What Is a Duct Filter?

That is a gas pipeline filter.

Natural gas produced from the formation often contains sand and other solid impurities (such as rust), as well as harmful substances such as water, water vapor, sulfides and carbon dioxide. Dust particles such as sand and iron move with the airflow in the conveying pipeline, wear and tear the components of the compressor, the pipeline, and the instrument, causing damage and damage, and sometimes they gather in some parts, affecting the normal operation of the gas transmission; if the mixed water is collected in the The low-lying part of the pipeline will reduce the gas transmission cross-section of the pipeline, increase the gas transmission resistance, and also form a layer of water film on the inner wall of the pipeline. It will form an acidic aqueous solution when it encounters acid gases (H ₂ S, CO2, etc.), causing corrosion to the inner wall of the pipeline. Causes the pipeline to be damaged; mixed with water under certain temperature and pressure conditions can also form ice-snow-like hydrates with certain components of natural gas, causing pipeline ice blocking. Therefore, filtering out solid impurities and other harmful substances in the natural gas entering the transmission pipeline is an important task to ensure the safe operation of the gas pipeline.

The liquid and solid impurities in the natural gas transmission system mainly come from three aspects: one is the condensate oil, condensate water and rock cuttings dust brought out from the well during gas production; the other is the dirt (contamination) left in the pipeline during pipeline construction. Materials) and welding slag; the third is the corrosion products in the pipeline and related equipment and instruments. Generally, separators, dust collectors and filters are provided at gas collection stations, gas compression stations, gas distribution stations, pressure regulation and metering stations, etc. to remove various solid (liquid) body impurities. Natural gas pipeline filters are generally used to remove solid particles and droplets smaller than 5µm. The polyester fiber filter element used has a long life and high filtration efficiency. It has been widely used in domestic natural gas transmission projects with good results. ^[1]

Structure

The natural gas pipeline filter is mainly composed of internal and external components such as a housing, a quick-opening blind plate, a filter assembly, and a fluid reservoir, and generally adopts a horizontal structure. The filter assembly is composed of a filter element, a filter seat, a gland, and a partition. The housing is divided into a filter chamber and an exhaust chamber through the partition of the filter assembly. The core component is the filter element, which is fixed to the partition in a certain arrangement. On the filter element seat of the plate, the filter element is regularly replaced to ensure its filtering efficiency.

2.Working principle

Dust-containing (liquid) natural gas enters the filter chamber through the air inlet, and is trapped by the filtering, inertia, adhesion, diffusion, static electricity and other effects when passing through the filter layer of the filter element. The purified gas comes out of the filter element and is exhausted. The air outlet of the chamber is discharged, and the captured liquid droplets and solid particles enter the liquid accumulation tank under the action of gravity. When the liquid level gauge shows that the liquid accumulation is full, the sewage valve is opened and discharged through the sewage discharge port. ^[1]

The filter assembly of the filter includes a partition, a filter element seat, a draw rod, a filter element, a gland, and a flower plate. The partition is welded to the filter cylinder, and the filter cylinder is divided into a filter chamber and an exhaust chamber. The seat is welded on the partition plate, and the other parts are combined into a whole through a tie rod and a bolt. There are multiple filter elements distributed in the module, and the number of filter elements is calculated by the process according to the temperature, pressure, flow rate and natural gas physical parameters of the natural gas operation provided by the user. The filter element is arranged in a ring. This arrangement can evenly distribute the gas entering the filter chamber and ensure good fluidity of the medium. At the same time, in order to facilitate the replacement and maintenance of the filter element, the structural position of the filter element is reasonably determined. The distance between open blind plates is generally not more than 200mm.

The filter element uses polyester fiber as the filter material, which has the characteristics of high efficiency, environmental protection and decomposability after use. It is suitable for natural gas, oil field gas, gas and other gas filtration with high filtration accuracy. Generally, solid dust can reach 0.56µm and droplets can reach 0.3. µm. The filter element is a consumable product. Generally, the service life is not less than 14 months under the design conditions. In order to facilitate the replacement of the filter assembly, the filter is generally designed as a structure of a quick-opening blind plate, which can realize the safe and rapid opening of the filter. The quick-opening blind plate has a safety self-locking system and a pressure alarm system. It cannot be opened under the condition of residual pressure, which can prevent misoperation. The compound self-tight sealing structure is adopted, which has reliable performance and convenient maintenance. It does not require any special tools for opening and closing. It can be operated by one person and the opening of the quick-opening blind plate can be completed within 1 minute. ^[1]

Natural gas filter is a pressure vessel. With the increase of natural gas delivery pressure, the general design pressure of the filter is more than 10MPa, and the manufacturing requirements are higher. In addition to the strict manufacturing inspection in accordance with GB150 "pressure vessel" standard, the manufacturing process should also pay attention to the following: A few points:

The first is the group welding of quick-opening blind plates. The quick opening blind plate is connected to the cylinder by welding. The roundness of the cylinder and the pair gap should be strictly controlled during the pairing process. When welding is performed by electrode arc welding, welding is symmetrical to prevent deformation and affect the sealing performance of the quick opening blind plate .

The second is the group welding of filter components. The filter assembly contains more filter elements. The filter element seat of each filter element needs to be welded to the separator. When welding with the separator, rigid fixing measures and a reasonable welding sequence are used to reduce welding deformation; Filter element, to ensure that the filter element is installed vertically with the partition, so that the gland can press the filter element to ensure its tightness.

The third is to clean up. After the filter is manufactured, its interior should be cleaned to ensure that the interior is clean and dry. ^[1]