Discuss common accidents that occur during normal operation of the low-temperature methanol washing process and their solutions!

Below are the posts I found on the forum; I hope they will be helpful to you. 1. Wushihua Fertilizer Plant: In 1987, catalyst bridging and collapse occurred during the CO conversion process in the low-temperature methanol washing unit; a large amount of catalyst dust entered this unit. During subsequent processing, the manholes of the absorption and regeneration towers in the methanol washing system were accidentally opened, allowing air to enter and cause oxidation, which further exacerbated corrosion. This results in contamination of the entire methanol washing system; the heat exchange efficiency of the heat exchangers declines significantly. Impurities present in the methanol solution cause pump clogs, requiring frequent cleaning of the pump inlet filters. A large amount of methanol is lost, which affects the regeneration of the methanol solution. The purification of the process gas is inadequate, with levels of trace CO2 and H2S exceeding acceptable limits; this poses a serious threat to the nitrogen washing process downstream. As a result, the production capacity can only be maintained at 80%–90%. Trying to resolve the issue by replacing the methanol several times proved ineffective. Based on the above circumstances, the root cause is that the system is too dirty, with large amounts of FeS corrosion products adhering to the surfaces of the heat exchangers, thereby affecting the heat exchange efficiency. Implement control measures: After a thorough chemical cleaning of the entire system, it is protected with nitrogen. A microporous filter is added to the solution outlet pipeline of the lean methanol storage tank to remove impurities carried in the solution. Increase the gas separator in the CO conversion process to control water content in the conversion gas. Add a lean methanol heat exchanger (E9) and improve its heat exchanger design by reducing the tube bundle spacing. Increase the boiler in the solution regeneration tower. Enlarge the methanol distillation tower. 2. At high load levels, the washing volume in the rough washing section of the absorption tower at the Jiujiang Petrochemical Fertilizer Plant remains fluctuating, making it difficult to control. Cause: The flow control circuit for the roughing stage cannot be operated in automatic mode, resulting in frequent fluctuations in the feed pump’s flow rate, which affects the safe operation of the equipment. Fluctuations in the amount of methanol in the roughing stage lead to variations in the liquid level at the bottom of the tower, thereby causing fluctuations in the flashing pressures throughout the regeneration tower; this can even threaten the proper operation of the carbon dioxide compressor in the urea production plant. The absorption conditions in the absorption tower as well as the efficiency of carbon dioxide removal are also affected, posing a serious risk to the stable operation of the decarburization unit. Cause analysis: Gas is entrained in the methanol at the bottom of the absorption tower, starting from the central tube at the 10th tray – this may be due to unstable flow patterns that cause localized flashing and the formation of bubbles. This results in cavitation within the pump, leading to fluctuations in its flow rate. Under low-load conditions, flow entrainment does not affect the pump’s flow rate either. Problems that have occurred at Ningxia Chemical Plant: 1. Low-temperature methanol washing unit – Imbalance in the cooling capacity of the methanol washing unit: Catalyst ash brought in from the conversion unit, along with corrosion products within the system, clog the heat exchange equipment, which affects the efficiency of heat exchange and leads to an imbalance in the system’s cooling capacity. The top temperature of the methanol absorption tower is often higher than the design value of -57°C in summer, reaching up to -52°C, which causes the trace components in the process gas to exceed acceptable levels and severely impacts the plant’s operation at high load. The moisture content in the recycled methanol is too high: Due to the poor separation performance of V3, excessive moisture is carried into the methanol washing unit along with the process gas, which increases the load on the C4 and C5 towers. As a result, the moisture content in the recycled methanol is high (the design value is <0.2%; during the initial trial production phase it was 2%–3%, and at times it even exceeded 4%). Incomplete methanol regeneration and increased circulation volume also reduce the absorption efficiency of the C1 tower. The original design for the outlet temperature of E9 contaminated methanol was 35.4°C. The actual temperature is often below 0°C, being about 40°C higher than the designed value, resulting in severe heat loss. The blockages are mainly composed of corrosion products from this unit and ash from the shift catalyst. To address the aforementioned issues, it is planned to modify some of the equipment: upgrading the C5 tower, increasing the heat exchange area of E11 and E15, adding an additional E9 unit, installing filters at its inlet, and replacing the large V1 unit. Implementation is currently being arranged on a step-by-step basis, starting with the C5 tower, E15 unit, and the filters. 2. The liquid nitrogen washing unit does not have sufficient cooling capacity. Due to this lack of cooling power, liquid nitrogen is frequently obtained from the air separation unit to provide additional cooling, and although some modifications have been made, the process conditions still deviate significantly from the design values

I wonder if there is more detailed information upstairs that could be shared?

I also found these posts on forums; there’s no more detailed information available.

What are the disadvantages of the low-temperature methanol washing process, and how can they be overcome? ? ? ? ? ? 、

I hope to learn more relevant knowledge, specifically regarding accidents and their handling in our factory.

The accidents that can be found online are either those that have already been reported or some minor accidents that aren’t significant. If it were a major accident that didn’t make it into the news, I guess no one would talk about it; who would want to bring shame upon themselves? ? ? ?

Could you provide a bit more so that we can learn* from it*.

In Hunan Dongtan, a serious fire broke out due to high levels of methanol in the exhaust gas venting pipeline of the reabsorption tower; subsequently, a separator was added at the exhaust gas outlet, four trays were removed from the exhaust gas section of the tower, and the liquid distribution pipe in that section was moved down to tray 83. Good results have been achieved since then.