Control of methanol content at the alcohol outlet
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What is the lowest level at which the methanol content in the ethanol outlet stream can generally be controlled for everyone’s processes? What are some good ways to reduce the methanol content at the alcohol outlet?
The temperature behind the water cooler should be kept as low as possible. It’s hard to say the same for mechanical equipment; theoretically, water washing is the most reliable method, but not many systems are operated in this way. Ultrafiltration is also used
The temperature behind our water cooler is only 32.5°C. An ultrafiltration unit is installed at the top of the separator, but methanol can often be detected in the drain lines at the compressor anti-surge cooler, and the amount is quite significant. Even if another water scrubber is added, methanol can be washed away, but water will be carried into the compressor as well; in that case, the same problem persists – liquid will inevitably end up inside the compressor.
The temperature isn’t that high either; it seems that the ultrafiltration system in your facility isn’t very reliable. Have you analyzed the methanol content? If so, you can compare it with the saturated vapor pressure of methanol to see if it has reached the saturated level
The methanol content in my off-gas analysis usually amounts to around 1,000 PPm; sometimes it cannot be detected, but in reality it is definitely present, as I can observe a considerable amount of liquid methanol being discharged from the drain at the anti-surge cooler each time.
Around 1000PPm is already quite low
But quite a amount of liquid methanol still often flows out through the drain, hehehe.
What are the inlet and outlet pressures at the circulation section? How is the temperature change? How often should the drain be emptied?
At the compressor inlet of the circulation section, the pressure is 4.4 MPa and the temperature is 31–33°C. Previously, little drainage was carried out before the drain line; I happened to do some drainage once a while ago and found a considerable amount of methanol present. Now, drainage is done once per shift, three times a day.
It’s getting cold, and the temperature of the process gas has also dropped.