Numerical and experimental study on co-firing of low volatile coal in a 330 MW tangentially fired boiler

Abstract

Burnout related problem occurs in the utility boiler burning low volatile coals. The in-furnace co-firing of low volatile coal (LV) experiments and simulation were carried out in a tangentially fired PC furnace to investigate the effect of co-firing ratio, injection position and particle size on NOx emission and carbon in fly ash (Cfh). The results of full-scale experiment show that Cfh increases from 2.16% to 4.21% as the LV co-firing ratio rises from 33% to 50%, while the NOx emission increases from 356.0 mg/Nm3 to 385.2 mg/Nm3 (@6% O2). The model is validated against the experimental data. The numerical simulation results show that NOx increases from 308 mg/Nm3 to 567 mg/Nm3 when the co-firing ratio of LV increases from 0% to 100%, while Cfh increases from 1.20% to 7.15%. It is found that the contribution of top two layers (E and F) to the total Cfh is significantly higher than that of the other layers. Under the working conditions of burning bituminous coal in the bottom layer and lean coal (particle size 70 μm) in the upper five layers, Cfh is 5.4%. When the particle size of lean coal in the five layers is reduced to 40 μm, Cfh rapidly decreases to 2.0%. And the Cfh can be reduced to 2.5% when only the top two layers feeding lean coal with smaller particle size (40 μm). Only 40% marginal cost of coal grinding is needed to reach the marginal benefit corresponding to 83% Cfh improvement while all layers of LV coal are ground into the small size.