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Show Testing in the Pilot-Scale Slagging Furnace The pilot-scale slagging furnace design is designed to be as fuel-flexible as possible, with furnace exit temperatures of at least 2700°F in order to maintain desired slag flow. It has a nominal firing rate of 2.5 million Btu/hr and a range of 2.0 to 3.0 million Btu/hr using a single burner. The design is based on a bituminous coal (Illinois No. 6, 11,100 Btu/lb) and a nominal furnace residence time of 3.5 seconds. Resulting flue gas flow rates range from roughly 425 to 640 scfm, with a nominal value of 530 scfm based on 2 0 % excess air. Firing a subbituminous coal or lignite increases the flue gas volume, decreasing residence time to roughly 3 seconds. However, the high volatility of the low-rank fuels results in a high combustion efficiency (>99%). The furnace is oriented vertically (downfired) and base the burner design on a swirl burner currently used on two E E R C pilot-scale pulverized coal (pc)-fired units that are fired at 600,000 Btu/hr. Slagging furnace dimensions will be 48-in. inside diameter (ID) by roughly 16 ft in length. Combustion air preheat capabilities range from 300° to 900°F. The primary burner is both natural gas- and coal-capable, with coal particle size assumed to be a standard utility grind, 7 0 % -200 mesh. Burner development and testing are not objectives within this activity. However, some burner turndown is desirable and has been factored into the burner design. Flame stability is be assessed by observation of the flame and its relation to the burner quarl as a function of secondary air swirl and operating conditions at full load and under turndown conditions. The basic burner design, an International Flame Research Foundation (IFRF)-type adjustable secondary air swirl generator. A n JFRF-type adjustable secondary air swirl generator uses primary and secondary air at approximately 1 5 % and 8 5 % of the total air, respectively, to adjust swirl between 0 and a m a x i m u m of 1.9. Secondary air swirl is used to stabilize the flame. In the absence of swirl, loss of flame may result, increasing the risk of dust explosion. A s swirl is applied to the combustion air, coal particles are entrained in the internal recirculation zone, increasing the heating rate of the particles, leading to increased release of volatiles and char combustion. The flame becomes more compact and intense as swirl is increased to an optimum level, which is characterized in existing E E R C pilot-scale test facilities as the point at which the flame makes contact with the burner quarl. Increasing swirl beyond this level can pull the flame into the burner region, unnecessarily exposing metal burner components to the intense heat of the flame and possible combustion in the coal pipe. Increasing swirl to provide flame stability and increased carbon conversion can also affect the formation of N O x . The high flame temperatures and increased coal-air mixing associated with increased swirl create an ideal situation under which N O x may form. In full-scale burners with adjustable vanes, swirl is often increased to reach the optimum condition and then decreased slightly to reduce the production of N O x . Although N O x emissions are of interest, their control is not a key objective for the pilot-scale slagging furnace. Therefore, burner operational settings are based on achieving desired furnace exit temperatures and slag conditions in the furnace. Flame stability under turndown conditions is characterized by firing the test fuel at reduced load (typically 6 6 % to 8 5 % of the full load rate), maintaining the same primary air flow and adjusting |
