Experimental study on NOx emissions of pulverized coal combustion preheated by a 2 MW novel self-sustained preheating combustor

Abstract

In the study, a potentially feasible low-NOx combustion technology, based on self-sustained preheating combustion of pulverized coal, is proposed. A 2 MW novel self-sustained preheating combustion test rig was employed, and bituminous coal was used in the experiment. A novel internal fluidized bed combustor (IFBC) was used as the preheating chamber for pulverized coal, followed by air staging in the combustion chamber. Preheating characteristics of the IFBC and the temperature distribution in the primary combustion zone were discussed. Next, the effects of the air staging ratio of the preheated fuel burner and the positions of tertiary air on the combustion characteristics and NOx emissions of bituminous coal were investigated. The results demonstrated that pulverized coal led to a clean and efficient operation, producing a minimum NOx emission of 72 mg/Nm3 (@ 6% O2). The fuel could be preheated to above 900 °C stably, and the obtained conversion rate of fuel-bound N (fuel-N) was up to 80.2% in the IFBC. Moreover, the temperature profile in the primary combustion zone exhibited a symmetrical distribution along the central axis of the preheated fuel burner. The high-temperature primary combustion zone moved upward with increasing air staging ratio of the preheated fuel burner, and a region with low oxygen and strong reducibility was formed, inhibiting NOx generation. To maximally reduce NOx emission, a large retention time in the reducing zone and uniform mixing of reactants were crucial. The multi-layer arrangement and delayed supply of tertiary air were found to be conducive to significantly reducing NOx emissions.