The issue of flash tank pressure in NHD decarburization
Thread Content
I’ve recently encountered a problem and would like to seek advice from everyone. With the amount of material in the decarboxylation cycle remaining unchanged, as well as the pressure in the ammonia cooler – and thus the temperature of the lean liquid – staying constant, the pressure in the decarboxylation system decreases, while the volume of gas produced during decarboxylation increases by about 1000. The CO2 level at the outlet of the decarboxylation process rises as well. Why does the pressure in the high-flash tank for decarboxylation also increase? When the circulation rate is increased to reduce the CO2 level, the pressure in the flash tank drops as well. I hope that those who understand my issue can explain it to me.
It’s simple: an increase of 1000 Nm3/h in the amount of gas used for decarburization, with the solution circulation rate remaining unchanged, means that the load increases. As a result, the liquid-to-gas ratio decreases and the system pressure drops, which is not conducive to absorption and leads to poor absorption efficiency; hence, the CO2 level at the decarburization outlet rises. The pressure increase in the flash tank is due to an increase in the amount of decarburization gas by 1000 Nm3/h; with the solution circulation rate remaining unchanged, the saturation level of the solution is high, resulting in more gas being desorbed in the flash tank. As the circulation volume increases, the saturation of the solution decreases; as a result, the amount of gas desorbed decreases, and the pressure drops as well.
The analysis on the second floor makes sense: an increase in volume of gas while the liquid volume remains unchanged will inevitably lead to an increased load. As a result, the amount of vapor generated in the high-flash tank increases, causing the pressure to rise. The higher the pressure, the worse the regeneration effect, which creates a vicious cycle. This is why the carbon dioxide level at the outlet exceeds the specified limits. By increasing the circulation rate, the aforementioned problems can be resolved.