179-Discussion on the key technical aspects of the upgrade project for the conventional separators used in the recycle gas of hydrogenation carbonylation units, involving the use of vane separators

This post was last edited by luoli519 on 2021-3-8 17:50. In units such as hydrogenation and carbonylation plants, the reactions are typically gas-liquid-solid or gas-solid reactions. Excess amounts of reactant gases such as hydrogen and CO are used; the large amount of unreacted gas flows out of the reaction unit along with the product stream. By cooling, the reaction products are liquefied as much as possible from the mixed gas stream, and then the liquid is separated using a gas-liquid separator. Subsequently, the gas is pressurized by a compressor (compression cylinder) and returned to the reaction apparatus to participate in the cyclic reaction. It can be seen that the gas-liquid separator is one of the core devices in these systems. However, for a long time in the past, both design firms and clients treated the gas-liquid separator as a simple static vessel; at most, they would fill it with things such as wire mesh or packing, relying on experience, rough estimates, or simply guessing that the liquid would fall out of the gas stream and get separated. On these similar reaction units, the screen separator is naturally considered as an option for gas-liquid separation. For example, the separator shown in the DCS screenshot provided by the owner is as follows:

As can be seen from this flowchart and the location of the separator marked, this separator plays a very important role: firstly, its performance level directly determines the yield per pass of the plant. The separator has low efficiency and poor performance, resulting in a small amount of liquid product being captured and separated in each pass. Secondly, it plays a crucial role in ensuring the normal operation of the core equipment in the subsequent cycle compressor (cycle compression cylinder), as well as minimizing operating and maintenance costs. Otherwise, the airflow carrying liquid enters the compressor, which can cause the compressor to surge in mild cases, and liquid hammer in more severe cases; this may even lead to serious safety incidents resulting in equipment damage and injuries. Thirdly, the recycled gas carries a significant amount of reaction products back into the reactor, which undermines the selectivity and activity of the catalysts in the reaction apparatus; this process repeats itself, creating a vicious cycle. Furthermore, the liquid reactants in the gas stream cannot be effectively captured and separated by the separator; they are repeatedly cooled and reheated within the reaction cycle, resulting in unnecessary consumption of cooling energy, heat energy, electricity, and water, and thus causing the operating costs of the facility to rise over time.

The owners’ unit for separating recycled gas also uses a traditional mesh separator; its low efficiency has an impact on yield and operating energy consumption, and all of these issues are attributed to the catalyst in the reaction unit, with the blame being shifted onto the catalyst itself. However, the low separation efficiency causes liquid to be carried in the circulating gas into the circulation compressor, leading to \"surge\" and \"cylinder knocking\" in the compressor; thus, it is impossible to keep the circulating gas separator uninvolved in this issue. However, as for how to carry out technical upgrades to this screen separator, they had no choice but to turn to the design institute. The institute could not come up with a better solution; it suggested adding another set of filters between the cycle separator and the compressor in order to improve the separation efficiency. Yet the improvement in separation performance after adding these filters was minimal, and the compressor continued to experience surging and cylinder knocking. This is a flow diagram drawn by the owner, showing a set of filters added between the cyclone separator and the compressor, for everyone’s discussion.

As we have discussed in previous technical posts, a screen separator separates the liquid-solid heavy phases carried in the airflow by using the screen elements to block and trap them. As for the mesh components, whether they are loose mesh or woven mesh, interception is achieved through the mutual “bridging” of the mesh fibers to form “cells” of varying sizes. These bridge-formed irregular \"cells\" vary in size, with pore diameters ranging from a few micrometers to over a hundred micrometers; therefore, mesh separation is a type of non-quantitative precision separation that cannot achieve quantitative separation for specific sizes. These mesh \"cells\" trap solid particles carried in the gas stream, such as broken catalyst dust particles and polymers produced by reactions, on the surface and within the depths of the mesh. These particles accumulate over time, blocking the gas flow channels, which leads to an increasing operating pressure drop and poor gas transmission. It is particularly important to note that regarding the tiny liquid droplets and mist carried in the separated gas stream, their equivalent diameter changes significantly as they pass through the \"pores\"; this results in a spindle-shaped shape, which then returns to its original larger size after passing through the mesh. Therefore, separation elements based on pore-based blocking and interception, such as meshes, filters, filter cartridges, and filter media, cannot be used for precise, quantitative, and efficient gas-liquid separation.

The owner hopes that Novai Company will provide them with tailored solutions to address the aforementioned separation issues; the feather-shaped separator is precisely such a device based on advanced dynamic separation technology, designed as an upgrade to the separation method involving obstruction by grids. The figure below is a CFD sketch of the external shape of the feather leaf separator, provided for reference and discussion.

This post was last edited by luoli519 on 2021-3-8 at 19:56. Generally speaking, the appearance of the feather-shaped separator is similar to that of conventional separators, but its diameter is reduced by about 1/3. The main difference lies in their internal structure and the resulting performance. The internal components of the vane separator mainly include: 1. Inlet separation assembly ； II. Primary Pre-allocated Coalescing Internal Component Set ； III. Precision feather-leaf separation inner component set ； IV. New type of anti-siphon short-circuit liquid dropping internal component set. In addition, some vane separators are also equipped with an online swirl spray cleaning system for the internal components. Each set of internal components is designed and manufactured in a modular manner; it is supplied as a fully tested unit before leaving the factory, and is installed modularly on-site to ensure that the configuration and performance of the vane separator components inside the customer’s equipment are exactly the same as those after comprehensive testing in the factory. This approach avoids potential structural, performance, and safety issues that could arise from assembling the components on-site when there are no conditions for conducting full tests. Another advantage of modular design and manufacturing is the ease of installation and disassembly. The installation of a separator with a diameter of 7 meters can be completed within 24 hours, which is only a fraction or even a small fraction of the time required for on-site assembly from individual components. Moreover, this approach ensures that the configuration of the internal components of the vane separators installed in the customer’s equipment is identical to their performance during overall testing before they leave the factory.

This post was last edited by luoli519 on 2021-3-8 21:27. I. Regarding the inlet separation assembly: The inlet separation assembly serves two main purposes. First, it helps to pre-separate and remove the slug flow as well as large-sized heavy-phase particles contained in the airflow, thereby reducing the workload on the subsequent separation components； Secondly, it ensures a uniform distribution of the kinetic energy and momentum of the gas flowing into the separator from the inlet pipe, thereby creating the dynamic conditions necessary for efficient separation as the gas passes through the subsequent separation elements. In the early days, baffles were installed at the inlet of conventional separators; their main function was to prevent the fluid from eroding the inner wall of the separator shell on the opposite side of the inlet. They contributed little to gas-liquid separation, and instead, due to their inadequate design, they exacerbated gas-liquid mixing and liquid entrainment. Later, a semi-open tube was used to replace the initial baffle, which improved the gas-liquid separation performance compared to the baffle. However, the corresponding space inside the separator housing must meet the installation requirements. In recent years, a feather-leaf separated inlet assembly has been developed. It not only effectively prevents the fluid from eroding the inner wall of the separator shell opposite the inlet, but also improves the efficiency of pre-separating and removing slug flows and large-sized heavy-phase particles carried in the gas stream, as well as its ability to homogenize the kinetic energy and momentum of the gas flow, by at least 50% compared to semi-open tubes. However, to develop a reliable technical solution for the airfoil separation inlet assembly, it is necessary to rely on a system platform for calculation using precise dynamics separation techniques and for configuration design, in order to accurately determine structural parameters such as the number of airfoil separation elements, their elevation angle, contraction angle, as well as their outward and inward movement.

This post was last edited by luoli519 on 2021-3-8 at 21:24. The image below shows a finned inlet separation assembly named “SCHOEPENTOETER” as specified in Shell Oil Engineering’s DEP standards; the corresponding model from Novell is NOVEL G50B-1. The SCHOEPENTOETER entrance assembly also requires a reliable technical solution to be developed through precise dynamics separation techniques as well as systematic design and configuration; it cannot be based on approximations, estimates, or arbitrary decisions.

This post was last edited by luoli519 on 2023-3-23 at 13:08. The image below shows the inlet separation assembly for feather separation in Novail Energy Technology Company, with the model number NOVEL G50B-2. The vane-separated inlet separation assembly builds on the NOVEL G50B-1 inlet assembly by adding fin-shaped, radial-stabilizing vane separation elements, which further improves the efficiency of gas-liquid separation as well as the stability of the airflow pattern. It is capable of performing separation preprocessing on airflows containing up to 75% liquid content, thus enabling effective handling of both extreme conditions related to gas-liquid separation and liquid degassing.

If there is significant foaming and sediment in the inlet mixture stream, the NOVEL G50B-3 inlet separation assembly from Novell Energy Technologies can be selected. Its image is as follows: