A Quarterly Scientific Journal of Pakistan Atomic Energy Commission

The Nucleus, 46 (3) 2009: 205-211 The Nucleus

A Quarterly Scientific Journal of Pakistan Atomic Energy Commission

NCLEAM, ISSN 0029-5698

ASSESSMENT  AND  IDENTIFICATION  OF  SOME  NOVEL NO_X REDUCING REAGENTS FOR SNCR PROCESS

A. MAHMOOD, *M. T. JAVED, N. IRFAN, A. HAMID and K. WAHEED¹

Department of Chemical and Materials Engineering, P.O. PIEAS, Nilore, Islamabad, Pakistan 1

Department of Nuclear Engineering, PIEAS, Nilore, Islamabad, Pakistan

Nitrogen oxides (NO_x) are one of the most hazardous air pollutants arising from the combustion processes. Because of the implementation of strict emission limits many NO_x removal technologies have been developed. In the present work post combustion NO_x removal technique that is Selective Non-Catalytic Reduction (SNCR) has been investigated in a pilot scale 150 kW combustion rig facility. Investigation has been performed using some novel NO_x reducing reagents like urea, ammonium carbonate and mixture of their 50%-50% aqueous solution within the temperature range of 700 to 1200 ^oC, at 1.1% excess oxygen and background NO_x level of 500 ppm. The effects of these reagents were determined in term of their temperature characteristics and molar ratio. Among the reducing reagents used urea solution gave the highest NO_x removal efficiency (81%) and was attractive due to its superior high temperature (1000 to 1150 ^oC) performance, ammonium carbonate was more effective at lower temperature range (850 to 950 ^oC) though its efficiency (32%) was lower than urea, while 50-50% solution of urea and ammonium carbonate gave higher efficiency than ammonium carbonate but slightly lesser than urea within a wide temperature range (875 to 1125 ^oC). It was also observed that the NO_x removal efficiency was increased with increasing the molar ratio.

Keywords: Nitrogen oxides (NO_x), SNCR, Urea, Ammonium carbonate, Molar ratio

1.       Introduction

The rapid industrialization brought severe air pollution problems caused by combustion processes in industries and transportation sector. Nitrogen oxides (NO_x) are one of the most hazardous pollutants arising from these processes. Generally the term NO_x is used to mean the total concentration of NO plus NO₂ and it exclude other oxides of nitrogen. Nitrogen oxides are formed during high temperature combustion processes from the oxidation of nitrogen in the air or fuel and are released into the atmosphere mainly in the form of NO, which is then readily oxidized to NO₂ by reaction with ozone. Elevated levels of NO_x occur in urban environments under stable meteorological conditions, when the air mass is unable to disperse. Emissions of NO_x play an important role in many environmental issues, including acidification, eutrophication, ozone formation and hence the greenhouse effect. Because of these air pollution problems, air quality has become worse and worse so that the air pollution control regulations became stringent accordingly. Therefore, new technologies should

^∗_TP Corresponding author :  m.t.javed@pieas.edu.pk PT

be developed to reduce the pollutants within the regulation limit from combustion processes.  Numerous studies have been reported for costeffective NO_x reduction from stationary combustion sources. These technologies include selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR). The SNCR process is a useful method for NO_x reduction by injecting amines (–NH–) or cyanides (–CN–) containing selective reducing agents such as NH₃, urea and cyanuric acid into the flue gases [1,2]. The SNCR process could reduce nitric oxides to nitrogen and water rapidly and effectively at rather higher (1073–1373 K) temperatures as compared to SCR [3]. It has been reported that injection of some additives together with the reducing agents in SNCR processes can lower and widen the optimum reaction temperature window for NO_x reduction

[4, 5].

2.      Experimental Setup and Procedure

2.1.     Experimental Setup

The experimental work was performed on the

1.   Combustion Section	2.   Temp. Control Section	3.   Injection Section	4.   Reaction Section
5.   Flue Gas Ehaust	6.   Control Valve	7.   Rota Meters	8.   Mass Flow Controller
9.   Methane Gas	10. Air	11. Ammonia (For B.G)	12. Burner
13. Control Panel	14. Peristaltic Pump	15. Liquid Reagents	16. Carrier Gas (Air/N2)
17. Pressure Guage	18. Injector	19. Thermocouples	20. Cooling Coils
21. Sampling Probe	22. Water Inlet	23. Water Outlet	24. Flue Gas Analyzer

Figure 1. Schematic representation of experimental setup.