Parameter issues of the amine solution regeneration system
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The delayed coking unit I work at uses nitrogen-grade diethanolamine. The bottom temperature of the amine regeneration tower is generally maintained at 120–125°C, while the top temperature fluctuates around 80–100°C. The pressure in the acidic water tank at the top of the tower is kept at 0.07 MPa. I’ve looked up some information; it says that a regeneration effect is better when the temperature at the top of the tower is kept around 110°C. However, in my setup, it’s difficult to reach 110°C even without using a cold reflux stream at the tower top. Could this be related to the large processing capacity of my system? The amine solution processing capacity of my unit is 60–70 t/h, and the temperature of the rich solution entering the regeneration tower is 95–100°C. I’m curious to know what the amine solution regeneration systems like in other places are like
There is a one-to-one relationship between saturated vapor pressure and temperature. Check it – yours is normal: at 90°C, the pressure is 0.07 MPa! Your pressure at the bottom of the tower is 0.22 MPa, and the pressure drop across the tower is 0.15 MPa, which is quite high; it seems that the tower is overloaded! It is recommended to provide some reflux at the top of the regeneration tower; its main purpose is to increase the vapor load in the tower, which facilitates the stripping of H2S and CO2 as well as the recovery of the aqueous phase and solvents from the tower top. The amount of reflux should not be too large – a reflux ratio of 2-3 is sufficient. An excessively high reflux ratio will increase the steam consumption at the bottom of the tower.
How do you know that the pressure at the bottom of our tower is 0.22 MPa? The load is indeed a bit excessive; now the liquid level in the regeneration tower can’t be discharged, and the bypass valve for the bottom liquid control valve has opened. Regarding the reflux at the tower top, a certain amount of reflux is always provided; when the reflux rate is kept between 600 and 900 m3/h, the temperature at the tower top can be raised to just over 90°C. However, the liquid level in the reflux tank cannot be controlled and keeps rising ； If the reflux rate is high and the top temperature is low, staying below 90.
If the liquid level in the reflux tank continues to rise, then some of the liquid needs to be sent out. The volume of liquid over these past few days has been quite high: around 5 tons for the liquefied gas desulfurization tower, around 60 tons for the dry gas, plus an additional amount that goes into the gas holder
When the processing volume increases, reducing the circulation rate of the amine solution will cause the temperature at the top of the regeneration tower to rise. It is important to maintain this temperature above 100 degrees, as this facilitates an effective regeneration process.
Acidic water contains some amine solution; excessive external delivery will increase the consumption of diethanolamine. A decrease in the circulation rate of the amine solution will raise the temperature at the top of the regeneration tower, but dry desulfurization and liquefied gas desulfurization will fail to meet the required standards. One can only find a balance in the middle: ensuring the effectiveness of regeneration while also guaranteeing that the product meets quality standards.
The amine solution concentration can be appropriately increased to reduce the pressure at the top of the regeneration tower
What is the appropriate concentration of the amine solution? I checked some information; some manufacturers say that a level of over 20% is sufficient. Our installation currently has a level of over 30%, and it can reach almost 40% at times.
If it’s too high, the desulfurization effect will be poor instead.
The temperature of the rich liquid entering the tower is too low; ours is around 100-110. Check whether there is an internal leak in your rich/lean liquid heat exchanger, or if there are issues with its heat exchange efficiency
May I ask what role does the recirculation at the top of the tower play? What causes high voltage drop? ?