Decarbonisation Technology - February 2022 Issue

Eide et al ., have recently published a case study that investigates barriers to the implementation of large- scale offshore CO 2 -EOR projects and differences between onshore and offshore CO 2 -EOR emerging technologies, with the objective of suggesting non-technological incentives that may enable implementation (Eide, et al. , 2019). Negative emissions technologies Napp & Mazur in their publication A survey of key technological innovations for the low-carbon economy define ‘direct air capture’ (DAC) as the process where CO 2 is directly removed, physically or chemically, from air, and is subsequently used as raw feedstock material in chemical processes (Napp & Mazur, 2017). DAC systems typically employ solid supported amine-based adsorbents, wherein amine functional groups are bound to the surface of cellulose, porous polymer networks, and porous silica materials. Carbon Engineering, a Canadian start-up, funded in part by Bill Gates, has started to develop commercial models for DAC (Brown, et al. , 2016). The key challenges in DAC are the relatively low concentration of CO 2 in the atmosphere (~0.0004 atm vs ~0.15 atm in coal-fired post- combustion capture) and the high energy required for the regeneration of the absorption chemicals. Some primary examples of such technologies are summarised here:  Bioenergy with CCS The bioenergy process involves direct combustion of biomass in power plants fitted with carbon capture and storage (BECCS). In this process, the plants absorb CO 2 from the atmosphere during growth, and are then harvested, processed, and turned either into pellets or chips, which are then used as fuel in power plants. The main goal of BECCS is to remove CO 2 from the atmosphere while occasionally providing some electricity to the power market. BECCS is currently considered the most feasible negative emissions technology, but it still requires appropriate policy support and integration with general CCS deployment strategies for significant commercial- scale applications.  Bio-char Bio-char is produced by combusting carbon-rich biomass in a low (or no) oxygen atmosphere (called pyrolysis) at temperatures below 700°C. During this process, three products are often generated: a carbon-rich solid i.e. bio-char, a gas (syngas), and a liquid (biofuel) byproduct. Bio-char

distances small volumes CO 2 can be transported by truck or rail. Transport by pipeline is the most economic and is already deployed. The US has an extensive onshore CO 2 pipeline network with a combined length of more than 8,000 km. Large-scale transportation of CO 2 by ship has not been done, but similarities with the shipping of liquefied petroleum gas (LPG) and LNG suggest it can be. Nonetheless, considerable possibilities for innovation remain, in particular for offshore unloading of CO 2 , and spillovers from the general shipping industry, including automation and new propulsion technologies. Long-term storage of CO 2 involves the injection of captured CO 2 into a deep underground geological reservoir of porous rock overlaid by an impermeable layer of rocks, which seals the reservoir and prevents the upward migration and escape of CO 2 into the atmosphere (IEA, 2020). There are several types of reservoir suitable for CO 2 storage, with deep saline formations and depleted oil and gas reservoirs having the largest capacity. Deep saline formations are layers of porous and permeable rocks saturated with salty water (brine), which are widespread in both onshore and offshore sedimentary basins. Depleted oil and gas reservoirs are porous rock formations that have trapped crude oil or gas for millions of years and which can similarly trap injected CO 2 . When CO 2 is injected into a reservoir, it flows through it, filling the pore space. The gas is usually compressed first to increase its density, turning it into a liquid. The reservoir must be at depths greater than 800m to retain the CO 2 in a dense liquid state. The CO 2 is permanently trapped in the reservoir through several mechanisms: structural trapping by the seal, solubility trapping in pore space water, residual trapping in individual or groups of pores, and mineral trapping by reacting with the reservoir rocks to form carbonate minerals. CO 2 storage in rock formations (basalts) that have high concentrations of reactive chemicals is also possible, but is in an early stage of development. The injected CO 2 reacts with the chemical components to form stable minerals. Such formations also exist in places such as India, where there may be limited conventional storage capacity, potentially opening up new opportunities for CCUS. However, further testing and research is required to develop the technology, notably to determine water requirements, which can be considerable.