Promotion of CO Oxidization and Inhibition of NO Formation by Gaseous Iron Species during High-Temperature Off-Gas Combustion

Abstract

The promotion of CO oxidization and inhibition of NO formation by gaseous iron species were analyzed using the Sandia SENKIN program. It is shown that the relative ratio of CO oxidization dramatically varies with combustion time at early burning stage in the presence of iron species, and all peak values are greater than 2.4. The relative ratio of CO oxidization decreases with the increase of air stoichiometric ratio and CO concentration in off-gas. The circulation reactions of Fe-FeO/FeO 2 -Fe achieve the catalytic effect on CO oxidization. Gaseous iron species can greatly inhibit NO formation, NO reduction ratio can reach above 70% at T = 2073 and 2273 K, and gaseous iron species can effectively inhibit NO formation when combustion temperature is not higher than 2273 K during the off-gas combustion. There are O 2 competitive reactions between thermal NO formation and Fe oxidization, and high chemical activity of iron species inhibits thermal-NO formation. INTRODUCTIONA large amount of high-temperature off-gas is produced during oxygen converter steelmaking, the major compositions of off-gas are CO and CO 2 , CO concentration varies from 15 to 70%, and off-gas temperature can reach 1900 K. 1 In the meantime, off-gas entrains a large amount of fine dusts (Fe, FeO, Fe 2 O 3 , etc.) and the amount of the dusts entrained by off-gas is about 80-150 g/m 3 . 2 The high-temperature off-gas is a precious valuable fuel. It is often discharged into the cooling stack to be combusted, and the peak temperature of flame can reach above 2000°C where CO 2 may decompose and NO x is significantly formed. 3 CO emission concentration can reach above 2000 mg/m 3 which is always over emission standards (300 mg/m 3 in China). 4,5 CO is a toxic gas which is dangerous to human health. High CO emission results in not only atmospheric pollutant but also fuel loss. NO x is a known precursor to the formation of ozone and acid rain, and it can react with volatile organic compounds to form photochemical smog. 6 Iron oxide catalyst is widely used either as single metal oxide or as a mixed oxide in industrial processes, and iron oxide exhibits intermediate activity in the complete oxidation of methane and carbon monoxide. 7-9 NO reduction by iron species has been studied in fluidized bed, and the results indicate that iron or its oxides cause a chemical reduction of NO in the presence of CO. 10 It has been discovered that injection of iron-containing compounds into the combustion and reburning zones of conventional gas-and coal-fired combustors can increase the efficiency of NO x reduction by up to 20% in comparison with that which can be achieved by basic reburning. 11 During the combustion of high-temperature off-gas entraining a large amount of dust containing iron and iron oxides, gaseous iron species is present at T > 2073 K, and it has effects on CO oxidization and NO formation. A detailed chemical kinetic mechanism for gaseous iron-species inhibition of flames, iron pentacarbonyl (Fe(CO) 5 ) mechanism, has been introduced, 12 and modeling ...

Analysis of the Impact of Using Catalytic Additives to Fuel on Exhaust Emissions from a Diesel Engine

“…Consequently, the heat transfer to the unburned fuel is increased by a higher flame temperature, which results in a higher burning rate and a shorter burning time. The findings are consistent with the literature based on observation, which was the grounds for arguing that a small number of iron atoms in a flame can promote ignition and hydrogen burning rate [33,34], CO [35] and methane [36].…”

NO reduction by CO over a Fe-based catalyst in FCC regenerator conditions

“…Iron oxide catalyst is widely used either as single metal oxide or as a mixed oxide in industrial processes, and iron oxide exhibits intermediate activity in the complete oxidation of CO [36][37][38]. The utilization of iron for reducing NO has also been suggested [39].…”

Kinetic Modeling Study of the Effect of Iron on Ignition and Combustion of n-Heptane in Counter-flow Diffusion Flames

“…A detailed kinetic mechanism proposed by Rumminger et al for gas-phase iron species was also employed in the present simulations. This mechanism has been validated in methane, carbon monoxide, and hydrogen combustion. The combined mechanism of n -heptane and the gas-phase iron species is provided in the Supporting Information.…”

“…Diesel ignition and combustion in CI engines are characterized by rich premixed ignition and subsequent premixed combustion, followed by diffusion combustion . The effect of iron in premixed combustion of hydrocarbon fuels has been studied and reported in the literature. − Therefore, the present kinetic modeling approach included two parts, an idealized premixed ignition model and an opposed counter-flow diffusion flame model. Because of the complex composition of real diesels, n -heptane ( n -C 7 H 16 ) was chosen as a model fuel because it has a similar cetane number to diesel and has also been frequently used as a diesel fuel surrogate …”

“…In addition to the studies on the performance of the catalyst in diesel engines, as shown in Table , there have been few studies with an effort to understand working mechanisms of organometallic-based catalysts in the ignition and combustion processes of different fuels recently. Iron pentacarbonyl [Fe­(CO) 5 ] was shown to accelerate ignition and combustion of CO, H 2 , and hydrocarbons. − Staude et al measured the temperature profiles in a premixed lean laminar flame of H 2 /O 2 /Ar with Fe­(CO) 5 added and found that the addition of Fe­(CO) 5 increased the flame temperature throughout the combustion zone. Shvartsberg et al numerically modeled hydrogen flames at a low pressure of 3 kPa and found that the addition of iron to the flame resulted in additional heat release and higher flame temperatures.…”