Oxy-fuel combustion of coal and biomass blends

Abstract

The ignition temperature, burnout and NO emissions of blends of a semi-anthracite and a high-volatile bituminous coal with 10 and 20 wt.% of olive waste were studied under oxy-fuel combustion conditions in an entrained flow reactor (EFR). The results obtained under several oxy-fuel atmospheres (21%O 2 -79%CO 2 , 30%O 2 -70% CO 2 and 35%O 2 -65%CO 2 ) were compared with those attained in air. The results indicated that replacing N 2 by CO 2 in the combustion atmosphere with 21% of O 2 caused an increase in the temperature of ignition and a decrease in the burnout value. When the O 2 concentration was increased to 30 and 35%, the temperature of ignition was lower and the burnout value was higher than in air conditions. A significant reduction in ignition temperature and a slight increase in the burnout value was observed after the addition of biomass, this trend becoming more noticeable as the biomass concentration was increased. The emissions of NO during oxy-fuel combustion were lower than under air-firing. However, they remained similar under all the oxy-fuel atmospheres with increasing O 2 concentrations. Emissions of NO were significantly reduced by the addition of biomass to the bituminous coal, although this effect was less noticeable in the case of the semianthracite.

Single particle ignition and combustion of anthracite, semi-anthracite and bituminous coals in air and simulated oxy-fuel conditions

“…Increasing the oxygen concentration to such values also led to shortened burnout times and temperature hikes, although they are less remarkable. These results are in agreement with previous studies carried out for other fuels with different experimental devices [10,30,31]. These observations have practical ramifications in the operation of future furnaces operating under oxy-coal combustion conditions.…”

Biomass co-firing under oxy-fuel conditions: A computational fluid dynamics modelling study and experimental validation

“…The experimental findings on burnout (defined in this study as the ratio of mass loss of a fuel sample during its combustion to the original mass of the fuel feed) and NO emissions have been reported in a previous paper on experimental study [12]. Here, the results were used to validate the CFD simulations, in order to evaluate the effect of biomass co-firing on burnout and NO emissions under various conditions and to establish the modelling capability for oxy-fuel combustion of biomass/coal blends.…”

“…Co-firing biomass with fossil fuels in existing utility boilers is also a feasible technology which can not only significantly reduce CO 2 emissions but also increase the share of renewable energy sources in energy co-firing under oxy-fuel is likely to bring up more uncertainties. Biomass co-firing under oxy-fuel conditions is an attractive option to simultaneously increase the use of renewable energy sources, exploit the favorable synergy effects of biomass/coal cofiring and achieve below-zero CO 2 emissions, which has been very little investigated so far [9][10][11][12]. For instance Smart et al [11] evaluated the impact of co-firing biomass on pollutant formation, burnout and heat transfer under oxy-fuel conditions in a 0.5 MWt combustion test facility.…”

“…For instance Smart et al [11] evaluated the impact of co-firing biomass on pollutant formation, burnout and heat transfer under oxy-fuel conditions in a 0.5 MWt combustion test facility. Experiments at laboratory scale have been focused on the effects of different co-firing ratios on burnout and NO emissions [12].…”

Biomass devolatilization at high temperature under N2 and CO2: Char morphology and reactivity

“…The speed of flame propagation and stability may decrease while the unburned carbon content may increase. During the oxy-fuel combustion process, these problems can be overcome by increasing the oxygen concentration in the oxidizer (up to approximately 30%) in order to match the combustion performance achieved in air in relation to the flame temperature, ignition time, heat transfer, gas temperature profile and char burnout [17]. This implies that the differences in reactivity found in the present work between the chars obtained in N 2 and CO 2 reflect to some extent their different morphological and structural characteristics.…”