A spray drying tower is a drying machine that directly dries a solution into solid particles.

The spray drying tower is the fastest-developing and most widely used type of drying equipment. It is suitable for converting liquid feedstocks—such as solutions, emulsions, and pumpable suspensions—into powdered, granular, or lumpy solid products. The choice of atomizer, airflow pattern, and drying chamber design is determined by the material’s specific drying characteristics—such as heat sensitivity, viscosity, and flowability—as well as the product’s quality requirements, including particle size, particle size distribution, residual moisture content, bulk density, and particle shape.

The slurry, which has been ground in a ball mill, is further mixed uniformly in a mixing tank and heated to above 35°C. Pressure is then applied to the mixing tank; under this pressure, the slurry is fed to the atomizer, where it is atomized and sprayed into the tower from the bottom. N₂ heated by the oil-gas heat exchanger is delivered by a blower to the gas distributor at the top of the tower. After passing through the gas distributor, the N₂ enters the tower uniformly in a cyclonic pattern to dry and granulate the atomized slurry. Upon contact with the hot gas, the liquid on the surface of the granules evaporates rapidly, while the internal gas migrates to the surface during the subsequent drying process and is carried away by the hot gas. The dried granules fall to the bottom of the tower and are recovered intermittently via a pair of butterfly valves.

The gas remaining after the slurry is dried contains vaporized hexane and a small amount of fine dust. This gas is first sent by a pressure blower to a cyclone separator for preliminary dust separation, and then directed to the condensation-scrubbing tower. Inside the scrubbing tower, the gas undergoes thorough scrubbing; the hexane contained in the gas is condensed and collected at the bottom of the scrubbing tower, while the scrubbed gas is sent to an oil-gas heat exchanger for reheating and reuse. During operation, the system maintains a slight positive pressure, automatically controlled by an air supply valve and an exhaust valve.

To avoid the drawbacks of hot-air vortices and axial flow, a hot-air straightening chamber has been installed. At the outlet of the straightening chamber, fixed blades resembling the guide vanes of a honeycomb-type rotary-paddle water turbine are fitted. The hot air flows radially out from the fixed blades, further altering its direction before being blown into the drying tower. In this way, the fixed blades convert the turbulent hot air into an axial flow supplied to the drying tower, achieving the purpose of flow straightening. This is highly effective in resolving the issue of product adhesion inside the drying tower. Furthermore, the straightened flow prevents the hot air from recirculating, ensuring that the spray is heated uniformly as it descends and minimizing thermal variations in the final product, thereby improving product quality.

The spray drying tower is very convenient to use, offers excellent sealing, and delivers outstanding performance. The drying speed is extremely fast.

A spray drying tower is a drying device that directly converts solutions or suspensions into solid particles. It allows the direct production of dry products from the feed liquid, eliminating the need for unit operations such as evaporation, crystallization, separation, and grinding. It enables continuous, automated production with stable operation. With this drying method, the spray drying tower features a large gas-solid contact surface area and a short drying time—typically 5 to 30 seconds—making it suitable for drying heat-sensitive materials. The resulting product is of high quality, with particle sizes ranging from 30 to 50 μm, and exhibits good flowability and rapid solubility. The drawbacks include the large size of the dryer and a low heat transfer coefficient, which lead to low thermal efficiency and high power consumption.

The spray drying tower is a type of continuous, atmospheric-pressure dryer. Special equipment is used to atomize the liquid feed into a mist, which is then dried through contact with hot air. It is used to dry certain heat-sensitive liquids, suspensions, and viscous liquids, such as milk, eggs, tannins, and pharmaceuticals. It is also used to dry fuels, intermediates, soap powder, and inorganic salts.

The drying rate is fast; after atomization, the surface area of the feed liquid increases significantly. In the hot air stream, 95%–98% of the moisture can be evaporated instantly, with the entire drying process taking only a few seconds, making it particularly suitable for drying heat-sensitive materials.

The final product exhibits good uniformity, flowability, and solubility, with high purity and excellent quality. The production process is simplified, and operation and control are convenient. Liquids with a moisture content of 40–60% (up to 90% for special materials) can be dried into powdered or granular products in a single step. No grinding or screening is required after drying, which reduces production steps and improves product purity. Product particle size, bulk density, and moisture content can be adjusted within a certain range by altering operating conditions, making control and management very convenient.

There are many ways to classify spray drying towers. Based on the direction of gas and liquid flow, they can be divided into co-current, counter-current, and mixed-flow types; based on the installation method of the atomizer, they can be divided into top-to-bottom and bottom-to-top types; based on the structure of the atomizer, they can be divided into centrifugal, pressure, and air-jet types; and based on whether the heating gas is recirculated, they can be divided into open, partially recirculating, and closed types.