321 改質アンモニアインジェクション法における脱硝メカニズム(大気環境保全・改善技術(3))

To broaden and lower the narrow temperature window of the selective non catalytic reduction (SNCR) of nitric oxide (NO), the use of activated ammonia as the reduction agent was examined A xenon excimer lamp emitting a wavelength of 172 nm (i.e., vacuum ultraviolet; VUV) was employed as the excitation source for molecular ammonia. The effects of reaction temperatures, oxygen concentrations, and NH_3/NO molar ratios (MRs) on NO removal were investigated in a lab-scale plug flow reactor. Temperatures ranged from 500℃ to 850℃. A temperature window enlargement of 150℃ was achieved at the lower boundary of the temperature window. Above 600℃, NO removal was effected by injection of activated ammonia, while around 750℃, conventional SNCR by injection of molecular ammonia was effective. An approximate 80% NO removal was attained at 700℃ with an MR=2.0 and 8.3% O_2.

Pilot-scale tests were conducted to develop a combined nitrogen oxide (NOx) reduction technology using both selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR). A commercially available vanadium- and titanium-based composite honeycomb catalyst and enhanced urea (NH2CONH2) were used with a natural-gas-fired furnace at a NOx concentration of 110 ppm. Changes in SNCR chemical injection temperature and stoichiometry led to varying levels of post-furnace ammonia (NH3), which acts as the reductant feed to the downstream SCR catalyst. The urea-based chemical could routinely achieve SNCR plus SCR total NOx reductions of 85 percent with less than 3 ppm NH3 slip at reductant/NOx stoichiometries ranging from about 1.5 to 2.5 and SCR space velocities of 18,000 to 32,000 h−1. This pilot-scale research has shown that SNCR and SCR can be integrated to achieve high NOx removal. SNCR provides high temperature reduction of NOx followed by further removal of NOx and minimization of NH3 slip by a significantly downsized (high-space velocity) SCR.

CeO2 nanorods impregnated with 2.5 atom % of NiO (NiO/CeO2 nanorods) were successfully synthesized and examined as catalysts for the NH3-selective catalytic reduction (NH3-SCR) of nitric oxide (NO). The catalytic activity of NiO/CeO2 nanorods resulted in up to ∼90% NO conversion at 250 °C, which is superior to that of pure CeO2 nanorods or NiO nanoparticles. Subsequently, extensive studies of the NiO/CeO2-catalyzed reduction of NO were conducted using X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, temperature-programmed desorption, and density functional theory periodic calculations. Compared to that of the pure CeO2 nanorods, the results demonstrated that the NiO/CeO2 nanorods resulted in (i) a higher concentration of Ce3+ chemical species, (ii) a larger amount of active Oα, (iii) lower temperature reducibility, (iv) a lower amount of energy required for oxygen vacancy distortion, and (v) a significant adsorption of and strong interaction between NO and NH3 molecules. Our findings therefore elucidated considerable details of the structural properties of the NiO/CeO2 nanorods that were decisive for achieving a highly efficient conversion of NO by the NH3-SCR process at low temperatures.

96/03196 - Epidemiological evaluation of release of monocyte TNF-alpha as an exposure and effect marker in pneumonoconiosis: A five year follow up study of coal workers

Fundamentals of NO reduction by liquid wastes: The first application in hazardous waste incineration

Activity and selectivity of pure manganese oxides in the selective catalytic reduction of nitric oxide with ammonia

99/03849 Latest design of a soda recovery boiler and process for gasification of black liquor: Duda, Z. Przegl. Papier., 1998, 54, (2),85–88. (In Polish)

In this work, a novel phenomenon was discovered that N2O selectivity of NO reduction over MnOx/TiO2 was related to the concentration of gaseous NO and that lower concentration of gaseous NO would cause higher N2O selectivity. In situ DRIFTS and transient reaction studies demonstrated that both the Eley–Rideal mechanism (the reaction of over-activated NH3 with gaseous NO) and the Langmuir–Hinshelwood mechanism (the reaction of adsorbed NO3− with adsorbed NH3 on the adjacent sites) could contribute to the formation of N2O. Kinetic study demonstrated that N2O selectivity would be independent of gaseous NO concentration if NO reduction over MnOx/TiO2 mainly followed the Langmuir–Hinshelwood mechanism. If NO reduction over MnOx/TiO2 mainly followed the Eley–Rideal mechanism, there was competition between the selective catalytic reduction (SCR) reaction and non selective catalytic reduction (NSCR) reaction. As gaseous NO concentration increased, more –NH2 was used to reduce gaseous NO to form N2 and the further oxidization of –NH2 to –NH was restrained, resulting in an obvious decrease of N2O selectivity. The Eley–Rideal mechanism played an important role in NO reduction over MnOx/TiO2, especially at higher temperatures. Therefore, N2O selectivity of the low temperature SCR reaction over MnOx/TiO2 decreased especially at higher temperatures after the increase of gaseous NO concentration.

Selective Non-Catalytic Reduction (SNCR) of nitric oxide has been studied experimentally by injecting aqueous urea solution with and without additive in a pilot-scale diesel fired tunnel furnace at 3-4 % excess oxygen level and with low ppm of baseline NOx ranging from 65 to 75 ppm within the investigated temperature range. The tests have been carried out using commercial grade urea as NOx reducing agent and commercial grade sodium carbonate as additive. The furnace simulated the small-scale combustion systems, where the operating temperatures are usually in the range of about 973 to 1323 K and NOx emission level remains below 100 ppm. With 5% plain urea solution, at Normalized Stoichiometric Ratio (NSR) of 4 as much as 54% reduction was achieved at 1128 K, whilst in the additive case the NOx reduction was improved to as much as 69% at 1093 K. Apart from this improvement, in the additive case, the effective temperature window as well as peak temperature of NOx reduction shifted towards lower temperatures. The result is quite significant, especially for this investigated level of baseline NOx. The ammonia slip measurements showed that in both cases the slip was below 16 ppm at NSR of 4 and optimum temperature of NOx reduction. Finally, the investigations demonstrated that urea based SNCR is quite applicable to small-scale combustion applications and commercial grade sodium carbonate is a potential additive.

Reduction of nitrogen oxides in flue gases

The U. S. Department of Energy (DOE), Electric Power Research Institute (EPRI), Pennsylvania Electric Energy Research Council, (PEERC), New York State Electric and Gas and GPU Generation, Inc. jointly funded a demonstration to determine the capabilities for Hybrid SNCR/SCR (Selective Non-Catalytic Reduction/Selective Catalytic Reduction) technology. The demonstration site was GPU Generation's Seward Unit No.5 (147MW) located in Seward Pennsylvania. The demonstration began in October of 1997 and ended in December 1998. DOE funding was provided through Grant No. DE-FG22-96PC96256 with T. J. Feeley as the Project Manager. EPRI funding was provided through agreements TC4599-001-26999 and TC4599-002-26999 with E. Hughes as the Project Manager. This project demonstrated the operation of the Hybrid SNCR/SCR NO{sub x} control process on a full-scale coal fired utility boiler. The hybrid technology was expected to provide a cost-effective method of reducing NO{sub x} while balancing capital and operation costs. An existing urea based SNCR system was modified with an expanded-duct catalyst to provide increased NO{sub x} reduction efficiency from the SNCR while producing increased ammonia slip levels to the catalyst. The catalyst was sized to reduce the ammonia slip to the air heaters to less than 2 ppm while providing equivalent NO{sub x} reductions. The project goals were to demonstrate hybrid technology is capable of achieving at least a 55% reduction in NO{sub x} emissions while maintaining less than 2ppm ammonia slip to the air heaters, maintain flyash marketability, verify the cost benefit and applicability of Hybrid post combustion technology, and reduce forced outages due to ammonium bisulfate (ABS) fouling of the air heaters. Early system limitations, due to gas temperature stratification, restricted the Hybrid NO{sub x} reduction capabilities to 48% with an ammonia slip of 6.1 mg/Nm{sup 3} (8 ppm) at the catalyst inlet. After resolving the stratification problem, the catalyst did not have sufficient activity in order to continue the planned test program. Arsenic poisoning was found to be the cause of premature catalyst deactivation.

Effect of crystal morphology in selective catalytic reduction of nitric oxide over V 2O 5 catalysts

Simultaneous mercury oxidation and NO reduction in a membrane biofilm reactor

Complexing agents-free bioelectrochemical trickling systems for highly-efficient mesothermal NO removal: The role of extracellular polymer substances

Selective catalytic reduction (SCR) of nitrogen oxides (NO{sub x}) in flue gas or engine exhaust gas with hydrocarbons as the reductant has great potential for less expense, less pollution, and easier operation than SCR with ammonia. Methane is the preferred reducing gas because of its low cost and low toxicity. Stable, low-cost catalysts for SCR with methane are required to demonstrate this technology for controlling NO{sub x} emissions. Several cobalt and nickel catalysts on synthetic clay and uranium oxide supports were investigated for their activities in reducing NO{sub x} with methane in the presence of air. The efficiency of the synthetic clay-supported nickel and cobalt catalysts for nitric oxide (NO) reduction with methane as the reducing gas was poor. The nickel oxide-uranium oxide catalyst, which was chosen for its high stability, was also ineffective. Results from the two-step experiments conducted at two temperatures produced some interesting information on the reactions of methane with the catalysts and the reactivity of the carbonaceous intermediate. The carbonaceous material formed from methane dissociation at 450{degrees}C not only reduces NO to N{sub 2}O at lower temperatures, but also prevents oxidation of NO to NO{sub 2}. Unfortunately, the carbonaceous forms that reduce the NO are not available for reactions at 400{degrees}C in the presence of oxygen. A two-step process employing this chemistry would be difficult because the catalyst would have to be cycled between the two temperatures. Also the desired reduction to nitrogen is not very efficient.