High-efficiency sieve plate columns in distillation

High-efficiency guiding sieve plate: The high-efficiency guiding sieve plate is a new type of efficient tray developed by Beijing University of Chemical Technology as a result of in-depth research on various types of trays, including sieve trays. Building on the advantages of sieve trays such as their simple structure and low cost, it overcomes their shortcomings of high liquid leakage rates and low efficiency. This tray was created through thorough research and comparative analysis of different trays, taking into account the findings related to fluid dynamics and mass transfer in trays. High-efficiency guiding sieve plates feature large production capacity, high efficiency of the tray, reduced tower pressure, simple structure, low cost, and easy maintenance. It is currently widely used in the chemical industry, petrochemical industry, fine chemical industry, light chemical industry, pharmaceutical industry, fragrance industry, nuclear energy industry, etc. The systems in which it is applied include methanol-water (with impurities such as viscous resins and foaming agents in the raw materials), ethanol-water (for producing ethanol from fermentation broth), acetic acid-vinyl acetate, methyl acetate-vinyl acetate-water, acetylene-acetaldehyde-vinyl acetate, polyvinyl acetate-vinyl acetate-methanol, ethylbenzene-styrene, o-nitrochlorobenzene-p-nitrochlorobenzene, geraniol separation, heavy water separation, and so on. High-efficiency guiding sieve plates have been applied in hundreds of distillation and absorption towers, and have won multiple provincial and ministerial-level science and technology advancement awards. 　 The working principle of the high-efficiency guiding sieve plate is as follows: As shown in the diagram, this sieve plate is equipped with a large number of sieve holes as well as a small number of guiding holes. The gas passing through the sieve holes flows counter-currently to the liquid on the tray, rising vertically through the liquid layer. The gas passing through the guiding holes moves horizontally across the tray, transferring momentum to the liquid that is flowing horizontally there, thereby promoting uniform and steady movement of the liquid across the tray. This approach overcomes the issues of liquid level differences and backmixing that occurred in traditional trays, improves production capacity and tray efficiency, and resolves problems such as tray blockage and flooding. Furthermore, in traditional trays, due to the liquid level gradient, there is always an unactivated zone upstream of the tray, where the gas flow cannot penetrate through the liquid layer to rise and form bubbles. In the case of float valve trays, the first few rows of float valves upstream cannot open, while in the case of sieve trays, no bubbles are formed in an area upstream of the tray. According to experimental measurements, the area of the unactivated zone usually accounts for about 1/3 of the cross-sectional area of the tower. The high-efficiency guiding sieve plate features an upwardly protruding, stepped-shaped bubbling promoter at the liquid inlet, which facilitates bubbling as soon as the liquid enters the tray, thereby improving gas-liquid contact and mass transfer. High-efficiency guiding sieve plates have the following characteristics: 1. High production capacity. For the reasons listed below, high-efficiency guiding sieve plates offer a production capacity that is 50–100% higher, or even more, than that of traditional tray plates. (1) It overcame the deactivation zone present upstream of the liquid flow, thereby increasing the gas flow channel by more than 1/3. (2) The liquid surface gradient was eliminated, resulting in uniform gas velocity. In traditional trays, due to the thicker liquid layer upstream and the thinner one downstream, the gas velocity is uneven across the entire tray section; the gas velocity is higher in the areas where the liquid layer is thinner. When the liquid layer in these areas is blown away first, the maximum production capacity is attained. For the guiding sieve plate, since the gas velocity is uniform across the entire tower cross-section, the production capacity is at its maximum only when the average gas velocity throughout the tower reaches its highest value. (3) The gas rising from the sieve pores moves vertically upward, while the gas rising from the guide holes moves horizontally forward; the resultant gas velocity is at an angle upward. This not only prolongs the path of movement of the gas-carrying mist droplets, reducing mist entrainment, but also increases the gas velocity and production capacity. (4) Due to the high efficiency of the guiding sieve plate, the reflux ratio can be reduced with the same number of trays, thereby increasing the tower’s load and production capacity. 2. High efficiency: (1) By overcoming the non-activation zone, the bubbling area on the tray is increased, which enhances the opportunities for gas-liquid mass transfer and thus improves the efficiency of the tray. (2) Liquid phase backmixing is one of the most important factors affecting tray efficiency. The highly efficient guiding sieve plate effectively overcomes liquid-phase backmixing, thereby improving the efficiency of the tray. (3) It eliminated the liquid level gradient, reduced liquid leakage and foam entrainment, and improved the efficiency of the tray. 3. Lower pressure drop: Compared with trays such as bubble trays and floating valve trays, sieve trays have the lowest operating pressure drop due to their simple structure and smooth airflow channels. Experimental and production experience show that the pressure drop in guide holes is about 20% lower than that in sieve pores, while the pressure drop in guide sieve trays is about 10% lower than that in sieve tray columns. 4. Strong anti-clogging capability: Since the gas ejected from the guide holes pushes the material forward horizontally across the tray, this enhances the flow of the liquid over the tray; for viscous materials, more guide holes can be installed. It has unique advantages, especially in areas such as the distillation of fermented broths and the separation of polymers from monomers. 5. Simple structure and low cost: Since the high-efficiency guiding sieve plate merely consists of sieve holes and guiding holes drilled in a steel plate, with no other components, it has a simple structure and is lightweight, which makes it very convenient for workers to assemble and disassemble it. The corresponding cost is also low; the cost of efficient guide trays is 40–50% of that of bubble trays, and 60–70% of that of floating valve trays. In summary, the high-efficiency guided sieve tray is suitable for applications that require high production capacity or capacity expansion, for situations where high separation efficiency and precise separation are needed, as well as for applications involving low pressures, especially in vacuum distillation. It exhibits strong resistance to fouling and clogging when dealing with viscous materials or those containing solid particles. It can also effectively break up foam on the tray surfaces, reduce mist entrainment, and prevent flooding. Another advantage of the high-efficiency guiding sieve plate is its simple structure, low cost, and ease of disassembly and assembly. Application Example 1: Technical transformation for the distillation of high-viscosity materials. In the polymerization section of polyvinyl alcohol production, vinyl acetate reacts in a polymerization reactor to form polyvinyl acetate, and the polymer is separated from the unpolymerized monomer in a polymerization tower. The reaction mixture coming out of the polymerization reactor contains up to 36% polyvinyl acetate, and its high viscosity poses difficulties for the monomer removal distillation in the polymerization tower. The tower originally used bubble cap trays; the high flow resistance of the material on these trays often led to production problems such as liquid flooding and tower blockages. Therefore, production requirements necessitate technical modifications to the polymerization tower. Jiangxi Chemical Fiber and Chemical Industry Group Co., Ltd. carried out a technical upgrade of the polymerization tower using guide trays; the tower has a diameter of 2000 mm, 40 trays in total, with a tray spacing of 285 mm. By replacing the original bubble tray with high-efficiency guiding trays alone, without altering the tower body or its internal supports, the unit has been operating stably and normally since it was put into use in March 1997; it is in good condition and has achieved very high technical performance standards. Separation parameters of the tower: Name, Top of tower composition %, Bottom of tower composition %, VAC extraction rate %, VAC MeOH, PVAC, VAC H2O. Original parameters: 50, 49, 30, 0.26, 0.15, 99.3. Required parameters: 55, 44, 30–33, ≤0.08, ≤0.1, 99.8. Parameters achieved: 60, 39, 30–33, 0.02–0.03, 0.05, 99.85–99.9. Reflux ratio of the tower: Name, Parameters before the technical upgrade, Parameters required after the upgrade, Parameters after the technical upgrade. Reflux ratio of the tower: 1.3, 1.0, 0.7. As can be seen from the table above, the VAC content in the bottom of the tower decreased from 0.26% to 0.02–0.03% after the technical upgrade, **which improved the recovery rate of VAC (vinyl acetate) and the quality of the polymer. The VAC content at the tower top was increased from 50% to 60%, reducing the processing load and energy consumption in subsequent units. At the same time, due to the high efficiency of the guided sieve tray plates, the reflux ratio in the polymerization column was reduced from 1.3 for bubble tray plates to 0.7, a decrease of 45%, resulting in 36% energy savings. Moreover, the technical upgrades completely resolved issues such as tower blockage and flooding during production. The polymerization tower is a large tower with a diameter of 2000 mm and 40 trays; the investment required for the technical upgrade is approximately 220,000 yuan. Considering only the benefits related to energy savings, water conservation, an increased VAC recovery rate, and improved product quality, the annual additional profit amounts to about 3.21 million yuan, meaning that the payback period for this investment is less than one month. Furthermore, the technical upgrades also increased the VAC processing capacity in the polymerization section from 5400 l/h to 8200 l/h, resulting in a 50% increase in output. Application Example 2: Technical renovation of the polymerization tower and recovery tower. At Shijiazhuang Chemical Fiber Co., Ltd., the guided sieve plate technology was employed to combine the polymerization tower (Φ800mm) with the recovery tower (Φ1200mm) into a single tower. After the renovation, the smaller of the original two towers, namely the polymerization tower (Φ800mm, with 30 layers of sieve plates), was used; the tower structure itself remained unchanged, only the original sieve plates were replaced with high-efficiency guided sieve plates. As a result, production capacity increased by 150%, the reflux ratio dropped from 4.2 to 1.8, and the methanol purity at the tower top increased from 99.5% to 99.8%, achieving the goals of increased production, energy savings, and reduced consumption. Application Example 3: Renovation of the single-column recovery technology. In the renovation of the single-column recovery technology at Guangxi Vinylon (Group) Co., Ltd., the tower diameter was 1600 mm and it had 40 trays; a high-efficiency guided sieve tray tower was used. Production capacity was increased by 50%, while the reflux ratio was reduced from 2.5 to 1.8. The methyl acetate content at the tower top increased from 65% to 83%, **reducing the load and energy consumption of this tower as well as the subsequent processing units. The methyl acetate content in the tower bottom was reduced from 0.2% to 0.05%, improving its recovery rate and achieving high technical standards as well as good economic benefits. Application Example 4: Technical design of the acetic acid purification tower. The six-tower recovery system (acetic acid purification tower) developed by Shanxi Sanwei Group Co., Ltd. has a processing capacity of 18 tons per hour, and it is required that the output acetic acid meet industry standards. To achieve this, high-efficiency guided sieve tray technology was employed in the design. The tower’s diameter is 2500 mm/2900 mm, with 50 trays in total. This tower can utilize n-butyl acetate and isopropyl acetate as azeotropes for the purification of acetic acid, resulting in an acetic acid product quality of over 99.5%, thus fulfilling the production requirements successfully. Application Example 5: Technical renovation of the methanol distillation tower. The methanol distillation tower (recovery tower No. 4) of Guizhou Crystal Organic Chemicals Group Company has a tower diameter of 2000 mm and 36 trays, and is used for the separation of the methanol-water mixture. The original tower used sieve trays, which resulted in low separation efficiency and limited capacity. After research, a technical upgrade was carried out by employing high-efficiency guiding sieve trays in combination with new types of packing. As a result of this upgrade, the quality of methanol produced at the top of the tower remained stable at over 99.5%, achieving very good outcomes. In Application Example 6, the Sinopec Beijing Organic Chemical Plant utilized high-efficiency guided sieve plate technology to refine vinyl acetate, which tends to polymerize easily, thereby producing vinyl acetate products of high purity. The content of ethyl acetate, whose boiling point differs from that of vinyl acetate by only about 4°C, is ≤100 ppm. Other impurities are essentially undetectable. The product quality is superior to imported products, with an acetic acid content of 200 ppm. It replaced imported products, creating new product varieties and sources of increased profitability. High-efficiency guiding sieve plates have been used in hundreds of distillation and absorption towers across industries such as petrochemicals, chemicals, textiles, and light industry; they have generated economic benefits worth billions of yuan, while also bringing significant environmental and social benefits. The high-efficiency guiding sieve plate is a patented technology of Beijing University of Chemical Technology, with patent number 01220319.X. Choose patented technologies and avoid infringement.