Navigating corrosion challenges in column overhead systems
Case-by-case methodology as part of best engineering practices, and integration of computer tools as accurate means to predict, identify, and mitigate corrosion issues
Rodolfo Tellez-Schmill and Soni Malik KBC (A Yokogawa Company) Ezequiel Vicent OLI Systems
T he oil and gas industry invests billions of dollars annu- ally to uphold its integrity. In Europe alone, corrosion imposes a financial toll that costs the economy more than €463 billion per year. In 2013, the European Union reported that corrosion caused more than 20 major refinery accidents since 2000. 1 Controlling corrosion in oil refining equipment and pipeline systems is very complex, as it involves managing multiple factors in a dynamic system. Typically, corrosion can be min- imised when the operating conditions such as composition and phase state, temperature, pressure, equipment selec - tion, metallurgy, and anticorrosion measures are maintained with minimal variation. However, the industry is facing multiple challenges due to the constant changes in how crude oil and raw materials are processed. The drastic changes in composition, processing philosophy, and flow rates result in varying distribution and degrees of corrosion in the same process equipment and piping. Furthermore, the recent rise in renewable fuel pro- duction further complicates refining operations. Corrosion risks Currently, there is a growing global trend to produce low-car- bon fuels. As biogenic materials are co-processed with
crude oil fractions, studying corrosion in refineries attracts attention. Vegetable oil, composed of fatty acids, contains oxygen, which is part of the carboxyl group of the fatty acid molecule, and chlorides. Typically, co-processing happens in hydrotreating units. When oxygen is present, fatty acids produce water (H₂O), carbon monoxide (CO), and carbon dioxide (CO₂). Furthermore, including chloride-containing groups will form hydrogen chloride (HCl). The reactor effluent will con - tain these four components. These components may not have been considered in the hydrotreater’s original design and material selection. In a diesel hydrotreater using co-pro- cessing vegetable oil or animal fats, the reactor effluent needs to be carefully handled to avoid corrosion. In refinery hydrotreating processes, the reactor effluent system is prone to fouling and corrosion from two main cul- prits: ammonium bisulphide (NH₄HS) and ammonium chlo - ride (NH₄Cl). To minimise corrosion-related issues, API RP 932-B² is a trusted recommendation. This recommended practice also provides guidelines for the design and operation of reactor effluent air cooling (REAC) systems and addresses velocity limits, metallurgy selection, sour water composition, wash water quality, and rates. However, the industry needs a computer tool that
Reactor feed e uent exchangers
Recycle gas
Reactor e uent air coolers
Acid gas condenser
Overhead condenser
Acid gas K. O. drum
Reactor e uent
Sour gas
Condensate receiver
Reactor feed
Stripper re ux drum
Stripper feed heater
Wash water
Sour water
Sour water
Stripper
Wild naphtha
Stripping steam
Diesel to storage
Figure 1 Reactor effluent cooling train and separation plant
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PTQ Q3 2024
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