1 Removal, Recovery, and Disposal of Carbon Dioxide 朱 信 Hsin Chu Professor Dept. of Environmental Engineering National Cheng Kung University

2 1. Introduction  Three potential control points 1)The atmosphere 2)The surface waters of the oceans 3)The stacks: high CO 2 conc.  Next slide (Table 5.1) Next slide (Table 5.1) Practical energy required >> 10 × (the thermodynamic min.)  Removal:non fossil fuel energy source – nuclear or solar The only current feasible method: grow biomass – plants or algae Disposal (storge) Reuse Disposal (storge) Reuse

4 2. Removal and Recovery of CO 2 From Fossil-Fuel Combustion  Sources: The electrical power generation sector: large and relatively easy to remove CO 2 The industrial and domestic thermal generation sector: small per unit The transportation power sector: tiny per unit  Next slide (Table 5.2) Next slide (Table 5.2) methods for a coal-fired power plant

6 2.1 Absorption/Stripping  Solvents (liquid) Alkanolamines (monoethanolamine (MEA)): the lowest energy required Alcohols (methanol) Glycols  Absorption: lower temp Stripping: heated by steam 2.2 Adsorption/Stripping  Sorbents (solid) charcoal Molecular sieves  Adsorption: higher pressure Stripping: lower pressure

7 2.3 Refrigeration (Cryogenic) Gases are compressed → cooled down to a liquid or a solid 2.4 Membrane Separation  Membrane (different pore sizes) Polymers Metals Rubber composites  Gas absorption membrane composites Absorbing liquid on one side of a porous membrane: providing a large surface-contacting area

8 2.5 Seawater Absorption  Does not work: solubility!  Alternative: pumping flue gas deep into the ocean where the partial pressure of the dissolving CO 2 is equal to the pressure of the ocean at that depth. 2.6 Oxygen/Coal-Fired Power Plant  Use pure O 2 for combustion  Pure CO 2 in the flue gas → liquefying → sequestering or reusing  Next slide (Fig. 5.1) Next slide (Fig. 5.1) Oxygen coal-fired plant flow chart

10 3. Disposal of CO 2 1)Ocean disposal 2)Depleted gas wells 3)Active oil wells (enhanced oil recovery) and depleted oil wells 4)Coal beds and mines 5)Salt domes 6)Aquifers 7)Natural minerals

Ocean Disposal  The upper layer of the ocean is in equilibrium with the atmosphere CO 2. Thermocline: about 1000ft below sea surface, at which point the ocean temperature abruptly decreases. Below the thermocline: the concentration of dissolved CO 2 is negligible. CO 2 can be pumped down and readily dissolved at the ocean depths.  The capacity for dissolution of CO 2 in the ocean is adequate to absorb all the CO 2 from combustion of all the earth’s resources of fossil fuels. If liquid CO 2 is pumped deep enough within the ocean, the density of liquid CO 2 becomes greater than the density of seawater at that depth: liquid CO 2 can sink to the bottom floor of the ocean and form a lake of clathrates (solid compounds of a CO 2 molecule surrounded by about 5.75 molecules of water).  liquid CO 2 is the most economical form to be disposed compared to gas or solid CO 2 (dry ice)

Depleted Gas Wells  Natural gas wells: high pressure without leakage Up to several thousand pounds per square inch Hundreds of depleted gas wells in the world: the capacity is limited  Can only sequester the CO 2 from natural gas combustion (not enough for oil or coal): one volume of natural gas combustion produces one volume of CO active oil wells  Primary oil production only removes about a third of the oil from an active oil well.  Various media, such as hot water, nitrogen, polymers, and CO 2 have been used for removal of the remaining two-thirds.  CO 2 is preferred: in addition to displacement, CO 2 dissolves in the oil and reduces its viscosity, making it easier to pump out.  Only a fraction of the oil combustion CO 2 can be sequestered in oil wells: gaseous CO 2 vol. >> liquid oil vol.

Coal Mines and Deep Beds  Storage of CO 2 in mined-out and abandoned coal mine fields is not feasible: coal mines can’t be readily sealed to hold the pressure, gaseous CO 2 vol. >> solid coal vol.  Deep coal deposits: CH 4 coexists with coal. Displacement of coal-bedded methane with CO 2 : production of CH 4, twice the volume of CO 2 can be absorbed on the surface of the coal than the natural gas originally present in the coal.

Salt Domes  Pumping seawater from and to the ocean for solution mining salt: the salt domes have been used to store oil, storing the CO 2 is also possible. 3.6 Aquifers  Shallow aquifers: water supply Deep aquifers: usually saline, a significant capacity for sequestering CO 2  Pressurized CO 2 could displace the water as well as dissolve in the water of deep aquifers

Natural Minerals  Carbonate minerals: cannot be used  Igneous rock: can react with CO 2 Magnesium oxide bound to silica: MgSiO 3 Alumina-forming aluminosilicates

16 4. Capacity for Sequestering CO 2  Next slide (Table 5.3) Next slide (Table 5.3) 300 years: equivalent to the recoverable coal reserves

18 5.System Study A pplication of the absorption/stripping system and disposal of the CO 2 Base year: CO 2 Removal and Recovery System for Fossil-Fuel Power Plant Flue Gases 5.1.1CO 2 Emissions from Fossil Fuel  Next slide (Table 5.4) Next slide (Table 5.4) CO 2 production by natural gas and fuel oil: 50% and 80% compared to coal

CO 2 Removal and Recovery Using Improved Solvent Process MEA absorption/stripping: conventional A newer alkanolamine-based solvent (DOW Gas/spec FS-1): more energy efficient  Next slide (Table 5.5) Next slide (Table 5.5) Energy required: DOW FS-1 < MEA  Following slide (Fig. 5.2) Following slide (Fig. 5.2) Flue gas > 250 ℉ Quenching → 120 ℉ before entering the absorber

23  DOW FS-1 Reaction  (steam)  CO 2 liquefying Compressed to 2000 psia in a four-stage compression system Passed through a cooler Liquefied in a condenser at about 80 ℉ Liquefying energy: kwh(e)/lb of CO 2 recovered  Nest slide (Table 5.6) Nest slide (Table 5.6) Energy required: mainly removal and liquefaction

Integration of Power Plant and CO 2 Recovery System  Next slide (Fig. 5.3) Next slide (Fig. 5.3) The extraction of latent heat from the low- pressure steam: otherwise would be lost in the condenser  Following slide (Table 5.7) Following slide (Table 5.7) Integrated plant: efficiency drops a little

CO 2 Recovery Plant Costs 100~1000 tons CO 2 /day ≒ 5.1 ~ 51 MWe power plant 15 US$/ton of CO 2  Next slide (Table 5.8) Next slide (Table 5.8) CO 2 recovery and disposal may double the electricity cost CO 2 recovery and disposal may double the electricity cost Total power consumption for CO 2 mitigation > 17% Plus conventional power plant in plant consumption < 8%

CO 2 Disposal Systems 6” pipeline from power plants to collection centers 36” pipeline from collection centers to the final sites Ocean Disposal  The density of liquid carbon dioxide < seawater but liquid CO 2 is much more compressible than seawater and has a much higher thermal coefficient of expansion. Therefore, the density of CO 2 > seawater of similar temp. (37 ℉ ) at about 3000 m depth  Ocean depths of 3000 m: 4400 psia about 200 miles from the shoreline of most continents  Alternative: 2000 psia liquid CO 2 pressure at a depth of 500 m already lower than thermocline About 100 miles from the shoreline of most continents  Next slide (Fig. 5.4): 500 m depth disposal Next slide (Fig. 5.4)500 m depth disposal

32  An experiment is actually planned between the US nd Japan to inject CO 2 in the ocean off the coast of Hawaii and monitor the conc. of CO 2 at various ocean depth levels.  Next slide (Fig. 5.4A) Next slide (Fig. 5.4A) Other injection methods (3, 4, 5)

Oil and Gas Wells Disposal The US has 12,000 spent oil and gas wells Depleted wells: usually 100 ~ 500 psia An increase of about 10 ℉ for every 1000 ft of depth 10,000ft-depth well: 180 ℉ Recovered 80 ℉ 2,000 psia CO 2 → 180 ℉, 3,000 psia or more (10,000 psia) Disposal in Salt Carverns Again, 3,000 psia or more

35 6. Comparison of Capture and Disposal Costs  Next slide (Table 5.16) Next slide (Table 5.16) Only for capture  Disposal cost US $ 15~50/tonne CO 2 for 100 km distance

37 7. Problems Associated with Sequestering CO 2 in the Ocean  Economic Capital and operating costs  Engineering Deep CO 2 pipelines: a challenging problem  Environmental effects The acidity of the ocean ↑ pH ↓ to < 8 Would kill marine organisms  Rapid release of sequestered CO 2 Thermal plumes and volcanic action in the ocean could suddly release the sequestered CO 2