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Project: Plate tower, Packed tower. Production capacity: The opening ratio of the tray plates generally accounts for 7% to 13% of the tower’s cross-sectional area； The production capacity per unit tower cross-sectional area is low. The opening ratio of the components inside the tower is usually above 50%, while the porosity of the packing layer exceeds 90%; as a result, the flooding point is generally high, leading to a high production capacity per unit tower cross-sectional area. Separation efficiency: Under normal circumstances, plate towers typically have no more than 2 theoretical stages per meter. At reduced pressure, atmospheric pressure, and low pressure, its efficiency is significantly lower than that of a packed tower; whereas at high pressure, the separation efficiency of a plate tower is better than that of a packed tower. Generally, in industrial applications, packed towers are used with 2 to 8 theoretical stages per meter. At reduced pressure, normal pressure, and low pressure (pressure less than 0.3 MPa), the separation efficiency of packed towers is significantly better than that of plate towers; at high pressure, however, the separation efficiency of plate towers is superior. In terms of pressure drop, the pressure drop per theoretical stage in a plate tower is generally around 0.4–1.1 kPa, which is about 5 times higher than that in a packed tower. Packed towers have an advantage in terms of their higher porosity, with a pressure drop per theoretical stage of around 0.01–0.3 kPa, far lower than that of plate towers. Generally, reduced pressure not only lowers operating costs and energy consumption but also, in the case of distillation processes, helps to reduce the temperature at the bottom of the tower, which is beneficial for the separation of heat-sensitive materials. Operational flexibility: Plate towers have limited operational flexibility due to issues such as liquid flooding and leakage on the plates; however, well-designed plate towers possess much greater operational flexibility than packed towers. The operational flexibility of packed towers depends on the wetting properties of the packing material and the design of the tower internals. When the liquid load is low, it is difficult to ensure adequate wetting of the packing surface, even with a properly designed liquid distributor; hence, packed towers have less operational flexibility than plate towers. Liquid holdup: Approximately 8%–12% of the tower volume. Approximately 1%–6% of the tower volume. Liquid-to-gas ratio: The range within which the liquid-to-gas ratio can vary is relatively wide. At low liquid-to-gas ratios, poor wetting of the packing may occur; therefore, plate towers are more commonly used. The acceptable range for the liquid-to-gas ratio is relatively narrow. At high liquid-to-gas ratios, packed towers are preferred due to their higher capacity for gas and liquid flow. Material requirements: These towers are generally made of metallic materials, but non-metallic corrosion-resistant materials can also be used. Structure and manufacturing: Their structure is more complex than that of packed towers, making manufacturing more difficult; however, their structure is simpler than that of plate towers, so manufacturing is relatively easier. Installation, maintenance, and cleaning: These towers are more convenient for these tasks compared to packed towers. Cost: When the diameter is greater than 800 mm, their cost is generally lower than that of packed towers; when the diameter is less than 800 mm, their cost is generally lower than that of plate towers. Tower weight: Lighter. Heavier. How do plate towers and packed towers operate and are they regulated? The normal operation and adjustment of plate towers and packed towers should be the same, but the following points should be taken into account for packed towers: Their operating range is narrower, and they are particularly sensitive to changes in liquid load. When the liquid load is low, the filler surface cannot be properly wetted, resulting in a sharp decline in mass transfer efficiency; conversely, flooding is likely to occur. Packed towers are not suitable for handling materials that are prone to polymerization or contain solid suspensions. For systems prone to foaming, packed towers are more suitable, as they provide restrictions on foam and help to break it down. Packed towers are often used for thermosensitive systems, as the liquid holdup is lower than that in plate towers, resulting in a shorter residence time of the material inside the tower. Packed towers are more suitable for operation under negative pressure; they have a lower pressure drop compared to plate towers, resulting in less energy consumption. In terms of equipment installation and maintenance, packing is more expensive than trays, has a shorter installation time, and is less convenient to maintain compared to trays. Moreover, the installation requirements are higher than those for tray plates. In particular, the levelness of the distributor; it can be said that whether a packed tower can operate successfully depends to a large extent on the quality of its distributor’s design and installation. Original startup operation techniques for distillation towers: Inspection – Conduct verification one by one in accordance with the installation process diagram. Blowing and cleaning: In the equipment and pipelines of tower systems that have been newly built or overhauled, there are often various contaminants such as dust from the installation process and welding slag. To prevent these debris from blocking the pipes or jamming the valves while driving, they must be blown away or cleaned using compressed air. Before purging, the flanges connected to the equipment and valves should be removed in sequence according to the gas-liquid flow path, so that the substances to be purged can be discharged from there. During cleaning, use high-speed compressed air to blow out the residue in sections and gently tap the outer wall with a wooden hammer. After blowing out each section, install the flange immediately. The purging process should involve blowing from the higher part of the equipment to the lower part. System hydrostatic and airtightness tests: To check the density and mechanical strength of the equipment’s welds, hydrostatic tests must be conducted before use. Hydraulic testing is generally carried out in accordance with the requirements specified in the design drawings. The hydrostatic test should be carried out using clean water at room temperature, and the water should be injected from the lowest point of the equipment to allow the gas inside to escape through the top. To ensure that no gas leaks from the flanges and welds while the unit is in operation, thereby maintaining continuous and stable tower performance, a system airtightness test must be conducted. The test method involves using a compressor to introduce air into the system, gradually increasing the pressure to 1.05 times the operating pressure. Then, soap water was applied to each weld and flange on all equipment and pipelines to check for leaks. Once the leak is located, mark or record it, and address it after depressurization. If there is no leakage, maintain the pressure for 30 minutes; if the pressure does not drop, it is considered acceptable. Finally, release the gas. There are single-unit tests and combined tests: Single-unit tests are conducted to verify that the equipment that is in operation or about to be operated (such as air compressors and centrifugal pumps) functions properly and meets the relevant technical specifications. Single-unit testing is carried out without materials and under no load. First, disconnect the coupling and operate the motor alone for 48 hours, observing whether the motor heats up, vibrates, makes any abnormal noises, and whether its rotation direction is correct. Joint commissioning is a type of test run that simulates production conditions by using water or other materials similar to the production materials, in place of the actual production materials. The purpose is to test the ability of the production facility to continuously process materials. During the joint commissioning, heat the feed water and observe whether the instruments accurately display data such as flow rate, temperature, and pressure, as well as whether the equipment is operating properly. System displacement: In industrial production, the substances that are separated are mostly organic compounds, which are flammable and explosive. If the air inside the equipment is not removed before it is put into use, it can easily combine with these organic compounds to form explosive substances. Therefore, before feeding the mixture into the system, the air within it should first be displaced with an inert gas (nitrogen), so that the oxygen content in the displaced gas is no more than 0.5%. System startup: Once the system replacement is completed successfully, the system can be started. Techniques for normal startup and shutdown of distillation towers. Normal startup: Production can begin once the system equipment has been properly purged. The normal startup of distillation operations is divided into startup after a short-term shutdown and startup after a long-term shutdown. a. Driving after short-term parking: Check the raw material inventory, determine the feeding amount, and feed it into the bottom of the tower. Once the liquid level is visible, increase the temperature slowly. During this process, as the tower pressure rises, the inert gas inside the tower is gradually expelled; at this point, the amount of condensate should be increased accordingly, and full reflux operation should be carried out. Feeding can begin when the liquid level at the bottom of the tower is between 1/2 and 2/3. Once the tower operates normally as the temperature rises, feeding should be stopped to allow natural circulation within the tower. After the analysis of the reflux liquid shows it meets the requirements, product extraction can start, and feeding can continue for production purposes. During its own circulation process, it operates in a full reflux mode; when continuous feeding and continuous extraction are achieved, the operation is considered successful. When feeding material into an empty tower and starting to raise the temperature, the rate of temperature increase should be slow, as there is no liquid reflux at this stage, and gas-liquid contact as well as mass exchange have not yet taken place on the tray; as a result, the upward velocity of the gas is faster than under normal operating conditions. As the temperature rises, the vapor evaporated at the top of the tower is condensed and then returned to the top of the tower, flowing down along the tray sections where a liquid layer gradually forms; thus, mass and heat transfer processes take place within the tower. If this is not done, the poorly volatile components will be carried to the top of the tower, resulting in defective products. b. Driving after long-term parking Driving after long-term parking generally refers to driving after maintenance. First, check whether all equipment, pipelines, valves, sampling points, electrical systems, and instruments are in good condition and functioning properly ； Then the system is purged, cleaned, and tested for strength and airtightness, as well as having its contents replaced. Once everything is normal and meets the requirements, the startup procedures after a short-term shutdown are followed. Shutting down in chemical production depends on the condition of the system before shutdown; generally, there are three methods: a. Normal shutdown – A planned shutdown that takes place after production has continued for a certain period of time, when the equipment needs to be inspected or repaired. This type of parking involves gradually reducing the addition of material until it is completely stopped. After the material has been vaporized, stop supplying gas for heating, allow the temperature to drop, and release the pressure in the system; then stop supplying water and drain the solution in the system completely (into the solution storage tank). Open the system vent valve and clean the system. If the feed gas contains flammable or explosive gases, the system must be purged with an inert gas. After parking, for certain equipment that requires maintenance, blind flanges must be used to shut off the material pipelines on the equipment, in order to prevent the leakage of flammable substances and avoid accidents. b. Emergency shutdown: A shutdown that occurs under some unexpected special circumstances during production is called an emergency shutdown. If certain equipment is damaged, there is a fault in the power supply for some electrical components, or one or more instruments stop functioning, it can all lead to an emergency shutdown of the production facility. In the event of an emergency shutdown, feeding must be stopped first, and the heating steam to the reactor bottom as well as the amount of condensate removed must be adjusted so that the equipment is in a standby state for production. At this point, efforts should be made promptly to repair the equipment and eliminate the fault; once the cause of the shutdown has been resolved, production can be resumed following the startup procedures. c. Full emergency shutdown: A full emergency shutdown is required when there is a sudden power outage, water outage, gas outage, or a major accident during the production process. To prevent a complete shutdown, typical chemical plants are equipped with backup power supplies; when the primary power supply fails, the secondary power supply should supply power immediately.