How to control the reflux ratio in a vacuum distillation column
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Our company has a continuous vacuum distillation column, which is equipped with corrugated plate-type structured packing. The tower is 30m tall. Previously, an external reflux method was used, in which the condensed liquid was pumped back to the top of the tower for reflux. Currently, we are preparing to install a new distillation tower, with the condenser planned to be placed directly at the top of the tower. The condensed liquid is collected, with part of it being recycled and part being taken out. I would like to ask: how is the ratio between extraction and backflow controlled? Are there any well-established cases in industry? (Note: The vacuum level at the top of the tower is -0.095 MPa; the sampling point at the top of the tower is 30 meters above the ground level, and the density of the material is 1.1 tons per cubic meter.)
Our factory previously used a negative-pressure distillation column with internal reflux, controlling the reflux ratio via a top extract control valve. There is no automatic control; the control valve is set to manual mode. It runs without any problems.
If the extraction is controlled, then the amount of material that condenses per hour should be quite stable, right? In that case, the amount harvested is known, but the exact value of the reflux is probably unknown, right?
A continuously operating distillation column should represent a relatively steady-state process. In our column, parameters such as the feed flow rate, the vapor from the bottom of the column, and the amount of product taken from there are all automatically controlled by control valves; as a result, the amount of evaporation remains stable, and so does the amount of condensation. For him with internal recirculation, neither the recirculation volume nor the recirculation ratio can be obtained directly. The main purpose of the reflux ratio is to control the purity at the top and bottom of the tower. As long as the purity is satisfactory and the production capacity meets the requirements, there is no need to know the amount of reflux; the purity at the top and bottom of the tower can be controlled by indirectly adjusting the reflux ratio based on the yield from the top of the tower.
I suggest you use the original reflux control method, as it is easier to handle. If the pump really has to be removed, as you said, \"the condenser is planned to be placed directly on top of the tower.\" The condensed liquid is collected, with part of it being recycled and part being taken out” ； It is also assumed that a orifice plate + control valve is used to control the reflux ratio, while the production is controlled based on the liquid level in that collection tank. The aforementioned resistance resulting from measurement and adjustment is based on a 5-meter liquid column, with an additional 2 meters of margin; therefore, the elevation at the bottom of the collection tank needs to be 30 + 7 = 37 meters. The condenser, in turn, must be at a higher elevation than the collection tank. In my opinion, the cost of building such structures is quite high. If you are considering \"internal reflux,\" I’m not sure whether the reflux ratio can be precisely controlled; those with experience in this area, please share your thoughts. J If 7 ?! B @8
Hehe, I think the same way. Also, I would like to ask how your tower controls the reactor temperature and the yield from the bottom of the reactor? In our case, the temperature of the reactor is generally controlled by adjusting the flow rate of the heating medium, while the output volume from the bottom of the reactor is controlled based on the liquid level. For several connected continuous distillation columns, the fluctuations in the preceding column often affect the operation of the subsequent columns. I don’t know how to overcome this kind of problem?
To precisely control the reflux ratio, a reflux ratio controller can be installed on the reflux pipeline; the reflux ratio can be set as desired and is adjustable. It’s installed on the distillation tower in our facility.
Typically, the bottom of the tower temperature is interlocked with the control valve for steam or hot oil, while the product withdrawal from the bottom of the tower is interlocked with the liquid level.
First, control according to the original tower top temperature and analyze product recovery! Adjust the reflux by analyzing the sample! Regulating valves can be used for both reflux and production The consumption in terms of processing has indeed decreased ； But there’s one thing I don’t understand: according to what you said, the collection tanks used in your production process are located within a vacuum system, right? Our distillation towers are more or less of the same height, and the pressure difference between the top and bottom of the tower is no more than 100 mbar. How do you plan to address the issue of continuous production – by manually switching the extraction tanks?