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Show Low N0V Coal Burner Many, if not all, new utility and industrial boilers with a thermal input greater than 35 MW will be fired with pulverized coal. Wall-fired, field-erected watertube boilers constitute a dominant fraction of the capacity in these boiler classes. The low N0X coal burner has the potential for direct application to new and existing boilers. The program consists of three major elements: (a) burner design and scale-up criteria, (b) extension of the applicability of the technology, and (c) field evaluation of its performance on practical boilers. Burner design. Since the control of both thermal and fuel N0X from pulverized coal combustion is strongly dependent on the temperature and stoichiometry in the primary zone, the most direct approach is to redesign the burner to achieve the required fuel/air distribution. In 1971 the EPA initiated a small scale study to identify the important burner design parameters for N0X control. This study identified a distributed air burner concept that had the potential for very low N0X emissions with both high carbon utilization efficiency and acceptable flame characteristics. This pilot scale work was carried out at thermal heat inputs of 1.5 to 3.0 MW, which is a factor of 10 to 40 less than practical pulverized coal burners currently in use. Due to difficulties in scaling burner thermal performance by even a factor of 2, current design practice is to make incremental capacity changes, or simply install more burners of the same size. Therefore, to obtain industry acceptance of the low N0X burner technology, it was necessary to identify scaling criteria and to evaluate the burner performance at as close to practical size as possible. A project was initiated to develop scaling criteria for low emission burners. As an essential part of the program, a unique combustion facility capable of firing coal and other fuels at a thermal input up to 40 MW was designed, constructed, and used to study burner scale-up. The basis of the low N0X coal burner is a distribution of the combustion air to control the reaction history of the coal. This is shown conceptually in Figure 2. The coal is introduced with primary air and the initial devolatili-zation reaction takes place at a very rich stoichiometric ratio (SR^) which results in evolution of fuel nitrogen intermediates (XN) under conditions 3-13 13 |
