Catalytic cracking fractionator bottom temperature
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In my workshop, at the current stage, the temperature at the bottom of the distillation tower fluctuates greatly, ranging from 10 to 25 degrees. The liquid level at the bottom of the tower is kept at 35%, but this level also cannot be stabilized. The amount of slurry being discharged is 2 tons per hour, while the amount of oil being reprocessed is 6 tons per hour. The amount of slurry that goes back up and down the tower is controlled manually. May I ask the experts what’s causing this issue and how it can be stabilized? Thank you!!
How long has your device been in operation? What ingredients are used in it? Sulfur-containing char and group composition? Has the scale inhibitor been used continuously? What other additives do you use? Has the pressure resulting from your reactions on the pressure difference at the top of the fractionation tower increased compared to before? Does the gas-phase temperature of the chevron baffle also fluctuate greatly?
The original poster’s question is not clear; it is suggested that the moderator give a warning.
This should be a process issue! Could you provide some detailed data? I can do the calculations for you and help find a solution to the problem!
First of all, thanks to the original poster for their help. The device has been in use for 3 months now? It is made from M-100 raw material – does it contain sulfur-containing char and group composition? Use scale inhibitors continuously? A CDC catalyst is used; the reaction pressure and the pressure difference at the top of the fractionation tower are roughly equal. The gas phase temperature near the baffle plates also fluctuates significantly. The temperature at the bottom of the tower is kept at no more than 340 degrees, while it is no more than 370 degrees on the baffle plates. The liquid level in the tower is controlled at 35%. The temperature of the oil-gas mixture entering the tower is 480 degrees; heat exchange between the oil slurry and the feed material prior to its return to the tower occurs at temperatures above 300 degrees
I’m asking you these questions because I want to consider the possibility of coking on your V-shaped baffles. The coking tendency of the M-100 feedstock is likely to be quite high (specific gravity: 0.900–0.939 g/cm³; residual carbon content: 5.5–7.5%). Since it is not blended with other wax oils, coking may occur in the slurry system, including at the chevron baffles. This can result in poor distribution of the liquid after it enters the tower, reduced washing efficiency, and diminished heat exchange capabilities, thereby preventing effective heat exchange with the oil gas – and this is what might cause such problems. Of course, let’s all sit down together and analyze it to see what other external factors there are, and whether there are any elements that cause instability in the load entering the distillation tower
Identify the problem through simulation calculations! Provide some calculation data!
OP, based on my practical experience, the fluctuations in the temperature at the bottom of your tower are caused by fluctuations in the liquid level. There are many reasons for fluctuations in liquid level. In terms of processing M-100 oil in our equipment, the key is to have the diesel with a high density. High reprocessing ratio, low processing volume, higher diesel production (up to 400% for 95% grade, with a positive dew point). Diesel prices fluctuate easily, and can even soar to extreme levels. The M-100 caused me to be fined a lot of money.
1. The coking tendency of the M-100 feedstock is likely to be quite severe; coking may occur in the slurry system, including at the diagonal baffles. This can result in poor distribution of the liquid after it enters the tower, as well as inferior washing and heat exchange effects. It also hinders effective heat exchange with the oil and gas, which could lead to such phenomena. 2. It is advisable to maintain the anti-tower temperature and the weight of M-100 oil at 260–280. 3. Adjust the reaction depth and address it from various perspectives.
1. The V-shaped baffle may experience coking. 2. Pulling the diesel too hard can also easily cause fluctuations in the lower section. 3. Identify the root cause from the reaction conditions.
Is the pressure at the top of your distillation column fluctuating? Has the pressure drop across the distillation column increased? Has the pressure drop associated with the reaction process increased as well? Has the flow rate of the slurry decreased? It is possible to determine where the problem lies by examining the pressure changes at various points; if the reaction leads to an increase in distillation pressure, it may be due to coking in the oil and gas pipelines ； If the pressure drop in the distillation column increases, it may be due to coking at the bottom of the column or salt formation at the top. Salt formation has less impact on the bottom of the column; once salt formation is ruled out, coking at the bottom of the column and on the lower trays could be the cause ； If the slurry circulation rate decreases, coking is likely to occur in both the bottom of the tower and the slurry heat exchange system.
Let’s still find the basis in the gas-liquid phase equilibrium of the fractionation tower; increase the circulation volume of the slurry and the amount of oil being reprocessed