Development of a computationally efficient model for the control of Ziegler-Natta catalysed industrial production of high density polyethylene

High density polyethylene is commonly produced by the slurry phase co-polymerisation of ethylene and other alkenes, using heterogeneous titanium-based Ziegler-Natta catalysts. During grade transitions, when reactor conditions are manipulated to change polymer properties, significant quantities of off-specification product result. Implementing a model-predictive controller based on a dynamic reactor model may allow for minimising losses during unsteady-state operation. Such a model must be developed from a fundamental understanding of polymerisation reaction kinetics and the interaction of effects at various scales, including those of catalyst sites, catalyst/polymer particles and reactor hydrodynamics. The model must also be computationally efficient enough for application to real-time control. The recently-developed pseudo-sites model was used as a fundamental kinetic explanation of polymer property distributions and catalyst activity profiles, in contrast to empirical multi-site models. Laboratory polymerisation experiments were performed at industrially-relevant conditions. Kinetic parameters were fitted to the data, using a novel proposed regression procedure to extract meaningful kinetic parameters. A dynamic reactor model was developed, based on the Segregation Approach. Whereas the more common Population Balance Model must consider multivariate distributions of population members within a chosen volume and requires partial differential equation solution, the Segregation Approach can generate the moments of a distribution by evaluating the evolution of properties without requiring solution over the whole volume. The Segregation Approach and PBM were rigorously compared in the context of Particle Size Distributions, and the Segregation Approach shown to be an order of magnitude more computationally efficient. Steady-state industrial data was used to reconcile model predictions for laboratory and industrial polymerisation. This was the first application of the pseudo-sites model to laboratory data, and first extension to industrial scale. Unsteady-state data from three industrial grade transitions was used to validate the reactor model, which closely matched industrial reactor performance. The model simulated 30-40 hours of real time in 15-25 seconds of calculation time. The reactor model was used to propose improved grade transition strategies; transition duration and waste production were improved by 20-40%. The reactor model has been shown to accurately reproduce real-world results, and is computationally efficient enough to be applied to model-based control applications

Development of novel form-stable composite phase change materials and integration in building for thermal regulation

The integration of phase change materials (PCMs) into building components has attracted in-creasing interest in stabilising indoor temperatures by enhancing the thermal energy storage (TES) capacity and decreasing temperature swings, which lead to an improvement in buildings' thermal comfort and energy efficiency. Gypsum board, with the advantages of low cost and ease of placement, has wide applications for ceiling or wall covering. Thus, PCMs have great potential to be incorporated into gypsum board to improve the energy performance of buildings. However, the application of PCMs has been remarkably restrained by their poor shape stability during the phase change process. Accordingly, a challenge to practical application is that the PCM leak from the building materials. Moreover, due to its low thermal conductivity, the low heat transfer rate of normal PCM also acts as a block upon the wide utilisation of its enormous TES capacity benefits. As yet, very little research has been conducted to study the performance and benefits of using PCMs in real houses, especially in combination with thermal insulation. This study aims to overcome the above issues by containing PCM in porous diatomite material to develop form-stable composite PCM (FSPCM) and study the influence of using FSPCM in max-imising the TES capacity of gypsum board for improving the thermal performance of houses. Test results showed that the produced FSPCM with 48.7 wt.% of diatomite enhanced the thermal conductivity of PCM by 63.7% and eliminated the leakage issue above the PCM melting point. Experimental studies were conducted to develop an energy storage gypsum board by incorporating 40 wt.% of FSPCM in the board. An experimental study and a numerical investigation were conducted to investigate the feasibility of using the FSPCM board as a retrofitting solution to a model house in Sydney, Australia. Furthermore, the effectiveness of the combined use of FSPCM board and thermal insulation in improving the energy efficiency of residential houses was investigated

Advanced combined iodine dispenser and detector

A total weight of 1.23 kg (2.7 lb), a total volume of 1213 cu m (74 cu in), and an average power consumption of 5.5W was achieved in the advanced combined iodine dispenser/detector by integrating the detector with the iodine source, arranging all iodinator components within a compact package and lowering the parasitic power to the detector and electronics circuits. These achievements surpassed the design goals of 1.36 kg (3.0 lb), 1671 cu m (102 cu in) and 8W. The reliability and maintainability were improved by reducing the detector lamp power, using an interchangeable lamp concept, making the electronic circuit boards easily accessible, providing redundant water seals and improving the accessibility to the iodine accumulator for refilling. The system was designed to iodinate (to 5 ppm iodine) the fuel cell water generated during 27 seven-day orbiter missions (equivalent to 18,500 kg (40,700 lb) of water) before the unit must be recharged with iodine crystals

Development of new packed reactor using TiO2 pellet for drinking water treatment

[no abstract

Synthesis and processing of sub-micron hafnium diboride powders and carbon-fibre hafnium diboride composite

A vehicle flying at hypersonic speeds, i.e. at speeds greater than Mach 4, needs to be able to withstand the heat arising from friction and shock waves, which can reach temperatures of up to 3000oC. The current project focuses on producing thermal protection systems based on ultra high temperature ceramic (UHTC) impregnated carbon-carbon composites. The carbon fibres offer low mass and excellent resistance to thermal shock; their vulnerability is to oxidation above 500oC. The aim of introducing HfB2, a UHTC, as a coating on the fibre tows or as particulate reinforcement into the carbon fibre preform, was to improve this property. The objectives of this project were to: i) identify a low temperature synthesis route for group IV diborides, ii) produce a powder fine enough to reduce the difficulties associated with sintering the refractory diborides, iii) develop sol-gel coating of HfB2 onto carbon fibre tows iv) improve the solid loading of the particulate reinforcement into the carbon fibre preform, which should, in turn, increase the oxidation protection. In order to achieve the above set objectives, fine HfB2 powder was synthesized through a low temperature sol gel and boro/carbothermal reduction process, using a range of different carbon sources. Study of the formation mechanism of HfB2 revealed an intermediate boron sub-oxide and/or active boron formation that yielded HfB2 formation at 1300oC. At higher temperatures the formation of HfB2 could be via intermediate HfC formation and/or B4C formation. Growth mechanism analysis showed that the nucleated particles possessed screw dislocations which indicated that the formation of HfB2 was not only through a substitution reaction, but there could have been an element of a precipitation nucleation mechanism that lead to anisotropic growth under certain conditions. The effect of carbon sources during the boro/carbothermal reduction reaction on the size of the final HfB2 powders was analysed and it was found that a direct relation existed between the size and level of agglomeration of the carbon sources and the resulting HfB2 powders. A powder phenolic resin source led to the finest powder, with particle sizes in the range 30 to 150 nm. SPS sintering of the powder revealed that 99% theoretical density could be achieved without the need for sintering aids at 2200oC. Sol-gel coatings and slurry impregnation of HfB2 on carbon fibres tows was performed using dip coating and a ‘squeeze–tube’ method respectively. Crack free coatings and non-porous matrix infiltration were successfully achieved. The solid loading of the fine HfB2 into the carbon fibre preform was carried out through impregnation of a HfB2 / phenolic resin / acetone slurry using vacuum impregnation. Although the sub-micron Loughborough (LU) powders were expected to improve the solid loading, compared to the commercially available micron sized powders, due to the slurry made from them having a higher viscosity because of the fine particle size, the solids loading achieved was consequently decreased. Optimisation of the rheology of the slurry with LU HfB2 still requires more work. A comparison of the oxidation and ablation resistance of the Cf-HfB2 composites prepared with both commercial micron sized HfB2 powder and Loughborough sub-micron sized HfB2 powder, each with similar level of solid loading, was carried out using oxyacetylene torch testing. It was found that the composite containing the finer, Loughborough powders suffered a larger erosion volume than the composite with the coarser commercial powders indicating that the former offered worse ablation and oxidation resistance than the latter. A full investigation of the effect of solids loading and particle size, including the option of using mixtures of fine and coarse powders, is still required

Proceedings of the International RILEM Conference Materials, Systems and Structures in Civil Engineering segment on Service Life of Cement-Based Materials and Structures

Vol. 1O volume II encontra-se disponível em: http://hdl.handle.net/1822/4390

International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Service Life of Cement-Based Materials and Structures

Vol. 2O volume I encontra-se disponível em: http://hdl.handle.net/1822/4341

Application of Enhanced Desorption-Sorption as a New Process for Remediation of the Sediments

Contamination of the sediments by organics and inorganics is a rising concern. However, remediation of contaminated sediments is complex and challenging. As yet, the application of the enhanced desorption combined with the sorption for remediation of the contaminated solid media has not been investigated. In environmental research, few studies have focused on closed-loop remediation methods. This study was to evaluate a desorption-sorption process and the influential parameters for remediation of hydrocarbon-contaminated sediments. Also, it aimed to investigate the adsorption capacity of the sorbent (silica aerogel), adsorption isotherms and adsorption kinetics, as well as the fate of heavy metals, phosphorus and nitrogen, and regeneration of aerogels by solvents and heat in the desorption-sorption process. A laboratory-scale system was designed and built for fast remediation of sediments. A strong turbulence vessel was used to increase the desorption of contaminants from sediments. A packed column containing hydrophobic silica aerogel granules was used to remove the contaminants from the effluent slurry. The results showed 29.5% total petroleum hydrocarbon (TPH) removal from sediment after 45 minutes of vigorous agitation at 15900 rpm. The processed sediment and effluent water met Canadian governmental and provincial quality criteria. Higher agitation speeds (22100 rpm) increased the leaching of hydrocarbons from sediments by 31%. In a warm environment (35oC), the desorption of TPH from sediments was 28.9% higher than at ambient temperature (22oC), but in a cold environment (10oC), it was 16.3% lower than at ambient temperature. The sorption capacity of aerogels was increased from 9.6 mg/g at 22 oC to 10.5 mg/g at 10oC but decreased to 6.7 mg/g at 35oC. pH (5, 7 and 9), salinity (3.5%), solid load (5, 10 and 15 g/l) and retention time (11.5 and 26 seconds) did not show a significant effect on the efficiency of the process. Adsorption data suggested a pseudo-second-order kinetics and a Freundlich adsorption model were the most appropriate. The sediment quality including the content of investigated heavy metals (Cr, As, Cd, Pb, Cu, Zn, Ni, Mn, Co, Mo), nitrogen, and phosphorus did not change significantly after the desorption-sorption process. The concentration of heavy metals in the effluent water was significantly lower than the drinking and freshwater standards. Aerogels showed a low affinity towards the heavy metals but decreased the concentration of total phosphorus and total Kjeldahl nitrogen in water by 65% and more than 95%, respectively. Regeneration of the aerogels by organic solvents was not feasible. Repetitive regeneration by heat reduced the sorption capacity of aerogels. This research introduces a new environmentally-friendly methodology for remediation of sediments and other solid environmental media

Salt-gradient Solar Ponds: Summary of US Department of Energy Sponsored Research

The solar pond research program conducted by the United States Department of Energy was discontinued after 1983. This document summarizes the results of the program, reviews the state of the art, and identifies the remaining outstanding issues. Solar ponds is a generic term but, in the context of this report, the term solar pond refers specifically to saltgradient solar pond. Several small research solar ponds have been built and successfully tested. Procedures for filling the pond, maintaining the gradient, adjusting the zone boundaries, and extracting heat were developed. Theories and models were developed and verified. The major remaining unknowns or issues involve the physical behavior of large ponds; i.e., wind mixing of the surface, lateral range or reach of horizontally injected fluids, ground thermal losses, and gradient zone boundary erosion caused by pumping fluid for heat extraction. These issues cannot be scaled and must be studied in a large outdoor solar pond