Study on fouling mechanism in a boiler burning Xinjiang coal with high content of calcium and sodium

The fouling deposits were collected along the flue gas in a 350 MW boiler burning Xinjiang coal with high content of calcium and sodium. Through the coupling study on the transformation of Na/Ca/S/Cl and the ash deposition on cooling surface in laboratory, the fouling mechanism for burning high calcium and sodium coal was proposed. The results indicate that the deposition of calcium and sodium sulfate aerosol on heating surface plays an important role in the fouling process. Sodium is mainly released in the gaseous forms of element, oxide, and chloride, in which more than 50% is released below 600 ℃. The gaseous sodium species react with sulfur oxides in flue gas at high temperatures to produce sulfates that condense and then deposit. Calcium is quickly released in the forms of oxide and element at higher temperature more than 1 100 ℃, and more than 80% is released at the temperature more than 1200 ℃. The released calcium species also react with sulfur oxides to produce sulfate, and then with the decreasing in gas temperature, the calcium sulfates condense and deposit.