Robust multivariable control of complex biological processes

This paper addresses advanced control of a biological nutrient removal (BNR) activated sludge process. Based on a previously validated distributed parameter model of the BNR activated sludge process, we present robust multivariable controller designs for the process, involving loop shaping of plant model, robust stability and performance analyses. Results from three design case studies showed that a multivariable controller with stability margins of 0.163, 0.492 and 1.062 measured by the normalised coprime factor, multiplicative and additive uncertainties respectively give the best results for meeting performance robustness specifications. The controller robustly stabilises effluent nutrients in the presence of uncertainties with the behaviour of phosphorus accumulating organisms as well as to effectively attenuate major disturbances introduced as step changes. This study also shows that, performance of the multivariable robust controller is superior to multi-loops SISO PI controllers for regulating the BNR activated sludge process in terms of robust stability and performance and controlling the process using inlet feed flowrate is infeasible. (C) 2003 Elsevier Ltd. All rights reserved.

Rugulotrosins A and B: Two new antibacterial metabolites from an Australian isolate of a penicillium sp.

Two new antibacterial agents, rugulotrosin A (1) and B (2), were obtained from cultures of a Penicillium sp. isolated from soil samples acquired near Sussex Inlet, New South Wales, Australia. Rugulotrosin A (1) is a chiral symmetric dimer, and its relative stereostructure was determined by spectroscopic and X-ray crystallographic analysis. Rugulotrosin B (2) is a chiral asymmetric dimer isomeric with 1. Its structure was determined by spectroscopic analysis with comparison to the co-metabolite 1 and previously reported fungal metabolites. Both rugulotrosins A and B displayed significant antibacterial activity against Bacillus subtilis, while rugulotrosin A was also strongly active against Enterococcus faecalis and B. cereus.

Application of central composite rotatable design to modelling the effect of some operating variables on the performance of the three-product cyclone

The central composite rotatable design (CCRD) was used to design an experimental program to model the effects of inlet pressure, feed density, and length and diameter of the inner vortex finder on the operational performance of a 150-min three-product cyclone. The ranges of values of the variables used in the design were: inlet pressure: 80-130 kPa, feed density: 30 60%; length of IVF below the OVF: 50-585 mm; diameter of IVF: 35-50 mm. A total of 30 tests were conducted, which is 51 less; an that required for a three-level full factorial design. Because the model allows confident performance prediction by interpolation over the range of data in the database, it was used to construct response surface graphs to describe the effects of the variables on the performance of the three-product cyclone. To obtain a simple and yet a realistic model, it was refitted using only the variable terms that are significant at greater than or equal to 90% confidence level. Considering the selected operating variables, the resultant model is significant and predicts the experimental data well. (c) 2005 Elsevier B.V. All rights reserved.

Significance of frictional heating for effects of high pressure homogenisation on milk

High pressure homogenisation (HPH) is a novel dairy processing tool, which has many effects on enzymes, microbes, fat globules and proteins in milk. The effects of HPH on milk are due to a combination of shear forces and frictional heating of the milk during processing; the relative importance of these different factors is unclear, and was the focus of this study. The effect of milk inlet temperature (in the range 10-50 degrees C) on residual plasmin, alkaline phosphatase, lactoperoxidase and lipase activities in raw whole bovine milk homogenised at 200 MPa was investigated. HPH caused significant heating of the milk; outlet temperature increased in a linear fashion (0(.)5887 degrees C/degrees C, R-2 =0-9994) with increasing inlet temperature. As milk was held for 20 s at the final temperature before cooling, samples of the same milk were heated isothermally in glass capillary tubes for the same time/temperature combinations. Inactivation profiles of alkaline phosphatase in milk were similar for isothermal heating or HPH, indicating that loss of enzyme activity was due to heating alone. Loss of plasmin and lactoperoxidase activity in HPH milk, however, was greater than that in heated milk. Large differences in residual lipase activities in milks subjected to heating or HPH were observed due to the significant increase in lipase activity in homogenised milk. Denaturation of beta-lactoglobulin was more extensive following HPH than the equivalent heat treatment. Inactivation of plasmin was correlated with increasing fat/serum interfacial area but was not correlated with denaturation of beta-lactoglobulin. Thus, while some effects of HPH on milk are due to thermal effects alone, many are induced by the combination of forces and heating to which the milk is exposed during HPH.

Optimization of pipeline transport for CO2 sequestration

Coal fired power generation will continue to provide energy to the world for the foreseeable future. However, this energy use is a significant contributor to increased atmospheric CO2 concentration and, hence, global warming. Capture and disposal Of CO2 has received increased R&D attention in the last decade as the technology promises to be the most cost effective for large scale reductions in CO2 emissions. This paper addresses CO2 transport via pipeline from capture site to disposal site, in terms of system optimization, energy efficiency and overall economics. Technically, CO2 can be transported through pipelines in the form of a gas, a supercritical. fluid or in the subcooled liquid state. Operationally, most CO2 pipelines used for enhanced oil recovery transport CO2 as a supercritical fluid. In this paper, supercritical fluid and subcooled liquid transport are examined and compared, including their impacts on energy efficiency and cost. Using a commercially available process simulator, ASPEN PLUS 10.1, the results show that subcooled liquid transport maximizes the energy efficiency and minimizes the Cost Of CO2 transport over long distances under both isothermal and adiabatic conditions. Pipeline transport of subcooled liquid CO2 can be ideally used in areas of cold climate or by burying and insulating the pipeline. In very warm climates, periodic refrigeration to cool the CO2 below its critical point of 31.1 degrees C, may prove economical. Simulations have been used to determine the maximum safe pipeline distances to subsequent booster stations as a function of inlet pressure, environmental temperature and ground level heat flux conditions. (c) 2005 Published by Elsevier Ltd.

Using computational fluid dynamics in combating erosion-corrosion

Computational fluid dynamics was used to search for the links between the observed pattern of attack seen in a bauxite refinery's heat exchanger headers and the hydrodynamics inside the header. Validation of the computational fluid dynamics results was done by comparing then with flow parameters measured in a 1:5 scale model of the first pass header in the laboratory. Computational fluid dynamics simulations were used to establish hydrodynamic similarity between the 1:5 scale and full scale models of the first pass header. It was found that the erosion-corrosion damage seen at the tubesheet of the first pass header was a consequence of increased levels of turbulence at the tubesheet caused by a rapidly turning flow. A prismatic flow corrections device introduced in the past helped in rectifying the problem at the tubesheet but exaggerated the erosion-corrosion problem at the first pass header shell. A number of alternative flow correction devices were tested using computational fluid dynamics. Axial ribbing in the first pass header and an inlet flow diffuser have shown the best performance and were recommended for implementation. Computational fluid dynamics simulations have revealed a smooth orderly low turbulence flow pattern in the second, third and fourth pass as well as the exit headers where no erosion-corrosion was seen in practice. This study has confirmed that near-wall turbulence intensity, which can be successfully predicted by using computational fluid dynamics, is a good hydrodynamic predictor of erosion-corrosion damage in complex geometries. (c) 2006 Published by Elsevier Ltd.

Measurement of the aerodynamic performance of a scramjet-powered vehicle in a shock tunnel

A force balance system for measuring lift, thrust and pitching moment has been used to measure the performance of fueled scramjet-powered vehicle in the T4 Shock Tunnel at The University of Queensland. Detailed measurements have been made of the effects of different fuel flow rates corresponding to equivalence ratios between 0.0 and 1.5. For proposed scramjet-powered vehicles, the fore-body of the vehicle acts as part of the inlet to the engine and the aft-body acts as the thrust surface for the engine. This type of engine-integrated design leads to a strong coupling between the performance of the engine and the lift and trim characteristics of the vehicle. The measurements show that the lift force increased by approximately 50% and centre-of-pressure changed by approximately 10% of the chord of the vehicle when the equivalence ratio varied from 0.0 to 1.0. The results demonstrate the importance of engine performance to the overall aerodynamic characteristics of engine-integrated scramjet vehicles and that such characteristics can be measured in a shock tunnel.