Design and combustion characteristics of a swirling pulverized coal burner with central hydrogen blending

Against the backdrop of the deep integration of clean energy and hydrogen production via water electrolysis, this study proposes a swirl pulverized-coal and hydrogen co-firing burner featuring the capability for online, flexible adjustment of both inner and outer secondary air swirl intensities, aiming for achieving low-carbon operation and flexible combustion control. Recognizing that central hydrogen injection into the core high-temperature recirculation zone enhances ignition and flame stability, this study investigates four representative central hydrogen blending schemes: a single-tube jet (Case 2), a two-layer small-orifice axial jet (Case 3), a two-layer small-orifice outward-expanding jet (Case 4), and a scheme involving an altered injection position (Case 5). Under a fixed hydrogen blending ratio of 30%, numerical simulations were conducted to systematically compare the flow and combustion characteristics. Results show that central hydrogen doping significantly reshapes the recirculation zone: compared to pure pulverized coal combustion (Case 1), the recirculation zone diameter shrinks to 0.61–0.83 times its original size, the flame elongates, and the peak temperature rises by over 300 K. The two-layer small-orifice jet structure promotes rapid hydrogen–oxygen mixing, thereby accelerating the reaction rates and shifting the high-temperature zone upstream. Although hydrogen doping effectively reduces the oxygen concentration at the furnace outlet and enhances the overall burnout rate, it leads to a significant increase in NO x emissions, reaching a maximum of 910 ppm. Among the schemes, Case 5 demonstrates superior performance in terms of intensifying mixing, shortening flame length, and accelerating reaction rates, yet further optimization with low-NO x control strategies is still required.