PLANTWIDE CONTROL OF ACETYLENE HYDROGENATION PROCESS

As an application of Plantwide control, where few papers have been published about the integrated process design and control of complete plants, the acetylene hydrogenation process has been considered as the goal of this research. Firstly, all plant units were controlled separately using PID controllers, then, complete plant control was based on the 15 steps of Luyben’s plantwide control strategy. An acceptable overall plant control behavior was achieved in terms of settling times and overshoot. An improvement was also, noticed on the plantwide control application when cascaded controllers are used for the developed control system. The improvement was clearly on the temperature control

Implementation of an effective time-saving two-stage methodology for microstructural characterization of cemented carbides

Linear intercept on scanning electron microscopy micrographs is the most commonly used measurement method to determine carbide grain size and contiguity in WC–Co cemented carbides (hardmetals). However, it involves manual time-consuming measurements and is critically dependent on the quality of the micrographs as well as on the identification and definition of grain boundaries. In this study a two-stage methodology for microstructural characterization of hardmetals is presented. First, a digital semi-automatic image analysis procedure for grain size determination of the carbide phase is presented. It involves an experimental assessment of grain size on processed images corresponding to a series of WC–Co and WC–Ni cemented carbide grades with different microstructural characteristics. Obtained results are then compared to the values obtained by means of the linear intercept technique. A good correlation between the mean grain sizes determined following both measurement techniques was attained. Based on experimental findings, a series of empirical relations were found to correlate grain size distributions obtained following both methods. Second, an empirical relation for estimating carbide contiguity in WC–Co cemented carbides is proposed. This relation considers simultaneously the influence of the binder content and the experimentally determined mean grain size on contiguity. The proposed equation for contiguity estimation is based on extensive data collection from open literature. An excellent agreement was attained between contiguity values estimated from such equation and those obtained using the linear intercept technique. This validates the two-stage procedure as an effective time-saving methodology for microstructural characterization of WC–Co cemented carbides.Peer ReviewedPostprint (author's final draft

Residual strength of WC-Co cemented carbides after being subjected to abrupt temperature changes

Thermal shock and thermal fatigue are recognized as common failure modes for WC - Co cemented carbides (hardmetals) in several applications in volving service temperature changes. However, information on microstructure - performance for these materials when subjected to abrupt changes in temper ature is rather limited. In this investigation, the thermal shock resistance of two WC - Co cemented carbides is studied on the basis of their residual strength after being subjected to temperature changes. The materials studied correspond to grades with dif ferent grain size (medium and ultrafine) but similar binder content. Thermal shock variables include two temperature difference ranges (400ºC and 550ºC) as well as number of abrupt changes (1, 3 and 10). Residual strength results were related to parameters extracted from Hasselman’s theory . It is found that medium - sized hardmetal exhibits a higher strength loss in the first quenching cycle but a greater damage tolerance to repeated thermal shocks than the ultrafine - sized. The assessed residual strength tren ds are in agreement with those expected from evaluation of Hasselman’s parameters for quantifying resistance to either crack initiation or crack propagation induced by thermal shockPostprint (published version

Rotary moulding of ceramic hollow wares

A novel processing method for the fast and economic production of hollow ceramic components has been developed by combining in-situ coagulation moulding with a modified version of the technique of rotary moulding, the latter being adapted from the polymer industry. The process was found to require a high solids content suspension, hence development work was performed in this direction though in the end a new, commercial suspension was utilised. Of the three forming routes of gel casting, direct coagulation casting and in-situ coagulation moulding, the latter was found to be the most promising for the new process of rotary moulding of ceramics. Due to the low value of clay-based ceramics, a new low cost coagulant was identified and the effect of lactone concentration and temperature on setting time determined. Following substantial optimisation work, it was found that a two-speed approach to multi-axial rotation was the most successful; medium sized cream jugs could be produced in just 7 minutes. With respect to mould materials, the porous resin normally used for pressure casting of sanitary ware was found to be the best option, though since this is quite expensive conventional plaster-of-paris moulds were found to be a suitable material to enable companies, particularly SMEs, to become familiar with the technology whilst avoiding high costs for trials. The processed articles could be successfully fired and glazed using gas-fired kilns with no sign of any black cores. Major advantages of the process include the ability to precisely calculate the amount of ceramic slip required, eliminating either slip wastage or the need to pour used slip back into the virgin material as currently happens with slip casting. In addition, since the precursor suspension has a very high solids content, the time and energy required to dry the green product and associated moulds has been considerably reduced

Strength degradation of cemented carbides due to thermal shock

Despite the recognition of thermal shock and thermal fatigue as common failure modes in cemented carbide applications, the information on the influence of the microstructure on the resistance of hardmetals to abrupt temperature changes is rather scarce. In this paper, the strength behaviour of cemented carbides after severe thermal shock damage is investigated. In doing so, cemented carbides were subjected to thermal shock at two temperature ranges (¿T of 400ºC and 550ºC) and their retained strength evaluated as a measure of their thermal shock resistance. Residual strength results are then related to crack initiation (R) and propagation (R’’’’) Hasselman parameters. Results indicate that the finer the microstructure, the better the resistance to the nucleation of thermal shock damage of hardmetals. This strength trend is in accordance with higher R and lower R’’’’ parameters for the studied materials.Peer ReviewedPostprint (author's final draft

Corrosion damage in WC-Co cemented carbides: Residual strength assessment and 3D FIB-FESEM tomography characterization

The effect of corrosion damage on cemented carbides was investigated. The study included residual strength assessment and detailed fractographic inspection of corroded specimens as well as detailed 3D FIB-FESEM tomography characterization. Experimental results point out a strong strength decrease associated with localized corrosion damage, i.e. corrosion pits acting as stress raisers, concentrated in the binder phase. These pits exhibit a variable and partial interconnectivity, as a function of depth from the surface, and are the result of heterogeneous dissolution of the metallic phase, specifically at the corrosion front. However, as corrosion advances the ratio between pit depth and thickness of damaged layer decreases. Thus, stress concentration effect ascribed to corrosion pits gets geometrically lessened, damage becomes effectively homogenized and relatively changes in residual strength as exposure time gets longer are found to be less pronounced.Postprint (published version

Reusable photocatalytic optical fibers for underground, deep-sea, and turbid water remediation

An approach for underground, deep, and turbid water remediation is presented based on optical fibers with a photocatalytic coating. Thus, photocatalytic TiO2 P25 nanoparticles immobilized in a poly(vinylidene difluoride) (PVDF) matrix are coated on polymeric optical fibers (POFs) and the photocatalytic performance of the system is assessed under artificial sunlight. To the best of our knowledge, poly(methyl methacrylate)-POF coated with TiO2/PVDF and the reusability of any type of POF for photocatalytic applications are not previously reported. The photocatalytic efficiency of the hybrid material in the degradation of ciprofloxacin (CIP) and its reusability are evaluated here. It is shown that 50 w/w% of TiO2 P25 achieves a degradation of 95% after 72 h under artificial sunlight and a reusability of three times leads to a loss of activity inferior to 11%. The efficient removal of ciprofloxacin and the stability of the POF coated with TiO2 P25 successfully demonstrate its suitability in the degradation of pollutants with potential application in regions with low light illumination, as in underground and deep water.Peer ReviewedPostprint (published version

A comprehensive review on rheological studies of sludge from various sections of municipal wastewater treatment plants for enhancement of process performance

Large quantities of sludge is generated from different sections of a wastewater treatment plant operation. Sludge can be a solid, semisolid or liquid muddy residual material. Understanding the flow behaviour and rheological properties of sewage sludge at different sections of a wastewater treatment plant (WWTP) is important for the design of pumping system, mixing, hydrodynamics and mass transfer rates of various sludge treatment units, optimization of conditioning dose and for sustainable sludge management. The current article provides a comprehensive review on up to date literature information on rheological behaviour of raw primary sludge, excess activated sludge, thickened excess activated sludge, mixture of raw primary and thickened excess activated sludge (mixed sludge), digested sludge, and biosolid under the influence of different operating parameters and their impacts on process performance. The influences of various process parameters such as solid concentration, temperature, pH, floc particle size, primary to secondary sludge mixing ratio, aging and conditioning agent doses on the rheological behaviour of sludge from different treatment units of WWTPs are critically analysed here. Yield stress was reported to increase with increasing solid concentration for all types of sludge whereas viscosity showed a decreasing trend with decreasing total solid concentration and percentage of thickened excess activated sludge in the mixture. Temperature showed an inverse relationship with yield stress and viscosity. Viscosity was reported to be decreased with decrease in pH. The effect of various conditioning agents on the rheological behaviour of sludge are also discussed here. The applicability and practical significance of various rheological models such as Bingham, Power Law (Ostwald), Herschel-Bulkley, Casson, Sisko, Careau, and Cross models to experimental rheological characteristics of various sludges were presented here. The reported results on various rheological parameters such as shear stress, yield stress, flow index, infinite, zero-rate viscosity, and flow consistency index of different sludge types obtained from the best fitted model were also compiled here. Conclusions have been drawn from the literature reviewed and few suggestions for future research direction are proposed

METHANOL REMOVAL FROM METHANOL-WATER MIXTURE USING MUNICIPAL ACTIVATED SLUDGE

Methanol plants produce large volume of wastewater containing less than 10% methanol during the startup and shut-down operations, such amount is considered as an industrial waste problem. An experimental work has been carried out in order to examine the removal of methanol from methanol-water mixture using activated sludge. The results showed that the methanol was totally consumed by the bacteria as quick as the feed enters the sludge vessel. The bacteria indicated adaption and growth during experiment with adaptation time of 1 hour. However, an inverse effect on bacterial growth has been observed, when the methanol concentration is higher than 5%