Low-temperature methanol washing of feed gas
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If the low-temperature methanol wash stops the feed gas flow but methanol circulation must still be maintained, should tower T1 be purged with nitrogen to maintain pressure? And does the flash tank at the inlet of the circulator need to be purged as well to maintain pressure? Can it operate properly at pressures below normal operating pressure?
The inlet flash tank of the circulation machine needs to be pressurized; if this pressure is not maintained, a large amount of gas will flash out, resulting in pressure buildup and potentially an explosion. It is not possible to do this, as the methanol solution cannot be pumped in, the absorption efficiency is poor, and the purified gas does not meet the required standards – the levels of H2S and CO2 will be too high.
In our operations, we usually shut down the recycle gas compressor. The pressure in high-pressure systems generally needs to be maintained at above 60% of the normal operating pressure; the operating pressures in medium-pressure and low-pressure systems usually remain unchanged at their original operating pressures
The inlet flash tank of the circulation machine needs to be pressurized to maintain pressure; otherwise, pressure buildup will occur
The inlet flash tank of the circulation machine is equipped with a pressure control valve; how can pressure build up to the point of causing an explosion? The circulating gas has been cut off; as a result, the purified gas will also fail to meet the standards, with excessive levels of H2S and CO2. ? ? It seems like what you’re saying is incomprehensible to everyone!
In the short period immediately after shutdown, the pressure can still remain at normal levels; thereafter, the pressure in the flash tank drops rapidly. Once it drops to a certain level, the solution in the flash tank can no longer be forced into Tower T2 due to the pressure difference. At this point, the control room must promptly reduce the pressure in Tower T2 to ensure normal circulation of the solution, and it is also necessary to inform the site staff to immediately open the nitrogen filling valve in order to maintain normal pressure! In low-pressure systems, the pressure can generally be maintained. In high-pressure systems, when the pressure drops to an extent that creates a large pressure difference at the outlet of the lean methanol pump, it has a significant impact on the valve (the lean fluid flow control valve); if conditions permit, it should be flushed as soon as possible!
The cycle compressor should be turned off. Generally, the nitrogen flushing line has a diameter of only 2 inches, making it difficult to maintain the required flow rate and pressure at the compressor inlet; as a result, the compressor is prone to surge. Even if the anti-surge valves are fully opened to ensure the compressor can operate, keeping them in that position is then pointless
With the raw material gas supply cut off, what’s the point of keeping the circulator running to facilitate circulation? It’s just a waste of electricity!
After cutting off the raw gas, open the nitrogen filling valves for systems C1 and C2 to maintain system pressure. There is then no need to keep the cycle gas compressor running. .