188-Upgrade plan for the gas-liquid separation at the top of the esterification tower in the syngas ethylene glycol project using vane-type demister technology

As is well known, various types of towers are used in industries such as petroleum refining, coal chemical processing, fertilizer production, fine chemicals, natural gas processing, pharmaceuticals, and environmental protection. Poor gas-liquid separation at the top of the tower can cause excess liquid within the tower to be carried out of the tower by the airflow. This not only leads to loss of liquid material but also causes problems for the proper operation of downstream processes. This post is based on a practical case of the gas-liquid separation modification at the top of an esterification tower for an ethylene glycol project using waste gas/syngas, and it is intended to facilitate discussion among everyone. We are more skilled at carrying out professional upgrades and modifications to the existing old units with limited pressure resistance, without causing any damage, by separating the vanes and internal components, thus meeting the owner’s safety requirements that prohibit on-site welding on the inner walls of the existing towers.

The syngas ethylene glycol project is currently designed and constructed on the basis of a production line capacity of 200,000 tons per year per unit. The existing esterification towers that have been upgraded using vane-type demisters are part of a dual-production series consisting of four towers; the diameter of these towers is 4500 mm, and they are made of S30403 material. It turns out that in the early versions of these esterification towers, gas-liquid separation was achieved solely through gravity settling, with no internal components for gas-liquid separation installed; as a result, significant loss of liquid material occurred within the tower. Later, the owner adopted a wire mesh demister, but due to the severe operating conditions, the pressure drop across this demister was high, which often led to phenomena such as \"liquid flooding\" and \"liquid surging.\" These issues caused the internal components of the wire mesh demister, along with the supporting beams, to be displaced repeatedly, forcing frequent shutdowns for maintenance and adjustment; as a result, operation was not smooth at all, and eventually the situation was left unaddressed.

This post was last edited by luoli519 on 2021-8-19 at 18:49. The operating condition data provided by the customer are as follows: 1. Operating temperature: 35℃； 2. Operating pressure: 0.5 MPaG ； 3. Gas flow rate: 182480 Nm^3/h; 4. Gas viscosity: 0.014 cp ； 5. Vapor density: 8.36 kg/m^3; 6. Vapor molecular weight: 34.5 ； 7. Liquid flow rate: 18.3 m^3/h; 8. Apparent density of the liquid foam: 770.5 kg/m^3; 9. Surface tension of the liquid foam: 21.0 dyne/cm.

Customer requirements: 1. Separate and remove liquid droplets and foam with a size of 10 microns or larger from the airflow at a rate of 99.9%； 2. The operating pressure drop shall not exceed 2 kPa ； 3. It is preferable not to perform welding of the internal components of the vane-type demister to the inner wall of the esterification tower; if welding is still carried out, responsibility for on-site heat treatment lies with the relevant party.

Based on the actual operating parameters at the top of the esterification tower provided by the customer, we utilized NOVEL’s precise kinetic separation technology to calculate and design the system platform. The main components of the fan-shaped blade separation demister are as follows: 1. Main components of the fan-shaped blade separation demister: 1.1 Pre-distribution coalescer, model: G50D4500/12-V, material: S30403; 1.2 Precision internal component set for fan-shaped blade separation, model: G50-D BANK-240/1000-V, material: S30403; 1.3 New type of liquid dropping system internal component set resistant to “siphon short circuits”, model: G50LD12P-V, material: S30403. II. Dimensions of the vane-type demister: ID 4500 mm * TL/TL 495 mm. III. Weld-free skid-mounted.

The performance parameters corresponding to the aforementioned vane-type demister are as follows: (1) Gas flow rate under the baseline design conditions: 182,480 Nm^3/h； (2) Baseline design operating temperature: 35℃ ； (3) Operating pressure under the baseline design condition: 0.50 MPaG ； (4) Operational flexibility: at least 15%-130%, with a maximum of 140% ； (5) Separation efficiency: 99.9% removal of liquid droplets with a size of 4.70 and above @ OT of 35°C, OP of 0.50 MPaG, and flow rate of 182,480 Nm^3/h ； (6) Maximum operating pressure drop: 0.82 kPa at OT of 35°C and OP of 0.50 MPaG and 182,480 Nm^3/h; (7) Maximum operating noise level: 25.24 dB at OT of 35°C and OP of 0.50 MPaG and 182,480 Nm^3/h.

We introduce the various components of the feather-leaf separated demister as follows: Part 1: Pre-distributed coalescing internal component set. Based on design and application examples of separation internals in dynamic separation technologies at home and abroad over the past few decades, it can be seen that regardless of the configuration in which the separation internals are arranged within the separator shell, there are significant spatial dimension differences (asymmetric uniformity) in the working surfaces of these internals in both the radial and axial directions of the separator. As a result, there are notable variations in the flow velocity, momentum, kinetic energy, as well as the flow pattern and regime of the gas flowing onto these working surfaces. Therefore, from a technical standpoint, it is necessary to use a combined design that incorporates both \"pre-distribution\" and \"precision separation\" types of internals. This is especially true for separators of larger size, with high gas flow rates and high requirements for gas-liquid separation. In accordance with international design practices for dynamic gas-liquid separators, it is technically required to use a combined design of \"pre-distribution\" and \"precision separation\" types of internal components; that is, the pre-distribution component set is closely attached to the surface of the precision separation component set, with the pre-distribution coalescing component set placed at the front end of the precision separation component set. The main functions of this pre-distribution coalescing internal component set are as follows: First, the airflow at the upper part inside the shell enters the pre-distribution internal component, where the flow velocity, momentum, and kinetic energy of the airflow are further refined and distributed, and the flow pattern is adjusted to ensure uniformity. This ensures that the airflow meets the dynamic conditions required for efficient and stable operation before it reaches the subsequent precision separation internal component set, thereby enabling efficient and stable gas-liquid separation. II. By coordinating with the downstream precision separation elements, it pre-coalesces the tiny liquid droplets carried in the airflow, increasing their size; this enables the downstream precision separation elements to remove a greater amount of residual liquid from the airflow, thereby achieving a level of separation that is difficult to attain using only those downstream precision elements. III. Under special operating conditions, it can intercept sharp particles with high kinetic energy and high surface hardness carried by high-speed airflow (such as catalyst fragmentation particles, iron shavings, etc.), preventing them from causing frequent erosion of the precision separation components and thus extending their lifespan or avoiding damage; it provides cost-effective protection for the downstream precision separation components. The pre-allocated coalescing internals set included in this quotation is designed and manufactured using a modular, containerized design that enables easy removal and installation, allowing users to adjust it flexibly according to actual conditions at any time.

Part Two: Precision internal component set for vane separation. Thanks to its design based on proprietary technology and special configuration, it possesses a higher capture capacity for liquid droplets and mist carried in the airflow compared to conventional configuration structures – especially for those droplets and mist present in high-speed airflow. This ensures that the precision internal components used for vane separation enable efficient gas-liquid separation, lower levels of residual liquid droplets, improved resistance to clogging, more stable operation, and a greater range of operational flexibility. The vane separation precision internal component set in this solution is designed, manufactured, and installed using a skid-mounted approach. Its key technical advantages are as follows: First, it ensures that the vane separation internal component modules installed within the separator housing have exactly the same configuration, dimensions, and performance characteristics as those tested in the NOVEL factory, thereby preventing potential performance issues that could arise from the inability to detect defects in the component configuration or performance losses due to the lack of appropriate testing conditions at the installation site after the components are assembled there. II. It enables more convenient loading and unloading; its operation time is usually only about 1/4 of that required for the traditional method of separating the blade components and placing them in the shell in a bulk manner. This reduces the intensity and difficulty of on-site work, significantly speeds up the installation process, and has won high approval from owners and on-site workers. This vane-separated precision internal component set is an essential installation for gas-liquid separation and foam removal at the top of towers.

Part Three: New type of liquid dropping assembly resistant to “siphon short circuit”. Gas-liquid separators all require a liquid descent system to transport the separated liquid through a separate channel, thereby preventing secondary mixing between gas and liquid. Traditional gas-liquid separators use a simple downcomer inserted into a liquid seal chamber structure. Once the dimensions of the separator equipment are finalized, the lengths of the downcomer and the liquid seal cylinder are fixed. However, under actual operating conditions, the increased variability in the volumetric flow rate of the gas stream causes the actual operating pressure drop across the separation element to exceed the allowable limit; in some cases, local blockages within the separation element lead to a sharp rise in pressure drop. As a result, the pressure at the rear end of the separation element is significantly lower than the pressure at its inlet. Under this pressure difference, liquid is forced back into the downcomer and continuously flows toward the rear end of the separation element, creating a \"siphon shortcut\" effect. This leads to severe liquid contamination in the gas stream exiting the separator, far exceeding the limits permitted by the process requirements. In particular, a \"siphon short circuit\" can occur in the downcomer system of the compressor inlet separator, causing the airflow to become heavily laden with liquid in an instant, which has catastrophic effects on the compressor. In this solution, the truly efficient gas-liquid separator utilizes a new type of liquid dropping assembly equipped with anti-siphon short-circuit technology. Even when the actual flow volume of the gas increases significantly, the operating pressure drop exceeds the upper limit by tens of kilopascals, or there is localized blockage that leads to a sharp rise in pressure drop, a siphon short-circuit phenomenon does not occur. Thus, this technology upgrade effectively solves the problems associated with the simple liquid dropping tube + liquid seal chamber structure. This new anti-siphon short-circuit liquid dropping assembly is an essential component for the compressor inlet separator.

The internal component set for the vane-separated demister in this technical solution (pre-distributed coalescing component set + vane-separation precision component set + a new liquid-drop reduction system to prevent \"siphon short-circuiting\") represents a patented internal component set with an outstanding cost-performance ratio on the international stage. Its advanced performance and reliability are characterized as follows: First, it has a high design processing capacity, with an operating flexibility range of 15% to 130%, which exceeds the typical operating range of 50% to 110% for conventional separators. This represents the highest level of technical expertise among international peers in similar technologies. II. High separation efficiency and precision. Under normal operating conditions, the separation efficiency for droplets with a diameter of 4.7 microns and larger is 99.9%, which exceeds the owner’s requirement of 99.9% for droplets with a diameter of 10 microns and larger. III. The overall operating pressure is reduced. Under normal design conditions, the overall operating pressure drop is better than the owner’s specified requirements. IV. Low operating noise. Under normal design operating conditions, the overall operating noise of the separator does not exceed 50% of the industrially allowable noise level, which is far below the noise requirements for industrial equipment. Among international peers, only a very small number of specialized dynamic separation technology companies possess the capability to calculate and design for internal component noise. V. Significant technical advantages in resisting “siphon short circuits”. This technical solution employs a new type of liquid dropping assembly based on NOVEL’s proprietary technology against \"siphon short circuits\"; it prevents the occurrence of liquid phase \"siphon short circuits\" under various complex operating conditions, which can result from a sharp increase in the actual operating pressure drop in the separator and lead to liquid being carried in the gas stream, thereby causing damage to downstream pipelines and compression equipment. This new anti-siphon short-circuit liquid dropping assembly is an essential component of the compressor inlet separator, and it represents NOVEL’s proprietary technology on a global scale.