Experimental Study on Two-Stage Modification, Combustion and NOx Emission Characteristics of Pulverized Coal in a Purification-Combustion Reaction System

To achieve deep NOx control, we investigated a purification-combustion system consisting of devolatilizer, swirl burner and down-fired combustor, and explored the influences of primary and secondary air ratios (lambda(p) and lambda(2)) on two-stage modification, combustion and NOx emission of pulverized coal in a 30 kW purification-combustion experimental bench. In devolatilizer and swirl burner, the temperature in different positions increases with lambda(p) and lambda(2) rising. Moreover, the location of main burning zone in swirl burner could be changed by increasing lambda(p) rather than lambda(2). CO and H-2 are the main burnable components in modified gases, and their concentrations decrease with lambda(p) and lambda(2) increasing. By contrast, the CH4 concentration is extremely low. Purification system composed of devolatilizer and swirl burner outperformed single-stage devolatilizer in increasing specific surface area, pore volume, pore diameter and fuel conversion rate of pulverized coal as well as improving its carbon microcrystalline structure, and these indexes of modified char are better and better with lambda(p) and lambda(2) increasing properly in this system. In down-fired combustor, as lambda(p) and lambda(2) increase, the temperature changes slightly in reduction region, while it decreases in complete combustion region only at lower lambda(2). Properly rising lambda(p) and lambda(2) will reduce the NOx emission with high efficiency of above 99.00%, but the emission reduction driven by lambda(2) is limited.