The issue of uneven feed flow rates to the distillation feed heaters
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I would like to ask everyone about the issue of uneven feed flow rates in the feed heating furnace used in distillation. The distillation section of the hydroprocessing unit where I work uses a dual-tower stripping scheme; the product distillation tower is heated by a feed heating furnace, and the flow control of the four feed streams from this furnace is regulated through cascade control based on the liquid level in the stripping tower. In actual production, due to instrument inaccuracies, the flow rates of the four feed streams are always uneven, which makes it impossible to use cascade control and causes significant inconvenience in production. Does anyone have any good ways to solve this problem?
Modify the control scheme: before the signal outputs from the four flow control valves reach the valves themselves, a certain bias can be applied to these outputs based on the deviation between the measured temperature at the outlet of each of the four furnace tubes and the average outlet temperature. The maximum value of this bias I’ve seen is 10%; it’s recommended to start with 5% first. Attention should also be paid to the minimum flow limit of the furnace tube; a soft limit can be used. This is because, when the furnace flame is not biased and everything is normal, the outlet temperature of the furnace tube with the lower actual flow rate will be higher; the specific relationship between the bias and the deviation in outlet temperature needs to be estimated based on the specific conditions of the furnace.