Systems of undergrate (underfire) blast

The system of undergrate (underfire) blast is designed with the purpose of improving burn-up and efficiency of boiler plant at combusting lignites and brown coals. Most separating mills-ventilators produce comparatively rough dust, including particles, which are more than 1 mm in size. As a rule, these particles are not burnt up in a furnace, and most of them are precipitated as slag, thus increasing heat losses accompanied with mechanical underburning.

To reduce heat losses, we are presently successfully operating system of undergrate (underfire) blast, which is actually a system of hot air flows delivered all along the slopes of sloping bottom by the adjacent-opposite scheme at the velocity of 35 m/s. A share of the air given from the undergrate (underfire) blast nozzle is ~ 12…17% of the overall air consumption (see the figure). Removal of this part of air does not only improve the coefficient of efficiency, but it also provides diminishing the NOx emissions.

System of undergrate (underfire) blast installed in the P—64 boiler plant and the P—68 boiler plant of the 210 MW power generating unit at TPP “Bitola” (Macedonia).

System of undergrate (underfire) blast in sloping bottom  is most effectively applied to the boiler plants combusting lignites with more content of xylites. At TPP “Bitola” in Macedonia, a share of xylites in total amount of lignites is up to 10-12% (see the figure). In addition to the said above, undergrate (underfire) blast provides growing the temperature of gases in the lower section of a furnace up to 150-160ºC, which results in increasing stability of combustion and of heat exchange in that area, and in improving the temperature mode on all heating surfaces of the boiler plant.

System of undergrate (underfire) blast in sloping bottom  was put into production at a number of power stations in Russia and former Soviet republics (CIS), including such facilities as the Troitsk and the Novo-Angrensk State District Power Plants (SDPPs). Operating experience shows that customers are recommend introducing this system into boiler plants combusting lignites and coarse-ground brown coals.