When fuels are burned there remains, besides ash, a certain number of gas components. If these still contain combustion heat, they are called heating gases. As soon as they have conveyed their energy to the absorbing surfaces of a heat exchanger, they are called flue or stack gases.
Its composition depends on what is being burned, but it usually consists of mostly nitrogen (typically more than two-thirds) derived from the combustion air, carbon dioxide (CO2) and water vapor as well as excess oxygen (also derived from the combustion air).
Example of a typical Flue Gas composition from coal fired power plant
|
Component |
N2 |
CO2 |
O2 |
SO2 |
NOx |
Soot dust |
|
Concentration |
82% |
12% |
5.5% |
400 ppm |
120 ppm |
50 mg/m3 |
It
further contains a small percentage of pollutants such as particulate
matter, carbon monoxide, nitrogen oxides and sulfur oxides.
Carbon dioxide (CO2)—the primary greenhouse gas responsible for global warming—along with other pollutants.
The algae uses Photosynthesis to combine water and the CO2
in the flue gas to grow additional algae and form oxygen and water
vapor. The organisms also absorb nitrogen oxide and sulfur dioxide,
which contribute to acid rain.
The
research Academy of Sciences of the Czech Republic and Fuel Research
Institute conducted a research on the Utilization of flue gas for
cultivation of microalgae Chlorella spp., in an outdoor open
thin-layer photobioreactor. In this, Flue gas generated by combustion
of natural gas in a boiler was used for outdoor cultivation of
Chlorella sp. in a 55 m2 culture area photobioreactor. It
was estimated that about 50% of flue gas decarbonization can be
attained in the photobioreactor.
