The degradation of carbon steels due to corrosion and gaseous permeation phenomena can be significantly reduced by a thin alumina coating. Tubular carbon steel structures, commonly employed in nuclear establishments are particularly vulnerable to chemical degradation on the inner surface due to the flow of corrosive fluids. In the present work, a fluidization-based chemical vapour deposition process is applied as a one-step solution for simultaneous chemical passivation of both inner and outer substrate surfaces meanwhile optimizing precursor inventory by utilizing fluidized bed sublimation and induction heating techniques. The process is studied by using a 2D-1D mathematical model, which has been validated with experimental results for different carbon steel grades. It was observed that there exists an optimum fluidization velocity for a specified initial mass fraction of precursor powder at which mass of alumina deposited per unit mass of precursor sublimated is maximized.
Erosion of graphite packing in continuously operating fixed bed sodium amalgam decomposers leads to performance degradation accompanied by clogging in the downstream process lines which not only increases the maintenance and catalyst refilling costs but also aggravates the risk of mercury vapour exposure. To overcome this drawback, the present work utilizes tubular SS-304 packing coated with tungsten carbide (WC) on the outer surface. The coating is obtained using an indigenously developed laser-directed energy deposition facility. Dedicated experimental setup is developed for each set of process parameters to comparatively study the fixed bed decomposition kinetics at steady state for three types of WC-coated SS-304 packing and a conventional spherical graphite packing. In parallel, a numerical 3D-1D model is implemented using open source computational solvers and is experimentally validated. The algorithm of this model is based on proposed drop-fill approach for WC-coated SS-304 packing and modified drop approach for spherical graphite packing, respectively. In terms of decomposition rates, the performance of WC-coated SS-304 packing surpasses that of spherical graphite packing at high amalgam flowrates; meanwhile, the average alteration in experimental steadystate temperature profile after continuous operation of 2 years is around 2% for WC-coated SS-304 packing as compared to nearly 17% for spherical graphite packing.
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