The problem of NOx emissions reduction is gaining increased attention from those concerned with air pollution control activities. HEW proposes to issue criteria for the control of nitrogen oxides within the year. The Los Angeles Air Pollution Control District (LAAPCD) has already published regulations which limit emissions from combustion sources to a fixed rate of 140 lb/hr NOx. This is equivalent to an allowable emission concentration of about 20 ppm for a 500 MW power station. Two of the major contributors to oxides of nitrogen air pollution in the United States are Industrial Processes and Stationary Combustion Sources, both being responsible for over 50 percent of the total NOx emissions. Motor vehicles contribute the remainder for a total of 20 million tons per year. Although some advances have been made in the development of commercial control equipment for Industrial Process emissions, there is very little well-developed technology available for NOx emissions control from Stationary Combustion Sources. Two of the most promising areas being investigated are: • Stoichiometric variations of the air-fuel feed and partial recycling of the combustion products. • Advanced design of combustion equipment. The former system of control, in a test program with 17 commercial boilers, has been responsible for the reduction of NOx emissions from about 350–150 ppm. An advanced design combustor, operated at a heat release level of 105 Btu/hr, has produced NOx emission values of about 150 ppm. When coupled with simulated combustion gas recycle, the emissions were further reduced to 100 ppm. Although both the “stoichiometric” and “combustor” approach to the problem of NOx emissions represent a good beginning, greater efforts must be expended on these and other promising control techniques in preparation for future regulations.
LON G I T U DIN A LOP TIC ALP H 0 NON -P LAS M 0 NCO U P LIN GIN CdS S1 where the distance between carrier electrons, dee, divided by the effective Bohr radius, ao', is not less than 1 at concentrations of 1018/cc. For cases where r. is less than 1, the self-consistent field theoryl8 is applicable and the polarizabilities of the electrons and 18 J. Lindhard, Kg!. Danske Videnskab, Selskab, Mat.-Fys.Medd., 28, 8 (1954). ions may be taken as additive. Varga's results are then derived for r. < 1 from the equations of motion of Born and Huang 19 and the Poisson equation.The second reflectivity minimum is one of the main points needing examination.The use of a line-source transient-heat-transfer technique to determine the thermal conductivities of He, Ne, Ar, and of their mixtures is reported along with results. The method employs existing rigorous analytical theory for a finite line source possessing heat capacity. The experimental and analytical techniques minimize the effects of instrument size, radiation, free convection, and thermal separation of the mixtures. The linesource diameter was 0.00763 cm with a central 0.OO203-cm nickel temperature sensing coil to provide temperature data. Experimental times of 270 msec or less and total temperature rises of less than lOoC were used to minimize radiation, free convection, and thermal separation effects. The data show excellent agreement with existing data and an internal consistency and accuracy believed to demonstrate elimination of undesirable effects upon over-all thermal-conductivity determinations.
An experimental investigation has been made of the sound-absorbing properties of liquid-base foams and of their ability to reduce jet noise. Protein, detergent, and polymer foaming agents were used in water solutions. A method of foam generation was developed to permit systematic variation of the foam density. The investigation included measurements of sound-absorption coefficients for both plane normal incidence waves and diffuse sound fields. The intrinsic acoustic properties of foam, e.g., the characteristic impedance and the propagation constant, were also determined. The sound emitted by a 1-in.-diam cold nitrogen jet was measured for subsonic (300 m/sec) and supersonic (422 m/sec) jets, with and without foam injection. Noise reductions up to 10 PNdB were measured.
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