1 Engineering Capability Opportunities for Negative Emission Technologies London, Wednesday 13 th March 2013 Professor Richard Darton FREng Co-Director, Oxford Geoengineering Programme Department of Engineering Science University of Oxford

2 Human activity-related CO 2 emissions: around 80 million tpd or 1 million tons every 18 minutes. 15 million tons of CO 2 are photosynthesised every 18 minutes CO 2 in the atmosphere: Technology to remove it

3 Removing CO 2 from air is proven technology, eg at the front end of cryogenic air separation units Temperature swing adsorption is often used Energy is required, mostly to regenerate adsorbent – this is the main opex Air Products CO 2 in the atmosphere: Technology to remove it

4 Capturing CO 2 from air requires much larger equipment (~100x), because larger gas volumes must be treated Carbon dioxide removal Flue gas treating or air capture? Flue gas Air

5 How much equipment would be needed ? At atmospheric conditions, velocities in process equipment are ~2.5 m/s. Capturing 1 million t/y CO 2 needs 18 thousand m 2 cross-sectional area.  230 contactors of 10m diameter, plus associated plant. To capture the 250 Mt CO 2 produced by UK electricity generation takes such contactors – about one for every 1000 people. Capturing this CO 2 before the chimney needs one 10m contactor for every people. (Pre- combustion or oxyfuel capture would be better.) Carbon dioxide removal Flue gas treating or air capture?

6 Capturing CO 2 from air takes more than 2.5 times as much minimum reversible work Carbon dioxide removal Flue gas treating or air capture? Flue gas Air

7 Efficiency of air capture process = 0.136/2.5 ~ 5.4% kWh/kgCO2: Reversible work of separation = 0.136; Thermal energy requirement = 2.5 (estimate) Why are separation processes (apparently) so inefficient? We need work of separation. Using heat to make work, we need at least (T H -T C )/T H ~ twice as much kWh, or more… We cannot simulate Reversibility in practice Negative Emission Technologies: Process engineering aspects

8 Reversibility means no diffusion of any kind: No friction (diffusion of momentum in fluids ) No diffusion of heat No diffusion of matter All temperature and concentration differences are negligible: all heat exchange and mass exchange equipment is infinitely large. The processes work at zero rate. We have to design equipment of finite size in practice, and this consumes more energy than a reversible process. Streams and utilities are only available at fixed temperatures, so further reversibility losses are unavoidable. Consider… Negative Emission Technologies: Process engineering aspects

9 A process in which some (cold) streams need heating and some (hot) need cooling. Plot composite heating and cooling curves: Pinch Minimum ΔT Minimum Heating, 120 Minimum Cooling, 70 Negative Emission Technologies: Process engineering aspects

10 In the next two decades Drivers for decarbonisation strengthen Response: CCS projects developed Competition for resource ($, manpower, storage, permits) At an investment rate* $30 bn/y, in 6 years we could be sequestering 1 bn tpy from flue gas. (basis APS: $180/tCO 2 /y) Direct Air Capture does not compete. (basis APS: $2200/tCO 2 /y) But pressure mounts for alternatives to CCS, including lower cost and more environmentally friendly NETs * Basis 10 times recent investment rate in LNG plants. CO 2 removal scenarios What is going to happen? Chen et al. Progress in Energy and Combustion science MW

11 Conclusions To be useful, any NETs process must be able to treat very large volumes of air. Flue Gas Capture and Direct Air Capture can both be engineered, but FGC will out-compete DAC for resource. We need processes that do not rely on “reservoir storage” of CO 2. We MUST learn more about NETs – what they can offer us We MUST use less fossil fuel