The temperature of the reflux returning to the tower in the middle section is low; how to deal with this? Urgent help needed
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This post was last edited by 105943081 on 2010-10-6 at 10:49. In our plant’s catalytic cracking unit, the temperature of the mid-stage reflux returning to the tower is low, ranging between 170–178 degrees; the mid-stage cooler has not yet been put into use. The temperature at the bottom of the distillation tower is 333–350 degrees. But the mid-section reflux temperature just won’t rise. Previously, when the temperature at the bottom of the distillation tower was between 325 and 340 degrees, the temperature of the material returning to the tower in the middle section was between 180 and 200 degrees; at that time, a middle-section cooler was also used to regulate this temperature with cooling water. Most of the valves that need to be closed have been closed, and most of those that need to be opened have been opened. It’s just that the temperature doesn’t rise. Is there some problem with the device? I hope experts can give me some advice. . . . . . . . . . . Thank you. As a supplementary note, we have here a heat exchanger that exchanges heat with the oil slurry; there are also two absorption and stabilization reboilers that serve as heat sources. That’s all~~~
Is the cold reflux set too high? What kind of device is a fractionating tower?
Reply to 2# Light as a swallow: The cold reflux in the catalytic cracking distillation column is not high; the top temperature is kept between 112-120 degrees. It’s the issue that the temperature returning to the tower in the middle section doesn’t rise. Thank you for your reply
Increased heat load? Missed it? Vaporization of light oil products
Reply to 3# 105943081: Has there been any change in the distillation temperature at that middle stage? What is the quality of the product?
The explanation is a bit simple; it’s necessary to take into account the overall heat distribution throughout the tower. For now, it can only be said that the temperature in the middle section is low. It’s possible that more heat is being extracted from the lower part, or that more heat is being taken away by the heat exchangers in the middle section (for example, due to increased steam generation from the slurry, or an increase in the volume of the stable internal circulation), or perhaps the load on the plant has decreased, etc
Low processing volume, low load! Take a look at the temperature of the oil and gas entering the distillation tower (it’s usually around 400 degrees); you can also adjust it based on the overall load of the tower!
1. Has the circulation volume in Unit 1 decreased compared to before? 2. Under the condition of ensuring normal heat supply to the slurry, appropriately reduce the amount of slurry returning to the tower, thereby shifting the thermal load of the entire distillation tower upward. 3. Adjust the three-way valve that controls vaporization of the slurry in order to increase the temperature of the slurry returning to the tower. 4. Has there been an addition of light contaminated oil for reprocessing in this system? 5. What impact does the cold air from the north and the resulting temperature drop have? ? ? ? ?
Based on what the poster has said, your catalytic cracking unit has only one mid-stage reflux. In this case, a mid-stage return tower temperature of 170–178°C is considered a normal value. If the temperature seems lower compared to before, consider whether there is a leak in the reboiler at the bottom of the desorption tower or the stabilization tower. Samples are taken at the outlet of the intermediate pump and before the return to the tower at that stage for analysis, in order to determine whether there is an internal leak. The system pressure under stable conditions is generally higher than that of the intermediate section, so it is impossible for oil from the intermediate section to leak into the gasoline.
The low load of the catalytic fractionation tower is also a reason for the low temperature of the intermediate stream returning to the tower. If the quality of diesel is within a controllable range and there is some operational flexibility, then there are no strict process control parameters for the temperature at the mid-stage return to the tower.
The heat uptake during stabilization is relatively high; steam can be introduced to heat the bottom of the stabilization tower. When the heat uptake for stabilization is high, steam is used to reduce the amount of heat required for reflux in the middle section, thereby ensuring an appropriate temperature in the tower