Comparison of life-cycle assessment between bio-catalyzed and promoted potassium carbonate processes and amine-based carbon capture technologies

Abstract

Up until today, the technology used for the capture and production of pure CO2 in post-combustion applications for both use and sequestration relies primarily on the use of chemical amine solvents such as monoethanolamine (MEA). However, these solvents require significant amounts of valuable, high-grade process heat for solvent regeneration and suffer from substantial operational and environmental issues including degradation, toxic aerosol emissions, sensitivity to flue gas contaminants, and corrosivity. CO2 Solutions Inc (CSI) recently developed and deployed a new technology to solve these challenges by employing a non-toxic low-cost, stable salt solution as an absorption solution and the carbonic anhydrase enzyme as a catalyst for carbon management. The result is both fast CO2 absorption kinetics and significantly reduced energy costs by allowing to use low-grade heat to drive the solution regeneration. This study aims to analyze and compare the environmental profile of capture processes such as CSI, MEA and UNO MK3 (a precipitating potassium carbonate separation process). The context of the study is CO2 capture from the flue gas stream of a 550 MW coal-fired power station in the midwestern USA. To fulfill the objective, we performed an attributional cradle-to-gate LCA comparing the three systems. This study was conducted according to the requirements of ISO 14040 & 14044 and reviewed by an independent panel which concluded that “The LCA requirements of ISO 14040 and ISO 14044 have been answered in the best possible manner.” Data were mainly based on process simulation of the three technologies. The impact assessment was carried out with the Impact 2002+ method. This method considers four indicators at endpoint level (Climate change, Human health, Ecosystem quality and Resources) and sixteen indicators at midpoint level (for instance Aquatic Acidification or Ozone formation). Results show that the CSI carbon capture unit has significantly lower potential impacts than the MEA and UNO MK3 units. The CSI system presents lower scores than the MEA and the UNO MK3 systems for all midpoint and endpoint indicators. The operation stage, and more especially its energy consumption, is the main contributor to the environmental profile of all three systems. The CSI system differs radically from the MEA and UNO MK3 systems as it can use hot water instead of steam for its regeneration step. Hot water is a waste from the power plant, whereas steam consumption reduces the production of electricity at the power plant, which needs to be compensated elsewhere. In this study, it is considered that these losses of electricity production will affect the regional market in which the power plant is located, and therefore the lost electricity is produced by an average electricity grid mix coming from this regional market. Other inputs do not contribute significantly to the environmental profile of the systems at endpoint level. Among them, chemical inputs are the top contributors. However, the midpoint category where CSI technology differentiates itself the most from other technologies is when comparing the MEA Respiratory Organics score, which is 3.5 times higher than CSI. The several sensitivity analysis conducted typically do not affect the conclusion.

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