207-Technical solution for dry gas sealing gas compression unit inlet section in natural gas transmission pipeline booster stations: multi-factor swirl parent-child separator + coalescing vane mist remover – NOVEL

The project in question is part of the natural gas collection and transmission system at the first station of China’s West-to-East Gas Transmission Project; it is primarily responsible for cleaning, filtering, and increasing the pressure of the natural gas coming from upstream sources, thereby creating favorable technical conditions for the subsequent collection and transmission of this gas. The natural gas supplied to this station includes not only gas from abroad but also gas produced by the Tarim Oil Field, all of which are fed into the pipeline network for processing and transportation.

The owner reported that in recent years, this station has been affected by fluctuations in the operating conditions of the gas supplied from the Tarim oil and gas field, which have led to repeated shutdowns of the compression units and even damage to the dry gas seals, resulting in significant economic losses. Therefore, the owner decided to install high-efficiency pre-condensate removal devices in front of the 2 RR units on Line 2 West. Each such pre-condensate removal device consists of a primary multi-factor cyclone mother-son separator plus a secondary coalescing vane mist remover.

This post was last edited by luoli519 on 2023-3-23 at 13:55. The PID diagram provided by the design agency is attached here to facilitate further discussion.

Judging from the PID diagram provided by the design unit, it copies the process flow diagram of high-pressure pure hydrogen emitted by the pure hydrogen compressor unit of a certain project as the dry gas seal gas medium, without even making timely corrections to the names. The dry gas seal gas at this station is supplied by the natural gas flowing in, and its composition, as well as the components and quantities of condensate it contains, differ significantly from those of pure hydrogen. The designers need to have a clear understanding of this technological process and the corresponding separation technology and equipment solutions.

This post was last edited by luoli519 on 2022-8-12 at 14:52. Let’s first take a look at the first-stage cyclone separator in the flowchart of the design unit. An IN-LINE coaxial cyclone separator type is required, primarily used to separate and remove large-sized liquid droplets, mist, and particulates carried in the gas stream. The dimensions and processing capacity corresponding to the first-stage cyclone separator on the PID diagram are based on the data for pure hydrogen media; there is no correspondence for the dry gas sealing condition of the natural gas fluid mentioned in the question.

Take a look again at the secondary coalescing vane-type separator demister on the flowchart of the design unit. A separator of the composite type consisting of a vane separator and a candle-type coalescing filter element is required, primarily to precisely separate and remove tiny liquid droplets, mist, and particulates carried in the airflow. The dimensions and processing capacity of the second-stage coalescing vane-type demister shown on the PID diagram correspond to the data for pure hydrogen as the working medium; there is no corresponding value for the dry gas sealing condition using natural gas as the working medium as mentioned in the question.

In this post, the dry gas sealing gas for the natural gas boosting station uses natural gas as the working medium. The natural gas composition data provided by the design unit is shown in the attached figure:

The data sheet for the high-efficiency liquid removal device placed before the dry gas seal air compressor unit, provided by the design agency, is shown in this attached diagram:

According to the data sheet provided by the design firm for the high-efficiency liquid removal device installed before the dry gas seal gas compression unit, the maximum operating pressure under normal conditions is 10 MPaG, while the operating temperature is 45°C. The minimum processing capacity per unit is 1500 Nm^3/h. These values differ significantly from those indicated in the PID diagram on the 4th floor, where the maximum operating pressure for pure hydrogen is 9950 kPaG, the operating temperature is 65°C, and the minimum processing capacity per unit is 1450 Nm^3/h. Therefore, the equipment dimensions and processing capacity parameters for these two systems need to be treated separately.

One of the aspects that most tests the technical capabilities of separation technologies and equipment suppliers in this project is the fact that the design agency commissioned by the owner did not provide the physicochemical property parameters for the gas and liquid phases of the dry gas sealing gas under various operating conditions. In particular, there is a lack of data related to separation processes, such as the apparent density, viscosity, and surface tension of the condensates carried by natural gas – including condensate oil and liquid water – under respective operating conditions. The owner said that this requires professional separation technology companies with genuine technical design capabilities and database expertise; only by using their proprietary, precise dynamics separation technology system platforms and databases to supplement and refine these characteristic data can system design work be carried out.