Multiscale energy reduction of amine-based absorbent SO2 capture technology: Absorbent screening and process improvement

Abstract

The high total regeneration energy consumption (Qtot) limits the industrial application of amine-based absorbent SO2 capture technology, and regeneration energy consumption can be divided into desorption reaction heat (Qdes), latent heat consumption (Qlat) and sensible heat consumption. This work focused on developing an energy-efficient SO2 capture technology through amine-based adsorbent screening and process improvement, in which desorption reaction heat, being the internal cause of high regeneration energy consumption, was only related to the type of adsorbent. An absorbent screening method was established with SO2 absorption capacity (α) and desorption reaction heat values as indicators. The screening results showed the functional relationship of Qdes-α for five organic diamines ethylenediamine (EDA), piperazine (PZ), N-hydroxyethylpiperazine (HEP), N, N'-dihydroxyethylpiperazine (DIHEP), and N-hydroxyethyl-N'-hydroxypropylpiperazine (HEHPP)): according to αEDA > αPZ > αHEHPP > αHEP > αDIHEP, Qdes(EDA) > Qdes(PZ) > Qdes(HEHPP) > Qdes(DIHEP) > Qdes(HEP). The latent heat consumption and sensible heat consumption were related to process configuration, and N-methyldiethanolamine (MDEA), EDA, PZ and HEP were screened as amine-based absorbers for process modeling. The energy analysis showed that the order for regeneration energy consumption of the four absorbents followed Qtot(MDEA) > Qtot(EDA) > Qtot(PZ) > Qtot(HEP), and the energy distribution calculations showed that latent heat consumption had the largest proportion in regeneration energy consumption. Three improved processes (the rich-split, the lean-flash heat pump and the top-steam heat pump processes) were designed to recover the energy available in the system. Compared to the conventional process, the top-steam heat pump case could greatly reduce the regeneration energy consumption, and the Qtot values of the four absorbents (MDEA, EDA, PZ, and HEP) in the top-steam heat pump case were 4.28 GJ·t−1 SO2, 3.10 GJ·t−1 SO2, 3.13 GJ·t−1 SO2 and 3.68 GJ·t−1 SO2, respectively. According to technical and economic analyses, the top-steam heat pump case under the PZ absorbent system had the most potential for the flue gas SO2 capture process.