Filters are widely used in petroleum and chemical industries. Solid impurities contained in gas and liquid phase materials are separated through filter elements to prevent equipment and pipe fittings from being damaged or blocked after entering the unit, to ensure regular and stable operation of production units. Therefore, how to design and use the filter correctly, safely, economically and reasonably is particularly important.Now, Let's introduce how to choose pipe filters and filtration systems. And their respective characteristics.
According to its structure, the filter is mainly divided into two types: pipeline type filter and equipment type filter. This paper will compare and differentiate the two types of filters in terms of structure, performance, and application scope.
Pipe Type Filter
Pipe type filter is a typical coarse filter in the petrochemical industry. It is a pipeline element that ensures the reqular operation of process equipment by filtering solid impurities. According to its structure, it is generally divided into Y-type, T-type, etc
The Y-type filter is usually installed at the inlet end of pressure reducing valve, constant water level valve or other equipment to remove impurities in the medium Y-type screen has the characteristics of advanced structure, low resistance and natural drainage.
The T-type filter is widely used in the pipeline of steam, air, water, oil and other media to protect all kinds of equipment on the pipeline system, such as pumps, valves, etc. from rust, welding slag and other sundries in the pipeline to block and damage the pipe. The T-type filter has the characteristics of strong anti-pollution performance, convenient drainage, large circulation area, small pressure loss, simple structure, low volume, etc.
The filter element inside the T-type filter is made of SS316L stainless steel，strong corrosion-resistance, long service life; the T-type filter is also divided into direct current type and baffle type, and the density of the filter screen is ten mesh - 120 mesh, temperature 0 ~ 450 ℃, can be selected according to user needs.
Selection Principle and Application Scope
The design and selection of pipeline filter are generally based on the nominal diameter of the inlet pipe, following SH / T 3411-1999 selection, inspection and acceptance of screen for petrochemical pump and HG / T 21637-1991 chemical pipeline filter：
- First, the filter type is selected according to the nature of medium, temperature and pressure
- The pressure level of the screen is generally one level higher than that of the medium in the pipeline
- For the medium with the high freezing point, high viscosity and more suspended solids, which needs to be purged frequently when the pipeline is shut down, it is better to select the horizontal backwash filter
- For a medium with more solid impurities and higher viscosity, basket filter is generally used
- For flammable, explosive and toxic media, the filter connected by butt welding should be used. When the pipe diameter is less than DN40, the screen connected by socket welding should be applied
- When the pipe is straight When the diameter is less than DN400, Y-type / T-type filters should be selected. When the pipe diameter is greater than or equal to dn400, T-type filters should be chosen
- When the pipe diameter is less than or equal to DN80, Y-type filter should be selected; when the pipe diameter is more excellent than DN80, T-type filter and temporary filter should be selected; when the pipe diameter is less than or equal to DN100, the cone-shaped screen should be chosen
Choice of Washable Filter Basket Specifications
The nominal diameter of the pipeline filter is generally DN15 ~ DN600. The filter basket made of single-layer stainless steel wire mesh is used as the filter element. The filter basket is made of 30 mesh/inch single-layer stainless steel wire mesh with filter accuracy as the standard mesh.
The mesh selection of the filter basket needs to meet the needs of the process or the protection function of the pump, compressor and other fluid conveying machinery Objective: the active filtering area of the filter basket is generally more than twice the cross-sectional area of the connected Pipe type filter. The wire diameter and aperture specification of stainless steel wire mesh shall be selected according to GB / T 53302003.
As a high-precision filter, the Filtering system is equipped with single or multiple filter elements. The equipment body is designed, manufactured, inspected and accepted according to the relevant standards of petrochemical pressure vessels.
Filter process design, as a critical step of equipment filter design, is generally based on medium process conditions, such as temperature, pressure, viscosity, density, flow, reliable impurity content, stable impurity process index at medium outlet, allowable pressure drop value, backwash requirements, instrument condition and other characteristic index requirements, etc., through determining filter element material and quantity, filter accuracy, equipment material and external structure size, and then design and manufacture the equipment shell according to the relevant standards of pressure vessel.
The pipeline filter is usually installed on the inlet of the pump, compressor or the front pipe of the flow instrument to protect the equipment or device, unless, in particular, circumstances, it can be placed on the outlet of the pump, for example, in the catalyst production process, it can be placed on the outlet pipe of the shoe. The equipment filter is usually installed at the battery limit of the production unit and the entrance of coalescer to protect the regular operation of the device and the service life and safety of the equipment.
The main differences between Filtering system and pipeline filter are different filter elements, filter precision, equipment size, equipment design and manufacturing requirements. Although the pipeline filter has the advantages of simple structure, low manufacturing cost and small equipment size, it has the problems of low filtering accuracy, small filtering area and low structural strength of filter basket.
However, the Filtering system, due to its large filtering area and settling time, high filtering accuracy and structural strength, long service life and online flushing and replacement of filter elements can effectively solve the related problems of the above pipeline type filter and is more suitable for the long-term and stable operation of the device.
But compared with the pipeline filter, the Filtering system has a higher manufacturing cost. In industrial application, it can be used safely, economically and reasonably according to the use situation, physical properties of the medium and the requirements of the production process