Weekly Topic on Ammonia Synthesis: Protection of Ammonia Synthesis Catalysts During Overhaul 29/10/2011
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Weekly Topic on Ammonia Synthesis: Protecting Ammonia Synthesis Catalysts During Overhaul Periods. How to protect ammonia synthesis catalysts during long-term shutdowns and overhauls? The process from parking until the major repair period. Higher scores will be given as appropriate based on level of participation; everyone is encouraged to get actively involved.
We mainly use nitrogen for protection, analyze the oxygen content in the nitrogen on a regular daily basis, and pay attention to monitoring changes in the temperature of the coal bed. Stop nitrogen charging once a temperature rise occurs.
1. First, dry the catalyst with hot nitrogen so that the water content at the outlet is less than 0.5%. 2. Cool down. 3. Pass nitrogen gas to maintain a slight positive pressure. Cooling step: The temperature is reduced as the production load decreases. As production falls, the amount of steam used is gradually increased, and the amount of water sprayed is also increased accordingly, so that the temperature at the hot spots in the catalyst layer drops at a rate of 25°C per hour; the temperature of these hot spots is brought down to 200°C. This process takes approximately 2 hours. * S o& E. U5 `* t Cooling of dry gas: Once the entire plant has been shut down and depressurized, the shift in the gas generation workshop should switch the blind flanges on the circulation cooling pipes used for desulfurization to blind rings, close the inlet valve of the low-temperature transformer, and open the bypass valve for heating the low-temperature transformer, so that the conversion system operates using compressor-driven circulation cooling. The converter is connected to both the desulfurization unit and the compressor; the control system maintains a pressure of around 0.4 MPa. Dry gas is used to cool the low-pressure converter, causing the temperature of the catalyst bed in that converter to decrease at a rate of 15°C per hour. During the cooling process, it is necessary to coordinate properly with the urea cycle water flow, pay attention to the cooling effect of the cooling tower, and reduce the temperature of the low-temperature shift catalyst bed to below 60°C. This process will take about 10 hours. After the cooling of the low-temperature converter is complete and the inert gas replacement is successful, the inlet and outlet valves as well as the heating bypass valves are closed. Blind flanges are installed at these valves, the low-temperature converter is isolated from the conversion system, and nitrogen is introduced to maintain positive pressure. Precautions for cooling down: 7 b4 }% d; e- t9 }. x 1. Strictly follow the operating procedures, carry out the cooling process in accordance with the established plan, and keep proper records of the cooling process. During the cooling process, it is necessary to maintain good communication with the circulating water team in order to control the temperature of the shift gas according to the standard parameters. 3. During the cooling process, if special circumstances arise that prevent normal cooling, it is necessary to immediately bring the system into a safe shutdown state, inform the dispatch team promptly, and restore normal cooling as soon as possible. 4. During the cooling process, personnel in the new conversion unit, gas generation unit on the third floor, desulfurization unit, compressors, and other related positions must strengthen communication among themselves, remain firmly at their posts, enhance their sense of responsibility, and follow the unified instructions of the dispatch team. 5. During the cooling process, the instrument operator must calibrate the temperature promptly at the start of each shift to ensure that all temperature measurement points are accurate and reliable. 0 H" T" i, C$ m, a. E 6. Other matters not covered shall be handled in accordance with relevant regulations!
When parking, we first fill it with nitrogen to maintain pressure; it’s best to keep the pressure high. If the vehicle is parked for a long time and the pressure drops, pressure should be replenished promptly
Under nitrogen protection, that is, by cutting off the synthesis loop and directly introducing nitrogen into the tower near it, the pressure inside the tower is maintained at around 0.5–2 kg.
Use qualified nitrogen for protection; if the blind plate is installed properly, only a small amount of nitrogen is needed to maintain a slight positive pressure. This slight positive pressure ensures that, as the temperature inside the tower drops, no external gases will enter, and it also prevents a negative pressure from forming, which could allow air to enter when the blind plate is removed. If the pressure can be well maintained after installing the blind flange, careful monitoring is sufficient.
1. Isolate and fill with nitrogen to maintain positive pressure, preventing air from entering. 2. Monitor parameters such as temperature and pressure during parking. 3. Perform replacement and analysis before driving.
Nitrogen protection is a must! Has anyone discussed how to cool down and relieve pressure? Combined with ammonia discharge from the synthesis loop, huh
After the synthesis section is shut down, the valves in the hot section of the synthesis process are closed via interlock; the valves connecting to the cold section must be manually closed by the control room operators after releasing pressure in the synthesis circuit to 100 kilograms, thereby isolating the hot and cold sections of the synthesis process. Then the hot section cools down naturally. As for the cold section, including the refrigeration system, we do not release ammonia during major maintenance shutdowns, unless there are repair tasks required for the relevant equipment.
Apart from filling it with nitrogen to maintain positive pressure and paying attention to the tower wall temperature, I really can’t think of any other solutions. If anyone has better ideas, please share them with me