Rich methanol outlet temperature of the transformed gas scrubber tower
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Is there a temperature difference between sulfur-containing rich methanol and sulfur-free rich methanol in the shift gas scrubber? The sulfur-containing rich methanol extracted from the bottom of the tower should be at a lower temperature than the sulfur-free rich methanol extracted laterally, but why, according to the data from Dalian University of Technology, is the temperature difference between the two less than one degree? Why is this? How to explain it? I would appreciate some guidance from those with more experience. Thank you!
Mainly, the methanol solution that absorbs CO2 in the lower column reflux liquid is distilled off in the lower part of the column; however, the cooling energy required for this distillation process is balanced by the heat of dissolution of H2S. Thus, it can be seen that the temperature difference is not significant, basically 1–2 degrees.
The heat of solution released when hydrogen sulfide and thiocarbonic acid are absorbed in the lower tower is compensated by the desorption heat of carbon dioxide from methanol, preventing the temperature in the desulfurization section from rising; that’s why the temperature difference between the two values you see is not significant! !
Can carbon dioxide be separated out in the desulfurization section of the lower tower? Is there any theoretical basis for this? And what is the amount of analysis involved? I hope the experts will kindly share their insights! Thank you!
There won’t be any analysis, right? Judging from the CO2 content in the two streams of methanol-rich gas, sulfur-containing methanol still contains more sulfur than sulfur-free methanol
The temperature difference between the two is about 2 degrees! ! The temperature difference isn’t very large; it’s usually around 10 degrees
CO2 will not be dissociated at the lower tower.
The methanol-rich liquid coming down from the upper column is essentially saturated with carbon dioxide; it comes into countercurrent contact with the shift gas in the lower column, and the shift gas can be considered as a stripping medium that removes some of the carbon dioxide (the carbon dioxide removed in this way is then absorbed again in the upper column!) ), it can be seen that the heat absorbed is roughly balanced by the heat released upon the absorption of hydrogen sulfide; as a result, the temperatures of sulfur-containing methanol and sulfur-free methanol are essentially the same, with little difference in temperature!
The temperature for methanol containing sulfur needs to be slightly higher, because although the methanol used for absorbing sulfides is methanol with a high amount of CO2, it cannot reach saturation in the absorption tower. In addition to absorbing sulfides, it can also continue to absorb a small amount of CO2; therefore, the temperature needs to be raised slightly
The temperature in the lower tower is a few degrees higher than that in the upper tower, mainly because the methanol entering the lower tower is rich methanol that has absorbed CO2； And the amount of CO2 absorbed by the methanol entering the lower column is about 1%–2.5% of that in the upper column; moreover, the hydrogen sulfide content is even lower! So the main reason why the temperature rise in the lower column is relatively small is that fewer acidic gases are absorbed in the lower column!
I checked our flowchart today, and the CO2 content in the methanol entering the lower column is lower than that in the methanol exiting the lower column； So I think there is definitely desorption in this process, but less desorption occurs than absorption【it is a dynamic equilibrium】, therefore the heat released during desorption is lower than the heat absorbed.
The amount of methanol required to absorb H2S is half that needed to absorb CO2; this indicates that the absorption of H2S occurs at saturation (as the amount of H2S in the process gas is low). Meanwhile, the lower column essentially stops absorbing CO2. The heat released during absorption is greater than the heat absorbed during desorption, so the temperature rises!