Types of dust collection systems

Depending on the physical principle of operation, industrial separators are classified into dry mechanical, wet scrubbers, electric precipitators and bag filters. Figure 3 shows the classification of separators.

Table 3. Classification of separators

Dry mechanical separators

Dry mechanical separators are one of the most widely used dust collectors in industry. This type of device is characterized by its simple design and ease of maintenance and repair. However, when used alone, dry mechanical separators have low final efficiency. Therefore, the most common is a combination of a number of separator types or as multi-stage separators.

Dry mechanical separators are classified according to the type of aeromechanical forces involved. There are gravitational, inertial and centrifugal dust settling chambers.

In gravitational dust settling chambers, particle deposition occurs due to gravitational forces (Fig. 1). The advantages of this type of device are ease of manufacture and operation. But the efficiency values ​​of such installations are small, and the space they occupy is significant. That's why this type Dust collectors are rarely used, except in cases in which they are pre-collectors for other separators, i.e. perform a pre-cleaning function.

Rice. 3. Dust settling chamber: a - simple camera; b - chamber with partitions; c - multi-shelf chamber; 1 - body; 2 - bunkers; 3 - partition; 4 - shelf

The dust deposition rate of dry mechanical dust collectors is calculated as follows:

Where X h- particle sedimentation speed, m/s; d h - particle diameter, m; sch- particle density, kg/m3; sg- gas density, kg/m3; g- acceleration free fall, m/s 2 ; O h- particle drag coefficient.

The minimum size of dust particles that will be completely deposited by gravity is found using Stokes' law using the following relationship:

Where V G- volumetric gas flow, m 3 /m; m G - dynamic viscosity coefficient, Pa s; B, L- width and length of the chamber, m.

The next type of dry dust collectors are inertial dust collectors. In these types of devices, dust particles, under the influence of inertial force, will move in the same direction and, after a sharp turn, fall into the hopper. Unfortunately, the effectiveness of such devices is low. Chambers with smooth rotation have the least hydraulic resistance. With particle sizes of 25-30 microns, the degree of particle capture reaches 65-80%. Figure 2 shows different kinds dust collectors.

Rice. 4. Inertial dust collectors: a - with a partition; b - with a smooth rotation of the gas flow; c - with an expanding cone; g - with lateral gas supply

One of the commonly used dust collectors is cyclone dust collectors. Cyclone dust collectors are less commonly used individually due to their low efficiency. Cases of single use of this type of filter are possible if the functionality or reliability of other types of separators is unsatisfactory. The following requirements are imposed on cyclone dust collectors: optimal separation efficiency under variable production parameters, taking into account low requirements for maintenance and repair of permanently operating installations, resistance to abrasive wear, high temperatures, accumulation of adhering dust, provision of preventive measures against the explosion of flammable dust, small space and etc.

The main geometric characteristic of this type of apparatus is its diameter. With large diameters their throughput decreases. Therefore, cyclones of small diameters (150 - 630 mm) are usually used.

If it is necessary to clean the gas flow with a large throughput A series of parallel installed cyclones with a diameter of 475 - 2500 mm are used.

To determine the separation efficiency in cyclone separators, the total separation efficiency obtained on the basis of experimental data is calculated. This calculation gives the most accurate result. To get more high efficiency, small-diameter separators are grouped into blocks consisting of 2 to 12 separate cyclones.

The main advantages of cyclone devices are: 1) the absence of moving parts in the device; 2) reliable operation at gas temperatures up to 500 °C; 3) the ability to capture abrasive materials during protection internal surfaces cyclones with special coatings; 4) dry dust collection; 5) almost constant hydraulic resistance of the apparatus; 6) successful work at high pressures gases; 7) ease of manufacture; 8) maintaining high fractional cleaning efficiency with increasing dust content of gases. The disadvantages are: 1) high hydraulic resistance: 1250 - 1500 Pa; 2) poor capture of particles of size< 5 мкм ; 3) невозможность использования для очистки газов от липких загрязнений.

The main types of cyclones are shown in Fig. 3:

Rice. 5. The main types of cyclones (for gas supply): a - spiral; b - tangential; c - helical; g, d - axial (rosette)

The efficiency of collecting dust particles in a cyclone separator is directly proportional to the gas velocity to the power of S and inversely proportional to the diameter of the apparatus, also to the power of S.

In practice, cylindrical and conical cyclones are most often used. At the same time, cylindrical cyclones are highly productive, and conical ones are highly efficient. The diameter of cylindrical cyclones does not exceed 2000 mm, and the diameter of conical cyclones does not exceed 3000 mm.

The hydraulic resistance of single cyclones is determined by the formula:

Where X G- gas velocity in an arbitrary section of the apparatus, relative to which the value is calculated O ts, m/s; O ts- resistance coefficient, which is determined as follows:

Where K 1 - coefficient correspondingly equal to 16 for cyclones with tangential gas inlet and 7.5 for cyclones with rosette inlet; h 1 ,b- dimensions of the inlet pipe, m; D TR- exhaust pipe diameter, m.

The resistance coefficient for group cyclones is calculated using the following relationship:

Where O ts- coefficient of hydraulic resistance of a single cyclone; D TR- coefficient taking into account additional pressure losses associated with the arrangement of cyclones in a group (tabular value).

Another type of dry dust collectors is vortex dust collectors. Their main difference from the previous type is the presence of an auxiliary swirling gas flow. Fresh gas can be used as a secondary gas flow in vortex dust collectors. atmospheric air. When using dusty gases as a secondary gas, the productivity of the device increases by 40 - 65% without a noticeable decrease in cleaning efficiency. The critical diameter of particles completely captured in the dust collector is determined by formula 15:

Where X G- gas velocity in the free section of the apparatus, m/s; H- height of the dust collection chamber, m; D up- apparatus diameter, m; D tr- diameter of the supply pipe, m; sch- rotation speed, m/s.

Advantages of vortex dust collectors compared to cyclone ones:

• 1) higher efficiency of collecting highly dispersed dust;
• 2) absence of abrasive wear of internal heating surfaces;
• 3) the possibility of gas purification at higher temperatures due to the use of cold gas;
• 4) the ability to regulate the separation process by changing the amount of secondary gas. Disadvantages of this type dust collectors:
• 1) the need to use an additional blowing device;
• 2) increasing the total volume of gases passing through the separator due to secondary air;
• 3) the device is very difficult to operate.

Below are the characteristic parameters of dry mechanical dust collectors.

Table 4. Characteristic parameters of dry mechanical dust collectors

If you do not take special measures to remove mechanical waste and dusty air from working area woodworking machine, the surrounding space soon after the start of work becomes unsuitable for a person not equipped by individual means protection, and extremely fire hazardous. Dust collection (aspiration) installations are aimed at cleaning the atmosphere of the production room and making the work of personnel comfortable and safe.

APPLICATION AREA

Autonomous dust collection (aspiration) devices are used in industrial premises, which are equipped with centralized system air purification and waste removal seems impossible or impractical. Such installations are used mainly in areas for processing wood and similar materials of small enterprises in the furniture, construction and other industries.

DESIGN FEATURES

Structurally, the cleaning scheme for the mixture of air with shavings and sawdust removed from the machining zone by an exhaust fan creating a vacuum involves filtering it by passing it through a layer of fabric from which the receiving container is made. The solid component of the mixture separated by the filter is deposited in the lower part of the device, which acts as a waste storage tank.

High degree air purification, reaching 99.9%, frees workers from the need to use individual protective devices(respirators, etc.) and reduce the level fire danger up to the standard level.

The design of most modern woodworking machines provides the possibility of connecting them to a workshop aspiration system or to dust collection unit.

Dust collecting devices are equipped with either one or several filter blocks, consisting of stacked fabric bags: filter and storage. Depending on the volume of waste emitted by the equipment, you can select an installation of appropriate productivity. As a rule, several emission sources can be connected to one unit.

Many models of dust collection units can be used in vacuum cleaner mode when cleaning a production area.

MAIN ADVANTAGES

Steel dust collection systems mandatory element organization of woodworking production. Without such devices it is impossible to fulfill the established sanitary standards requirements for working conditions and ensure compliance with fire safety standards.

Ventilation dust collection units UVP (Individual chip ejectors UVP-IN series) designed to remove and clean air from shavings and sawdust and collect waste in storage bags. Chip ejectors are designed for use in small enterprises with a small amount of waste generated. The degree of air purification by the installations is 99.9%. The units are used to remove contaminated air from individual machines or groups of machines and have an air capacity of up to 7000 m 3 /hour. Due to the design, the distance from the machine to the chip ejector, as a rule, should not exceed 2 m. The installation consists of a housing with a built-in dust fan; filters and waste storage devices are attached to the housing using easily removable clamps.

CHARACTERISTICS OF CHIP EXTRACTORS UVP:

Productivity, m3/hour
Air flow speed at the inlet, not less than m/sec.
Created vacuum, Pa
Degree of air purification, %
Number and diameter of air ducts, pcs./mm
Number and total volume of drives, pcs./m3
Overall dimensions of the installation, mm (length x width x height)					2450x1050x2500	Z090x1050x2540
Weight no more, kg
Electric motor power, kW

Execution options.

• To purify the air from sawdust, shavings, chipboard sawdust, plastics, etc.
• To clean the air from sawdust, dust generated as a result of processing milling machines MDF and similar materials with increased filtering area.
  When using IN series installations to purify air from shavings, sawdust, dust resulting from the processing of MDF, chipboard, fiberboard and other materials in which the proportion of light fine fraction in the waste composition is relatively high, it is recommended to use filters with an increased filtration area. An increase in area is necessary to reduce the gas and dust load on the filter material. This prevents dust particles from penetrating deeply into the material and increases the service life of the filter. The units are intended for indoor use.

Aspiration is a process in rooms with high dust levels. Such areas are equipped with special filtration equipment. In particular, they are used. The premises of a variety of enterprises are equipped with such equipment: from factories for the industrial production of bricks to grain processing plants. Let's look further at what types of dust collection units (UVP).

Classification characteristics

Dust collection (UVP) is equipment designed to filter air. The separation of impurities is carried out in special filters.

Depending on the mechanism of action, these elements are divided into:

1. Gravitational.
2. Wet.
3. Electrical.
4. Oily.
5. Inertial.
6. Porous.
7. Combined.
8. Acoustic.
9. Fabric, etc.

Main types of equipment

Depending on the degree of filtration, installations can be:

1. Rough cleaning. The efficiency of particle retention in such equipment is 40-70%. Such units include large-sized cyclones and sediment chambers.
2. Medium cleaning. They provide particle retention of 70-90%. This category includes louvered, rotary units, cyclones, etc.
3. Fine cleaning. In them, the particle retention rate can reach 90-99.9%. This group includes hose, electric, roll, cell, foam units, etc.

Depending on the areas of application, the devices are divided into 2 categories. The first includes units used for filtering ventilation and industrial emissions into the atmosphere, the second includes devices designed to clean flow streams, as well as air masses returned to the workshop during recirculation. Businesses can use different dust collection systems at the same time. The price of equipment ranges from 36 to 400 thousand rubles.

Technical and economic indicators

They determine how effective it is at a particular enterprise. Key technical and economic indicators include:

1. Dust capacity.
2. Hydraulic resistance.
3. Performance.
4. Dust collection efficiency (fractional and total).
5. Cost of filtration.
6. Maintenance costs.

Comparative characteristics

The simplest is considered to be one whose mechanism of action is based on gravity. As a rule, it involves coarse filtration. The particle capture efficiency is no more than 50%. In this case, elements larger than 50 microns are absorbed. Cyclone - more effective. In it, filtration is based on the use of centrifugal force. During the rotation process, particles of substances are thrown towards the walls of the unit, and then fall into a special bunker. Purified air, rotating, leaves the installation through a pipe. The filtration efficiency of cyclones today is 80-90%.

Currently, such units have the most different designs. If it is necessary to clean a large volume of air flow, several devices are combined into groups or battery cyclones are used. They are presented in the form of a large number of small units installed in one housing and placed on one bunker. The most popular today, however, are wet dust collectors. Due to contact with the liquid medium, the particles are wetted and enlarged, and then removed from the apparatus in the form of sludge. Such units can have very different designs. For example, these could be rotary cyclones, disintegrators, and so on.

Foam units also belong to the class of wet installations. They supply water to a perforated grid. Filtered air also passes through it. A threshold (drain partition) is provided on the grille. It allows you to maintain a certain thickness of the foam layer. This one is different high efficiency- up to 99%. The unit is capable of filtering particles larger than 15 microns. The industry produces PGP-LTI and PGS-LTI devices with a capacity of 3-50 thousand m/h.

Scheme

Foam includes:

1. Receiving box.
2. Frame.
3. Lattice.
4. Threshold.
5. Drain box.

Has the following design:

1. Inlet pipe.
2. Sleeve.
3. Suspension.
4. Shaking mechanism.
5. Outlet pipe.
6. Bunker.

The electrostatic precipitator consists of:

1. Inlet pipe.
2. Corona electrode.
3. Filter housings (collection electrode).
4. Outlet pipe.
5. Bunker.
6. Rectifier.

Mechanism of action

Sleeve mouth dust-collecting ventilation unit filters air through fabric. It is stitched in a special way and placed in a sealed casing of the device. The air being cleaned is sucked out of the filter by a fan and released into the atmosphere. The hoses are periodically cleaned using a shaking mechanism with backflow. Filters can be of pressure and suction type. For their manufacture, dense synthetic or natural fabric. The efficiency of the hoses is 95-99%. In practice, the most common filters are FTNS, FRM, FVK.

Electrical devices are widely used in the purification of industrial and ventilation emissions. The mechanism of their operation is based on the following: when gas is passed between two differently charged plates, ionization of the air occurs. Ions and dust particles collide, the latter receive electric charges. Under their influence, they begin to move towards the electrodes opposite sign and settle there. The filtration efficiency in such devices is 99.9%. Electrical installations are considered economical to operate. They can filter streams at temperatures up to 450 degrees. However, electrical installations must not be used to capture explosive particles.

Specifics of aspiration

This process involves not just removing dust from the air, but also further purifying it. The system functions in such a way that it prevents the accumulation of particles and the creation of traffic jams. This ensures uninterrupted operation of personnel and equipment in the premises. Taking into account the huge volume of waste in industrial enterprises, we can conclude that aspiration is becoming even more in demand due to established standards Occupational health and safety when personnel work in hazardous conditions.

This method differs from other methods of indoor air purification in that the systems are located at a certain angle. This prevents the formation of stagnant zones and localizes areas of maximum pollution release. As a result, filtering is implemented. The concentration of harmful compounds does not exceed acceptable limits.

Chip suckers

They are used not only in the chemical and metallurgical industries, but also in woodworking, grinding and crushing shops. In such premises, installation of filtering equipment requires special knowledge, so professionals are invited to install it. The design of an aspiration system begins with an examination of the premises. Based on it, a preliminary calculation of the power and size of the equipment is made. IN furniture production There is a huge volume of fine waste. They must be removed from the workspace without fail. For this purpose, a chip suction system is used. The equipment is considered a type of aspiration apparatus.

The chip ejector can remove particles with a diameter of up to 5 microns. The cyclone equipment contains a special fan and filtered bags. A separate machine is connected to the chip ejector using a flexible duct system made of reinforced or corrugated pipe. The operating principle is quite simple. The fan sucks in polluted air, which is filtered. Dust particles are collected in a bag. From there they are sent to a special filter for final cleaning. When the bag is full, the bag is removed and cleaned or replaced with a new one. Chip ejectors are easy to connect and easy to transport.

Requirements

The devices must function uninterruptedly, reliably, with indicators corresponding to the design or obtained during commissioning activities and agreed with the developer. Gas purification installations must be equipped with auxiliary devices and equipment. When using such units responsible persons maintain documentation. It reflects the main indicators by which the operating mode of the equipment is characterized. In particular, we are talking about deviation from optimal scheme operation, identified malfunctions, failure of individual devices or the entire complex as a whole, etc. All units must be registered with the State Inspectorate for Gas Purification. At least once every six months, units must be inspected to assess their technical condition. This procedure is carried out by a commission appointed by the head of the enterprise.

General rules for the operation of gas purification and dust collection plants

Not allowed to use technological equipment with the filter devices turned off. In each case of turning off the cleaning device while the machine is operating, the management of the organization is obliged to notify the State Inspectorate. In this case, it is necessary to obtain a release permit approved by the supervisory authorities.

When operating dust collection installations for filtering gas with a high content of explosive (flammable) elements, it is necessary to especially carefully ensure that the specified pressure indicators and the tightness of the structures are maintained, and that the devices and communications are properly purged to prevent ignition and explosion.

During the manufacturing process of various furniture products, a significant amount of fine dust and particles of the original workpieces are produced. Such dust not only worsens the working conditions of production personnel, but also contributes to possible failures of moving equipment parts. That is why mass woodworking processes require the presence of dust collection units.

Operating principle and device

The systems under consideration perform the function of collecting and removing dust and small industrial debris, which includes such unsafe components as resins, alkaloids, toxic organic and inorganic particles. When inhaled as dust, they can cause a wide range of allergic reactions, skin problems and respiratory problems. Often used in woodworking, plywood, MDF and chipboard are particularly problematic due to the adhesive resins required to make them. The sequence of operation of modern dust collection ventilation units consists of the following stages:

1. Collecting dust at its sources.
2. Extraction of small wood particles using suction fans.
3. Filtration by factions.
4. Disposal into special dust containers.

   To achieve the assigned tasks, the dust collection installation includes an air duct system, a set of coarse and fine filters, supply and exhaust fans, and containers for waste collection. Appropriate areas are necessarily provided for when designing production areas, and the balance of energy costs includes the energy consumption to drive the moving parts of the equipment in question.

   To reduce noise levels, motors and assemblies are usually installed outside the production area. At the same time, this simplifies access for cleaning and maintenance of all components of dust collection ventilation units.

   How operating parameters are selected

   The initial indicators for choosing the size and power of a dust collection unit are:

   • Volume of air (in m3/min) that needs to be moved/removed;
   • Maximum possible dust concentration (MPC) in the room;
   • Complexity of the air duct system.

To remove fine wood dust in branches, a capacity of at least 110...130 m3/min is usually required to adequately draw dust into the main duct. Depending on how many pieces of production equipment are connected to the system and the length of the ductwork, one or more ventilation units may be required.

In accordance with the hygienic standards established by Rospotrebnadzor (GN 2.1.6.1125-2002), the maximum permissible concentration of dust in woodworking areas is 0.5 mg/m3, while the maximum permissible concentration of harmful components should not exceed 30% of the specified norm. Proper installation and grounding of the collection system (and especially the duct work) is important to prevent the build-up of static electricity and to develop levels of negative pressure generated by air ventilation.

Brief description of the components of the dust collection system

The choice of filter type, number and performance is critical. Modern filtration filtration units contain washable pre-filters. They capture dust particles as small as 3 microns (smaller particles are captured by smoke filters).

Inside the filtration unit there is a disposable bag, the dimensions of which depend on the performance of the unit. In woodworking industries, it is recommended to install combined filters that allow you to purify the air both in the machine operating area and in the general room.

Some of the dust collection ventilation units come with local work lights, making them good choice for installation directly next to process equipment. Preference is given to equipment that includes a remote control.

The main requirement for a ventilation unit is the ability to capture toxic aerosols, fog, gases, vapors, smoke and dust while effectively filtering the air entering the air ducts.

The MDM-TECHNO company offers design, supply, installation supervision and supervision services for the operation of dust collection plants. Upon conclusion of the contract, the company’s qualified specialists will carry out a technical justification for the project, select the appropriate equipment, install and connect it with high quality. Customers are provided with a quality certificate. Post-warranty maintenance of equipment is possible.