Discussion on the setting of distillation column pressure
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I’ve been trying to figure out these issues for some time now, but I don’t really understand them. For a self-refluxing plate tower, the equipment consists of a reboiler, a condenser, and the tower itself. When the tower pressure was set at 0.25 MPaG, the return temperature of the condenser’s circulating water reached around 55°C. Due to the high temperature of the circulating water, scaling is likely to occur inside the condenser; therefore, it is necessary to adjust the return temperature of the condenser water to below 45°C (as required by the company). The following three methods were tried, but with little effect; I hope to hear other people’s opinions. 1. The return temperature of the circulating water is high. The simplest solution is to add more circulating water; however, during this process, the return temperature drops by about 5°C, but the tower pressure falls to 0.2 MPaG, which does not meet the production requirements. 2. Reducing steam flow and thus heat input presents two challenges: one is the issue of tower pressure, and the other is that a decrease in heat leads to a reduction in the reflux rate, which hinders the separation efficiency of the distillation tower. 3. This method was advised by an expert today, but it cannot meet the actual operating conditions. It involves adding pressure to the distillation tower; however, since nitrogen/hydrogen is introduced directly into the tower and the pressure control device is a shut-off valve, precise control is not possible, so this method can only be used intermittently, which poses certain safety risks. Therefore, this method was not adopted. If any expert has other opinions, please feel free to explain them.
So what is the heat load of the entire condenser? Before and after increasing the cooling water?
Under normal conditions, as the circulating water volume increases, the amount of condensate at the top of the tower rises, causing the pressure to drop temporarily. If no exhaust gas is released from the top of the tower, the pressure there will gradually increase. Under such operating conditions, as the cold energy increases and the amount of non-condensable gas at the top of the tower decreases, the opening degree of the pressure control valve at the top of the tower should be reduced compared to before
If no exhaust gas is released from the top of the tower, the amount of non-condensable gas inside the tower will gradually increase, and the pressure at the top of the tower will rise accordingly. Therefore, the method of inflating air from above is feasible; it’s just necessary to avoid releasing the non-condensable gas
Adding non-condensable gas at the top of the tower can also be understood as a reduction in the effective heat exchange area of the heat exchanger. It seems quite reasonable. If the non-condensable gas is not condensed in the tower top condenser, will there be any other effects on this condenser device?
I also feel like it’s an opportunity to broaden my horizons. Now, a question that arises is: could it have any impact on the equipment?
Controlling the tower pressure with inert gases is a common practice, and it does not have any adverse effect on the equipment. The poster understands that inflation reduces the heat exchange area of the condenser; I don’t quite get it.
Just add a self-standing nitrogen pressure regulator to supply additional pressure
The last edit to this post was made by wiseboy on 2018-5-17 at 18:53: “It’s about adding pressure to the distillation column; by introducing nitrogen/hydrogen directly into the column, this contaminates the product within the column and alters its thermodynamic equilibrium as well as its separation capabilities, resulting in the column no longer having its original performance.” The role of the tower is to separate impurities, and you are adding impurities (nitrogen/hydrogen) to it. There is also the effect of the condenser, which immediately reduces it by N times. Because your condenser wasn’t originally designed to have impurities (nitrogen/hydrogen) added to it. Generally speaking, the initial design did not take the addition of impurities (nitrogen/hydrogen) into account. Doing so now is definitely not possible without modifying the tower or associated equipment (such as condensers); there’s no need even to consider it.