Process of Algae-based CO2 Capture

Of the stationary sources of carbon dioxide emission, power plant emissions constitute more than 50%, of which the principal emitters are coal-based power plants. Algae thrive on a high concentration of carbon dioxide and nitrogen dioxide (NO2), a pollutant of power plants, is a nutrient for the algae. Algae production facilities can thus be fed exhaust gases from fossil fuel power plants to significantly increase productivity and clean up the air.

Conceptually, algae cultivation near power plants is fairly simple. The idea is to pipe the flue gas from the exhaust to the open (eg. ponds) or closed (e.g. photobioreactors) algae cultivation systems which are preferably located nearby the power plant.

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To capture the carbon given off by coal‐fired power plants, existing plants must be retrofitted, and newly designed plants must incorporate carbon capture into the exhaust scrubbing system.

Integrating power plant design with algal carbon capture could be a means of controlling emissions and capturing SOx, NOx and heavy metals such as mercury (Hg) and perhaps additional contaminants from the flue stream.

Peer reviewed research articles

  • Effect of cultivation mode on microalgal  growth and CO2 fixation (Zhao et al. 2010) - Read more
  • Biological sequestration of carbon dioxide  from thermal power plant emissions, by absorbtion in microalgal culture media  (Velea et al. 2009) - Read more
  • Simultaneous flue gas bioremediation and reduction  of microalgal biomass production costs (Douskova et al., 2008) - Read more

    Moreclick here

 

The algae-based carbon capture involves the following steps:

 

Step 1 - In the process, flue gas is withdrawn from a power plant unit and transported through pipes to the microalgae production plant.


Step 2- Flue gases from electric power stations emit CO2, NOx and other gases and substances. It can be extremely toxic to algae because of the presence of H2 and SO2 reference. Flue gases are subjected to desulphurization or FGD reference. SO2 can undergo wet scrubbing with limestone to produce CaSO3 which is then used to produce gypsum


Step 3 -The flue gas downstream of the FGD contains a high percentage of water vapour however, so the gas is dried before propelled with the aid of a fan through a pipe to the greenhouse.



Step 4 - The exhaust gas is cooled before it reaches the capture process itself in order to optimise the process. The flue-gas cooler is the largest consumer of cooling water in the process, typically using 50% of the cooling water.


Step 5 -  Propeller propels the flue gas to the aerator and the flowmeter monitors the flow rate of flue gas.


Step 6 - Appropriate proportion of flue gas and air are mixed and pumped in to the algae feeding vessel.


Step 7 -  In the feeding vessel algae culture, required water, nutrients and also the air mixed with flue gas are added. The contents of the feeding vessel after going through a process of QC are pumped in to the photobioreactor.

Schematic Sketch of Algae-based CO2 Cultivation Near Power plants

Step 8 : Photobioreactor facilitates mixing and provides optimal environment for algae growth. Mixing is necessary to prevent sedimentation of the algae, to ensure that all cells of the population are equally exposed to the light and nutrients, to avoid thermal stratification (e.g. in outdoor cultures) and to improve gas exchange between the culture medium and the air.

Step 9:  After reaching the considerable cell density, the algae are harvested from the photobioreactor by pumping more medium (water + nutrients).

Step 10:     High-density algal cultures can be concentrated in the dewatering and harvesting unit by either chemical flocculation or centrifugation. Products such as aluminum sulphate and ferric chloride cause cells to coagulate and precipitate to the bottom or float to the surface. Recovery of the algal biomass is then accomplished by, respectively, siphoning off the supernatant or skimming cells off the surface.

 


Step 11: The algal slurry is then transported to the drying unit.


Step 12:   In drying unit the algae are dried either by using solar dryer or the waste heat generated from the power plant.


Step 13:  The dried biomass is processed further to obtain the desired product

Each step involved in the process has been explained in detail in the subsequent pages