The Effect of Oxygen Staging on Nitrogen Conversion in Oxy-Fuel CFB Environment

Abstract

This paper presents a study on nitrogen conversion in oxy-fuel coal combustion in a pilot scale CFB 0.1 MW th facility. The paper is focused on fuel-N behaviour in the combustion chamber when the combustion process is accomplished under oxy-fuel CFB conditions. The analysis is based on infurnace sampling of flue gas and calculations of the conversion ratios of fuel-nitrogen (fuel-N) to NO, NO 2 , N 2 O, NH 3 and HCN. For the tests, O 2 /CO 2 mixtures with the oxygen content of 21 vol.% (primary gas) and with the oxygen content varied from 21 to 35 vol.% (secondary gas), were used as the fluidising gas. Measurements were carried out in 4 control points located along the combustion chamber: 0.43 m, 1.45 m, 2.50 m and 4.88 m. Results presented below indicate that an increased oxygen concentration in the higher part of the combustion chamber has strong influence on the behaviour of fuel based nitrogen compounds.

Inner Relationship between CO, NO, and Hg in a 6 kWth Circulating Fluidized Bed Combustor under an O2/CO2 Atmosphere

“…Fuel NO x was the main source of NO x under the circulating fluidized bed combustion, and fuel N will be mainly thermal decomposition into NH 3 and HCN and other intermediates . As Figure shows, with the increase of the oxygen concentration in the oxygen-enriched combustion, the NO concentration increases, which is consistent with the former reports. , As a result of the same heat input during the oxy-coal combustion, as the oxygen concentration increased, the flue gas volume decreased . Therefore, NO emissions decreased.…”

“…16 As Figure 7 shows, with the increase of the oxygen concentration in the oxygen-enriched combustion, the NO concentration increases, which is consistent with the former reports. 38,39 As a result of the same heat input during the oxycoal combustion, as the oxygen concentration increased, the flue gas volume decreased. 15 Therefore, NO emissions decreased.…”

Ash and Flue Gas from Oil Shale Oxy-Fuel Circulating Fluidized Bed Combustion

“…Our experiments showed that switching to oxy-fuel combustion did not alter the NO x emissions. The nitrogen conversion ratio to NO x was up to 24%, similar to results from Jankowska et al [32] with bituminous coal (20-25%). However, Pikkarainen et al [33] measured higher nitrogen conversion ratios (28-50%).…”

“…One advantage of oxy-fuel technology is its potentially lower NO x production. Results from different experimental facilities are rather diverse [18,[29][30][31][32][33]. Overall, the results indicate that nitrogen behavior in the oxy-fuel mode is similar to combustion in air and no drastic changes are expected in fuel nitrogen conversion to oxides.…”

Analysis of the Transition Time From Air to Oxy-Combustion

“…Moreover, the process can decrease emissions of gaseous pollutants, especially if nitrogen oxides (NOx) are taken into account (Jankowska et al, 2014;Toftegaard et al, 2010) Currently, the application of oxy-fuel technology in big-, industrial-scale is still being discussed and considered. The construction of new oxy-fuel boilers is taken into account, although retrofitting an existing power plant to an oxy-firing system (Fei et al, 2015;Fry et al, 2011) provides another solution.…”