Benzene yield issue
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In our plant, the yield of crude benzene has always been low. Half is around 0.97. Let me first introduce the manufacturing process here; I would appreciate it if the experts could help analyze it. After passing through the thiamine unit, the gas is cooled to around 25 degrees through final cooling; it is then sprayed with cold water in two stages. After that, the gas proceeds to the benzene washing tower, which is a packed tower made of steel mesh (built last year). The lean oil is cooled to around 29 degrees before being sprayed, while the rich oil is heated to over 180 degrees through heat exchange and in a tubular furnace, after which it enters the benzene removal tower, where steam is used for benzene removal. Before entering the tower, part of the rich oil goes into a regenerator. Scraping is carried out intermittently on Mondays and Thursdays. Routine testing parameters: low oil content, high oil content, benzene content, water content, and viscosity; a full set of tests is conducted once a week. The benzene content in the feed before the tower is unstable, ranging around 25 and 2.5; it is kept below 0.3 grams after the tower. The benzene content in the lean stream is also 0.3. The flow rate of the lean stream is 218 cubic meters per hour, while the coal feeding rate is 300 tons per hour. The benzene removal tower uses strip-type bubble caps, with superheated steam at a temperature of over 450 degrees
0.97 should be considered high; our factory has always maintained a level of 0.9%.
It’s probably related to your manufacturing process; you might as well try making changes starting from the first step
A yield of 0.97 is already quite high!
Steel mesh fillers and strip-shaped blister packs are not used very often these days
If financial resources are available, the benzene washing tower can be converted to a packed-type design, using stainless steel perforated corrugated packing； The benzene removal tower was modified to use radial side-guided spray tray internals. After upgrading these two towers, your production can increase by about 10%. 0.97 on its own is already a significant figure, but what is the volatility content of your raw coal? In Shandong and Jiangsu, the volatile content can reach 37%, while in Shanxi it is generally around 27%; in some factories it is even around 23%. Therefore, just stating that the yield is 0.97 doesn’t tell us whether it is high or low. However, based on the structure of the benzene washing tower and benzene removal tower you described, there should be significant room for improvement.
The main factors affecting the absorption of aromatic hydrocarbons: 1) Absorption temperature (depends on the temperature of the gas and the washing oil, and is also influenced by atmospheric temperature). When the content of aromatic hydrocarbons in the gas remains constant, the lower the absorption temperature, the higher the content of aromatic hydrocarbons in the washing oil ； Conversely, the lower the content of aromatic hydrocarbons in the washing oil. ) 2) Quality of washing oil – Tar-based washing oil is used as an absorbent; this process should be carried out regularly. Generally, whether it involves regeneration with lean oil or rich oil, the results are similar. As for slag removal, experience plays a key role. 3) Amount of circulating washing oil – The greater the amount of circulating washing oil, the better, as this helps to reduce the benzene content in the washing oil and improves the absorption efficiency. However, it’s necessary to consider the amount of washing oil required per ton of crude benzene, as this can be uneconomical. There is also a ratio between oil and gas, which should be between 1.6 and 1.8:1. 4) Benzene content in lean oil – The benzene content in lean oil is one of the main factors determining the benzene level after the tower. It’s important to monitor this level regularly; values vary from plant to plant, ranging from 2 g/m3 to 4 g/m3 or even 6 g/m3. A lower value indicates better benzene removal efficiency, while maintaining a higher value is more economical. 5) Absorption surface area – Both the gas and liquid phases need to have a certain contact surface area and contact time. For packed towers, the absorption surface area is related to the type of packing, the spraying efficiency of the nozzles, and whether the packing is clogged or not. The larger the absorption surface area, the longer the contact time between the gas and liquid phases, resulting in more complete recovery of benzene derivatives from the gas
The yield of crude tar from your plant is not low; you might want to check the volatiles content in the coal mixture used there. If the volatiles content is above 28%, the yield of crude tar can reach 1%
Our plant uses top-mounted coke ovens, and the recovery rate of crude benzene is around 0.85
Hehe, last month the yield of crude benzene in my workshop was 1.1, with the volatility content of the coal being around 34
Due to equipment and process issues, our yield is generally around 1.2%, with the volatile content being around 29%. Given the configuration of your device, the yield is quite high as well
It can be said that your recovery rate is already quite good; last month our recovery rate was 1.27, with the volatility level at around 36. Since the benzene content in the gas after the tower is not high, nor is it high in the oil-free stream, this indicates that the absorption and benzene removal processes are functioning adequately. The issue with you is that your volatility level is too low. Also, the temperature of the oil-rich mixture should not be too high; exceeding 180 degrees can accelerate the aging of the washing oil. We generally keep it between 170 and 175 degrees.
What is the volatility of the blending coal? Generally speaking, for top-loading furnaces, your recovery rate should be quite high.