193– Multi-factor cyclone parent-child separator for ethane recovery in the ethane dehydrogenation to ethylene project: Cyclone separation technology plan

When selecting equipment for gas-liquid separation in oil and gas projects, domestic design institutes tend to opt for cyclone separation equipment, seemingly showing a preference for such devices. It is also possible that these design institutes have pre-defined cyclone separation equipment designs as technical modules, and whenever gas-liquid separation is required in oil and gas applications, they simply use these pre-defined technical modules. One might as well look into more oil and gas projects, as well as refining projects, and conduct statistics; it becomes clear that domestic design institutes tend to prefer cyclone separation technology and equipment. But preferences are one thing, and technology is another; this technical post uses this actual case for analysis and discussion.

This post was last edited by luoli519 on 2021-8-31 at 15:21. I previously created a dedicated thread to analyze and discuss gas-liquid separation technologies and equipment selection for oil and gas projects, with a comparative analysis focusing on the two main types of such technologies and equipment: cyclone separation and vane separation. Only the essence can be extracted here to provide a brief explanation for this post. Cyclone separation technology and equipment primarily utilize the strong centrifugal field generated by the high-speed, stable rotational flow of fluids, as well as the differences in kinetic energy and momentum between the different fluid phases, to achieve phase separation. The key to its separate operation lies in: first, a high-speed and stable rotating flow ； II. Differences in kinetic energy and momentum for each phase in the multiphase flow. Based on the key points of separation operation for cyclone separation technology and equipment, and considering that cyclone separation devices are static systems that force the fluid to rotate at high speeds within them without the devices themselves rotating, the energy equation dictates that sufficient static pressure energy must be converted into kinetic energy at high speeds in order to achieve effective separation. This means that when the cyclone separation technology equipment operates separately, a very high pressure drop is inevitably generated ； Conversely, without a high enough pressure drop, it is impossible to achieve a high separation efficiency. Cyclone separation technology devices achieve high separation efficiency, which necessarily relies on a high pressure drop; as a result, the actual operating conditions must be able to support and provide a high-pressure environment, one that is stable. Otherwise, when the high-pressure conditions of the fluid during actual operation are unstable and subject to fluctuations, the centrifugal field of the fluid within the cyclone separation device changes significantly, resulting in a noticeable deviation in its actual separation efficiency or even rendering it ineffective. Therefore, the prerequisite for selecting equipment for cyclone separation technology is: 1. Stable operating conditions ； 2. The operating condition involves high pressure, and a high pressure drop must be tolerated. Otherwise, it is not advisable to choose cyclone separation technology and equipment.

Feather-leaf separation technology and equipment utilize the surface tension and viscosity properties of liquid-mixed fluid droplets to carry out multi-stage, efficient transformations of momentum and kinetic energy within the special dynamic microchannels of the feather-leaf separation components, enabling the separation of light and heavy phases through the combined action of various separation techniques such as collisions between droplets, coalescence and growth, vectorial separation, and utilization of surface free energy. The key to its separate operation lies in: first, the liquid-containing mixed flow ； II. Special dynamic microchannels for the feather-leaf separated internal component set. Based on the key points of separation operation for the vane separation technology and equipment, separating the liquid-phase components of the mixed flow is crucial, while the vane separation internal components are essential. Since the mixed fluid within the vane separation device undergoes multi-stage, efficient transformations of momentum and kinetic energy in the special dynamic microchannels of the vane separation internals, droplets and foam achieve phase separation through the combined action of various separation techniques such as collision, coalescence and growth, vectorial separation, and surface free energy capture; as a result, it features wider operational adaptability, greater operational flexibility, and lower operating pressure drops, and can still achieve excellent separation efficiency even under normal pressure or even vacuum conditions. Therefore, the prerequisite for selecting equipment for the vane separation technique is: a liquid-bearing mixed flow. Otherwise, it is not advisable to choose the feather leaf separation technology and equipment.

Regarding the selection of gas-liquid separation equipment for the separation and metering unit in the ethane dehydration to ethylene project, part of the natural gas ethane recovery facilities analyzed and discussed in this technical post, the client’s design team still failed to set aside their preferences and decided to choose cyclone separation equipment, requiring us to develop a design plan according to their specifications. Next, let’s all analyze and discuss its adaptability together.

This post was last edited by luoli519 on 2021-8-31 at 15:53. The operating conditions for the gas-liquid separator in the separation and metering unit of a natural gas ethane recovery project provided by a client in a certain northwestern oil field are as follows: 1. Inlet flow rate: 750*10000 Nm^3/d; 2. Medium type: natural gas along with any condensate and dust particles it contains； 3. Operating temperature: 20-40℃ ； 4. Operating pressure: 6.0–6.4 MPaG. The molar composition (% ) of the natural gas mixture is as follows: carbon dioxide 0.90, nitrogen 1.43, methane 89.24, ethane 6.29, propane 1.39, isobutane 0.25, n-butane 0.27, isopentane 0.08, n-pentane 0.06, hexane 0.05, heptane 0.04.

The technical requirements specified by the customer are: 1. Droplet separation efficiency and accuracy, with 99% removal of droplets and bubbles larger than 5 microns in size； 2. Efficiency and precision of solid impurity separation: 99% removal of solid impurities with a size of 5 microns or larger ； 3. Operating pressure drop, not exceeding 5 kPa ； 4. Operational flexibility: 70%-120%, with compliance to the worst-case conditions.

When considering the separation efficiency and precision requirements from the customer’s perspective, as well as the relevant operating condition parameters, the customer has not provided the various characteristic parameters of gases, liquids, and solids under those operating conditions; parameters such as gas viscosity, gas density, foam viscosity, foam density, foam surface tension, and the apparent density of the solid phase are missing. When the customer does not provide the various characteristic parameters of gases, liquids, and solids under the operating conditions in question – such as gas viscosity, gas density, foam viscosity, foam density, foam surface tension, and the apparent density of the solid phase – it is necessary to design a gas-liquid separator that meets the required separation efficiency and accuracy. To do this, a company specializing in dynamic separation technologies must use its database to obtain the missing parameters before proceeding with the design of a dynamic separation solution. Otherwise, the technical solution will be completely mismatched.

The customer selected a cyclone separator for the technical specification of this equipment and specified the materials for each component. Please see the table below:

The following figure is the elevation view of the swirl separator nozzle provided by the customer:

Here is also a top-view diagram of the nozzle orientation of the natural gas cyclone separator in this separation and metering unit, provided by the customer: