Nitrogen oxides from waste incineration: control by selective non-catalytic reduction Sarantuyaa Zandaryaa * , Renato Gavasci, Francesco Lombardi, Antonella Fiore Department of Civil Engineering, University of Rome ``Tor Vergata'', Via di Tor Vergata, 00133 Rome, Italy Abstract An experimental study of the selective non-catalytic reduction (SNCR) process was carried out to determine the eciency of NO x removal and NH 3 mass balance, the NO x reducing reagent used. Experimental tests were conducted on a full-scale SNCR system installed in a hospital waste incineration plant. Anhydrous NH 3 was injected at the boiler entrance for NO x removal. Ammonia was analyzed after each ¯ue-gas treatment unit in order to establish its mass balance and NH 3 slip in the stack gas was monitored as well. The eective fraction of NH 3 for the thermal NO x re- duction was calculated from measured values of injected and residual NH 3 . Results show that a NO x reduction e- ciency in the range of 46.7±76.7% is possible at a NH 3 /NO molar ratio of 0.9±1.5. The fraction of NH 3 used in NO x removal was found to decrease with rising NH 3 /NO molar ratio. The NH 3 slip in the stack gas was very low, below permitted limits, even at the higher NH 3 dosages used. No direct correlation was found between the NH 3 /NO molar ratio and the NH 3 slip in the stack gas since the major part of the residual NH 3 was converted into ammonium salts in the dry scrubbing reactor and subsequently collected in the fabric ®lter. Moreover, another fraction of NH 3 was dis- solved in the scrubbing liquor. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Waste incineration; Thermal DeNO x ; Ammonia; Mass balance 1. Introduction Environmental protection and stringent emission limits both require a signi®cant reduction of nitrogen oxides (NO x ) emissions from industrial boilers and as well as waste incineration plants. In recent years, the selective non-catalytic reduction (SNCR) technology, a ¯ue-gas treatment method for NO x emission control, has achieved commercial application to stationary combus- tion sources. The SNCR technology is becoming wide- spread in waste incineration plants, where in most cases a NO x removal over 70% is not required. The SNCR application is attractive due to its simplicity and low operation costs. Generally, SNCR technology is only capable to achieve a moderate eciency of NO x re- moval. NO reductions in the range of 60±80% at a molar NH 3 /NO ratio of 2 and about 90% at a ratio of 4 (Furrer et al., 1998) have been reported. The SNCR process is considered as an easily retro®ttable NO x control tech- nology as well. Although the technology is considered simple to in- stall and operate, it has a quite complex chemistry and requires speci®c operational conditions. In addition, its eciency of NO x reduction is speci®c to each application depending on process parameters and operational conditions. The SNCR method may have undesirable conse- quences such as ammonia slip in the stack gas and the formation of ammonium bisulfate (NH 4 HSO 4 ) (Rosen- berg et al., 1980; Radojevic, 1998) in case the parameters that control the process are not set within the range required for optimum performance. Chemosphere 42 (2001) 491±497 * Corresponding author. Tel: +39-06-72597022; Fax: +39- 06-72597005. E-mail address: sara@ing.uniroma2.it (S. Zandaryaa). 0045-6535/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 4 5 - 6 5 3 5 ( 0 0 ) 0 0 2 2 1 - 6