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Show 2 Introduction Field test programs to characterize the NOx emissions from coal-fired utility boilers have become an increasingly important effort as utilities comply with the Clean Air Act Amendment requirements. Since NOx emissions are so strongly dependent on furnace combustion conditions, diagnostic techniques and test protocols have been developed to aid in evaluating the boiler combustion process. The evaluation of combustion uniformity in the burner zone is one of the most critical, but difficult and time consuming, tasks in a NOx emissions test program. The use of these diagnostic techniques has become increasingly important in all phases of NOx emissions compliance testing including: • • • obtaining representative baseline NOx emissions (e.g., for Phase II units); making a preliminary assessment of the NOx reduction potential of combustion modifications (e.g., simulated OFA); identifying equipment-related operating constraints that impact combustion uniformity and NOx emissions (applicable to post-retrofit tuning and warranty tests). The primary focus of most utility NOx control efforts is currently on achieving compliance with the Phase I regulations for 1995, but efforts to maintain compliance with a variety of different coal types and boiler operating modes will be just beginning. Some utilities with smaller, older units with inherently low NOx emissions are investigating boiler tuning and combustion modifications as an alternative to high capital cost 10w-NOx burner retrofits. Combustion diagnostics efforts to maintain optimum NOx emissions will become an ongoing key element in the compliance strategy for those units. It should be noted that the paper is intended to be a "hands-on", operations-oriented synopsis of a recommended combustion diagnostics methodology, as opposed to a case history paper of experiences at one plant. This approach provides the opportunity to include examples of field test data from a variety of different boiler types and problem areas. The key elements of a boiler tuning and NOx optimization test plan are outlined, as well as the benefits of using advanced combustion diagnostiCS instrumentation in performing these activities. This paper draws on the NOx field test experiences at several coal-fired units in the Consumers Power Company system as well as other test sites in a large EPRVDOE coal quality impact test program associated with the development of a Coal auality Expert (CaE) software package. NOx emissions testing became a key element of the CaE test program as utilities evaluated both the 802 and NOx emissions implications of blending or switching to a low-sulfur coal. Test results from other CaE project related activities are summarized in References 1 to 4. Factors That Inhibit Low-NOx Firing NOx emissions are strongly dependent upon boiler combustion conditions, unlike S02 emissions which are primarily dictated by fuel properties. One of the dominant boiler |