Reduction and removal of SO₂ and NO_x from simulated flue gas using iron oxide as catalyst/absorbent

Abstract

Iron oxide supported on alumina is a promising catalyst/absorbent for use in the simultaneous removal of NO, and SO, from power plant stack gases. A dry-contacting process is under development which would operate under net reducing conditions at temperatures of 370° to 540OC. Iron oxide is converted to the ferrous state, NO is reduced to Nz or NH3, and SOz is removed as ferrous sulfide or sulfate. Regeneration with air produces SO2 and reforms Fe20s.The reduction of SOz by CO and H2 was studied in fixed-bed reactors to determine the effects of temperature and of the other reactive components of flue gas (excepting fly ash) on the rate of reaction and the products formed. H2S and COS react with FeO to form FeS. Under readily attainable conditions, virtually complete removal of sulfur compounds was achieved for gas-phase residence times of about 1 to 10 ms. NO and Oz were also reduced. Conditions under which oxygen poisons the catalyst were determined. DAVID T. CLAY and SCOTT LYNN Department of Chemical EngineeringUniversity of California Berkeley, Colifornia 94720 SCOPESulfur dioxide and nitric oxide are major air pollutants in the United States. Fossil-fueled power plants are major sources of both. Wet processes for SO2 removal are currently being developed commercially, but to date no process for simultaneous SO2 and NO removal has passed the laboratory scale. A dry removal process would be preferred, since this would avoid flue-gas reheating, the problems of contacting the gas with a liquid or slurry, and the crystallization phenomena usually encountered in flue-gas scrubbing. The objective of this study was to develop a dry process which not only achieves high NO and SO2 removals, but also converts NO to innocuous materials and SO2 to a salable product and is potentially economical to operate.The process flow sheet is shown in Figure 1. Iron oxide, supported on alumina, acts as a catalyst for the reduction of both SOz and NO by CO and H2. Simultaneously, it acts as an absorbent for sulfur compounds, converting them to FeS. The catalyst/absorbent is in the form of fine pellets (0.05 to 0.10 mm) and contacts the gas as a falling bed in concurrent flow at 370° to 540OC. The solid is regenerated with air at 675OC to produce a rich stream of SO2, suitable for conversion to H2SO4 or elemental sulfur. Fez03 is reformed in the particles. Experiments in fixed-bed reactors using mixtures of helium and one or more reactant gases were run to demonstrate the basic process chemistry, to estimate rates for preliminary design purposes, and to look for interfering reactions. A preliminary estimation of the capital and operating costs of the process was made on the basis of the results obtained. CONCLUSIONS AND SIGNIFICANCEThe overall reactions listed in Table 1 were shown to proceed rapidly at 370" to 540°C in fixed-bed reactors using pellets of supported iron oxide 3.2 mm x 3.2 mm or particles 0.25 to 0.50 mm diameter. Iron oxide was reduced to the ferrous state, SO2 was reduced by both CO and H2, and the sulfur was absorbed ...

Chemistry-nuclear chemistry division. Progress report, October 1979-September 1980

“…The reaction of CO and SO 2 has also been studied quite extensively over a variety of catalysts. 109 Under our conditions even at 200°C, no appreciable reaction of CO with SO 2 was observed over 5% Ru/Al 2 O 3 . Because Ru/Al 2 O 3 catalyzes the conversion of CO and H 2 to hydrocarbons (Fischer-Tropsch reactions) at moderate temperatures, the mixture of CO, SO 2 , and H 2 was not examined.…”

“…The isotope 107 Ag can be produced by nuclear reactions with 108 Pd (atom abundance of 26.7%) and "°Pd (11.8% abundance), but 109 Ag can be made only from ll0 Pd. Thus, a high fluence of energetic cosmic-ray particles would produce an excess of 107 Ag relative to 109 Ag by nuclear reactions with palladium isotopes.…”

“…There are several measured and theoretical cross sections for the llo Pd(n,2n) 1O9 Pd reactions 241242 that were evaluated to provide an excitation function for the production of 109 Ag (produced by the decay of 109 Pd) by GCR-produced neutrons. Cross sections for the reactions "°Pd(p,pn) 109 Pd and 1IO Pd(p,2n) IO9 Ag by highenergy protons were estimated from cross sections for similar reactions with othsr nuclei. Because of the long half life for 107 Pd, no 108 Pd(n,2n) 107 Pd or 108 Pd(p,pn) 107 Pd cross sections have been measured.…”

“…The radionuclide "Mn is made by low-energy reactions with iron similar to the reactions that make 107 Ag and 109 Ag from palladium, so using calculated production ratios for these silver isotopes from palladium and for 53 Mn from iron and using measured 53 Mn activities seemed the best way to estimate the production rates of silver isotopes. The cross sections used for the production of 53 Mn from iron were estimated ones 244 for energies below 35 MeV and experimental proton-induced cross sections 245 above 45 MeV.…”

Reduzierende Rauchgas‐Entschwefelung, Teil I: Gleichgewichtslage

“…3imVergleichmitzweiin [3] [5]. Es ist weiterhin auf indirektem Wege [6] uber entsprechende Stoffaustauschmessungen und vor allem direkt durch Laser-Doppler-anemometrische (LDA)-Messungen [7] bekannt, daB bei Tensid-Konzentrationen oberhaib der kritischen Mizellbildungskonzentration (CMC) die Empfindlichkeit des Stoffstromes gegenuber adsorptiven Verunreinigungen aufgehoben ist und damit der Referenzzustand einer sauberen Phasengrenze fur quantitative Auswertungen vorliegt. Stoffaustauschmessungen, ausgerichtet auf die Adsorbatempfindlichkeit von Marangoni-InstabilitPten be1 erzwungener Konvektion sind damit moglic h .…”