Numerical simulation studies of mass transfer under steady and unsteady fluid flow in two- and three-dimensional spacer-filled channels

Hollow fibre and spiral wound membrane (SWM) modules are the most common commercially available membrane modules. The latter dominate especially for RO, NF and UF and are the focus of this study. The main difficulty these types of modules face is concentration polarisation. In SWM modules, the spacer meshes that keep the membrane leaves apart also help reduce the effects of concentration polarisation. The spacer filaments act as flow obstructions, and thus encourage flow destabilisation and increase mass transfer enhancement. One of the detrimental aspects of the use of spacers is an increase of pressure losses in SWM modules. This study analyses the mechanisms that give rise to mass transfer enhancement in narrow spacer-filled channels, and investigates the relationship between flow destabilisation, energy losses and mass transfer. It shows that the regions of high mass transfer on the membrane surface correlate mainly with those regions where the fluid flow is towards the membrane. Based on the insights gained from this analysis, a series of multi-layer spacer designs are proposed and evaluated. In this thesis, a Computational Fluid Dynamics (CFD) model was used to simulate steady and unsteady flows with mass transfer in two- and three-dimensional narrow channels containing spacers. A solute with a Schmidt number of 600 dissolving from the wall and channel Reynolds numbers up to 1683 were considered. A fully-developed concentration profile boundary condition was utilised in order to reduce the computational costs of the simulations. Time averaging and Fourier analysis were performed to gain insight into the dynamics of the different flow regimes encountered, ranging from steady flow to vortex shedding behind the spacer filaments. The relationships between 3D flow effects, vortical flow, pressure drop and mass transfer enhancement were explored. Greater mass transfer enhancement was found for the 3D geometries modelled, when compared with 2D geometries, due to wall shear perpendicular to the bulk flow and streamwise vortices. Form drag was identified as the main component of energy loss for the flow conditions analysed. Implications for the design of improved spacer meshes, such as extra layers of spacer filaments to direct the bulk flow towards the membrane walls, and filament profiles to reduce form drag are discussed

Using Desalination to Improve Agricultural Yields: Success Cases in Mexico

Water scarcity is a global problem, motivating growth and development of new technologies for water treatment, reuse and desalination. For many arid regions in Mexico, especially in the northwest, agriculture is an important economic activity. The Yaqui Valley in Sonora, Mexico, faces problems related to aquifer overexploitation and saline intrusion, which have increased salt concentration in well water to 2000–9000 mg/L total dissolved solids (TDS) and led to soil salinization and low crop yields. This work evaluates the effect of TDS in irrigation water on crop yield. A 150 m3/d desalination plant was used, consisting of 12 SWC4B-MAX membrane modules, with 98% rejection and 75% recovery. Two crops were irrigated with control (4000 mg/L) and desalinated water (200 mg/L). Sorghum (Sorghum) had yields of 7.9 and 8.8 ton/ha, whereas tomatillo (Physalis philadelphica) had yields of 30.82 and 35.88 ton/ha, respectively. Evidently, the desalination process influences agricultural yields

Development, Characterization, and Applications of Capsaicin Composite Nanofiltration Membranes

Biofouling in reverse osmosis (RO) membranes is a severe problem, causing a decrease in both permeate flux and salt rejection and increasing transmembrane pressure. Capsaicin extract inhibits bacterial growth and is therefore used in this study to prepare a thin-film composite membrane and membrane support. Four types of nanofiltration (NF) membranes were prepared by interfacial polymerization onto a porous support prepared by the phase inversion method. Membrane A was the control membrane with no capsaicin extract, membrane B contains capsaicin in the polyamide thin film, membrane C contains capsaicin in the porous support, and membrane D contains capsaicin in both the thin film and support layers. Three different salts (Na2SO4, MgSO4, and NaCl) were used at different concentrations (1000, 3000, and 5000 ppm) to test the performance of the membranes in terms of salt rejection and permeate flux. Membrane B showed the highest rejection for all the salts and concentrations tested. For 5000 ppm NaCl, the permeate flux for membrane B was 14.81% higher, and salt rejection was 19.6% higher than membrane A. Future work will evaluate the anti-biofouling properties of the membranes prepared with capsaicin, when exposed to seawater microorganisms

Desalación por ósmosis inversa y su aprovechamiento en agricultura en el valle del Yaqui, Sonora, México

Sonora, situado al noroeste de México, ocupa el segundo lugar en cultivos de riego en el país. Los problemas de disponibilidad de los recursos hídricos, principalmente para agricultura en ese estado, se deben a la alta concentración de sales en los pozos, que van desde 2 000 hasta 5000 mg/l de sólidos disueltos totales (SDT). Estos altos valores de SDT son atribuidos a efectos de intrusión salina (Dévora, Gonzalez, & Saldivar, 2009), al tener una excesiva explotación del manto acuífero (Conagua, 2011). Sin embargo, el uso de tecnologías de desalación y modelos de predicción del proceso permiten aprovechar el recurso de manera óptima tanto en agua producto como en el rechazo. Es por esto que el objetivo es definir un modelo matemático de simulación para la predicción de la operación de una planta desaladora de ósmosis inversa alimentada por agua salobre, validando que el agua producto cumpla con los límites permisibles para su uso en agricultura. Con motivo de validar el modelo, el experimento consistió en habilitar una planta desaladora por ósmosis inversa (OI), con capacidad nominal de 100 m3/d, compuesta por ocho membranas SWC4 de 8”X40”, para ser utilizada en el riego del cultivo de sorgo (Sorghum), el cual presenta un rendimiento de 100%, a una concentración máxima de 2 000 mg/l de SDT en el agua de riego (4 mS/cm), en un área de 0.25 ha, con la finalidad de evaluar rendimiento en kg/m2 (ton/ha). Se regó la mitad del terreno con agua desalinizada (promedio de 64.8 mg/l de SDT) y la otra mitad con agua salobre de pozos subterráneos (promedio de 6 610 mg/l de SDT). Con el apoyo de un equipo de medición multiparamétrico modelo YSI 556 se determinó en el agua de alimentación, rechazo y permeado, la conductividad eléctrica (ìS/cm), sólidos disueltos totales (mg/l), pH y temperatura (°C). Con los datos obtenidos de la planta piloto se diseñó un modelo de simulación en la plataforma de MATLAB R2009a, usando Simulink, que cumple con la función de predecir el comportamiento de la planta desaladora, obteniendo concentraciones de agua producto y rechazo en diferentes arreglos con iteraciones de control, que incluye recirculación de salmuera en diferentes volúmenes. De forma subsecuente, este modelo fue utilizado para simular el aprovechamiento de caudal en el agua de rechazo, con la finalidad de incrementar la sustentabilidad del proceso. Los resultados del estudio muestran que al alimentar un agua de 6 610 mg/l de SDT, las corrientes de producto y rechazo son de 64.8 y 21 300 mg/l de SDT, respectivamente. La evaluación del proceso muestra que el costo de producción de agua es de 6.05 MX$/m3, muy similar a lo reportado por la International Desalination Association, que es de 6.70 MX$/m3. Con el uso de esta agua desalinizada se logró un incremento de producción de 1 ton/ha de sorgo, comparado al riego con agua salada. Estos datos se usaron para validar y calibrar el modelo. Los resultados de la modelación de recirculación muestran que conforme sea menor el porcentaje de recirculación de salmuera se pueden realizar hasta cinco iteraciones, sin incrementar la concentración del agua de alimentación por arriba de 42 000 mg/l, que es lo máximo permitido por la membrana utilizada en la planta. Se incrementó la productividad agrícola, por lo cual las inversiones públicas y privadas en el sector rural se consideran viables en el corto plazo. Se encontró que es posible, para las condiciones de la planta de 100 m3/d, recircular total o parcialmente la corriente de salmuera. Se pueden hacer varias iteraciones con esta corriente sin afectar de modo significativo el agua producto ni llevar al máximo la capacidad de la planta. Entre mayor sea el porcentaje de salmuera recirculada, menos iteraciones podrán realizarse, pero serán reducidas en mayor medida las descargas al medio ambiente

Feasibility assessment of Bioenergy with Carbon Capture and Storage (BECCS) deployment with Municipal Solid Waste (MSW) co-combustion at New South Wales (NSW) coal power plants

Burning coal to produce electricity is one of the main contributors of carbon dioxide emissions to the atmosphere. This study aims to find out if it is practical and cost-effective to reduce those emissions in NSW by burning waste materials along with the coal, separating the carbon dioxide from the rest of the combustion gases and storing the carbon dioxide deep underground Municipal Solid Waste (MSW), or rubbish, is a combination of many different materials, many of which cannot be burned (such as glass and metal), but also many that can burn. The materials this study is interested in are dry materials that were derived from plants, such as wood and paper waste, as they are easier to burn in a power plant and can be separated more easily than other wastes. When wood and paper are burned, the carbon in them just returns to the atmosphere because it was absorbed from the air when the plants were growing, but if that carbon is separated and stored deep underground, then the amount of carbon dioxide in the atmosphere is reduced. This technology is known as “Bioenergy with Carbon Capture and Storage”, or BECCS. For this study, BECCS involves burning coal along with wood and paper waste to generate electricity, while separating the carbon dioxide, transporting it via pipeline, compressing and storing it deep underground in western NSW, at a well site in the Darling Basin: Mena Murtee-1 in the Pondie Range Trough. We consider implementing this type of BECCS at the three younger coal power plants in NSW where wood and paper could be easily burned: Mt Piper, Eraring and Bayswater. We also consider burning different amounts of waste at each power plant, but even if all available wood and paper waste in NSW was used, it would only amount to about 5% of the fuel burned in those three plants. According to this study, burning paper and wood waste alongside coal reduces the amount of carbon dioxide added to the atmosphere, but produces more ash than burning coal alone. This means it will be necessary to add extra equipment to catch the extra dust before it is released to the atmosphere. If one-tenth of the fuel is wood and paper, carbon emissions are only slightly reduced (less than 3%), but if carbon capture and storage is also implemented (thereby implementing BECCS) then the power plant will only emit about one-fifth of the emissions of a normal coal plant over its whole life, which is similar to the overall emissions of electricity produced by solar panels. BECCS can also completely offset the carbon emissions from coal if more than a third of the fuel burned is wood and paper waste, thereby achieving negative emissions. Although the cost of getting rid of the carbon dioxide becomes lower as more waste is burned, the cost of the electricity is increased, because less electricity is produced. This study concludes that BECCS can help significantly reduce carbon emissions in NSW. Still, it is important to consider other waste sources (for example textiles, garden waste, agricultural waste), as availability of waste is a strong limitation for further use of this technology