Carbon sequestration in the cement industry

Transcription

1 Carbon sequestration in the cement industry Alan Maries Mineral Carbonation Workshop 28 November 2012

2 30 years ago... Research at Redland in the early 1980s improving manufacturing process for concrete roof tiles target of handleable ( biscuit ) strength within 2 minutes (normally several hours) Achieved by accelerated carbonation uptake of CO 2 gas 10-15% w/w cement long-term strength and durability Cost-effectiveness the only driver at that time CO 2 not yet on the radar!

3 ... today Portland cement annual global manufacture exceeds 3,000 Mtonnes growing steadily at ~ 4% a year Concrete contains ~ 10% w/w cement ~ 10 km 3 (!) produced world-wide volume 10x greater than all other man-made materials of great strategic importance embodied carbon low w.r.t. steel etc.

4 Cement manufacture Environmental impact > 2,500 Mtonnes CO 2 released every year ~ 55% from de-carbonation of limestone, ~ 45% from process (mainly heating) ~ 6% man-made emissions now 4 th on the global emissions black-list, after electricity generation, vehicle exhausts and aviation

5 Environmental mitigation Wastes can be used as fuel only to a certain extent fossil fuels: high calorific value, purity, available in large enough quantities CCS feasible but not currently viable? considerable technical obstacles would double the present production cost Cement can be diluted in concrete with supplementary binders ground slag, fly ash carbon neutral only at present limits to cement substitution

6 Low-carbon cements Modified Portland cement (Ca alumino-silicates) sulfo-aluminates, geopolymer, activated pozzolans, Lafarge Aether,etc. Alternative chemistries Ca aluminates, phosphates Calera: carbonation of alkaline brine/seawater (?) Mg hydroxy-carbonate (Novacem carbon negative ) BUT raw materials not as widely distributed as limestone & clay able to supply only niche or local markets consistent performance? (ASTM C9, BS12 ~ 1904) robust and durable? (Portland cement ~ 150 years experience)

7 Carbon sequestration Natural carbonation (set concrete) CO % v/v in air very slow process, extent unquantified lowers ph, de-passivates steel reinforcement Accelerated Carbonation (fresh concrete) 100% CO 2 (waste) at atmospheric pressure precast concrete ~ 1 / 3 rd total (1,000 Mtonnes cement globally) CO 2 uptake 10% w/w cement realistic potential capture for ALL global precast ~100 million tonnes of CO 2 in perspective ~ 1 / 5 th UK total emissions

8 Accelerated Carbonation Commercial opportunities High aspect ratio preferable tiles, slabs, pipes steel reinforcement not de-passivated Carbon Sense Solutions (Nova Scotia) lightweight concrete blocks, pavers ( CarbonCure ) carbon intensity 17%, energy 38%, cement 10%, strength 15% Non-precast applications set-on-demand concrete geo-engineering

9 Research needs Scale-up engineering challenge cement & concrete markets very mature and very large bench-top industrial process typically 9-10 orders of magnitude Accelerated Carbonation understanding the process better complex physics and chemistry reactions in gas/liquid/solid phases sequential, step-wise process

10 gas phase pore fluid CO 2 C 3 S 6 9 solid phases 7 CH, C-S-H 8 C 3 A S-H CaCO 3

11 Sequential carbonation model Overall speed governed by slowest, rate-limiting step(s) [3] SOLVATION: high internal surface area beneficial (particle size distribution) [4] HYDRATION: homogeneous catalysis (4 classes) physical accelerators results applicable to any mineral sequestration process Activated low-energy self-pulverising cement -dicalcium silicate not hydraulically active CO 2 40% v/v at cement kiln pre-calciner use to activate precast concrete