Weekly Topic 10.11.01, Issue 1: Please list the types, internal structures, as well as advantages and disadvantages of methanol synthesis towers.

The internal components of medium-pressure methanol synthesis towers in China mainly include cold-tube type, cold-jet type, and combined cold-tube and cold-jet type. Among cold-tube-type internals, the single-tube baffle type (uniform-temperature type) has been used quite successfully. It features an ideal temperature distribution, high production capacity, and great operational flexibility. Moreover, the activity of the catalyst is less affected by poisons and thermal aging, which makes it suitable for the narrow temperature range required by methanol synthesis catalysts; as a result, it is widely used. Although cold-stirred internals have a simple structure, allow for a large amount of catalyst to be used, are easy to install and remove, and result in low pressure drops, they exhibit a large temperature difference within the catalyst bed. Methanol synthesis is a highly exothermic reaction that occurs in multiple directions, requiring repeated cold stimulation. The introduction of cold gas exposes the entire catalyst layer in the tower to factors such as poisons and thermal aging, which leads to a short catalyst lifespan and a low yield of methanol per ton of catalyst under the existing process conditions.

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Features of Luchi water-cooled towers: larger heat exchange area, uniform temperature distribution, suitable conditions for catalyst use, and easy installation and removal； It is highly functional, combining a reactor, a waste heat boiler, and a startup heater in one unit, which facilitates operation under various conditions; it represents the best option for methanol synthesis reactors of all types. It has a low efficiency, a small loading factor, high consumption of materials, high requirements for manufacturing and material quality, a large weight, difficulties in transportation and installation, and greater challenges when attempting to make it larger in size.

Large horizontal water-cooled synthesis reactors from Zhejiang Linda Chemical Technology Engineering Co., Ltd.: Features: ① High volume ratio, with catalysts installed outside the heat exchange tubes； ②Strong heat transfer capacity ； ③Low cycle ratio, high net product value ； ④The pressure drop is low, with a tower pressure drop of 0.03–0.05 MPa. ⑤Production capacity can be increased by increasing the length of the catalytic bed ； ⑥The outer shell and the inner components are separate, allowing the inner components to be replaced individually.

The GC-type water-cooled plate methanol synthesis towers produced by Nanjing Guochang Chemical Technology Co., Ltd. have a capacity of 100,000 to 1,000,000 tons per year per tower. Their features include: ① gas radial and baffled distribution technology, with a pressure drop typically ranging from 0.1 to 0.2 MPa； ②Improve the heat transfer properties of the catalyst bed; increase the heat transfer coefficient and enhance the heat transfer capacity ； ③It has a high catalyst loading factor and high production capacity.

Shell-and-tube type, shaft-radial type, triple-tube type, upper and lower catalyst chambers, etc

The tubular synthesis tower has a low cost and is suitable for pressures up to ~5 MPa; it is commonly used in small and medium-sized methanol synthesis plants. Plate-type synthesis towers are expensive and suitable for pressures of up to ~8 MPa; they are commonly found in large-scale methanol synthesis plants.

Reply to 4# liujianguo1116: Lugi no longer uses single water-cooled towers; instead, it employs a combination of water cooling and air cooling, which improves heat utilization rate and virtually eliminates any waste of heat.

The Cassali plate-exchanger type methanol synthesis tower offers excellent heat exchange performance, high conversion rates in methanol synthesis, and easy temperature control

1 Methanol synthesis process: The conversion gas and methanol recycle gas are pressurized to 7.9 MPa by a combined compressor, then heated to around 140°C by an inlet gas preheater. They enter the cold tubes of the methanol synthesis tower, where they exchange heat with the reaction gas outside the tubes, resulting in a temperature rise to 240°C. After that, they exit the cold tubes and proceed to the catalytic bed outside the tower for further reaction; the gas exiting the synthesis tower has a temperature of about 250°C. It then enters a waste heat boiler to produce steam, and after that it passes through the tubes of the inlet gas preheater, which heats the incoming gas while cooling itself further. Finally, it goes through a desalinated water preheater and a methanol water cooler, reducing the temperature of the reaction gas to 40°C, before entering the methanol separator. The crude methanol obtained after separation is subjected to vacuum flash evaporation in a flash tank before being sent to the methanol distillation unit. Most of the gas produced as a result of this separation is pressurized again using a compressor and fed back into the methanol synthesis tower for further reaction, while a small portion is used as vent gas for hydrogen recovery. The process flow is shown in Figure 1. Figure 1: Schematic diagram of the low-pressure methanol synthesis process. Table 1: List of main equipment used in methanol synthesis. Figure 2: Simplified diagram of the isothermal methanol synthesis tower. Figure 3: Structure of the isothermal methanol synthesis tower. As shown in Figure 2, the gas entering the tower passes through the gas inlet 1 and is distributed evenly to each ring tube 8 via the gas distribution pipes 6; this design ensures a uniform radial distribution of the gas within the tower. Then the gas enters the downward cold tube 10, where it exchanges heat with the gas in the catalytic bed to increase its temperature; it subsequently enters the upward cold tube 9, where it further exchanges heat with the gas in the catalytic bed in a counter-current manner to raise its temperature. Once the gas reaches the temperature required for catalyst activity, it enters the catalytic bed 17 to undergo methanol synthesis. After the reaction, the gas exits the methanol synthesis tower through outlet 16. The Inner Mongolia Tianye JW3000 isothermal methanol synthesis tower is equipped with 4 sets of 28 temperature measurement points in total, which enables better monitoring of the temperature in the catalytic bed during the production process, thus providing a more comprehensive understanding of the methanol synthesis reaction. 4 Temperature rise reduction of the catalyst: For methanol synthesis, the XNC-98 low-pressure methanol catalyst produced by Sichuan Tianyi Technology Co., Ltd. was used, with a loading amount of 74.05 tons. The quality of temperature-induced reduction will directly affect the performance of the catalyst. The basic principle for temperature-induced reduction is to strictly control the water vapor concentration at no more than 3.0 g/m3, and to produce as much water as possible at low temperatures. Due to the certain lag and errors in measuring water vapor concentration, it is generally converted into the amount of water output to control the rate of heating and reduction. Low-temperature outlet water is beneficial for the activation of the catalyst. The temperature-induced reduction of methanol synthesis catalysts is given high priority by Aino Company’s methanol production plant; to this end, meetings were held with catalyst manufacturers, Linda Company, and plant technicians to discuss the matter, and the following reduction scheme was established. (1) The methanol synthesis catalyst begins hydrogenation reduction at 140°C. (2) Before reduction, test the accuracy of the flow meter FI01412 in the hydrogen supply line, and analyze the hydrogen content at the outlet of the synthesis tower. (3) Hydrogen content requirements