How is reflux established in batch distillation when the content of the light component is low?
Thread Content
Intermittent vacuum distillation is carried out at a pressure of 9 kPa. The material is added to the distillation vessel in one go; the key component in the crude product is the heavy fraction, with the light fraction accounting for only 3–4% of it. By controlling the temperature of the vessel, the light fraction is removed first, and then the heavy fraction – both of which emerge from the top of the tower. However, in practice it has been found that even if all the light fraction is removed through reflux, 70–80% of the medium fraction still makes it up to the top. To prevent the heavy fraction from reaching the top, almost no reflux is used. After reflux was established, the top temperature exceeded the limit again, reaching the boiling point of the heavier components under vacuum; it seems impossible to establish reflux using the lighter components. As a result, a large proportion of the front slurry must now be removed in order to reorganize the components for discharge. During the current modification, a concentration tank has been added at the top of the tower when separating the light components. The goal is to use a full reflux–full drawoff pulse testing method to rapidly concentrate the light components in this tank, but it was found that the concentration rate is very slow, and it becomes difficult to increase the proportion of light components to 30%. It’s hard to tell now whether it’s a problem with the operation, an insufficient number of trays, an inadequate tower diameter, or whether there are any specific requirements regarding the amount of material loaded into the distillation vessel in case of batch distillation
There are too few light components; the total amount of light components is so low that full reflux cannot be established at the top of the tower. It’s difficult to concentrate the light components, which indicates that they cannot be separated easily from the intermediate components. Try increasing the reflux ratio during concentration to see if that helps. The diameter of a batch tower is related to the speed of evaporation, and it has little to do with whether the separation is effective or not.
During the tuning process, the reflux ratio was also set very high, but the results were still not satisfactory. We have come up with a method that we haven’t tried yet: to use the light components collected in the condensation tank from previous distillations to create a reflux stream, with a high reflux ratio and a low draw rate; each time a distillation takes place, those light components are retained in the condensation tank to facilitate reflux
The initial fractions can be collected separately first, and then these fractions can be recovered together. If it still can’t be separated well, then the tower isn’t tall enough.
It is recommended to use full reflux and keep the reflux temperature at the bubble point.
Points mined in Tazhong: sleepy: then continuous feeding