Shutdown issues of the methanol synthesis unit

For short-term shutdowns, the system is depressurized to 1.0 MPA, and the compressor can remain operational. For long-term shutdowns, the compressor can be stopped after nitrogen purging is completed to ensure proper depressurization; the BW cycle in the synthesis tower can be halted once its temperature drops to 120 degrees, allowing it to cool down naturally

The compressor doesn’t need to be stopped for short-term parking, right? For long-term parking, we first reduce the circulation rate without using nitrogen for displacement, then lower the speed; once the resonance condition is passed, the motor can be stopped. I’m not entirely sure either, so let’s exchange ideas: handshake

For a short-term shutdown of methanol production, my advice is not to shut down the compressor, as doing so can cause significant damage to the machine. The machine’s anti-surge valve can be opened, and the fresh gas inlet valve can be closed. Open the system for venting to reduce pressure, until the system pressure is lower than that of nitrogen. Then, nitrogen is used for displacement to keep the CO2 and CO content in the system below 0.2%, thereby preventing damage to the catalyst. Open the steam injector in the synthesis tower in a timely manner to prevent the tower temperature from dropping too rapidly. Reduce the alcohol level to the lowest possible. Turn off the drum blowdown and make-up water.

Different processes certainly require different treatment methods, but the general principle remains the same: to facilitate smoother operation without damaging the equipment and catalysts. Here, we use steam turbines to drive the compressors; centrifugal compressors are employed in our system. If we need to park the system for an extended period, we have to purge the synthesis loop with nitrogen; for short-term parking, the pressure is usually reduced to that of the front system when it is shut down. When we park here, the synthesis system is isolated from the front system. In this way, when driving and the synthesis system is connected in series with the preceding system, there is no need to pressurize the synthesis system; operating the compressor at low power can save a great deal of steam. It is better to balance the steam pipeline network. When choosing an operation plan, the poster should consider their own manufacturing processes and equipment.

Is it necessary to protect the temperature of the catalyst layer?

The steam pressure of the heavy tower is stable, but there are slight fluctuations in the reflux volume and significant variations in the liquid level. What could be the reason?

For short-term parking, all feed gas is shut off, the compressor continues to operate, anti-surge measures are fully activated, and the dry gas seal is promptly switched to N80. The synthesis system is set to release gas at appropriate levels, and a certain liquid level is maintained in the drum. During this period, the start-up injector is activated in a timely manner to prevent too rapid a drop in temperature. The temperature of the synthesis tower must not exceed a certain limit; therefore, the system needs to be vented slightly to ensure proper circulation and prevent the formation of dead air. In this way, the catalyst will also not overheat and get damaged. Once the conditions are suitable, more water can be added to the boiler, and the startup injector can be activated to raise the temperature of the synthesis tower. After that, feeding can begin. The recycle gas compressor needs to prevent liquid from entering the gas stream, so it is necessary to control the liquid level in the separator properly – ideally, an high-level interlock should be installed. It also depends on the feed; when making adjustments, look at the trend. For long-term parking, the compressor must be shut down, but the nitrogen isolation cannot be stopped immediately. The isolation gas can only be turned off 10 minutes after the oil system has stopped; otherwise, oil will enter the compressor cylinder. Parking sequence: First, close the inlet valves for the main materials (feed gas, hydrogen, etc.), and also close the bypass valves. While filling the boiler with water, stop the process and open N80 to purge the system and reduce its temperature, thereby preventing damage to the catalyst and the synthesis tower due to overheating. After successful purification, open N5 to fill the system again, and slightly open the drain to allow fluid to flow out.

What should the synthesis system do if the syngas compressor (centrifugal type) shuts down? Also, when the synthesis system cannot establish a cycle, can the start-up injector be used? If it is put into use, will it cause local overheating?

It is sufficient to maintain a certain liquid level in the drum; there is no need to activate the steam ejector. As long as a proper degree of pressure relief is maintained, so that the gaseous fluid does not cause localized overheating, we have encountered problems related to localized overheating in the past – this was due to attempts to maintain heat and pressure, which resulted in some pipes in the synthesis tower being damaged and having to be sealed off. Therefore, it is essential to relieve pressure while also keeping the liquid level in the drum under control, so that the heat generated in the synthesis tower can be dissipated, thereby avoiding problems.