Corrosion Control in Sulphur Recovery Units – Claus Process

Abstract

Abstract Today there are more than 100 Sulphur Recovery Units in the Middle East and many of them have been in operation for 10 years or longer. Corrosion can be one of the most challenging issues in these units due to the presence of hydrogen sulfide, sulphur dioxide, elemental sulphur and water. If operated within the normal operating temperature range, corrosive conditions should not occur; however, if upset conditions result in temperatures which are too high or too low, several corrosion mechanisms are possible. This issue has resulted in many instances in which existing units have been forced into emergency shutdown for several days to perform maintenance. This results in production loss and the potential for significant environmental impact due to flaring acid gases. API 571 documents most of the major corrosion mechanisms in the Claus process such as sulfidation, oxidation, flue gas dewpoint corrosion and wet sulphur corrosion. However, it does not address specific means of controlling corrosion, taking into account different technologies available for tail gas treatment. This paper demonstrates the fundamental corrosion issues encountered in SRUs and proposes protective actions. Guidance related to start-up, shutdown and normal operation is also provided for establishing appropriate operating limits to achieve safe and reliable operation for corrosion avoidance. This paper takes a unique approach which considers both theoretical and practical, real-world experience in the mitigation and monitoring of corrosion control. Operators are provided with tangible recommendations that can be applied to their facilities. Protection against atmospheric corrosion is not in the scope of this paper. This paper has been prepared based on a review of several industry publications, which address specific corrosion mechanisms in SRUs. The main objective of this paper is to provide a high-level overview of these works, while also offering guidance on the safe operating envelope of the facility, to avoid excessive corrosion. Most of the metallurgy in an SRU is typically specified as carbon steel, which is adequate when the unit is operated within safe operating limits. However, if operated outside the acceptable range (above or below), corrosion can be swift and severe, as will be described.