Laurea in Scienza dei Materiali Materiali Inorganici Funzionali Carbon Capture and Storage CCS Prof. Dr. Antonella Glisenti -- Dip. Scienze Chimiche -- Università degli Studi di di Padova
Bibliography 1. A.A. Olajire, Energie 35 (2010) 2610 2. Z. Jiang, et al. Phil. Trans. R. Soc. A 368 (2010)3343 3. J. Davison et al. Proc. IMechE Part A 223 (2009) 201 4. M.S. Shafeeyan et al. J. Anal. Appl. Pyrolysis 89 (2010) 143 5. H. Arakawa et al. Chem. Rev. 101 (2001) 953
CO 2 emissions Fossil fuel emission levels (pounds/billion BTU of energy input). Natural gas issues and trends. Energy Information Administration (EIA); 1998. Sources of CO 2 for sequestration.
Technology options for CO 2 separation. The choice of a suitable technology depends on the characteristi cs of the flue gas stream, which depend mainly on the powerplant technology.
CO 2 capture.
Post-combustion capture Involves separating CO 2 from the flue gas produced by fuel combustion. 1. Low concentration of CO 2 in power-plant flue gas (typically 4-14%) = large volume of gas has to be handled = large equipment sizes and high capital costs. 2. Low partial pressure of the CO 2 (powerful chemical solvents) 3. High temperature of the flue gas 4. High energy required for solvent regeneration compatibility with the current energy supply infrastructure well understood health, safety and environmental practices, Capture and storage alone do not stabilize CO 2 concentrations Retrofitting existing plants with capture technology is costly Energy penalty = Parasitic effects of the capture process on overall plant efficiency and CO 2 balance Lack of experience with underground storage and potential leakage Separation technologies: Chemical absorption Membrane Technology Cryogenics
Pre-combustion capture The profit of pre-combustion capture is based on transformation of carbon fuel to carbonless fuel. Fuel is reacted 1. with oxygen or air, and in some cases steam, 2. The mixture (mainly CO and H 2 ) is treated with steam The CO 2 is separated and the H 2 is used as fuel carbon natural gas autothermal CO 2 partial pressure is up to 1000 times higher than that in postcombustion capture = physical solvents, which combine less strongly with CO 2. Penality 10% Rectisol process Selexol process Fluor process
Oxyfuel capture Combustion carried out fuelling a power plant with an oxygen-enriched gas mix instead of air. Most of the nitrogen in the input air is removed in an air reactor, resulting in 95% oxygen. The flue gas has a CO 2 concentration over 80 %, so only relatively simple CO 2 purification is required Large quantity of oxygen is required (O 2 separation) Impurities: SOx NOx Hg
Oxyfuel capture - CLC Chemical-looping combustion is a new technology that applies the idea of combusting the fuel with O 2 instead of with air, but in contrast to oxyfuel combustion, O 2 is brought in contact with the fuel by a carrier material in a fluidised bed, for example small metal particles the exhaust stream does not contain NOx or SOx, but only CO 2 and water vapour which can be separated by condensation. Chemical-looping combustion
Block diagrams for post, pre oxyfuel combustions
CO 2 separation State of the Art
Amine Absorption Technologies Monoethanolamine solvent scrubbing C 2 H 4 OHNH 2 + H 2 O + CO 2 = C 2 H 4 OHNH 3+ + HCO 3-1. The flue gas is bubbled through the solvent in a packed absorber column, where the solvent preferentially removes the CO 2 from the flue gas. 2. The solvent passes through a regenerator unit, where the absorbed CO 2 is stripped from the solvent by counterflowing steam at 100-200 C. 3. Water vapour is condensed, leaving a highly concentrated (over 99%) CO 2 stream, which may be compressed for commercial utilization or storage. 4. The lean solvent is cooled to 40-65 C and is recycled into the absorption column
Disadvantages: 1. low carbon dioxide loading capacity (g CO 2 absorbed/ g absorbent); 2. high equipment corrosion rate 3. High energy consumption during high temperature absorbent regeneration 4. amine degradation by SO 2, NO 2, HCl and HF and oxygen in flue gas which induces a high absorbent makeup rate Degradation MEA by CO 2 and O 2
Other amines Diethanolamine (DEA) and Methyl diethanolamine Proposed reaction sequence for the capture of carbon dioxide by liquid amine-based systems 2 mol-amine/mol-co 2 for the formation of stable bicarbonate compounds Mixed amines have been reported to maximize the desirable qualities of the individual amines. Sterically hindered amines have an amino group attached to a bulky alkyl group, The rotation of the bulky alkyl group around the aminocarbamate group is restricted in sterically hindered amines; and these result in considerably low stability of the carbamate compound. The carbamate compound is thus likely to react with water and forms free amine and bicarbonate ions
Aqua Ammonia Process - AAP To capture all three major acid gases (SO 2, NO x, CO 2 ) plus HCl and HF, which may co-exist in the flue gas The major by-products from the aqueous ammonia process include ammonium bicarbonate, ammonium nitrate and ammonium sulfate (fertilizers). T > 140 C RT, 1 atm irreversible Forward reactions; dominant at RT Backward reactions: 38-60 C
Physical Absorption Processes CO 2 is physically absorbed in organic solvents (Henry s Law), solubility depending on the partial pressure and on the temperature > CO 2 partial pressure and < temperature = > solubility The solvents are regenerated by either heating or pressure reduction. The interaction between CO 2 and the absorbent is weak decreasing the energy requirement for regeneration. Solexol Union Carbide Selexol solvent = dimethylether polyethylene glycol [CH 3 (CH 2 CH 2 O)nCH 3 ]; n = 3-9 Absorption: 0-5 C Desorption: < P or by stripping with air, inert gas or steam. Rectisol Methanol, -35 to -70 C Fluor Propylene carbonate (C 4 H 6 O 3 ), a polar solvent with high affinity for CO 2.
Solexol Rectisol Fluor Low heat rise: no chemical reactions Gas comes out dry: high affinity of Solexol with water Initial plant and operating costs minimal Regeneration by air stripping; no re-boiler s heat Process can be operated at low pressure Carbon steel Solvent has high affinity to heavy hydrocarons (HC loss) Process more efficient at high pressures Solvent miscible with water: no loss High thermal and chemical stability Non corrosive; no degradation problems; C steel Regeneration by flashing at low pressure no re-boiler s heat Solvent capable of absorbing metallic traces Complex scheme and need to refrigerate: operating cost High CO 2 solubility, high yield Dry gas obtained; no water make up No heat for solvent regeneration Solvent expensive Solvent has high affinity to heavy hydrocarons (HC loss)
1. Adsorption: Physical Adsorption Processes Selective removal of CO 2 from a gas stream to the adsorbent (zeolite or charcoal), Physisorption Chemisorption 2. Desorption Regeneration (desorption) Pressure reduction (Pressure-Swing Adsorption or PSA), Temperature increment (Temperature Swing Adsorption, or TSA) Electric current (Electrical Swing Adsorption, or ESA) Washing Process hybrids (PTSA) Molecular sieves Activated carbon Litium compounds Oxides
Molecular Sieves Physisorption Chemisorption High surface area inorganic supports with basic organic groups (amines) Interaction = surface ammonium carbamates (anhydrous conditions) and ammonium bicarbonate and carbonates (in presence of water) Surface reaction of amine groups with CO 2
Activated carbon Basicity of activated carbon: 1. resonating π-electrons of carbon aromatic rings that attract protons 2. basic surface functionalities (e.g., nitrogen containing groups) capable of binding with protons Heat treatment Ammonia treatment to remove or neutralize acidic groups, to replace acidic groups with basic groups (basic nitrogen functionalities)
Heat treatment Temperature 1000 C (inert atmosphere) The basicity arises from the oxygen-free Lewis basic sites on the graphene layers and from the few remaining basic oxygen containing groups (pyrone and chromene) Surface oxygen containing groups on carbon and their decomposition by TPD
Ammonia treatment Temperature 600-1000 C (ammonia atmosphere) Types of nitrogen surface functional groups: (a) pyrrole, (b) primary amine, (c) secondary amine, (d) pyridine, (e) imine, (f) tertiary amine, (g) nitro, (h) nitroso, (i) amide, (j) pyridone, (k) pyridine-n-oxide, (l) quaternary nitrogen
Litium compounds Litium zirconate (Li 2 ZrO 3 ) Reaction is reversible 450-590 C; Combination of binary alkali carbonate, binary alkali/alkali earth carbonate, ternary alkali carbonate and ternary alkali carbonate/halide Li 2 ZrO 3(s) + CO 2(g) = Li 2 CO 3(s) + ZrO 2(s) Litium silicate (Li 4 SiO 4 ) Lithium silicate adsorbs CO 2 below 720 C and releases CO 2 above 720 C; Li 4 SiO 4(s) + CO 2(g) = Li 2 CO 3(s) + Li 2 SiO 3(s)
Membrane technology Polymeric membrane; Inorganic membrane; Zeolite membrane; Silica membrane; Membrane technology Inorganic Polymeric
Polymeric membranes
CO 2 separation technologies: advantages and disadvantages
NGCC Natural Gas; PC polverized carbon; IGCC Integrated gas; Power plant performance and cost data Post-combustion MEA