How to avoid using a flare when starting up a catalytic unit?
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Traditionally, refineries would have thick plumes of smoke from their flares when catalytic units were brought online; however, environmental regulations now require that as little flare emission as possible, or none at all, occur during catalyst startup. Some refineries have already achieved this, and we would appreciate it if fellow industry professionals could share their experiences. Our approach is to fill the gas separator tank at the compressor inlet with gas before injecting fuel into the lift pipe, operate the compressor at a low speed, and keep the anti-backflow valve fully open.
All of the catalyzed rich gas is fed into the gas holder before it is integrated into the system; the height of the gas holder is controlled in advance. Once the gas holder is connected to the catalyzed rich gas, the compressor in the gas holder is operated at full capacity to send the gas to the high-pressure gas pipeline network. The heat electric boiler and generator increase their load (or additional units are started) to maintain balance of the gas in the holder. The condensate oil from the cylinder of the gas holder compressor is sent for desulfurization in the gas separation unit; some of the condensate oil remains at the bottom of the gas holder and will be processed once operations resume normally.
Whether to use a flare is determined by the need to control the pressure at the top of the distillation tower and the need to protect the compressor; if these two conditions are met, there is no need to use a flare. The approaches of both of the above are viable; personally, I think the method suggested by LZ is more preferable. The method from the second floor involves some waste and is also more complicated to implement.
The original poster explained it very well! Our plant also doesn’t operate a flare when it starts up! At this time, attention must be paid to controlling the reaction pressure, as it is different from normal control! Although both are controlled by the speed of the air compressor, at this time the higher the speed of the air compressor, the greater the pressure, as the counterflow is fully open! The speed of the air compressor must be well controlled; special care must be taken when starting it up!
To achieve catalytic operation without using a flare, it is essential to properly coordinate reaction pressure control with the operation of the compressor. Before injecting fuel into the reactor, the compressor runs at low speed to warm up; after fuel injection, its speed is increased gradually based on the pressure in the reactor. Once the reaction pressure is under stable control, the compressor maintains the inlet flow rate and speed required to ensure the desired outlet pressure. In particular, it is important to maintain a low pressure during absorption, with the pressure being increased gradually as the speed rises. Coordination among several positions is of the utmost importance.
The folks upstairs have good experience. Our unit is small; we use a centrifugal air compressor, and we control the pressure with inlet valves. With the backflow valve fully open, the problem of releasing gas during startup is essentially eliminated.