The necessary technical device of the gas distribution system is a gas filter - a device that performs the functions of elementary cleaning of the working medium from contamination. But how does it work and can you do without it? This is what we will talk about in our publication - we will consider the design features of filters, their varieties.
We will also give recommendations on the correct choice of a suitable option, based on the characteristics of the operation. In addition to the material presented, we will select illustrative photos, diagrams and thematic videos.
The content of the article:
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Filter design and features
- How does a gas filter work from the inside?
- Differential pressure and principle of operation
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Optimal pressure drop control
- Option # 1 - single pointer indicator
- Option # 2 - indicator with two arrows
- Features of the choice of a gas filter
- Conclusions and useful video on the topic
Filter design and features
Elements such as filters installed on the line ensure long-term operation of instrumentation, valves and other significant components. Therefore, equipping gas systems with filter elements is not only desirable, but a prerequisite, given the technological features.
using household gas.Despite the apparent external simplicity of execution, gas filters are quite diverse in technical and operational terms. So, in practice, devices are used that are structural performance should be conditionally subdivided into corner and linear.
The photo shows an angle-type filter element designed for the transport of a gas flow. This is one of the existing variations of the range of devices of this kind.
In addition, differences in the designs of gas filters are also manifested by direction of travel gas flow through the device. Accordingly, there are two types of execution: straight-through and turning.
Traditionally, the body part of gas filters is made of metals - cast iron, steel, aluminum, and here you should also consider the variety hull structures.
Finally, gas filters are also divided according to such a criterion as filtration material:
- reticulate;
- cassette.
The first option is characterized by metal grid, woven from a thin wire.
In the second case, we are usually talking about special rammed cassetteswhere a thin nylon thread or horsehair is used. These materials are additionally impregnated with a special (viscin) oil.
Viscinic oil is a product traditionally used to treat cassette filter elements in order to ensure efficiency. It is used not only for natural gas filtration devices, but also in other systems
The filter material used in the construction of gas filters must have appropriate chemical and physical properties, provide physical resistance to the working environment. All these nuances are taken into account during development and design.
How does a gas filter work from the inside?
Regardless of the variety of gas filters, almost all have a similar internal technological system, with the exception of some individual details.
The picture below shows diagrams of typical gas filters that are widely used in the operation of gas networks.
The internal structure of a gas filter on the example of two widespread devices - mesh and cassette: 1 - cover; 2 - body part; 3 - wire mesh; 4, 5 - cassette stuffed with horsehair or silk thread; 6 - branch pipe (outlet)
Some subtleties of the internal design should be noted. For example, metal mesh filters have an inherent factor of increasing the degree of fineness of cleaning due to the accumulation of blockages. At the same time, the throughput of the filter element is correspondingly reduced. This effect is especially pronounced in multilayer structures.
In case of cassette systems, where horsehair is used as a filter element, on the contrary, the degree of purification fineness is weakened. This is due to the fact that the passing gas flow during the operation of the device gradually carries away part of the filter material in the form of small particles.
Therefore, in order to reduce the amount of carried away particles and maintain effective filtration, they strive to select the optimal speed of movement of the working medium when operating cassette-type filters.
Differential pressure and principle of operation
In general, the limit values for differential pressure when using gas filters should be 5,000 Pa (for mesh elements) and 10,000 Pa (for cassette-type elements).
Accordingly, at the time of the start of operation of any type of gas filter, these parameters must correspond to the numbers:
- 2,000 - 2,500 Pa (for mesh elements);
- 4,000 - 5,000 Pa (for cassette-type elements).
It is not difficult to describe the operation of the filter mesh mechanism: the household gas passing through the pipeline system meets the filter on its way and passes into the device through the inlet pipe.
Penetrating through the metal mesh, the household gas is cleaned of foreign contents and then passes to the outlet pipe.
Linear cassette household gas filter and replaceable cassette in case of complete failure of the filtering material of the cassette in operation with the filter
The debris trapped by the mesh falls into the lower area of the mesh filter housing (in some designs) or is forcibly cleaned out. During maintenance, the debris accumulated in the bottom area is removed through the hole, which remains closed with a plug at the time of filter operation.
The cassette filter element works somewhat more "sophisticated", taking into account the peculiarities of the material used. A cassette filled with hair is placed inside the filter along the working medium. Additionally, a bump stop is installed in front of it - a metal plate that protects the cassette from damage by large foreign bodies of a rigid structure.
The device of such a cassette is simple - it is usually a rectangular (tubular) frame, the outer parts of which are covered with a wire mesh. The inner area of the frame is filled with filamentary nylon or natural (horsehair) material. When filling, a homogeneous material is tightly packed and additional lubricant is added.
The gas passing through such a cassette is cleaned of foreign contents and enters the perforated metal grate. This is another component of the cassette filter that prevents particles of the filter material from being carried into the system.
As the cassette becomes clogged, it is removed during maintenance and cleaned / rinsed with special solvents.
Optimal pressure drop control
Almost all gas filter designs provide differential pressure control. Some designs (usually of an outdated sample) are equipped with fittings for such purposes, where an indicator is provided.
One of the designs of the gas filter that uses a differential pressure indicator. To connect it, there are fittings in the device case
Other, more modern products are equipped with an indicator element directly. Such an element is built into the body of the device and is an information scale, as a rule, divided by color zones (green and red). There are indicators with one and two pointers.
Option # 1 - single pointer indicator
Under normal operating conditions of the gas filter, the indicator pointer is in the green area, which clearly shows the optimal level of pressure drop.
If the indicator arrow moves to the area of the scale, colored red, this factor signals that the filter is clogged.
On such differential indicators, the primary attention of the maintenance personnel is given to the red segment of the scale and the corresponding indicator. When the red arrow is present in the area of the red segment, the filter is subject to preventive maintenance followed by cleaning or replacing the filter material.
Option # 2 - indicator with two arrows
For this version, the control bar is divided into two segments, colored black and red. The directional elements (arrows) also correspond to the colors of the segments.
The black colored area is intended to control the pressure drop at the current time. The red area is used to control the difference at times of maximum consumption.
Built-in indicator that fixes the level of the differential pressure with two arrows on two segments: 1 - the current level of the differential; 2 - the achieved level of the difference at the maximum consumption; 3 - manual reset point of the red pointer (during maintenance)
The peculiarities of such indicators are that if the pointer of the black segment of the scale has the ability to return to the direction of the origin, the pointer of the red segment is not endowed with such ability.
If an overestimated differential is recorded by the red pointer, the arrow (red) will irrevocably stop at the reached mark. Return to zero is only possible manually during service.
Features of the choice of a gas filter
When choosing a suitable gas filter, the following features should be taken into account:
- pipeline diameterwhere the installation is supposed to be;
- gas consumption (calculated parameter);
- pressure - you need to know the value of the absolute pressure at the inlet of the filtering device;
- density - it is desirable to have data on the density of the gaseous medium.
Filtering devices from different manufacturers differ in appearance and characteristics. However, each product is labeled accordingly. The marking allows you to select a filter taking into account the main criteria.
Marking on the FN series gas filter: 1 - series marker; 2 - mounting dimensions (in inches); 3 - working pressure (nominal), bar; 4 - device performance class; 5 - presence (absence) of a built-in indicator; 6 - material of the device body
In order to maintain a sufficient degree of cleaning by the filter element, usually the selection takes into account the limitation of the flow rate of the medium passing through the filter device.
The speed parameter is usually determined by the parameter of the maximum allowable pressure drop. If the filter is clean, then the difference is allowed at a level of no more than 50% of the maximum allowable value.
Usually, in order to accurately select a filter for a gas pipe, it is convenient to use special tables. If access to the tables is not possible or a unique selection is required, it is logical to use the calculation formula shown in the figure below.
Calculation formula for gas filter selection: Qm - device throughput, m3 / h; P is the value of the inlet pressure, kPa; Pm - pressure value on the filter, kPa; p is the value of the density of the gaseous medium
Traditionally, the choice of a gas filter has been compared with diameter line pipeline on which the device is supposed to be installed. In this case, the throughput of the device is associated with the flow parameters at the gas distribution point - they are guided by a similar value or higher.
Conclusions and useful video on the topic
Video about gas filters, their features and the need to use them:
The operation of gas lines without the use of filters will be ineffective and impractical. Under such operating conditions, there is a risk of rapid failure of technological equipment, which affects the economic side of the systems operation. Of course, the absence of filters affects the safety of the equipment.
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