Modeling study of the heat of absorption and solid precipitation for CO2 capture by chilled ammonia

Qiang Zhou; Lan Liu; Eric Croiset; Zhongchao Tan; Qingcai Liu; Jian Yang

doi:10.1039/c9ra00164f

Modeling study of the heat of absorption and solid precipitation for CO₂ capture by chilled ammonia

RSC Adv. 2019 Jun 27;9(35):20075-20086. doi: 10.1039/c9ra00164f. eCollection 2019 Jun 25.

Authors

Qiang Zhou^{1

2}, Lan Liu¹, Eric Croiset², Zhongchao Tan², Qingcai Liu¹, Jian Yang¹

Affiliations

¹ College of Materials Science & Engineering, Chongqing University Chongqing China skyinjune@cqu.edu.cn.
² Faculty of Engineering, University of Waterloo 200 University Avenue West Waterloo Ontario Canada N2L 3G1.

Abstract

The contribution of individual reactions to the overall heat of CO₂ absorption, as well as conditions for solid NH₄HCO₃(s) formation in a chilled ammonia process (CAP) were studied using Aspen Plus at temperatures between 2 and 40 °C. The overall heat of absorption in the CAP first decreased and then increased with increasing CO₂ loading. The increase in overall heat of absorption at high CO₂ loading was found to be caused mostly by the prominent heat release from the formation of NH₄HCO₃(s). It was found that NH₄HCO₃(s) precipitation was promoted for conditions of CO₂ loading above 0.7 mol CO₂/mol NH₃ and temperatures less than 20 °C, which at the same time can dramatically increase the heat of CO₂ absorption. As such, the CO₂ loading is recommended to be around 0.6-0.7 mol CO₂/mol NH₃ at temperatures below 20 °C, so that the overall absorption heat is at a low state (less than 60 kJ mol^-1 CO₂). It was also found that the overall heat of CO₂ absorption did not change much with temperature when CO₂ loading was less than 0.5 mol CO₂/mol NH₃, while, when the CO₂ loading exceeded 0.7 mol CO₂/mol NH₃, the heat of absorption increased with decreasing temperature.