The synthesis system emits inert gas
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When the hydrogen-to-nitrogen ratio in the synthesis system is severely out of balance, it is necessary to vent the system; where is the best place for such venting?
Venting behind the tower is preferable, as this separates some of the ammonia product and addresses areas where the hydrogen-to-nitrogen ratio is significantly out of balance.
It would be better to increase the volume of hydrogen recovered; the venting losses are likely to be high.
Generally, venting is done at the back of the tower; however, venting not only leads to waste but also, if it lasts too long, can exacerbate the imbalance in the hydrogen-to-nitrogen ratio. The best approach is to adjust the ratio of nitrogen or air in the preceding process.
The vent is located after the tower where primary ammonia separation takes place; at this point, part of the liquid ammonia is separated and does not mix with the make-up gas, resulting in a relatively high content of inert gases
Increasing the amount of hydrogen recovered is equivalent to venting it behind the tower; in our operations, we generally vent hydrogen from the front of the tower when its concentration is high, and from the back of the tower when its concentration is low.
Tiered emission should be adopted; once an imbalance in the hydrogen-to-nitrogen ratio is detected, it is necessary to consider the composition of the supplementary gas. If adding gas components helps reduce misalignment, post-tower discharge should be used. Otherwise, apply make-up power or pre-tower compensation (at the location where the offset occurs), until the make-up gas is adjusted to help reduce the offset, after which switch to post-tower compensation. This method of staged emission even needs to be extended to the preceding units, allowing for direct discharge into gas holders, desulfurization, shift conversion, and refining.