132- Design issues of the vaned separator dedicated to the inlet of the recycle hydrogen compressor in hydrogenation pretreatment, hydrogenation refining, and hydrocracking units

As is well known, the recycle gas in reaction units often contains a significant amount of heavy-phase entrained materials. In units such as feedstock pretreatment hydrogenation plants, diesel hydrogenation plants, olefin hydrogenation plants, and carbonylation synthesis plants, the reaction raw materials, solvents, reaction intermediates, and reaction products present in the recycle gas are usually carried along in the form of agglomerated streams or dispersed droplets and bubbles within the recycle gas flow. The specialized separator for the inlet section of the cycle gas compression unit, designed to meet the actual operating conditions of such cycle gas, requires a great deal of attention to be paid to its technical configuration and structural setup.

Firstly, in terms of the external design of the separator, if the circulating airflow carries a large amount of heavy-phase material at high flow rates, and the process requirements dictate that the liquid phase remain in the separator for an extended period of time, then a horizontal-mounted separator should be chosen for such cases； In addition, a vertically arranged separator can be chosen. In principle, separators with two different configurations can both meet the technical requirements of the process, thanks to specialized dynamic separation internals technology ； However, horizontal-mounted separators require more space, necessitating larger installation areas and maintenance spaces to be reserved in the overall layout.

This post was last edited by luoli519 on 2019-6-8 at 11:38. Next, it is necessary to consider using a dedicated inlet separation assembly to rectify the inlet gas-liquid mixture flow. The inlet separation assembly serves two purposes: first, it removes from the airflow, in advance, slug flows, lumped flows, and large-sized liquid droplets ； Secondly, it performs preliminary kinetic energy and momentum homogenization and rectification on the fluid entering the separator via the inlet pipeline. The airflow passing through the inlet separation assembly generally meets the dynamics separation conditions required for the proper operation of the next stage of separation components. Otherwise, it may interfere with the normal, efficient, and long-term stable operation of the downstream dynamic separation internals assembly, or even cause failures.

This post was last edited by luoli519 on 2019-7-2 at 13:31. Currently, the commonly used inlet separation assembly internationally is the vane-type inlet separation assembly named Schoepentoeter, which is designed and manufactured in accordance with Shell’s DEP standards; it is the G50B-2 type vane inlet separation assembly. Domestic projects also use such inlet separation assemblies when adopting foreign process packages, such as the Lummus process package, UOP process package, SD process package, Davy process package, Linde process package, Lurgie process package, Topsoe process package, and Casale process package, among others. The following image shows the vane inlet separation assembly of the G50B-2 type:

This post was last edited by luoli519 on 2019-7-2 at 13:31. The Schoepentoeter mentioned above must be precisely calculated and designed in strict accordance with Shell Oil Company’s DEP standards; it cannot be designed and provided casually, as many domestic companies that are not specialized in dynamic separation technologies do. The number of vanes, the shape and amplitude of these vanes, as well as the configuration dimensions of the Schoepentoeter all have distinct characteristics, allowing design firms and clients to easily determine whether it has been precisely calculated and manufactured by a professional company specializing in dynamic separation technologies, in compliance with Shell Oil Company’s DEP standards. The figure below shows the counterfeit Schoepentoeter design and manufacturing drawings provided by a domestic company specializing in non-professional dynamics separation technologies to a domestic petrochemical enterprise; these drawings were outright rejected by the process package provider, the design institute, and the project owner.

This post was last edited by luoli519 on 2019-7-2 at 13:38. Next, a pre-coalescing and redistribution internal component set needs to be used; its main functions are as follows: first, to pre-coalesce and enlarge the numerous tiny liquid droplets present in the airflow, thereby reducing the total amount of such droplets in the airflow； II. Further regulate and distribute the airflow pattern as it enters the subsequent precision vane separation components, to ensure efficient and stable operation of these components for purification purposes ； III. Ensure the efficient and stable operation of the subsequent precision feather-leaf separation components over an extremely long service life. For circulating gas compressors with high requirements regarding the residual amount of heavy-phase material carried by the gas flow, a pre-coalescing and redistribution internal component is one of the dynamic separation components that must be installed. The corresponding series of pre-agglomeration redistribution internals is the G50D series. The image below shows the photos of the G50D series pre-coalescing redistribution internals:

This post was last edited by luoli519 on 2023-9-26 at 16:57. The airflow, after being processed by the pre-agglomeration and redistribution internal components, enters the precision vane separation internal components randomly, thereby enabling efficient and stable removal of the heavy-phase contaminants carried in the airflow. The main advantages of the precision feather-shaped separation internal component set are: 1- It is generally capable of quantitatively removing heavy-phase entrained substances with sizes of 5-8 microns or larger at a separation efficiency of 4N level ； 2- It has a large operating flexibility, typically ranging from 15% to 135% of the designed rated processing capacity, and is especially suitable for unstable and variable operating conditions, such as those characterized by unstable operating temperatures, pressures, flow rates, and the mass of heavy phase carried ； 3-Resistant to clogging and operates at low pressure, making it particularly suitable for special operating conditions involving the transport of viscous substances or particulate matter in gas streams ； 4-It can operate in both online cleaning and offline cleaning modes, with a lifespan of 15-20 years or even longer. The following image shows photos of the D-BANK series precision vane separation internal components:

Finally, it should be emphasized that the heavy-phase entrained substances separated from the airflow by the precision vane separation internals must be delivered, through a specially designed independent liquid dropping system, to the storage area for heavy-phase entrained substances in the separator, without any backmixing or carryover with the airflow. The liquid dropping systems used in the past, both domestically and internationally, typically consisted of a simple liquid dropping tube with a liquid seal chamber simply welded to its bottom to immerse in the liquid phase for basic liquid sealing. However, due to the variable operating conditions of the separator, the operating pressure drop across the separation internals fluctuates sharply, causing the heavy phase particles that have already been separated to be sucked back into the gas stream through the originally simple-designed downcomers via a siphon effect, resulting in severe entrainment.

This post was last edited by luoli519 on 2019-7-2 at 13:39. The simple downcomers that were used in the past caused a \"siphoning\" effect during actual operation, which led to the previously separated liquid being drawn back into the gas stream, resulting in more severe liquid entrainment. This phenomenon has occurred frequently in applications such as the olefin water separator in MTO units and the inlet separator of the recycle compressor in methanol synthesis units. The reason for this is that when operating conditions fluctuate, the pressure loss in the separation internals increases, causing the downcomers and liquid seal chambers submerged in the liquid layer to form a communicating vessel with the separation internals ； The low pressure generated at the end of the separation internals due to operational pressure losses forces the liquid at the bottom of the separator to enter the downcomer, forming a column of liquid that helps balance the higher pressure at the front part of the separation internals. When the pressure loss caused by the separation internals is high, and even when the liquid enters the downcomer and fills it entirely, it is still not sufficient to balance the high pressure at the front end of the separator, a continuous \"siphoning\" phenomenon occurs in the liquid at the bottom of the separator. This phenomenon draws the liquid from the bottom of the separator continuously toward the end of the separation internals, where it is dispersed back into the gas stream, resulting in severe liquid carryover in the gas as it exits the separator. The figure below illustrates briefly the principle of pressure equilibrium in the communicating vessel between the separation internals, the downcomer, and the liquid layer at the bottom of the separator:

The last edit to this post was made by luoli519 on 2019-7-2 at 13:40. NOVEL Company has developed its own proprietary new type of liquid drainage system to address the shortcomings of traditional systems; this system provides an excellent solution for high-demand scenarios. It has been used by various petrochemical, coal chemical, and fine chemical companies to upgrade their traditional liquid seal drum drainage pipes. Even when the pressure drop caused by the operating airflow exceeds the design value by 260%, resulting in actual pressure losses of several tens of kilopascals, this system still effectively prevents the problem of liquid being carried along due to siphoning effects. The image below shows NOVEL Company’s new liquid dropping system: