Installation location of the safety valve on the tower
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The installation location of the safety valve in a tower: For towers of lower height, it doesn’t matter whether the valve is installed at the top or the bottom of the tower. However, for tall towers (with a height of over 50 meters), there are differences between installing the safety valve at the top and at the bottom. Could you please tell me where the safety valves are located in our propylene distillation towers, and what are the advantages and disadvantages of each location? In our case, the valves are installed at the top, and this makes it very troublesome to carry out maintenance or replacement of those valves
I also have serious doubts about this. For the same type of equipment, in some distillation towers the safety valves are installed at the top of the tower, at a height of dozens of meters, while in others they are placed on the oil and gas pipelines at the top of the tower, at a much lower height. Why is there such a difference in design? Those who are experts in design, please explain.
Strictly speaking, it should be the point at the very top of the gas phase section of the tower, vertically aligned with the tower; in most cases, this is the highest point on the gas phase component line at the tower top. I have seen some installations where, for the sake of ease of maintenance, safety valves are placed on the horizontal section below the gas phase line; in such cases, if there is a significant amount of liquid in the gas phase, it can affect the safe operation of the system!
If the tower is tall, it is troublesome to disassemble and assemble the safety valve for maintenance and pressure setting. It’s difficult to operate using lifting columns; a crane is required, with a capacity of at least 100 tons, in order to reach such a height.
Considering the effects of propylene’s boiling point and vapor pressure, propylene remains in a gaseous state at normal room temperatures; propane at the bottom of the tower is also in a gaseous state under these conditions. Therefore, as long as the pressure is properly controlled, the material coming out of the vapor line at the top of the tower will be in a gaseous state. The situation in the deethanizer and the depropanizer is essentially the same: at the top temperature of these columns, the material is in gaseous form. Even in the event of an abnormal surge in flow, the back pressure in the flare system remains slightly positive, which ensures that the liquefied gas vaporizes quickly; this should be feasible in theory. However, I have indeed seen designs in which the safety valve at the top of the distillation tower is located on the distillation platform; this is probably because, at the temperature at the top of the tower, there is a relatively large amount of gas phase.