Abstract <p>Changing the operating power of a pulverized coal-fired boiler can be an important tool to compensate for fluctuations in wind generation and stabilize power system. Pulverized coal-fired boilers were originally designed for baseload operation but technical modernization and application of new technologies and improved control systems make it possible to use them in balancing power lines with a relatively high contribution of renewable energy sources. A BKZ-540-140-1 boiler serves as an example in a numerical study of the effect of blast oxygen concentration on coal dust combustion processes and ignition stability at low loads. An increase in the blast oxygen concentration stabilizes ignition and increases the efficiency of coal combustion in the boiler. Analysis of the calculated results shows that increasing the oxygen concentration at low-critical loads allows for a localized increase in temperature, which contributes to a reduction in flame size. An increase in the oxygen concentration by 5 and 10% leads to a reduction in the heat loss with flue gas by 13.5 and 20.5%, respectively.</p>