CCS post-combustion scrubbing

In the previous post on Carbon Capture and Storage (CCS), I outlined several processes for carbon capture including post-combustion scrubbing, pre-combustion decarbonization, and a technique where oxygen is separated from air and then burned with hydrocarbons to produce an exhaust with a high concentration of CO₂.

In this blog, I’d like to explore in a bit more detail the process of post-combustion scrubbing as a carbon capture technique.

Post-combustion scrubbing is considered the first step towards large-scale capture where CO₂ is removed from exhaust gas after combustion. This technology can typically be retrofitted to existing equipment in coal or heavy oil burning plants.

The CCS discussion has focused on pre-combustion capture of CO2, since it has been assumed that it is easier and cheaper than trying to capture the CO2 post-combustion from the flue gas (exhaust stream). However, a challenge in pre-combustion capture is that it is limited to newer plants supporting integrated gasification combined cycle (IGCC) technology which can be expensive to build and maintain.

In post-combustion, CO2 can be captured from exhaust gas after the fuel is burned, using solvent such as amines, in a process known as absorption. The CO2 is absorbed by the amines at particular temperatures and pressures and can be removed by varying the temperature and pressure. Most systems of this sort can achieve a CO2 recovery rate of up to 98%, with a purity of 99+%. However, at present, only a relatively small number of fossil fuel fired power plants in operation use amine scrubbers for CO2 capture and only a handful of potential suppliers have implemented their process for CCS at commercial scale.

While a promising short term process for CO2 capture, post-combustion scrubber-based systems require substantial capital equipment and overall plant efficiency can be negatively impacted. Solvent based scrubber systems also tend to work better where there are more concentrated CO2 exhaust streams combined with higher operating pressures.

In the next post, we will review pre-combustion decarbonization as a promising capture technology for CCS and look at some of it's application in our industry.

Kambiz.