The design and operation of the bag filter: the pros and cons + features of replacing the filter bag

Of course, compliance with environmental standards is an important condition for the successful and safe functioning of any production. The purification of air contaminated with processed products is the main requirement for mining, cement, chemical, flour, metallurgical and other enterprises, in the process of which a large amount of dust, soot and other microscopic pollutants is generated.

But modern cleaning structures can effectively solve the problem of excessive dustiness of the air: the device and the operation of the bag filter are aimed specifically at removing the smallest particles of harmful suspensions. After installing this unit, all dust and dirt settle on the walls of the filter, and lighter and free of impurities air is emitted into the atmosphere.

In this material, we will consider the structure and principles of the bag filter, learn about how to self-regenerate and replace them, and also reveal the advantages and disadvantages of this cleaning design.

The need for air purification in production

The environmental crisis on the planet is aggravated every day. Manufacturing enterprises play an important role in this: chemical leakage, pollution of water bodies by sewage and dust emissions adversely affect both the state of nature and human health.

In addition to direct harm to workers and residents living near production, dust causes damage to the enterprise itself. Dust deposits adversely affect the operation of the equipment, worsens the conditionventilation system and heat exchangers.These factors can lead to a decrease in the quality of manufactured products and even increase their cost due to breakdowns and faster wear of the equipment used.

Dust suppression in enterprises is organized by various methods. In addition to capturing the suspension with special filters, a fogging system can be used, thanks to which dirt particles settle together with microdrops of water

That is why high-quality dust collection and neutralization is an integral stage of the entire technological process in production. The bag filter effectively copes with the tasks and protects not only nature and people, but also the equipment of the enterprise.

How is the bag filter arranged and working?

Cleaning equipment with a bag filter can be used as part of internal ventilation, providing for the return of purified air back to the room, as well as a system of complete air purification before it is discharged into the environment.

Bag filter is a fairly simple design, which consists of the main elements:

• housings for filter units;
• chambers for clean and dirty air;
• hoppers and supports;
• an inlet valve through which the air mixture passes;
• a cleaning sleeve or a complex of sleeves that are located in the air path;
• an outlet valve with a pressure regulator passing through the cleaned stream;
• filter regeneration system, which allows you to periodically clean the sleeve from dust.

The design of the device is designed to pass a sufficiently large amount of air or gas. Flows carried away by the inlet valve pass through the system, leaving particles of dust or soot on the surface of the filter on a woven or non-woven basis.

The diagram above illustrates the structure of the bag filter and the direction of flow of contaminated and purified air through the air purification system

The filter can be single, but complexes with a battery of sleeves, which more effectively clean the air, remain more effective. After the sleeve, the recycled air is discharged through an outlet valve equipped with automatic equipment for regulating the pressure.

In fact, the design performs three main tasks:

• qualitatively cleans the gas-air mixture from pollutants;
• provides uniformity of dust loading;
• adjusts the amount of air coming in for filtering.

The separation of small particles in the exhaust air makes it possible to ensure the proper purity of the exhaust stream. Unwanted suspensions are firmly held inside the sleeve, which is self-cleaning during the regeneration phase.

The main types of filter bags

The selection of a suitable bag filter is based on the characteristics of the production and the nature of the dust produced during its process. The main criteria that should be relied upon in the selection of this equipment are the performance of the installation and the depth of purification of the incoming air. The remaining parameters are individual: the degree of their importance depends on the production conditions.

For example, the choice of material from which the filter is made depends entirely on the characteristics of dust pollutants that occur during production.

No. 1: Difference in equipment performance

Bag filters are divided into two main types: round and flat. The first type is designed for operation in enterprises with a large dust load and is capable of passing and cleaning quite serious volumes of air: more than 100 thousand m³ in hour.

However, the operation of such productive equipment requires an additional supply of compressed air to the system. Flow rates can reach 4000 liters per minute

Flat sleeves have more modest performance, but they also have a more compact design.Such cleaning systems are suitable for workshops with a small dust load.

No. 2: Classification by the type of installation of hoses

By the type of installation, systems with bag filters can be vertical or horizontal. The latter remain more effective as they let in more air or gas.

The flow path along the sleeve itself is quite long, so the pores of the filter material trap more pollutants.

Sleeves are also distinguished in shape: ellipsoidal, cylindrical, rectangular.

No. 3: Varieties by material of manufacture

The classification and principle of operation of the bag filter is also affected by the material from which the filter element is made. Often it is made of fabric.

The material from which the bag filter is made directly affects the wear resistance of the equipment. Some types of fabrics are less prone to tearing and depressurization, which contributes to a more rare filter

It can be either natural cotton or wool, or synthetic materials:

• polyester;
• fiberglass;
• polyamide;
• meta-aramid;
• polytetrafluoroethylene;
• polyacrylonitrile, etc.

The choice of sleeve material is based on the type of production, the characteristics of the mixture being filtered, the dispersion and the properties of dust, and the aggressiveness of the medium.

Recently, nonwoven filters with a more uniform and finely porous structure, which retain more pollutants due to the fibrous surface, have been especially popular.

No. 4: Classification by the method of regeneration

The filter recovery method can be considered another classification category for these devices. The regeneration of the hose assembly is an important stage in the construction, so it is worth paying special attention to it.

The most popular bag filter regeneration method is pulse purge, as shown in the diagram above. However, this method of purification is not suitable for all types of industries.

In fact, regeneration is a process of cleaning the sleeve of accumulated dirt.

The procedure can be carried out by several methods, the choice of which depends on the nature of the dust:

1. Vibrocleaningduring which the sleeve or battery of the sleeves is shaken intensively, after which the particles of impurities fall into a special hopper for subsequent removal. Dust is removed from it by means of a dust transport system: a screw or pneumatic conveyor, a rotary vestibule, a scraper chain, a slide gate or a valve.
2. Pulse purge or air purification. The filter is subjected to pulsed purging or pneumatic cleaning using a reverse air flow, which knocks out microparticles from the pores.
3. Combined cleaning. The battery or single sleeve is subjected to combined cleaning, during which the filter is shaken and surrounded by streams of clean air.

Vibro-cleaning can occur not only automatically: the regeneration process is sometimes carried out manually thanks to a special handle and is called mechanical cleaning of the sleeve.

But most often, the regeneration process is carried out automatically due to the work of pollution sensors, which respond to the amount of litter collected and determine the pressure and throughput of the sleeve. If the pressure at the outlet of the structure drops, the sensor starts the purge process or the shaking mechanism.

Regeneration is systematic and can significantly extend the life of the bag filter. On average, the use of the filter element can reach three years.

With a low dust load in a non-aggressive environment in a small production area, the full functioning of the bag filter can reach five years, after which it will need to be replaced regularly.

Bag Filter Replacement Features

Like the installation, the replacement of used filters is carried out on the basis of design documentation and the conditions in which the cleaning device operates.

Many key factors are taken into account:

• dust load;
• dispersion of dust and its quality;
• characteristics of the working environment;
• filter performance;
• place of installation;
• mixture cleaning depth, etc.

If only one sleeve is out of order in the battery, you can cut off its operation without replacement. To do this, the filter is clogged at the level of the tube sheet. There is no need to remove the purge pipe or frame.

The bag filter is replaced after it is completely worn out or the regeneration efficiency decreases. If through holes form in the material, replacement can take place much earlier than the due date.

If the node requires a complete replacement, you must perform the following steps:

1. Close the shutters at the entrance and exit to the compartment, if this is provided for by the design features of the system.
2. Through the inspection window, remove the purge pipe leading to the replaceable sleeve or battery.
3. Remove the sleeve frame.
4. Remove the sleeve from the structure. It can be lifted along the tube sheet or dumped into the dust bin. In the latter case, the filter will need to be removed from the compartment through the inspection window.
5. Install the new sleeve in the reverse order. After connecting, fasten the frame, lead the purge pipe.

After replacement measures, it is necessary to carry out a test run of the equipment to make sure that it is working.

It is better to entrust a replacement to a specialized company whose employees have the skills and experience in removing and installing bag filters.

We also have an article on the site with detailed instructions on replacing the filter in the supply ventilation.

Advantages and disadvantages of devices

Like any other cleaning equipment and systems, for example, aspirationThe bag filter has its own operating features, during which the characteristic advantages and disadvantages of the system are identified.

The advantages of this complex are much greater than flaws, so bag filters are widely used in various fields of production.

The arrangement of a ventilation system with a bag filter is suitable not only for large-scale and complex production, for example, in the metallurgical industry. A similar air filtration system is appropriate in small workshops for the production of furniture, paving slabs and other

The indisputable advantages of bag filters include the following features:

1. The design is universal, therefore it is easily integrated into the ventilation and purification systems of various industrial sectors.
2. The complex with a bag filter is easily integrated into the production line and is not very demanding on the amount of space required for its arrangement.
3. The degree of purification of the gas-air mixture reaches 90-99%, which is an extremely high indicator for the dry cleaning system.
4. Filtration is equally effective both at extremely low air temperature, and in a heated room.
5. Management of the complex is very simple and can be fully automated.
6. Scheduled replacement of used bag filters is carried out once every two to three years.

In addition to the advantages, the bag filter has minor disadvantages. The main one is the need for compressed air supply in conditions of filtration of air volumes of more than 150 m³ in hour.

For certain types of production or aggressive operating conditions, filters from expensive materials, such as fiberglass or meta-aramid, which are more resistant to wear, may be needed.

Other types of filters are also used in the ventilation system. Read more about air and coal filtration systems. in the next article.

Conclusions and useful video on the topic

The structure and principle of operation of the cleaning system with a bag filter is clearly shown in the video below:

The process of testing the sleeves and the filter cleaning mechanism was demonstrated by the manufacturer of cleaning equipment:

Bag filter is one of the simplest and most effective ways to dry clean air from dust of various origin. A universal system can be successfully integrated into almost any technological process, during which large volumes of filtration medium are formed, requiring the maximum removal of unwanted suspensions. Sleeves are quite simple to replace, do not require complicated or expensive maintenance. Therefore, the owners of production facilities should definitely look at this type of purification of exhaust air.

Do you want to supplement the above material with useful information or talk about the features of the use of filters based on personal experience? Write your comments and additions, ask questions to our experts - the feedback block is located below.