Flowsheet modelling and techno-economic analysis of CO2 capture coupled pyro-hydrolysis of CaCl2 waste for HCl acid regeneration

Abstract

Pyro-hydrolysis of CaCl2 waste for HCl regeneration, which entails high temperatures and substantial energy consumption, remains challenging due to concerns regarding cost and CO2 emissions. This study presents a low-emission process integrating CO2 capture with SiO2-assisted CaCl2 pyro-hydrolysis technology for HCl regeneration, with a comparative techno-economic feasibility evaluation using Aspen Plus. When employing the same process components as for FeCl2 pyro-hydrolysis, it is demonstrated that 18 wt% HCl acid, a similar concentration to that generated from FeCl2 pyro-hydrolysis, can be produced from SiO2-assisted CaCl2 pyro-hydrolysis with a higher energy consumption. The CaCl2 pyro-hydrolysis were further optimized with the integration of water recycling and exhaust heat recovery, reducing the water and energy consumption down to −1.1 kg/kg-HCl gas and 21,601 kJ/kg-HCl gas, respectively. The water consumption is lower than that of the FeCl2 process (+ 5.4 kg/kg-HCl gas) and the energy consumption is at a comparable level with the FeCl2 process (20,989 kJ/kg-HCl gas). Furthermore, with the integration of a two-stage CO2 capture unit, the CO2 emission was reduced down to 0.07 kg/kg-HCl gas with a CO2 capture efficiency of 91%. Economic analysis results reveal that the capital and annual operating cost for the CO2 capture coupled CaCl2 pyro-hydrolysis is 12.5 million A$, and 4.1 million A$, respectively. The NPV, IRR, and payback duration of 13 million A$, 12.04%, and 8.6 years, respectively, could be achieved for the optimized CaCl2 pyro-hydrolysis scenario. The sensitive analysis results suggest that the HCl market price and annual operating cost are the most influential parameters and should be especially considered in a future deployment.