157-Upgrade plan using vane separation technology for the main separator of the recycle gas in the hydrogenation synthesis unit and the inlet separator of the recycle gas compressor

In gas-liquid-solid three-phase reaction systems, such as hydroreforming, hydroprocessing, gasoline hydrotreating, diesel hydrotreating, and other similar gas-liquid-solid three-phase reactions, the one-pass conversion rate of the gaseous reactants is often low. After a large amount of gaseous reactants and reaction products exit the reaction vessel, the circulating gas, after having the reaction products removed from it, needs to be reintroduced into the reaction vessel for recycling in order to increase the overall conversion rate.

This post was last edited by luoli519 on 2020-6-18 at 21:27. Typically, in a gas-liquid-solid circulating reaction system, the high-temperature mixture exiting the reactor is cooled to a specified temperature range so that the reaction products can condense fully from vapor form. Thereafter, the liquid-phase reaction products carried in the gas stream are separated using a main separator; the circulating gas is further separated via an inlet separator before being fed into a circulating gas compressor to increase its pressure and then injected back into the reaction system for further reaction. The attached drawings illustrate Novae Energy Technology Company’s patented technology related to gas-liquid-solid cyclic reaction and cyclic gas separation processes; both the main separator and the cyclic compression separator utilize the vane separation patented technology as well as specific internal components.

In units such as hydrogenation pretreatment, gasoline hydrorefining, diesel hydroprocessing, and hydroreforming, hydrogen sulfide generated during hydrogenation can poison the catalysts in these reaction units and reduce their activity; therefore, desulfurization units are also added for the purification of the recycle gas. For example, the LC-FINING process flow at Chevron Roumes:

In the aforementioned process flow, the gas-liquid mixture coming out of the hydrogenation reactor first enters a hot high-pressure separator for preliminary gas-liquid separation. The liquid stream exiting this separator is then sent to a low-pressure separator to recover any dissolved gases. The gas streams from both separators are combined to recover thermal energy; after cooling, they pass through an inlet separator to have the liquid removed, before entering the compressor to be pressurized and injected back into the reactor to participate in the cyclic reaction.

These hot high-pressure separators, low-pressure separators, and inlet separators for the cycle compressors originally used traditional screen separation internals, which offered limited operational flexibility, low separation efficiency, and were often clogged by viscous substances carried in the gas flow, resulting in high pressure drops and a short service life for these internals. The MDEA desulfurization tower and regeneration tower also originally used these mesh separators. At the beginning of 2000, at the request of domestic design institutes, we designed and provided multi-tube cyclone separators to replace the original screen separators; as a result, in China cyclone separators for hydrogenation unit cycle hydrogen appeared under various names such as cyclone amine removal units, cyclone hydrocarbon removal units, cyclone liquid separation units, and cyclone liquid removal units. These circulating hydrogen cyclone separators perform fairly well in terms of separation in some hydrogenation units, but their separation performance is unstable in other units, with occasional significant liquid carryover.

A cyclone separator, which belongs to the category of dynamic separators, must be designed on a \"one-to-one\" basis using a precise dynamic separation technology design platform, taking into account various parameters such as temperature, pressure, gas phase composition, gas flow rate, gas viscosity, eccentricity factor, compressibility factor, gas density, liquid phase composition, liquid flow rate, liquid density, liquid viscosity, and liquid surface tension, depending on the specific operating conditions of the device. For two hydrogenation units of the same scale, their actual operating conditions certainly cannot be exactly identical; it is not possible to simply select and copy models based on the fluid handling capacity, as is done in many enterprises today, without carrying out precise design. Recently, I have seen some business owners purchase cyclone liquid separators for MDEA desulfurization towers used in hydrogen purification cycles; they tend to order copies of standard equipment based on experience alone, which is an incorrect approach. A cyclone separator is not a standard device; it must be designed on a “one-to-one” basis, taking into account the specific operating conditions. Otherwise, its actual separation efficiency is poor, and it may not even be as effective as conventional screen defoamers. This is the main reason for the generation of liquid in the gas stream of the cyclone separators in some current devices.

Cyclone separator, (dry gas) cyclone hydrocarbon remover, (dry gas) cyclone liquid separator, (dry gas) cyclone liquid remover – these devices utilize the centrifugal force generated by the high-speed rotation of fluids within a cyclone tube to separate light and heavy phases. Based on decades of technical design and application experiences both domestically and internationally, cyclone separators possess several notable technical characteristics that deserve attention: The first one is the operating conditions – the requirements under which they are used must be stable! Otherwise, the performance of separate operation is highly sensitive to fluctuations in operating conditions, resulting in large variations. One of the reasons is that the method used by the cyclone separator for separating light and heavy phases relies on the concentrated centrifugal force generated by the rotation of the fluid. Once the operating conditions become unstable, the centrifugal force changes significantly beyond acceptable limits; either the centrifugal force becomes negligible, or liquid droplets splash and break apart, causing the process to shift from \"separation\" to \"dispersion\", which greatly affects the efficiency. The second reason is that the cyclone separator has a simple structure with few separation stages; once the heavy phase escapes due to fluctuations in operating conditions, there is no effective mechanism to remedy the situation and enable the internal components to function properly. Taking the measure of \"plugging the tubes\" in the counter-rotating swirl tube internals to address fluctuations in operating conditions often amounts to a \"reactive action\" taken after the fact, and it cannot prevent a deterioration in separation efficiency caused by subsequent adverse fluctuations in operating conditions. Secondly, operational characteristics: high pressure drop! A cyclone separator achieves the separation of light and heavy phases by relying on the centrifugal force generated by the high-speed rotation of the fluid within the cyclone tube. To effectively separate light and heavy components, the fluid must rotate at high speed along the inner wall of the swirl tube to create a strong centrifugal field. The driving force for the fluid to rotate at high speed along the inner wall of the swirl tube arises from the difference in kinetic and potential energy carried by the fluid (including the difference in static pressure energy). Therefore, for low-pressure operating conditions where pressure drop is a concern, especially at atmospheric pressure or in vacuum conditions, choosing cyclone separation technology is a wrong approach. Thirdly, inherent operational drawbacks: phenomena of ‘carrying along’ light and heavy components as well as ‘back-mixing’ are evident. In a cyclone separator, the flow channels for the light and heavy phases are the same, and the flow directions of these phases are either 180° or 0° apart, which easily leads to significant phenomena of \"entrainment\" and \"backmixing\" between the light and heavy phases. Fourth, inherent operational drawbacks: unstable discharge and poor flow of material. The heavy-phase stream separated by the cyclone separator must first be discharged from the common flow channel. However, the high operating pressure drop caused by the rapid swirling of the fluid often results in poor discharge of the separated heavy-phase stream at the end of the common flow channel for both phases, and may even lead to secondary \"entrainment\" and dispersion. Therefore, it is particularly emphasized that, unless the operating conditions are stable and the pressure is at a high or ultra-high level, resulting in a difference between the density of the gas phase and that of the liquid phase of around 30–40 kg/m^3 due to intense compression of the gas phase, or unless there is a need to use a cyclone separator because the gas stream contains a large amount of sharp particles with high surface hardness, cyclone separation technology should be avoided as much as possible in other situations.

So, what are the better technical options? From the perspective of professional dynamics separation technologies, feather leaf separation equipment is a rare and valuable option! The basis for this is as follows: The vaned separator utilizes a specially designed hydrodynamic flow channel based on patented technology, which enables the fluid to form vortices with smaller rotation radii within multiple series-connected separation units located inside the vaned elements. Through coordinated processes of mutual aggregation, vectorial separation, and separation driven by surface free energy, efficient separation of light and heavy phases is achieved after multiple sequential stages of separation. Feather leaf separation incorporates both swirl separation technology and coalescence separation, vector separation technology, as well as liquid film surface free energy capture separation technology, thereby greatly expanding the range of applicable operating conditions. Compared to cyclone separators, vane separators have the following notable technical features: Firstly, regarding application conditions, they offer a wide range of operational suitability! Except in situations where high-pressure or ultra-high-pressure conditions force the use of cyclone separators, resulting in a density difference between the gas phase and the liquid phase of around 30–40 kg/m^3 due to intense compression of the gas phase, or in cases where the gas stream contains a large amount of sharp particles with high surface hardness, vane separation technology should be preferred in all other cases. One of the reasons is that the separation of light and heavy components in the feather leaf separator relies on the coordinated use of multiple technical methods, resulting in a separation performance that is not sensitive to fluctuations in operating conditions. The second reason is that the vane separator uses 4–6 separation units arranged in series; should the separation efficiency drop to 90% due to certain operational conditions, the escape rate of the heavy phase material will be 10% (that is, 100% – 90%). After being captured again by the second separation unit, the escape rate of the heavy phase material becomes 10% * 10%, and after being captured once more by the third separation unit, it becomes 10% * 10% * 10%, and so on. The internal structure of the level 4–6 serial separation unit features a \"preemptive\" structural design to address even significant fluctuations in operating conditions, thereby effectively preventing adverse fluctuations in subsequent operating conditions. The effective operating flexibility range of the feather leaf separator is as high as 15%-130%, or even higher! Secondly, operational characteristics: at the same separation efficiency, the operating pressure drop of the vane-type separation internals is no more than 0.4 kPa or even lower, which is only a fraction of the operating pressure drop of cyclone separators! Cyclone separation is used only as one of the separation methods in vane separators; and under the same centrifugal field conditions, the driving force required due to the difference in kinetic and potential energy of the fluid is significantly reduced as the radius of rotation of the fluid decreases. Therefore, for low-pressure operating conditions where pressure drop is a concern, especially at atmospheric pressure or in vacuum conditions, choosing the vane separation technology is an excellent technical option. Thirdly, operational characteristics: it effectively prevents the phenomena of light and heavy materials being \"carried along\" or \"mixed back\" together. The light and heavy fluid channels of the feather vane separator are independent of each other ； The flow directions of the light and heavy phases are 90° orthogonal to each other, effectively preventing significant phenomena of \"entrainment\" and \"backmixing\" between the light and heavy phases. Fourth, operational characteristics: It features a anti-siphon liquid dropping system that ensures smooth discharge even when the operating pressure drop in the separator rises by dozens or hundreds of kilopascals, or even more, due to special operating conditions. This system effectively prevents the separated heavy-phase material from being drawn back into the clean airflow due to the high pressure difference, thereby avoiding secondary entrainment that could damage downstream pipeline equipment.

Next, a detailed discussion will be presented using the design plan for the upgrade of the inlet separator (cyclone separator) of the recycle gas compressor in a certain enterprise’s facility, with the vane separation technology applied in this case.