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The stirring and mixing behavior of gas-liquid-solid three-phase systems refers to the process in which gas is introduced into a liquid, while a solid phase dissolves or is formed, or both are involved in chemical reactions. Stirring is generally not required for processes involving gas emission. The mixing behavior of gas-liquid-solid three-phase systems mainly focuses on how the flow patterns generated by the stirrer affect it (1) Dispersion: The dispersion of gas in the container is affected by the solid particle concentration and particle size distribution. (2) Suspension: The suspension of solid particles in the container is affected by the gas flow rate and bubble size. Three-phase systems often involve the use of multiple agitators to achieve gas-liquid dispersion and solid-liquid suspension, respectively. 1. Critical speed: In a three-phase mixed system, there are two critical speeds: the critical speed for gas dispersion and the critical suspension speed for solid particles. The relative magnitude of the particle density and the liquid density has a significant impact on the critical speed. When the particle density is much greater than the liquid density, it is more difficult to suspend the particles than to disperse gases, and aeration has an adverse effect on particle suspension. When their densities are similar, it is easier to suspend particles than to disperse gases. Moreover, the higher the gas velocity, the lower the critical rotation speed for particle suspension. 2. Three-phase mixing equipment mainly includes the tank, impellers, distributor, baffles, etc. The kettle type is mostly an upright cylindrical vessel with a flat or disc-shaped bottom; common paddle types include straight-blade disc turbines, upward-acting inclined-blade disc turbines, downward-acting inclined-blade disc turbines, upward-acting inclined-blade turbines, downward-acting inclined-blade open turbines, propeller paddles, and three-blade swept paddles; baffle types include flat baffles and finger-shaped baffles; gas distributors include single-hole vertical tubes, horizontal tubes, horizontal cross-tubes, distribution rings, concentric clusters of distribution rings, and conical distributors; furthermore, when finger-shaped baffles are used, they often serve simultaneously as distributors as well. 2.1 The shape of the bottom of the tank has a significant impact on the suspension of particles, as the flow pattern created by the stirrer is streamlined. The non-streamlined shape of a flat-bottomed tank hinders the flow pattern generated by the stirrer, which can result in a reduced flow velocity of the liquid. The prerequisite for particle suspension is the sliding of the particles at the bottom of the tank, and the force driving this sliding is the flow velocity of the liquid. Therefore, a flat-bottomed tank is not conducive to suspending particles; it results in the formation of bands of deposited particles in the center or along the sides of the tank bottom. These particles are the hardest to keep suspended, which is why the suspension performance of a flat-bottomed tank is inferior to that of tanks with spherical or dish-shaped bottoms. At the same gas volume, the larger the reactor diameter and the lower the gas velocity, the lesser the impact of the gas on particle suspension. 2.2, Agitator: When straight-blade disc turbines or upward-acting inclined-blade disc turbines are used, the particles that remain suspended end up on an annular band near the center of the tank bottom; whereas with downward-acting inclined-blade open turbines, they end up at the corners of the tank bottom wall. This indicates that the difficulties in suspending and the methods for dispersing particles using different agitator types vary, and it is appropriate to study the suspension and dispersion of particles from the perspective of flow patterns. 2.3 Gas distributor: When a distributor is present but there is no air flow, the distributor located at the bottom of the tank poses a significant obstacle to the suspension of particles; a higher rotation speed is required to keep the particles suspended. If the distance of the distribution ring from the bottom of the tank is too small, it is not conducive to the complete suspension of the particles. The larger the diameter of the gas distribution ring and the more openings there are on it, the lower the critical speed. This is because with a larger distribution ring, the bubbles emerging from the openings have a relatively lower velocity; moreover, the more openings there are, the lower the velocity of the bubbles emerging from them, which results in less impact on the suspension of particles at the bottom of the tank. 3. Operating process conditions: From the perspective of the critical dispersion speed, the optimal structural parameters vary depending on the process conditions. For low gas volumes, a downward-acting turbine is suitable, while for high gas volumes, an upward-acting turbine is the best choice. This is because the lift effect is very strong when the gas volume is high, and only by coordinating the lift effect with the mixing action can the best results be achieved. Furthermore, among various gas distribution rings, the larger ones are preferred. 4. Typical gas-liquid-solid three-phase stirred reaction: Liquid-phase catalytic hydrogenation is a typical gas-liquid-solid three-phase stirred reaction. Liquid-phase hydrogenation technology has widely replaced traditional reduction methods such as iron powder, alkali sulfides, and hydrazine hydrate, enabling a reduction of waste emissions by over 90% while improving the yield and quality of the products. This technique is mainly used for the reduction of alkynes, aromatics, and unsaturated compounds containing cyano, nitro, imino, carbonyl, and other functional groups. In liquid-phase catalytic hydrogenation, the gas phase is hydrogen, and the solid phase is catalyst particles. Among various hydrogenation equipment, the most typical combination is a self-priming mixer and an axial flow impeller. Due to the relatively limited amount of hydrogen supplied, this can severely hinder an increase in the reaction rate. By using a self-priming mixer to draw the hydrogen at the liquid surface back into the tank and disperse it within the liquid phase, the gas content and the contact area between the gas and liquid phases can be significantly increased, thereby boosting the reaction rate. If the liquid is deep, the suction capacity and gas dispersion efficiency of the self-priming mixer will **decrease**; in such cases, axial flow impellers need to be used to improve the flow pattern and enhance suction as well as gas dispersion.