From O2/CO2 to O2/H2O combustion: The effect of large steam addition on anthracite ignition, burnout and NOx formation

Abstract

Steam-moderated combustion has been proposed to supress flue gas recycling in oxy-fired units, but the influence of replacing CO2 by H2O has to be deeply studied. In this paper, oxy-fuel combustion of anthracite with large steam addition has been experimentally characterized, and main results are discussed as concerns the influence upon the ignition temperature, the burnout and the NOx formation. The tests have been carried out in an electrically-heated entrained flow reactor for a set of O2/CO2 and O2/H2O/CO2 atmospheres, with steam addition up to 40 % vol. The results show that ignition temperature diminishes when steam is added in low rates (maximum decrease of 16 ºC), but the trend is reversed for the higher steam concentrations (maximum increase of 18 ºC). The effect of steam addition on coal burnout rates is more significant for the 21 % vol. O2 atmosphere, with a decrease of 2.2-5.3 percentage points, and almost negligible for the 35 % vol. O2. An outstanding reduction of NO specific emissions is detected when adding H2O, with decrements ranging 28-45 % compared to the dry conditions. The transition from O2/CO2 combustion to O2/H2O combustion barely affects the anthracite conversion but significantly diminishes NOx formation rates.

Oxy-steam combustion: The effect of coal rank and steam concentration on combustion characteristics

“…When oxygen concentration is augmented from 21% to 35%, the trend is the same but the evolution is flattened with softer temperature variations. The effect of the steam is attenuated under high O2 concentrations, which is consistent with previous experiences [4,8]. In comparison to the dry O2/CO2 atmospheres, a 40% CO2 replacement by H2O barely affects the ignition temperature, with maximum differences of 6 K.…”

“…Finally, a continuous emission monitoring system provides the flue gas composition at the cold-end section: non-dispersive infrared sensors for CO2, CO SO2, NO, and paramagnetic sensor for O2. A more detailed description of the facility can be found elsewhere [8]. The effect of oxygen concentration (21 and 35% O2) and steam addition (0, 10, 25 and 40%) over the ignition temperature has been experimentally assessed for the two selected coals (SA bituminous and CB sub-bituminous).…”

“…A third coal is also included for comparison purposes: high-rank anthracite, which was tested in the same facility and under the same conditions. Details about those tests and specific results can be found in reference [8]. As seen in the Figure 7, the higher the coal rank, the larger the influence of steam in reducing NO formation rates: maximum reductions of 45% in the case of the anthracite, and 24% in the case of the SA bituminous coal.…”

Effect of O2 concentration on combustion behavior and kinetics of coal gangue during oxy‐fuel combustion and oxy‐steam combustion

“…Here, it should to be pointed out that the (dW/dt) max in O 2 /H 2 O atmosphere was higher than that in O 2 /N 2 atmosphere at 5% O 2 concentration, which may be attributed to that the (dW/dt) max depended on the combination of oxidation reaction and gasification reaction at low O 2 concentration (i.e., high H 2 O concentration), and gasification reaction occurred accelerated the overall carbon consumption 12 . From all above, we found that with the increasing of O 2 concentration, the contribution of oxidation reaction to carbon consumption rate increased, and this made the proportion of gasification reaction negligible, which is just coinciding with the result of the literatures 34 …”

Effect of Co-combustion of Multiple Additives with Coal on NO Removal

“…Energy is produced through the combustion of coal, and nitrogen oxides (NO x ) are the main air pollutants produced in the process. 1 Currently, the main technologies for reducing NO x emissions are flue gas denitrification and low-NO x combustion technology. 2 The technology and equipment required for low-NO x combustion are not yet ready for comprehensive application.…”