Gas Processing- Rich/Lean Amine Loading

Rich/Lean Amine Loading - Amine loading, the amount of acid gases contained within a given amount of amine is critical in the operation, maintenance and performance of an amine plant.

Rich Amine Loading (RAL) is determined by measuring the amount of acid gas contained in the amine stream exiting the Amine Contactor. This is typically represented in a mol ratio ((mol of CO2 + mol H2S)/mol amine). Generally speaking, this measurement is almost impossible to accurately measure in the field or in a lab so plant simulations are often times used to determine the RAL and adjust amine circulation rates and concentrations to meet desired results.

As RAL increases above a value of 0.40 mol AG/mol amine, several detrimental effects may be encountered  especially in an all CO2 acid gas system. These effects may include higher corrosion rates, higher temperature bulges within the Contactor and lower recovery of the acid gases due to slower reaction kinetics and capacity.

Thus, if the Rich Amine Loading exceeds recommended limits acid gas breakthrough may occur, process piping may erode/corrode (resulting in piping failures) and equipment may fail. For these reasons it is recommended employing stainless steel materials in the most critical areas of the plant.

Lean Amine Loading (LAL) is determined by measuring the amount of acid gas contained in the amine stream exiting the Amine Regenerator and is measured in the same manner as the RAL described above. This is a much easier and more reliable measurement.

LAL values will vary, depending on the type of amine being used. For MEA which is one of the most corrosive amines a LAL of up to 0.15 mol/mol may be seen while in an MDEA system (one of the weakest and least corrosive amines) a LAL of 0.005 mol/mol is not uncommon.

Lean Amine Loading will be affected by the reboiler duty, reflux ratio and the number of fractionation stages within the Amine Still. If the lean amine is not properly maintained, the acid gases corrosion may be encountered in the hot portions of the plant specifically the Amine Still Reboiler and associated piping. Also if the LAL is too high, the ability of the amine to remove the acid gases from the inlet gas stream in the Amine Contactor may be diminished and product specifications may not be met. This is especially true of MDEA systems that try to meet a very low level H2S specification.

Therefore, when designing and operating an amine plant care should be given to making sure the system is large enough to avoid overloading the amine with acid gases (high RAL) and ensuring that the amine regenerator has sufficient capabilities to properly strip the acid gases from the amine (low LAL).