Nitrogen Oxides, Sulfur Trioxide, and Mercury Emissions during Oxy-fuel Fluidized Bed Combustion of Victorian Brown Coal

Abstract

This study investigates, for the first time, the NOx, N2O, SO3, and Hg emissions from combustion of a Victorian brown coal in a 10 kWth fluidized bed unit under oxy-fuel combustion conditions. Compared to air combustion, lower NOx emissions and higher N2O formation were observed in the oxy-fuel atmosphere. These NOx reduction and N2O formations were further enhanced with steam in the combustion environment. The NOx concentration level in the flue gas was within the permissible limit in coal-fired power plants in Victoria. Therefore, an additional NOx removal system will not be required using this coal. In contrast, both SO3 and gaseous mercury concentrations were considerably higher under oxy-fuel combustion compared to that in the air combustion. Around 83% of total gaseous mercury released was Hg(0), with the rest emitted as Hg(2+). Therefore, to control harmful Hg(0), a mercury removal system may need to be considered to avoid corrosion in the boiler and CO2 separation units during the oxy-fuel fluidized-bed combustion using this coal.

A review of oxy-fuel combustion in fluidized bed reactors

“…Furthermore, NOx emissions were found to increase with the increasing O 2 concentrations in feed gas, which is as a result of an increase in particle temperature, thus enhancing NOx conversion. On the contrary, N 2 O formation was found to be greater under oxy‐combustion conditions than in air combustion; nonetheless, it was observed to decrease with an increase in bed temperature . Experimental results also showed that the addition of steam and maintaining a fixed O 2 concentration in the furnace promotes further NOx reduction and increase N 2 O formation .…”

“…NOx emissions from CFB combustion have been found to be typically less than half those from bubbling beds with similar fuels and operating temperatures . Experimental results in FB boilers showed that NO emission in oxy‐combustion is lower than that under air‐firing atmosphere, because of the lower temperatures as well as higher char and CO concentrations in the dense bed, which was common for several literature sources . The lower amount of NOx formation in Oxy‐fuel FB combustion can also be attributed to the absence of nitrogen in the oxidant feed.…”

“…Several research groups have investigated parameters influencing carbon conversion under oxy‐FB conditions . The evaluated factors influencing char burnout includes but is not limited to: O 2 feed concentration, temperature, fuel properties, particle size and loading and recycled flue gas.…”

“…Roy et al also studied the effect of O 2 concentration on oxy combustion and observed that CO 2 concentration in the flue gas increased with an increase in the inlet O 2 . Duan et al and Czakiert et al also found that combustion efficiency increase with feed O 2 concentration; the increase in the combustion rate was attributed to the increase in O 2 partial pressure.…”

Influences of activation agent impregnated sewage sludge pyrolysis on emission characteristics of volatile combustion and De-NOx performance of activated char

“…In addition, more N 2 O was emitted because the added KOH raised the pH of the sludge and various intermediate products, such as NH 2 OH and NO 2 À -N, were released into the volatile to form N 2 O [34]. However, N 2 O formation can be prevented by increasing the combustion temperature during the combustion [35]. The curves of NOx release as a function of the pyrolysis temperature were almost equivalent to those of NO as NO represented the major portion of NOx (Fig.…”