Flow rate perturbations for enhanced heat transfer and fouling mitigation in once-through steam generators

Abstract

Once-through steam generators (OTSGs) are widely employed in Steam-Assisted Gravity Drainage (SAGD) operations. Boiler feedwater, composed of treated produced water and fresh make-up water, retains dissolved solids that precipitate during steam generation, leading to fouling on tube surfaces, affecting heat transfer. This fouling causes localized temperature spikes on the tube walls, which can result in tube failure, operational shutdowns, and expensive repairs. This study investigates, for the first time, the impact of flow rate perturbations on heat transfer within a single pass of an operational OTSG by using a detailed multi-phase computation fluid dynamics model of a OTSG pass. Specifically, a controlled flow rate increase, doubling the baseline rate, is applied for 10 min every six hours. This perturbation effectively lowers tube wall temperatures, enhances heat transfer between the flue gas and tube wall, lowers the peak temperature in the tubes even in the presence of fouling. The moderation of tube overheating reduces the risk of tube failure. Consequently, the operational efficiency of the OTSG could be improved due to mitigation of fouling-related maintenance.