Experimental observations of CO2-water-basaltic glass interaction in a large column reactor experiment at 50 °C

Publisher's version (útgefin grein).Mineralization of water dissolved carbon dioxide injected into basaltic rocks occurs within two years in field-scale settings. Here we present the results from a CO2-water-basaltic glass laboratory experiment conducted at 50 °C and 80 bar pressure in a Ti high-pressure column flow reactor. We explore the possible sequence of saturation with Fe-Mg-Ca-carbonate minerals versus Fe-Mg-clay and Ca-zeolite saturation states, which all compete for divalent cations and pore space during injection of CO2 into basaltic rocks. Pure water (initially with atmospheric CO2) – basaltic glass reactions resulted in high pH (9–10) water saturated with respect to Mg-Fe-clays (saponites), Ca-zeolites, and Ca-carbonate. As CO2-charged water (˜20 mM) entered the column and mixed with the high pH water, all the Fe-Mg-Ca-carbonates became temporarily supersaturated along with clays and zeolites. Injected waters with dissolved CO2 reached carbonate mineral saturation within 12 h of fluid-rock interaction. Once the pH of the outflow water stabilized below 6, siderite was the only thermodynamically stable carbonate throughout the injection period, although no physical evidence of its precipitation was found. When CO2 injection stopped while continuing to inject pure water, pH rose rapidly in the outflow and all carbonates became undersaturated, whereas zeolites became more saturated and Mg-Fe-saponites supersaturated. Resuming CO2 injection lowered the pH from >8 to about 6, resulting in an undersaturation of the clays and Na-zeolites. These results along with geochemical modelling underscore the importance of initial pCO2 and pH values to obtain a balance between the formation of carbonates versus clays and zeolites. Moreover, modelling indicates that pauses in CO2 injection while still injecting water can result in enhanced large molar volume Ca-Na-zeolite and Mg-Fe-clay formation that consumes pore space within the rocks.This publication has been produced with support from the European Commission through the projects CarbFix (EC Project 283148), CO2-React (EC Project 317235), and S4CE (EC Project 764810). The authors would like to thank editor Charles Jenkins for handling the manuscript and to the anonymous reviewers for their constructive comments that helped improve the manuscript. Special thanks to Giulia Alessandrini for her indispensable assistance in running the experiment, Sydney Gunnarson for material preparation, and Þorsteinn Jónsson for preparing, setting up, and taking apart the column. We would also like to acknowledge Rebecca Neely and Tobias Linke for their help in the laboratory in addition to Eric Oelkers, Peter Rendel, and the CarbFix group for their support.Peer Reviewe

Design of a scaling reduction system for geothermal applications

The aim of the EU 2020 GeoSmart project relies on the demonstration of innovative solutions to improve the flexibility and the efficiency of geothermal heat and power systems. This specific study focuses on issues related to silica scaling and its deposition on the reinjection wells. A limiting constraint for geothermal plants to fully utilize the thermal energy form well fluids is in fact the need to reinject geothermal brine at a high enough temperature to prevent thermodynamic fouling by silica scale deposition. GeoSmart aims to develop a solution based on retention system technology to control and reduce the silica scale formation before re-injection. Lowering reinjection temperature would strongly increase plant efficiency by providing extra useful heat. Based on silica scaling numerical simulation, the effects of parameters like pH, temperature and brine composition on silica polymerization and scaling deposition rates, the design and optimization of the retention system has been developed. The design aims to promote polymerization phenomena inside the tank so that scaling is consequently inhibited in the reinjection well pipes. Chemical additives and specific coatings have also been evaluated to guarantee the optimal required conditions. The case study is based on real-data referred to operational conditions and brine composition of the Zorlu Kizildere plant in Turkey. The economic and environmental impact of the retention system has been evaluated with positive outcomes. The in-site test and validation at industrial level of the above mentioned technology will be provided during the next activities of the GeoSmart projec