Questions regarding the methanol dehydration tower in low-temperature methanol washing
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Dear colleagues, we have encountered a rather tricky issue with our installation and would like to seek your advice: In the methanol dehydration column of the Linde Classic 5-tower process, the temperature at the bottom of the column has been high recently. The normal temperature is around 125 degrees Celsius, but it is now 138 degrees Celsius. Meanwhile, the steam flow to the reboiler at the bottom of the column has actually decreased. The temperature at the top of the column remains within normal ranges. The problem currently is that the methanol concentration in the methanol wastewater at the bottom of the column is high, while the water content in the methanol at the top of the column is high. This ultimately results in a high methanol-water content in the entire device. We investigated the causes: 1. Blockage inside the tower (tray tower) or detachment of the trays. So the tower was disassembled; all 54 layers of trays were inspected and found to be in good condition, and the liquid drop pipes were not clogged either, ruling out this cause ； 2. Leakage inside the reboiler; isolation inspection showed no leakage ； 3. The medium entering the bottom of the tower changed, so the relevant heat exchangers and pipelines were checked, and all were found to be in good condition. Many adjustments were made to the process, but there was no improvement. I would like to ask fellow sailors if anyone has encountered this problem; please share your insights. Thank you.
:) After reading your description, has the water content kept increasing? It remains at a relatively high value and is stabilizing; what exactly is it? It is recommended that you consider the following issues and expand the scope of inspection beyond just T5: (1) Check whether the E12 water cooler in your system is leaking; take samples of the reflux liquid from T5. (2) Examine the operation of the regeneration tower to determine if there are any internal leaks in the reboiler. (3) If the nitrogen used for gas stripping at T3 comes from liquid nitrogen washing, check the water content in that nitrogen. Inspect all areas of the system where water might be present. (4) Adjustments to the methanol-water separation tower should not be made too quickly; observe the system as you make adjustments, as problems may not become apparent if inspections are done too frequently~
Is the reflux rate too low? If the reflux rate is low, the water content at the top of the tower increases; simultaneously, the system temperature rises as well. When the temperature is high, the amount of gas used decreases after adjustments are made. Is this the temperature that is being adjusted?
The gas flow rate to the reboiler is low, resulting in incomplete separation of methanol from the aqueous solution; after all, just having a high temperature is not sufficient for complete separation of methanol. The reflux rate should be reduced as well – it’s worth checking whether the operation of the reflux pump is normal! Personally, I’m here to learn *
My colleague said it might be due to high pressure; the pressure inside the tower is high, which raises the boiling point of the solution at the bottom of the tower, resulting in low evaporation rate of the solution and poor methanol separation efficiency
1. The temperature at the bottom of the tower is 13 degrees higher than normal, while the steam flow to the reboiler is actually lower. It indicates that the pressure at the bottom of the tower has increased by about 0.1 MPa compared to normal levels; the reasons for this may include an increase in the thickness of the liquid film on the tray plates and an increase in tower resistance. 2. It is recommended to check the components and flow rates of various media entering the tower, as well as those of the media exiting the tower. Has the temperature gradient of the tower changed, and from which part did the deviation start? ； 3. Check whether there is a leak in the feed heat exchanger of the methanol water distillation tower; the liquid entering the middle part of the tower may flow up to the upper part of the tower. 4. Check the condenser of the thermal regeneration tower to see if water has entered the upper part of the methanol water distillation tower.
How have you been lately? Have you checked what the situation is with direct steam supply?
Temperature and pressure are related to each other; one should not focus only on the increase in temperature, but also take into account the pressure at the top of the tower. When pressure increases, temperature certainly rises as well, but it’s not certain whether the parameters remain within acceptable limits
OP, how have you been lately? Any progress?