| OCR Text |
Show INTRODUCTION Nitrogen Oxides (NOx), including both nitric oxide (NO) and nitrogen dioxide (N02) , are known to be primary precursors to acid deposition and photochemical smog. The control of NOx emissions from utility boilers is required under the acid rain provisions of the 1990 Clean Air Act Amendments. Currently, there are three general types of NOx control approaches: precombustion fuel treatment, combustion modification, and post combustion flue gas treatment [1, 2, 3]. Fuel treatment reduces the amount of fuel-bound nitrogen. It is not cost effective and can only reduce fuel NOx. Combustion modification techniques inhibit the formation of NOx in combustors through changes in combustor design and operation. Only moderate amounts (30 to 40%) of NOx emissions can be reduced by combustion modification. Problems also exist in post combustion flue gas treatment techniques, which remove NOx from flue gas downstream. For example, selective catalytic reduction (SCR) can achieve high NOx reduction (90%). It is, however, costly and can produce secondary pollutants. To meet stringent regulations from government agencies and local legislatures, efforts are needed to search for new solutions or improvements to existing approaches. Among the post combustion flue gas treatment processes, a number of technologies are under development that use regenerable sorbent to adsorb NOx emitted from a combustor followed by desorption to produce a highly concentrated NOx-laden stream. This stream can then be sent back as part of combustion air to the same combustor or to a separate combustor, where the NOx is reduced in the flame. This concept is called NOx recycle, which has been developed by NOXSO Corporation and employed in the NOXSO Process [4, 5]. It is expected to be a simple, secondarypollutant- free, and cost-effective approach for NOx removal from flue gas, especially for 2 |
