CFD ANALYSIS OF NO x FORMATION IN WASTE-TO-ENERGY SYSTEMS USING DETAILED CHEMICAL KINETIC MODELING Alex Frank Columbia University New York, NY 10027 Marco J. Castaldi Columbia University New York, NY 10027 ABSTRACT This study was undertaken to better understand the governing processes and reaction conditions under which NO x is produced in Waste to Energy (WtE) boilers. A three dimensional CFD model was created and calculated using the GRI 3.0, 50 species, 309 step detailed chemical kinetic model (DCKM) for methane/ethane combustion. Model results for primary NO x emissions and other pollutants agree well with collected data, proving the fidelity of the model. NO was the primary pollutant accounting for approximately 99% of the total NO x emissions. Fuel bound nitrogen was found to be the main source of NO produced in the boiler with thermal and prompt mechanisms having lesser impacts. Three principal intermediates were identified in the formation of NO; NH, HNO, and NCO. The assumption of fuel nitrogen conversion to either NH 3 or HCN is an unknown parameter that was shown to have a small impact on NO emissions, indicating that this is an area that should not be explored further in this continuing study. Furthermore, varying the boiler pressure had a small impact on final NO emissions, indicating that this is not a condition that should be considered for plant operation. The next phase of this research will include the development of a reduced DCKM in order to expedite the running of new scenarios for future studies as well as optimization of boiler geometry and combustion mixing to achieve the lowest possible NO x emissions. INTRODUCTION Waste incineration is a technology commonly employed throughout the world due to its ability to reduce the mass and volume of waste by 70% and 90%, respectively, while also generating electricity. While it remains an effective way to reduce waste diverted to landfills, environmental concerns such as stack emissions are of great importance and under constant scrutiny. As a result, Waste-to-Energy (WtE) facility emissions have been on a steady decline for many years. This reduction has occurred due to both optimization of combustion within the boiler and the introduction of various control technologies. Of the various pollutants emitted, NO x emissions still pose a significant challenge. Currently, NO x is controlled mostly by Selective NonCatalytic Reduction (SNCR) and is able to meet the federal emission limit of 205 ppmdv and 150 ppmdv (7% O 2 ) for existing and new WTE facilities respectively [1]. Furthermore, there have been various control technologies developed such as the LN™ and VLN™ systems designed by Covanta Energy partnered with Martin GmbH. The VLN™ system draws cool gas from the rear of the waste bed and re-injects it in the upper section of the furnace while also optimizing the ratio between secondary and primary air in order to reduce the formation of NO x and improve combustion efficiency [2]. While these control technologies are proven to be very effective in plant operations around the world, the details governing the formation and destruction of NO x are not fully understood. Over the past several years, several CFD models have been built to better understand and optimize the design of WtE systems. Some models were simplified to include only a gaseous, over-bed boundary condition that ignores the solid waste burning on the bed [3]. More complex models simulate the solid waste combustion, burnout, mass reduction, and include fly ash among other phenomena in addition to the gaseous combustion products [4]. In the past, both of these model types generally assumed global reactions that encompassed the entire boiler, mostly ignoring kinetics and instead focusing solely on fluid dynamics. Therefore, they were good at predicting most pollutants, but generally lack the ability to model very intricate and complex kinetics present in the formation of NO x . Most often, when NO x is of interest, simulations are run which greatly simplify inlet boundary conditions and Proceedings of the 20th Annual North American Waste-to-Energy Conference NAWTEC20 April 23-25, 2012, Portland, Maine, USA NAWTEC20-70 1 Copyright © 2012 by ASME