High Temperature Corrosion Quantification in Renewable Diesel and Sustainable Aviation Fuel Production Applications

High Temperature Corrosion Quantification in Renewable Diesel and Sustainable Aviation Fuel Production Applications

Sridhar Srinivasan and Jeremy Staats

Production of Renewable Diesel (RD) and Sustainable Aviation Fuels (SAF) from biological sources (natural oils) has seen exponential growth in recent years, stemming from worldwide government mandated climate change initiatives alongside the need for carbon capture and sequestration.  Significant, rapid investments have occurred in retrofitting / adapting existing refinery hydroprocessing infrastructure to process natural oils or coprocess natural oils blended with crudes to produce RD and SAF.  Such investments are driven by the fact that natural oils have the hydrocarbon (HC) molecular structures to fit within the mid-distillate fuel product such as diesel and aviation fuel as well as that hydroprocessing units are optimized for removal of unwanted Sulfur and Oxygen removal.

In these modified hydroprocessing applications, high temperature decomposition of triglycerides (TRG) leads to production of RD and SAF through hydroprocessing of esters and free fatty acids (FFA).  The resulting oxygen free-RD and SAF products are completely fungible with petroleum hydrocarbons. Hydro-processing of refined natural oils has its own unique corrosion problems.

Over the last few years, the authors introduced a molecular mechanistic model to quantify simultaneous high temperature naphthenic acid and sulfidation corrosion (CorrExpert®-Crude) in refinery CDU/VDU operations.  This model has been adapted to address high temperature FFA corrosion, given that FFA are carboxylic acids, akin to naphthenic acids found in conventional fossil-fuel based crude unit process streams.

A key aspect of modeling corrosion for FFA is the inhibitive role of hydrogen in the presence of Iron sulfide species.  While natural oils do not contain sulfur compounds, presence of reactive sulfur species such as thiols and sulfides in coprocessing applications provides an easy pathway to provide for the formation of a potentially protective nano barrier layer of FeS.  Further, the presence of FeS acts as a catalyst towards dissociation of molecular H2 to atomic H and subsequent reduction of FFA through atomic hydrogen.

A threshold H2 partial pressure is required to ensure hydrogen reduction of FFA is kinetically dominant when compared to acid corrosion of Fe.  Residence time of acid is another key parameter that will impact propensity for corrosion and / or H2 inhibition and is considered in the development of the prediction model.  A framework incorporating the effects of H2 partial pressure, residence time and reactive S concentration is proposed for assessing FFA corrosion for various commonly utilized natural oils in renewable applications.

The prediction model described herein represents a first-of-its-kind solution to address the complex questions of assessing FFA corrosion risk and metallurgical performance in RD / SAF Units, and provides an easy-to-use tool to evaluate unit piping and equipment reliability.   https://becht.com/engineering-solutions/strategic-business-planning-2/


About The Author

Mr. Srinivasan is a globally recognized corrosion / reliability expert and modeling technology consultant with over 30 years of experience in delivering industry-leading predictive analytic modeling software and monitoring sensors for corrosion asset integrity and risk management. Mr. Srinivasan has applied his extensive knowledge to a range of problems related to corrosion, metallurgy and modeling, generating innovative engineering solutions to complex problems related to oil, gas and refinery corrosion mechanisms and unit operations. Mr. Srinivasan also functions as a Corrosion SME with deep expertise in refinery process corrosion as well as training and implementation related to industry best practices related to Integrity Operating Windows (API RP 584) and Corrosion Control Documents (API RP 970). Over the last 21 years, functioning as the leader of Honeywell-led Joint Industry Consortia Programs (JIP), Mr. Srinivasan worked with leading, global operating companies to develop corrosion data and prediction models related to crude oil corrosivity, alkaline sour water (NH4HS) corrosion, crude unit overhead corrosion as well for multiphase sour oil/gas production, HPHT wells and safe use limits for carbon and stainless steels. He is the solution architect for the Predict® suite of refining applications widely utilized by global operators, including models for naphthenic acid / sulfidic corrosion and rich / lean amine corrosion. His recent efforts focused on enhancing process safety through application of real time models integrated with process historians won him an international innovation award from Hydrocarbon Processing. Mr. Srinivasan has also functioned as the Program Manager for a key corrosion modeling effort for International Space Station (ISS) for Boeing/NASA, where he developed a customized phase behavior and speciation model for the ISS. As a leading industry consultant, Mr. Srinivasan has worked with a global base of customers in modeling corrosion, quantifying corrosion mechanisms as well as delivering digitalized solutions for asset and mechanical integrity. Mr. Srinivasan’s has been active in NACE unit committees (STG08, STG 34, STG 62) as well as NPRA and AFPM. He functioned as the chair of NACE STG 62 (Corrosion Monitoring and Measurement, 2016-2020) and is currently the chair of the NACE Task Group on Smart Sensors for Corrosion Monitoring (TEG-100x). Mr. Srinivasan has also served as a member of the Board of Directors at AFPM (2016-2019). He has authored chapters in the Uhlig Handbook as well as ASM Handbook on Corrosion and Cracking. He is widely published and has 100 plus conference and journal papers, technical articles and book chapters in the areas of corrosion, modeling, material selection and predictive analytics. Mr. Srinivasan worked for about 23 years at Honeywell International, Inc., initially leading the development of corrosion and material selection models and later as business leader for Honeywell’s Corrosion Center of Excellence (COE). He also spent eight years early in his career working for Cortest Labs, generating experimental materials / corrosion data as well as building materials and corrosion databases and models for oil/gas applications. Mr. Srinivasan received his BS in Mechanical Engineering from Bangalore University and an MS in Mechanical Engineering from The University of Houston. He has also achieved Six Sigma Green Belt Certification. Mr. Srinivasan is based in Houston, Texas.

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High Temperature Corrosion Quantification in Renewable Diesel and Sustainable Aviation Fuel Production Applications

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