Seeking advice on cyclone separators in circulating fluidized bed boilers

CFB cyclone separators are divided into three types: steam-cooled, water-cooled, and insulated. Those whose casing is surrounded by membrane-type heating tubes and cooled by steam from the steam drum (for the superheated heating surfaces) are known as steam-cooled separators. Those whose casing is surrounded by membrane-type heating tubes and cooled by feedwater or boiler water (for the evaporating heating surfaces) are known as water-cooled separators. Those with a steel plate casing, an inner layer of fire-resistant material, and an insulating layer, without any heating surfaces, are known as insulated or steel-plate type separators. The selection of the three types of separators is related to factors such as coal characteristics, boiler parameters, and heat transfer surface distribution; a comprehensive consideration is required before making a choice. The upper part of the air-cooled cyclone separator is cylindrical, while the lower part is conical. The flue gas outlet of the separator (the central cylinder of the cyclone separator) is a cylindrical structure made of cylindrical steel plates with one end open, and its length extends almost to halfway up the cylinder of the cyclone separator. The fine particles and flue gas that enter the separator flow downward in a rotational motion to the cylindrical area, where they then flow upward; the separated particles fall to the bottom of the cylinder and enter the vertical pipe and return conveyor connected to the separator. The fine particles that have not been separated, along with the flue gas, leave the separator through its flue gas outlet. The cyclone separator has a membrane-type wall-enclosed superheater structure. Its top and bottom are both connected to the annular header, and the wall tubes bend inward at the top, creating a sealing structure between the cyclone separator tubes and the flue gas outlet cylinder. The medium flowing inside it is superheated steam that has been heated by the heating surfaces in the inlet flue of the cyclone separator. This superheated steam first passes from the outlet header of the heating surfaces in the inlet flue to the lower annular header of the cyclone separator via steam guide pipes; thereafter, it is heated by the tubes surrounding the separator and then sent to the upper annular header, from where it enters the side wall superheater through steam guide pipes. A large number of short pins are welded to the inner surface of the cyclone separator, and an anti-wear material is applied, with a thickness of 20–30 mm from the outer surface of the tube. The outside of the air-cooled separator is equipped with a insulation layer and protective plates similar to those on the outside of a water-cooled wall.

The separation efficiency at the inlet of the separator volute is higher than that at the tangential inlet, and the pressure drop is reduced; however, the manufacturing cost is higher. Whether to use a volute inlet or a tangential inlet depends on the design. The inner surface of the cylinder should be lined with a high-temperature, wear-resistant cast material.