Operation of the debutanization tower in the hydrogenation unit
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The feed to the butane removal tower comes from the bottom oil of the previous absorption/desorption tower (naphtha, liquefied gas, and some dry gas). (Sometimes, due to effective absorption in the absorption/desorption tower, the bottom oil contains some dry gas, which can disrupt the operation of the butane removal tower; normally, the dry gas content in the liquefied gas exiting the butane removal tower is around 5%). ) Liquefied gas with a C5 content of not more than 0.5% is separated from the top of the debutanization tower, while crude naphtha is obtained from the bottom of the tower; there is a reboiler at the bottom of the tower that uses steam at 3.5 MPa as a heat source. However, due to the tendency of liquefied gas to vaporize easily, special care must be taken during production operations. Unlike ordinary distillation towers, liquefied gas vaporizes very readily; therefore, when adjusting the reflux flow at the tower top, it is necessary to take into account the situation where the endothermic vaporization of liquefied gas leads to an increase in pressure at the tower top. Additionally, too low a temperature at the tower top or an excessive reflux flow can result in the liquefied gas not having enough time to vaporize, and it may end up being pushed down to the bottom of the tower. As I am also a newcomer who has only just started learning, I don’t yet have a thorough understanding of how to operate this tower. I am unable to analyze in depth the impact of the reflux volume on the top and bottom of the tower from perspectives such as phase equilibrium and heat balance, nor can I address issues like bottom temperature control. If you also have such towers, feel free to discuss and learn together. Another DCS diagram is attached.
Operating this tower is not actually very difficult, as the boiling points of the media to be separated differ significantly. During normal operation, it is essential to control the feed material carefully, trying to avoid including light components of C2 or higher; otherwise, these components will accumulate at the top of the tower, causing an increase in tower pressure, which hinders the separation process
This operation of the degassing tower is primarily integrated with the operations of the preceding stripping tower and absorption tower. The key aspect of this operation is controlling the temperature at the bottom of the stripping tower; if it is too low, dry gas will enter the next tower, resulting in overpressure downstream, while if it is too high, the quality of the dry gas will be poor and the yield of liquefied gas will decrease. By analyzing the quality of the dry gas, a value of C3 greater than 3% indicates that the temperature at the bottom of the stripping tower is too high, whereas a value of liquefied gas less than C3 but greater than 0.42% suggests that the temperature in the preceding stage is too low. Additionally, both the temperature of the absorbent and its flow rate have a direct impact on the efficiency of absorption. 1. First, find the optimal cracking temperature. 2. Control the temperature at the bottom of the butane removal tower; this is done by adjusting based on the quality of the liquefied gas and its C5 content. The most important thing is to ensure stable operation, and it’s also necessary that the cooling effect at the top of the butane removal tower be good, which is relatively easy to control.