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I. Understanding the three-dimensional mass transfer tray CTST: Tower equipment is a key device widely used in industries such as chemical engineering, pharmaceuticals, petroleum processing, food, and light textiles. Plate towers are one of the most commonly used gas-liquid mass transfer devices, widely applied in processes such as distillation, absorption, desorption, stripping, and heat exchange. The new high-efficiency \"three-dimensional mass transfer tray CTST\" is the result of years of theoretical research and technological development by a team led by Professor Li Chunli from Hebei University of Technology; it has been granted a **patent (patent number: 93218445.6). "The three-dimensional mass transfer tray CTST boasts many advantages, including high throughput, high separation efficiency, great operational flexibility, low pressure drop, resistance to clogging, and suitability for processing materials that tend to foam. Upon evaluation and novelty verification, it was confirmed to be an international first; its performance reached an internationally advanced level. In 1999, it received the \"First Prize for Scientific and Technological Progress in Hebei Province\" as well as the \"Third Prize for Scientific and Technological Progress from the Ministry of Education.\" To date, this achievement has been successfully applied in hundreds of towers (with tower diameters ranging from φ400 to 3000 mm) at dozens of large and medium-sized enterprises in China’s chemical, petrochemical, pharmaceutical, fertilizer, and light industry sectors, generating significant economic and social benefits. The high-throughput efficient tray CTST is a new type of tray developed to meet the needs of expansion and technological upgrades in industries such as chemicals and petrochemicals. In industries such as chemicals, petrochemicals, pharmaceuticals, vinylon, and fertilizers, tower equipment is a key device used for separation. When carrying out technological upgrades for capacity expansion and equipment renewal, the use of high-throughput, efficient three-dimensional mass transfer trays allows the processing capacity of the equipment to be increased by 50%-100% simply by replacing the trays, without having to change the existing tower structure. This approach saves significant amounts of investment in equipment, while also helping to improve product quality, reduce energy consumption and raw material usage, thereby enhancing the technical level and competitiveness of the enterprise. The application of three-dimensional mass transfer trays is mainly focused on two areas: in equipment upgrades – such as capacity expansion, technical upgrades, and efficiency improvements – by using this technology, it is possible to replace the internal components of the tower without altering the original equipment casing. This approach can increase production by 50–200%, improve the quality of the product, and reduce energy consumption. As a result, the investment required for such upgrades is only 1/3 to 1/5 of that needed for traditional equipment, and the project timeline can be significantly shortened. New equipment design: By using this technology, equipment investment can be reduced by 1/3 to 1/2, and product quality can be improved while energy consumption is lowered. Numerous data show that the use of three-dimensional mass transfer trays, CTST, improves product quality and yield, reduces production costs, enhances efficiency, and lowers losses and energy consumption. Compared with traditional equipment, three-dimensional mass transfer trays offer advantages such as high production capacity (50–200% higher than that of traditional trays), high separation efficiency, great operational flexibility, and a wide range of applications. Theoretical studies, experimental research, and industrial applications have clearly shown that the research level of three-dimensional mass transfer tray technology is at the international advanced and domestically leading level. II. Main technical properties of the three-dimensional mass transfer tray CTST 1. Analysis of the structural features and operating conditions of the TST: The gas-liquid contact, heat transfer, and mass transfer elements of the three-dimensional mass transfer tray CTST are trapezoidal spray nozzles ； The tray features rectangular openings; above these rectangular openings there is a trapezoidal spray hood containing the sieve holes. The sides of the hood are spray plates with sieve holes, the two ends are trapezoidal end plates, and there is a separation plate at the top. An air-liquid channel is provided between the spray plate and the separation plate. There is a certain bottom gap between the spray plate and the tray, which serves as a passage for the liquid to enter the enclosure. The function of the separation plate is, first, to provide a space for gas-liquid contact, and second, to effectively separate the gas and liquid phases and reduce mist entrainment. The CTST is a gas-liquid co-current jet-type tray, and its operating conditions are as shown in the figure: gas enters the jet from the tray holes, where a constriction is formed at the tray holes, creating a low-pressure area in the vicinity of those holes ； The liquid enters the enclosure from beneath the cover gap, driven by the pressure difference between the inside and outside of the cover as well as the hydrostatic pressure resulting from the liquid level height on the surface of the plate ； The contact, heat transfer, and mass transfer between the gas and liquid phases proceed as follows: (1) The liquid is lifted by the gas and a film is formed ； (2) The gas breaks the entity into droplets ； (3) The gas and liquid droplets rise, collide with the separation plate, and then turn back, resulting in intense collisions between the rising gas and liquid; (4) The gas and liquid droplets are ejected upward from the side ejector plates of the enclosure; (5) Inside the enclosure, the gas and liquid droplets ejected from the enclosure collide with each other ； (6) The droplets fall back onto the plate surface and flow downstream, while the gas bypasses the separation plate and rises to the upper tray. On the tray, gas and liquid undergo six steps: film drawing → fragmentation → backflow to the top → spraying → mutual spraying → separation, all taking place in the three-dimensional space between the tray and the top of the cover, where the space utilization rate can reach 40%-60%. Within this spatial range, the gas is the continuous phase while the liquid is the discrete phase, namely tiny liquid droplets ； On the plate surface, the liquid forms a clear layer. 2. Main technical properties of the three-dimensional mass transfer tray CTST: Due to its unique structure and the conditions under which spraying takes place, the CTST possesses the following excellent technical properties. 1) High throughput: (1) Since the gas channels and tray openings in CTST are rectangular in shape, it is easy to arrange these openings; moreover, their area is quite large. Typically, the dimensions of these rectangular openings are greater than 40×120 mm, and in industrial applications, they can even reach 70×350 mm. As a result, the opening ratio can exceed 20%, a value that is difficult to achieve with other types of trays ； (2) High operating limit: Thanks to the effect of the separation plate, the ejected gas and liquid can be effectively separated, which significantly reduces mist entrainment and increases the operating limit. If 10% entrainment of mist is taken as the operational upper limit, the plate hole kinetic energy factor for the F1 float valve is 17, while that for CTST is 34; that is, at the same tray opening ratio, the operational upper limit for CTST is twice that of the F1 float valve. (See Figure 2) (3) Figure 3 shows the relationship between the pressure drop across a CTST tray with an opening ratio of 20%, foam entrainment, and the empty tray kinetic energy factor: when the empty tray kinetic energy factor is 3.0, the plate pressure drop is 81 mmH2O, and the foam entrainment is less than 0.01 kg of liquid per kg of gas. If the upper limit for the gas phase is set at 0.01 kg of liquid per kg of gas due to mist entrainment, the CTST adiabatic kinetic factor can exceed 3.4. (4) Large liquid flow capacity in the downcomer: One of the main functions of the downcomer is to separate the liquid that flows into it from the bubbles. The gas holdup on typical bubble-type trays is around 50%. Since the liquid on the CTST tray is a clear layer, the liquid flowing into the downcomer contains almost no bubbles, allowing the capacity of the downcomer to be doubled. During design, the minimum residence time of the downcomer can be reduced from 5 seconds to 2.5 seconds. Therefore, compared to floating valve trays, the gas and liquid fluxes in CTST can be increased by 50–100%. 2) High tray efficiency: Due to the high space utilization rate of CTST, which is 40%-60%, there is very thorough contact between the gas and liquid inside and between the trays. On one hand, the gas disperses the liquid into small droplets, thereby significantly increasing the contact area between the gas and liquid phases; on the other hand, the intense spraying conditions cause the surface of these droplets to be constantly renewed, thus maintaining a high driving force for mass and heat transfer. Therefore, CTST has a very high mass transfer efficiency. Compared to the highly efficient F1 floating valve trays, the tray efficiency is 10% higher at low gas phase loads and over 40% higher at high gas phase loads. 3) High operational flexibility: The lower operating limit of CTST is determined by plate leakage, just like that of the F1 float valve, while the upper operating limit is generally controlled by excessive mist entrainment. Experimental studies show that at an open area ratio of 11%, the lower operating limit for CTST is 4.7–6.3 for the plate pore kinetic energy factor, while the upper operating limit is 34; thus its operational flexibility ranges from 5.4–7.2. For the F1 floating valve, the lower limit is 4.0–4.8, the upper limit is 17, and its operational flexibility ranges from 3.4–4.3. 4) It has strong material adaptability, capable of handling materials containing solid particles, materials that tend to self-polymerize, as well as materials that are prone to foaming. Due to the large openings in the CTST, which are generally larger than 40×120 mm, and the injection speed of gases and liquids reaching 10–20 m/s, there is a self-cleaning effect on these injection holes; therefore, the CTST can handle materials with solid particles as well as those that tend to self-polymerize. Furthermore, due to the special jet-type operating conditions of CTST, the liquid on the tray is clear, meaning there is no foaming mechanism; moreover, the rapidly ejected droplets have an antifoaming effect, allowing it to handle systems prone to foaming that are difficult to process with conventional trays. 5) The effect of the liquid level gradient on the tray is minimal. When the tower diameter is large, the gradient of the liquid level on the tray becomes significant, resulting in uneven distribution of gas and liquid on the tray and affecting its separation efficiency; in severe cases, the tray may even fail to function properly. 6) Large liquid lifting volume: The liquid lifting volume is defined as the mass of liquid lifted per unit mass of gas, that is, the amount of interaction between the gas and the liquid. The study found that the increase in CTST was 4–10 kgL/kgG, which is 1.6–5.0 times that of New VST. This indicates that CTST provides more opportunities for gas-liquid contact and mass transfer than New VST. Therefore, the plate efficiency of CTST is high and stable over a wide range. 7) Stable space liquid holdup. Space liquid holdup refers to the amount of all liquid contained in the space above the liquid layer on the tray. This portion of the liquid exists primarily in the form of droplets, and it constitutes the majority of the liquid that is involved in gas-liquid mass transfer at any given moment. Studies show that within the normal operating range, namely when the kinetic factor of the plate pores is between 11 and 20, the spatial liquid holdup of the CTST remains essentially constant. This ensures that the tray maintains good gas-liquid contact over a wide operating range, thereby ensuring high mass transfer efficiency. 8) The pressure distribution within the shroud is reasonable, resulting in reduced plate pressure and lower energy consumption. Tests and studies were conducted on the pressure distribution inside the gas shroud in order to explore the mass transfer mechanism in CTST systems and optimize the structure of the tower plates. Research shows that: (1) when gas passes through the holes in the tray plates, pulsation occurs, and the pressure difference between the inside and outside of the hood resulting from this is the main driving force for the liquid to enter the hood ； (2) The dry plate resistance when gas passes through the plate holes accounts for about 70% of the total plate resistance; therefore, to further reduce the pressure drop across the plate, it is necessary to reduce the resistance of the plate holes ； (3) The plate voltage drop of CTST is about 20% lower than that of the F1 float valve, as shown in Figure-5. As can be seen from the above properties, using CTST for the design of new towers allows, under the same production capacity and separation requirements, an increase in production capacity by 50–100% merely by replacing the trays. It also improves the separation efficiency of the trays and reduces the pressure drop across them; moreover, it has a defoaming effect on systems prone to foaming. The anti-clogging capacity of the tower after modification has been significantly improved; there are no moving parts on the tray, and the maintenance cycle of the tower has been extended by more than twice. III. Successful Application of Three-Dimensional Mass Transfer Trays in the Fertilizer Industry: Shandong Luxi Fertilizer Plant – with an annual production capacity of 80,000 tons of synthetic ammonia. The design of the second desulfurization tower for the shift gas involved a high liquid flow rate; moreover, during operation, elemental substances would precipitate out, which could lead to blockages in the trays or packing. The original design called for a tray tower with a diameter of Φ3200 and 125Y corrugated packing. The tower is designed using the CTST tray design, with a diameter of Φ2800; it is a double-overflow tower. Since its commissioning at the beginning of 1996, it has been operating steadily and normally, without any blockages, and its processing capacity is sufficient to meet the needs of a plant producing 160,000 tons of synthetic ammonia per year. IV. Successful Application of Three-Dimensional Mass Transfer Trays in the Petrochemical Industry 1. Expansion and Renovation of Gas Towers for Sulfur-Containing Wastewater (Raising of the issue – Why carry out the renovation) The wastewater gas stripping process is a complex system involving chemistry, ionization, and phase equilibrium. Currently, domestic refineries generally use either a single-tower side-stream or a two-tower configuration; there is no fundamental difference between these two approaches. The three sewage gas towers upgraded by Hebei University of Technology all adopt a single-tower process. The single-tower side-stream process utilizes one tower to carry out the tasks of wastewater purification and separation. This tower is divided into three sections, and the wastewater to be treated is split into cold and hot streams, which enter the tower separately; the ratio of hot feed to cold feed is generally 4-5. The hot feed undergoes heat exchange with the gas withdrawn from the side lines and the water used for bottom purification, allowing its temperature to reach around 150°C. This temperature **exceeds the inflection point temperature for the hydrolysis reaction in the ionization of ammonium sulfide (110°C); as a result, both H2S and NH3 exist in the form of free molecules within the hot feed. The operating pressure in the stripping tower is lower than that in the feed line, and upon entry into the tower, H2S and NH3 transition from the liquid phase to the gas phase and move upward due to depressurized flashing and gas withdrawal at the top of the tower. The cold feed at around 30°C enters from the top of the tower, flowing in the opposite direction to the upward-moving H2S and NH3. Under conditions of low temperature and a pressure of 0.5 Mpa gauge, since the relative volatility of H2S is higher than that of NH3, while the solubility of NH3 is greater than that of H2S, most of the NH3 in the rising gas gets absorbed, with very little H2S being absorbed. As a result, acidic gas with high purity is obtained at the top of the tower, which can be sent to a sulfur recovery unit for sulfur extraction or burned in a flare. The cold feed, which has absorbed NH3 (and a small amount of H2S), is mixed with the hot feed from which NH3 and H2S have been flashed. This mixture flows from the middle part of the tower toward its lower section, where NH3 and H2S are repeatedly stripped by the hot gas streams rising from the lower part of the tower. Since the temperature in the middle part of the tower is much higher than that in the upper part, most of the H2S is eventually carried to the top of the tower, while NH3 is absorbed by the liquid flow and accumulates in the middle part of the tower. The gaseous stream from the side line at this middle section is then used to produce liquid ammonia through a three-stage condensation unit. Superheated steam is introduced directly at the bottom of the tower; the temperature at the bottom of the tower is around 160°C, and the purified water is discharged from there. The gas column can be divided into three sections: cold feed to the top of the column, and the H2S purification section ； Hot feed to the side line draw point, H2S stripping section ； The side-line extraction outlet leads to the bottom of the tower, the NH3 stripping section. The first section is generally a packed tower, while the latter two sections are usually float valve towers; due to the dirty nature of the wastewater, the towers need to be disassembled for maintenance every year. The CTST trays have been successfully applied in the technical upgrades of the sulfur-containing wastewater stripping towers at Tianjin Petrochemical Plant No. 1, Xin* Dushanzi Refinery, and Luoyang Petrochemical Complex Refinery. In all these upgrades, the original tower shells were left unchanged; only the traditional floating valve trays were replaced with CTST trays, while the upper packing section remained intact. As a result, the production capacity increased by more than twice, and the steam consumption decreased by over 12%. The upgraded systems operate stably and offer great operational flexibility, enabling them to adapt to significant changes in production load. Unit 1 of Tianjin Petrochemical is a tapered column with an original outer diameter of Φ800/Φ1000, equipped with 40 layers of floating valve trays. By replacing the original floating valve trays with CTST trays, the processing capacity was increased from 15 t/h to 35 t/h; moreover, the newly modified column can operate stably within a range of 8–35 t/h. The steam consumption per ton of wastewater dropped from 130 to 110 kg of steam/ton, resulting in a 13% energy savings. Since its commissioning in May 1995, this tower has been operating steadily and without any need for maintenance; it has effectively solved the problem of tower blockage. The original outer diameter of the tower at Luoyang Petrochemical Plant was Φ1000, with 37 floating valve trays. Without changing the original tower shell, only the trays were replaced with CTST trays, resulting in an increase in processing capacity from 35 t/h to 55 t/h. Moreover, the newly modified tower can operate stably within a range of 20–55 t/h. The tower was put into operation in March 1999, with a successful first trial run. The new *Dushanzi Refinery features a tower with an outer diameter of Φ900/Φ1200 and 40 layers of floating valve trays; the original floating valve trays have been replaced by CTST trays. The processing capacity has increased from 30 t/h to 69 t/h, and the newly modified tower can operate stably within a range of 20–69 t/h. The steam consumption per ton of wastewater dropped from 190 to 160 kg of steam/ton of wastewater, resulting in a 12% energy savings. Since its commissioning in June 1998, this tower has been operating stably and normally. The data for this tower are as follows: 2. Expansion and renovation of the crude oil initial sulfur removal tower. The original tower had a diameter of Φ3200 and was equipped with 20 layers of floating valve trays. When the processing capacity exceeded 10,000 t/d, black oil would appear in the side stream, indicating that the amount of mist entrained during operation was too high. Without changing the outer shell or the downcomer of the tower, simply replacing the tray type with CTST trays allowed the processing capacity to be increased to 18,000 t/d. This tower can handle a processing capacity in the range of 7,200–18,000 t/d. It was put into operation at the refinery of Luoyang Petrochemical Complex at the beginning of April 2000, and it has been operating stably. 3. Expansion and renovation of the stripping tower in the lubricating oil furfural refining unit: The original tower had a diameter of Φ1600 and was equipped with 18 floating valve trays. Without changing the existing tower shell or downcomers, only the tray type was replaced with CTST trays. As a result, the processing capacity increased from 45 t/h to 75 t/h. The furfural content in the refined oil at the bottom of the tower dropped from over 150 ppm to below 300 ppm. The tower operated under vacuum, with the vacuum level rising from 650 mmHg to 700 mmHg; this led to a 67% increase in processing capacity, while the pressure drop across the tower decreased. This fully demonstrates the excellent separation efficiency and low pressure drop characteristics of CTST trays. Since its commissioning in August 1999 at the refinery of Beijing Yanshan Petrochemical Group, this tower has been operating stably and normally. 4. Expansion and renovation of the solvent oil separation tower in the aromatic hydrocarbon extraction unit: The original tower had a diameter of Φ1000 and was equipped with 54 floating valve trays. Without changing the existing shell or downcomer, only the tray type was replaced with CTST trays, which increased the processing capacity from 4 t/h to 8 t/h. This tower was put into operation at Shijiazhuang Refinery in May 2000, and the initial trial run was successful; moreover, after the renovation, the tower can operate within a range of 4–10 t/h. V. Statistics on the Application of Three-Dimensional Mass Transfer Tray CTST (Partial) – Petrochemical Sector – Fertilizer Sector (end)