INCREASE ON INCINERATION CAPACITY AND NO_X CONTROL FOR AIR ENRICHMENT IN THE EXPERIMENTAL SIMULATION OF AQUEOUS RESIDUE INCINERATION

Abstract

An experimental investigation of air enrichment in a combustion chamber designed to incinerate aqueous residues is presented. Diesel fuel and liquefied petroleum gas (LPG) were used independently as fuels. An increase of 85% in the incineration capacity was obtained with nearly 50% O₂ in the oxidant gas, in comparison to incineration with air only. The incineration capacity continues increasing for enrichment levels above 50% O₂, although at a lower pace. For complete oxy-flame combustion (100% O₂), the increase of the incineration capacity was about 110% relative to the starting conditions and about 13.5% relative to the condition with 50% O₂. The CO concentration measured near the flame front decreases drastically with the increase of O₂ content in the oxidant gas. At the chamber exit, the CO concentration was always near zero, indicating that the chamber residence time was sufficient to complete fuel oxidation in any test setting. For diesel fuel, the NO_x was entirely formed in the first region of the combustion chamber. For diesel fuel, there was some increase in the NO_x concentration up to 35% of O₂ this increase became very sharp after that. From 60 ppm, at operation with air only, the NO_x concentration raises to 200 ppm at 35% O₂, and then to 2900 ppm at 74% O₂. The latter corresponds to six times more NO_x in terms of the ratio of mass of NO to mass of residue, compared to the situation of combustion with air only. For LPG, the NO_x concentrations reached 4200 ppm at 80% O₂, corresponding to nine times more, also in terms of the ratio of mass of NO to mass of residue, in comparison with combustion with air only. Results of different techniques used to control the NO_x emission during air enrichment are discussed: (a) variation of the recirculated zone intensity, (b) increase of the spray Sauter mean diameter, (c) fuel staging, (d) oxidizer staging, and (e) ammonia injection. The present paper shows that NO_x emission may be controlled without damage of the increase of incineration capacity by the enrichment and with low emission of partial oxidation pollutants such as CO.

Keywords:

• air enrichment
• aqueous residue incineration
• NO_x control

The authors acknowledge the support of FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) through projects 95/4167-7, 96/10310-0, and 97/5511-9.

Notes

φ is the theoretical equivalence ratio, m _LPG is the LPG mass flow rate, and m _diesel is the diesel mass flow rate.