from the radial and axial velocities. The operation at a smaller amplitude was shown to transform the flow more successfully from the radial direction to the upward and downward axial directions near the vessel wall.     

Jet impingement quenching phenomena for hot surfaces well above the limiting temperature for solid–liquid contact

Experiments were conducted to understand the phenomena that happen just after a subcooled free-surface circular water jet impinges on a high temperature surface. A 2 mm-water-jet of 5–80 K subcooling and 3–15 m/s velocity was impinged on the flat surface of a cylindrical steel/brass block that was preheated to 500–600 °C. The transient temperature data were recorded and used to predict the surface temperature by an inverse heat conduction technique. A high-speed video camera was also employed to capture the flow condition. It is found that for a certain period of time the surface temperature remains well above the thermodynamic limiting temperature that allows stable solid–liquid contact. What happens during this period and what makes the surface temperature drop to the limiting temperature are important questions whose possible answers are given in this article. The cooling curves at the center of the impinging surface for different experimental conditions are also explained in relation with the limiting temperature and three characteristic regions having different types of flow patterns are identified.     

Effect of V and Nb on precipitation behavior and mechanical properties of high Cr steel

Employment of high Cr steel as a main structural material is considered as a way to achieve economical competitiveness of fast breeder reactors. V and Nb are believed to improve the high temperature strength of high Cr steels by precipitating as carbides and/or nitrides, namely fine MX particles. However, the long term efficiency and stability of such precipitation strengthening mechanisms provided by the fine MX particles have not been clarified yet. A series of trial products controlling V and Nb contents is produced and mechanical tests are conducted to investigate the effect of these elements on the mechanical properties and the long term stability of the MX strengthening mechanism. Before and after a long term aging process, metallurgical examinations and quantitative analyses are conducted to investigate the effect of these elements on microstructure evolutions. Based on these results, the long term efficiency and stability of the strengthening mechanisms provided by the fine MX particles are discussed. Higher strength and lower ductility are obtained with the increases of V and Nb contents, although the influence of Nb content tends to be saturated at about 0.01 mass%. MX does not grow and any new precipitates cannot be observed after aging at 873 K for 6000 h. Therefore, it is expected that MX is stable after aging at 823 K for approximately 167,000 h based on Larson-Miller parameter.     

New compound ScTiNbO6 synthesized via phase transformation from anatase to srilankite-like structure

A new srilankite-like compound ScTiNbO₆ was synthesized as a single phase at 900 °C via phase transformation using anatase-type nanoparticles that were directly formed from solution mixture of Sc(NO₃)₃, TiOSO₄, and NbCl₅ under mild and weakly basic hydrothermal condition at 180 °C for 5 h. Anatase-type Sc_0.5Ti₂Nb_0.5O₆ nanoparticles transformed into rutile phase at 1000 °C. The new phase that was appeared via phase transformation was identified as srilankite-like structure with a trace of symptomatic wolframite, α-PbO₂ related structure. The optical band gap of ScTiNbO₆ was 3.58 eV. This titania-base material has potential for application as catalyst and photoluminescence, etc.     

Relationship between Spin Gap and Crystal Structure in La-214 Cuprate Superconductor

To investigate the intrinsic nature of spin correlations in La-214 high-T _c cuprate, we performed neutron scattering measurement on La_1.94−x Sr _x Ce_0.06CuO₄ (LSCCO) samples for two different hole concentrations. Since the Ce-doping reduces the hole concentration without changing the bulk lattice distortion, the corrugation of CuO₂ planes in the Sr and Ce co-doped LSCCO system is more relaxed compared with that in La_2−x Sr _x CuO₄ (LSCO) at equivalent hole concentration. In the optimally doped x=0.18 sample, clear spin gap structure was observed, as is the case of the optimally doped LSCO. Therefore, the spin gap structure is insensitive to the lattice distortion. In the underdoped x=0.14 sample, the local spin susceptibility (χ″(ω)) above 2 meV increases with increasing the energy transfer (ω) and reaches an intensity maximum at ∼7 meV, exhibiting a gap-like structure. The observation of gap-like structure in the present underdoped sample is quite different from the energy-independent χ″(ω) reported for underdoped LSCO. The possible origin of difference of spin excitations is discussed from the viewpoint of two-component picture for spin fluctuations.     

Microencapsulation of hydrophilic solid powder as fire retardant agent with epoxy resin by droplet coalescence method

To give water resistance to Bistetrazol–diammonium (BHT–2NH₃) as a fire retardant agent, microencapsulation with epoxy resin was tried by the droplet coalescence method. In this method, two kinds of epoxy resin droplets were prepared; one is the larger epoxy resin droplet containing BHT–2NH₃ as a core material and the other the smaller droplets containing Imidazole as a gelation agent. The larger epoxy resin droplets were made to coalesce with the many smaller droplets during the microencapsulation process to prepare microcapsules. In the experiment, the agitation velocities for preparation of the droplets and for coalescence were mainly changed. With increase in the impeller speed, the content of core material increased, became maximum because of increase in the coalescence frequency, and then decreased because of breakup of droplets. With increase in the impeller speed, the leakage ratio of core material decreased, became minimum, and then increased. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.     

Study on Solubility of Nb_2O_5 in KOH Solution and Alkali Leaching of Niobite

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