Regarding the C5 content in catalytic dry gas

The high C5 content in the catalytic dry gas is, in my opinion, caused by either an excessively high absorption temperature or a too low absorption pressure. This can be addressed by lowering the temperature of the absorbent or increasing the pressure in the absorption tower; it is also possible to add an additional diesel absorption tower, which could reduce the C5 content to a few hundredths (of course, this requires shutting down the plant first for the necessary modifications).

Typical catalytic stabilization systems are followed by a diesel reabsorption tower! I think the possible reasons are as follows: 1. The volume of dry gas is too high; once the absorption dose increases to a certain level, the fast-flowing dry gas will carry the absorbent (crude gasoline) into subsequent systems ； 2. Reducing the amount of gas fed for separation inevitably increases the light components in the deethanized gasoline; it is therefore not surprising that this leads to an increase in pressure in the stabilizer tower. Suggestions: 1. Check whether the dry gas volume has increased; if it has, identify the cause ； 2. The absorption dose can be appropriately reduced, and the temperature of the absorber can be appropriately lowered ； 3. Slightly increase the pressure in the absorption tower ； 4. Our plant’s original catalytic stabilization system featured a pressure relief line between the reflux tank at the top of the stabilizer tower and the condensate oil tank at the outlet of the vapor compressor; I wonder if your plant has something similar, as it could help to address the issue of overpressure in the stabilizer tower to some extent.

First, reduce the gas production rate of the device slightly, and lower the supplementary absorption dose – in other words, reduce the load that keeps absorption at a stable level! Restore the absorption tower to normal operation, and check if your dry gas carbon pentane level is still above the limit If it exceeds still, more floating valves on the absorption tower trays may fall off. Let’s increase the amount of oil absorbed by the large absorber to see if that can solve the problem! If it doesn’t exceed the limit, try increasing the catalytic processing volume to see if it still exceeds the limit The issue related to stabilizing the absorption load is usually caused by excessive absorption or desorption due to a mismatch between the absorbent and the amount of rich gas; attempting to reduce the load to achieve equilibrium is a good approach. Another option is to try increasing the pressure in the reabsorption tower—of course, the displacement of your compressor must be sufficient to prevent surging.

1. Check whether there is mid-stage reflux in the absorption tower; if so, ensure that the mid-stage reflux is properly set up. 2. Increase the pressure in the absorption tower appropriately, and verify whether the pressure is correct. 3. Use stable gasoline as a supplementary absorbent, and check whether the temperature and quantity are appropriate.

Typical catalytic stabilization systems are followed by a diesel reabsorption tower! I think the possible reasons are as follows: 1. The volume of dry gas is too high; once the absorption dose increases to a certain level, the fast-flowing dry gas will carry the absorbent (crude gasoline) into subsequent systems ； 2. Reducing the amount of gas fed for separation inevitably increases the light components in the deethanized gasoline; it is therefore not surprising that this leads to an increase in pressure in the stabilizer tower. Suggestions: 1. Check whether the dry gas volume has increased; if it has, identify the cause ； 2. The absorption dose can be appropriately reduced, and the temperature of the absorber can be appropriately lowered ； 3. Slightly increase the pressure in the absorption tower ； 4. Our plant’s original catalytic stabilization system featured a pressure relief line between the reflux tank at the top of the stabilizer tower and the condensate oil tank at the outlet of the vapor compressor; I wonder if your plant has something similar, as it could help to address the issue of overpressure in the stabilizer tower to some extent.

Is it a single-tower process or a dual-tower process? Your analyses are all very sound; also, is the processing load of your plant within the design specifications?

What you’re referring to is exactly the issue of \"dry gas vs. wet gas\" – it indicates that the dry gas contains a significant amount of liquid. In such cases, the size of the reabsorber can be increased. As for the high pressure in the liquefied gas reflux tank, it’s necessary to check whether the temperature in the desorption tower is too low, which prevents the C2 compounds from being desorbed, or whether the amount of cold reflux liquid is excessive. If the pressure of the liquefied gas is too high, it’s appropriate to relieve some of that pressure; after all, the safety of the installation comes first.

The issue of C5 in the dry gas is likely due to too low pressure in the absorption tower, which leads to flooding of the tower, as well as insufficient pressure and reabsorption capacity in the reabsorption tower. Solutions: 1. Increase the pressure in the absorption tower, being careful not to cause surging in the compressor. 2. Lower the temperature of the supplementary absorbent and crude gasoline. 3. Increase the amount of reabsorbent used; if necessary, replace the reabsorbent with top-loop oil instead of lean oil

It is recommended that you check whether there has been any change in the feed temperature of the desorption tower. Based on what you’ve described, the more likely issue is an increase in feed temperature. Depending on the specific process settings and operational objectives, the desorption tower usually has an optimal temperature. If you already have an FCC full-process simulation model, you can calculate the approximate optimization area. It is important to note not to exceed the load limit of the tray and the heat input limit at the bottom of the tower. As for temperature adjustment, it is advisable to make small adjustments. Wish you success. If there are any further questions, we can continue to discuss them. Kevin

We hadn’t been using the reabsorption tower for some time due to a shortage of diesel; now that the tower has been put into use, the results are better. However, the C5 content is still sometimes a little over 1%. Some people say it’s because the temperature of the absorbent is too high. So what should be the temperature of the cooled, stabilized gasoline? And does it still need to maintain a reaction temperature of 40 degrees for gasoline desulfurization?

An excessive amount of stabilizing gas or too little oxygen can cause flooding or an excessively high stabilizing gas temperature

Sometimes, when there is too much absorbent, it will be carried away by the gas.

Reducing the amount of gas undergoing separation inevitably leads to an increase in the pressure of the stabilizer tower, as insufficient separation results in the material entering the stabilizer tower containing a higher proportion of C2 components. After being heated by the reboiler at the bottom of the stabilizer tower, these C2 components accumulate at the top of the tower, causing the pressure to rise. In such cases, it is necessary to vent the non-condensable gases. If these gases are released into the pipeline system, they have no effect on the absorption tower; however, if they are sent to the overhead vapor equilibrium tank in the distillation system, they will return to the absorption tower. In fact, the goal of reducing the gas-phase load on the absorption tower through separation cannot be achieved. Moreover, the circulation of non-condensable gases between systems requires compressors to do work, resulting in energy waste. To address C5, it is still necessary to focus on enhancing absorption. Increasing the liquid-to-gas ratio and raising the tower pressure are both effective

Is there any change in the amount of dry gas? If dry gas is used for pre-heating, the amount of dry gas used for this purpose can be reduced and steam can be used instead. Thirdly, there are considerations regarding the quantity and temperature of diesel. Fourthly, the equipment, such as the tray trays

Is the liquid-to-gas ratio appropriate?； Is the temperature of the absorption tower too high? ； Lowering the resolution temperature leads to incomplete resolution, resulting in a high ethane content in the deethanized oil; this in turn causes the pressure in the stabilizer to rise excessively. The only way to control this pressure is by releasing non-condensable gases from the stabilizer ； Is the temperature in the reabsorption tower too high, resulting in severe carbon carryover in the dry gas? ； Is the liquid level in the reabsorption tower normal? ； Is the internal equipment of the absorption and reabsorption towers functioning properly?