PTQ Q1 2025 Issue

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x The MEA strength is lower than the reported value. y The plant loading data is inaccurate. It is important to understand that the analysed rich amine loading is most likely lower than the actual oper- ating loading. This is because a portion of the acid gas is always flashed off during sample capture, transportation, and when the sample bottle is opened for the laboratory analysis. This makes the simulation discrepancy even more pronounced. If the laboratory data is to be believed, the chances of corroding the contactor and the rich amine piping is high. Amines cannot infinitely absorb acid gases. At the contac - tor pressure, there is an equilibrium loading limit for acid gas to be absorbed by the solvent. Once this loading limit is reached, no additional CO₂ or H₂S can be removed by the MEA solvent regardless of how many trays are present in the contactor tower. Thus, there are two loading limits of importance in regard to corrosion:  The actual rich solvent loading. v How close the rich solvent loading is to the equilibrium maximum loading. It is recommended to never exceed 80% of the equi - librium loading limit to avoid acid gas breaking out of the amine solvent in the contactor or in the rich piping, as the rich amine is heated or goes through pressure drops and elbows in the piping. When the amine loading is too high, any acid gas liberated from the rich solvent cannot be re-absorbed because it is already ‘too full’ at the conditions present. This means the H₂S and CO₂ that were liberated are free to attack the steel surfaces in the unit, leading to corrosion. Since corrosion is a chemical reaction, increased temperatures will increase the corrosion rates, meaning rich amine corrosion and lean amine corrosion will primarily affect the hottest zones in the amine unit. Pressure is important to an amine unit because it is vital for ‘pushing’ the CO₂ or H₂S from the gas phase into the liquid phase, where the reaction of H₂S and CO₂ with MEA occurs. The lower the operating pressure, the harder it is to remove H₂S and CO₂ in the gas stream because the acid gas partial pressure is very low (partial pressure is the sys- tem pressure factored by the mole fraction of CO₂ or H₂S). Figure 5 Relative corrosion tendencies of alkanolamines (Depart, LRGCC 1991). Hot skin corrosion test, CO₂ atmosphere, carbon steel, seven-day test @210°F

Lean loading

Rich loading

Linear (Lean loading)

Linear (Rich loading)

Figure 6 Historic MEA lean and rich loading

The lower the pressure, the lower the equilibrium loading limit. The gas plant amine unit will reach the maximum equilibrium loading faster than a high-pressure plant, so high rich loadings are problematic for this facility. Corrosion in high loading amine units using MEA solvents is primarily focused where the contactor maximum temper ature occurs (bulge), which should be in the middle section of the contactor given the low absorption rates at the bot tom of the column. Thus, the corrosion would be more pro - nounced at this location in the column. Part 2 of the article will discuss the chemical and pro- cess implication of the corrosion events taking place at the amine unit in more detail. David Engel is the Managing Director of Nexo Solutions and has more than 25 years of industrial experience in a variety of areas of chemical engineering, material science and chemistry. He is the inventor of more than 20 US Invention Patents and author of more than 100 techni - cal and scientific papers, and conferences. He has worked in several technical and business capacities for companies such as Eastman Kodak, Eli Lilly, and General Electric, and has recently specialised in process optimisation and new technology development. He holds a BS in chemistry and a PhD in organic chemistry. He is Six Sigma certified and a member of several industrial committees and company board of directors. Scott Williams is a process engineer and part of the Engineering Group at Nexo Solutions. He has been instrumental in many projects and solutions for the company and active in several R&D and engi- neering initiatives. His latest focus is on liquid contaminant removal from liquid and gas streams and selective separation applications. He holds a BS in chemical and biological engineering from the University of Colorado at Boulder. Cody Ridge is a chemical engineer from Texas Tech and a lead pro- cess engineer at Nexo Solutions. He started his career as an operator and process engineer in the Permian Basin. He is responsible for field engineering, technology development, and operations. He is the sup - port engineer for the East Texas, Louisiana and Oklahoma region. He has more than five published papers and has consulted with 30+ gas plants and refineries.

PTQ Q1 2025