(326e) 3E (Engineering-Environmental-Economic) Triangle Model for Optimization of High-Gravity Carbonation Process: Establishment of Waste-to-Resource Supply Chain

An integrated portfolio of multi-waste treatment (i.e., steelmaking slag and wastewater) combined with CO₂ capture in the steelmaking industry can be achieved by the high-gravity carbonation (i.e., HiGCarb) process using a rotating packed bed (RPB).  It was noted that a high CO₂ capture efficiency (i.e., >98%) can be achieved by the HiGCarb process with a relatively short reaction time at ambient temperature and pressure.  It also has been proven that the process performance, i.e., rates of metal ion leaching and CO₂ dissolution, can be further promoted by introducing wastewater from the steelmaking industries.  Furthermore, since the reacted product (e.g., carbonated solid wastes) can be used as supplementary cementitious materials, CO₂ emissions from the cement industry can be avoided if a green supply chain between the steelmaking and cement industries is established.  However, several critical issues such as energy consumption, net CO₂ emission reduction, indirect CO₂ emission avoidance, and cost-benefit analysis of the HiGCarb process have still not been comprehensively addressed.  Therefore, the HiGCarb process should be critically assessed through a 3E (engineering, environment, and economy) triangle model.  

Since the complex relationships among different aspects can be easily visualized on a ternary plot among different scenarios, the triangle graphical presentation has been extensively used for evaluating key factors that are related but also complementary.  In this study, the 3E triangle model considers the aspects of life-cycle environmental impact (LCEI) on the X axis, engineering performance (EP) on the Y axis, and life-cycle cost (LCC) on the Z axis.  The objectives of this study were to (1) evaluate the energy consumption and net CO₂ capture amount by the HiGCarb process (engineering aspect); (2) quantify the environmental impacts of the HiGCarb process through LCA from the cradle-to-gate point of view (environmental aspect); (3) estimate the operating costs and revenue gained including carbon credits and product sale profits (economic aspect); and (4) determine the optimal operating modulus according to the results of the comprehensive performance evaluation using the 3E triangle model. 

The results indicated that an increase in CO₂ capture performance should simultaneously reduce the potential costs and environmental impacts, which make integration of the HiGCarb process into the steelmaking industry more economically viable and environmentally friendly.  It was concluded that an integrated approach to the proper treatment of alkaline wastes (i.e., wastewater and steelmaking slags) that permanently fixes CO₂ from the steelmaking industry while producing valuable supplementary cementitious materials from the cement industry can be achieved via the HiGCarb process.