Unit 4 - Carbon Capture and Storage Flashcards
What are the problems with taking CO2 directly from the air?
CO2 is relatively dilute and so capturing CO2 from air will require moving large amounts of air. This is very heavy and therefore energy intensive.
What features must be in a CCS device?
It must have a very high selectivity - some porous materials are very selective in the absorption of CO2.
The absorption needs to be unaffected by the presence of water or pollutants in the air.
The materials must be cheap.
Where does CO2 come from?
Burning fossil fuels (transport, power generation and space heating).
Industrial processes:
* making cement (CaCO3 → CaO + CO2)
* making hydrogen (CH4 + 2H2O → 4H2 + CO2)
* making steel (2Fe2O3 + 3C → 4Fe + 3CO2).
‘Natural Sources’ (fermentation processes, peat deposits that dry out when rainforests are cut down).
What are the two types of CO2 source?
Moving (planes, cars, lorries)
Fixed (factories, power stations)
What often needs to occur before CO2 is captured?
It needs to be separated from other components.
For example, if combustion occurs in air, it needs to be separated from nitrogen and water vapour.
What are the basic steps for carbon capture and storage?
1) Capture and purify the CO2.
2) Compress and transport the CO2.
3) Find somewhere to store it.
Where can CO2 be stored?
Somewhere with space underground/undersea.
Depleted gas fields, abandoned mines and coal deposits are suitable locations.
What pressure is CO2 intended to be transported at?
> 100 atmospheres but this requires lots of energy.
What is a problem if the CO2 isn’t dried before being transported?
To ensure the pipelines are cheap, poor quality steel is used but this is susceptible to corrosion. This can lead to leaks and as CO2 is denser than air, it can accumulate in low lying areas and suffocate people.
What is an example of the problems with CO2?
Lake Nyos in Cameroon.
Volcanic CO2 was emitted following an earthquake/landslide and this flowed down the valley and caused many casualties.
What is ‘blue ammonia’ and how does it differ to ‘grey ammonia’?
The first step in the production of ammonia is steam reforming of methane to generate hydrogen. This releases CO2.
‘Blue ammonia’ is where the CO2 is captured and stored but ‘grey ammonia’ is where the CO2 is not captured or stored.
How can the same approach as ‘blue ammonia’ be applied to power generation?
1) Carry out steam reforming of methane.
2) Separate the hydrogen from the CO2 which is sent to CCS.
3) Burn the hydrogen to make electricity.
The problem is that hydrogen produces less energy than burning methane.
What is ‘oxyfuel’?
The oxygen is separated from air and methane is burned in pure oxygen. The water is then separated from the CO2 which is ready for CCS.
What is a problem and a solution to oxyfuel?
Burning methane in oxygen requires a very high temperature flame.
The solution is to recycle some of the CO2 into the combustion to cool the flame.
What are the two strategies for power stations burning in air?
The CO2 produced needs to be separated from the nitrogen and water vapour.
Strategy 1: Reversible solid absorbents. These materials need to be inexpensive and long lived. Examples include activated carbons, metal organic frameworks and zeolites. The CO2 is released by heating the solid.
Strategy 2: A liquid absorber can be used. For example, amines. This is a reversible reaction to form carbamates (RNH2 + CO2 → RNH-CO2H)
They are both relatively energy expensive and results in a decrease in efficiency of 10% (50% → 40%)
