“We’re running the most dangerous experiment in history right now, which is to see how much carbon dioxide the atmosphere… can handle before there is an environmental catastrophe.” |
Elon Musk |
As carbon dioxide emission become more and more severe for the global atmosphere, emission reduction technologies emerge such as MEA-based carbon capture technology, electric car, low-carbon civil design, etc. Use of microalgae to sequestrate carbon emission from power plant has been proposed ten years ago. However, due to the unavailability of land resource in close proximity to emission outlet of power plant and inaccessibility of power generation group, this technology has not been well commercialized in the states. Some studies from US Department of Energy sponsored projects suggest that microalgae can grow in the feed of power plant flue gas and effectively absorb the carbon dioxide, SOx, NOx from the emission.
The prior requirement for microalgae-based carbon sequestration is the close proximity to power plant, less than 2.5km based on Dr. John Benemann’s report. Secondly, a 10M MWh coal-fired power plant usually emit about 10M tons CO2, which requires a super-large area of cultivation area that usually individual cannot afford. Finally, in order to duct power plant flue gas, pre-cast concrete pipes which connect the power plant gas outlet with the algae cultivation plant are built, where the distance are no further than 2.5km.
Figure 1. Pre-cast concrete pipe can be ducted from power plant outlet to deliver flue gas to the cultivation system
In the algae cultivation site, due to the heat in the flue gas from power plant, a cooling system are needed to reduce the temperature which carried by the flue gas. The heat which are captured by the cooling system can be exchanged into downstream process such as drying and HTL. After cooling, gases are delivered to a liquid interface that could effectively absorb the CO2, SOx and NOx component, and then the CO2-rich liquid are pump into the circulating system and start to feed into each cultivation system.
Figure 2.
A study funded by US Department of Energy shows that use of flue gas from power plant could grow microalgae in the industrial scale and concludes that:
- Microalgae are able to capture anthropogenic CO2 from a wide variety of simulated flue gases and from actual coal and propane combustion gases
- Microalgae are able to capture anthropogenic CO2 under a wide variety of pH and gas concentrations
- The efficiency of CO2 capture by microalgae is directly dependent on the pH of the culture but is not affected by differences in gas composition
- The process is scalable to industrially significant scales
Figure 3. Gas analysis of coal combustion gases before (IN) and after (OUT) passage through the pilot scale photobioreactor.