Switching of the filter in low-temperature methanol washing causes a deviation in the heat exchange load of the system’s heat exchangers
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When switching the lean methanol filter in our plant’s low-temperature methanol washing process, it is necessary to do so at a very slow speed. Running a bit faster will cause deviations in the heat transfer loads of the feed heat exchanger for the system’s methanol thermal regeneration tower, as well as of Heat Exchanger No. 1 and Heat Exchanger No. 2 for lean methanol; this results in cold flow moving toward the hot areas, leading to freezing of equipment at normal temperatures. What’s the reason for this? Are there any remedies?
Perhaps the device I’ve seen is different from LZ’s device; the devices I encountered before usually had a filter between the hydrogen sulfide concentration tower and the thermal regeneration tower. So the situation of the original poster is different from what I have seen before. Based on what lz described, my understanding is: when the filter is switched, the feed temperature of the thermal regeneration tower drops? In that case, it’s possible that the heat exchange capacity of the heat exchanger increases during the switching? Possible reasons for an increase in heat transfer rate: 1. Change in the heat transfer coefficient ； 2. The flow rate changes; 3. The heat exchange area changes. The likelihood of 2 and 3 occurring is low, so could it be that the heat transfer coefficient has changed? Could the original poster provide more details on the pressure difference before and after the filter was switched?
The thing I disagree with the person upstairs about is whether the cold air shifts towards the hot area? Is there something wrong with the steps to switch filters? I don’t know how the original poster switched the filters.
It’s likely that there was an issue with the procedure followed: the poster should try using the backup filter first, applying pressure slowly; once the pressure is balanced, then open the main inlet and outlet valves. After that, the filter that is clogged and needs to be cleaned can be removed – this should not cause any problems.
What is your order of switching? Is there no lean methanol passing through the heat exchanger? Isn’t the feed heat exchanger of the methanol thermal regeneration tower the 1# lean methanol heat exchanger? Equipment freezes at room temperature – what is equipment at room temperature?
Based on the poster’s description, the cause is essentially determined to be the reduction in the amount of methanol-poor fluid that occurs during the filter switching process; this leads to the sulfur-rich methanol being fed into the heat regeneration tower’s feed heat exchanger at a low temperature. As mentioned by the user from floor 5, if there is a spare filter, it should be used first. If no spare filter is available, then there must be a filter bypass system. The bypass should be gradually opened fully first, followed by slowly closing the inlet valve of the filter in use, and finally closing the outlet valve. This should resolve the issue. If it still doesn’t work, please post further details – we’ll keep an eye on it.