The effectiveness of a novel coal-igniting-fuel technology and application in a direct current burner

Abstract As alternative energy sources increase the proportion of intermittent energy supplies in power grids, coal-fired power plants have come to play an important role in flexible peak power regulation. The burner is the core of the pulverized-coal boiler, and so its performance greatly affects the ability to achieve stable combustion at low boiler loads and also determines the load adjustment range. A novel coal-igniting-fuel technology using intermediate frequency induction heating has been proposed as a means of obtaining better combustion stability at low and variable loads. This method involves the combustion of a small quantity of coal particles in the ignitor to form a central pilot flame that subsequently ignites the surrounding pulverized coal in the main burner to achieve stable combustion. The present work utilized numerical simulations and full-scale experiments to systematically investigate the coal ignition and combustion characteristics associated with this technology. The numerical results show that coal particles inside the ignitor are rapidly heated and ignited, after which the resulting flame is gathered and accelerated by the flame extension tube, thereby forming a pilot flame near the ignitor outlet. When applied to a direct current (DC) burner, this ignitor is able to ignite the primary coal/air flow in a timely manner to form a second high-temperature zone near the burner nozzle. Compared with the absence of an ignitor, the flame center area appears roughly 1.6 m ahead. In an experiment using a single ignitor, it is found that the induction heating coil can quickly heat coal particles, thereby generating a stable high-temperature heat source within 80 s. The application of this ignitor to a DC burner allows the rapid start of the burner at a low initial ambient temperature, and the load can be adjusted over wide ranges of 17.6% – 100% and 13.6% – 100% when burning Shenhua coal and Blended coal, respectively. The degree of coal burnout is found to gradually improve as the thermal load of the burner is increased, reaching a maximum of approximately 93% at full load.