A Brief Discussion on Inertial Dust Collectors and Their Applications

Inertial dust removal is a professional technology that uses structures such as baffles to change the direction of the gas flow, and separates the particulate dust in the gas flow by the inertial force, thereby purifying the gas. A dust collector designed and manufactured by using inertial dust removal technology is called an inertial dust collector.

In an inertial dust collector, the main phenomenon is that the airflow rapidly turns or impacts the baffle and then quickly changes direction. Due to the inertial effect (i.e., under the action of inertial force), the movement trajectory of the particulate dust deviates from the direction of the airflow, thus separating the two and purifying the gas. If the gas flow velocity is high, the inertial effect will be large, the dust removal effect will be good, and the degree of gas purification will be high. Therefore, the volume of the inertial dust collector can be greatly reduced. In addition, as inertial dust collectors have no moving parts, they can be used in high-temperature and high-concentration dust environments. The separation efficiency of fine particle dust has been greatly improved by gravity dust collectors, capable of capturing particles as small as 10μm. The main drawback of inertial dust collectors is that they wear out severely, which affects their service life.

According to structure and working principle, inertial dust collectors can be classified into five types: impact type, recirculation type, inertial sedimentation type, louver type and impact type. Since impact inertial dust collectors are mostly used for recovering acid mists and are not adopted in road construction and maintenance machinery, they will not be elaborated on in this article.

1. Impact-type inertial dust collector

The structural type of the impact inertial dust collector is shown in Figure 1. The characteristics of the collision-type inertial dust collector are as follows: One or several baffles are used to prevent the airflow from moving forward in a straight line. When the airflow turns rapidly, the dust particles are separated from the airflow under the action of inertial force. The collision-type inertial dust collector has relatively low resistance to the airflow, but its dust removal efficiency is also relatively low. Unlike gravity dust collectors, impact inertial dust collectors require a relatively high air flow velocity, approximately 18 to 20m/s, and the air flow is basically in a turbulent state.

a) Baffle type; b) Inverted form; c) Baffle reverse type; d) Impact reverse type

2. Reflux inertial dust collector

The structural type of the reflux inertial dust collector is shown in Figure 2. The characteristic of the reflux inertial dust collector is that the intake air flow is divided into small streams by baffles. To ensure that any airflow has the same small radius of rotation and large Angle of rotation, various louver baffle structures can be adopted.

a) Upward louver type; b) Downward louver type; c) Parallel inversion type; d) Baffle louver type

The louver baffle can increase the speed of the airflow before a sudden turn, effectively improving the separation efficiency. However, the speed should not be too high, otherwise it will cause the secondary flying of the already captured particle dust. Therefore, an airflow speed of 12-15m/s is generally selected.

The size of the louver baffle also has a certain impact on the separation efficiency. Generally, the length of the baffle selected (along the direction of the airflow) is about 20mm. The distance between the baffles is approximately 3 to 6 millimeters. The installation bevel of the baffle (the Angle with the vertical line) is approximately 30°, making the air flow rotation Angle about 150°.

Both theoretical analysis and practical experience have demonstrated that the dust removal efficiency of the louver reflux inertial dust collector is related to the diameter and density of dust particles, the rotation Angle, speed and radius of the gas flow, and the viscosity of the gas to a certain extent. For instance, after the dusty airflow enters (see Figure 3), it continuously flows out from the gaps of the louvers, and the particulate dust is also constantly separated. However, the lower it goes, the smaller the gas flow rate becomes, and the gas flow velocity gradually slows down. The inertial effect also decreases accordingly, and the separation efficiency gradually decreases. Therefore, if 10% of the gas flow can be drawn away at the bottom, that is, a louvered plate separator with a downflow, it will help improve the dust removal efficiency. In addition, the louver baffle can also be made in a curved shape to prevent the captured particle dust from being washed away by the air flow and flying again. Due to the use of curved louver baffles, the airflow path is tortuous, so it can be called a labyrinth inertial separator.

3. Inertial settling dust collector

The inertial settling dust collector combines the advantages of gravity dust collectors and inertial dust collectors. On the one hand, it enhances the inertial effect when the airflow turns; on the other hand, it combines inertia and gravity to more effectively separate the particulate dust in the airflow. This dust collector has two structural types: bell jar type and louver sedimentation type.

3.1 Bell Jar Inertial Dust collector

The structure of the bell jar type inertial dust collector is shown in Figure 4. The dusty gas discharged from the air duct rapidly changes direction due to the obstruction of the conical smoke shield 5. Meanwhile, due to the expansion of the cross-section, the gas flow rate sharply decreases. Dust particles, under the effect of gravity, settle at the bottom of settling chamber 4 and are discharged from the ash outlet, while the purified gas is discharged into the atmosphere through the upper air duct.

1 - Chimney flange; 2- Short smoke pipe; 3- Conical top of the settling chamber; 4- Settlement chamber 5- Conical smoke hood; 6- Pillar 7- Long smoke pipe

The bell jar type inertial dust collector has a simple structure, low resistance, does not require an induced draft fan, and can be directly installed on the exhaust stack or air duct. However, the dust removal efficiency of this type of dust collector is relatively low, generally only around 50%.

3.2 Louver settling dust collector

The structure of the louver sedimentation type dust collector is shown in Figure 5. The louver sedimentation type dust collector is suitable for the emission of dusty gas with a small amount of dust, and its dust removal efficiency is generally around 60%. The louver settling dust collector is composed of long and short smoke tubes, concentric louvers (assembled and arranged in a conical shape), and the inner and outer shells of the settling chamber, etc. The expanded airflow passes through the cross-section, reducing the gas flow rate. With the help of the airflow deflection and the interception of the louver blades, the dust particles are forced to separate from the airflow and are discharged from the ash discharge pipe at the bottom. The purified gas is discharged through the short flue pipe 9 at the top of the settling chamber.

1 - Conical top of the settling chamber; 2- Disc-shaped smoke separator; 3- Conical smoke separator; 4- Pillar 5- Settle the interior shell; 6- Settling type enclosure; 7- Concentric hundred blades; 8- Long smoke pipe; 9- Short smoke pipe

4. Louvered inertial dust collector

The louvered inertial dust collector is composed of a louvered ash barrier and a cyclone dust collector. Among them, the louvered ash barrier mainly serves to concentrate dust particles and comes in two forms: conical and "V" shaped. The louvered inertial dust collector also utilizes the sudden change of direction of the airflow to separate the particulate dust from the gas under the action of inertial force. When the dusty gas enters the louvered ash barrier 1, the vast majority of the gas enters the pipeline through the gaps between the blades of the ash barrier and is discharged into the atmosphere. This part of the gas was purified as it suddenly changed direction and separated from the particulate dust. Due to inertia, the particulate dust still moves forward in its original direction. The gas that passes through the ash screen and is purified generally accounts for 90% of the total gas volume. Additionally, 10% of the gas containing concentrated particulate dust enters the coarse particle removal chamber 3, where it is removed by inertia. Then, it enters the cyclone dust collector to remove fine dust. (If the exhaust volume is not large or the dust concentration is not high, the coarse particle removal chamber can also be cancelled.) The 10% of the gas to be treated can be returned to the ash screen through fan 2 or directly discharged into the atmosphere.

1 - Louvered grille; 2- Fan; 3- Coarse particle removal chamber; 4- Ash hopper 5- Cyclone dust collector

To prevent large pieces of ash, slag or crushed stones from entering the dust suction gap, causing blockage or thereby reducing the air flow sucked out and thus lowering the efficiency, a grid should be installed in front of the ash barrier to ensure the normal operation of the dust collector.

5. Application of Inertial Dust Collectors

5.1 Selection of Louvered Inertial Dust Collectors

The ash screen of the louvered inertial dust collector is preferably made of 20mm×20mm square to round shape and wear-resistant steel.

2) Install guide vanes in the middle of the pipe elbow in front of the ash barrier to keep the air flow velocity and dust concentration uniform in the cross-section of the pipe in front of the ash barrier.

3) The cyclone should usually be placed directly near the dust suction gap.

4) The cyclone should not collect the dust it has captured but should continuously discharge it. A well-performing ash discharge device should also be installed at the source of the original dust.

5) The louvered inertial dust collector can be installed in vertical, horizontal or inclined pipelines.

6) The higher the airflow velocity and the greater the Angle of airflow direction change of the inertial dust collector, the higher the dust removal efficiency it has when used to purify metal or mineral dust with larger density and particle size. However, for sticky and fibrous dust, it is not advisable to use it because it is prone to clogging.

5.2 Application Precautions

Inertial dust collectors, like gravity dust collectors, can be used independently or as pre-dust collectors for multi-stage dust collectors.

2) The blades in inertial dust collectors are prone to wear. Corresponding technical measures should be taken during manufacturing and application to extend their service life.

3) The recirculating inertial dust collector is one of the most commonly used types in practice. It is easy to configure and connect with the dust removal system, has a good dust removal effect, and can also be used as a pre-dust collector independently.

4) When used alone, there are two configuration methods for the louvered inertial dust collector: One is to install the dust collector behind the fan. Most of the gas is discharged through the dust collector's casing, while a small portion of the gas containing a large amount of dust is dusted by the cyclone dust collector before entering the fan, implementing a sealed circulation. This can prevent the dust completely removed by the cyclone dust collector from being discharged. Its drawback is that dust passing through the fan can easily wear out its impeller. Another option is to install the dust collector in front of the fan. This can reduce the wear of the fan impeller by the dust, but the dust not removed by the cyclone dust collector is directly discharged, that is, the dust removal efficiency is relatively low.

5) Inertial dust collectors are highly sensitive to air leakage in the device, especially when air leakage from the shell, blades, etc. affects the flow of dusty air, the dust removal efficiency will drop significantly.