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

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

doi:10.1039/c9ra00164f

Qiang Zhou, Zhongchao Tan + Show 4 more

Open Access

https://doi.org/10.1039/c9ra00164f

Copy DOI

Journal: RSC advances	Publication Date: Jan 1, 2019
Citations: 3	License type: CC BY 3.0

Affiliation: University of Waterloo, Chongqing University

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.

Highlights

CO2 is considered as the main greenhouse gas responsible for global warming and climate change.[1]
Two models that are commonly used in thermodynamics studies of CO2 capture process: (1) the extended UNIQUAC model developed by Thomsen and Rasmussen[33] and (2) the e-NRTL model proposed by Chen et al.[34]
The calculation results are obtained for vapor–liquid equilibrium (VLE), solid–liquid equilibrium (SLE), and solution speciation at different temperatures and NH3 concentrations

Summary

Introduction

CO2 is considered as the main greenhouse gas responsible for global warming and climate change.[1]. Post-combustion capture attracts the most attention because it can be more implemented on existing power plants.[7,8,9] In post-combustion capture, alkanolamine solutions, monoethanolamine (MEA) in particular, act as CO2 absorbents with high reaction rates.[10,11,12] amine-based capture suffers from corrosion and high operating cost, including absorbent degradation and relatively high energy consumption. These drawbacks greatly hinder its wide deployment in the electric power industry.[13,14,15,16] Many researchers investigated cost-effective alternatives with low heat of CO2 absorption.

Methods

Results

Conclusion