Methanol expansion tank
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The methanol produced through synthesis passes through a methanol separator before entering the methanol expansion tank (rough methanol storage tank), where it appears to undergo flashing to remove any dissolved gases. I wonder what gas is dissolved inside?
All the gases in the synthesis system will flash out; the specific amount depends on the partial pressures of the different components in the system, as well as the pressure and temperature in the flash tank.
Hydrogen, carbon monoxide, carbon dioxide, methanol vapor.
Reply to 2# Shouhou: The absorption capacity of that methanol for H2 and CO should be very low, while it is higher for CO2. Is it used to flash these gases?
Yes, the solubility of H2 is somewhat low, but the partial pressure of hydrogen is relatively high; as a result, a considerable amount of hydrogen is vaporized. You can conduct an analysis to find out more – different process requirements will lead to slight variations in the results.
That is, process gas and methanol vapor, along with some inert gas. The specific components are highly dependent on conditions such as actual operating temperature and pressure, so it is impossible to draw a definite conclusion; it is best to conduct an analysis using testing methods to determine all the components of the flash vapor.
Generally, they are flammable fuel gases with low solubility in methanol, such as hydrogen, carbon monoxide, and methanol vapor; there are also some cases involving carbon dioxide. Personally, I think hydrogen is the most common one! Because hydrogen is in excess throughout the reaction!
The main component is carbon dioxide, accounting for over 70 percent; other components include hydrogen, nitrogen, carbon monoxide, methane, and methanol vapor. The various components have different solubilities at high pressures; carbon dioxide has the highest solubility. When the pressure drops upon entering the flash tank, its solubility decreases accordingly, and it is flashed out.
Here is the composition of the vapor from the methanol expansion tank; although conditions vary from plant to plant, I hope this will be useful to the original poster: H2: 22.10%, CO: 20.49%, CO2: 45.00%, CH4: 1.77%, N2: 2.45%, Ar: 1.19%, CH3OH: 6.70%, H2O: 0.30%. The values above are given as mass percentages
Reply to 9# chenziang12: I’m not sure what your synthesis process is like – what is the pressure in the synthesis tower?
Reply to 10# kya15: Our company uses the Lurqi process; the synthesis tower is a \"tube-shell external cooling–insulated composite fixed-bed catalytic reactor\" developed by East China University of Science and Technology, using a copper-based catalyst. The system pressure is 5.3 MPa.