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Show In-Furnace Low NOx Solutions for Wall-Fired Boilers BACKGROUND As a result of the recent Clean Air Act and specific local regulations, boiler operators are addressing the need to reduce stack gas emissions. Current attention is focused upon controlling acid rain precursors, oxides of nitrogen (NOx) and sulfur dioxide (S02). Under Phase I of the ~Iean ~ir Act, a number of pre-NSPS coal burning wallfired bOilers will be required to reduce their NOx emissions by the mid 1990's. The proposed Federal upper lir.1it for NOx emissions from wall-fired units is 0.50 Ib/ MBtu fired. ABB Combustion Engineering Services, Inc. (ABB-CE) has been actively developing and commercially demonstrating low NOx technologies for coal-fired tangential and cyclone boiler arrangements. In order to meet the NOx reduction needs of coal wall-fired boilers, ABB-CE has embarked on an extensive low NOx coal burner development and commercial demonstration program building on its substantial wall-fired experience base with the ABB-CE Type R burner. The Type R horizontal burner was developed by Combustion Engineering Inc. in the early 1940's. This burner was designed to burn pulverized coal, oil, or gas, and is applicable to single wall or opposed wall firing in either single or multiple burner arrangements. In terms of experience, several thousand Type R burners have been installed and operated in a wide variety of boiler configurations ranging up to 160 MWe in capacity. Individual burner capacities have ranged from 20 MBtu/ hr to 120 MBtu/hr. As a result of this extensive field experience, ABB-CE has established Type R design standards which delineate proven materials of construction and fabrication techniques, Type R operating procedures are also firmly established. The Type R coal burner (illustrated in Figure 1), has several key hardware features. The centrally located coal nozzle has spiral rifling along the inner walls to promote swirl of the pulverized coal/primary air stream which is initially established by a tangential inlet nozzle. A convergent nozzle tip is located at the end of the coal nozzle. Five (5) deflector vanes, located near the tangential inlet nozzle, can be adjusted in terms of incident angle to vary coal/primary air stream swirl which in turn , influences final luminous flame shape. On the combustion air side, the total combustion air flow passes through an adjustable angle flat blade swirler assembly. Combustion air angular momentum can be varied to optimize the burner's flame stabilizing aerodynamic recirculation zone, directly influencing both flame stability and flame shape. LABORATORY DEVELOPMENT PROGRAM In order to respond to low NOx requirements for the wall- fired coal boiler retrofit market, ABB-CE embarked on a laboratory development program with the objective of developing a new low NOx wall-fired burner product. Figure 1: Type R Coal Burner The new burner, named the RO-II burner, would be capable of meeting the following performance targets: • NOx less than 0.5 Ib/106 Btu Fired • Zero or nominal increase in carbon loss and CO emissions under low NOx conditions • Acceptable flame envelope (length) • Zero or nominal increase in fuel system or combustion air windbox static pressure(s). At the onset of the development program. ABB-CE assessed the NOx reduction potential of the Type R burner design; upon review, it was decided to incorporate certain key design features of the Type R deSign into the new RO-II burner design. These features specifically included the tangential inlet. spirally rifled coal nozzle and an adjustable coal stream deflector vane assembly. The Type R combustion air register assembly was determined to not offer any advantages in terms of reducing total NOx so alternative air register assemblies were reviewed for incorporation into the new low NOx RO-II burner design. ABB-CE selected a patented. commercially available. air register for incorporation into the RO-II burner. Key features of the register are highlighted in Figure 2. These features include: 1. Two separate plenums which permit staged introduction of combustion air: - pilot air which is introduced concentrically adjacent to the centrally located coal nozzle - main air which surrounds the pilot air stream 2. Involute (spirally shaped) air inlets for each plenum which swirl total combustion air flow. |
