Empty Tower
The hollow scrubber, often simply referred to as the “empty tower,” is commonly used as the first-stage scrubbing unit. Structurally, it consists of a hollow cylindrical vessel; the scrubbing liquid is sprayed from nozzles located at the top and mid-section of the tower, while the medium-temperature dust-laden gas from the roasting process flows upward through the empty tower, where it comes into contact with the scrubbing liquid to achieve dust removal as well as mass and heat transfer. The gas exiting the empty tower is then cooled to the specified outlet temperature. Due to its low pressure drop, resistance to clogging, and ease of scaling up, the empty tower is widely employed in large sulfuric acid plants.
Packing Scrubber
It is commonly used as a secondary purification and scrubbing unit. The tower consists of a column shell, packing, and internal tower components. These internal components include liquid distributors, packing supports and retainers, liquid collectors, and gas distributors, among others. Packing materials may include structured packings made of polypropylene, such as Haier rings and saddle rings. Currently, packed towers constructed with fiberglass-reinforced plastic (FRP) column shells are widely employed due to their excellent overall integrity, lower capital investment, shorter fabrication lead times, and superior corrosion resistance.
Washer
The scrubber consists of three main components: a reverse-flow nozzle, spray nozzles, and a liquid collection tank. When the gas to be purified flows downward through the reverse-flow nozzle, the scrubbing liquid is sprayed upward from the nozzles, resulting in high-velocity gas–liquid impingement that creates a foam zone. Within this foam zone, mass transfer, heat transfer, and dust removal can take place. The scrubber exhibits strong adaptability to fluctuations in gas flow, making it widely used in acid-production units for smelting gases with large flow variations. Moreover, due to its ease of scaling up, it has seen increasing application in large-scale sulfur–iron ore–based acid-production plants in recent years.
Inclined-tube settler
The inclined-tube settler is a liquid–solid separation device designed based on the “shallow-tank sedimentation principle.” Compared with horizontal-flow sedimentation tanks, inclined-tube settlers feature a smaller footprint, greater treatment capacity, and higher sedimentation efficiency. Their moderately advanced technology and moderate cost make them widely used in the purification and dilute-acid treatment processes of sulfuric acid plants.
