**Primary methanol distillation tower

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Methanol distillation is an important post-treatment process for enterprises producing alcohols or monoalcohols. As the scope of methanol use continues to expand, many companies are planning or have already begun to expand their existing methanol production facilities, while other companies are actively raising funds to build new methanol plants. To provide guidance for methanol producers in terms of methanol distillation processes, equipment selection, and equipment expansion and renovation, this article offers insights based on the process characteristics, application performance, and technical advantages of new vertical sieve-plate methanol distillation towers. It presents suggestions regarding the expansion and energy-saving renovation of existing methanol distillation units, as well as the process design and equipment selection for new installations, for reference. II. Structural principle and technical characteristics of the new type of vertical sieve plate The mass transfer unit structure of the new type of vertical sieve plate column is shown in Figure 1; it consists of vapor rise holes on the tower plate in the form similar to Venturi nozzles, along with caps covering these holes. To meet various process requirements, the caps are available in various shapes and sizes such as cylindrical, semi-cylindrical, square, rectangular, and conical, among others, with the cylindrical cap being the most commonly used type at present. The mass and heat transfer process in gas-liquid contact is as follows: The gas rising from the lower tray passes through the upward gas holes, where the flow rate decreases and the static pressure falls. The liquid on the tray enters the cap zone due to its own hydrostatic pressure as well as the suction force exerted by the gas flow; there, it forms a gas-liquid mixture that undergoes mass and heat transfer while rising, thus completing the first stage of the mass transfer process, which is similar to that in conventional bubble-type trays ； After the gas-liquid mixture reaches the top of the hood, the liquid surface is refreshed, and the second stage of mass transfer takes place within the space of the hood ； Then, the gas-liquid mixture is sprayed horizontally through the openings in the upper side wall of the cap, and the liquid is dispersed into numerous droplets of varying diameters, thereby creating a large mass transfer surface. After the third mass transfer and heat transfer process takes place in the space above the liquid layer, the droplets return to the liquid layer on the plate, while the gas continues to rise to the upper trays. From the above introduction, it is easy to understand that the new type of vertical sieve plate possesses the following characteristics: ① High mass transfer efficiency and good utilization of the mass transfer space. Each layer of plate undergoes a mass transfer process in three stages. Based on experimental tests and comparisons with industrial applications, the mass transfer performance of the new vertical sieve tray is comparable to, or even higher than, that of the currently recognized highly efficient tray type—the floating valve tray. ②High processing capacity. Since the flow direction of the gas-liquid mixture ejected from the cap is horizontal, rather than vertical or upward at an angle as in conventional tray or packed towers, the vertical velocity component of the liquid droplets is very small, resulting in little entrainment of mist in the gas stream. This allows for high operating gas velocities even with a relatively small spacing between trays. Additionally, trays can have a higher open area ratio compared to floating valves, bubble caps, sieve trays, etc., which further increases the processing capacity of this tower. According to actual measurements, the processing capacity of this tower is more than 50% higher than that of float valves and sieve plates, and it is also 10%–20% greater than that of the currently recognized high-efficiency plate corrugated packing (250Y). ③High operational flexibility. The normal operating range is even larger than that of a floating valve tower. ④Simple structure and reliable. This tray has no moving parts, so the mass transfer units will not come loose due to wear or vibration, resulting in virtually no maintenance required. ⑤It has excellent anti-scaling and anti-clogging properties. Due to the high operating gas velocity, the airflow has a strong self-cleaning ability, and the diameter of the lift holes is large, making blockage unlikely. ⑥The spacing between mass transfer units is large, facilitating the installation of heating and cooling tubes. ⑦Ministry of Investment (see investment comparison table). ⑧The liquid surface gradient on the plate is small, resulting in good lateral mixing of the liquid surface, with no flow or mass transfer dead zones.