Implementation of a three-stage scheme for the co-combustion of pulverized coal and coal-water slurry in an industrial boiler to reduce NOx emissions

In this paper, the co-combustion process of coal-water slurry (CWS) and pulverized coal fuel (PCF) in E500 pilot boiler when using staged afterburning scheme, was investigated based on numerical simulation. A complex three-dimensional mathematical model and numerical methodology was used to describe the CWS and PCF co-combustion, as well as subprocesses in the combustion chamber. The proposed mathematical model was tested based on data obtained from a full-scale experiment. A good compliance was shown between the computational results and the experimental data. A detailed comparative analysis of the effect of changes in the design of a pilot boiler when using a three-stage combustion scheme and the flare-drip combustion technology for CWS on the physical-chemical processes in the combustion chamber and environmental indicators was carried out for the first time. The change of circulation zones depending on the method of coal fuel supply during three-stage combustion was investigated. Calculations have shown that the implementation of the proposed changes reduced the underburning of solid carbon from 1.9% to 0.51%. It was revealed that using CWS as a reducing agent diminishes the amount of harmful NOx emissions by more than 40% compared to the basic version.