Fouling performance issue

Another system under investigation is the iron/ chromium redox flow battery (Fe/Cr RFB) developed by NASA. The performance requirements of the membrane for Fe/Cr RFB are severe. The membrane must readily permit the passage of chloride ions, but should not allow any mixing of the chromium and iron ions. An anionic permselective membrane CDIL-AA5-LC-397, developed by Ionics, Inc., performed well in this system. ° It was prepared by a free radical polymerization of vinylbenzyl chloride and dimethylaminoethyl methacrylate in a 1 1 molar ratio. One major issue with the anionic membranes was its increase in resistance during the time it was exposed to a ferric chloride solution. The resistance increase termed fouling is related to the ability of the ferric ion to form ferric chloride complexes, which are not electrically repelled by the anionic membrane. An experiment by Arnold and Assink indicated that... 

Ralf Kuriyel (Millipore Corporation) addressed some of the issues related to the use of Dean vortices, formed during the flow of fluids in curved conduits, to enhance the performance of cross-flow filters by increasing the back transport of solutes. Results were presented on coiled hollow fibers with a varying radius of curvature, fiber diameter, and solution viscosity, to characterize the relationship between the back transport of solutes and hydrodynamic parameters. A performance parameter relating back transport to the Dean number and shear rate was derived, and a simple scaling methodology was developed in terms of the performance parameter. The use of Dean vortices may result in membrane systems with less fouling and improved performance. 

Several issues clearly remain regarding how blending biomass and coal will affect combustion performance, emissions, fouling and slagging propensities, corrosion, and ash salability. Nevertheless, several utilities have tested biomass/coal co-firing in utility boilers and the Electric Power Research Institute funded a study in 1997 to establish biomass co-firing guidelines.580... 

There are however concerns with durability or lifetime of the catalyst. There can be contaminants within the reformate, in particular sulfur compounds, that can render the catalyst completely inactive. In addition, if the reactor temperature operates too high or an unexpected over-temperature event occurs, the performance or durability of the catalyst can be seriously compromised. Additionally, the support of the catalyst can sinter over time on stream due to the presence of significant amounts of water. Fouling can be another issue, which impacts durability if very pure water or clean air is not used. While all these factors are present, catalyst formulations have been shown to operate for hundreds of hours with minimal to no degradation. 

Nevertheless, there is a long way to go before these systems can reach a commercial application level. There are two main issues. Power density (specific to membrane area unit) attainable by the current membranes (approximately 1 W/m ) is too low to make the technology cost-effective. However, the development of membranes for a specific purpose has just been started and significant improvements are expected in the next future in terms of performance, durability and cost. The second main issue is fouling caused by particles entrained by the streams contacted to membranes, which has to be controlled by expensive and possibly polluting water pretreatment processes. The latter problem is definitely avoided by the other two alternatives proposed, reverse vapor compression and hydrocratic generator, which on the other hand have not yet proved their technical feasibility. 

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