Operational challenges in the methanol-water column of low-temperature methanol washing
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Our low-temperature methanol washing process uses the Ruchi process with a nine-column setup (six of these columns are used for methanol recovery). Recently, in our methanol-water column (the 9th column), we have encountered the following issues: 1) no temperature gradient; 2) the temperature at the top of the column fails to drop; 3) the temperatures at the bottom and top of the column often exceed acceptable levels; 4) the column is prone to flooding. The measures we have taken include: 1) the tray plates were just cleaned; 2) the condenser at the top of the column was recently checked and found to be leak-free; 3) the reboiler at the bottom of the column was also cleaned and is not clogged; 4) introducing a stream of pure methanol as reflux did not help either. In front of the methanol-water column is an azeotropic column, which is used primarily to remove light oils from methanol and water
Check whether the pressure gauge at the top of the tower is damaged; high pressure can cause the above issues! It’s best to calibrate the pressure gauge.
The pressure at the top of the tower has been checked – it’s normal; the readings on site are the same as those from the remote monitoring system
May I ask what it means when there is no temperature gradient? My operations in the past weren’t as difficult as yours; increase the reflux rate, and make sure the steam pressure in the reboiler remains stable – even slight fluctuations can have a significant impact. Has the heat exchanger at the bottom of the tower ever become clogged? If there is a blockage, it may also affect the rise in the liquid level at the bottom of the tower as well as the increase in temperature there, thereby impacting operations. Also, are your feed flow rate and temperature stable? If not, it is likely that the design of the sensitive trays was incorrect or the feed position is not proper
I think, whether it’s the Linde process or the Lurgi process, the key to controlling the methanol-water separation tower lies in the boiling point of water at the corresponding operating pressure. Starting from this perspective and taking into account actual operations, one can see if there are any variations
Consult the patent holder of the tray; since the tray has just been cleaned, it’s possible that its original design was inadequate – there is no temperature gradient, which causes the heavier components to rise upward. Consider using a tray with better anti-clogging properties. Also, is the tray blockage severe?
Is the operating pressure of the tower normal? Also, is the amount of methanol returning to the top of the tower (the liquid phase flowing downward within the tower) too small or absent?
Is the steam volume in your reboiler not well controlled? Is it caused by a high steam quality?
Return flow and liquid distributors are important. If the backflow is fine, it should be a problem with the distributor.
I guess the pressure difference in your dehydration tower isn’t low – either the trays are blocked or too much steam is being supplied
The absence of a temperature gradient is not a problem. We are from Dalian University of Technology, and it’s the same there; what’s important is to control the reflux flow rate and reflux temperature at the top of the tower. The heat load inside the tower should not be too high, as an increase in heat load can lead to excessive methanol content in the liquid at the top of the tower. It’s necessary to keep the temperature at the top of the tower below 100 degrees, while keeping the temperature at the bottom of the tower above 138 degrees. If the temperature at the top of the tower keeps rising while the temperature at the bottom doesn’t decrease, it’s possible to gradually reduce the amount of steam used, thereby lowering the heat load to the level suitable for the bottom of the tower. That should solve the problem. 6# TUOHZHE