Carbon Capture and StorageCCS

Dr. Antonella Glisenti - Dip. Scienze Chimiche - Università degli Studi di PadovaProf. Antonella Glisenti - Dip. Scienze Chimiche - Università degli Studi di Padova

Laurea in Scienza dei Materiali

Materiali Inorganici Funzionali

Bibliography

1. A.A. Olajire, Energie 35 (2010) 26102. Z. Jiang, et al. Phil. Trans. R. Soc. A 368 (2010)33433. J. Davison et al. Proc. IMechE Part A 223 (2009) 2014. M.S. Shafeeyan et al. J. Anal. Appl. Pyrolysis 89 (2010) 1435. H. Arakawa et al. Chem. Rev. 101 (2001) 953

CO2 emissions

Sources of CO2 for sequestration.

Fossil fuel emission levels (pounds/billion BTU of energy input).

Natural gas issues and trends. Energy Information Administration (EIA);1998.

� Involves separating CO2 from the flue gas produced by fuel combustion.

1. Low concentration of CO2 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 CO2 (powerful chemical solvents) 3. High temperature of the flue gas4. High energy required for solvent regeneration

Post-combustion capture

Separation technologies: Chemical absorptionMembrane Technology

Cryogenics

� compatibility with the current energy supply infrastructure � well understood health, safety and environmental practices,

� Capture and storage alone do not stabilize CO2 concentrations� Retrofitting existing plants with capture technology is costly� Energy penalty = Parasitic effects of the capture process on overall plant efficiency and CO2 balance�Lack of experience with underground storage and potential leakage

� Fuel is reacted 1. with oxygen or air, and in some cases steam, 2. The mixture (mainly CO and H2) is treated with steam

� The CO2 is separated and the H2 is used as fuel

Pre-combustion captureThe profit of pre-combustion capture is based on transformation of carbon fuel to carbonless fuel.

carbon

natural gasautothermal …

� CO2 partial pressure is up to 1000 times higher than that in postcombustion capture = physical solvents, which combine less strongly with CO2.� Penality 10%

Rectisol processSelexol processFluor 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 CO2 concentration over 80 %, so only relatively

simple CO2 purification is required

���� Large quantity of oxygen is required (O2 separation)

���� Impurities: SOx NOx Hg

☺☺☺☺ the exhaust stream does not

contain NOx or SOx, but only CO2and water vapour which can be separated by condensation.

Oxyfuel capture - CLC

Chemical-looping combustion is a new technology that applies the idea of combusting the fuel with

O2 instead of with air, but in contrast to oxyfuelcombustion, O2 is brought in contact with the fuel by a

carrier material in a fluidised bed, for example small metal particles

Chemical-looping combustion

Technology options for CO2 separation.

The choice of a suitable

technology depends on

the characteristics of the flue gas stream, which depend mainly

onthe power-plant

technology.

Monoethanolamine solvent scrubbing

Amine Absorption Technologies

1. The flue gas is bubbled through the solvent in a packed absorber column, where the solvent preferentially removes the CO2 from the flue gas. 2. The solvent passes through a regenerator unit, where the absorbed CO2 is stripped from the solvent by counterflowing steam at 100-200 °C.3. Water vapour is condensed, leaving a highly concentrated (over 99%) CO2 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

C2H4OHNH2 + H2O + CO2 = C2H4OHNH3+ + HCO3-

Disadvantages:

1. low carbon dioxide loading capacity (g CO2 absorbed/ g absorbent); 2. high equipment corrosion rate 3. High energy consumption during high temperature absorbent regeneration4. amine degradation by SO2, NO2, HCl and HF and oxygen in fluegas which induces a high absorbent makeup rate

Degradation MEA by CO2 and O2

Other amines

2 mol-amine/mol-CO2 for the formation of stable bicarbonate compounds Mixed amines have been reported to maximize the desirable qualities of the individual amines.

Proposed reaction sequence for the capture of carbon dioxide by

liquidamine-based systems

Diethanolamine (DEA) and Methyl diethanolamine

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 (SO2, NOx, CO2) 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� CO2 is physically absorbed in organic solvents (Henry’s Law), solubility depending on the partial pressure and on the temperature � > CO2 partial pressure and < temperature = > solubility� The solvents are regenerated by either heating or pressure reduction. � The interaction between CO2 and the absorbent is weak decreasing the energy requirement for regeneration.

Solexol

Rectisol

Fluor

Union Carbide Selexol solvent = dimethylether polyethylene glycol [CH3(CH2CH2O)nCH3]; n = 3-9Absorption: 0-5°CDesorption: < P or by stripping with air, inert gas or steam.

Methanol, -35 to -70°C

Propylene carbonate (C4H6O3), a polar solvent with high affinity for CO2.

Physical Adsorption Processes

���� Physisorption���� Chemisorption

Molecular sieves

1. Absorption:Selective removal of CO2 from a gas stream to the adsorbent (zeolite or charcoal),

���� 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)

2. DesorptionRegeneration (desorption)

Activated carbon

Litium compounds

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 CO2

Activated carbon

Basicity of activated carbon:1. resonating π-electrons of carbon aromatic rings that attract protons2. 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 basicgroups (basic nitrogen functionalities)

Heat treatment

Surface oxygen containing groups on carbon and their decomposition by TPD

� 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)

Ammonia treatment

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

� Temperature 600-1000°C (ammonia atmosphere)

Litium compoundsLitium zirconate (Li2ZrO3)

� Reaction is reversible 450-590°C;� Combination of binary alkali carbonate, binary alkali/alkali earth carbonate, ternary alkali carbonate and ternary alkali carbonate/halide

Litium silicate (Li4SiO4)

� Lithium silicate adsorbs CO2 below 720°C and releases CO2 above 720°C;

Li2ZrO3(s) + CO2(g) = Li2CO3(s) + ZrO2(s)

Li4SiO4(s) + CO2(g) = Li2CO3(s) + Li2SiO3(s)

Membrane technology

Cryogenic method (-73.3°C)

Membrane technology

� Polymeric membrane;� Inorganic membrane;� Zeolite membrane;� Silica membrane;

CO2 separation technologies: advantages and disadvantages

Power plantperformance and cost data

� NGCC Natural Gas;� PC polverized carbon;� IGCC Integrated gas;