Overview of CO 2 Capture Processes

1. Overview of CO2 Capture Processes John Davison IEA Greenhouse Gas R&D Programme Workshop on CCS, KEPRI, 19th October 2007

2. Overview of this Presentation • Descriptions of leading CO2 capture technologies for power generation • Main advantages and disadvantages • Comparison of power plant efficiencies

3. CO2 Capture Technologies • Capture of CO2 from flue gases • Post-combustion capture • Burning fuel in pure oxygen instead of air • Oxy-combustion • Conversion of fuel to H2 and CO2 before combustion • Pre-combustion capture

4. Post-Combustion Capture Capture Power generation N2, O2, H2O to atmosphere Air Fuel Boiler or gas turbine (FGD) Solvent scrubbing Steam CO2 to storage Power CO2 compression Steam turbine

5. Liquid Solvent Scrubbing Reduced-CO2 flue gas CO2 CO2-lean solvent Condenser Absorber (40-60°C) Stripper (100-120°C) Flue gas Steam CO2-rich solvent Reboiler

6. Post-Combustion Solvent Scrubbing • Most common solvent is MEA (mono-ethanolamine) • Widely used for reducing gases, e.g. natural gas • Less widely used for oxidising flue gases • MEA is used in small post-combustion capture plants • CO2 is used mainly for chemicals and food and drink

7. Post-Combustion CO2 Capture • Warrior Run power plant, USA • 180 MWe coal fired circulating fluidised bed combustor • 150 t/d of CO2 is captured from a slipstream • About 5% of the total • MEA solvent is used

8. Post-Combustion Solvent Scrubbing • Up to 95%+ of CO2 can be captured in coal-fired plants • CO2 purity is high (99%+) • MEA solvent is degraded by oxygen and impurities • Low SOX (<10 ppm) and NO2 (<20 ppm) is recommended • Trade-off between costs of gas clean-up and solvent loss • Corrosion inhibitors are needed

9. Post-Combustion Solvent Scrubbing • New solvents are being developed and used • Amine blends, e.g. MEA - MDEA • Hindered amines, e,g MHI’s KS-1 solvent • Ammonia • Lower energy consumption, solvent losses and corrosion • Some solvents are more expensive • Overall cost may be lower if the rate of loss is lower

10. Post-Combustion CO2 Capture • Petronas urea plant • Kedah, Malaysia • 200 t/d of CO2 captured from gas fired furnace flue gas • KS-1 solvent is used Courtesy of MHI

11. Post-Combustion CO2 Capture • 3,000 t/d plant (MHI) • ‘Ready for delivery’ • Equivalent to 150 MWe coal fired plant • Larger designs being developed • Aim is to have one scrubber per boiler • The same as FGD Courtesy of MHI

12. Ammonia Scrubbing • Chilled ammonia scrubbing proposed by Alstom • Ammonium carbonate reacts with CO2 to form bicarbonate • 5 MWe plant built in Wisconsin, USA • 80,000 t/y plant to be built in Norway, more plants elsewhere • Advantages • Much lower solvent regeneration energy • High pressure regeneration - less CO2 compression power • Cheaper solvent • Waste production and disposal is less of a problem • Disadvantages • Power consumption for flue gas refrigeration and fans • Capital cost may be higher

13. Post-Combustion Capture - Summary • Advantages • Existing combustion technology can be used • Retrofit to existing plants is possible • Demonstrated at some small power plants • High CO2 purity • Disadvantages • High energy consumption • Penalty is being reduced by process developments • Solvent is degraded by oxygen and impurities • Scale-up is needed

14. Oxy-Combustion - Solid Fuel Air Air separation Recycled flue gas Vent Oxygen CO2 Fuel Boiler Cooling (+FGD) Purification/ compression Steam Steam turbine Power

15. Oxy-Combustion – Solid Fuel • Oxy-combustion boilers can be similar to conventional boilers • Air leakage into the boiler needs to be minimised • Heat transfer, ash deposition and corrosion are issues to be considered in the detailed design • Possibility of making more compact boilers • High percentage capture of CO2 • Impurities need to be removed from the CO2 • Cryogenic flash or distillation can be used • High cost of oxygen • Oxy-combustion is at a relatively small scale

16. Vattenfall 30MW Oxy-Combustion Plant Schwarze Pumpe, Germany Courtesy of Vattenfall

17. Oxy-Combustion – Gaseous Fuels Air Air separation Recycled flue gas Vent Oxygen CO2 Fuel Gas turbine HRSG Purification/ compression Steam Steam turbine Power

18. Oxy-Combustion – Gas Turbines • New types of gas turbine are needed • CO2 has different expansion properties to N2/O2 etc • Higher pressures are needed • Development of new turbines is very expensive • Will only happen if there is a large market • Retrofit to existing turbines is not possible • Quantity of oxygen required per tonne of CO2 is higher than for coal • For CH4, half the O2 is used to burn hydrogen • Water can be used instead of recycle CO2

19. Water Cycle Oxygen Fuel Fuel 80 bar 0.1 bar Combustor Water CO2 Compressor Condenser

20. CES Water Cycle Plant 5 MWe plant at Kimberlina, California

21. Chemical Looping Combustion • Iron, nickel, copper and manganese are considered • Early state of development • Durability of solids is a concern • Potential for low energy consumption Oxygen depleted air CO2 Metal oxide Fuel Reduced metal oxide Air

22. Oxy-combustion - Summary • Advantages • Existing boiler technology can be used • Possibility of avoiding FGD and SCR • Near-zero CO2 emissions are possible • Disadvantages • Least mature of the 3 leading capture technologies • High cost of oxygen production • CO2 purification is needed • New gas turbine designs are needed

23. Pre-Combustion Capture Sulphur recovery Sulphur IGCC without CO2 capture H2S Coal CO, H2O H2, CO2 etc Gasification Acid gas removal Fuel gas Oxygen Air Power Air separation Nitrogen Combined cycle Air Air

24. IGCC Without CO2 Capture • 4 coal-based IGCC demonstration plant in the USA, Netherlands and Spain • Availability has been poor but is improving • IGCC is not at present the preferred technology for new coal-fired power plants • Main commercial interest in IGCC is currently for use of petroleum residues • Several plants built and planned at refineries

25. IGCC without CO2 Capture Shell gasifier IGCC plant, Buggenum, Netherlands

26. Pre-Combustion Capture CO2 IGCC with CO2 capture CO2 compression Sulphur CO+H2O→H2+CO2 Coal H2S Gasification Sulphur recovery Shift conversion Acid gas removal Fuel gas (mainly H2) Oxygen Air Air separation Nitrogen Power Combined cycle Air Air

27. CO2 Capture in IGCC • Advantages of IGCC for CO2 capture • High CO2 concentration and high overall pressure • Lower energy consumption for CO2 separation • Compact equipment • Proven CO2 separation technology can be used • Possibility of co-production of hydrogen • CO2 capture is generally seen to improve the competitiveness of IGCC versus pulverised coal • IGCC is generally seen as more attractive for bituminous coals than for low rank coals.

28. CO2 Capture in IGCC • Disadvantages • IGCC is unfamiliar technology for power generators • Existing coal fired plants have had relatively low availability • IGCC without CO2 capture has generally higher costs than pulverised coal combustion • Different gas turbine combustors are needed • Hydrogen combustion is not available for the most advanced gas turbines

29. Pre-Combustion Capture – Gaseous Fuels CO2 CO2 compression CO+H2O→H2+CO2 Fuel Shift conversion Partial Oxidation Acid gas removal Fuel gas (mainly H2) Air separation Gas turbine Power Air Flue gas

30. CO2 Capture in Natural Gas Power Plants • Technology for production of hydrogen from natural gas is well proven • A large amount of extra equipment is needed for CO2 capture • Gas turbine issues are the same as for IGCC

31. Power Generation Efficiency Efficiency, % LHV Coal Natural gas Source: IEA GHG studies

32. Efficiency Decrease due to for Capture Percentage points Natural gas Coal

33. Summary • CO2 can be captured using existing technology • Capture technology needs to be demonstrated at larger scales • The optimum technology is uncertain • Depends on fuel type, other local conditions and future technology developments etc. • Utilities are seeking to gain experience of a broad range of technologies