Showing papers on "Selective catalytic reduction published in 1989"

Comparison of Nitric Oxide Removal by Cyanuric Acid and by Ammonia

Abstract: Selective, non-catalytic techniques for removing nitric oxide (NO) from the exhaust gases of combustion processes include the addition of cyanuric acid, ammonia, or urea to the hot exhaust. This paper compares the effects of temperature and exhaust gas composition on the cyanuric acid (CA) and the ammonia (NH3) nitric oxide reduction processes and examines the decomposition of dry urea. The experiments were conducted in an electrically heated quartz flow reactor using mixtures of N2, 02, H2, H2, O, CO, and NO that simulated exhaust gases from overall lean hydrocarbon combustion processes Comparison of the CA and the NH3 nitric oxide reduction processes shows that the effects of the exhaust O2, H2, O, and CO concentrations on the NO reduction level and the temperature range over which the NO reduction occurs are different for each process. The comparison also shows that the by-products of each process are different for some conditions. These differences indicate that the detailed chemical mechanis...

Catalysts for selective catalytic reduction denox technology

Abstract: Catalysts for the selective catalytic reduction of NOx by ammonia are made from porous formed supports having a certain fraction of the pores with pore diameters larger than 600 Angstrom units. Thus macropores can be introduced in a formed TiO₂ support by adding burnout materials or some inorganic oxide prior to forming the titania into the formed support. Alternatively, titania is precipitated onto a porous inorganic oxide such as SiO₂, Al₂O₃, ZrO₂, AlPO₄, Fe₂O₃ and B₂O₃ to form the support. Then conventional DeNOx catalytic metals are added. The support can be made by first impregnating the inorganic oxide particles with titania via a soluble precursor, forming titania and then shaping the coated particles into the desired shape such as a monolith. In a second embodiment, the inorganic oxide particles are first formed into the desired shape and then impregnated with the titania forming material. Barium sulfate can be added to the surface of the porous inorganic oxide to make an improved support.

Method for the catalytic removal of nitrogen oxides from exhaust gases by means of a reducing agent

Abstract: A method for the removal of nitrogen oxides contained in exhaust gases of an optionally fluctuating composition with a temperature of 0°-600° C. by means of catalytic reduction at a preselected stoichiometric ratio between the concentration of reducing agent and the concentration of nitrogen oxide in which the reducing agent is dosed in a pulsed manner.

Catalytic denitrification control process and system for combustion flue gases

Abstract: A control process and system for catalytic denitrification of NO x containing flue gases derived from a fuel combustion unit such as a gas turbine by ammonia addition to the flue gas upstream of a catalytic denitrification unit. The ammonia addition rate is controlled based on a basic signal which is generated based on functional parameters including the fuel being burned, its combustion temperature, flue gas flow rate, ammonia flow rate and the catalytic activity, so as to inject initially into the flue gas stream less ammonia than is theoretically required. Then the NO x concentration in the exhaust gas downstream of the catalytic unit is compared with the appropriate standard, the ammonia quantity initially being added is further adjusted until the NO x concentration is gas emitted to the atmopshere is reduced sufficiently to meet local clean air standards while avoiding unsatisfactory excess ammonia injection and system oscillation.

Advanced NOx reduction processes using-NH and -CN compounds in conjunction with staged air addition

Abstract: The effectiveness of combustion modifications for the control of nitrogen oxide emissions from coal fired combustors is most often limited by problems due to carbon burnout or flame impingement. This paper presents new data on the use of selective reducing agents suggesting that a hybrid control scheme is possible which uses combustion modification to provide those conditions which optimize, the selective reduction process. Very low emission levels appear possible that can presently only be achieved by catalytic reduction. The experimental studies were conducted in a tunnel furnace which simulated the thermal environment within a pulverized coal boiler. Application of each of the agents (ammonia, urea, cyanuric acid, and ammonium sulfate) to an overall fuel lean environment, produced NO reduction behavior very similar to that of thermal deNO x . However, if the agent was added to the fuel rich zone of a rich/lean staged combustor, very high NO reductions were obtained after the leanout point. The result of the staging was to extend the effectiveness of the agent to lower temperatures relative to overall lean injection. Parametric variations indicated that, in addition to temperature, the most important variable was the rich zone stoichiometry. Kinetic modeling suggests that the rich zone acts primarily as a source of CO. At the rich/lean transition the CO is oxidized and excess OH is produced by the, usual chain branching reactions. For low initial CO concentrations the excess radicals, are consumed by: NH 3 +OH=NH 2 +H 2 O HNCO+H=NH 2 +CO The NH 2 is then available for reaction with NO to eventually yield N 2 . The strong rich zone stoichiometry dependence is exerted mainly through the amount of CO, supplied to the lean zone. Insufficient CO will limit the extent of the initial NH 3 or HNCO reaction.

High-temperature three-way catalyst for treating automotive exhaust gases

Abstract: A three-way catalyst for use in treating automotive exhaust gases employs a delta alumina support which contains oxides of cerium plus barium and/or lanthanum, plus at least one Group VIII noble metal from the group consisting of platinum, palladium, rhodium, ruthenium and iridium.

Control of nitrogen oxide (NOx) emissions by selective catalytic reduction with hydrogen over hydrophobic catalysts

Abstract: The selective catalytic reduction of NO x with H 2 over noble -metal catalysts supported on hydrophobic material has been studied for the control of NO x emission from simulated stationary sources. The activity of the noble metal catalysts was found to be in the order Pt>Pd-Ru>Pd>Ru>>Au. The presence of O 2 in the feed tends to decrease the NO x conversion. The control of reaction temperature is crucial to the catalyst selectivity due to the competitive reaction between H 2 and O 2 . Optimum reaction temperature and space velocity lead to the minimum hydrogen requirement

Process using catalysts for selective catalytic reduction denox technology

Abstract: Catalysts for the selective catalytic reduction of NOx by ammonia are made from porous formed supports having a certain fraction of the pores with pore diameters larger than 600 Angstrom units. Thus macropores can be introduced in a formed TiO 2 support by adding burnout materials or some inorganic oxide prior to forming the titania into the formed support. Alternatively, titania is precipitated onto a porous inorganic oxide such as SiO 2 , Al 2 O 3 , ZrO 2 , AlPO 4 , Fe 2 O 3 and B 2 O 3 to form the support. Then conventional DeNOx catalytic metals are added. The support can be made by first impregnating the inorganic oxide particles with titania via a soluble precursor, forming titania and then shaping the coated particles into the desired shape such as a monolith. In a second embodiment, the inorganic oxide particles are first formed into the desired shape and then impregnated with the titania forming material. Barium sulfate can be added to the surface of the porous inorganic oxide to make an improved support.

Process for catalytic removal of nitrogen oxides from waste gases by a reducing agent

Abstract: A process for removing nitrogen oxides, which may fluctuate in exhaust gases at a temperature of 0 - 600 ° C., by catalytic reduction at a preselected stoichiometric ratio between the reducing agent and nitrogen oxide concentrations is presented, in which the reducing agent is metered in a pulsed manner.

Process for catalytic reduction of nitrogen oxides

Abstract: A process for catalytically reducing nitrogen oxides in an exhaust gas such as a combustion gas and a catalyst suitable for use therein. The catalyst comprises a zeolite Y which has been ion exchanged with lithium ions and/or rare earth metal ions, and may be dispersed in an amorphous oxide gel matrix.

Denitration using ammonia generated by hydrolyzing urea

Abstract: PURPOSE: To reduce the diameter of a urea feeding pipe and to selectively reduce and remove NOx in exhaust gas by reducing the NOx with ammonia generated by hydrolyzing urea in the presence of a catalyst as a reducing agent. CONSTITUTION: Urea U is mixed with water from a water feeding pipe 6 and heated with a jacket 4 while flowing zigzag downward on baffle plates 5 in a reaction tower 3. The water is evaporated, the urea U is volatilized and they react with each other during passing through a catalyst bed C at the lower part of the tower 3 to generate gaseous ammonia. This ammonia is fed into an exhaust gas duct 7 through a feeding pipe 8. The duct 7 has been packed with a Ti-V type denitration catalyst at the downstream side of the pipe 8. In the duct 7, NOx in exhaust gas is selectively reduced with the gaseous ammonia generated by hydrolyzing the urea U as a reducing agent. COPYRIGHT: (C)1990,JPO&Japio

Exhaust gas denitrification apparatus

Abstract: An improved exhaust gas denitrification apparatus for denitrifying nitrogen oxides in exhaust gas through a catalytic reduction method by making use of ammonia or precursor thereof as a reducing agent. A branch pipe for leading the exhaust gas to an evaporator is disposed at the upstream or at the downstream of the denitrification apparatus. The evaporator contains therein an ejection nozzle for spraying ammonia or precursor thereof, and a mixer for uniformly mixing sprayed mist of ammonia or pre­cursor thereof with the exhaust gas. At least one ejection nozzle for ejecting ammonia or precursor thereof evaporated by the exhaust gas within the evaporator and carried by the exhaust gas is provided in the flue and disposed at the upstream of a denitrification catalyst layer.

Process for eliminating nitrogen oxides from combustion exhaust gases

Abstract: In a process for eliminating nitrogen oxides from combustion exhaust gases which contain arsenic compounds as impurities, by selective catalytic reduction with ammonia, a catalyst is used which essentially contains titanium oxide and catalytically effective quantities of compounds of vanadium, molybdenum, tungsten and zinc. The catalyst contains A) titanium in the form of oxides, B) vanadium in the form of oxides or sulphates, C) molybdenum and/or tungsten in the form of oxides and D) zinc in the form of oxides or sulphates, with the proviso that the metal components A to D are present in the A/B/C/D atomic ratios of 1/0.0022-0.0165/0.021-0.21/0.009-0.028.

Process for catalytic reduction of carboxylic acids to aldehydes

Abstract: Monocarboxylic acids or esters thereof are reduced to aldehydes using hydrogen and a vanadium catalyst. For example, meta-phenoxybenzoic acid can be effectively converted to meta-phenoxybenzaldehyde in a vapor phase process using hydrogen as the carrier gas/reductant and a catalyst composed at least initially of vanadium pentoxide, either supported or unsupported.

Process for the preparation of hydroxy ammonium salts

Abstract: Process for the preparation of hydroxylammonium salts by catalytic reduction of nitrogen monoxide with hydrogen in dilute aqueous mineral acids in the presence of suspended supported platinum catalysts which are partially poisoned with sulphur, at elevated temperature, characterised in that catalysts are used which are obtainable by precipitation of metallic platinum from aqueous solutions of platinum salts onto supports suspended therein by means of reducing agents in the presence of at least one water-soluble, optionally substituted thiourea.

Yields of nh3 in radiation-catalytic reduction of molecular nitrogen

Abstract: The [MoOC1(dppe)2]Cl complex [dppe=(C6H6)2P(CH2)2 P(C6H5)2] was successfully examined in a process of reduction of molecular nitrogen in γ-radiation field. Yields of ammonia produced in this process were measured as a function of the Mo(IV) complex concentration and dose.

Process for producing aminobenzylamine

Abstract: A commercially advantageous process for producing m- or p-aminobenzylamine is provided, which is characterized by subjecting m- or p-nitrobenzaldehyde and ammonia to catalytic reduction in the presence of a reducing catalyst in an organic solvent; in the reduction, when nitrobenzaldehyde and ammonia are in advance made a mixed solution in an organic solvent, and this solution is added in divided manner, the yield being further improved.

High-temperature reduction of SO2 by methane at various CH4/SO2 ratios

Abstract: The character of the effect of initial reaction mixture and temperature on the selectivity of catalytic reduction of sulfur dioxide by methane in the presence of oxygen has been studied.

Treatment of exhaust gas

Abstract: PURPOSE: To simply produce a low-cost catalyst for catalytic reduction denitrification by using calcium oxide and/or calcium sulfate, aluminum oxide and silicon dioxide-based sulfide CONSTITUTION: In a selective catalytic reduction decomposition method using ammonia as a reducing agent as a dry denitrification method, calcium oxide and/or calcium sulfate, aluminum oxide and silicon dioxide-based sulfide are used as a catalyst This catalyst can be produced by utilizing a used desulfurizing agent and inexpensive starting materials such as coal ash in relatively simple stages This catalyst also acts as a removing agent for other harmful gases contained in exhaust gas COPYRIGHT: (C)1991,JPO&Japio

Metal-Doped Zeolites for Selective Catalytic Reduction of Nitrogen Oxides in Combustion Gases

Abstract: In the present work it is demonstrated that the activity of zeolites concerning the SCR-process can be increased significantly by metal doping. The SCR catalysts prepared by metal ion exchange of mordenite and Y-zeolite were tested in a laboratory plant to determine the efficiency of the conversion of nitric oxides with ammonia. Copper-doped Y-zeolite can be used as a SCR catalyst in a wide temperature range. Therefore, the operation is possible as well in a low-dust region, such as behind a desulphurization plant. A complicated temperature control for optimum conversion is not necessary. Also the excellent ammonia storage capacities of the zeolite catalysts can be demonstrated. Therefore, changes in the ammonia feed or the NO content in the exhaust gas can be compensated.