A Techno-economic Assessment for the Integration of a Sustainable Regeneration Cycle in Carbon Capture Processes.

Abstract

Carbon capture by chemical absorption is one of the recognized and viable options for mitigating global warming and climate change. In these processes, the acid gas is typically contacted with a solvent in an absorber before feeding the spent solution to a regenerator for recovery, with the latter step being energy intensive. One method calls for the use of alkaline solutions such as sodium hydroxide to perform the capture step. In it, NaOH reacts with CO2 and produces sodium carbonates. A large amount of energy is typically required to regenerate these solutions. Another method for its regeneration is by reacting the sodium carbonate solution with calcium hydroxide. This causticization step is a widely employed operation in the production of lime and results in an NaOH solution along with precipitated calcium carbonate. The lime production cycle however consists of three main subprocesses, namely, calcination, causticization, and slaking. The former is an energy-intensive step, while the latter generates heat. Recently, calciners that rely on direct solar irradiation are being investigated and results show that these solar kilns can reach the very high temperatures required to conduct the calcination reaction. Accordingly, the current work proposes the integration of a solar-powered lime cycle in a carbon capture loop to render the solvent regeneration more sustainable. In addition, the present approach considers harnessing the energy released by the slaker to produce green electricity through a steam cycle. To assess the feasibility of this approach, the various operations were simulated using Aspen Plus® and an economic analysis was conducted. In addition, and to accurately simulate the causticizer, the kinetics of the reaction were developed from published experimental measurements in the open literature. Since all the required technologies are currently available, the process was found technically feasible, albeit at a low return on investment over a 10-year period.