Measurement Techniques

Implementation of computer aided approach into hazard and operability (HAZOP) study is one of the most researched topics in the field of hazard identification improvement. However, acceptance of an automated HAZOP tool in the industrial practice is limited. This contribution provides retrospective analysis of application issues connected with the use of process simulations in computer aided HAZOP studies. As case studies, mathematical models utilising different sets of unit operations, e.g. plug flow reactor, continuous stirred-tank reactor, phase separator, heat exchanger etc. were analysed. Two different simulation platforms, commercial process simulator Aspen HYSYS and our own mathematical models in MATLAB, were employed. Relevant concerns regarding the use of process simulations in the HAZOP study such as model reliability and its parameter uncertainties effect on the HAZOP study output and interpretation variability of quantitative HAZOP deviations for process simulations are discussed. It is demonstrated that the application of process simulation is a feasible way to perform precise safety analyses of processes widely used in chemical industry. However, proper attention has to be paid to the construction and use of mathematical models in order to develop a suitable software solution.

This paper was aimed to illustrate the use of process simulation tools to find bottlenecks in a chemical plant. In practice, finding the first bottleneck of a plant is simply by increasing the capacity. However, two questions remain, e.g. what would the next bottleneck be and how big the first bottleneck needs to be expanded until the next bottleneck is reached. These questions can be repeated until eventually the whole equipment in the plant needs to be debottlenecked. Since it is impossible to answer the above questions in practice, a process simulation approach is utilized. Relevant equipment data and a validated thermodynamic model are used to build such a model. Plant performance trials are taken into account to estimate practical parameters such as fouling coefficients and plate tightness. This work requires strong interactions between operational people, consistent data gathering, and process simulation skill. The approach used in this work has shown that a reasonably accurate model can be built. The result has shown that the model can identify the first bottleneck as confirmed on the field. Sequence of bottlenecks and their corresponding increment of capacity increase have also been identified. The simulation results also illustrate the use of process simulation for plant debottlenecking.

The shear and extensional viscosities of a polypropylene resin were studied using a capillary rheometer and capillary dies of 1‐mm diameter and length of 10, 20, and 30 mm. Melt temperatures at 190, 205, and 220°C and shear rates between 100 and 5000 s−1 were used. At the highest shear rate a visible melt fracture was observed. An equation relating the pressure drop and die length was derived with consideration of pressure effects on melt viscosities and the end effect. After the correction for pressure effects the true wall shear stress and end effect at zero pressure were calculated. The end effect showed a critical stress of melt fracture around 105 Pa, and increased rapidly when shear stress increased above the critical stress. From shear stress the shear viscosity was calculated, and a power law behavior was observed. Extensional viscosity was calculated from the end effect and showed a decreasing trend when strain rate increased. After time–temperature superposition shift shear viscosity data correlated well, but an upward trend was observed in extensional viscosity when melt fracture occurred. Die swell ratio at different temperatures can be plotted as a function of wall shear stress and was higher for shorter dies. © 2002 Wiley Perioodicals, Inc. J Appl Polym Sci 84: 1269–1276, 2002; DOI 10.1002/app.10466

Metal injection molding feedstocks are typically highly filled thermoplastic systems. In this study, the effects of feedstock composition on flow properties are examined using the capillary rheometer and the extrusion plastometer. The two techniques are also compared with respect to sensitivity to feedstock composition and their utility in predicting variations in processing performance.

The influence of hydrogen bonding on the flow behavior of polymer melts at high shear rate has been investigated using a capillary extrusion rheometer. The systems studied were copolymers of ethylene and acrylic or methacrylic acid. Hydrogen bonding was found to substantially enhance both flow activation energy and viscosity level, as well as the degree of dependence of viscosity on rate of shear. It was also found that hydrogen bonding does not influence the critical shear stress for onset of “melt fracture.” The data support the view that hydrogen bonds act effectively as temporary (quasi‐) crosslinks during the short time scales of deformation involved in flow at high shear rates.

Introduction The use of process simulators during the capstone process design course has become an expected part of most chemical engineering curricula. Unfortunately, the mechanisms to teach students how to use these tools have often been ad hoc or completely lacking. Ideally, students would gain familiarity with process simulation throughout the curriculum so that when starting senior design, they have a good understanding of the benefits, limitations, and general functionality of the process simulator. In practice, most students arrive in their senior design classes without knowing how to use a simulator to help solve open-ended problems. In general, their experience has been with small, well-defined problems. To help alleviate this problem, a short-term design project has been developed to teach the basics of process simulation within the context of analyzing an existing plant and suggesting process improvements. Specific goals of this project include (1) learn how to simulate a wide variety of unit operations, (2) learn benefits and limitations of different thermodynamic models, and (3) understand system-wide effects of changing process variables (as part of the process improvement aspect).

For sorptional data to be useful in simulation and design purposes, they must be represented by equations valid in the conditions usually found in industrial practice. In this regard sorptional models that include the influence of temperature on desorption and sorption equilibrium values are most valuable. In this article, water desorption and sorption isotherms of rose hip fruits (Rosa Eglanteria) were experimentally determined by the gravimetric method, and from these the isosteric heat of sorption was calculated. According to the ANOVA test carried out for this fruits, no significant differences were found between experimental desorption and adsorption isotherms. Seven models were tested to mathematically represent the moisture content as a function of water activity (aw) in the aw range of 0.11 to 0.85 and temperatures of 20, 40, and 60°C, for further use in process simulation. The five-parameter GAB model was most accurate, with an MRE of −2,9 % and R2 = 0.989. The values obtained for the isosteric heat of sorption were fitted with a previous published equation, with an MRE% = −0.05. The isosteric heat of sorption derived from the GAB five parameters equation, for the corresponding monolayer moisture content, only differed by 1.25% with the calculated in this paper.

A structured kinetic model for recombinant protein production by Mut+ strain of Pichia pastoris

Chapter 8 - Artificial intelligence for HAZOP

Quantitative risk assessment integrated with process simulator for a new technology of methanol production plant using recycled CO2

A numerical methodology has been developed to fit cure kinetic reaction models based on DSC scans only, and not isothermally as traditionally done. A non-linear least squares Levenberg-Marquardt algorithm was used to fit the reaction rates with the autocatalytic Kamal-Sourour kinetic model. The technique avoids the use of isothermal DSC data which causes additional problems in the fitting procedure, such as oscillations in low temperature scans or lost information for fast reaction materials at high process temperature scans. The new methodology is based on a series expansion of the kinetic parameters as a function of temperature. The technique was first tested with the vulcanization process of silicone rubber which is dominated by a cross-linking single-event curing reaction. The method was also tested with phenolic formulations, which according to the hardener, present one or two reaction events. Additionally, the glass transition temperature, of these materials, during the curing process is mostly below the vitrification line, thus, diffusion effects can be neglected. The results show good agreement between the experimental DSC scans and the predicted reaction rates. The technique presented in this paper is intended for use in process simulation, and not to infer kinetic reaction mechanisms.

A structured kinetic model describing growth, differentiation, and penicillin production in submerged Penicillium chrysogenum fermentations is reported. The filamentous hyphae are divided into four distinct regions on the basis of the activities and structure of hyphal compartments, viz., actively growing (mainly apical) regions, nongrowing or penicillin producing regions, vacuoles, and degenerated or metabolically inactive regions. A mechanistic approach is taken to give quantitative descriptions of differentiation and degeneration as a consequence of vacuolation. The growth and degeneration of vacuoles are expressed in the form of a population balance. The model assumes that newly generated vacuoles appear by differentiation of healthy regions, grow in size with limitation of available substrate, and eventually give rise to empty hyphal compartments. In the model the penicillin production is related to the amounts of the nongrowing regions of the hyphae. The model is used for successful predictions of the amounts of the four hyphal regions and the penicillin G production rate throughout the fed-batch fermentations of an industrial P. chrysogenum strain under different glucose feeding regimes. Quantitative information on proportions of the hyphal regions was obtained from image analysis measurements and the parameters of the kinetic model were identified. When the glucose feed rate to the production culture is switched between a high and a low value, the model can successfully predict the dynamic changes of differentiation and the resulting penicillin production caused by the variations in the nutrient conditions. The use of image analysis to characterize differentiation as a basis for structured modeling of the penicillin fermentation appears to be very powerful, and the method has great potential for use in process simulation and control of antibiotic fermentations.

The present work aims to investigate the influence of flow geometry on volume instability associated to a linear polydimethylsiloxane (PDMS). To do so, a convergent radial flow is created at the die entrance. Particle Image Velocimetry (PIV) recordings performed under unstable flow regime, in the capillary rheometer, characterized with the new entrance zone, show a new pattern of streamlines above the die: elongational stresses are less pronounced; furthermore elongational stresses, as well as shear stresses, tend to concentrate near the lip of the capillary die. Photographs of extrudate strands obtained at the die exit, depict a new morphology of defect which appears with a well-established radial flow. These results lead to the agreement the correlation between the gross melt fracture and the flow instability at the entrance zone, as well as the importance of elongational and shear components linked to the upstream flow in the appearance and the development of volume distortion.

In this study, capillary extrusion experiments and rupture visualization experiments were carried out with a combined die configuration where two different dies were attached in a capillary rheometer. We observed that the gross melt fracture (GMF) and rupture of the melt occurred simultaneously when the diameter of the die located at the upstream position was larger than that of the die located downstream. However, when the location of the dies were interchanged, that is, the diameter of the upstream die was smaller than that of the downstream die, the upstream rupture did not accompany GMF up to a certain extent of shear rate. From these observations, we present a new theory on the origin of GMF. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Effect of thermal degradation on rheological properties for poly(3-hydroxybutyrate)