Experimental research of descaling characteristics using circumfluence dilution and uniform-temperature perturbation in a vacuum furnace

摘要

Vacuum furnace corrosion and scaling problem have seriously constrained the normal operation of the oil mixing transmission system in China. This study explores the effects of descaling in vacuum furnace tubes at the oil mixing transportation system with circumfluence dilution and uniform-temperature perturbation (CUP) to reduce scaling ion density and improve water velocity in heat exchange tubes and scaling distribution uniformity along the tubes. Applying circumfluence by-path tube (CBT) enables a part of the outlet water from the heat exchange tubes to flow back to the inlet and achieve improved water velocity in heat exchange tubes. The improved water velocity in heat exchange tubes enhanced the scouring of the wall layer, thereby reducing the scaling quality and scaling ion density in hot water because of recirculation. This method improved the average temperature of water in the heating process under the same outlet temperature of the vacuum furnace. Scaling sediments were transferred to the tube entrance section, thereby reducing the intensity of the scaling sediments congregated in the outlet segment of the tube. These three measures slowed down the scaling and improved the uniformity of scaling along the pipeline of the vacuum furnace. Moreover, scaling was distributed on the surface of the vacuum furnace pipeline, which extended the boiler cycle. Scaling weighing was used to investigate the effects of ion concentration, unboiled water velocity, heat exchange temperature difference, and circulation rate on descaling. Experimental results show that CUP has improved the optimum descaling cycle deferred rate and average descaling cycle deferred rate by 102.2% and 73.4%, respectively. CUP can effectively extend the scaling time of the boiler tube and maintenance cycle, thereby improving the operating efficiency of the boiler and reduce operating costs. (C) 2016 Elsevier Ltd. All rights reserved.