63- Discussion on the new composite weir-chamber structure design for three-phase separators and the retrofit design of traditional structures

As is known, Sinopec and CNPC have companies in Henan that are responsible for the design and manufacture of three-phase separators, but the three-phase separators produced by these companies are mostly of traditional design. In actual operation, problems such as unstable operation control and large fluctuations in separation efficiency occur. Many companies are also looking for opportunities to improve.

This post was last edited by luoli519 on 2016-12-13 at 13:07. A manufacturing company faced difficulties in getting its traditional three-phase separators to operate stably during production, so it turned to a filter manufacturer in Xinxiang for help. The filter manufacturer, in discussion with the owner, proposed a new solution to replace the original screen-type liquid-liquid separation element with a dynamic coalescence separation element. The following diagram shows a simplified structure of this filter manufacturer:

However, the filter manufacturer and the owner were unsure about the design configuration for dynamic separation internals, so they turned to NOVEL Company to develop a new design plan for them.

As can be seen from the provided figures, there are the following issues: First is the feed inlet, which uses two porous tubes as the inlet distribution assembly. However, the spacing between the two porous tubes is too small, causing the two feed streams to interfere with each other, which hinders liquid-liquid separation.

Secondly, no gas-liquid demisting and separation internals are installed in front of the gas-phase outlet pipe on the inside of the separator. Under conditions of fluctuating gas velocity and high gas velocities, it is difficult to achieve ideal separation of the liquid droplets and mist carried by the gas flow solely through gravity settling. The gas stream will carry a significant amount of liquid phase with it, escaping from the separator and causing liquid accumulation in the downstream pipelines; this can even severely affect the operation of the core equipment, leading to high costs for subsequent gas treatment.

Thirdly, looking at the dynamic separation element that is installed there, it is positioned across the radial cross-section of the entire horizontal container; as a result, the gas stream carrying liquid droplets and foam must pass through this element, as must the liquid-liquid mixture. This element is intended to carry out both gas-liquid separation and liquid-liquid separation in one go, with the hope of achieving everything at once! In fact, dynamic gas-liquid separation internals and dynamic liquid-liquid separation internals not only differ in terms of their structural design, but also have fundamentally different principles of dynamic separation.

This post was last edited by luoli519 on 2023-9-26 at 14:57. Gas-liquid dynamics separation internals, such as the G50 type vane separation internals, enable efficient and quantitative separation by means of momentum transformation of fluid elements, high-speed rotation, coalescence and growth, vector separation, and capture of droplet surface free energy, as the fluid flows through their specialized primary and secondary flow channels； However, the flow velocity and momentum of the fluid elements cannot be too low; otherwise, it is difficult to achieve efficient momentum conversion and thus effective separation ； The flow velocity and momentum of the fluid elements must also not be too high; otherwise, the airflow will pull the liquid that has already separated back into the clean airflow, causing it to become dispersed and reducing the separation efficiency.

For liquid-liquid dynamic separation internals, such as the G56 type finger fin internals, the flow condition required for efficient separation is that the fluid must be in a laminar state; efficient separation is achieved through mechanisms such as finger coalescence and shallow pool separation. The axial flow velocity of the fluid must be less than 0.02 m/s or even lower.

Fourthly, the liquid-liquid interface is positioned near the center line of the horizontal tank, and the top height of the partition (weir plate) also reaches the center line. This is clearly an empirical design, rather than the result of dynamic design optimization. Due to the varying ratios of the gas, liquid, and liquid phases, it is necessary to calculate and determine the positions of the gas-liquid interface and the liquid-liquid interfaces. This is done to enable the liquid phase in the gas phase to reach the liquid interface efficiently, as well as to ensure that the dispersed water droplets in the continuous liquid phase reach the water interface quickly, and similarly for the dispersed oil droplets in the continuous liquid phase reaching the oil interface. A comprehensive balance is required for this purpose. For traditional three-phase separators with a conventional structure, they often have to deal with fluctuations in operating conditions such as changes in the oil-to-water ratio and flow rates, as well as variations in the discharge rate at the water phase outlet. These factors cause changes in the position of the liquid-liquid interface, leading to significant variations in separation efficiency. This makes it difficult to achieve stable and reliable actual operation control.

Finally, consider that before the oil phase outlet on the inside of the separator, an anti-vortex device should be installed, rather than a foam breaker. It should be noted that vortex preventers and foam breakers differ in both structure and function, and cannot replace each other. A foam breaker finds it difficult to achieve the effectiveness of a vortex breaker.