João Alexandre Ferreira da Rocha Pereira

Pressure wave behaviour and leak detection in pipelines

Abstract In the present work on-line computational techniques have been developed and used in the analysis of hydraulic transients caused by leakage, in order to detect and locate pipeline ruptures. Pressure transients were obtained in two PVC pipelines 3 4 ″ diameter by using four pressure transducers connected to a PC computer equipped with A/D and D/A converters. The pipelines were 433 m and 1,248 m long. Leaks were simulated at different positions along the pipelines. Experiments were carried out for different liquid flow rates corresponding to Reynolds number in the range from 2,000 to 13,000. Leak percentage were in the range from 5% to 50% of the nominal liquid flow. A computer program to be run on-line was developed to simulate the leak, to read and filter the pressure transducers data, to display the pressure transient plots and to obtain leak location information. The detection system showed good performance in the detection of small leaks. Leaks as small as 5 % of the nominal liquid flow rate are readily detected. Leak locations were computed from pulse time delay between the various pressure transducers. The computed leak positions approached the actual values with precision. The developed software shows to be a very useful tool to the automatic supervision of pipelines as instantaneous leaks are readily detected and located.

Catalytic wet-air oxidation of lignin in a three-phase reactor with aromatic aldehyde production

In the present work a process of catalytic wet air oxidation of lignin obtained from sugar-cane bagasse is developed with the objective of producing vanillin, syringaldehyde and p-hydroxybenzaldehyde in a continuous regime. Palladium supported on g-alumina was used as the catalyst. The reactions in the lignin degradation and aldehyde production were described by a kinetic model as a system of complex parallel and series reactions, in which pseudo-first-order steps are found. For the purpose of producing aromatic aldehydes in continuous regime, a three-phase fluidized reactor was built, and it was operated using atmospheric air as the oxidizer. The best yield in aromatic aldehydes was of 12%. The experimental results were compatible with those values obtained by the pseudo-heterogeneous axial dispersion model (PHADM) applied to the liquid phase.

Fuzzy control of a PMMA batch reactor: Development and experimental testing

Abstract The present work is concerned with the design and experimental testing of a fuzzy control algorithm for temperature control of a methyl methacrylate (MMA) batch polymerization reactor. Ethyl acetate is used as solvent and benzoyl peroxide is the reaction initiator. The polymerization reaction is considered a challenge since it presents non-linear and transient behavior. The development of the fuzzy control and its comparison to a conventional PID (velocity form) controller is shown. In the design of PID–fuzzy control, the knowledge obtained from the process reaction curve procedure is employed to determine proper membership functions. Fine tuning is obtained altering the output scaling factor and cardinality. A digital filter was successfully used in order to overcome the oscillatory behavior of the temperature. According to experimental results, the PID–fuzzy was considered more suitable and reliable for this polymerization process control since it outperformed PID velocity form algorithm.

Control strategies analysis for a batch distillation column with experimental testing

Abstract The dynamic nature and the non-linear behaviour of batch distillation equipment pose challenging control system design when products of constant purity are to be recovered. Several alternative column configurations and operating policies have been studied. However, issues related to the on-line operation of such process have not been properly addressed. The present work describes the investigation with experimental verification of computer based control strategies to batch distillation: a programmable adaptive controller (PAC), a self-tuning regulator (STR) and a non-linear model predictive control (MPC). The developed control systems made the conventional batch distillation column more efficient and easy to operate. Experiments performed on the pilot column confirm the simulation results.

Kinetic evaluation of polyol production by three-phase catalytic hydrogenation of saccharides

Kinetic evaluations were accomplished in a discontinuous three-phase reactor for saccharose, glucose and fructose hydrogenations at 373, 393 and 413 K, and 24 atm. Selectivities attained values in the order of 99.05%. Langmuir-Hinshelwood models based on heterogeneous mechanisms were proposed and the optimization and kinetic quantification of the process were performed.

Digital filtering in the control of a batch distillation column

Abstract Measurement signals that a computer uses to take control actions are usually contaminated by noise. The presence of noise is undesirable because it may be detrimental to the operational control. In order to reduce the noise level in a batch distillation column control loop, two digital filters were experimentally tested: the double exponential filter and the moving average filter. The runs have shown how important the choice of the digital filter is to achieve a good control performance. For control tasks, this choice must be a compromise between data smoothing and the ability to respond rapidly to real changes in the process.

Experimental dynamic evaluation of three-phase reactors

The hydrodynamic parameters were determined for two different three-phase systems (fluidized-bed and trickle-bed) through the experimental evaluation of the dynamic residence time distribution in the gas or liquid phase. For different fluid phase flow rates the fluidized-bed system was operated with a tracer in the gas phase and in the trickle-bed with a tracer in the liquid phase. The analysis of the processes was achieved through the application of different models representing the dynamic behavior of tracers present in the gas and liquid phases with a simulation of experimental operations of the three-phase reactors. The transfer functions developed for the two systems made it possible to estimate the hydrodynamic parameters providing the gas holdup (2.22 x 10-2 to 8.42 x 10-2) and the gas phase Peclet number (54.18 to 41.20) for the fluidized-bed and the liquid holdup (0.16 to 0.25), the liquid phase Peclet number (20.37 to 4.52) and wetting efficiency (0.34 to 0.56) for the trickle-bed.

THE DEVELOPMENT AND EXPERIMENTAL TESTING OF A FUZZY CONTROL SYSTEM FOR BATCH DISTILLATION

The present work describes the development and implementation of fuzzy control algorithms in order to control on-line the overhead product composition of a batch distillation column. Firstly, the influence of design parameters was evaluated through computational simulations and then the algorithms were experimentally tested by monitoring a pilot column. Binary mixtures of n-hexane/n-heptane were distilled. Temperature measurements and vapor-liquid equilibrium data are the basis for the inference of overhead and bottom compositions. Two different operational strategies were used for the experimental runs: constant overhead product composition and previously determined set-point trajectory. Using the first strategy, the performance of the fuzzy controllers is compared to the performance of conventional feedback digital controllers. Experimental results show that fuzzy control presents a better performance than the conventional digital feedback control and also that fuzzy controllers were able to deal successfully with variable set-point strategy, albeit using constant design parameter values. Under conventional control, the average reflux rate implemented was higher than the average reflux rate implemented with fuzzy algorithms. Consequently, the process becomes less time- and energy-consuming under fuzzy control. Since fuzzy methodology is a promising new way of looking at process control problems and their solutions, the results of this work could provide control system designers with a better evaluation of the potential worth of fuzzy control.

Hydrodynamic and tray efficiency behavior in parastillation column

This work presents aspects of the parastillation process, which employs a unique distillation column where the vapor stream is divided into two equal parts and the falling liquid is alternately in contact with both vapor parts on a stage-by-stage basis. A laboratory-scale apparatus was used to study the parastillation column. Experiments were carried out under total and partial reflux conditions using an ethanol-water system. Experiments were conducted to analyze the effects of vapor flow rate and initial ethanol concentration in the reboiler on the hydrodynamic conditions. Limiting operating conditions were defined. Murphree separation efficiencies were calculated and discussed.

Sensitivity to guest–host force fields in adsorption equilibrium of cyclic hydrocarbons in one-dimensional molecular sieve

We have investigated the effect of different guest–host force fields (united atom, UA; all-atom, AA; and anisotropic united atom, AUA) on the adsorption of cyclic hydrocarbon molecules in AlPO4-5 molecular sieve. Grand canonical Monte Carlo (GCMC) simulations of benzene, xylene and cyclohexane adsorption and positioning are carried out. The results suggest that the force field choice affects considerably the positioning of benzene and cyclohexane molecules while xylenes presented a smaller sensibility. The force fields difference of sensibilities among cyclical molecules seems to be associated with the critical geometric condition identified by Yashonath and Santikary denominated levitation effect. In this condition, the net forces on the guest due to the host is at a minimum, the levitation ratio (γ) is close to unity and we have a weakly bound guest that can be easily moved from its balance position. Unlike xylene, that is only slightly affected by the choice of the force field, benzene and cyclohexane molecules in AlPO4-5 have such dimensions that result in levitation ratio (γ) close to unity. These results point out to the care that should be taken in the choice of the force field when the guest–host size ratio is near the value defined for the levitation effect.