The Capture and Sequestration of Carbon Dioxide

bullet1 Case Study

bullet2 The Method for Capture

Of which Chemical absorption processes (MEA) are the most likely candidate to gain current wide spread use as;

    1. Applicable to power generation technologies currently in general use
    2. Experience > 60 years. Proven technology, bears no risk.
    3. In use today, capturing CO2 for soft drinks
    4. Mainly in reducing atmospheres                      


Why MEA Absorption: -

  • As Concentration (partial pressure) of CO2 in Flue gases from all the leading power plants technologies is low.
  • MEA the Chemical absorbent has strong affinity for CO2, which is important for partial pressure of CO2 is low.
  • Can be used on a variety of power plants i.e. PF+FGD or GTCC, which are mainly in use.
  • MEA has a relatively high carrying capacity, which leads to low capital and operating cost.
  • Corrosion inhibitors are available to use carbon steel in plants.
  • Pre-treat for SO2 removal.
  • Cheap MEA, so makeup cost (due to significant oxidative and thermal degradation & pre-treat for SO2 removal) is acceptable.
  • Could make deep reductions in CO2 emissions (CO2 recovery rate=98% and product purity in excess of 99%)


Some Problems: -

  • Flue gases typically contain contaminants such as SOx, NOx, O2, hydrocarbons and particulates. The presence of such impurities reduces the absorption capacity of amines along with other operational problems.
  • Pre-treatment or use of chemical inhibitors in absorption process will be beneficial.
  • Using conventional trays or packed columns for gas liquid contact faces problems like:
    • Foaming
    • Vapor entrainment of solvent
    • Need to replenish solvent in low quantity.

However, these problems have a relatively small effect on the total system costs of the MEA based absorption process.


Avoiding oxidation:

Following steps can be adapted to control the rate of degradation in the oxidizing environment of a flue gas.

  • Minimize contact time with dissolved O2
  • Minimize dissolved metals, Nox
  • Add chelators or free radical scavengers
  • Use solvents that oxidize slower
    • Hindered amines with tertiary or quarterly C’s
    • Tertiary amines (?)
    • K2 CO3

Plant Materials:
  • CH4 & H2 Systems use Carbon Steel
    • High pressure & capital costs dominate
    • Corrosion by loaded solutions and degradation products
  • Corrosion inhibitors are effective with CS
    • For < 30% MEA, <0.45 loading, small salt concentration
    • Metals (Cu+2,V+5) give oxidized Fe2O3 film
    • But catalyze degradation
  • Corrosion resistant materials of construction
    • FRP, SS, lined CS: as in FGD systems
    • Cost effective with larger systems at 1 atmosphere
    • Relaxes constraints on solvent concentration and CO2 loading


Size of Plant:

A conventional CO2 absorption plant with capacity of treating CO2 from a 700 MW power plant is estimated to have a mass and plant area of 25,000 tonnes and 110mX110m, respectively. The treatment volume of exhaust gas from this plant is several times larger than the size of an optimal line in a CO2 recovery plant.