An investigation into the behaviour of concrete containing seawater-neutralised bauxite refinery residues in silage effluent

The farm production of silage as a winter-feed supplement is widespread. However, the bins in which silage is produced are subject to acidic and microbial attacks. Both these types of attack can lead to a weakening and failure of the concretes, especially on the outer lip of the open side of the silage pit. Consequently, the development of an acid-resistant concrete that can extend the life span of silage bins on farms could lead to considerable cost savings for farmers and, hence, can improve farm productivity. This paper reports on test results of an investigation into the behaviour of concrete containing seawater-neutralised bauxite refinery residues (Bauxsol™) exposed to sulphuric acid environments in the laboratory and to silage effluents. The concrete manufactured had a fixed water–cement ratio of 0.55 and natural sand was replaced with the Bauxsol™ at 0%, 5%, 10%, 15% and 20% by cement mass. Results indicated that the use of Bauxsol™ as a sand replacement material improved the behaviour of concrete both in sulphuric acid in the laboratory as well as in the silage effluent. Consequently, it is concluded that the Bauxsol™ can be used to replace 10% of natural sand to produce concrete that is resistant to silage effluents, providing an extended service life over conventional concretes used in silage pits.

Effects of seawater-neutralised bauxite refinery residue on properties of concrete

Various industrial by-products, such as fly ash, ground granulated blast-furnace slag and silica fume, have been used in concrete to improve its properties. This also enables any environmental issues associated with their disposal. Another material that is available in large quantities and requiring alternative methods of disposal is the Bauxite Refinery Reside (BRR) from the Bayer process used to extract alumina from bauxite. As this is highly caustic and causes many health hazards, Virotec International Ltd. developed a patented technology to convert this into a material that can be used commercially, known as Bauxsol™, for various environmental remediation applications. This use is limited to small quantities of seawater-neutralised BRR and hence an investigation was carried out to establish its potential utilisation as a sand replacement material in concrete. In addition to fresh properties of concrete containing seawater-neutralised BRR up to 20% by mass of Portland cement, mechanical and durability properties were determined. These properties indicated that seawater-neutralised BRR can be used to replace natural sand up to 10% by mass of cement to improve the durability properties of concrete without detrimentally affecting their physical properties. Combining these beneficial effects with environmental remediation applications, it can be concluded that there are specific applications where concretes containing seawater-neutralised BRR could be used.

Phase I and II biotransformation enzymes and polycyclic aromatic hydrocarbons in the Mediterranean mussel (Mytilus galloprovincialis, Lamarck, 1819) collected in front of an oil refinery

The aim of the present study was to investigate the responses of phase I and II biotransformation enzymes and levels of PAHs in the Mediterranean mussel (Mytilus galloprovincialis, Lamarck, 1819) collected from three sites at different distance from an oil refinery. Phase I enzyme activities as NAD(P)H-cyt c red, NADH ferry red, B(a)PMO and phase II as UDPGT. GST were measured in digestive gland while 16 PAHs (US-EPA) in whole soft tissue. An added value to the data obtained in the present study rely on the RDA analysis which showed close correlations between PAHs levels and phase I enzyme activities in mussels collected in front of the refinery. And again a significant spatial correlation between B(a)P levels and NADPH-cyt c red activities was observed using linear models. No differences among sites for B(a) PMO and phase II GST activities were observed, while the application of UDPGT as biomarkers requires further investigation. (C) 2012 Elsevier Ltd. All rights reserved.

Effect of Bauxol on properties of cement pastes

This paper presents the results of an experimental investigation carried out to evaluate the influence of Bauxsol, an artificially neutralised bauxite refinery residue (NBRR), on various properties of cement pastes. It was found that the NBRR does not have any pozzolanic properties and hence cannot be used as a supplementary cementitious material in concrete. In order to evaluate the effect of adding the product to Portland cement (PC) pastes, fresh properties (i.e. standard consistency and slump), setting time and heat of hydration were measured. In addition, its influence on chemical changes and compressive strength was investigated. It was found that the addition of this NBRR resulted in a decrease in compressive strength beyond 7 days. The setting time decreased with an increase in NBRR content in PC pastes. The rate of heat evolution for NBRR pastes was greater than that of the PC pastes, but a corresponding increase in the quantity of calcium hydroxide was not found. Therefore, it was concluded that unidentified hydration products when Bauxsol was used in PC pastes might have been the reason for the decrease in setting times.

Combination of CFD and DOE to analyse solid particle erosion in elbows

Solid particle erosion is a major concern in the engineering industry, particularly where transport of slurry flow is involved. Such flow regimes are characteristic of those in alumina refinement plants. The entrainment of particulate matter, for example sand, in the Bayer liquor can cause severe erosion in pipe fittings, especially in those which redirect the flow. The considerable costs involved in the maintenance and replacement of these eroded components led to an interest in research into erosion prediction by numerical methods at Rusal Aughinish alumina refinery, Limerick, Ireland, and the University of Limerick. The first stage of this study focused on the use of computational fluid dynamics (CFD) to simulate solid particle erosion in elbows. Subsequently an analysis of the factors that affect erosion of elbows was performed using design of experiments (DOE) techniques. Combining CFD with DOE harnesses the computational power of CFD in the most efficient manner for prediction of elbow erosion. An analysis of the factors that affect the erosion of elbows was undertaken with the intention of producing an erosion prediction model. © 2009 Taylor & Francis.

Performance assessment of cascade control loopswith non-Gaussian disturbances using entropy information

Cascade control is one of the routinely used control strategies in industrial processes because it can dramatically improve the performance of single-loop control, reducing both the maximum deviation and the integral error of the disturbance response. Currently, many control performance assessment methods of cascade control loops are developed based on the assumption that all the disturbances are subject to Gaussian distribution. However, in the practical condition, several disturbance sources occur in the manipulated variable or the upstream exhibits nonlinear behaviors. In this paper, a general and effective index of the performance assessment of the cascade control system subjected to the unknown disturbance distribution is proposed. Like the minimum variance control (MVC) design, the output variances of the primary and the secondary loops are decomposed into a cascade-invariant and a cascade-dependent term, but the estimated ARMA model for the cascade control loop based on the minimum entropy, instead of the minimum mean squares error, is developed for non-Gaussian disturbances. Unlike the MVC index, an innovative control performance index is given based on the information theory and the minimum entropy criterion. The index is informative and in agreement with the expected control knowledge. To elucidate wide applicability and effectiveness of the minimum entropy cascade control index, a simulation problem and a cascade control case of an oil refinery are applied. The comparison with MVC based cascade control is also included.