11.1 Oxy-Fuel Combustion and Carbon Capture

Oxy-fuel combustion uses pure oxygen instead of air, producing flue gas mainly composed of CO2 and water vapor. This process eliminates nitrogen, reducing NOx formation and achieving higher flame temperatures, which enhances overall combustion efficiency.

Carbon capture methods remove CO2 from power plant emissions. Post-combustion capture removes CO2 from flue gases, while pre-combustion capture removes carbon from fuel before burning. Both methods aim to reduce greenhouse gas emissions from energy production.

Oxy-Fuel Combustion Process

Enhanced Combustion with Pure Oxygen

Top images from around the web for Enhanced Combustion with Pure Oxygen

• 

  Development and demonstration of oxy-fuel CFB technology View original

  Is this image relevant?

• 

  Development and demonstration of oxy-fuel CFB technology View original

  Is this image relevant?

• 

  Development and demonstration of oxy-fuel CFB technology View original

  Is this image relevant?

• 

  Development and demonstration of oxy-fuel CFB technology View original

  Is this image relevant?

• 

  Development and demonstration of oxy-fuel CFB technology View original

  Is this image relevant?

1 of 3

Top images from around the web for Enhanced Combustion with Pure Oxygen

• 

  Development and demonstration of oxy-fuel CFB technology View original

  Is this image relevant?

• 

  Development and demonstration of oxy-fuel CFB technology View original

  Is this image relevant?

• 

  Development and demonstration of oxy-fuel CFB technology View original

  Is this image relevant?

• 

  Development and demonstration of oxy-fuel CFB technology View original

  Is this image relevant?

• 

  Development and demonstration of oxy-fuel CFB technology View original

  Is this image relevant?

1 of 3

• Oxy-fuel combustion uses pure oxygen instead of air for fuel combustion
• Produces flue gas primarily composed of CO2 and water vapor
• Eliminates nitrogen from the combustion process reduces NOx formation
• Achieves higher flame temperatures (up to 3000°C) compared to air combustion
• Requires fuel-specific burner designs to handle increased heat flux
• Enhances overall combustion efficiency by 3-5% due to reduced heat losses

Flue Gas Management and Recycling

• Flue gas recirculation involves redirecting a portion of exhaust gases back into the combustion chamber
• Controls flame temperature by diluting the oxygen concentration
• Typically recirculates 60-80% of flue gas to maintain optimal combustion conditions
• Helps regulate furnace temperature and heat transfer rates
• Reduces the overall volume of flue gas produced decreases downstream processing requirements
• Improves thermal efficiency by preheating the recycled flue gas

Oxygen Production Technologies

• Cryogenic air separation utilizes low temperatures to separate oxygen from air
• Involves cooling air to approximately -183°C where oxygen liquefies and can be separated
• Produces high-purity oxygen (99.5%+) suitable for oxy-fuel combustion
• Requires significant energy input accounts for 15-25% of total plant energy consumption
• Oxygen transport membranes offer an alternative to cryogenic separation
• Use ceramic materials to selectively allow oxygen ions to pass through at high temperatures (800-900°C)
• Potentially reduce energy consumption for oxygen production by 30-50% compared to cryogenic methods

Carbon Capture Methods

Post-Combustion Carbon Capture

• Carbon capture and storage (CCS) encompasses various technologies to capture, transport, and store CO2 emissions
• Post-combustion capture removes CO2 from flue gases after the combustion process
• Applicable to existing power plants without major modifications to the combustion system
• Typically captures 85-95% of CO2 emissions from the flue gas
• Requires large-scale equipment due to the low CO2 concentration in flue gas (12-15% for coal-fired plants)
• Faces challenges with energy penalties reduces overall plant efficiency by 20-30%

Pre-Combustion Carbon Capture

• Pre-combustion capture involves removing carbon from fuel before combustion
• Applies to integrated gasification combined cycle (IGCC) power plants
• Converts fuel into syngas (mixture of H2 and CO) through gasification
• Shifts CO to CO2 using the water-gas shift reaction then separates CO2
• Produces a hydrogen-rich fuel for combustion with reduced carbon content
• Achieves higher CO2 concentration in the gas stream (35-40%) facilitates easier separation
• Offers potential for polygeneration produces electricity, hydrogen, and other valuable chemicals

CO2 Separation Mechanisms

• Absorption utilizes liquid solvents to selectively remove CO2 from gas mixtures
• Commonly uses amine-based solvents (monoethanolamine, diethanolamine) for chemical absorption
• Involves cyclic process of absorption at low temperatures and desorption at high temperatures
• Achieves high CO2 capture rates (up to 98%) but requires significant energy for solvent regeneration
• Adsorption employs solid materials (activated carbon, zeolites) to capture CO2 on their surfaces
• Utilizes pressure or temperature swing cycles to adsorb and release CO2
• Offers potential for lower energy consumption compared to absorption processes
• Faces challenges with selectivity and capacity in the presence of other flue gas components

CO2 Separation Techniques

Purification and Compression of Captured CO2

• CO2 purification removes impurities to meet transportation and storage requirements
• Involves multi-stage compression to increase CO2 density for efficient transport
• Typically compresses CO2 to supercritical state (>73.8 bar) for pipeline transport
• Removes water vapor to prevent corrosion in pipelines and injection wells
• Eliminates other contaminants (SOx, NOx, O2) to meet purity specifications (>95% CO2)
• Utilizes various techniques including flash drums, distillation, and cryogenic separation
• Consumes significant energy accounts for 25-30% of the total energy penalty of CCS

Advanced Membrane Technologies for CO2 Separation

• Membrane separation uses selective permeation to separate CO2 from other gases
• Employs polymeric, inorganic, or mixed-matrix membranes with high CO2 selectivity
• Offers advantages of continuous operation, compact design, and low energy consumption
• Faces challenges with membrane stability and performance under real flue gas conditions
• Requires multi-stage configurations to achieve high CO2 purity and recovery
• Emerging technologies include facilitated transport membranes enhance CO2 permeation
• Explores hybrid systems combining membranes with other separation technologies (absorption, adsorption) to optimize performance