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

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.