Hello! Is the mechanism and equations for binary solutions same for multicomponent solutions as well? Or are there other methods used for multicomponent solutions? Thank you!
If steam is used as the stripping gas, the steam must have a temperature above 100°C. The rich solvent is liquid water + some solved ammonia. If the solvent is heated to a temperature above 100°C, the liquid water will also evaporate and the process won't work. If the solvent has a temperature below 100°C, there will be heat transfer between the steam and the liquid water. So how do we make sure, that this heat transfer wont lead to the steam condensing or to the solvent evaporating? Or is there something I don't get? Thanks a lot for you videos! They already helped me a ton. Greetings!
This is an excellent question. Remember that the pressure inside the column is not constant + the heat transfer is inevitable due to the difference in the temperatures. So, the boiling temperature of water varies along the column, and the rate of heat transfer is not high enough to vaporize all the water. There will be water evaporation of course, but the water will not be totally evaporated. In many cases, other solvents are chosen with better properties, among these properties is to have high boiling point to reduce the losses taking place during the stripping process.
Hello, I have another question: What happens in cases of more "extreme" molar ratios? Or are there other boundaries for the scrubbing and stripping process, that are not discusses in your videos? For example: I want to calculate the steam flow I need, to remove ammonia in water with x_NH3 = 0.5 (so X=1) at 90°C and 1 bar. We know from the equilibrium line at x=0.5, that the partial pressure of ammonia in the gas phase is ~18 bars at this point. But I'm only stripping at 1 bar. In this case, the operating line can't run underneath the equilibrium line at X=1, as there is no equilibrium at X=1 with a pressure under 18 bars at 90°C. By tendence, the low pressure should favor the ammonia adsorption from the water, as the driving force only gets higher with decreasing pressure. So the minimum required steam flow may not be impcated by that, as the "critical point" where equilibrium line and operating line get the closest is at a way lower molar ratio. But is this process still feasible? Or am I missing something? Best regards and thank you for the previous answer!
Hello, Sorry for the late reply! Absorption is usually used for removing a "gas impurity" from a gas mixture. To the best of my knowledge, the mole fraction/mole ratio of the impurity gas does not exceed 15% (the maximum I saw is 10%). So, I believe absorption is not a suitable method for such high concentrations like what you are talking about. Otherwise, you will need extremely large L/V ratio to have suitable driving force. This will make the process so costly and will not be economically feasible. In the case you mention, you can use flashing at low temperature. This will at least be an initial stage to get a gas stream with ammonia concentration that is suitable for absorption. Hope this answers your question.
Hello! Is the mechanism and equations for binary solutions same for multicomponent solutions as well? Or are there other methods used for multicomponent solutions? Thank you!
If steam is used as the stripping gas, the steam must have a temperature above 100°C. The rich solvent is liquid water + some solved ammonia. If the solvent is heated to a temperature above 100°C, the liquid water will also evaporate and the process won't work. If the solvent has a temperature below 100°C, there will be heat transfer between the steam and the liquid water. So how do we make sure, that this heat transfer wont lead to the steam condensing or to the solvent evaporating? Or is there something I don't get?
Thanks a lot for you videos! They already helped me a ton.
Greetings!
This is an excellent question.
Remember that the pressure inside the column is not constant + the heat transfer is inevitable due to the difference in the temperatures.
So, the boiling temperature of water varies along the column, and the rate of heat transfer is not high enough to vaporize all the water. There will be water evaporation of course, but the water will not be totally evaporated.
In many cases, other solvents are chosen with better properties, among these properties is to have high boiling point to reduce the losses taking place during the stripping process.
Hello, I have another question:
What happens in cases of more "extreme" molar ratios? Or are there other boundaries for the scrubbing and stripping process, that are not discusses in your videos?
For example: I want to calculate the steam flow I need, to remove ammonia in water with x_NH3 = 0.5 (so X=1) at 90°C and 1 bar. We know from the equilibrium line at x=0.5, that the partial pressure of ammonia in the gas phase is ~18 bars at this point. But I'm only stripping at 1 bar. In this case, the operating line can't run underneath the equilibrium line at X=1, as there is no equilibrium at X=1 with a pressure under 18 bars at 90°C.
By tendence, the low pressure should favor the ammonia adsorption from the water, as the driving force only gets higher with decreasing pressure. So the minimum required steam flow may not be impcated by that, as the "critical point" where equilibrium line and operating line get the closest is at a way lower molar ratio. But is this process still feasible? Or am I missing something?
Best regards and thank you for the previous answer!
Hello,
Sorry for the late reply!
Absorption is usually used for removing a "gas impurity" from a gas mixture. To the best of my knowledge, the mole fraction/mole ratio of the impurity gas does not exceed 15% (the maximum I saw is 10%). So, I believe absorption is not a suitable method for such high concentrations like what you are talking about. Otherwise, you will need extremely large L/V ratio to have suitable driving force. This will make the process so costly and will not be economically feasible.
In the case you mention, you can use flashing at low temperature. This will at least be an initial stage to get a gas stream with ammonia concentration that is suitable for absorption.
Hope this answers your question.
Can u share file
You can find it in this folder: drive.google.com/drive/folders/1Xkrlfnv_l3AezLohUxcoXN1BUy-1egPt