Let’s discuss together the nitrogen used for purging while driving! !
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As is well known, when starting up a methanol wash unit, the nitrogen used for gas stripping is introduced 30 minutes before starting the gas flow. Question: What is the standard for nitrogen usage? (1) What temperature drop at the outlet of the feed gas pre-cooler is used as the standard? (2) Should it be the amount of nitrogen during normal operation or that at half load? (3) Still based on other references. Everyone is welcome to discuss.
It is based on the amount of nitrogen at normal operation or at half load. Because the amount of gas is too small, it causes the gas to flow unevenly within the tower, preventing thorough contact between the gas and the liquid and resulting in poor gas treatment efficiency. An excessive amount of gas can lead to severe loss of cooling capacity; at the beginning of gas introduction, the temperature of the entire system has not yet dropped, and the methanol’s ability to absorb heat is limited. Therefore, the amount of gas cannot be too large nor too small.
Normally, half of the normal operating value is used to pre-cool the feed gas heat exchanger; there is no specific limit on the temperature to which it should be pre-cooled! In my opinion, it’s not necessary for the value to be exactly half of the normal level. The system load can be determined based on the amount of gas that goes through the transformation process, and the required amount of nitrogen for stripping can be calculated using an approximate ratio before it is used in practice. This approach not only achieves the purpose of pre-cooling the feed gas in the heat exchanger but also avoids the hassle of having to increase the amount of nitrogen used during the gas introduction process! (However, the load is usually reduced to half load or below before taking in air.)
Usually, half the amount of nitrogen required for normal operation is introduced, after which the amount is gradually increased to that required for normal load.
The nitrogen for gas lift should be put into use half an hour earlier~! The amount is roughly half of the nitrogen amount mentioned earlier when going upstairs~! Generally cooled to below -20 degrees