The vital issue is how much it will cost to remove the CO2. Already there are indications this has been cut from around $US60 to $US28 a tonne, and the global race is on to slash the cost further.
The CO2CRC is exploring a range of different technologies, including extraction of CO2 using solvents, membrane filters, pressure swing adsorption and carbon absorption, according to Hopper.
Solvents used to extract CO2 can be chemical (such as amines) or physical (for example, carbonates). The flue gas is pumped through a packed column and CO2 is preferentially absorbed by the solvent. The “loaded” solvent can then be processed to release pure CO2 for sequestration or other uses. The team is exploring various combinations of solvent, pressure and temperature to identify the most economical.
Membrane filters technologies being explored include the use of novel polymeric and ceramic membranes to “filter” the CO2 out of waste streams, and membrane/solvent combinations. Research is also underway to achieve high-temperature operation.
Pressure swing absorption involves using solid absorbents which absorb CO2 from waste streams and then, in a controlled way, release it in response to pressure, temperature or electrical stimulus. The CRC is testing new cycle designs to identify the most economical method.
Carbon absorption involves using carbon deposited in a sponge-like structure to preferentially absorb CO2 from exhaust streams containing nitrogen occurring in either air blown gasifiers or gas-to-liquid processing and low-temperature removal using hydrates and cryogenics. The CO2 is purified and concentrated at temperatures around minus 40C. The research is exploring technologies used in the gas industry for potential application in CO2 capture.
