Breakup mechanisms of brittle deposits in kraft recovery boilers – a fundamental study

The breakup mechanism of brittle deposits removed by sootblower jets in kraft recovery boilers was studied in the laboratory by blasting model deposits made of gypsum with an air jet, and documenting the process using high-speed cameras. The results show that thin brittle deposits fail quickly, as an axial crack forms and propagates through the sample. In thicker deposits, the jet first drills a small hole in the deposit. As the hole grows wider and deeper, an axial crack forms, allowing the air jet to penetrate the deposit. This causes the front side of the deposit to split, and subsequently the back side of the deposit to be blown apart. The mechanism implies that in order for a sootblower jet to remove a brittle deposit effectively, it must be able to drill a deep hole and form axial cracks in the deposit within the short blowing time.