Discussion on heating control of column reboiler

Figure 1 (without condensate buffer tank) uses the steam flow into the reboiler to control the tray temperature. The control is very direct, sensitive, and easy to use. The disadvantage is that the quality of the trap is very high, and there are two main problems.: 1. When the steam quality is not good, it is easy to block. It is recommended to add valves before and after, and set them into two groups, one for backup and one for use. ； 2. Poor-quality traps are prone to internal leakage, resulting in serious water hammer in the back channel. High-quality traps must be selected. Figure 2 (with a condensate buffer tank) I personally think that the temperature cannot be controlled. Should we add a control valve to the steam inlet of the reboiler, or use steam flow to control the temperature, and the condensate control valve controls the liquid level in the condensate tank.

If there is a condensate buffer tank, this method of liquid level control was suggested by someone from a small design institute. We haven't done it ourselves.

Adding a condensate tank and controlling the liquid level can solve the water hammer phenomenon caused by defective traps. However, using the liquid level of the condensate tank to cascade temperature control cannot be achieved.

Since the author did not disclose the name of the device, I would like to share some opinions based on general principles.: 1. The plan on the German drawing is to use the steam flow control valve entering the reboiler as the inner loop (secondary loop) of the cascade adjustment, and use the tower temperature as the main parameter to form a cascade adjustment loop together with the secondary loop. This is a typical control scheme for heating and controlling the temperature of distillation towers and other tower kettles. It is used a lot and has good effect in controlling the temperature of the tower kettles. ； However, the German diagram controls the temperature of the tray (or the temperature difference between the top and bottom, which is not very clear on the diagram). The channel is relatively long, and the control effect is not as good as controlling the temperature of the tower still. 2. The scheme on the transformation diagram is to control the tower temperature by controlling the liquid level of the condensate tank. The channel is longer than the German scheme. Moreover, the key is that the steam inlet of the reboiler is not controlled, and the effect of controlling the tower temperature will not be very good. Unless the condensate tank is heightened, the heat exchange area (steam addition amount) is adjusted by the liquid level in the reboiler, and the tower temperature is indirectly adjusted, the effect is estimated to be slightly better than the transformation plan. 3. Suggestions: If the drain valve is modified because it is not easy to use, you can use the condensate tank, liquid level gauge, and regulating valve in the modification diagram to improve the drain effect. ； Others are based on German drawings. If the tower temperature control effect is not good and the transformation is performed, it is recommended to introduce the tower kettle temperature into the regulating system, use it with the output of the original tower temperature regulator to perform high selection (or low selection, depending on the positive and negative effects), and then remove the auxiliary ring regulator. It is estimated that the effect will be improved.

Is there any master who is familiar with the operation of alcohol slide tower? I would like to ask some questions.

I think the design of Figure 1 is reasonable. Figure 2 cannot achieve effective control, it is not sensitive and direct, and it cannot be controlled if it contains non-condensable air.

Figure 2 shows that by adjusting the liquid level in the condensate tank, the heat exchange area of ​​the reboiler is adjusted to control the tower temperature. This design concept is to heat the tower when it is started and only to keep it warm after normal operation. It can be designed like this. This design also has the advantage of eliminating the need for a water trap, and is smaller in size than the control valve in Figure 1 and saves money. Figure 1. The control is sensitive and direct.

The analysis on the second floor is correct. I would like to add that Figure 1 actually reduces the steam pressure and controls the heat exchange temperature difference. Figure 2 is to control the heat exchange area, but there is a problem with the installation. The tank liquid level must be on the heat exchanger tube plate.

Of course, the flow rate controls the kettle temperature, and the traps will not often have problems during production. This is the first time I heard about the liquid level control of the condensate tank and the temperature of the kettle, and it seems to make no sense.

Personal humble opinion: Your two systems are used for different heating media. The German system is mostly used for hot water heating and is not suitable for steam heating. Steam is heated and condensed into condensate, which places high demands on traps. Hot water heating mostly uses sensible heat. There is no phase change in the large amount of water. Just use the regulating valve to control the water output to adjust the temperature. Steam After the phase change, the requirements for traps are high, and the requirements for the combination of calculation and reality are high. Not only is it not done well in China, but also abroad, many are blind and blind. If the amount of condensate is large, use a separator tank as shown in Figure 2 to replace the trap. The outlet valve of this tank controls the condensate level, and the reboiler inlet valve plus a flow meter controls the tower temperature.