Carbon Sequestration

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Carbon Sequestration

• Justin Coe
• ECE 510 Renewable Energy

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Background

• Atmospheric levels of CO2 have risen from
  pre-industrial levels of 280 parts per million
  (ppm) to present levels of 375 ppm. Evidence
  suggests this observed rise in atmospheric CO2
  levels is due primarily to expanding use of
  fossil fuels for energy.
• Predictions of global energy use in the next
  century suggest a continued increase in carbon
  emissions and rising concentrations of CO2 in the
  atmosphere unless major changes are made in the
  way we produce and use energy- in particular, how
  we manage carbon.

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Sequestration Techniques

• Captured at source (fossil fuel plants)
• Flue gas separation
• Oxy-fuel combustion
• Pre-combustion capture
• Captured from air (terrestrial sequestration)
• Oceanic uptake of carbon
• Uptake from plant life

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Source Capture Flue gas separation

• CO2 composes 10-15 volume of flue gas exhaust
• Flue gas is bubbled through a solvent (aqueous
  amines) in a packed absorber column that removes
  the CO2, the solvent then passes through a
  regenerator column where counter flowing steam
  removes the CO2. The steam then condenses,
  leaving a stream of highly concentrated CO2.
• Raises cost of electricity production by 84,
  from 4.9 cents/kWh to 9.0 cents/kWh

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Source Capture Oxy-fuel combustion

• Burning the fuel in pure or enriched oxygen, as
  opposed to atmospheric air, results in exhaust
  composed nearly exclusively of CO2 and H2O.
• This alleviates the need to separate CO2 from
  other flue gases (mostly N2), which is very
  costly
• The CO2 is then extracted via water condensation
• This technique requires air separation at the
  source, rather than at the exhaust, also very
  expensive
• Pilot scale studies show that this method of CO2
  capture can be retrofitted to existing pulverized
  coal (PC) plants.

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Source Capture Pre-combustion capture

• Applied in coal gasification combined cycle
  (IGCC) power plants
• This process includes gasifying the coal to
  produce a synthesis gas composed of CO and H2
  reacting the CO with water (water-gas shift
  reaction) to produce CO2 and H2 capturing the
  CO2 and sending the H2 to a turbine to produce
  electricity.
• PC plants produce cheaper electricity than IGCC
  plants currently
• Cannot retrofit PC plants, requires new plant
  production

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Source Capture - Costs
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Storing CO2 Depleted oil and gas reservoirs

• These are formations that held crude oil and
  natural gas over geologic time frames.  In
  general they are a layer of porous rock with a
  layer of non-porous rock above such that the
  non-porous layer forms a dome. These domes could
  be used to store CO2.

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Storing CO2 Saline formations

• Saline formations are layers of porous rock that
  are saturated with brine. 
• They are much more commonplace than coal seams or
  oil and gas reservoirs, and represent an enormous
  potential for CO2 storage capacity.
• Much less is known about saline formations than
  is known about crude oil reservoirs and coal
  seams and there is a greater amount of
  uncertainty about how well they can provide CO2
  storage. 

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Storing CO2 Oceanic storage

• The oceans have the greatest potential for CO2
  storage
• CO2 could be injected deep into the ocean
• Environmental concerns of affecting the pH of
  ocean waters
• Also concern that natural ocean current cycles
  may become saturated with CO2, minimizing the
  oceans absorption capacity

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Storing CO2 Potential storage sites
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Terrestrial Sequestration

• Increasing photosynthetic capacity on earth will
  reduce atmospheric levels of CO2
• Focus on decreasing rapid deforestation,
  particularly rainforests
• Research is being done into increasing net
  oceanic uptake from the atmosphere by
  fertilization of phytoplankton with nutrients

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Storing CO2 Regional hubs

• By concentrating fossil fuel plants in certain
  areas, it is possible to have one major carbon
  sequestration plant that serves many electricity
  generation plants. The idea is to reduce the per
  unit cost. The cost of carbon sequestration less
  expensive as the size of total generation
  increases

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Carbon Sequestration Regional hubs
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Conclusions

• Carbon sequestration must be further researched
  and implemented. The cost of carbon sequestration
  to industry is high, and there are not enough
  current incentives to promote it.
• Penalties, or possibly carbon permit trading,
  should be introduced to make carbon sequestration
  projects more economically viable.