There are two control valves on the flare line at the inlet of the catalytic rich gas compressor. Why is this arrangement used?

I think one of the pipelines should have a larger diameter while the other has a smaller one, right? The thicker one is used for releasing flares in the event of an accident, while the smaller pipeline is used to regulate the reactor pressure at the start-up stage, before the compressor is activated. :lol

Yes, the thicker pipeline is 700, and it uses a cylinder-type butterfly valve; the other one is only 350 in diameter, and it uses a regular butterfly valve.

Both the large and small valves are used for venting gas to the flare; generally, the small valve can be set to automatic operation, while the large valve is opened manually when the small valve is unable to handle the flow rate. This control method provides greater precision and safety.

The small valve is set for automatic control (fine adjustment), while the large valve is under manual control (coarse adjustment).

Two flare valves, one large and one small, are installed at the inlet of the catalytic rich gas compressor. The large flame arrestor is designed to prevent a negative pressure difference between the two vessels, as well as backflow of oil and gas, which could lead to fires or explosions in the event of an accident, such as a disruption in the main air supply. The small flare valve is used for pressure adjustment under normal conditions; for example, regular testing of flares in winter is carried out using this small flare valve.

The conditions vary from one unit to another. In our unit, the flare is activated in response to a signal indicating that the compressor has stopped operating; it is opened to 30% of its capacity automatically. This is done not only in winter, but also once a week. A large-flame flare is used for this purpose – firstly, to check whether the downstream pathways are unobstructed, and secondly, to test the flexibility of the flare valve, ensuring that it functions properly during interlocks.

Pipes come in different sizes, one primary and one secondary, one automatic and one manual – these are commonly seen in the safe production of chemicals.

The instructor from UOP told us that foreign catalytic units do not have flare valves; instead, there is only a 400-size manual vent valve in front of the flare tank, which is used to expel air before starting up the unit. During normal shutdowns, no flaring takes place, and indeed we also do not flare during our current shutdown

What is the scale of the device used by the poster?

The small-diameter flare line at the compressor inlet is equipped with interlocking; that is, the compressor shutdown signal directly triggers the full opening of the small-diameter inlet flare valve, while the large-diameter flare line is manually opened based on the reaction pressure in emergency situations.

The small valve is used for automatic control to regulate the reaction pressure under normal conditions, while the large flare is employed when the reaction pressure cannot be reduced in case of an accident

So how do you relieve the pressure in your settler?

When the compressor is operating, the unit does not require a flare to be used at any time, whether it is starting up, shutting down, or dealing with accidents. However, when the compressor fails and stops suddenly, it is necessary to release pressure through a flare promptly in order to maintain a relatively stable pressure difference between the two vessels, prevent them from intermingling, and ensure the safety of the unit.

When the reaction pressure is high, we reduce the processing volume to control it; if it remains high, the low reaction temperature resulting from high pressure will cause a chain shutdown. During this shutdown, regardless of whether the main fan stops or not, the reaction pressure remains positive, meaning no flare is used. The air compressor can operate at a low speed of 1000–1200 revolutions per minute, but it’s important to ensure that both the regeneration slide valve and the standby slide valve are closed. When starting up, since the reaction pressure is positive and the air compressor is also running, it’s easy to feed material into the system

There is still a gap between China and the United States in terms of environmental protection, and this practice is a good indication of that

By the way, outdated concepts, including outdated design concepts, also mean that operational concepts cannot be advanced. I used to think that domestic catalytic units were already at the world’s leading level in terms of design and operation, but it was only after coming into contact with UOP process packages that I realized we are still quite behind

If the compressor stops operating, the reaction pressure will become extremely high. What should be done when the reaction temperature has not yet reached the value at which operation can be stopped? We have safety valves installed both in the crude gasoline tank and at the top of the distillation tower, and these valves allow for pressure relief in three stages, rather than all at once as is the case in some domestic systems; this reduces the impact on the external network of the facility as well

After reviewing some information, I’ve learned that foreigners have different approaches in certain areas compared to those in China, including aspects such as process design, equipment manufacturing, layout planning, and construction quality control, among many others. Foreigners have a much stronger attitude toward surgery – one that is more rigorous and serious – than those in China; there are many things worth learning from them, and the differences become especially apparent when comparing the two approaches. But in some aspects, it is due to different habits, so it cannot be generalized. Overall, the Americans are indeed much better. In recent years, many aspects in the field of catalysis in China have been following the lead of the United States, including the initial use of lower-quality catalyst materials followed by the use of higher-quality ones, catalyst precursor preprocessing such as the hydrogenation of wax oil and residue, flue gas purification, and S_zorb technology. It is estimated that this trend will continue over the next 10 years. In my opinion, China is 10-20 years behind Europe and the United States in areas such as petrochemicals and environmental protection; the problems we face now are the same ones that those regions faced 10-20 years ago.