How long does it take for low flow and deviation to cause coking in the furnace tubes?
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Today, the feed rate to the furnace decreased due to problems with the pump; each of the four feed lines saw a reduction of about 10 tons, whereas the normal feed rate is around 40 tons. The temperature at the furnace outlet increased by about 4 degrees, with the normal temperature being 266°C. Since this issue was not detected in time, it persisted for approximately 3 hours. I would like to ask whether this could cause coking in the furnace tubes?
If the medium is oil, it should not be. The furnace exit temperature is not high, below 300°C, so coking does not occur easily. In practical operation, one can check whether there is a change in the pressure difference before and after the furnace tube to determine if coking has occurred
The possibility of coking is low; with a feed rate of 40 t/h per stream, reducing it by 10 t per stream brings it down to around 75% of the original level. The operating range for such plants is generally between 60% and 120%. Of course, all of this assumes that 40 t/h represents full capacity, or 100% load； Additionally, the properties of the raw materials need to be taken into account. I agree with what the teacher above said: generally, oil-based materials should not coking at temperatures below 300 degrees, and it is important to monitor the pressure difference before and after the furnace tubes
But the furnace temperature is around 600 degrees, so I’m still worried. There are no pressure gauges before and after the furnace tubes here
Generally, there are pressure gauges both in front of and behind the furnace; check the historical pressure differences
It’s just as if you’re reducing the flow rate; fluid still passes through and carries away heat. The dry point of your oil shouldn’t exactly be 300 degrees, and instead you should consider whether too low a flow rate could affect the catalyst bed.