What are the causes of surge in the main fan?
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The catalytic cracking unit uses a full regeneration method. In other words, there is an excess of air flow. What I want to know is: due to the air compressor or distillation, if the pressure in the settler suddenly becomes extremely high, will the main fan experience surge for some time under such conditions? What are the possible reasons for surge to occur?
The cause of surge in the main fan is low flow rate and high pressure ratio. If the system causes an increase in the pressure in the settler, it is necessary to reduce this pressure first (for example, by venting it); otherwise, too high a pressure can lead to backflow between the two vessels, which is dangerous. This situation should not have a direct impact on the main fan, but if the regeneration pressure is increased at this time to maintain the pressure difference between the two vessels, it may cause the main fan to reach its surge point and experience surging.
The causes of surge usually include: 1) the butterfly valve at the fan inlet suddenly closing or one of the valves on the outlet pipeline suddenly shutting off; 2) a low flow rate at the fan inlet, resulting in pressure buildup in the regeneration system; 3) instrument failures leading to surge; 4) excessive pressure in the regeneration system
In my opinion, the cause of surge is generally low flow at the fan inlet or high pressure at the fan outlet.
I have a question and would appreciate your advice. The main fan is driven by a turbine, and the steam pressure at the turbine inlet drops rapidly. Without installing controls at the fan’s outlet, surge occurs every time, which leads to the main fan engaging its overspeed protection mechanism. Please help analyze the reasons for this. (The turbine is of medium pressure; during fluctuations in steam pressure, the back pressure remains stable.)