What is an appropriate emission level for ground flares in petrochemical plants?

It is very small under normal production conditions, but the emission level is extremely high under abnormal operating conditions； The design capacity varies depending on the scale of the device.

Generally, the choice between ground-based flares and elevated flares is not based on emission levels; floor space is the main factor. This is because elevated flares require a fire protection radius of 90 meters, whereas ground-based flares take up less space. However, surface torches also have their limitations; for example, highly toxic substances such as H2S cannot be processed using surface torches. SH3009-2013 states that the processing capacity of ground torches should not exceed 100 tons, but that refers to the capacity of a single tower; currently, the highest processing capacity achieved is 170 tons. When the emission volume is particularly high, such as 300–400 tons, multiple towers can be used in parallel for treatment. Relatively speaking, ground-based torches have a higher cost than elevated torches, but they require less space; the choice should be made based on the specific requirements of the project.

It needs to be determined based on the emission volume; when the emission volume is less than 100 T/hr, a ground-mounted enclosed flare can be used, while for volumes greater than 100 T/hr, an elevated flare or an open-ground flare can be employed. Since open-ground flares require more space, this option must be considered in light of the conditions of the industrial site. Special note: Under specific operating conditions, an elevated flare + underground enclosed flare system can be considered for treatment

These days, it’s common to find single-tower systems capable of handling over 100T, so making a choice based solely on this factor does not reflect reality

The amount of 100T is merely a recommendation based on standards; it is a rational suggestion tailored to actual conditions, primarily driven by considerations related to smoke reduction. Additionally, the 90-meter distance refers not to the fire-resistant rain, but rather to the thermal radiation radius of the torch

Sorry, I misunderstood what you meant. It’s the 90-firestorm radius, taking safety risks into account

You probably aren’t involved in torch design, and the recommendation of 100T isn’t based on considerations related to smoke reduction. When the processing capacity of a closed-ground flare is around 100 t/h, the diameter of the flue gas emission stack is generally about 17 m; if the processing capacity increases, the diameter of the flue gas emission stack also increases accordingly. When the diameter of the flue gas exhaust stack increases significantly, it affects the air intake volume of the ground flare, thereby impacting the combustion of the flare gas. There are clear explanatory provisions for this in SH3009-2013; you can read the standard in more detail

I’m an amateur; feel free to exchange ideas and discuss

It is explained in API 521