How is the diameter of the torch main pipe of the device determined?

The Aspen FlareNet software can perform the calculations. You can search for it.

In general, there are two principles: first, the diameter of the exhaust pipe you choose must meet the requirements of the back pressure, under the most demanding conditions in various operating scenarios. Generally, the pressure drop of the external pipeline network outside the flare zone is determined by the design institute, while the pressure drop for the flare zone itself is provided by the flare manufacturer; these values are then combined for overall calculation. Secondly, the exit Mach number of the flare varies depending on the type of medium being emitted. Media with a low calorific value are difficult to burn, and for those that require a high degree of combustion completion, the exit Mach number is generally low; hydrocarbon flares typically have an exit Mach number of less than 0.5, unless a very high back pressure exists, in which case a sonic flare is used.

At that time, I determined the flow rate of the flare main based on the discharge volume of the safety valve with the highest discharge rate. Since the flow at that discharge point was significantly higher than that at the other points, there was no need to consider the possibility of flow accumulation; API521 makes this clear. I suggest you take a look at it. If the discharge rates at various points don’t differ much, things get complicated, and it’s necessary to carefully consider whether there is a problem of flow accumulation. Generally, such a situation does occur. In process engineering, we deal with things based on facts. Since I’m not aware of the specifics of your installation, I can only give general advice; you can just use this as a rough guide~:lol Once the flow rate is known, and after determining the velocity as suggested by the guy above, the pipe diameter can be determined accordingly~