Control of propylene content in the dry gas of the absorption stabilization system

““The propylene content in the dry gas of absorption stabilization systems is usually around 80%.” I’ve never heard of that; how can something with a propylene content of around 80% be considered dry gas? In ordinary liquefied gas, the propylene content is at most 60%.

Do you mean that propylene accounts for 80% of the components with a carbon number of 3 or higher? Otherwise, it cannot be called dry gas at all. In fact, there is a minimum value for the propylene content in the dry gas; beyond this value, increasing the absorption efficiency will lead to over-absorption, causing some C2 compounds to circulate within the absorbed fraction, which ultimately results in overload of the desorption tower and frequent flooding of it. Because if the design value is reached, there is no need to keep striving to increase the propylene absorption rate. Propylene accounts for about 1.5% in our dry gas. I’m not sure if what I said is correct! :)

For quality purposes, our criteria are as follows: the C1 and C2 contents in the dry gas must be at least 95%, the propylene content must not exceed 1.5%, and the C2 content in the liquefied gas must not be higher than 2%. The propylene content in our liquefied gas is typically around 45%. For specific methods, refer to: What are the measures to improve the liquefied gas yield using catalytic units? http://bbs.hcbbs.com/thread-130693-1-1.html Study on the reaction patterns for catalytic reforming of gasoline to reduce olefins and increase propylene production http://bbs.hcbbs.com/thread-102173-1-1.html

I’m not sure which system the absorption stabilization referred to by the original poster belongs to. However, the 80% propylene content mentioned seems a bit high. To reduce the C3 content in the dry gas, absorption stabilization systems generally adopt the following measures: 1. Lower the temperature at the top of the absorption tower; 2. Increase the oil-to-gas ratio; 3. Reduce the emission of non-condensable gases to avoid unnecessary circulation; 4. Ensure proper operation to maintain a reasonable temperature distribution within the tower; 5. Increase the operating pressure to enhance the absorption effect; 6. Avoid excessive desorption

To avoid excessive desorption, the feed temperature of the separation tower can be reduced, and the bottom temperature of the tower can be increased

The content of compounds with C3 content or higher in catalytic dry gas is generally kept below 5%; some catalytic units require this level to be below 3%. It is somewhat more difficult to control the amount of such compounds in coking dry gas, with levels sometimes ranging from 5% to 10%. It is important to properly control the temperature at the bottom of the stripping tower and at the top of the absorption tower, as well as the amount and temperature of the diesel used in the reabsorption tower (the reabsorbent). Is low-temperature water a low-temperature heat source water? That definitely won’t work

Low-temperature water can be used, and it works better in summer. In fact, it uses a low-temperature heat source, and lithium bromide air conditioning is employed to produce cold water at around 7°C. The coking unit at Jinling Petrochemical underwent this technical upgrade, with excellent results. The owner’s facility is likely a coking unit; the propylene content in the dry gas is somewhat high.

In our facility, the propylene content in the dry gas is required to be no more than 1%; if it is too high, propylene is wasted, and it also affects the purity of ethylbenzene and styrene； During operation, the main factors contributing to a high C3 content in the dry gas are: 1. Excessively low pressure in the absorption tower or large pressure fluctuations ； 2. Excessive rich gas volume leads to an increase in the C3 content in the dry gas ； 3. Insufficient absorbent or supplementary absorption dose, low liquid-to-vapor ratio, resulting in an increased C3 content in the dry gas ； 4. High temperature at the top of the absorption tower results in poor absorption, leading to an increase in the C3 content in the dry gas. 5. A high temperature of the rich gas entering the absorption tower or reduced heat absorption from mid-stage reflux leads to an increase in the C3 content in the dry gas ； 6. Excessive desorption occurs in the desorption tower; the C3 and C4 components are present in high concentrations in the desorbed gas, resulting in an increased C3 content in the dry gas ； 7. An increase in light components in the absorbent and supplementary absorbent leads to an increase in the C3 content in the dry gas. Adjustment method: The main methods to reduce the C3 content in dry gas are to increase the pressure of the absorption system, lower the absorption temperature, and increase the liquid-to-gas ratio. 1. Increase the absorbed dose or lower the temperature of the absorber ； 2. Increase the supplementary absorption dose or lower the temperature of the supplementary absorber ； 3. Slightly increase the pressure in the absorption tower and maintain stable control ； 4. Adjust the reflux flow rate at each intermediate stage or reduce the reflux temperature in order to lower the absorption temperature ； 5. Adjust the flow rate of water in E‑305 and E‑306 to reduce the temperature of the rich gas entering the tower ； 6. Adjust the operation of the desorption tower to prevent excessive desorption ； 7. Increase the temperature in the stabilizer column to minimize the amount of C3 and C4 compounds carried in the stabilized gasoline.

By controlling the balance between absorption and desorption, the concentration of components other than C3 in the dry gas from my device is less than 1%, while the propylene concentration is around 0.5%

It is very difficult to achieve 40% propylene content in liquid hydrocarbons; could the original poster explain this further?

1) Under normal circumstances, appropriately adjust the steam stabilization absorption dose to control the appropriate oil-to-gas ratio； (2) Appropriately adjust the reflux flow at the middle stage of each section to reduce the temperature returning to the tower; the heat absorbed by the reflux at the middle stage of each section should be uniform ； (3) Control the temperature at the bottom of the desorption tower to ensure an appropriate desorption effect ； (4) Appropriately increase the reabsorption dose, or lower the temperature of the reabsorber ； (5) Minimize the outlet temperature of Cold 401 to improve the separation efficiency of Container 401 ； (6) Minimize the temperature of the absorbers for crude gasoline and stabilized gasoline, as well as reduce the top temperature of the absorption tower ； (7) Control the level of vessel 301 properly to ensure that the crude gasoline is free of water.