Life cycle assessment of CO2 sequestration in magnesium silicate rock – A comparative study

This paper addresses the energy and environmental implications of sequestrating CO2 from a coal power plant using magnesium silicate rock. An accounting type life cycle assessment (LCA) of the mineralization method under development at Åbo Akademi University (ÅAU), Finland, is presented and the results are compared with the process developed at the National Energy Technology Laboratory (NETL), formerly Albany Research Council (ARC) in the US. The ÅAU process is a multi-staged route where CO2 is sequestered via a process that first produces magnesium hydroxide, Mg(OH)2 from Mg silicate. The Mg(OH)2 produced is later reacted with CO2 in a high temperature gas/solid pressurized fluidized bed (FB) reactor, forming pure, stable and environmentally benign MgCO3 product. This study addresses the following important issues; (a) the material and energy requirements of sequestering 1 ton of CO2 (t-CO2) in mineral silicate, (b) the overall environmental burdens associated with CO2 sequestration using serpentinite mineral, (c) the priorities and opportunities for reduction of energy requirements and environmental impacts associated with mineralizing CO2, and (d) comparison of LCA results of the ÅAU mineralization process route with that of the mineralization process developed by NETL. Exergy calculations show that with heat recovery mineralizing 1 t-CO2 using the ÅAU process requires 3.6 GJ/t-CO2 while that of the NETL needs 3.4 GJ/t-CO2. Applying results of exergy analysis in the life cycle inventory (LCI) models of the ÅAU and the NETL processes leads to 517 kg CO2e and 683 kg CO2e of greenhouse gas emissions (in CO2 equivalents) respectively, for every ton of CO2 mineralized in serpentinite.

► Life cycle GHG emissions of ÅAU and NETL mineralization processes were modeled and compared.
► Using exergy analysis, we evaluated the GHG emissions burden of fixing 1 t-CO2 in Mg–silicates.
► For 1 t-CO2 stored, the ÅAU and NETL processes emit 517 kg CO2e and 683 kg CO2e respectively.
► Process heat requirement was identified as the most significant contributor of GHG emissions.