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Show EFFECT OF OPERATING PARAMETERS ON N O X PRODUCTION IN A FLAT GLASS FURNACE 4 Soot Model. The two-step Tesner model (Tesner et al., 1971; Magnussen and Hjertager, 1976) was used in the combustion chamber for predicting the soot concentration. The soot model predicts the generation of radical nuclei and the formation of soot on these nuclei. The transport equations for the radical nucleus concentration and the soot concentration are solved. NOx Model. The NOx module used in this study provides the capability to model thermal, prompt, and fuel N O x formation in the combustion system. In the high temperature environment of natural gas-fired glass furnaces, thermal N O x is the dominant formation mechanism. To predict N O x emission, the model solves a transport equation for nitric oxide (NO) concentration. The governing equations are derived from the principle of species conservation. The N O x transport equations are solved based on a given flow field and combustion solution. NOx REDUCTION APPROACHES The general geometric design of the furnace simulated was one for which exhaust and combustion space measurements have been reported previously (Newbold et al., 1997). The furnace is a nominally 550 ton/day facility. Natural gas comprised primarily of methane (87.5%) and ethane (3.7%), but with significant nitrogen (6.8%) was used as fuel in the study. The base case for comparison was a typical regenerative furnace condition with combustion air preheated to H O O K . The crown and furnace breast walls were taken to be adiabatic with an emissivity of 0.6. An emissivity of 0.9 was imposed on the glass melt surface, and a linear temperature profile varying from 1750K at the center of the furnace (midway between the ports) to 1700K at the furnace walls. T w o different techniques for reducing N O x were explored as part of this study: 1) Oxygen lance, and 2) oxygen/fuel firing. Additionally, the effect of soot on the N O x levels in the exhaust was also studied. In addition, the impact of soot on the combustion characteristics and furnace operation figures of merit outlined previously was explored by performing predictions with and without soot generation in the combustion process. The N O x reduction methodologies and specific cases investigated are n o w briefly described. Oxygen Lance. As a byproduct of other processes in a typical glass production and fabrication plant oxygen exists in non-negligible amounts. This is available for use as oxidizer in the furnace. The preheated combustion air flow rate was reduced to accommodate an oxygen lance issuing from a position along the furnace breast wall midway between the port centerplane and the symmetry line dividing adjacent ports, as shown in Fig. 3. Three different lance cases were investigated: 1) 1 0 % of the total furnace oxygen flow was introduced as pure 0 2 in the lance with a global furnace stoichiometry of 1 1 9 % theoretical 0 2 (the remaining oxygen was introduced in the conventional Preheated air port centerline Q lance symmetry line Figure 3. Schematic illustration of the oxygen lance geometry. |