Study of Oxy-fuel Coal Combustion in a 0.1 MW_th Circulating Fluidized Bed at High Oxygen Concentrations

Abstract

The combustion and emission characteristics under three kinds of firing modes [O 2 /N 2 , O 2 /CO 2 , and O 2 / recycled flue gas (RFG)] at high oxygen concentrations were investigated in a 0.1 MW th circulating fluidized-bed combustion system. The 0.1 MW th circulating fluidized-bed combustion unit was built in 2010 and retrofitted to use RFG in 2012, which was specially designed for combustion at high oxygen concentrations (up to 55%). The experimental results showed that CO 2 concentrations in the flue gas reached a maximum of 93% when the overall oxygen concentration was in the range of 46.4−54.6% during the combustion. Under the O 2 /RFG firing mode, the CO concentration dropped from 803.4 to below 100 mg/MJ with the increase of the concentration of oxygen in the flue gas from 1.1 to 7.5%. The fuel N to NO conversion was in the range of 3.5−4.6% under the O 2 /RFG firing mode, which was much less than that observed under the O 2 /N 2 mode (8.1−8.4%) and O 2 / CO 2 mode (6.5−7.6%). The limestone utilization in the O 2 /RFG firing mode was found to be much lower than that for both O 2 /N 2 and O 2 /CO 2 modes. Sulfur capture efficiencies were 70.2 and 93.7% under O 2 /RFG and O 2 /N 2 firing mode conditions, respectively, with a Ca/S molar ratio of 2.2. An increase in the Ca/S molar ratio to 3 resulted in sulfur capture efficiencies of 83.9% under the O 2 /RFG firing mode.

A review of oxy-fuel combustion in fluidized bed reactors

“…Although other authors observed that even though NOx concentration is higher for oxy‐fuel combustion, fuel‐N conversion to NOx is generally lower under oxy‐fuel than air combustion. Conversely, Li et al found that both NOx concentration and fuel‐N conversion were lower under oxy‐fuel. The operating condition of these studies are typically the same, with operating temperatures ranging from 850 to 950 °C and at an average O 2 oxidant concentration of 21%.…”

Three-Dimensional Eulerian–Eulerian Simulation of Coal Combustion under Air Atmosphere in a Circulating Fluidized Bed Combustor

“…Nowadays, it is still under rapid development and has been experimentally studied in the chemical, energy, and environmental industries for applications − such as fluid catalytic cracking (FCC), fuel combustion and gasification, as well as pollutant emission reduction. Besides, with the increasing concerns about global warming, it is also a promising method for CO 2 capture when combined with the O 2 /CO 2 combustion technology. − …”

Combustion Characteristics and Pollutant Emissions in Transient Oxy-Combustion of a Single Biomass Particle: A Numerical Study

“…Increasing the excess air resulted in an increase in NO emissions, while NO emissions decreased with increasing the scale of the air staging. Li et al 22 ,…”

“…Increasing the excess air resulted in an increase in NO emissions, while NO emissions decreased with increasing the scale of the air staging. Li et al, 22 Duan et al, 23 and Daood et al 24 reported that NO emissions are much lower in oxy-fuel combustion than in air combustion. Shao et al 25 found that the average NO x concentration increased along with increasing oxygen concentration, and the maximum value and peak shape of the NO x concentration curve changed with temperature.…”