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Why are chevron baffles used instead of trays in the oil slurry heat exchange section at the lower part of the catalytic fractionation tower? Note: This question was provided by Explorer; the provider is requested to pay close attention and provide a summary or answer within 24 hours. This post was last edited by 263525689 on 2009-2-13 12:10]
The feed to the catalytic cracking fractionator is superheated oil and gas with a temperature of over 450°C, along with catalyst dust entrained in it, which is what sets it apart significantly from other fractionators. The lower part of the catalytic fractionation tower contains an oil slurry heat exchange section. The circulating oil slurry is drawn out from the bottom of the tower, and after heat exchange and cooling, it is returned to the tower where it comes into counterflow contact with the rising oil and gas. This helps to rapidly cool the oil and gas, thereby preventing coking ； On the other hand, it also washes away the catalyst dust entrained in the oil and gas. In the slurry heat exchange section, due to the high temperatures and the presence of catalyst dust, triangular baffles are generally used instead of trays.
Since the material below consists mainly of heavy components and has very high viscosity, trays cannot be used.:lol
The superheating removal section at the bottom of the catalytic cracking fractionator is equipped with about ten herringbone baffles. Since the feed is superheated oil gas containing catalyst powder at over 460°C, it is necessary to first cool the oil gas to a saturated state and wash away the entrained dust in order to carry out distillation and prevent blockage of the trays. Thus, the oil slurry drawn from the bottom of the tower is cooled and then returned above the herringbone baffle, where it comes into counterflow contact with the oil and gas rising from the bottom of the tower. This not only cools the oil and gas to a saturated state but also removes the dust carried by them.
The feed to a catalytic fractionation tower is generally superheated gas at a temperature of over 460 degrees and containing catalyst powder, rather than a gas-liquid mixture. The heaviest components in the reaction gas oil must be condensed out of the gas oil and obtained as the bottom liquid product. To prevent contamination by side products, it is necessary to first cool the oil and gas to a saturated state and wash away the dust carried in them, so as to enable distillation and avoid blockage of the tower trays. To this end, 8 or 10 layers of herringbone baffles are installed at the bottom of the distillation tower; this section is known as the superheat removal section, or also the flushing and cooling section. It is greatly affected by the operating cycle, resulting in large operational fluctuations. The gas phase entering the distillation tower is unstable, and it easily carries some coke particles, which can lead to blockages in the tray columns. Additionally, the high inlet temperature of the coking distillation tower causes coking to occur easily in the lower tray columns. Therefore, a herringbone baffle is used. This is the description of the catalytic distillation column in the book; the feed to the coking distillation column contains more impurities compared to that of the catalytic distillation column, so it is definitely not possible to use trays in this case. The coking reaction products entering the distillation column from the coke tower contain a small amount of coke powder; to reduce the tendency for coking and blockages on the tray surfaces, herringbone baffles are generally used. There are also trays with a large open area, such as those using disc-ring baffles or truncated-disc baffles. I think trays can be used, but the plate pressure drop needs to be very low. In the desuperheating section, heat transfer is mainly carried out by the reaction oil gas and slurry. So currently, it is designed with V-shaped and circular baffles. So, there are tray alternatives to baffles that also work quite well. The function and purpose of the herringbone baffles in a coking distillation tower are to wash the catalyst and remove excess heat. Herringbone baffles are used instead of ordinary trays in order to prevent coking and blockages. The feed to the coking distillation tower consists of superheated oil and gas at a temperature of around 420°C, along with coke particles. The heat exchange section, which serves to remove excess heat and wash away coke particles, tends to form coke due to the high temperatures; therefore, diagonal baffles are generally used instead of trays. The raw material used for coking is generally atmospheric and vacuum residue, without catalysts. The fractional distillation feed is the oil and gas coming from the top of the coke tower, which contains coke powder. Herringbone baffles are generally used at the bottom of distillation towers, and tray baffles are not employed in order to prevent coke particles from clogging the bottom of the tower. In some petrochemical plants, spiral baffles are also used at the bottom of distillation towers; the principle remains the same.
The superheating removal section at the bottom of the catalytic cracking fractionator is equipped with about ten herringbone baffles. Since the feed is superheated oil gas containing catalyst powder at over 460°C, it is necessary to first cool the oil gas to a saturated state and wash away the entrained dust in order to carry out distillation and prevent blockage of the trays. Thus, the oil slurry drawn from the bottom of the tower is cooled and then returned above the herringbone baffle, where it comes into counterflow contact with the oil and gas rising from the bottom of the tower. This not only cools the oil and gas to a saturated state but also removes the dust entrained in them.
The feed to the catalytic cracking fractionator is superheated oil and gas with a temperature of over 450°C, along with catalyst dust. At the lower part of the catalytic fractionation tower, there is a slurry heat exchange section. Due to the high temperatures, circulating slurry is drawn out from the bottom of the tower; after heat exchange and cooling, it is returned to the tower where it comes into counterflow contact with the rising oil and gas. This helps to rapidly cool the oil and gas, thereby preventing coking ； On the other hand, it also washes away the catalyst dust entrained in the oil and gas. Therefore, herringbone baffles are commonly used instead of trays.
To put it simply, the baffle is not prone to clogging, while the tray is
Since the medium consists of high-density components, has high viscosity and a high temperature, plus catalyst dust, the aim is to prevent clogging.
The oil slurry here is too viscous and contains many impurities; on one hand, the gas phase finds it difficult to pass through this highly viscous oil slurry, and on the other hand, the trays can become clogged by the oil slurry. Moreover, precise contact and exchange between the two phases are not required in this area. Therefore, chevron baffles are used to provide a preliminary washing and cooling effect on the feed.
In the oil slurry heat exchange section at the lower part of the catalytic fractionation tower, circulating oil slurry is drawn out from the bottom of the tower; after heat exchange and cooling, it is returned to the tower where it comes into counterflow contact with the rising oil and gas. This process not only rapidly cools the oil and gas to prevent coking but also washes away the CAT dust carried by the oil and gas. Due to the high temperatures and the presence of CAT dust in this heat exchange section, zigzag baffles are generally used instead of trays.
The feed to the catalytic cracking fractionator is superheated oil and gas with a temperature of over 450°C, along with catalyst dust. At the lower part of the catalytic fractionation tower, there is an oil slurry heat exchange section. The circulating oil slurry is drawn from the bottom of the tower; after heat exchange and cooling, it is returned to the tower where it comes into counterflow contact with the rising oil and gas. This process helps to rapidly cool the oil and gas, thereby preventing coking ； On the other hand, it also washes away the catalyst dust entrained in the oil and gas, which is why V-shaped baffles are commonly used. This post was last edited by zkj7421 on 2009-2-5 14:11]
In fact, the viscosity of the slurry is not very high at high temperatures; the herringbone baffles are installed at the lower part of the catalytic fractionation tower due to the presence of a small amount of catalyst fines in the slurry. The feed to the catalytic fractionation tower is superheated oil and gas at 460–480°C coming from the settler, along with a small amount of catalyst fine powder. To create the conditions for distillation, it is necessary to first cool the superheated oil and gas to a saturated state and remove any catalyst fines carried along, so as to prevent blockage of the trays during distillation. To this end, an overheating removal section is installed at the lower part of the distillation tower, equipped with herringbone baffles. The slurry drawn from the bottom of the tower is cooled and heat-exchanged before being returned above the baffles, where it comes into counterflow contact with the rising oil and gas to remove dust and eliminate overheating.