135- Discussion on the selection of various kinetic separators for the petrochemical industry based on Shell Oil’s DEP recommendations

In the design and selection of separation technology equipment for industries such as petroleum refining, oil and gas extraction, natural gas purification and transportation, coal gasification, bulk chemicals, pharmaceuticals, and environmental protection, many engineering companies, design institutes, and project owners may refer to Shell’s DEP specifications when choosing appropriate separation technology equipment for their projects. However, those who select and design using the separation technology equipment recommended in Shell’s DEP specifications must have a thorough and in-depth understanding of the prerequisites and application scenarios for such equipment, as well as a deep grasp of the fundamentals of dynamic separation technology ； Otherwise, one might get confused by the DEP recommendation table and choose devices that belong to more than one category, resulting in significant differences in actual performance. In actual operation, technical upgrades and modifications also have to be carried out multiple times without achieving the desired results.

This post was last edited by luoli519 on 2019-7-20 at 12:52. I. Operational flexibility of separation technology equipment: In the DEP specifications and in the actual use of separators, there are at least two terms related to the operational flexibility of such equipment. The first is the upper limit processing capacity of the separation technology equipment, and the second is the ratio of the maximum to the minimum processing capacity of such equipment, which is referred to in English as the turn-down ratio. For equipment using dynamic separation technology, an \"actual effective maximum processing capacity value\" emerges only when the equipment is operating under conditions that meet the requirements of specific high-efficiency separation techniques. The \"actual effective maximum processing capacity value\" of the separation equipment is extremely important for the facility, attracting particular attention from the owners. When the operation of the equipment fails to meet the technical requirements of specific high-efficiency separators, it ultimately falls back to a pure gravity sedimentation separation mode, resulting in a separation efficiency as low as that of pure gravity sedimentation. In Shell’s DEP separation equipment recommendation list, it is questionable that the umbrella separator is ranked first in terms of the maximum processing capacity of separation technology equipment. The umbrella separator, also known as a \"cyclone plate\" separator, is used as a pre-separator in practical applications both domestically and internationally, where high requirements are not placed on its separation efficiency or precision. For example, in the SD process package, the requirements for the separation efficiency and accuracy of the umbrella separator are 99.9%*70+ microns. From the perspective of applications in specialized dynamics separation, it is only meaningful to compare and select separation equipment with a higher maximum processing capacity when the same high separation efficiency and precision are required. If the separation efficiency and speed of the separator are low, even if its maximum processing capacity is high, it has little practical value. The umbrella separator (cyclone plate separator) falls under the category of cyclone separators; such devices are already in use for flue gas desulfurization in thermal power plants and refining facilities. However, their actual separation efficiency is not sufficient to meet the requirements of plant operators.

This post was last edited by luoli519 on 2019-8-14 at 10:42. Looking again, the ratio of the maximum to the minimum processing capacity of separation technology equipment is referred to in English as the turn-down ratio. The minimum processing volume used as the denominator must be the actual minimum value specific to a particular efficient separation device; it is not acceptable to use values corresponding to flow rates and velocities that are very low, resulting in conditions close to pure gravitational sedimentation, as the minimum value ； Otherwise, the denominator is very small; even if the maximum processing capacity as the numerator is not impressive, the ratio of the maximum to minimum processing capacities resulting from mathematical calculations is quite large, which is clearly misleading for most researchers who are not specialists in dynamic separation techniques. For example, some in the industry consider the minimum processing capacity of screen defoamers to be very low; yet as is well known from practical applications, screen separation elements allow an actual flow velocity of the fluid passing through them of 0.1 m/s, with an upper limit set at 110%, which classifies them as low-speed separation elements among dynamic separation elements. When the flow velocity of the gas reaching the screen is very low, approaching zero, not only is it difficult for the gas to pass through the screen, but the fluid’s own kinetic energy and momentum are also very low; in essence, it falls under the category of pure gravitational settling. In such a situation, it cannot be considered as the actual minimum processing capacity for a separator. Not only is this mistake prone to be made by most researchers who are not specialists in dynamic separation techniques, but it is also made in the recommendations for DEP: although it clearly states that in practical applications the maximum flow velocity of the fluid passing through the screen separator should be 110%, it mistakenly takes the processing capacity of separators based on pure gravity sedimentation as the actual minimum processing capacity. As a result, the \"maximum-to-minimum ratio for screen demisters\" recommended is higher than that for vane-type and cyclone separators, which is clearly misleading. Please be aware of this mistake, colleagues. An example will make this very clear: for a wire mesh demister, according to industry standards, the maximum operating limit is 110%; if 10% is taken as the minimum operating limit, then the mathematical ratio of the maximum to minimum processing capacity is 110/10 = 11. For the technically upgraded version of the vane-type separator, namely the Feather Vane separator, the conservatively stated maximum operating range is 130%, while the conservatively stated minimum operating range is 15%. Thus, the actual maximum/minimum processing capacity ratio is 130/15 = 8.7. In industrial applications, for owners, it is far more important that the separator operates at a minimum level below 50% of its designed processing capacity than for it to operate above that capacity. The chances of the separator operating at less than 50% of its designed capacity are rare, usually occurring only during short periods of startup or shutdown. On the other hand, there are more opportunities for the separator to operate above its designed capacity, and this is what owners prefer the most, especially when they aim to improve and maximize production efficiency. It can be seen that although the actual turn-down ratio of the feather vane separator, which represents the ratio of its maximum to minimum processing capacity, is only 8.7, it is more significant and practical than the calculated turn-down ratio of 11 for the mesh demister recommended by Shell DEP; this makes it a more attractive option for owners.

This post was last edited by luoli519 on 2019-7-17 at 17:40. II. Regarding \"liquid flooding\" and \"liquid surge\": When phenomena such as liquid flooding or liquid surge occur in separation equipment, it is definitely because the airflow conditions exceed the maximum operating capacity allowed for that equipment. At this point, the liquid phase carried in the gas stream accumulates within the separation element, resulting in a gas-liquid fluid phase dominated by the liquid phase. This not only causes the separation element to lose some or all of its separation capacity, but also leads to a ‘surge’ of this liquid-dominated gas-liquid fluid phase on the element, thereby damaging the separation element and even the separator shell. For example, the \"fluidization\" and \"surge\" failures that occur in commonly used screen defoamers and packing internals when the operating load exceeds 110% of their design value. In Shell Oil’s DEP separation equipment recommendation table, the types of separation equipment prone to phenomena such as \"liquid flooding,\" \"liquid surge,\" and \"slug flow\" are listed as follows: 1. Separation equipment equipped with wire mesh demister elements ； 2. Separation equipment with filter element internals ； 3. Separation equipment with reflective flow swirl internals ； 4. Separation equipment with original Chevron baffle plates. It should be noted that, “3. Separation equipment with a swirl element that generates a reflected flow” ； 4. “Separation equipment equipped with original Chevron baffle plates,” which allows issues such as \"liquid flooding\" and \"liquid surging\" to be resolved through a pre-separator. And “1. Separation equipment equipped with a mesh foam remover ； 2. “Separation equipment with filter elements”; even the addition of a pre-separator makes it difficult to resolve issues such as \"liquid flooding\" and \"liquid surge.\"

III. Regarding separation efficiency and separation precision: Among the separation devices recommended in Shell’s DEP specifications, those with precision filter elements and super filtration separators equipped with axial flow cyclone separation elements are ranked at the top in terms of separation efficiency and separation precision； Separators with screen internals are arranged in the second sequence ； Separators with vane-type internal components are ranked in the third sequence ； Separators equipped with reflective flow-type cyclone separation internals are in the fourth sequence ； Separators that only have an inlet separation assembly are ranked in the fifth sequence. As can be seen from the above, the separation technology and equipment with high separation efficiency and precision recommended by DEP are often those with a low maximum processing capacity and prone to phenomena such as \"liquid surge\" and \"liquid flooding\". When there are significant fluctuations in the actual operating conditions, causing these conditions to exceed their limited design capacity, phenomena such as flooding or surging occur, resulting in a partial or total loss of its separation capability. The equipment recommended for high separation efficiency and precision in such situations has only theoretical value and no practical significance. Therefore, in practical use, it is often a combination of components from several separation techniques that is employed.

IV. Regarding anti-clogging performance: According to the classification for anti-clogging performance recommended by Shell DEP, the order is as follows: separators equipped only with an inlet separation assembly, umbrella-type separators (cyclone plate separators, counterflow cyclone separators, axial flow cyclone separators, separators with vane-type internal components, separators with mesh internal components, and super filtration separators with precision filter elements). As can be seen, any device that relies on fibers interlocking to form physical pores for barrier-based separation has the worst resistance to clogging. At the same time, the anti-clogging performance generally follows the reverse order of \"fluid flooding,\" \"fluid surge,\" separation accuracy, and separation depth. In practical applications, separation accuracy, separation depth, resistance to flooding and surging, as well as anti-clogging performance are often the most critical technical requirements for separators. As a result of trade-offs, reflex flow cyclone separators, axial flow cyclone separators, and separators equipped with vaned internal components are those that receive the most attention and preference.

The last edit to this post was made by luoli519 on 2019-7-18 at 16:41. V. Regarding actual operating pressure losses: According to Shell DEP’s recommendations regarding the order of operating pressure drops, the devices are as follows: separators with tight-filter elements, counterflow cyclone separators, axial-flow cyclone separators, screen separators, vane separators, and separators that only have an inlet separation assembly. In fact, the operating pressure loss of a separator is closely related to the separation mechanism; devices that rely on fibers interlocking to form physical pores for barrier-based separation exhibit high operating pressure drops. Devices that generate frictional pressure loss by the high-speed rotation of fluid against the equipment have high operating pressure losses. Perhaps Shell DEP’s preference for certain screens leads to inaccurate and biased recommendations regarding them, so it is important to remind everyone to be cautious when making a choice. As a company with many years of experience in the research, development, and promotion of dynamic separation technologies, it is recommended to pay more attention to vane-type separators, especially those of the feather vane type that have undergone multiple technical upgrades. Such separators deserve greater attention than traditional mesh-type separators; their poor resistance to clogging, as well as the tendency to experience phenomena such as liquid flooding and surging, are the main reasons for a sharp increase in operating pressure drops. Generally speaking, the efficient separation range for feather vane separators is 15%-130%, and the corresponding maximum/minimum processing capacity ratio is actually close to 9, making them a topic worthy of special attention.

Through the aforementioned summary, analysis, and examination, it is believed that by grasping the key points and taking into account the actual application results, one can make a relatively accurate choice regarding separation technology equipment. It should be noted here that for any separation processes involving compressible gas streams as the main component, such as gas-liquid separation, gas-solid separation, gas-liquid-solid separation, and gas-liquid-liquid-solid separation, these all fall under the category of kinetic separation technologies. To ensure the satisfactory operation of such equipment, it is necessary to rely on precise kinetic separation technology for calculations and design platforms in order to develop accurate technical solutions and equipment. Next, an analysis based on some actual operation examples will be provided, which will help everyone understand and grasp it better:

This post was last edited by luoli519 on 2019-7-19 11:09. Example 1: Analysis of natural gas dehydration and hydrocarbon removal separators in oil and gas fields. As can be seen from the actual use of such separation equipment in oil and gas fields, Shell has introduced separators such as the SM series and 3S series, which are used for separation at wellheads as well as in processing facilities both domestically and internationally. Let’s start by discussing the SM series of natural gas dehydration and dehydrogenation separators as an example. The following diagram shows the development of the SM series separators: