Regarding how to handle the ammonia-rich methanol at the top of the regenerator in the low-temperature methanol washing system
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Since coal-to-gas production generates ammonia, part of the ammonia present in the shift gas is removed through an ammonia scrubber; this ammonia then enters the low-temperature methanol washing system. Due to the concentration of hydrogen sulfide, some ammonia accumulates over time within this system, which can lead to high ammonia levels in the lean methanol stream and can also cause blockages in the acid gas cooler at the outlet of the regeneration tower. Do anyone have any good methods to reduce the ammonia content in lean methanol?
There is a shortcut for the H2S fraction cooler; when the ammonia content is high, it is vented through this shortcut to control the ammonia level in the methanol-rich stream
Handling it in this way will result in severe penalties if detected by the environmental protection agency. Illegal discharge.
Intermittently increase the temperature of the cooler to evaporate the ammonia
Raising the temperature of the acidic gas to above -30°C resolves the issue easily
We use the Luchi process, which requires regular ammonia emission control. Ammonia is sent to the sulfur recovery unit for combustion.
At present, there is no particularly good method to completely solve this problem, whether it’s Lind, Luchi, or the processes used at Dalian University of Technology – ammonia will accumulate as long as it enters the low-temperature system. Method 1: Some facilities discharge ammonia through a bypass around the heat exchanger at the top of the regeneration tower, and send it to the sulfur recovery unit where it is burned directly. However, this approach results in methanol being carried away. First, it causes black sulfur to be produced in the sulfur recovery process (although this issue can be addressed by adding steam, it is still not an ideal solution). Second, it increases the methanol consumption in the low-methanol unit; in some cases, this consumption can reach up to three times the designed level ； Method 2: In some cases, ammonia is discharged to the methanol storage area at the outlet of the reflux pump at the top of the tower. This, again, leads to excessive loss of methanol; it is also difficult to handle this methanol in the methanol distillation process. It would be better to store this methanol in a separate tank or to dispose of it as fusel oil. It is recommended to use either of the two methods mentioned above for control; the choice can be determined based on the process requirements and the conditions of the pipelines on site. The goal is to find a balance point for the ammonia content in the lean solution, so as to minimize methanol losses without affecting the absorption process. Generally, an ammonia content in the lean solution below 200 will not have any impact on absorption