Increased pressure drop across the stripped vapour return line and/or the liquid line at a given liquid head (H) also limits this gravity hydrau- lics. Fouling, improper pipeline sizing, control valve limitation, and side stripper configuration changes, especially from the reboiled stripper to the steam stripped stripper, are common root causes of hydraulic limita- tion. The author has observed that the pressure drop across the stripped vapour return line is often overlooked in the hydraulic evaluation of the side strippers. Equipment selection Choosing the proper equip- ment type for side stripping is also critical to ensure the desired performance. Trays are commonly selected for side stripping services. Trays usually provide higher fouling resist- ance and liquid handling capa- bilities compared to packing. 3 Overall efficiencies between 25 and 33% are typical values in most side stripping services. Fouling, damaging, and/or inadequate tray design can fur- ther downgrade tray efficien - cies. Trays with higher net rise fixed valves are preferred for high fouling-prone side strip- ping services.
O gas
Cold re ux
Sour water
Top pumparound
Unstabilised light naphtha
Stripping steam
Heavy naphtha
Kerosene pumparound
Stripping steam
Diesel pumparound
Kerosene
Diesel pumparound
Wash oil
Stripping steam
Diesel
Desalted crude
Stripping steam
ATB
Figure 3 Case study 1 crude distillation unit configuration
The frequency of fouling cases has increased in kerosene side stripper operations due to phosphorus. Each tray open area for vapour traffic should be carefully selected espe - cially for the stripping steam side stripper trays. Either tray weeping at the bottom stripping tray or severe entrainment at the top stripping tray can be experienced if a single same-open area is applied for the entire stripping trays. Instead, progressively varied tray open areas matching a given vapour traffic profile can ensure performance targets in the steam strippers. If the side stripper diameter is too large at given process conditions, reduced active area and/or valve open area can be a solution. Adding multiple blanking strips for tray open area reduction is the cheapest solution. However, non- uniform blanking patterns may adversely affect strip- ping tray performance. New tray design using parallel (or channel) baffles can eliminate non-uniform tray open area issues. In addition, rectangular active area geometry with parallel baffles can achieve plug flow of liquid across the active area and enhance stripping efficiency.
Locations of the bottom stripping tray seal pan, the reboiler return, or the stripping media nozzles should not be ignored. The author observed that the bottom stripping tray seal pan was too close to the reboiler return stream inlet nozzle horizontally.⁴ The down-flowing liquid from the seal was entrained by the high-velocity reboiler return stream. Adding a segregation baffle between the seal pan and the reboiler return nozzle may resolve this issue. Adding a properly designed sparger at the reboiler return or the stripping media inlet nozzles could enhance vapour dis- tribution across the side stripper. In particular, tray damage often occurs in the steam strippers. Uplift force-resistant ‘heavy duty’ tray design can increase tray survival chances. Implementation of packing on the side stripper is not common. In the past, it was believed that low pressure drop across packing could enhance stripping efficiency. Nevertheless, weak fouling resistance is a major disad - vantage in packed side strippers. Reduced run lengths of the packed side strippers are often observed in actual CDU operations. A mismatch between design and actual
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PTQ Q3 2025
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