Operability and flexibility studies of a MDEA-based CO2 absorption process

ELEONORA ERDMANN; GUTIERREZ JUAN PABLO; ENRIQUE TARIFA

Barcelona

Congreso; 10th World Congress of Chemical Engineering; 2017

In a chemical CO2 absorption process, an important energy requirement is needed for the regeneration of the cycling solvent, i. e. an alkanolamine. Therefore, different literature articles deal with the optimization of the process, minimizing the reboiler duty per absorbed CO2 mass unit. However, the results that can be obtained when optimizing the process operation and their implementation are limited by the design capacity. The degree of flexibility of a process is determined by the variations of the unpredicted parameters that a plant can admit. In this sense, a scalar flexibility index can be defined to measure the size of the region where the reliability of the process is high, in a context of uncertain parameters.In this work, the design limitations of a MDEA-based CO2 absorption process are determined through a system operability study together with flexibility analysis. In this respect, the ability of the process to perform in a range of conditions while minimizing the reboiler duty ratio is determined. For the purpose, the steady-state of a CO2 removal from natural gas plant is simulated using Aspen Hysys v8.8. Different scenarios are evaluated, including disturbances cases from the nominal values and variations on the manipulated variables. Particularly, the disturbances or uncertain parameters scenarios include deviations from the inlet natural gas regular conditions, temperature, pressure and molar flow. For each scenario, the ratio between the reboiler duty and the absorbed CO2 and the optimal values of the manipulated variables, lean amine molar flow, lean amine temperature, flash separator pressure and the temperature of the MDEA to regeneration are fully determined. In addition to this, the scalar flexibility index is calculated using operating considerations, study cases, parametric sensitivity analyses and simulation tools. With the application of the operability and flexibility concepts in the process under study, it was possible to determine the boundaries of the system. From the results, the limits are defined for which CO2 absorption is feasible. In all of the cases, the specification of CO2 in the outlet natural gas is not overpassed and thus the high reliability region was possible to size.