When is the Lind process exhaust gas scrubber put into operation (for gas bypass), and what are the key points to note?
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When is the Lind process exhaust gas scrubber put into operation (for gas bypass), and what are the key points to note? Firstly, the conditions that low-temperature methanol washing must meet before gas introduction are as follows: one is that the chiller should be operating properly, and the temperature of the lean methanol entering the absorption tower should be below -20°C (when ammonia is used as the cooling medium) or -30°C (when propylene is used as the cooling medium) ； Second, the stripped N2 gas is discharged after passing through the exhaust process gas heat exchanger (at temperatures below -20). Therefore, the exhaust gas can only be fed into the exhaust gas scrubber when the temperature of the exhaust gas after it has passed through the process gas inlet system and the heat exchanger is above 0 degrees Celsius. Be aware of low-temperature freezing in the exhaust gas scrubber.
To reduce the driving time, the nitrogen used for stripping should be activated before gas introduction, so that the cooling capacity can be utilized in the raw material gas cooler to cool the process gas (by condensing the water contained in the process gas and thereby reducing the amount of methanol that enters the methanol system). However, when no gas is being introduced, the temperature of the N2 is equal to the temperature of the ammonia or propylene cooling medium; under such conditions, the exhaust gas cannot be fed into the scrubber to prevent ice formation in the scrubber； The exhaust gas can only be fed into the scrubber tower when its temperature is measured at 0!
We also paid close attention to the temperature of the exhaust gas entering and leaving the exhaust gas scrubber. During the initial operation phase, due to a lack of experience, this aspect was often overlooked when switching off the gas supply, and the exhaust gas was not diverted away from the scrubber (mainly because of large fluctuations in the liquid level during that process). However, freezing of the scrubber does not occur within a certain period of time; in the worst cases, it takes a few hours before slight freezing is detected in the scrubber. This is mainly because the exhaust gas contains a high amount of methanol, which lowers the freezing point of water. At this time, two points need to be noted: first, prevent the level gauge from freezing, especially in the winters of the north. Secondly, it is necessary to modify the range of the thermometers in the exhaust gas scrubber; typically, design firms set the lower limit of this range at zero degrees Celsius, which eliminates any basis for making judgments. Overshoot often occurs.
As you said, is it possible to deliberately reduce the operating pressure of the H2S concentration tower or increase the amount of nitrogen stripped during the gas guiding process, in order to raise the methanol content in the exhaust gas? ?
When driving the vehicle initially, is it possible to refrain from using the exhaust gas scrubber, that is, to avoid supplying water to it, allowing the exhaust gas to pass through the tower without being cleaned? The scrubber tower is put into operation once the heat exchange between the exhaust gas and the feed gas reaches above 0 degrees.