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The overflash volume in atmospheric distillation is an important indicator for effective and well balanced operation of the distillation column. A precise measurement of this quantity poses a special challenge.

Driven only by gravity, the medium moves at very low flow velocities of around 0,45 ft/s, with a maximum flow rate of 10 tons/hr. Therefore, in order to reach a reasonable accuracy, the previously installed orifice plates had very small diameters. This resulted in a high pressure loss which could almost not be overcome by the hydrostatic conditions.

Another challenge for the measuring system was the high medium temperature of around 720 °F. After successful testing, a flow measuring system using FLEXIM's WaveInjector was installed at the measuring point, which is located in an ATEX 1 / FM Class I, Div. 1 explosion hazard zone. The installation was completed without any modification to the existing system.

The higher accuracy of the overflash measurement now allows a drastic improvement in process efficiency. The investment costs were quickly paid for by the higher yield.


  • Measurement without any pressure losses
  • Accurate and reliable measurement even at very low flow velocities
  • Process optimization
  • Easy upgrading without intrusion into the pipe system
  • Highly improved accuracy in comparison to conventional orifice meters