5. CCS Flashcards
What are the three main CCS processes and which technologies suit each?
- Post Combustion Capture - High T, Low P, lends itself well to chemical absorption, MEA.
- Oxy-Fuel Combustion - High T, low P, rich CO2 stream allows easier separation. MEA or Gas Membrane Absorption.
- Pre Combustion - Low T, High P, lends well to physical solvents such as Rectisol or Selexol
Draw MEA absorption / scrubbing process.
Sketch
Why is MEA a good solvent?
- Contains an amine and hydroxyl group.
- Amine is basic, reactive site to absorb CO2.
- Hydroxyl group reduces vapour pressure, increases solubility.
Draw Pre-Combustion process.
Sketch
Explain how Pre-Combustion works in conjunction with WGS.
Pre-combustion uses gasification and pyrolysis to produce syngas, CO and H2. The H2 is removed as fuel, CO2 undergoes WGS producing H2 and CO2. These can be separated using gas separation membrane due to drastically different sizes.
What are conditions for WGS?
- 300-400 C, iron-chromium catalyst.
Define Henry’s Law.
At constant temperature, the amount of given gas dissolved in liquid is directly proportional to partial pressure of gas in equilibrium with the liquid.
Why may solid adsorpants be good? What are the challenges?
- Low re-generation energy.
- Potentially very high CO2 uptake.
- Must have high capacity, good stability, physical resistance and reasonable cost.
Define the two types of membrane separation.
- Gas Separation relies on size difference.
- Gas Absorption allows membrane to act as physical barrier between flue gas and absorption fluid.
How is CO2 transported?
- Transported as a supercritical fluid, can be pumped like a liquid, and has a low resistance to flow, like a gas.
Name the common CO2 storage possibilities. Outline each.
- Depleted oil and gas reservoirs.
- Unmineable coal seams.
- Saline aquifers.
What does geological storage depend on?
- Porosity
- Depth
- Permeability
Assess methods of CO2 trapping from a high level.
- After CO2 injected, it will rise and spread due to its buoyancy.
- Initially must be trapped structurally (cap-rock).
- Residual trapping by capillary blockage will slow the spread of CO2.
- Over time CO2 becomes trapped as solid carbonate minerals.
What are common CCS concerns?
- Will it contaminate drinking water?
- Will it leak and poison atmosphere?
- Can it cause earthquakes?
- How long will it remain in place?
What are barriers to CCS development?
- Lack of commitment.
- Lack of CO2 pipeline.
- High energy costs.
- Absence of rules for saline stoarge.
