Abstract: [Objectives] To address the challenges of nitrogen oxide (NOx) emission control in a domestic circulating fluidized bed boiler burning lean coal with an adiabatic separator, this study investigates the influence of post-combustion characteristics of fuel on NOx emissions. [Methods] Measurements of flue gas temperature and composition at both inlet and outlet of the separator are conducted using a flue gas temperature probe and a gas analyzer equipped with water-cooled sampling devices. [Results] Significant post-combustion phenomena are observed within the separator due to three main factors: the low volatile content of boiler fuel, the structural design of adiabatic separator, and the combustion configuration in the furnace. This post-combustion leads to a flue gas temperature increase of up to about 62 ℃ at the separator outlet, along with reduced O2 levels and elevated CO concentrations. Without selective non-catalytic reduction (SNCR) denitrification, NOx concentration in the flue gas rises due to post-combustion phenomenon, with a maximum mass concentration difference of 33 mg/m³ between the separator inlet and outlet. Switching to high-volatility coal or optimizing in-furnace combustion can effectively eliminate post-combustion within the separator. [Conclusions] For circulating fluidized bed boilers burning low-volatility coal, extending fuel residence time through optimized particle size distribution and air distribution adjustments can mitigate post-combustion. The SNCR capacity and denitration efficiency can be improved by installing additional injection lances at the separator outlet flue. These findings provide practical guidance for improving the environmental and economic performance of circulating fluidized bed boiler operation.

Key words: circulating fluidized bed, boiler, clean combustion, selective non-catalytic reduction (SNCR), denitration, coal-fired power unit, ultra-low emissions, nitrogen oxides, adiabatic separator