Abstract: Concerning the abnormal increase in corrosion rates in the dehydrogenation tail gas system of a styrene unit, which has threatened the safe and stable operation of the unit, this paper conducts an analysis of the corrosion mechanism and research on the innovations for long-term operation. Corrosion in the dehydrogenation tail gas system of the styrene unit primarily occurs in areas such as the inlet pipelines, shell heads and outlet condensate pipelines of the tail gas cooler, exhibiting typical localized CO₂ corrosion morphologies like pitting, groove-like and plateau-like features. Mechanism analysis reveals that the corrosion is primarily induced by electrochemical corrosion resulting from carbonic acid formation when CO₂ in the medium dissolves in water. The corrosion rate is influenced by the coupling of multiple factors including temperature, pressure, CO₂ content, precipitate alkalinity, water composition and flow conditions. This paper focuses on discussing the effects of medium temperature, CO₂ partial pressure, and impact of medium flow velocity on the CO₂ corrosion rate. Based on the results of the corrosion mechanism analysis, a series of modification measures have been proposed and implemented covering the addition of a quencher and a salt cooler to reduce the medium temperature, CO₂ partial pressure and flow velocity. After the modifications, the corrosion rates in the tail gas system's heat exchangers and pipelines significantly decreased. No significant signs of corrosion were observed after two years of full-load operation, indicating that CO₂ corrosion in the system has been effectively controlled. This research has achieved safe and stable operation of the dehydrogenation tail gas system and effectively extended the operational cycle of the unit. It provides a reference for addressing corrosion protection issues in similar units.

Key words: dehydrogenation tail gas system, research on innovations, corrosion mechanism, CO₂ localized corrosion