Pressure control for nitrogen recovery in low-temperature methanol washing
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How is the pressure for nitrogen extraction in low-temperature methanol washing controlled? What’s the minimum? The designed nitrogen pressure is 0.5 MPa; the actual nitrogen pressure at tower T3 is 0.45 MPa. When the gas flow rate reaches the designed value, the pressure drops to 0.27 MPa. Will this affect the gas lift?
What is your design capacity? What is the full-load process gas flow rate? Where does the exhaust gas go in the end?
1. Generally, there is no such thing as pressure control for nitrogen gas; the amount of nitrogen gas used is determined by the degree of excess cooling capacity in the system! 2. Is the 0.27 MPA you mentioned the pressure in Tower T3, or the pressure in the nitrogen pipeline when the gas flow reaches the design value? If it is T3 pressure, then the tower pressure can be controlled. As far as I know, the pressure in the T3 tower is generally not kept that high; it’s around 0.08 MPa! If it’s due to the pipeline network pressure, it only indicates that your design capacity is insufficient, or the air separation unit hasn’t increased its operating load! 3. You still don’t understand the definition of stripping; nitrogen stripping is used to reduce the partial pressure of CO2 or H2S, thereby allowing them to be separated and releasing heat in the process! A high pressure in your tower (0.27 MPa) will only affect the efficiency of the separation process for methanol-rich stream entering T3; of course, if there is enough nitrogen available, then it’s not a problem!
When the unit is operating at full load, has your nitrogen stripping flow rate reached the design value? Whether the flow rate of nitrogen used for stripping is appropriate can be determined by the CO2 content in the methanol at the bottom of the hydrogen sulfide concentration tower. The CO2 content is generally around 1%; a value higher than 1% indicates that the flow rate of nitrogen used for stripping is too low, while a value lower than 1% suggests that the flow rate is too high, resulting in waste. A pressure of 0.45 MPa in the gas nitrogen pipeline network is sufficient to meet the process requirements, while the pressure in the hydrogen sulfide concentration tower is generally below 0.1 MPa.
I’m talking about the low pressure of the low-pressure nitrogen – does this affect gas lifting? The pressure in Tower T3 has dropped to 0.27 MPa; it’s been reduced now