Improvement of protective sleeve

An improvement of protective sleeve for acid-making fire-tube exhaust-heat boiler is characterized in that: the protective sleeve comprises two parts, the tail is columnar and the front is a hollow hexagonal head structure; the material is made of a special high fire-resistant, and high-strength material. The utility model is matched with a tube plate and a tube hole arranged in hexagonal array, which makes the counter-fire face of the front tube plate is covered the hexagonal head which can protect the sleeve; heat resistance concrete is filled into the gap between the hexagonal head and the round tail and tamped, which can avoid the washing-away of high-temperature fume and prevent the cracking and collapsing of the heat resistance concrete, thereby protecting the front tube plate effectively.