While organizing the materials, I found an introduction to the synthesis tower

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Introduction to the synthesis tower: The low-pressure methanol synthesis tower designed by the German company Lurgi is of shell-and-tube design. Catalysts are filled inside the tubes, where the methanol synthesis reaction takes place under medium-to-low pressure conditions. Heat is removed from between the tubes through boiling water, generating medium-pressure steam that helps to control the temperature of the catalyst bed, extend its lifespan, and prevent the occurrence of side reactions. Its main performance features are as follows: a catalyst is placed inside the tubes, while circulating boiling water flows between them; a large heat exchange area is used to remove the heat generated by the reaction. Theoretically, this results in a small temperature difference across the catalyst layer, thereby achieving nearly isothermal reaction conditions and allowing the synthesis reaction to take place under almost isothermal conditions, with a low circulation ratio. To accommodate the trend toward larger-scale installations, Lurgi improved the shell-and-tube methanol synthesis reactors and developed a two-stage isothermal methanol synthesis process (gas-cooled and water-cooled dual reactors). This process consists of two shell-and-tube methanol synthesis reactors: in the first reactor, the heat of reaction is removed by utilizing the by-produced medium-pressure steam, while in the second reactor, the heat of reaction is removed through counterflow heat exchange with fresh syngas. In the second reactor, fresh syngas flows through the tubes, while the reaction gas flows through the shell. The 1.65 million tons per year methanol plant built using this technology has already been put into operation. Compared with the single shell-and-tube synthesis tower process, the two-stage isothermal methanol synthesis process has the following features: —— Compared with a single reaction tower, the size of the first reactor is reduced by about 50%. ——The syngas circulation ratio was reduced by about 50%. ——It features high heat recovery efficiency, reducing cooling costs. ——The capacity of a single series can exceed 5,000 tons per day. ——The investment in the entire synthesis loop (including the cycle compressor, heat exchangers, etc.) has been reduced by nearly 40%. (2) Switzerland’s Casale: Casale was the first company to develop vertical insulated axial radial reactors. These reactors are characterized by an unsealed top portion of the circular catalyst bed, with no openings on the side walls; this results in axial flow of air in the upper part of the catalyst bed, while the air flow in the main part of the bed is radial. The main structural features of the large-diameter radial methanol synthesis reactor developed by Casale: —— The top of the circular catalyst bed is not sealed, and there are no openings in the side walls, which results in axial flow of the gas stream above the catalyst bed; —— The gas stream in the main part of the bed flows radially ； ——The outer wall of the catalyst basket is equipped with holes distributed in different patterns to ensure even airflow distribution ； ——The bottom of each bed layer is sealed, and the gas after reaction flows through the central tube into the heat exchanger outside the synthesis tower to recover heat. Since direct cooling is not used and external heat exchange is employed, the methanol concentration at the outlets of each bed section is high, resulting in a lower number of bed sections required. Due to the significant reduction in bed resistance drop (24% less than that of ICI axial towers), it is possible to increase the height of the synthesis tower and reduce its wall thickness; towers with a high height-to-diameter ratio can be used to lower costs. Compared to cold-jet adiabatic towers, axial-radial mixed-flow towers can save investment, simplify the control process, and reduce the number of control instruments. The disadvantage of the shaft-radial synthesis tower is that the catalyst basket needs to be replaced, and the loading and unloading of the catalyst are complex. The advantage is its great potential for scaling up. The production capacity of a shaft-type radial synthesis tower depends on its height; an excessively tall tower makes it difficult to load and unload the catalyst. The typical tower height is 16 m, with a corresponding production capacity of 5,000 t/d. (3) British ICI: The multi-stage cold-quench type methanol reactor developed by the British ICI company is the most commonly used reactor type in methanol production facilities abroad; it is a fully axial multi-stage cold-quench type synthesis reactor. Its simple structure is its unique advantage. The synthesis tower consists of a tower body, multiple bed layers, and a special triangular distributor. Diamond-shaped distributors are embedded in the catalytic bed, with one set installed at each level of the bed; a total of three to four sets are installed throughout the tower. It enables the cold shock gas and reaction gas to mix evenly. The catalyst has a large loading capacity and a long service life, typically up to 6 years. The downside is that it involves an adiabatic reaction, resulting in a large axial temperature difference within the catalyst bed. To control the temperature of the synthesis tower bed, raw material gas is used for cooling; cold raw material gas is injected between various sections of the catalyst bed in order to reduce the temperature of the reaction gas. Therefore, the cooling process diluted the methanol content in the reaction gas, affecting the catalyst utilization rate. To prevent the catalyst from overheating, a high space velocity is used; the methanol content in the gas leaving the tower is less than 4%, and the amount of by-product steam is low, making it impossible to recover the high-energy reaction heat. The circulation volume is large, resulting in high tower pressure, typically ranging from 0.1 MPa to 0.4 MPa, which leads to high operating costs. Due to resistance constraints, its height-to-diameter ratio is small, usually ranging from 2.2 to 4.0; when made larger, its diameter becomes very large (4–6 meters), which makes transportation difficult ； Due to the simple structure of ICI’s cold-jet methanol synthesis towers, their reliable operation, ease of handling, design flexibility, low material requirements, low investment costs, and suitability for large-scale implementation, they remain a major type of tower used in large methanol plants. ICI still holds the record for the largest single-unit capacity; it has several plants with a capacity of 3,000 t/d, and it is reported that the largest existing plant has a capacity of 7,500 t/d. To address the shortcomings of cold-jet towers, in the 1980s ICI developed two types of cold-tube towers. One of these was the water-cooled tower known as LCM. Unlike methanol synthesis towers of the Ruhr-type with tubular reactors, water flowed inside the tubes while catalysts were placed outside them; this design allowed the expansion issues associated with the tubules to be addressed more effectively through its expansion ring structure. Additionally, it featured a radial-flow catalytic bed design, which not only reduced resistance but also increased the heat transfer coefficient. Currently, many large-scale methanol plants around the world use multi-stage quench methanol synthesis towers. In recent years, on the basis of the original design, extensive and diverse improvements and enhancements have been made to cold-jet synthesis towers, resulting in the introduction of a series of improved versions of such towers. The cold-stirred synthesis tower has the following characteristics: ——The synthesis tower has a high production capacity per unit, making it suitable for large or super-large plants. ——The methanol synthesis tower has a simple structure, and the catalyst is easy to install and remove. ——Cold shock is applied using a specially designed distribution system, making temperature control more convenient. ——The high-grade heat energy generated during methanol synthesis cannot be recovered, resulting in a large volume of circulating gas in the synthesis loop. ——There is inter-stage mixing of the catalysts, resulting in a low methanol content at the outlet of the synthesis tower. ——The space-time yield of the catalyst is low, and a large amount of it is required. (1) Methanol synthesis is an exothermic, reversible, and complex reaction process in which CO, CO2, and H2 react under certain temperature, pressure, and catalyst conditions to primarily produce CH3OH and H2O. The main reaction equations are as follows: CO + 2H2 → CH3OH; CO2 + 3H2 → CH3OH + H2O. Currently, CuO-ZnO-Al2O3 or CuO-ZnO-Cr2O3 catalysts are commonly used in methanol production, with their active regions lying between 473 and 563 K, and the optimal operating temperature range for maximum activity being between 500 and 530 K. The active temperature range is narrow, and the methanol synthesis reaction is a highly exothermic reaction. Although, for chemical reactions, an increase in temperature speeds up molecular movement, increases the number of effective collisions within molecules, and thus increases the chances of effective molecular combination, thereby accelerating the methanol synthesis reaction; however, since the reaction in which CO, CO2, and H2 combine to form CH3OH is a reversible exothermic reaction, an increase in temperature raises the equilibrium constant of the reverse reaction, which is unfavorable for methanol formation. Therefore, the heat released by the methanol reaction must be removed promptly. Furthermore, as can be seen from the above chemical reaction equations, the reaction in which CO, CO2, and H2 react to form CH3OH is a reaction that results in a decrease in volume; increasing the synthesis pressure is beneficial for this reaction. Thanks to the development of highly active catalysts by catalyst manufacturers, low-pressure methanol synthesis processes have been widely used in recent years. 2 Introduction to Low-Pressure Methanol Synthesis Towers at Home and Abroad. Currently, the main low-pressure methanol synthesis towers in use worldwide include the IC I adiabatic shock tower from the UK, the shell-and-tube low-pressure synthesis tower from Lurgi in Germany, the low-pressure radial synthesis tower from Topsoe in Denmark, the MRF low-pressure synthesis tower from Japan’s TEC Engineering Company, and the IMC low-pressure synthesis tower from Cassali in Switzerland. Domestically developed ones include the adiabatic isothermal low-pressure synthesis tower by East China University of Science and Technology, among others. Many of the basic steps in methanol synthesis processes using different techniques are the same; these mainly include methanol synthesis and methanol separation. The main difference lies in the methods used for heat transfer and heat recovery. In terms of the structure of the synthesis tower, different manufacturers employ various heat exchange designs, aiming to utilize smaller heat exchangers to remove more reaction heat, thereby increasing the utilization efficiency of the tower and allowing for the use of more catalyst. 2.1 IC I Low-pressure Quench-type Methanol Synthesis Tower: The ICI quench-type methanol synthesis tower utilizes four adiabatic beds, with three quenching steps between each bed. Syngas, composed of H2, CO, CO2, and a small amount of CH4, undergoes a shift reaction to adjust the CO/CO2 ratio. It is then pressurized to 5 MPa using a centrifugal compressor and fed into a quench reactor at 270 °C equipped with a low-temperature active copper-based catalyst. After the reaction, the gas is cooled to separate methanol; the unreacted gas is compressed and mixed with fresh feed gas before being sent back into the reactor. The methane accumulated during the reaction is returned to the converter as vent gas to be used in the production of syngas. Although this type of methanol tower has a simple structure and high production capacity, it features a large axial temperature difference within the bed, low outlet concentration, and low synthesis efficiency. The staged cooling applied to reduce temperature prevents the catalyst from being damaged due to excessively high local temperatures during the reaction; however, it also reduces the conversion rate per unit volume of the reactor, resulting in an increase in the amount of gas circulated, higher compression energy consumption, and a reduced efficiency in the recovery and utilization of reaction heat. 2.2 Lurgi low-pressure shell-and-tube methanol synthesis reactor: The Lurgi shell-and-tube methanol synthesis reactor features a tube-in-tube structure. The catalyst is loaded in the tube side, while boiler water is added to the shell side; heat is removed after boiling. The reaction temperature is regulated by controlling the pressure of the boiling water in the reactor’s shell side. The operating temperature ranges from 250 to 260 °C, and the operating pressure is 5 to 6 MPa. This type of column catalyst bed has a small temperature difference, operates more stably, and achieves a high conversion rate; it can also produce medium-pressure steam as a by-product. However, since the shell side occupies a large amount of space, the catalyst loading capacity is low (only 35%). To address the issue of thermal expansion stress, such towers must use special stainless steel materials with two different coefficients of expansion; the tubes need to be imported, which results in a long supply cycle and high equipment costs. In recent years, to meet the demands of large-scale methanol production (above 2,500 t/d), Lurgi has developed combined synthesis units that consist of shell-and-tube reactors and cold-tube reactors in series. These units utilize water cooling and air cooling for heat transfer respectively; the preheated gas exits from the top and enters the catalyst bed inside the shell-and-tube reactor where it reacts. Boiler feedwater is passed outside the reactor, where it boils and absorbs heat. The gas exiting the reactor then goes to the catalyst bed at the upper part of the cold-tube reactor to continue reacting. The gas exiting the cold tubes recovers heat, and after its temperature drops, it enters a methanol separator for separation. The gas is recycled as circulating gas; due to the use of series-connected synthesis towers, the amount of gas that needs to be recycled is relatively small, which helps to save energy consumption. The Lurgi process utilizes the reaction heat to generate medium-pressure steam, enabling efficient energy recovery; it offers better economic efficiency and operational reliability. 2.3 The MRF methanol synthesis tower of Nippon Toyo Engineering Company The MRF methanol synthesis tower developed by Nippon Toyo Engineering Company (TEC) features vertical double-layer water-cooling tubes that are bayonet-shaped. Boiler feedwater enters these cooling tubes from the bottom, and the steam generated collects in a steam chamber. The reaction gas flows radially through the catalyst bed, resulting in low pressure drop; hence, the resistance of the tower is low, the power required for gas circulation is significantly reduced, and the heat transfer coefficient for cooling is also high. Since the bayonet type is vertical and located at the top, dirt does not accumulate, and dry burning of the outer tube does not occur. During the construction of the reactor, its axial length can be increased. Thanks to the presence of heat exchangers and coolers inside the reactor, it is easy to maintain a uniform temperature across the catalyst bed. This allows for a significant increase in the concentration and rate of methanol production. The reaction temperature is easy to control, less catalyst is required, and the structure of the reactor is compact. However, this reactor has many components, is complex to manufacture, and is relatively expensive. Currently, this tower is used in Lutianhua’s 400,000 t/a methanol plant, and it performs very well. 2.4 IMC Methanol Synthesis Tower by Casali, Switzerland: Building on the horizontal tower design, Casali of Switzerland developed the IMC methanol synthesis tower, whose cooling element consists of heat exchange plates embedded within the catalyst bed. Each heat exchange plate is formed by welding two SS304 metal sheets together; the two sheets are welded along their perimeters and also spot-welded on their surfaces, after which they are stamped to give them a shape similar to that of a pillow. The heat exchange plates are arranged radially and in concentric fan shapes, thereby providing support at the bottom. A catalyst is filled inside the heat exchange plate, and heat-resistant inert aluminum balls are placed beneath the catalyst to serve as a support for it. Boiler feed water flows through the heat exchange plate to carry away the reaction heat, and medium-pressure steam can be produced as a by-product. 2.5 The process of Danish Nissui – Topsoe: To meet the needs of large-scale methanol production facilities, Topsoe has developed synthetic units that consist of three insulated radial synthesis towers connected in series. Heat transfer occurs between these towers through water. For facilities with a capacity of less than 600,000 tons per year, it is possible to operate using just one tower; in this case, the fresh gas entering the tower first passes through a catalyst that ensures complete desulfurization and dearsenification of the gas, after which it is mixed with recycled gas before entering the synthesis tower. By choosing a catalyst (MK-121) that is highly active, highly selective, and highly operational flexible, it is possible to produce 500,000–600,000 tons of methanol per year by using 30–40 m3 of catalyst, even with a relatively small tower volume. Compared with other processes, the temperature difference between the inlet and outlet of the synthesis tower in the Topso process is relatively small, at only 32 °C. The single-stage conversion rate of this tower can reach 15%, while the highest single-stage conversion rate for other processes is only 7% to 8%. The amount of catalyst required in this process is relatively low – 29.9 tons under the same conditions – whereas other processes require around 60 tons. However, to ensure desulfurization in this process, the fresh gas and recycled gas are only mixed outside the cylinder; compared with mixing inside the cylinder, it is somewhat difficult to match the high-pressure section and the recycled gas section during compression. Scaling up methanol production facilities can significantly reduce the investment required for producing the product as well as its cost. The enlargement of methanol plants has become a trend in the development of China’s methanol industry. The core equipment for methanol synthesis is the synthesis tower. Choosing a stable, energy-efficient, high-yield, and cost-effective synthesis tower is crucial for manufacturers. Considering aspects such as operation, structure, materials, and maintenance, the basic requirements for a methanol synthesis tower are: 1. Good stability and reliable structure ； 2. Operationally, the catalyst temperature must be easy to control and allow for flexible adjustment ； The synthesis reactor has a high conversion rate ； Catalysts feature high production efficiency, as well as high activity and stability ； Reaction heat that can be recovered as high-grade energy ； The gas is evenly distributed in the bed layer ； Pressure decreases. 3. The catalyst can be easily heated and reduced, with thorough reduction achieved ； 4. Gas can pass through the catalyst layer evenly, with low resistance and high methanol yield ； 5. Stable operation and easy adjustment, capable of adapting to changes in various operating conditions ； 6. The catalyst is easy to load and unload, and its manufacturing, installation, and maintenance are simple ； 7. The connections and insulation of various internal components are appropriate, allowing them to move freely within the tower and preventing the generation of thermal stress. One of the key technologies in the design of methanol synthesis towers is to efficiently remove and utilize the large amount of heat generated by the methanol synthesis reaction. Methanol synthesis reactors come in many different types depending on the method used for heat recovery from the reaction. Below, several of the more commonly used types will be briefly introduced one by one. I. I.C.I reactor: The low-pressure methanol synthesis reactors used by the British company ICI employ multi-layered, adiabatic reactors equipped with 3–6 layers of catalyst. A large amount of catalyst is used; most of the syngas is introduced into the reactor as a cooling gas, via diamond-shaped distributors placed at different heights within the catalyst bed. Another portion of the syngas enters the reactor from the top. The hot gases resulting from the reaction mix evenly with the cooling gas, thereby regulating the reaction temperature in the catalyst bed and ensuring uniform distribution of the gas across its cross-section. The heat of the final reaction gas is recovered by generating low-pressure steam in a waste heat boiler or by using it to heat the boiler feedwater. This method features a large volume of circulating gas, and the temperature distribution within the reactor is uneven, taking on a serrated shape. The ICI cold shock tower has a simple structure, requires less material, has low requirements, and is easy to scale up. A single tower has a high production capacity. However, since the various sections of the catalyst bed undergo adiabatic reactions, a large temperature difference exists within the catalyst bed. At a pressure of 8.4 MPa and an space velocity of 12,000 h^-1, when the methanol concentration in the gas leaving the tower is 4%, the temperatures in the first and second sections rise by about 50°C; as a result, there are many reaction by-products, the catalyst’s service life is shortened, and significant energy is required to compress the recycle gas. Cold raw gas is injected between the catalyst sections to lower the temperature of the reaction gas. Therefore, as the temperature decreased, the methanol content in the reaction gas was diluted, which affected the catalyst utilization rate; moreover, the reaction heat could only be recovered as low-pressure steam using a low-pressure waste boiler at the reactor outlet. To prevent catalyst overheating, a high space velocity is used, resulting in a methanol content of less than 4% in the gas leaving the tower. The largest capacity is 3,000 t/d, with over 40 units in operation worldwide. II. German Linde Lurgi shell-and-tube reactor, water-cooled type. Figure 2: The Lurgi methanol synthesis reactor has a shell-and-tube structure. A catalyst is placed inside the tube, while medium-pressure boiling water fills the outside of the tube for heat exchange. The synthesis reaction takes place almost under isothermal conditions; the reactor is capable of removing excess heat, which allows for the use of gases with higher CO content. By employing a low circulation gas flow rate and limiting the maximum reaction temperature, the reaction proceeds isothermally, resulting in high conversion rates, reduced formation of impurities, lower energy consumption for compression during recycling. Moreover, the heat generated by the synthesis reaction produces medium-pressure steam, facilitating the comprehensive utilization of waste heat. It can be seen that Lurgi adopted the tubular reactor precisely due to the high heat generation in the methanol synthesis reaction and the poor heat resistance of existing copper-based catalysts. The tubes are filled with catalyst, and circulating boiling water is used between the tubes; a large heat exchange area is employed to remove the heat of reaction, thereby achieving a nearly isothermal reaction condition. As a result, the methanol content in the gas exiting the tower as well as the space-time yield are higher compared to those in a cold-quench tower, and the catalyst also has a longer service life. Its main performance characteristics are: a small temperature difference in the catalyst layer during reaction, low by-product formation, and a large heat transfer surface area required. However, this reactor has a more complex structure than an I.C.I reactor, with numerous joints and weld points at the upper and lower tube sheets, making it difficult to manufacture. To prevent welding thermal stress between the shell, tube sheets, and reaction tubes, high requirements are placed on the materials and manufacturing processes, resulting in high investment costs. The catalyst loading factor of the reactor is also lower than that of I.C.I reactors, at only 30%, and it is inconvenient to load and unload the catalyst. The tower has a large diameter, making transportation difficult. Lurgi shell-and-tube reactors have been used in many methanol plants in China; however, in large-scale methanol production facilities, due to their complex structure, large number of reaction tubes, and large size, they are not yet widely used in China at present. The maximum production capacity of a single tower is 1,250 tons per day. As the production volume increases, the reactor diameter becomes too large, and due to the large number of tubes, the length of the reaction tubes can only be 10 meters, which poses difficulties in design and manufacturing. Ruchi Company proposed a process with two towers in parallel, and in recent years has also proposed a process in series with cold-tube types to meet the needs of larger-scale production, but neither of these has been put into industrial use yet. The largest capacity is 3,000 t/d (two towers); there are currently 29 methanol plants worldwide (approximately 40 synthesis towers), with a total production capacity of 8.1 million tons per year. III. The MRF reactor of TEC Company The MRF reactor is a multi-stage indirectly cooled radial flow reactor; forced circulation of water from a shell-and-tube boiler is used to cool the by-product steam. The reaction gas flows radially through catalyst layers located outside the multiple cooling tubes arranged radially, resulting in a multi-stage Z-shaped temperature distribution. This improved temperature distribution helps to extend the lifespan of the catalyst ； Radial flow reduces the resistance to gas flow through the bed ； The perforated plate ensures uniform gas distribution ； The catalyst is packed outside the tube, which appropriately increases the catalyst packing factor of the reactor and facilitates larger-scale production; however, its structure is complex and manufacturing it is difficult. It is understood that TEC can achieve a production capacity of 5,000 tons per day using a single MRF-Z type reactor; the methanol tower has a diameter of 5 meters, the reactor tubes are 22.4 meters long, and the catalyst loading amount is 350 m3. For a reactor with a capacity of 140,000 tons per year, the diameter is 2.5 meters, the bed height is 12 meters, the catalyst loading volume is 43 m3, the synthesis pressure is 5.82 MPa, and the catalyst production rate is approximately 0.4 tons/m3·h. Industrial performance: Trinidad 1380t/d ； China 315t/d ； Lutianhua is building a facility with an annual capacity of 400,000 tons. IV. Japanese Mitsubishi MGC air-cooled and water-cooled types. Double-tube reactor, with a catalyst installed between the inner and outer tubes. Cold air in the inner tube, with natural circulation of boiling water between the outer tubes. The reaction proceeds isothermally near the optimal equilibrium line, resulting in a high one-pass conversion rate and a high concentration at the outlet. The amount of catalyst required for the same scale is reduced by 30%, the circulation volume is decreased by 50%, and the steam production increases by 25%. The equipment is complex, costly, has high bed resistance, and makes it inconvenient to load and unload the catalyst. The maximum capacity is 2500 t/d. A 500 t/d plant in Japan in 1993, and a 2500 t/d plant in Saudi Arabia in 1999. Chongqing Huayi and Mitsubishi’s 850,000 tons/year (two towers) project is under construction. V. German Linde spiral tube reactor, water-cooled type. Linde installs spiral tubes in the catalytic reaction layer, using natural convection of boiler water to remove the heat generated by the reaction in the catalyst layer outside the tubes. The shell-side reaction material is in lateral contact with the spiral cooling tubes, resulting in extremely high heat transfer efficiency; the required cooling area is 60–75% of that of a tubular design. The hemispherical tube sheet eliminates thermal stress, eliminates the need for expensive duplex steel, combines the drum with the synthesis tower through the upper hemispherical tube sheet, and provides a high catalyst loading capacity, which is advantageous for larger-scale applications. However, the difficulty of processing these devices increases further; it is reported that only the Chuanwei Factory in China uses one set of such equipment. There are already 5 methanol plants worldwide. The maximum capacity is 4,000 t/d. VI. Danish TopФse insulated-water-cooled type. It consists of three adiabatic radial flow reactors, with external heat exchangers placed between them to remove heat; the gas flows centrifugally through the bed layers. Radial flow results in lower pressure, which allows for an increase in space velocity and thus an increase in yield. Catalysts with a small particle size can be used to improve efficiency within the particles and enhance the overall reaction rate. The production scale can be increased simply by raising the height, while keeping the diameter unchanged. There are already 3 methanol plants worldwide. The maximum capacity is 2000 t/d. VII. Domestic adiabatic isothermal mixed-type methanol synthesis reactor: The Southwest Chemical Engineering Research and Design Institute, East China University of Science and Technology, and Lunan Fertilizer Factory jointly developed an adiabatic isothermal mixed-type methanol synthesis reactor that combines the features of I.C.I and Lurgi reactors. It is essentially a tubular reactor, with a 300 mm thick layer of adiabatic catalyst installed at the top of the tube sheet; the catalyst is placed inside the tubes, and boiling water between the tubes is used to remove the heat generated by the reaction. The temperature difference across the catalyst bed is small, resulting in a higher synthesis efficiency compared to the cold-stirred type; moreover, steam can be produced as a by-product, enabling efficient heat recovery. It not only inherits the advantages of the I.C.I reactor, such as a high catalyst loading factor and a low temperature difference across the bed layer, but also possesses independent intellectual property rights; it has been used with great success in the 100,000 tons per year methanol plant at Lunan Fertilizer Factory and the 200,000 tons per year methanol plant at Shanghai Coking Plant. However, due to its structure, thermometers can only be installed at the inlet and outlet, which makes it difficult to determine and control the axial temperature difference. Moreover, its complex structure requires higher-grade materials, increasing the cost. Moreover, there is no experience in constructing synthesis towers with a capacity of over 200,000 tons. VI. JW Homogeneous Temperature Methanol Synthesis Tower by Hangzhou Linda Company. The JW homogeneous temperature methanol synthesis tower produced by Hangzhou Linda Company is characterized by the use of freely expandable and movable components throughout all the catalyst beds. The catalyst loading factor is 70–75%. The heat of reaction outside the tube is continuously absorbed by cold air or cold water inside the tube; there is both co-current heat exchange and counter-current indirect heat exchange between the cold air or cold water inside the tube and the reactant gas in the catalyst layer. Temperature monitoring points can be installed at any location within the catalyst layer or the tower. Heat is recovered using low-pressure steam generated in an external waste boiler or a boiler feedwater heater. The loading factor of the Linda isothermal tower catalyst is, like that of the quench tower, above 70%; however, due to the near-isothermal reaction, there is no need to use quench gas for cooling in order to prevent a decrease in the methanol concentration within the reactor. According to the comparison between the uniform temperature type and the cold shock type in gasification, under the same conditions of feed gas volume, gas flow rate into the tower, synthesis pressure, and catalyst loading, the production capacity can be increased by 50%. More production will be achieved at the same effective pressure of the gas entering the tower. Therefore, to achieve the same capacity, the reactor size can be reduced by more than 1/3 compared to a quench tower. This synthesis tower is widely used in small-scale plants in China, such as the 40,000-ton upgrade at Haha Gasification in 2000 ； 80,000 tons in 2001 ； 55,000 tons in Qujing, Yunnan in 2005 ； For projects such as the 200,000-ton capacity plant in Weihe, in order to keep up with the trend toward larger methanol production facilities, Linda Company developed an optimized methanol production process in 2001 and filed a PCT international patent for it. This technology utilizes a series arrangement of self-heating internal cooling reactors and externally cooled reactors connected one after another. The maximum capacity is 300 t/d. VII. Mitsubishi Gas Super Polymerization Column (SPC): This is a large-scale polymerization column that has been widely used around the world in recent years, and it is part of the technology developed by Mitsubishi Gas Chemical Company. The tower is of double-tube type. The gas entering the tower is first preheated to 150–170°C. After entering the tower, it is distributed into the inner tubes of the double-tube structure, where it absorbs the heat of reaction between the outer tube and the inner tube. Once preheated to the reaction temperature of 240°C, it enters the catalyst layer located between the tubes; the peak temperature during the reaction is around 250°C. The heat of reaction is removed simultaneously by the cold air in the inner tubes and the boiling water in the outer tube’s outer shell. The temperature of the gas after passing through the catalyst layer is around 205–230°C, with a methanol content of 8.5% in the gas exiting the tower. The SPC has a lower recycle ratio than Lurgi isothermal reactors and a higher space-time yield than those reactors. The inner diameter of the SPC’s double-tube design is 75 mm, which is much larger than the Ф24 diameter of Lurgi tubular reactors; moreover, the number of tubes in the SPC is much smaller, making it easier to load and unload the catalyst. The outer tube of the SPC has a thicker wall thickness, resulting in better mechanical strength compared to tubular reactors. The inner tube, flexible tubes, and partitions are non-pressure-bearing components, and the catalyst pressure drop across these parts is at most 2–3 kg/m2. Therefore, scaling up is easy, with the maximum output per unit reaching 2500 MT/D. VIII. IMC methanol synthesis tower of Swiss company MCSA: This tower utilizes plate heat exchange technology to remove the heat generated during the methanol synthesis reaction. The design involves embedding heat exchange plates within the catalyst bed as cooling elements; boiler feed water or other cooling media flow through these plates, thereby removing the reaction heat from the catalyst bed while generating medium-pressure saturated steam. The steam pressure can reach up to 39 bar. The heat exchange plates are arranged radially and in a concentric fan shape; the cooling medium flows through them (boiler feedwater or fresh syngas). The heat exchange plates are supported at the bottom of the bed, while the central tube serves as a channel in the lower part of the synthesis tower. The catalyst is supported by an inert medium bed at the bottom, and it can be removed through the bottom discharge port. The heat exchange elements are pre-assembled heat exchange plates, which are inserted into the synthesis tower through access holes at the top (applicable to both new and renovated synthesis towers). The heat exchange plates are arranged radially, and the catalyst fills the space from the inner wall to the outer wall of the tower internals; each heat exchange element has inlet and outlet ports that are connected respectively to the main cooling medium supply pipe and the main cooling medium return pipe. Each heat exchange plate is welded together from two SS 304 metal plates (for gas heat exchange) or DUPLEX metal plates (for steam heat exchange), making it highly mechanically strong and rigid. This type of heat exchange plate structure is a mature technology that has been tested in multiple installations. This structure is manufactured automatically, with all heat exchange plates within the same synthesis tower being identical. Many standard specifications can be used to test these heat exchange plates, which are marked with a “U” quality mark. Each heat exchange plate is subjected to a pressure test after being manufactured. Gases can flow co-currently or counter-currently, axially or radially. An insulating layer can be installed on the upper part of the isothermal bed (the by-product steam internals do not have an insulating layer). This structure allows other fluids to be used as heat exchange media, entering and exiting the heat exchanger without mixing with the reaction gas. The heat exchange plates can be assembled sequentially along the fan shape very conveniently. All the components are modular standard parts that can be easily replaced if damaged. The heat exchange plate is hollow; two metal sheets are welded along the perimeter and also spot-welded at the surfaces, after which it is stamped into shape. The final shape is similar to that of a pillow; it features a large heat exchange area for the internal components, a high catalyst loading factor, high utilization of the high-pressure space, small equipment size, low investment costs, and is easy to transport and install. The maximum scale is expected to reach 7,000 t/d; in 2002 there was a plant in Russia with a capacity of 425 t/d, and in 2004 another plant in Russia had a capacity of 840 t/d. A 7,000 t/d project in Iran is under negotiation. IX. Future Development of Synthesis Tower Technologies In the synthesis of methanol, the one-pass conversion rate of CO is low. To overcome the shortcomings of traditional gas-phase methanol synthesis processes, several new types of reactors have been developed in recent years; notable examples include GSSTFR, RSIPR, gas-liquid coexisting reactors, and slurry-bed methanol synthesis processes. 1. The GSSTFR (Gas-Solid-Solid Droplet Flow Reactor) uses an extremely fine adsorbent (such as silicoaluminate) that moves in the opposite direction to the reaction gases inside the reactor; the methanol produced during the reaction is absorbed by this solid adsorbent, thereby shifting the equilibrium in favor of methanol production. This type of reaction process generally involves several reactors connected in series, with coolers between them to cool the reaction gas to an appropriate temperature. The adsorbent that has absorbed methanol is desorbed through external heating in the reactor, and the regenerated adsorbent can be reused. The CO one-way conversion rate of this method can reach 100%. 2. RSIPR (Inter-stage Product Removal Reactor): There is an absorption tower between the reactors, filled with tetraethylene glycol dimethyl ether; the gases generated during the reaction proceed to the next reactor for further processing, and the volume of the reactors decreases gradually as the gas flows forward. The solvent, after reaching saturation in absorption, can be regenerated and reused. The CO conversion rate in a fourth-stage reactor can reach 97%. Its advantage is that it has low requirements regarding the V(CO)/V(H2) ratio of the feed gas, which simplifies the gas production process; moreover, this process also features lower raw material consumption and energy usage. 3. Gas-liquid coexisting reaction process: With both gas and liquid phases present, some of the methanol produced is circulated within the reactor, where it forms a liquid film on the surface of the catalyst. The methanol generated during the reaction dissolves in this liquid film. It has been reported that when the composition of the feed gas is approximately CO–29.2%; CO2–3.0%; H2–67.5%, the conversion rate of CO+CO2 in a single reactor using this process can exceed 90%. 4. Slurry-bed (three-phase bed) methanol synthesis process: The slurry-bed methanol synthesis process involves using hydrogen, carbon monoxide, and carbon dioxide as the gaseous feedstocks for methanol production; an inert liquid serves as the medium in the liquid phase, while fine particle solids act as catalysts in the solid phase. Under certain temperature and pressure conditions, mass transfer occurs among the gas, liquid, and solid phases within the reactor, and reactions take place on the active surface of the solid catalysts to produce methanol. This process exhibits good heat transfer and thermal stability; the reaction temperature remains close to isothermal conditions, making it easy to control. The one-way conversion rates of carbon monoxide and carbon dioxide, as well as the percentage of methanol in the gaseous products, are higher than those in traditional gas-solid phase catalytic methods.