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Part 1: Addressing the Impacts of Changing Regulations and Feedstocks in Sulfur Recovery Units

Part One of a five part series.

Introduction

The efficient and reliable operation of sulfur recovery units (SRUs) continues to be critical to hydrocarbon processors, which are tasked with delivering end products that contain lower levels of sulfur while simultaneously reducing the amount of sulfur that is emitted to the local environment. In January 2020, the International Maritime Organization’s initiative to lower pollution from ships – often referred to as IMO 2020 or MARPOL 2020 – represented the most recent global regulatory requirement on an end product that directly affected refiners. This change lowered the available H2S content in fuel oil from 3.5% to 0.5%, driving ever greater removal of sulfur components in processing operations and higher recovery efficiency of elemental sulfur (SX) in SRUs. Local and national jurisdictions are continuously reviewing and modifying emission maximums, further impacting the design and operation of SRUs.

As a reminder, an SRU is tasked with one primary objective – to recover some amount (often 96+%) of the elemental sulfur that has been delivered to it. Hydrocarbon feedstocks that are used in most natural gas processing facilities and refineries contain sulfur that must be removed. The sulfur contains very little energy value and, more importantly, can negatively impact final product purity requirements. There is a positive element to recovering elemental sulfur however, as it can be sold and used in fertilizer and medical drug production. During hydrocarbon processing, sulfur components can be stripped out of the feedstocks using combinations of catalysts, temperature, pressure, and the introduction of excess hydrogen, and sent to the SRU for elemental sulfur removal. The gas streams delivered to the SRUs are typically referred to as acid gas and/or sour water stripper gas and, unfortunately, frequently consist of components other than just ‘sulfur compounds’, which will be touched upon later in this article. Upon entering the SRU, the feedstocks undergo a modified Claus reaction to have SX removed. The gas enters a reactor furnace, continues through a series of converters and condensers – where the elemental sulfur is captured – and then either enters a tail gas treatment unit (TGTU) before being burned in a thermal oxidizer, or the TGTU is either bypassed or not required and the gas stream is burned in the thermal oxidizer before exiting the SRU via a stack (Figure 1).
Sulfur Recovery Unit Diagram

Figure 1. Typical SRU layout, with common analyzer locations

Part Two - Feed Gas Analysis
Part Three - Tail Gas/Air Demand Analyzer
Part Four - Tail Gas Treatment
Part Five - Continuous Emission Monitoring Systems

Learn more about sulfur recovery processes.

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