Reasons for excessive moisture content in pure methanol
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1. For two-tower systems, the reflux ratio of the heavy tower is too low or the temperature is too high; for three-tower systems, the pressure tower, the atmospheric pressure tower, and the recovery tower all have a reflux ratio that is too low or a reflux temperature that is too high. 2. The bottom temperature of each tower is too high. 3. The top pressure of each tower is too low. 4. The moisture content at the bottom of the tower is too high, or the liquid level is too high. 5. Low-pressure steam, etc., leak into the tower.
I have doubts about this conclusion: 1. Aren’t low pressure and high temperature contradictory? 2. A high water content at the bottom of the tower simply indicates the quality of the crude alcohol you are using; this cannot be considered a reason for your product to be deemed defective! 3. A low pressure at the top of the tower can increase the relative volatility of alcohol and water, which is beneficial for distillation. Of course, if the pressure is too low, it can affect steam savings and energy balance; however, as long as the process requirements can be met, I don’t consider a low pressure to be the main reason for substandard product quality ； 4. It doesn’t specify what type of tower you have, nor your requirements regarding the feed – whether the feed inlet is suitable or not! 5. Are there any requirements regarding the residue in the tower bottom?
I also have doubts: 1) The bottom temperature of each tower is too high. If the bottom temperature is high, but there is sufficient reflux, then the top temperature can be controlled, the quality of the product obtained will be good, and proper discharge of the bottom water can be ensured; however, energy consumption will be higher. 2) The pressure at the top of each tower is too low. As mentioned earlier, a low pressure means a low temperature as well, and the quality of the product obtained will still be satisfactory, but this applies to atmospheric-pressure towers. The discharge of bottom water from recovery towers is even more concerning. 3) Low-pressure steam leaks into the towers. If the pressure level of the low-pressure steam is lower than the operating pressure of the pressurized tower, the low-pressure steam will not leak into the tower. In the case of a three-tower system, the heat source for the atmospheric-pressure tower is methanol steam, which does not come into contact with the low-pressure steam.