| OCR Text |
Show This paper summarizes the results of a feasibility study funded by the Gas Research Institute to evaluate the potential for the application of gas reburning to glass furnaces. Glass furnaces produce high concentrations of oxides of nitrogen (NO,rJ due to the high combustion temperatures required to melt the glass batch materials. Increasingly stringent air quality regulations are forcing the glass industry to reduce emissions of NOx. Two NOx control technologies that result in moderate, 40 to 50 percent, reductions at relatively low cost are 10w-NOx burners (LNB) and Oxygen Enriched Air Staging (OEAS). Two technologies capable of achieving high, 85 to 90 percent, reductions in NOx emissions are Selective Catalytic Reduction (SCR) and Oxy-Fuel. However, SCR has very high capital costs and Oxy-Fuel has very high operating costs, resulting in a high overall annualized cost of control for these technologies. Further, SCR is poorly suited to glass furnaces because the alkalis present in the exhaust gas can rapidly poison the catalyst. As demonstrated in this paper, gas rebuming is a technology which can be applied to glass furnaces to achieve NOx emissions levels potentially similar to Oxy-Fuel with a cost effectiveness equivalent to LNB and OEAS on an annualized cost per ton of NOx abated basis. The gas reburning process, as shown in Figure 1, divides the chemical pathway into three zones. The first zone is the primary zone where fuel and air are burned under nonnal conditions. In the second zone, a small amount of natural gas is injected downstream of the primary combustion zone to drive the overall stoichiometry slightly fuel rich. Depending upon the primary zone combustion stoichiometry, the amount of fuel required is 10 to 20 percent of the primary zone fuel. Hydrocarbon radicals formed from natural gas in the fuel rich reburning zone, primarily CH species, react with NO formed in the primary zone to fonn other reduced nitrogen species such as HCN and NH3. Once formed, these species rapidly react with the remaining primary NO molecules to fonn molecular nitrogen (N2)' Following the reburning zone, additional combustion air is injected to complete oxidation of the reburning fuel. In the burnout zone, any remaining reduced nitrogen species are converted to molecular nitrogen or back to NO. High combustion gas temperatures and high primary NOx concentrations can improve the NOx reduction achievable with gas rebuming. If gas reburning can be accomplished under nearly isothennal conditions and at residence times of roughly half a second, significant NOx reductions (greater than 80 percent) are theoretically possible. Glass furnaces appear to be good candidates for a successful installation of gas reburning because of their large post melter cavities (furnace ports and regenerator crown). Overall, NOx reductions of up to 85 percent have been estimated for glass furnaces using empirical and computational modelling tools. There are several potential approaches for application of gas reburning to glass furnaces. In the approach used in this study, it was assumed that the reburning fuel would be injected into the ports opposite the firing side to avoid major impacts on the heat distribution above the melt. For glass furnaces with sufficient gas residence time between the rebuming fuel injection point and the heat recovery device (Le. regenerator or recuperator), the burnout air would be injected just upstream of the heat recovery device. This makes gas rebuming an attractive technology for retrofit applications since the modifications necessary to install the technology are minimized. Application of rebuming during a furnace rebuild offers the potential for minimizing the impacts of reburning on furnace thermal performance and for increasing NOx reductions. For example, regenerators can be redesigned to substantially improve recovery of the reburning fuel heat content, and to implement advanced versions of the rebuming process. The objective of this feasibility study has been to assess the potential for successful application of gas reburning to control NO x emissions from glass furnaces used in the manufacture of container. flat and fiber glass. The overall effort was focused on retrofit applications since this is believed to be the current market. Conceptual designs were developed for retrofitting reburning systems on 2 |
