The issue of crude benzene
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After shutting down for nearly several months due to oil leakage in the tubular furnace in the crude benzene processing area, our facility has resumed production of crude benzene. At the start of operation, all the washing oil in the crude benzene system was replaced. In the early stages of operation, the benzene washing tower – which is a packed tower equipped with stainless steel corrugated orifice plates – was cleaned using steam, resulting in the removal of a large amount of oil residue. The U-shaped liquid seal in the benzene washing tower often failed due to high gas pressure, so it was modified by being made longer. After crude benzene production began, blockages in the heat exchangers occurred because the temperature of the oil stream entering the tower dropped to 30 degrees; therefore, the temperature of this oil stream was kept around 35 degrees, while the gas temperature was 27 degrees. Nevertheless, there was a problem of insufficient oil flow in the system. After a thorough inspection, it was found that there was washing oil present in the liquid seal behind the benzene washing tower as well as in the liquid seals in the subsequent desulfurization unit. The analysis indicates that it is caused by gas entrainment; please help analyze what is leading to the low oil level in the system. The issue of low oil levels does not occur every day – it happens from time to time, with 7-8 tons of oil missing at times per day.
A blockage in the 30-degree lean oil cooler indicates that there are still issues with the cleaning oil. 7-8 tons of oil are consumed per day – that’s way too much. If all other methods have been checked, it is advisable to verify whether the U-tubes in the benzene washing tower are obstructed, as this could cause the washing oil to flow back from the gas inlet and be discharged through the water seal tank. Is there a risk of flooding in the secondary degassing tower, leading to unstable liquid levels?
Has the mist catcher of the benzene washing tower been checked?/
1. In the benzene washing tower, the washing oil enters the tank at the bottom of the tower through U-tubes. If these U-tubes are not unobstructed, or if their diameter is too small, or if the circulation volume of the washing oil is increased arbitrarily, or if that circulation volume is unstable； All of these will cause an excessive accumulation of oil at the bottom of the packing in the benzene washing tower, which in turn allows the washing oil to enter the gas pipeline and flow out through the next gas water seal. 2. The temperature of the washing oil should not be too high; it is best to keep it 2-5 degrees higher than the temperature of the gas. If it is too high, it is detrimental to the benzene washing process, and it also causes the washing oil mist to be lost along with the gas. 3. Find an opportunity to check whether the mist capture layer at the top of the benzene washing tower is functioning properly.
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OP, what other equipment do you have before washing the benzene tower? How much gas is used? What is the pressure behind the blower? What is the amount of oil used for cyclic washing? Running 7-8 tons of washing oil per day is absolutely impossible.
1. During the process of storing and transporting the washed oil, check for any leaks or spills (as operations have just resumed after maintenance). 2. When discharging slag from the washed oil regenerator, keep the temperature below 300 degrees Celsius and control the amount of distillate produced. 3. Inspection of the mist catcher at the gas outlet of the benzene washing tower. 4. Conduct a comprehensive analysis of the quality of the washing oil. Under normal conditions, the tar washing oil consumption per ton of benzene is around 50–75 Kg
With such high temperature control for your gas and lean oil, how much heat needs to be removed! ! ! There’s also a problem with your cleaning oil; it’s impossible for it to crystallize at 30 degrees
Oil droplets from the water seal flow behind the tower can be seen; the high temperature of the lean oil is due to blockages that often occur after cooling in the lean oil cooler.
I agree with the analysis on floor 4; I think these 3 points are the main ones, and in addition, we should check the quality of the cleaning oil
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It’s possible that you didn’t clean thoroughly; some of the oil distribution pipes at the top of the benzene washing tower are blocked by oil residues, which results in uneven spraying of the washing oil. As a result, some of the gas isn’t exposed to the washing oil. When this gas exits the benzene washing tower, it flows at high speed and in a direction that intersects with that of the washing oil, leading to excessive entrainment. In such cases, the benzene content downstream of the tower is high. In our plant, it has happened that the oil seal elbows in the benzene washing tower became corroded, which caused the gas entering the tower to force large amounts of washing oil into the oil seals. The oil discharged from these seals was sent to the mechanical clarification tank through the oil drainage channel, resulting in a daily consumption of 5–8 tons of washing oil.
Your cleaning oil tends to crystallize too much; such oil tends to accumulate on the packing in the benzene removal tower and clog the distribution pipes. Its quality needs to be improved. I’m curious about the situation regarding the extraction of naphthalene oil from the benzene removal tower in your plant – it’s necessary to increase the amount of oil extracted, and the regenerator should also discharge more slag. Our factory consumes 47 kg of benzene wash oil per ton.
The washing oil is required to have no crystallization at 15 degrees, a initial boiling point of not less than 230 degrees, 90% to emerge by 300 degrees, and more than 50% to emerge by 270 degrees
If the mist catcher is corroded and damaged, it can lead to excessive entrainment; if it is blocked, the amount of entrainment will not be high. In my opinion, your tower may be experiencing flow deviation, mainly because some of the oil residues carried by the purge gas cause local blockages in the distribution pipes and distributor, resulting in flow deviation and thus excessive entrainment.
Hello, I have a factory that produces waste distillate remaining after the processing of refining oils. This waste contains a significant amount of methylnaphthalene, and the crystalline substances such as industrial fluorene and industrial acenaphthene, which are found in the fraction above 300 degrees Celsius, have already been extracted by the previous manufacturer, so they are basically absent. I’m not sure what the effectiveness of this material would be for benzene purification. My phone number is 18721012998; the factory is located in Shanxi, and it produces between 100 and 200 tons of this waste distillate per month. It’s cheaper than traditional cleaning oils, so feel free to contact me if you’re interested.
I produce the cleaning oil myself here, so I don’t need to purchase it from outside. It’s good if it doesn’t contain acene or fluorene, but what’s more important are your boiling range specifications
The temperature difference between the washing oil and the gas is too large, which causes water in the washing oil to separate out and some of the washing oil mist to be carried into the gas and lost. When the water content in the washing oil is extremely high, this method of dehydration is used by increasing the temperature difference to 15 degrees. Taking as an example a flow rate of Q=170 m³ with a 10% water content, the problem can be largely resolved after 3 hours of dehydration using this method; therefore, when the temperature difference is too large, the loss of washing oil occurs quite rapidly
This post was last edited by hao101029 on 2012-6-10 22:38. The optimal temperature for benzene washing is 25 degrees; how do you manage to keep it at 35 degrees? Can this be done without wasting cleaning oil?
Our company faced the same issue when it first started operations: gas carried along washing oil, which resulted in a significant amount of such oil in the water seal. Later, a unit equipped with a water separator was added to the workshop to recover the washing oil carried along by the gas, and this approach proved effective.