Pressure control in the diesel hydrogenation unit, stabilizer tower
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In diesel hydrogenation, what is the pressure control level for the stabilizer tower, and how is it controlled? Thank you
The pressure is higher than the pressure of the flare system. The amount of exhaust gas extracted is controlled via the pressure control valve of the tower top reflux tank.
It is generally controlled in stages, just like the fractional distillation reflux tank and the feed tank. The reflux tank is equipped with nitrogen pressure supplementation and low-pressure venting. The pressure is generally slightly positive
Stabilizing the pressure at the top of the stabilizer depends on what product is produced there; the pressure varies depending on the product formulation. In our case, it involves diesel hydroprocessing, with two columns – one for hydrogen sulfide removal and another for distillation. The top product of the hydrogen sulfide removal column is acidic naphtha, with a pressure of 0.2 MPa, while the top product of the distillation column is low-freezing-point diesel, with a pressure of 0.15 MPa
The amount of acidic gas extracted from the tower top is used to control the tower pressure.
Why is it controlled at 0.2 instead of 0.3 or something else?
The pressure is determined based on the tower load; a high pressure results in incomplete separation of hydrogen sulfide, leading to diesel products that do not meet quality standards. On the other hand, a low pressure causes an excessive vapor load at the top of the tower, which also affects the efficiency of the tower trays.