Decarbonisation Technology - May 2023 Issue

transforms CO 2 into aqueous carbonate. By adding calcium ions, derived from materials such as construction and demolition waste, to the capture solution, solid precipitates of CaCO 3 are formed. These synthetic limestones can be used to produce aggregates with high mechanical strength, making them suitable for construction. At end of life, they can re-enter the mineralisation-based CCUS process as calcium-rich feedstock. Therefore, the process is completely circular and a valuable way to endlessly store carbon. Case study: manufacture of carbon-negative synthetic limestone aggregate A key example of the benefits of CCUS for aggregate production is offered by Blue Planet, whose patented geomimetic process can permanently sequester large volumes of CO 2 within construction materials (see Figure 4 ). When looking for a technology partner to commercialise its novel mineralisation process, Blue Planet partnered with Sulzer Chemtech. The collaboration involves the use of Sulzer Chemtech’s separation technologies to support the development of an efficient and effective carbon capture unit within San Francisco Bay Aggregates’ first pilot-scale plant in Pittsburg, California, USA. This can effectively treat flue gas streams of variable CO 2 content. The captured CO 2 from emissions generated by heavy industries does not need to be purified or liquified before being combined in solution with metal ions obtained from concrete or other industrial wastes. The process delivers carbonate minerals that are worked up into synthetic limestone aggregates. These can then be combined with cement to produce high-quality, sustainable concrete. The process can store up to 440 kg (970 lb) of CO 2 per tonne of aggregate produced. As a result, it is possible to curb the environmental footprint of cement, producing carbon-negative concrete. In particular, by including Blue Planet’s resulting coarse and fine aggregates within a typical concrete mix formulation, it is possible to store 508 kg (1,120 lb) of CO 2 in less than a cubic metre of concrete, shifting the embodied emissions from more than 272 kg (600 lb) of CO 2 to -224 kg (-494 lb).

Figure 4 Blue Planet’s patented geomimetic process can permanently sequester large volumes of CO 2 within construction materials The energy load of Blue Planet’s solution, less than 0.1 MWh per tonne of CO 2 eq as projected by the company’s lifecycle assessment, is well below conventional CCS estimations. Therefore, users can reduce the operational costs and environmental footprint

of such activities, driving effective decarbonisation strategies forward.

MellapakCC, AYPlusDC and MellaTech are trademarks of Sulzer Chemtech. geomimetic is a trademark of Blue Planet.


Cecilia Mondelli

Brent Konstantz


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