Radiation and convective heat transfer, and burnout in oxy-coal combustion

Abstract

Measurements of radiative and convective heat transfer, and carbon-in-ash have been taken on the RWEn 0.5 MWth combustion test facility (CTF) firing two different coals under oxy-fuel firing conditions. A 0.5 MWth scaled version of an IFRF Aerodynamically Air Staged Burner (AASB) was used under oxy-fuel firing conditions using simulated dry recycled flue gas. The two coals fired were a Russian Coal and a South African Coal. Recycle ratios were varied within the range of 65–75% dependent on coal. Furnace exit O 2 values were maintained at 3% and 6% for the majority of tests. Air firing tests were also performed to generate baseline data. The work described in the main text gives a comprehensive insight into the effect of oxy-fuel combustion on both radiative and convective heat transfer, and carbon-in-ash compared to air under dry simulated recycle conditions. Results have shown peak radiative heat flux values are inversely related to the recycle ratio for the two coals studied. Conversely, the convective heat flux values increase with increasing recycle ratio. It was also observed that the axial position of the peak in radiative heat flux moves downstream away from the burner as recycle ratio is increased. It has been shown that a “working range” of recycle ratios exist where both the radiative and convective heat fluxes are comparable with air. Carbon-in-ash (CIA) was measured for selected conditions. For air firing of Russian Coal, the CIA for follows and expected trend with CIA decreasing with increasing furnace exit O 2. The CIA data for the two recycle ratios of 72% and 68% for the same coal show that the CIA values are lower than for air firing for corresponding furnace exit O 2 levels and vary little with the value of furnace exit O 2. CIA measurements were taken for the South African Coal for a range of recycle ratios at 3% and 6% furnace exit O 2 levels. Results indicate that the CIA values are lower for higher furnace exit O 2 as would be expected. There appears to be a marginal general decrease in CIA as recycle ratio increases but it is suggested that at these generally low levels of CIA (i.e. < 0.7%) it is difficult to be conclusive.