A Study on the Slagging And Fouling Propensity of Imported Coals Blended with Indian Coal

Coal blending excercises are becoming popular in the present day scenario with many of the Indian thermal power plants. Blending of an inferior variety of indigeneous coal with that of high quality imported coal is gaining importance. With the depleting coal reserves in the country leading to deterioration of the indigeneous coal quality and less availability of the high grade coals, it has become imperative on part of the power generation plants to import high quality coals and blend them with inferior variety of indigeneous coal and burn them in the boilers for power generation.
It is challenging to ensure that the resulting coal blend will maintain the required plant output without damaging the boiler and high temperature components.
Combustion of various coalsblends in the boiler lead to a variety of complex thermochemical reactions. The inert residue of coal combustion product which is ash is composed of complex oxides of various minerals. The quantity and the characteristic of the ash is inherent to the particular type of coal combusted. The fusion of this ash in the boiler during combustion may sometime lead to slag forming and fouling problems. This slagging and fouling phenomenon is dependent on a number of factors such as the ash chemical composition, combustion temperature, combustion atmosphere, boiler operating parameters etc., Deposition of coal ash/slag and fouling impedes the heat transfer there by increasing the Flue Gas Exit Temperature (FEGT). Ash deposits due to fouling on convective pass tube banks can block flow passages. Large deposits in the upper furnace or radiant zone dislodge and fall which may cause damages to the lower furnace pressure parts. Extreme ash deposition leads to forced outages and corrosion problems. Keeping the above in view it is important to study the various parameters related with blended coal so as to ascertain the proper blend ratios, operating temperature, boiler conditions and other factors.
In this study 3 types of imported coals and an Indian coal was blended in various proportions and the blended coals were studied for their various paratmeters such as ash fusion temperatures, chemical compositions etc., and by applying certain indices, the behavior of the residual blended coalash for its slagging and fouling propensity have been reported.