Research on combustion and emission characteristics of circulating fluidized bed during load changes

Abstract

The conventional design of circulating fluidized bed (CFB) focuses more on high combustion efficiency and low pollutant emission. However, as the proportion of new energy generation in China continues to increase, the power grid is placing higher demands on the operational flexibility of thermal power units. The CFB has the advantage of a wide range of load regulations, and it is an inevitable choice to participate in the deep and flexible peak regulation of the power grid. In order to conduct research on the features of CFB during load changes, this work used 0.1 MWth CFB as the research object and examined its combustion and emission characteristics at different loads, as well as the change in temperature and pollutant emissions during load changes. The results showed that the temperature distribution along the height direction of the furnace was not uniform at lower load, while the inhomogeneity of the temperature distribution decreased, and both the temperature and pressure of the furnace increased as the load increased. Moreover, NOx emission and combustion efficiency both rose with the load. When the load increased from 30% to 100%, the NOx emission increased from 228 mg/m3 to 324 mg/m3, the CO emission decreased from 1422 mg/m3 to 104 mg/m3, and the carbon content of the fly ash decreased from 39.2% to 27.6%. If the temperature stability was used as the reference standard for load stability, the load-change rates on the combustion side of the experiment platform from 50% load to 75% load and from 75% load to 100% load under conventional combustion were 0.69%/min and 0.81%/min, respectively. In general, the load variation range of the CFB was wide, but the load-change rate on the combustion side and the combustion efficiency at low loads need to be further improved.