Lappeenrannan-Lahden teknillinen yliopisto LUT

Improvement of cellulosic ultrafiltration membrane durability was studied.With no protective modifications, the com. regenerated cellulose membrane showed notable signs of degradation when in contact with lake water for several days.The most evident signs of degradation were increasing permeate fluxes and decreasing model substance retentions.Differing degrees of protection were achieved through TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) -mediated oxidation of the membranes and charge-adhered coatings.Mere TEMPO-oxidation and consecutive coating with either poly(diallyldimethylammonium chloride)/poly(styrene sulfonate) (PDADMAC/PSS) or microfibrillar cellulose slightly improved the durability, whereas the poly(vinyl amine)/poly(acrylic acid) (PVAm/PAA) coating system made the membrane stable enough that no signs of degradation were observed during the testing period.The performed modifications did not alter the substrate membrane filtration properties significantly.The most notable changes were attributed to the [PVAm/PAA]₁ coating that reduced both pure water permeance and mol. weight cut-off value by approx. 10%.It is suggested that the [PVAm/PAA]₁ coating was sufficiently tight to block the cellulose-degrading substances that were present.Nevertheless, the structure was loose enough to sustain the desired properties of the substrate membrane.In concentrating filtrations, said coating mitigated flux decrease and the coated membrane ultimately had better filtration capacity than the non-coated alternatives.

This study examines the performance of a 90 MWth Circulating Fluidized Bed (CFB) power plant utilizing a range of fuels, specifically coal, Refuse-Derived Fuel (RDF), and biomass.To this end, a detailed process simulation model was developed using EBSILON Professional software, based on a com. CFB power plant originally designed for coal combustion.The model was then modified to assess its operational capabilities when using RDF and biomass fuels.The simulation includes key components of the fluidized bed combustion system, such as the riser, cyclone, flue gas path with heat exchangers, steam turbine, feedwater preheaters, and a district heating system supplying thermal energy to nearby facilities.To ensure the model's accuracy and reliability, it underwent a thorough validation process, comparing simulated pressure and temperature profiles along the riser with measured data, as well as assessing the performance of the water-steam side.Following this validation, the model was used to explore fuel composition variations, transitioning from 100% coal to 100% RDF and biomass, under both air and oxy-fuel combustion conditions.The study also considers two operational scenarios: maximising electricity generation during peak summer months and optimizing district heating during the winter months when thermal demand is at its highest.

Thermal hydraulic experiments with the modular integral test facility, MOTEL, were performed as a part of the European McSAFER research project.The facility models an integral pressure water small modular reactor (SMR) with a helical steam generator and a core with sep. heater rod groups, in which power can be individually controlled.Different asym. and ring-shaped radial core power distributions were imposed in the experiments to provoke cross flows in the buoyancy-driven coolant flow.The purpose of the experiments was to produce new SMR-relevant data for the validation of computational fluid dynamic (CFD) and thermal-hydraulic subchannel codes.The exptl. measurements revealed cross flow mixing effects, mainly in the top part of the core.Obtaining visible differences in the fluid temperature measurements between different heater regions required significant power gradients between the regions.CFD simulations were performed using ANSYS CFX with a detailed model comprising the whole primary side of the facility, and addnl. investigations were conducted with a stand-alone model of the heat exchanger.Good agreement with the measurements was obtained with the CFD simulations, which also revealed further details of the core flow characteristics in an asym. heating case.Furthermore, simulations with the subchannel codes, CTF and VIPRE-01, were performed.The simulations with CTF highlighted the code's capability to handle flow rates typical to natural circulation driven SMRs, as the results agreed well with the experiments and were able to predict the correct axial temperature profiles in the different regions of the core.VIPRE-01 solution stability was found to be highly sensitive to the flow rate, the power level, and the axial nodalization.Simulations with VIPRE-01 ended unsuccessfully due to convergence issues, and it was concluded that the conditions of the experiments are beyond the current capabilities of the code.