Experimental and Kinetic Study on the Influence of Iron Oxide on the Selective Noncatalytic Reduction DeNO_x Process

Abstract

The influence of Fe 2 O 3 on the SNCR deNO x process was investigated in a fixed-bed reactor. The experimental results demonstrated that Fe 2 O 3 has an inhibitory effect on the SNCR deNO x process that is more notable at low temperatures. Interactions between Fe 2 O 3 and NH 3 , Fe 2 O 3 -catalyzed NH 3 oxidation, and NO reduction by NH 3 were studied experimentally. In the absence of O 2 , Fe 2 O 3 was reduced by NH 3 to form Fe, which then catalyzed NH 3 decomposition to N 2 and H 2 . Fe 2 O 3 also catalyzed NO reduction by NH 3 . In the presence of O 2 , Fe 2 O 3 mainly catalyzed NH 3 oxidation. All reactions showed first-order characteristics with respect to NH 3 , which indicates that the adsorption of NH 3 and its dissociation into −NH 2 on the surface of Fe 2 O 3 is the rate-controlling step in these processes. The presence of O 2 and NO affected the selectivity of further −NH 2 reaction. A kinetic model was developed, and the simulation results agreed well with the experimental data.

Experimental Investigation into NO Removal over Circulating Ash in Selective Noncatalytic Reduction during Circulating Fluidized Bed Combustion

“…Tests were carried out to investigate its effects on the characteristics of NO removal over circulating ash (series 1 in Table ). The tendencies of NO concentrations in NH 3 -SNCR with circulating ash are provided in Figure a, and the previous results over iron oxide and CaO are also listed for comparison. It was found that the changes of NO concentrations over circulating ash obtained in the present study were similar to those over iron oxide and CaO particles reported in previous studies, which indicated that the circulating ash exhibited significant catalytic effects on NO removal in the NH 3 -SNCR process.…”

“…Then, these precursors could dissociate to NO in the gas phase as eq , resulting in the catalytic oxidation of NH 3 over circulating ash. Besides, part of the NH 2 adsorbed species could also react with the gaseous or adsorbed NO species, as eq to eq , leading to the reduction of NO especially at high temperatures. According to the results in the present study, compared with the homogeneous gas-phase reactions, the presence of circulating ash could dominantly enhance the catalytic oxidation of NH 3 adsorbed species (NH 2 intermediates) to generate the precursors of NO, resulting in the suppression of NO reduction in the NH 3 -SNCR process. …”

“…16 Na and K were the positive additives to widen the "temperature window", 17 but the influences of Fe-based additives were contradictory in previous studies. Lissianski et al 18 and Daood et al 19 suggested that the application of iron additives could significantly enhance the reduction between NO and gaseous reductants (CO, CH 4 , and NH 3 ), while Fu et al 20 stated that iron oxide exhibited a negative effect on NO removal with NH 3 .…”

A Mass-Transfer Model of Nitric Oxide Removal In a Rotating Drum Biofilter Coupled with FeII(EDTA) Absorption

“…2−4 A number of processes for the removal of nitrogen oxides (NO x ) emitted from stationary combustion facilities have been developed, such as selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR). 5,6 However, SCR requires expensive catalysts, SNCR requires high temperatures, (i.e., increased process costs). In addition to the dry denitrification above, there are also wet denitrification such as oxidation denitrification 7 and complexation reduction denitration.…”

“…The nitrogen oxides (NO x ) are mainly produced by industrial production and vehicle exhaust. , NO x and its secondary pollutants induced by NO x such as photochemical smog, acid rain, ozone hole, and PM 2.5 , are harmful to the human health. − A number of processes for the removal of nitrogen oxides (NO x ) emitted from stationary combustion facilities have been developed, such as selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR). , However, SCR requires expensive catalysts, SNCR requires high temperatures, (i.e., increased process costs). In addition to the dry denitrification above, there are also wet denitrification such as oxidation denitrification and complexation reduction denitration. , And all of these processes require the continuous addition of oxidizing agents or reducing agents to maintain the denitrification efficiency.…”