By how much must the pressure ratio of the desorption tower be higher than that of the stabilizer tower in order to shut down the bottom pump of the desorption tower?

Our plant does not rely on self-pressure; however, when I was working at another plant, they did use self-pressure. There are pressure control valves at the top of the desorption tower – the pressure there is 13 kilograms, and the pressure at the top of the stabilization tower is 10 kilograms, which is no problem. However, we can make an estimate: assuming that the feed to the stabilizer tower is 25 meters below the bottom of the desorption tower, the pressure drop is approximately 1.8 kilograms. Adding in the pressure drops due to the pipelines and heat exchangers, this value rises to at most 2.5 kilograms. The pressure at the bottom of the desorption tower is about 1 kilogram or more higher than the pressure at its top. Therefore, it can be inferred that the pressure at the top of the desorption tower must be at least 1.5 kilograms higher than the pressure at the top of the stabilizer tower in order to eliminate the need for an ethane removal pump.

However, as the pressure in the distillation column increases, the distillation temperature at the bottom of the column also has to rise significantly; thermal energy considerations must be taken into account. Also, when considering self-pressure, the pipe diameter needs to be taken into account as well. Generally, it is still necessary to analyze the bottom pump.

In fact, relying on self-pressure, the most important thing is to ensure that the condensation cooling load at the top of the stabilizer is sufficient. If the self-pressurization force is insufficient, the pressure in the desorption tower is increased. First, the pressure-bearing capacity of the equipment must be taken into account; secondly, this will inevitably lead to a deterioration in the efficiency of separation, further contributing to an increase in the pressure in the stabilizer, thus creating a vicious cycle. As you said, if we talk about the temperature at the bottom of the desorption tower again, it involves the issue of heat utilization. For self-pressure, it mainly depends on the pressure at the top of the stabilizer.

I don’t think it makes sense to remove the bottom pump of the desorption tower; increasing the operating pressure of the desorption tower is necessary. To ensure that the C2 content in the liquefied gas is within acceptable levels, the load on the desorption tower increases, which in turn raises energy consumption. When the pressure difference between the desorption tower and the stabilization tower is too small, it becomes difficult to control the liquid level in the desorption tower, and the overall stabilization process is disrupted.

The desorption tower pressure can be 0.3 Mpa higher than that of the stabilization tower to enable feed to the stabilization tower under self-pressure.

Under normal operating conditions, the deethanized gasoline from our unit flows into the stabilizer by its own pressure; in abnormal conditions, it is necessary to activate the bottom pump. Generally, the absorption tower is maintained at a pressure of 1 MP, while the stabilizer is kept at a pressure of 0.75 MP. During periods of abnormal operation, a pressure difference of 0.15 MP between the front and rear towers is generally sufficient to effectively control the operation of these towers; if the pressure difference is lower, it becomes difficult to control the liquid level in the absorption tower. Of course, the actual situation will vary depending on the device.

Our system achieves self-pressure transfer from the rectifier column to the stabilizer column by keeping the pressure control in the reabsorption tower above 1.0 Mpa, while keeping the pressure control in the stabilizer column at or below 1.0 Mpa! ! Our value shows that a pressure difference of 0.05 Mpa is sufficient! !

The pressure at the bottom of the desorption tower is higher than that at the top by about 0.5 Kg/Cm3; therefore, the difference in top pressures between the desorption towers and stabilizer towers of various units varies. In any case, however, the pressure difference does not need to be very large. However, when evaluating the energy-saving effects resulting from such a design, it is not necessarily advantageous. Increasing the pressure in the desorption tower leads to an increase in the heating load at the bottom of the tower; moreover, the load on the pump located at the bottom of the tower is not high, giving this pump strong resistance to interference. Overall, both types of designs are available, but there are no specific comparative energy-saving data.

The top pressure control valve and the bypass line of our plant’s absorption tower are both fully open, and the top pressure is slightly higher than that of the absorption tower. The pressure control of the absorption tower is 1.1 MPa. The low-temperature control of the decompression tower is around 115 degrees. The stabilizer column pressure is controlled at 0.95 MPa. The condensed oil at the bottom of the distillation tower is pumped to the stabilizer tower using a pump; the opening degree of the control valve is generally around 20-30. The pump has been vibrating quite heavily. Could the pressure in the separation tower be increased so that the pump can be stopped and the flow can proceed to the stabilization tower under its own pressure? Of course, to achieve a satisfactory separation effect, it is necessary to increase the temperature at the bottom of the separation tower. I don’t know which company has implemented this; what level of high pressure difference is required to ensure the flow rate?

We control the pressure in the desorption tower at 1.2 MPa, and the pressure in the stabilizer at 0.95 MPa. The deethanized gasoline from the bottom of the distillation tower is sent to the stabilizer by self-pressure, ensuring stable operation.