Carbon Dioxide (CO2) Capture at Coal-Fired Power Plants. Presented By Brian McNamara

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1 Carbon Dioxide (CO2) Capture at Coal-Fired Power Plants Presented By Brian McNamara

2 What is CO2 Capture? A process consisting of separating CO2 from energy-related sources before it enters the atmosphere The current goal is to capture approximately 90% of CO2 emissions from these sources CO2 capture is most applicable to large, centralized sources like power plants

3 Reasons to Consider CO2 Capture Coal is the largest contributor to global CO2 emissions from energy use (41%), and its share is projected to increase 50% of the electricity generated in the U.S. is from coal In 2006, coal-fired power plants produced approximately 36% of the total U.S. CO2 emissions The U.S. produces about 1.5 billion tons per year of CO2 from coal-burning power plants In the U.S., electricity demand is expected to nearly double over the next 30 years China and India are rapidly expanding their use of coal for energy generation

4 Why is the Future Use of Coal Likely to Coal is cheap Coal is abundant Increase? The United States, Russia, China and India have immense coal reserves The economics and security of supply are significant incentives for the continuing use of coal

5 CO2 Separation Technologies

6 Separation occurs when CO2-containing gas comes in contact with a sorbent/solvent that is capable of capturing the CO2 Regeneration of the sorbent/solvent after being heated, after pressure decrease or other change in condition releases the CO2 Recycled and make-up sorbent/solvent is sent back to capture more CO2 CO2 Separation with Sorbents/Solvents

7 CO2 Separation with Membranes Membranes are manufactured materials (polymeric, metallic, ceramic) that allow the selective permeation of CO2 through them The selective permeation of CO2 is usually driven by a pressure difference across the membrane (high pressure is usually preferred)

8 CO2 Separation by Cryogenic CO2 can be separated from other gases through a series of compression, cooling and expansion steps Once in liquid form, the components of the gas can be separated in a distillation column Distillation

9 CO2 Capture Systems

10 Post-Combustion CO2 Capture Systems Defined as the separation of CO2 from the flue gases produced after burning coal in air The CO2 separation and recovery from the flue gas occur at low concentration and low partial pressure The most common separation method used are chemical solvents (amines)

11 Post-Combustion CO2 Capture System: Chemical Absorption with Amines The CO2 is captured from the flue gas stream by absorption into an amine solution in an absorption tower The absorbed CO2 must then be stripped from the amine solution via a temperature increase, regenerating the solution for use again in the absorption tower The recovered CO2 is cooled, dried, and compressed to a supercritical fluid The CO2 is then ready to be piped to storage

12 Post-Combustion CO2 Capture System: Chemical Absorption with Amines

13 Challenges of Post-Combustion CO2 Capture Low pressure and dilute CO2 concentration of the flue gas requires a high volume of gas to be treated CO2 removal from the flue gas requires a lot of energy Compression of the captured CO2 requires a lot of energy The low-pressure steam used for the regeneration of the amine solution reduces steam to the turbine which reduces the net power output of the generating plant For existing plants, the coal input must be increased and the plant size expanded to maintain constant net power generation

14 Pre-Combustion CO2 Capture Systems Defined as the separation of coal into CO2 and hydrogen before combustion The capture process involves the following stages: First, the coal is processed in a reactor with steam and air or oxygen to produce a mixture consisting mainly of carbon monoxide and hydrogen ( synthesis gas ) Second, in another reactor (a shift reactor ) the synthesis gas is reacted with steam to produce an additional mix of CO2 and hydrogen Third, the resulting mixture of CO2 and hydrogen can then be separated into separate gas streams Fourth, the CO2 can be captured and the hydrogen used as fuel to generate a gas turbine Pre-combustion would be used at power plants that employ integrated gasification combined cycle (IGCC) technology

15 Pre-Combustion CO2 Capture System: Integrated Gasification Combined Cycle System (IGCC) A gasifier transforms the coal to a synthesis gas The synthesis gas goes through several stages of cleanup (shift reactors) where the CO2 can be captured A gas turbine burns the cleaned synthesis gas to produce electricity and exhaust heat Exhaust heat from the gas turbine is recovered to produce steam to power a steam turbine The system produces energy through the two turbines gas turbine and steam turbine

16 Pre-Combustion CO2 Capture System: IGCC with CO2 Capture

17 Challenges of Pre-Combustion CO2 Capture for IGCC Plants Perception of poor availability and operability Current demonstration plants required between 3-5 years to reach % availability Operating issues No single process component is responsible for the majority of shutdowns Operational performance has not typically exceeded 80% Cost Requires more maintenance than a PC unit Spare gasifier ($$) provides better availability Maturity IGCC system is not mature enough for coal-based electric generation

18 Oxy-Fuel Combustion CO2 Capture Systems The system uses oxygen rather than air for the combustion of coal Combustion produces flue gas that is mainly water vapor and CO2 Flue gas has a relatively high CO2 concentration (greater than 80% by volume) CO2 is separated from the water vapor by cooling and compressing the flue gas Flue gas may be further treated to remove air pollutants and non-condensed gases before the CO2 is captured

19 Oxy-Fuel Combustion CO2 Capture System

20 Challenges for Oxy-Fuel Combustion CO2 Capture The technology is only at a development stage (no commercial experience to rely upon) The air-separation unit that supplies the oxygen consumes a lot of energy and reduces the plant s efficiency

21 Retrofit or Rebuild the Existing U.S. Coal-Based Generating Plants?

22 U.S. Coal-Based Generating Plants Average age of the fleet is over 35 years old There are more than 1,000 boilers in the U.S. fleet Average generating efficiency of the fleet is about 33% Current life-extension capabilities could keep some units in operation for another 30+ years More than 100 new coal-based power plants are being considered for construction

23 Post-Combustion CO2 Capture Retrofits Retrofit refers to installing CO2 capture systems to existing units Retrofit with CO2 capture systems seem unlikely due to: Reductions in unit efficiency and output Increased on-site space requirements Unit downtime

24 Post-Combustion CO2 Capture Rebuilds Rebuild refers to rebuilding the core of an existing unit by installing higher efficiency technology along with CO2 capture Rebuilds appear more attractive than retrofits because Cost of both are about the same Units with rebuilds have higher efficiency

25 Pre-Combustion CO2 Capture Retrofits & Rebuilds Retrofitting an IGCC unit would appear to be less expensive than retrofitting a PC unit Retrofitting would not make the unit an optimum CO2 capturing unit Rebuilding would involve significant changes in most components of the unit to optimize CO2 capture

26 Oxy-Fuel Retrofits and Rebuilds Good option for retrofitting PC units because the boiler and steam cycle are less affected The major impact is the increased energy requirement of the air-separation unit Rebuilds to improve efficiency appear to be competitive with post-combustion rebuilds

27 Retrofit or Rebuild the Existing U.S. Coal-Based Generating Plants?

28 Retrofit or Rebuild the Existing U.S. Coal-Based Generating Plants?

29 What will the Application of CO2 Technical maturity Costs Capture Depend on? Diffusion and transfer of the technology to developing countries and their capacity to apply the technology Regulatory aspects Environmental issues Public perception