with Physical Absorption

Transcription

1 meinschaft Mitglied der Helmholtz-Gem Pre-Combustion Carbon Capture with Physical Absorption Sebastian Schiebahn, Li Zhao, Marcus Grünewald 5. Juli 2011 IEK-3, Forschungszentrum Jülich, Germany ICEPE Frankfurt am Main June, 2011

2 Outline 1. Introduction of IGCC process and Pre-combustion 2. Physical absorption for CO 2 separation 3. Physical solvents 4. Process design 5. Concluding remarks Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 1/21

3 Integrated Gasification Combined Cycle (IGCC) Process Gasification Gas Cleaning Coal O 2 Gasification Cooling/ Dedusting/ Washing COS Hydrolysis/ Desulphurisation Saturation/ Reheating Air Separation Unit N 2 Air Compressor Combustion Chamber Turbine Heat Recovery Steam Generator Flue Gas Combined Cycle Idea of IGCC concept: Use of high efficient combined cycle by transforming solid coal into combustible gas via gasification Opportunity for CO 2 capture: Separation of CO 2 prior to final combustion Separation easier due to elevated partial pressures of CO 2, but prior to separation, CO has to be transformed to CO 2 by shift reaction Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 2/21

4 IGCC with CO 2 capture using physical scrubbing Gas Cleaning Coal O 2 Gasification Cooling/ Dedusting/ Washing WGS Reactor Physical Scrubbing Air Separation Unit N 2 Saturation/ CO 2 Reheating Air Compressor Combustion Chamber Turbine Heat Recovery Steam Generator Flue Gas Key technologies: Water Gas Shift (WGS) reactor CO 2 physical scrubbing H 2 gas turbine Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 3/21

5 Gas composition prior to physical scrubbing Composition Mole fraction prior to WGS reactor* Mole fraction (wf) subsequent to WGS reactor (95% CO conv.) CO 53.3 % 1,92% H % 58,37% H 2 O 11.8 % dry CO % 36,76% N % 1,87% Ar 0.7 % 0.5% H 2 S 7350 ppm 5619 ppm COS 550 ppm - *p = 26.8 bar and T = 133 C, Source: Kloster,1999 Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 4/21

6 Why Physical Absorption? Based on the physical solubility of gases, according to Henry s Law: x CO2 H CO2, L yco2 p Partial press sure p p 1 h phys. Advantages for high pressure applications: chem. Lower circulation rate due to the high cyclic loading capacity. Lower electric energy and heat consumption for regeneration, p 2 c=0 Δc ch Loading c (Vol. Sour Gas / Vol. Solvent) Good stability of the solvent, because no reactions occur. c 2 ch c 1 ch Capable of separating acid gases c 2 ph Δc ph c1 ph Loading c = vol. Sour gas / vol. Solvent selectively parallel H 2 S and CO 2 separation Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 5/21

7 Requirements for solvents High solubility for acid gases, especially CO 2 and H 2 S low solvent circulation rate High selectivity towards H 2 and CO low co-absorption of valuable components Low vapor pressure at operating temperature minimize solvent losses Low viscosity at operating temperature sufficient heat and mass transfer capabilities Non-corrosive and chemically inert Cheap Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 6/21

8 Commercially Solvents Process Name Solvent Process Licensor Physical Solvents Rectisol Methanol Lurgi and Linde AG Selexol Dimethyl ether of polyethylene glycol Union Carbide / UOP (DMPEG) Purisol n-methyl-2-pyrrolidone lid (NMP) Lurgi Fluor Solvent Propylene carbonate (PC) Fluor Daniel Sepasolv MPE Methyl isopropyl ether of polyethylene glycol (MPE) Badische (BASF) Ifpexol Methanol Institut t Français du Pétrole (IFP) Mixed Physical/Chemical Solvents Sulfinol l Sulfolane + DIPA or MDEA Shell Global l Solutions Amisol Methanol + secondary alkylamine Lurgi *for process description and solvent parameters Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 7/21

9 Solvent Properties Solvent Methanol DMPEG NMP PC 25 C / cp Specific 25 C/ kg m Molecular l Weight / g/mol Vapour 25 C/ Pa 16.7 x 10³ Freezing Point / CC Boiling 1 atm / C Thermal conductivity / W m -1 K Maximum Operating Temperature / C Specific 25 C / kj kg -1 K CO 2 25 C / m 3 CO2 m -3 Solvent *for comparison, the solubility of CO 2 in water at 35 C and 1 atm CO 2 partial pressure is 0.6 m 3 CO2 m -3 Water Sources: Bucklin, 1984; Burr 2009 Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 8/21

10 Effect of Partial Pressure on Solubility pressure e / atm CO 2 partial C -30 C Solubility of CO 2 in MeOH / m³(stp)/m³ Source: Hochgesand, 1968 Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 9/21

11 Solvent Solubilities Solvent Gas Methanol DMPEG NMP PC (Rectisol) Selectivity ty Solubility to CO 25 C* / 2 m 3 m -25 C / - 25 C / m 3 m -3 (Selexol) Selectivity ty rel. to CO 25 C / - 25 C / m 3 m -3 (Purisol) Selectivity ty rel. to CO 25 C / - (Fluor Solvent) 25 C / m 3 m -3 Selectivity ty rel. to CO 25 C / - Hydrogen Nitrogen Carbon Monoxide Methane Ethane Carbon Dioxide Propane n-butane Carbonyl Sulphide Hydrogen Sulphide Ammonia Dioxide Water *Solubilities in 25 C calculated with selectivities of -25 C Sources: Bucklin, 1984; Burr 2009 Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 10/21

12 Influence of temperature on solubility - CO 2 in Methanol 100 Solubility / m³(st TP)/m³ CO 2 in methanol atm CO 2 partial pressure Source: Herbert, 1956 Temperature / C Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 11/21

13 Alternative Solvents Mixed solvents: Mixture of physical and chemical solvents to combine positive characteristics, e.g. Sulfinol = Sulfolane + DIPA or MDEA Amisol = Methanol + secondary alkylamine High bulk removal due to physical solvent + high purification degree due to chemical bonding with the amine Ionic Liquids: Liquid salts, which melt at or below 100 CC Very low volatility Possibility to absorb at higher temperatures Can be designed d for specific application Very promising, but still under investigation Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 12/21

14 Process layout Physical absorption processes are not fixed, but can be designed flexible to achieve the required goals (e.g. separation degree, purity, energy consumption) A variety of tools exist e.g. different methods of regeneration or intermediate flashes with recirculation Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 13/21

15 Solvent Regeneration - Flashing Treated Gas Off gas I Off gas II Off gas III Principle: Reduction of pressure (multiple steps) Solved gases are released until equilibrium is reached again Effects: Easiest way of regeneration with no further energetic effort Feed F Regeneration limited to the equilibrium partial pressure Reasonable for bulk removal a) Flashing Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 14/21

16 Solvent Regeneration - Stripping Treated Gas Off gas I Off gas II + Strip gas Principle: Use of (inert) stripping gas Partial pressure at the inlet of stripping gas is zero Effects: I High purity achievable Product is diluted with stripping gas Feed Strip gas b) Stripping Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 15/21

17 Solvent Regeneration Thermal regeneration Treated Gas Off gas Principle: Boiling of solution s Higher temperature level decreases solubility Produced vapor works as internal stripping gas Effects: Feed Most energy consuming method Highest purities achievable c) Thermal regeneration Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 16/21

18 Criteria for design of process Extend of acid gas removal required, for CO 2 removal and requested sulfur content Required purity of the product streams Acceptable energetic effort Possible integration into the plant (e.g. steam for regeneration) Capital and operating costs Acceptable loss of valuable components Process complexity, affecting availability and flexibility Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 17/21

19 Example: 2-stage Selexol Process to fuel saturator CO 2 absorber CO 2 for sequestration to Claus Feed H 2 S absorber b Flash drums H 2 S stripper H 2 S concentrator Source: UOP Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 18/21

20 Concluding remarks Applicability for high pressure CO 2 removal of syngas for years, making them feasible for CCS High flexibility of the process design enables the adaptability of the physical scrubbing process to the required specifications A variety of commercially available solvents exist Operating temperature t is below that t of the WGS reactor, this leads to an extensive and expensive use of heat exchangers, resulting in high investment cost and exergetic heat losses Ionic Liquids are a promising alternative offering the opportunity to separate carbon dioxide at elevated temperatures with almost no solvent losses Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 19/21

21 Thank you for your attention! Sebastian Schiebahn Institut für Energie- und Klimaforschung Brennstoffzellen (IEK-3) 20/21