Carbon dioxide sequestration using steelmaking slags as raw material

Transcription

1 Carbon dioxide sequestration using steelmaking s as raw material Lic. Sc. (Tech.) Sanni Eloneva Research group of energy engineering and environmental protection, Department of Energy Technology, Aalto University School of Science and Technology Nordic Recycling Day V,

2 Means for reducing emissions Reduce utilization of fossil fuels Replace fossil fuels by nuclear power or renewable energy Switch from coal to natural gas Reduce energy consumption Increase energy efficiency Reforestation Carbon dioxide capture and storage (CCS) World total primary energy supply (2006) 6.2 % 20.5 % 2.2 % 10.1 % 0.6 % 34.3 % 26.0 % IEA, Key world energy statistics. Coal/Peat Oil Gas Nuclear Hydro Combustible renewables and waste Others 2/14

3 Capture and Storage (CCS) Capture Schematic diagram of possible CCS systems Concentrated stream From a large point source & Transport Ship or pipeline & Storage Geological formations Ocean Mineral carbonation SRCCS Figure TS-1 IPCC Special Report on Carbon Dioxide Capture and Storage, ( oxide_graphics.htm) 3/14

4 Mineral carbonation for emissions reduction (Mg,Ca) x Si y O x+2y+z H 2z (s)+x (g) x(mg,ca)co 3 (s)+ysio 2 (s)+zh 2 O Silicate mineral: rock, industrial waste material Carbonation process Carbonate, silica, water, etc. Energy, chemicals 4/14

5 Steelmaking carbonation Raw materials World s annual steelmaking generation: Mt sequestration potential: Mt Steel plant Steel /a Other Ca/Mg-containing by products/waste materials suitable for sequestration by carbonation: Waste cement Ashes Steelmaking Carbonation plant -lean gas Finland: Annual emissions: kt kt/a steelmaking s Carbonated material Sequestration potential: 700 kt /a Other by products: kt /a 5/14

6 Direct aqueous carbonation of steelmaking s Imitates and tries to enhance the slow natural carbonation of ultramafic rocks H 2 O+ Steelmaking Carbonic acid extracts calcium from the (g)+h 2 O(l) H + (aq)+hco 3- (aq) CaSiO 3 (s)+2 H + (aq) Ca 2+ (aq)+sio 2 (s)+ H 2 O(l) Dissolved calcium reacts with bicarbonate ions forming solid carbonate Ca 2+ (aq)+2hco 3- (aq) CaCO 3 (s)+ 2 H + (aq) Elevated pressures and temperatures The maximum carbonation degree of steel : Carbonation reactor Carbonated material 74% of the Ca content (30 min, 19 bar pressure, 100 C, <38 µm) by Huijgen et al.(2005) Huijgen W. J. J., Witkamp G.-J., Comans R. J., Mineral CO2 Sequestration by Steel Slag Carbonation. Environ. Sci. Technol., 39, /14

7 Valuable end product? Limestone (=impure CaCO 3 ) If the calcium is separated from the material prior carbonation, the end product should be calcium carbonate (CaCO 3 ) CaCO 3 is used in various applications Cement manufacture, agricultural use, lime manufacture... Billions of tons mined annually ~1 Gt/a in U.S. alone 1.5 Mt mined annually in Finland Pure precipitated calcium carbonate (PCC) >100 /t Filler and coating material in paper ~13 Mt/a in the world Manufactured from the limestone emissions of 0.23 t/t CaCO 3 Fuel Lime kiln Slaker: CaO+H 2 O Carbonation reactor CaCO 3 Conventional PCC production process 7/14

8 Advantages of producing PCC from s Raw materials Reduced emissions No burning of limestone Steel plant Steel New utilization option for s PCC times more valuable than Savings in natural resources No limestone needed Steelmaking Carbonation plant Steelmaking suitable for industrial use? -lean gas Paper mill CaCO 3 8/14

9 Acetic acid process route and steelmaking s 440 kg reduction per ton of CaCO 3 produced Additional 220 kg per every conventionally produced PCC replaced However, indirect emissions from the production of the chemicals used in the process, would most likely exceed these reductions The costs of the chemical consumption: > 1000 /t of CaCO 3 produced Acetic acid solution NaOH Steelmaking Separation of Calcium Carbonation Residual Calcium acetate solution Sodium acetate Ca(CH 3 COO) 2 +H 2 O+ 2CH 3 COOH+CaCO 3 CaCO 3 9/14

10 Search for the better solvent: Key issue for developing a feasible process for producing pure calcium carbonate from steelmaking s: To find an effective Ca-selective solvent that at the same time can be fully recovered and reused Steelmaking This means that: 1. Solvent should dissolve calcium selectively from the 2. Calcium carbonate should precipitate from the formed solution without need for additives Solvent Calcium extraction step Residual Calcium containing solution Precipitation step CaCO 3 10/14

11 Step 1: Solvent selection Solvent selection using various relatively common acids and salts, as well as few other solvents Significant amount of the s Ca (>50 %) dissolved only in various acids and ammonium salts All the ammonium salt solutions dissolved Ca selectively from the Also weak concentrations of acetic acid and nitric acid were selective for Ca Acids not suitable for precipitation of calcium carbonate Ammonium salts seem to be the most promising solvents from the tested ones Steelmaking Solvent Calcium extraction step Residual Calcium containing solution Precipitation step CaCO 3 11/14

12 Step 2: Precipitation experiments Carbonation of Ca containing ammonium salt solution Precipitates consisted of calcium carbonate as rhombohedral calcite ~99.8 % CaCO 3 Ca conversion from the solution into the precipitate was ~ % Solution can be reused Solvent Steelmaking Calcium extraction step Precipitation step Residual Calcium containing solution CaCO 3 SEM pictures of the precipitates produced from the solution of ammonium salt and steel converter 12/14

13 Summary Direct aqueous carbonation of steelmaking s At elevated pressures and temperatures Simpler method But endproduct is carbonated material Pure CaCO 3 can be produced from the steel converter by using an aqueous solution of ammonium salt as a solvent At low temperatures and pressures Without additional chemicals i.e. solvent can be recycled Clearly negative emissions The ammonium salt based process route has economical potential Unfortunately seems to be suitable only for steel converter, desulphurization and AOD process 13/14

14 Thank you for your attention! Contact information: The Graduate School for Energy Science and Technology (EST) 14/14