Cement Manufacturers Association (CMA)

52 capture and storage, where the CO2 is captured at the point of emission and stored in a stable form. Pre-combustion, post-combustion and oxy-fuel combustion represent the three main routes for point source carbon capture 15. For the purposes of our study, we shall restrict the scope of literature to the relatively mature post-combustion carbon capture and storage, where CO2 is captured from the flue gas stream of a combustion process. Amine scrubbing, adsorption by metal organic frameworks 16, micro-algae bio-fixation 17, carbonaceous adsorption 18 and membrane separation 19 are the major techniques involved in carbon capture from flue gas streams. The captured carbon is then recovered, processed and transported into underground geological formations, such as saline aquifers and sedimentary basins, for long-term storage 20. The captured CO2 may also be used for enhanced oil recovery to offset the costs associated with carbon capture and storage 21. Currently, there are no carbon capture and storage projects operational in India 22. While the post-combustion technologies are relatively mature, they have dominant disadvantages of high capital cost and significant energy footprint. However, even if these challenges are subsequently overcome, such processes can at best help us transition to a net-zero future. However, the IPCC has estimated that 5-10 GtCO2- eq has to be removed from the atmosphere each year by the middle of the century 23. To facilitate this scale of atmospheric CO2 capture, non-point source carbon capture technologies have to be scaled up and decoupled from combustion processes, in contrast to point-source technologies, where the combustion process and the carbon capture process are coupled. Direct Air Capture: The Current Inadequacies of Capturing Carbon One such solution is direct air capture (DAC) which removes CO2 from ambient air through solid sorbents and liquid solvents 24. According to the International Energy Agency, there are 15 DAC plants operational worldwide 25. Scaling up DAC technologies by 1.5 GtCO2-eq/year is estimated to require significant sorbent production and energy to the tune of 300 EJ/year by 2100 26. For the liquid solvent DAC process, Carbon Engineering puts the energy requirement at 8.81 GJ natural gas or 5.25 GJ natural gas buttressed with 366 kWh of electricity, putting the process cost between $94 and $232 per tonne of captured CO2 27. Climeworks, a Switzerland based company, reports a levelised cost of carbon capture of $500-$600/tCO2-eq and requires about 2000 kWh of electricity per tonne of captured CO2 28. The capital cost for the Climeworks Hinwil DAC system with a capacity of 900 tCO2yr-1 was about $3-4 million, which is the biggest contributor to the high cost of carbon capture. Global Thermostat, a US based company, uses heat to regenerate the solid sorbent and separate the captured CO2 at temperatures between 100-130°C, bringing their projected costs to $168-232 per tonne of captured CO2 29. Despite the developments in the carbon capture and utilisation domain, the biggest carbon capture plant is Climeworks’ Orca in Iceland, with a capacity to capture 4000 tCo2yr-1 30. It is quite evident that the present state of the DAC technologies are lagging behind the required order of magnitude of CO2 capture to limit global warming to less than 1.5°C. Furthermore, there are significant challenges to the accelerated scaling up of DAC technologies such as high capital cost, amplified sorbent production and high operational energy in the form of heat and/or electricity. These impediments prevent such technologies from being adopted in developing countries with limited access to climate finance. Therefore, in order to deploy giga-ton level carbon capture technologies, it is essential to explore processes of atmospheric CO2 removal which have low capital cost, low energy footprint and low material requirements. In this context atmospheric CO2 capture through photosynthesis presents a promising avenue. However, conventional bio- sequestration routes such as afforestation and reforestation are inadequate, both temporally and spatially, to meet our targets of giga-ton level CO2 removal by the middle of the century. The Azonian Process: Multi-level Carbon Sequestration through Nitrogen Capture Azolla is a freshwater fern that has one of the lowest recorded biomass doubling times, doubling in about 2-5 days under optimal conditions. Azolla prefers partial shade (15-18 Klux), moderate