To limit global warming to 1.5 to 2°C and at least mitigate the negative effects of climate change, the European Climate Act 2021 enshrined in law the target of reducing anthropogenic greenhouse gas emissions to net zero by 2050. A significant contribution to this target must be made in the case of fossil fuel fired power plants, which are among the largest point sources of CO2. This requires at least short- and medium-term measures to retain and store the CO2 produced during these combustion processes.
The most technically advanced process for retaining this CO2 is an amine scrubbing process for downstream capture from the flue gas. However, this requires further optimization for a comprehensive application, especially regarding CO2 avoidance costs. The use of a spray scrubber for the absorption process instead of a packed column, which has so far been little studied, can make a significant contribution to this due to the lower investment and operating costs and additional process advantages.
Within the scope of this work, the rate of absorption of CO2 by individual falling absorbent droplets is measured in a specially developed test setup. By varying the relevant process parameters such as CO2 partial pressure, loading of the absorbent and droplet size, data is obtained for various absorbents that enable a rough dimensioning of a spray scrubber for large-scale applications. At the same time, important insights into the influence of the individual process parameters on the efficiency of the spray scrubbing process are gained.
The required height of the spray scrubber is considered as major criterion for the economic feasibility. For an idealized spray scrubbing process with the absorbent monoethanolamine 30 weight-%, which was investigated as a reference case, and absorbent droplets with a diameter of 2 mm, the result is a required height of 33 m. While this already clearly indicates good economic feasibility, the results show further optimization potential, for example by absorbent selection or adjusting the range absorbent loading. The drop size is shown to be a decisive influencing factor, whereby smaller drops lead to an overproportionate reduction in the required height.
For an even more precise dimensioning of the spray scrubber, further investigations should consider real droplet size distributions and the heating due to the reaction enthalpy.