Engineering

Publication Search Results

Now showing 1 - 10 of 11
  • (2008) Ho, Minh; Allinson, G; Wiley, Dianne
    Journal Article
    Studies of CO2 capture using membrane technology from coal-fired power-plant flue gas typically assume compression of the feed to achieve a driving force across the membrane. The high CO2 capture cost of these systems reflects the need to compress the low-pressure feed gas (1 bar) and the low CO2 purity of the product stream. This article investigates how costs for CO2 capture using membranes can be reduced by operating under vacuum conditions. The flue gas is pressurized to 1.5 bar, whereas the permeate stream is at 0.08 bar. Under these operating conditions, the capture cost is U.S. $54/tonne CO2 avoided compared to U.S. $82/ tonne CO2 avoided using, membrane processes with a pressurized feed. This is a reduction of 35%. The article also investigates the effect on the capture cost of improvements in CO2 permeability and selectivity. The results show that the capture cost can be reduced to less than U.S. $25/tonne CO2 avoided when the CO2 permeability is 300 barrer, CO2/N2 selectivity is 250, and the membrane cost is U.S. $10/m2.

  • (2008) Power, M; Marlon, J; Ortiz, N; Bartlein, P; Harrison, Simon; Mayle, F; Ballouche, A; Bradshaw, R; Carcaillet, C; Cordova, C; Mooney, Scott; Moreno, P; Prentice, I; Thonicke, K; Tinner, W; Whitlock, C; Zhang, Yanling; Zhao, Yong; Ali, Amna; Anderson, Richard; Beer, R; Behling, H; Briles, C; Brown, Katherine; Brunelle, A; Bush, M; Camill, P; Chu, G; Clark, J; Colombaroli, D; Connor, Stuart; Daniau, A; Daniels, M; Dodson, John; Doughty, E; Edwards, Meredith; Finsinger, W; Foster, Douglas; Frechette, J; Gaillard, M; Gavin, D; Gobet, E; Haberle, Simon; Hallett, D; Higuera, P; Hope, G; Horn, S; Inoue, J; Kaltenrieder, P; Kennedy, Liz; Kong, Z; Larsen, C; Long, C; Lynch, Jodi; Lynch, E; McGlone, M; Meeks, S; Mensing, S; Meyer, G; Minckley, T; Mohr, J; Nelson, D; New, J; Newnham, R; Noti, R; Oswald, W; Pierce, J; Richard, P; Rowe, C; Goni, M; Shuman, B; Takahara, H; Toney, J; Turney, C; Urrego-Sanchez, D; Umbanhowar, C; Vandergoes, M; Vanniere, B; Vescovi, E
    Journal Article
    Fire activity has varied globally and continuously since the last glacial maximum (LGM) in response to long-term changes in global climate and shorter-term regional changes in climate, vegetation, and human land use. We have synthesized sedimentary charcoal records of biomass burning since the LGM and present global maps showing changes in fire activity for time slices during the past 21,000 years (as differences in charcoal accumulation values compared to pre-industrial). There is strong broad-scale coherence in fire activity after the LGM, but spatial heterogeneity in the signals increases thereafter. In North America, Europe and southern South America, charcoal records indicate less-than-present fire activity during the deglacial period, from 21,000 to ∼11,000 cal yr BP. In contrast, the tropical latitudes of South America and Africa show greater-than-present fire activity from ∼19,000 to ∼17,000 cal yr BP and most sites from Indochina and Australia show greater-than-present fire activity from 16,000 to ∼13,000 cal yr BP. Many sites indicate greater-than-present or near-present activity during the Holocene with the exception of eastern North America and eastern Asia from 8,000 to ∼3,000 cal yr BP, Indonesia and Australia from 11,000 to 4,000 cal yr BP, and southern South America from 6,000 to 3,000 cal yr BP where fire activity was less than present. Regional coherence in the patterns of change in fire activity was evident throughout the post-glacial period. These complex patterns can largely be explained in terms of large-scale climate controls modulated by local changes in vegetation and fuel load.

  • (2008) Mcdowall, Lyndal; Chen, Gaojian; Stenzel-Rosenbaum, Martina
    Journal Article
    A poly(vinyl pyrrolidone) (PVP) seven-arms star polymer with lysozyme core was synthesized by conjugating linear N-succinimidyl ester terminated PVP polymer to lysozyme. Reactive PVP polymers were synthesized using a MADIX/RAFT agent functionalized with N-succinimidyl ester. The polymerization of N-vinyl pyrrolidone proceeded in a living fashion up to more than 90% conversion reaching molecular weight of up to 33 000 g . mol(-1) with narrow molecular weight distributions. The PVP polymer was conjugated to lysozyme resulting in the attachment of seven PVP polymers to one lysozyme core. While the reaction was found to be complete when using low-molecular weight PVP, some by-products with less than seven arms were observed when using PVP with a molecular weight of 33 000 g . mol(-1).

  • (2008) Fane, Anthony; Chen, Vicki; Wu, J; Le-Clech, Pierre; Stuetz, Richard
    Journal Article
    Relaxation and/or backwashing have been incorporated in most membrane bioreactor (MBR) designs as standard operating strategies to limit fouling. However, to maintain a certain net permeate production, higher instantaneous fluxes have to be applied to compensate for the loss of permeate caused by those modes of operation. To assess the effects of the different operational parameters on fouling for the same water productivity, and to study the fouling mechanisms, three relaxation and five backwashing conditions were applied in a lab-scale aerobic MBR and compared to the continuous filtration mode. Moreover, the fouling behaviour was analyzed in terms of the consequential increase in trans-membrane pressure, resistance fractions and the biopolymeric composition of the fouling layer. The Pearson correlation analysis was applied to identify the major contributor to fouling. From this study, it was found that fouling could be retarded effectively when the appropriate filtration mode was applied. The instantaneous flux applied to compensate for the loss of productivity during backwashing or relaxation periods was the major factor affecting fouling rate for either relaxation or back-washing, which was significantly correlated with the amount of solids and soluble fractions deposited on the membrane surface. The relaxation and backwashing conditions (i.e. duration, interval, strength) also considerably affected the fouling rate. In addition, it was found that pore blocking was more likely to be due to protein rather than carbohydrates and that the cake layer was the major contributor to fouling. (C) 2008 Elsevier B.V. All rights reserved.

  • (2008) Fane, Anthony; Chen, Vicki; Wu, J; Le-Clech, Pierre; Stuetz, Richard
    Journal Article
    A novel filtration mode is presented to reduce fouling propensity in membrane bioreactors (MBR). During this mode, an elevated high instantaneous flux (60 L m-2 h-1) is initially applied for a short time (120 s), followed by a longer filtration (290 s) at lower flux (10.3 L m-2 h-1) and a backwash in each filtration cycle. The mixed mode is expected to limit irreversible fouling as the reversible fouling created during the initial stage appears to protect the membrane. Hydraulic performance and the components of foulants were analyzed and compared with conventional continuous and backwash modes. It was found that the mixed mode featured lower trans-membrane pressure (TMP) after 24 h of filtration when compared to other modes. The mixed mode was effective in preventing soluble microbial products (SMP) attaching directly onto the membrane surface, keeping the cake layer weakly compressed, and reducing the mixed liquor suspended solids (MLSS) accumulation on the membrane. This strategy reduced the resistances of both the cake layer and the gel layer. A factorial experimental design was carried out for eight runs with different conditions to identify the major operational parameters affecting the hydraulic performances. The results showed that the value of the flux in the initial high-flux period had the most effect on the performance of the mixed mode: high initial flux (60 L m-2 h-1) led to improved performance. © 2008 Elsevier Ltd. All rights reserved.

  • (2008) Chen, Vicki; Marselina, Yulita; Le-Clech, Pierre; Stuetz, Richard
    Journal Article
    Direct observation (DO) technique allowed the visualisation of fouling deposition and removal in real time and in a non-invasive manner. The DO setup was relatively simple and featured a crossflow hollow fibre membrane module, a microscope and a video camera. Transmembrane pressure (TMP) and fouling height were observed to characterise in detail the mechanisms of fouling deposition. At the end of the bentonite filtration at crossflow velocity (CFV) of 4 mm/s, the fouling thickness was measured as 85 ìm. Specific cake resistance was calculated by taking into account the cake height measurements with this technique. The DO technique also allowed unique insights into the mechanisms related to the fouling removal. The effect of bentonite concentrations were assessed to provide credibility of the technique. © 2008 Elsevier B.V. All rights reserved.

  • (2008) Chen, Gaojian; Wright, P.M.; Geng, J.; Mantovani, G.; Haddleton, D.M.
    Journal Article
    Polymers containing poly(ethylene glycol) methacrylate and 2-(2-methoxyethoxy)ethyl methacrylate have been synthesized by Cu(0)-mediated radical polymerisation for use as thermoresponsive water-dispersants for carbon nanotubes.

  • (2008) Chang, Sheng; Fane, Anthony; Waite, T; Yeo, A
    Journal Article
    Freshly wetted, submerged hollow fiber polypropylene membranes have been observed to exhibit unstable behavior characterized by fluctuating suction pressure-time profiles on filtration of MilliQ water. Filtration results with single hollow fibers reveal that the observed suction pressure fluctuation could be caused by an unstable local resistance at some location inside the fiber lumen. The evidence from X-ray microimaging of the fiber lumen suggests that abnormal local flow conditions were induced by the presence of stagnant bubbles firmly attached to the internal wall of the hollow fiber membranes. The formation of these stagnant bubbles is attributed to some `dry` points existing on the internal surface of the hollow fiber membrane. It appears that these `dry` points cause significant and unstable local resistances for the permeate flow inside the fiber lumen. For a fixed average flux the high local resistance results in increased suction pressure in the lumen region downstream of the `dry point` and this shifts an additional flux load to this region. The resultant maldistribution of local fluxes caused by abnormal local flow resistances can markedly affect the filtration behavior of the hollow fiber membrane. Interestingly the effect was not observed for all fibers and appears to require local `dry point` existence within the lumen. The filtration of latex particle suspensions under different conditions showed that those fresh fibers with fluctuating suction pressure-time profiles also exhibited a sharp increase in the suction pressure and had limited run times for filtration. A pre-treatment protocol using pressurized water (PW) applied to the freshly ethanol-wetted fibers was found to result in marked improvement in the stability of the hollow fiber membranes tested. © 2007 Elsevier B.V. All rights reserved.

  • (2008) Wang, XiaoMao; Kovalsky, Peter; Waite, T
    Journal Article
    Separation of liquid from concentrated slurry is a significant process in laboratory and engineering applications. In an earlier paper (X.M. Wang, S. Chang, P. Kovalsky, T.D. Waite, Multiphase flow models in quantifying constant pressure dead-end filtration and subsequent cake compression. 1. Dilute slurry filtration, J. Membr. Sci., in press), we investigated the applicability of the Smiles and Tiller multiphase flow models to description of the filtration behavior of dilute yeast slurries and here extend the analysis to consideration of concentrated slurries. Smiles` and Tiller`s models are employed to quantify dynamic filtration behavior while a numerical technique derived from Smiles` method is utilized for cake compression stage characterization. The numerical method for Smiles` model for concentrated slurry filtration is the same as that for dilute slurry, while an iteration step is added to the method for Tiller`s model. The results obtained indicate that the Smiles and Tiller models are equivalent in quantifying filtration behavior and cake structure of concentrated slurry and reveal that the cake structure and the ensuing filtration behavior are affected by the initial slurry solid fraction. The cake formed from slurry with a higher initial solid fraction tends to have a lower average solid fraction and a lower average specific resistance than is the case for lower initial slurry solid fractions. The variance of superficial liquid velocity through the cake during concentrated slurry filtration is much more significant than is the case during dilute slurry filtration suggesting that caution should be exercised in employing the conventional filtration model in concentrated slurry filtration data analysis. During the compression stage, the compression rate is relatively constant at the beginning then drops sharply before adopting a relatively stable value at longer times. Concomitantly, the solid compressive pressure of the upper surface of the cake increases

  • (2008) Wang, XiaoMao; Chang, Shang; Kovalsky, Peter; Waite, T
    Journal Article
    Apart from the empirical conventional filtration model, a number of rigorous multiphase flow models are available for the description of the dead-end cake filtration of compressible slurries. In this study, Tiller`s and Smiles` models are compared with regard to their quantification of the dynamic filtration behavior of `dilute` flocculated yeast slurry during dead-end constant pressure filtration. Steady-state filtration is employed to obtain the compressive yield stress and specific resistance of the cake as functions of solid fraction. It is found that, by virtue of these cake properties, the governing equations of Smiles` and Tiller`s model can be numerically solved. The results show that Smiles` and Tiller`s models are equivalent in quantifying filterability and specific resistance, as well as solid fraction, superficial liquid velocity and solid pressure profiles. The compressible property of the cake is demonstrated by the dependence of either filterability or average specific resistance on the applied pressure. For dilute slurries, the applied pressure has a significant influence on solid fraction profile but has little influence on superficial liquid velocity profile with the maximum variance in superficial liquid velocity in the cake being determined by the solid fraction of the slurry. In the dead-end filtration of dilute slurry, the superficial liquid velocity through the cake is almost uniform and the specific resistance can be approximately obtained from correlation of filtration data by the conventional model. © 2007 Elsevier B.V. All rights reserved.