Why is the pressure in the recovery tower of the aromatic extraction unit negative?
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Top pressure of solvent recovery tower, kPagPIC4008-50-55~ -45 Recirculation ratio (R/D) FC4009/FI4010 0.65 0.5~0.7 Steam-to-water ratio (SW/S) FC4014/FC4002 0.015 0.012~0.018 Flow rate of steam condensate, t/h FC4008 2715~30 Top temperature of tower, °C TI4024 71 Bottom temperature of tower, °C TIC4026 176 174~178
Applying negative pressure can effectively reduce the temperature at the bottom of the tower, preventing thermal decomposition of the solvent. On the other hand, it reduces the energy consumption of the system. It is also easy to achieve negative pressure in the recovery tower: 1) The steam used for stripping at the bottom of the tower is cooled by air to convert it into a liquid phase, thereby creating negative pressure; 2) A vacuum pump is installed in the gas phase downstream of the reflux tank.
Vapor phase condensation leads to a reduction in volume, and the saturated vapor pressure is lower than the pressure drop resulting from this volume reduction
Because these aromatics are liquids at normal temperature and pressure
Is it related to the state of the solute and aromatic hydrocarbons under negative pressure?
Well, that’s not the reason, right? Could you be more specific?
At around -50 kPa, the bottom temperature is maintained between 174 and 178 degrees, allowing for proper separation of the solvent and aromatics; under normal or positive pressure conditions, a higher temperature is required to achieve the same separation. However, under industrial conditions, sulfolane begins to decompose slowly at temperatures above 200 degrees, producing sulfur dioxide which acidifies the environment in the tower, leading to corrosion and increased solvent consumption. Furthermore, operating under negative pressure reduces the temperature at the bottom of the tower, which in turn **lowers the heat required for separating each unit of material**, thus reducing energy consumption. Then, the heat source requirements needed to maintain a lower bottom temperature of the tower are also **reduced, which eases the operating conditions and lowers the equipment pressure rating as well.