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Show Work is now in progress at ABB C-E, under ENEL funding, to both extend the capabilities of the CCTFS to multi-fuel design boilers as well as evaluate other promising in-furnace NO reduction technologies . Multi-fuel firing capability is of interest to ~NEL because all of ENEL's coal designed boilers are also capable of oil and natural gas firing . The low NO firing system development program includes an evaluation of fuel admis~ion assemblies, overfire air (OFA) , flue gas recirculation ( FGR) , and reburning system design and operating v ariables . The evaluation is being performed in ABB C-E's Boiler Simulation Facility at a scale varying from 15 MWt to 30 MWt . A number of tests are being performed under conditions which simulate coal, oil, and gas-fired ENEL boilers of the ABB C-E/F . T.C. radiant reheat pendant type . For each , the furnace volumes and heat release rates vary greatly and influence the choice of low NO firing modifications. For instance , lower overall NO emissions are ac~ievable with oil and gas firing in a coal capable x (multi-fuel ) boiler as compared with an oil-designed unit . Pil~t scale testing suggests that the targeted emissions level of 200 mg/Nm for oil in a multi-fuel designed unit may be reached with combustion modifications alone, thus avoiding the necessity of other abatement systems . However , this emissions level is more difficult to achieve on oil design units . Therefore, ENEL's present plan is to proceed with the installation of hi~h-?~jt type Selective Catalytic Reduction systems (SCR) in those unlts . CCTFS Although tangential firing ?~j the lowest proven NO emissions of any standard firing arrangement ,ABB C-E has maintai~ed an active development role in controlling NO formation through in-furnace combustion techniques . This polic~ has been pursued since the early-1970's in order to provide customers and licensees with several options for cost effective NO reduction methods for different NO emissions levels . x x Building upon this experience, ABB C-E has advanced the state-of-the-art in NO emissions control with a new system called the Concentric Clustered Tange~tial Firing System (CCTFS). Like earlier ABB C-E firing systems , CCTFS is designed to control the availability of oxygen to the fuel throughout the combustion process. CCTFS (Figure 1 ) is a "deeply staged" combustion technique that employes multiple elevations of Overfire Air (OFA) to minimize the available O 2 in the primary combustion zone . OFA is introduced at the top of the main windbox of the fuel admission assemblies (as close coupled OFA) and at a higher elevation (as separated OFA). The two levels of OFA, together with variable injection angle and velocity, permit tailoring the mixing rates of OFA and furnace gases to maximize NO reduction for a given boiler and fuel . Since the main windbox height doe~ not change in most retrofit applications , pressure part and other structural modifications are minimized. The CCTFS design also utilizes the patented concentric firing principt~ ) of directing the auxiliary air away from the fuel toward the waterwalls . This may serve to protect the waterwalls from the near-reducing atmosphere inherent when bulk furnace combustion staging techniques are employed . In certain cases , concentric firing has demonstrated an ability to control 2 |