Carbon Dioxide Capture At Coal-Fired Power Plants
Carbon Dioxide (CO2) Capture atCoal-Fired Power PlantsPresented ByBrian McNamarabmcnamara@kentlaw.edu
What is CO2 Capture? A process consisting of separating CO2 fromenergy-related sources before it enters theatmosphere The current goal is to capture approximately90% of CO2 emissions from these sources CO2 capture is most applicable to large,centralized sources like power plants
Reasons to Consider CO2 Capture Coal is the largest contributor to global CO2 emissionsfrom energy use (41%), and its share is projected toincrease 50% of the electricity generated in the U.S. is from coal In 2006, coal-fired power plants producedapproximately 36% of the total U.S. CO2 emissions The U.S. produces about 1.5 billion tons per year ofCO2 from coal-burning power plants In the U.S., electricity demand is expected to nearlydouble over the next 30 years China and India are rapidly expanding their use of coalfor energy generation
Why is the Future Use of Coal Likely toIncrease? Coal is cheap Coal is abundant The United States, Russia, China and Indiahave immense coal reserves The economics and security of supply aresignificant incentives for the continuing use ofcoal
CO2 Separation Technologies
CO2 Separation withSorbents/Solvents Separation occurs whenCO2-containing gas comesin contact with asorbent/solvent that iscapable of capturing theCO2 Regeneration of thesorbent/solvent after beingheated, after pressuredecrease or other change incondition releases the CO2 Recycled and make-upsorbent/solvent is sent backto capture more CO2
CO2 Separation with Membranes Membranes aremanufactured materials(polymeric, metallic,ceramic) that allow theselective permeation ofCO2 through them The selective permeationof CO2 is usually drivenby a pressure differenceacross the membrane(high pressure is usuallypreferred)
CO2 Separation by CryogenicDistillation CO2 can be separatedfrom other gasesthrough a series ofcompression, coolingand expansion steps Once in liquid form, thecomponents of the gascan be separated in adistillation column
CO2 Capture Systems
Post-Combustion CO2 CaptureSystems Defined as the separation of CO2 from theflue gases produced after burning coal in air The CO2 separation and recovery from theflue gas occur at low concentration and lowpartial pressure The most common separation method usedare chemical solvents (amines)
Post-Combustion CO2 Capture System:Chemical Absorption with Amines The CO2 is captured from the flue gas stream byabsorption into an amine solution in anabsorption tower The absorbed CO2 must then be stripped fromthe amine solution via a temperature increase,regenerating the solution for use again in theabsorption tower The recovered CO2 is cooled, dried, andcompressed to a supercritical fluid The CO2 is then ready to be piped to storage
Post-Combustion CO2 Capture System:Chemical Absorption with Amines
Challenges of Post-Combustion CO2Capture Low pressure and dilute CO2 concentration of the fluegas 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 ofenergy The low-pressure steam used for the regeneration ofthe amine solution reduces steam to the turbine whichreduces the net power output of the generating plant For existing plants, the coal input must be increasedand the plant size expanded to maintain constant netpower generation
Pre-Combustion CO2 Capture Systems Defined as the separation of coal into CO2 and hydrogenbefore combustion The capture process involves the following stages:– First, the coal is processed in a reactor with steam and air oroxygen to produce a mixture consisting mainly of carbonmonoxide and hydrogen (“synthesis gas”)– Second, in another reactor (a “shift reactor”) the synthesis gas isreacted with steam to produce an additional mix of CO2 andhydrogen– Third, the resulting mixture of CO2 and hydrogen can then beseparated into separate gas streams– Fourth, the CO2 can be captured and the hydrogen used as fuelto generate a gas turbine Pre-combustion would be used at power plants thatemploy integrated gasification combined cycle (IGCC)technology
Pre-Combustion CO2 Capture System:Integrated Gasification CombinedCycle System (IGCC) A gasifier transforms the coal to a synthesis gas The synthesis gas goes through several stages ofcleanup (shift reactors) where the CO2 can be captured A gas turbine burns the cleaned synthesis gas toproduce electricity and exhaust heat Exhaust heat from the gas turbine is recovered toproduce steam to power a steam turbine The system produces energy through the two turbines– gas turbine and steam turbine
Pre-Combustion CO2 Capture System:IGCC with CO2 Capture
Challenges of Pre-Combustion CO2Capture for IGCC Plants Perception of poor availability and operability– Current demonstration plants required between 3-5 yearsto reach 70 – 80 % availability Operating issues– No single process component is responsible for themajority 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 electricgeneration
Oxy-Fuel Combustion CO2 CaptureSystems The system uses oxygen rather than air for thecombustion of coal Combustion produces flue gas that is mainlywater vapor and CO2 Flue gas has a relatively high CO2 concentration(greater than 80% by volume) CO2 is separated from the water vapor by coolingand compressing the flue gas Flue gas may be further treated to remove airpollutants and non-condensed gases before theCO2 is captured
Oxy-Fuel Combustion CO2 CaptureSystem
Challenges for Oxy-Fuel CombustionCO2 Capture The technology is only at a development stage(no commercial experience to rely upon) The air-separation unit that supplies theoxygen consumes a lot of energy and reducesthe plant’s efficiency
Retrofit or Rebuild the Existing U.S.Coal-Based Generating Plants?
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 isabout 33% Current life-extension capabilities could keepsome units in operation for another 30 years More than 100 new coal-based power plantsare being considered for construction
Post-Combustion CO2 CaptureRetrofits Retrofit refers to installing CO2 capturesystems to existing units Retrofit with CO2 capture systems seemunlikely due to:– Reductions in unit efficiency and output– Increased on-site space requirements– Unit downtime
Post-Combustion CO2 CaptureRebuilds Rebuild refers to rebuilding the core of anexisting unit by installing higher efficiencytechnology along with CO2 capture Rebuilds appear more attractive than retrofitsbecause– Cost of both are about the same– Units with rebuilds have higher efficiency
Pre-Combustion CO2 Capture Retrofits& Rebuilds Retrofitting an IGCC unit would appear to beless expensive than retrofitting a PC unit Retrofitting would not make the unit anoptimum CO2 capturing unit Rebuilding would involve significant changesin most components of the unit to optimizeCO2 capture
Oxy-Fuel Retrofits and Rebuilds Good option for retrofitting PC units becausethe boiler and steam cycle are less affected The major impact is the increased energyrequirement of the air-separation unit Rebuilds to improve efficiency appear to becompetitive with post-combustion rebuilds
Retrofit or Rebuild the Existing U.S.Coal-Based Generating Plants?
Retrofit or Rebuild the Existing U.S.Coal-Based Generating Plants?
What will the Application of CO2Capture Depend on? Technical maturity Costs Diffusion and transfer of the technology todeveloping countries and their capacity toapply the technology Regulatory aspects Environmental issues Public perception
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
Our main source of coal comes from a coal mine near Butler, Missouri. A stock pile of coal for unexpected emergencies is maintained at Blue Valley. A 90-day supply of coal consists of 45,000 tons of coal. Coal Feeders Feeding coal from the bunkers to the pulverizers is the purpose of the coal feeders. The pulverizers grind the coal into a fine .
as.edu / n e Resources -Coal 1 Based on -The Coal Resource by World Coal Institute 2005.-The Coal Resource Base, Chapter 2 of Producing Liquid Fuels from Coal by J.T. Bartis, F. Camm and D.S. Ortiz. Published by RAND 2008. ISBN: 978--8330-4511-9. -The Role of Coal in Energy Growth and CO2 Emissions, Chapter 2 of The Future of Coal, an Interdisciplinary MIT Study, 2007.
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carbon equivalent per year (Song et al. 2002). Carbon dioxide emissions from these fossil fuel industries are from combustion gases and byproduct carbon dioxide, mainly from synthesis gas but also from other sources. There is an excess of 120 million tons per year of high-purity carbon dioxide from the exponential
There is, however, considerable evidence that gentle warming and increased carbon dioxide are beneficial to plants. Also, more people die in winter than in summer. The present level of carbon dioxide is about 390 ppm (parts per million). All plants need carbon dioxide; that is what plants use to grow: The more carbon dioxide the faster they grow.
and 5 – 6% of global carbon dioxide emissions could be used, respectively. However, there is one estimate that suggests approximately 15% of global emissions of carbon dioxide could be used per year by 203011. In terms of net carbon dioxide are likely to account for less than 1% of global emissions reduction12. For net
IEA Clean Coal Centre – New regulatory trends: effect on coal-fired power plant and coal demand 4 . Abstract . This review presents the recent regulatory trends, practices and developments, in major coal producing and consuming countries, which are affecting and may influence future demand for coal and coal-fired power generation.
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