Activated carbon for control of nitrogen oxide emissions
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Activated carbons were used to selectively remove NOX from simulated flue gas at temperatures between 25 and 125 °C. Processing conditions and physical/chemical characteristics of the carbons which affected NOX adsorption, storage, and release were investigated. Oxygen as a coreactant was necessary to maximize the conversion of NO to NO2 and condensation of NO2 within the pores of the carbons. A NO-to-NO2 conversion mechanism is presented and discussed relative to previous research. A process for selectively removing NOX and concentrating it as NO 2 in an alternate process stream is outlined. The purified NO2 stream could be used for chemicals manufacturing.
I. INTRODUCTION The regulated control of emissions from stationary, fossil fuel power sources in the United States has focused on SO2 because of its association with acid deposition. The recent passage of the Clean Air Act Amendments of 1990 also sets a timetable for control of nitrogen oxides (NOX). These NO^ regulations will impact significantly the operation of electric utility boilers, fossil fuel fired industrial boilers, and combustion turbines.1 The nitrogen oxides, including NO and NO 2 , are considered as precursors to acid precipitation and can play an important role in the formation of ozone and haze. N 2 O is also considered a component of NO^, and is a greenhouse gas. Hence, during the next decade, the power industry shall be required to invest in NOX control technologies and is currently examining the options and economics of such technologies. The most studied and commercially available NO* control technology is selective catalytic reduction (SCR).2 During SCR within stationary power sources, the conversion of NOX to N 2 has to occur under relatively difficult processing conditions in the presence of excess oxygen.3"5 In general, SCR catalysts are highly efficient at temperatures above and near 300 °C, which is considerably greater than the ~100 °C exhaust gas temperature of a fossil power unit. Additionally, catalyst plugging, poisoning, or fouling can lead to the slippage of reductant past the catalyst bed6-7; it has also been determined that HCN can be formed when NH 3 is used as a reductant.8 Another NOX decomposition technology that has been studied and is under commercial testing is associated with the reduction of NO* by a carbonaceous material or by catalytic decomposition using CO.9"11 These types of reactions can reduce NO very efficiently, although it has been shown that N2O, instead of N2, can be produced at relatively large and unwanted concentra562
http://journals.cambridge.org
J. Mater. Res., Vol. 10, No. 3, Mar 1995
Downloaded: 17 Sep 2015
tions. In addition, the temperature of optimal conversion to N 2 is normally near 250-450 °C, again significantly greater than exhaust gas temperatures in fossil fuel power stations. Rather than examine in more detail these options for NO^ control strategies, our work has focused on a chemically benign processing scheme which captures NOX from the flue gas and concentrates it as nitrogen di
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