Analysis of Refinery Hydrotreater Separators

MySep studio predictions for liquid-liquid performance of HP and LP separators in a Refinery Diesel Hydrotreater application are discussed.  Comparison is made with plant data and a good level of agreement is found.

MySep | Refinery Diesel HP / LP Separator MySep Studio

Business Problem

A refinery operator experienced a high corrosion rate and ammonium salt fouling in the stripper column of a Diesel Hydrotreater Unit (DHTU). This resulted in increased maintenance costs and reduced time between plant shutdowns. Excessive free water entrainment in the hydrocarbon liquid was suspected to be the root cause.

Analysis

MySep Studio was used to analyse the liquid-liquid separation performance of the HP Separator and LP Separator, located between the DHTU reactor and stripper column. MySep Studio was then used to verify the impact of increased water wash flowrate and to develop a strategy for retrofit reconfiguration of the separators.

Detailed analysis with the program revealed that the shearing caused by the high pressure drop letdown valve between the two separators created very small water droplets (< 50 µm). Further analysis showed that the LP Separator was not contributing to the water removal from the DHTU reactor effluent.

Validation

The measured field data on free water-in-hydrocarbon concentration going to the stripper column matched with the MySep Studio predictions. Understanding the root cause of the water carry-over and subsequently the ammonium salt fouling and high corrosion rate, allowed the development of a retrofit solution in the HP Separator.

Plant Data Comparison

For 2 water wash rates MySep Studio predicted 0.8% and 1.5% volume carry-over of water with hydrocarbon. The customer field measurements indicated 0.6% and 1.8% volume carry-over.

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