**8. Dust collector types**

There are four major types of dust collectors for particulate contaminants: electrostatic precipitators, fabric collectors, wet collectors, and dry centrifugal collectors.

#### **8.1. Fabric collectors**

The "fabric" may be constructed of any fibrous material, either man-made or natural, and regardless of construction may be spun into a yarn and woven or felted by needling, impacting, or bonding. The fabric represents a porous mass through which the gas is passed in directional such that dust particles are retained on the dirty side and the cleaned gas passes on through. The ability of the fabric to pass air is called "permeability." It is defined as the cubic feet of air passed through one square foot of fabric each minute at a pressure drop of 0.5 " wg. Usual permeability amounts for commonly used fabrics range from 25 to 40 cfm. A highly efficient fabric that cannot be cleaned represents an excessive resistance to air flow and is not an economical engineering solution. Final fabric selection is generally a compromise between efficiency and permeability. The efficiency of the fabric as a filter is meaningful when new fabric is first put into service. Even after cleaning, a residual and/or redeposited dust cake provides higher collection efficiency and additional filtration surface than obtainable with new fabric*.* Fabric collectors are not 100% efficient. But well-designed, adequately sized, and properly operated fabric collectors can be expected to operate at efficiencies in excess of 99% and often as high as 99.9% or more on a mass basis*.* The fabric collector should be leak tested for mechanical leaks where extremely high collection efficiency is essential. The combination of fabric and collected dust becomes increasingly efficient as the dust cake accumulates on the fabric surface*.* Fabric collectors are suitable for service on relatively heavy dust concentrations. The amount of dust collected on a well-designed and single square yard of fabric may exceed 5 pounds per hour. Commercially available fabric collectors employ fabric configured as bags or tubes, envelopes (flat bags), rigid elements, or pleated cartridges. Most of the available fabrics are employed in either bag or envelope configuration. The variable design features of the many available fabric collectors are as follows:


Damage to farms or contribution to air pollution problems of distant cities can affect the need for and importance of effective collection equipment in remote locations. Many industries, originally located away from residential areas, have failed to anticipate the residential building construction which frequently develops around a plant. Such lack of foresight has required installation of air cleaning equipment at greater expense. Nowadays, the remotely located plant must comply with the same regulations as the plant located in an urban area in most cases. Management can continue to expect criticism for excessive emissions of air contaminants whether located in a heavy industry section of a city or in an area closer to residential zones with the present emphasis on public nuisance, public health, and preservation and improvement of community air quality. Also, the mass rate of emission will affect selection of equipment. For a given concentration, the larger the exhaust volumetric flow rate, the greater the need for better equipment. While a smaller industrial pulverized fuel boiler might be able to use slightly less efficient collectors, large central steam-generating stations might select high efficiency electrostatic precipitators or fabric collectors for their pulverized coal boiler stacks. A safe recommendation in selecting equipment is to select the collector that will allow the least possible amount of contaminant to escape and also while meeting all prevailing air pollution regulations is reasonable in first cost and maintenance. It must be remembered that visibility of an effluent will be a function of the light reflecting surface area of the escaping material. Surface area per pound increases inversely as the square of particle size. In other words, the removal of 80% or more of the dust on a weight basis may remove only the coarse particles

154 Air Pollution - Monitoring, Quantification and Removal of Gases and Particles

The contaminant characteristics will also affect equipment selection. Emitted chemicals may attack collector elements or corrode wet type collectors. Sticky materials can adhere to collector elements, plugging collector passages. Linty materials adhere to certain types of collector surfaces or elements. Abrasive materials in moderate to heavy concentrations will cause rapid wear on dry metal surfaces. Particle size, density, and shape will rule out certain designs. The combustible nature of many finely divided materials requires specific collector designs to assure safe operation. The characteristics of the carrier gas stream can have a marked bearing on selecting equipment. It is possible that temperature of the gas stream limit the material choices in fabric collectors. Condensation of water vapor will cause packing and plugging of air or dust passages in dry collectors. We can reach optimum and high removal efficiency with optimization and more study about design

There are four major types of dust collectors for particulate contaminants: electrostatic pre-

The "fabric" may be constructed of any fibrous material, either man-made or natural, and regardless of construction may be spun into a yarn and woven or felted by needling,

cipitators, fabric collectors, wet collectors, and dry centrifugal collectors.

without altering the stack appearance.

parameters in each type of collectors.

**8. Dust collector types**

**8.1. Fabric collectors**

Due to many variables and their range of variation, fabric collector sizing is judged based on experience. Also, a combination of shaking and reverse air flow has been utilized. It is possible that reverse-jet, continuous-duty fabric collectors use envelopes or tubes of nonwoven fabric, pleated cartridges of non-woven mat (paper-like) in cylindrical or panel configuration, or rigid elements such as sintered polyethylene. Based on our experience, when tubes have 6–11 inches diameter and can be as long as 10 feet, permeability 10–25, reverse-jet 6–8 atmosphere (in high load of pollution each 1 minute, 1 second pulse jet; and in low load of pollution each 2–3 minute, 1 second pulse jet), and air velocity inside the chamber selected 300 fpm, the bag filter becomes optimal and economic in removal efficiency. Solenoid valves which control the pulses of compressed air may be open for a tenth of a second or less. An EPA-sponsored research has shown that superior performance results from downward flow of the dirty air stream. This downward air flow reduces redeposition since it aids gravity in moving dust particles toward the hopper. **Figure 5** shows the fabric collector [1, 2].

use of water may introduce corrosive conditions within the collector, and if collectors are located outdoors in cold climates, freeze protection may be necessary. Wet collectors are frequently the solution to air pollution problems. It should be recognized that disposal of collected material in water without clarification or treatment may create water pollution problems. Wet collectors have one characteristic not found in other collectors, the inherent ability to humidify. Humidification, the process of adding water vapor to the air stream through evaporation, may be either advantageous or disadvantageous depending on the situation. All wet collectors humidify; the amount of humidification varies for different designs. According to our experiences, although wet collectors have different types, the spray tower and packed towers, which are more practical and economic, are simple to make and assemble and have

Spray tower collectors consist of a rectangular or round chamber into which water is introduced by spray nozzles. There are many variations of design, but the principal mechanism is impaction of dust particles on the liquid droplets created by the nozzles. These droplets are separated from the air stream by pump force. The pressure drop is relatively low (on the

are the exception rather than the rule. This type of collector generally utilizes low-pressure supply water and operates in the lower efficiency range for wet collectors. Collection efficiency can reach the upper range of wet collector performance where water is supplied under high pressure. For conventional equipment, water requirements are reasonable with a maximum of about 5 gpm per thousand cfm of particle, and fogging types using high water pressure may require as much as 10 gpm per thousand cfm of gas. **Figure 6** shows this collector. Air flow inside all of the scrubbers has adiabatic revolution with 90% efficiency; in other words, air flow in scrubber will be cool and increase humidity to 90% relative humidity. **Figure 7** shows this

Based on our experiences, design velocity in spray towers takes 250 feet per minute (fpm), and the performance of spray tower will be optimum since no droplet in fan housing or stack was detected. Design parameters of spray towers can influence the removal efficiency of air pollutants. Design parameters included type (solid cone or hollow cone), array and position and number of spray nozzles, size, liquid pressure, diffraction angle of spray nozzle, L/G (liquid to gas ratio), etc. The operating pressure of scrubbing liquid not only is an important parameter but also directly influences the liquid distribution, droplet size, and liquid flow rate. According to our experience, operating pressure, nozzle size 80–800 micron (the nozzle

increase mass transfer and removal efficiency, decrease and save operational costs, and optimize the "mechanical" performance of spray towers. The area and pressure drop of spray

wg), but water pressures range from 10 to 400 psig. The high-pressure devices

s law constant of each gas), and multistage spray nozzle could

ds = 2 √

hlS = 1.5 × VP

\_\_\_ \_\_ Q 14 b = 2.5 ds

Industrial Air Pollution Control

157

http://dx.doi.org/10.5772/intechopen.80678

(7)

appropriated removal efficiency in air pollution control.

*8.2.1. Spray tower*

order of 0.5–1.5 "

change.

size directly depends on Henry'

towers were calculated Eq. (7) [2, 4–6]:

The area and pressure drop of spray towers:

**Figure 5.** Fabric collector.

#### **8.2. Wet collectors**

Wet collectors or scrubbers are commercially available in different designs, with pressure drops from 1.5 times of exit duct velocity pressure. There is a corresponding variation in collector performance. It is generally accepted that efficiency depends on the energy utilized in air to water contact and is independent of operating principle for well-designed equipment. Whether the energy is supplied to the air or to the water, efficiency is a function of total energy input per cfm. In other words, if equivalent power is utilized, well-designed collectors by different manufacturers provide similar efficiency. Wet collectors have the ability to handle high-temperature and moisture-laden gases. The collection of dust in a wetted form minimizes a secondary dust problem in disposal of collected material. Some dusts represent explosion or fire hazards when it is dry. Wet collection minimizes the hazard; however, the use of water may introduce corrosive conditions within the collector, and if collectors are located outdoors in cold climates, freeze protection may be necessary. Wet collectors are frequently the solution to air pollution problems. It should be recognized that disposal of collected material in water without clarification or treatment may create water pollution problems. Wet collectors have one characteristic not found in other collectors, the inherent ability to humidify. Humidification, the process of adding water vapor to the air stream through evaporation, may be either advantageous or disadvantageous depending on the situation. All wet collectors humidify; the amount of humidification varies for different designs. According to our experiences, although wet collectors have different types, the spray tower and packed towers, which are more practical and economic, are simple to make and assemble and have appropriated removal efficiency in air pollution control.

#### *8.2.1. Spray tower*

**8.2. Wet collectors**

**Figure 5.** Fabric collector.

156 Air Pollution - Monitoring, Quantification and Removal of Gases and Particles

Wet collectors or scrubbers are commercially available in different designs, with pressure drops from 1.5 times of exit duct velocity pressure. There is a corresponding variation in collector performance. It is generally accepted that efficiency depends on the energy utilized in air to water contact and is independent of operating principle for well-designed equipment. Whether the energy is supplied to the air or to the water, efficiency is a function of total energy input per cfm. In other words, if equivalent power is utilized, well-designed collectors by different manufacturers provide similar efficiency. Wet collectors have the ability to handle high-temperature and moisture-laden gases. The collection of dust in a wetted form minimizes a secondary dust problem in disposal of collected material. Some dusts represent explosion or fire hazards when it is dry. Wet collection minimizes the hazard; however, the Spray tower collectors consist of a rectangular or round chamber into which water is introduced by spray nozzles. There are many variations of design, but the principal mechanism is impaction of dust particles on the liquid droplets created by the nozzles. These droplets are separated from the air stream by pump force. The pressure drop is relatively low (on the order of 0.5–1.5 " wg), but water pressures range from 10 to 400 psig. The high-pressure devices are the exception rather than the rule. This type of collector generally utilizes low-pressure supply water and operates in the lower efficiency range for wet collectors. Collection efficiency can reach the upper range of wet collector performance where water is supplied under high pressure. For conventional equipment, water requirements are reasonable with a maximum of about 5 gpm per thousand cfm of particle, and fogging types using high water pressure may require as much as 10 gpm per thousand cfm of gas. **Figure 6** shows this collector. Air flow inside all of the scrubbers has adiabatic revolution with 90% efficiency; in other words, air flow in scrubber will be cool and increase humidity to 90% relative humidity. **Figure 7** shows this change.

Based on our experiences, design velocity in spray towers takes 250 feet per minute (fpm), and the performance of spray tower will be optimum since no droplet in fan housing or stack was detected. Design parameters of spray towers can influence the removal efficiency of air pollutants. Design parameters included type (solid cone or hollow cone), array and position and number of spray nozzles, size, liquid pressure, diffraction angle of spray nozzle, L/G (liquid to gas ratio), etc. The operating pressure of scrubbing liquid not only is an important parameter but also directly influences the liquid distribution, droplet size, and liquid flow rate. According to our experience, operating pressure, nozzle size 80–800 micron (the nozzle size directly depends on Henry' s law constant of each gas), and multistage spray nozzle could increase mass transfer and removal efficiency, decrease and save operational costs, and optimize the "mechanical" performance of spray towers. The area and pressure drop of spray towers were calculated Eq. (7) [2, 4–6]:

$$\begin{aligned} \mathbf{d\_s} &= 2\sqrt{\frac{\mathbf{Q}}{14}}\\ \text{The area and pressure drop of spray towards:} \quad \mathbf{b} &= 2.5 \,\mathrm{d\_s} \\ \mathbf{h\_{is}} &= 1.5 \times \mathrm{VP} \end{aligned} \tag{7}$$

**8.3. Packed towers**

**Figure 8.** Low-efficiency cyclone.

Packed towers are essentially contact beds through which liquid and gases pass concurrently, counter-currently, or in cross-flow. They are used primarily for applications involving vapor, gas, and mist removal. These collectors can capture solid particulate matter, but they are not used for that purpose since dust plugs the packing and requires unreasonable maintenance.

Industrial Air Pollution Control

159

http://dx.doi.org/10.5772/intechopen.80678

**Figure 6.** Spray tower.

**Figure 7.** Adiabatic revolution.

where Q is the flow rate at scrubber outlet (cfm), bS is the inlet duct to nozzle height (ft), hlS is the scrubber pressure drop (" WG), *d<sup>s</sup>* is the scrubber diameter (ft), and VP is the velocity pressure at the outlet duct (" WG).

#### **8.3. Packed towers**

Packed towers are essentially contact beds through which liquid and gases pass concurrently, counter-currently, or in cross-flow. They are used primarily for applications involving vapor, gas, and mist removal. These collectors can capture solid particulate matter, but they are not used for that purpose since dust plugs the packing and requires unreasonable maintenance.

**Figure 8.** Low-efficiency cyclone.

where Q is the flow rate at scrubber outlet (cfm), bS

158 Air Pollution - Monitoring, Quantification and Removal of Gases and Particles

WG), *d<sup>s</sup>*

WG).

is the scrubber pressure drop ("

pressure at the outlet duct ("

**Figure 7.** Adiabatic revolution.

**Figure 6.** Spray tower.

is the inlet duct to nozzle height (ft), hlS

is the scrubber diameter (ft), and VP is the velocity

Water rates of 5–10 gpm per thousand cfm are typical for packed towers. Water is distributed over V-notched ceramic or plastic weirs. High-temperature deterioration is avoided by using brick linings, allowing gas temperatures as high as 1600 F to be handled directly from furnace flues. Based on shapes, the packing is divided into the following types:

*8.4.2. High-efficiency cyclone*

cyclone diameter (in).

*8.4.3. Multiple cyclone*

**Figure 10.** Multiple cyclone.

In this collector, air velocity is 4000–4800 fpm with pressure drops 3–6"

where Q is the cyclone flow rate (cfm), hl is the cyclone pressure drop ("

/ 0

These collectors (see **Figure 10**) consist of a chamber that some number of high-efficiency cyclone put on this chamber. Not only the inlets of cyclones are connected together but also

\_\_\_\_\_ 0.083 hl ) 0.25 √ \_\_

**Figure 9**) can absorb with efficiency more than 900

diameter of this collector can be calculated based on Eq. (8):

The diameter of high efficiency cyclone:d = (

wg. This cyclone (see

Industrial Air Pollution Control

161

WG), and d is the

Q, hl = 3 to 6 (" WG) (8)

the particle size more than 13 micron. The

http://dx.doi.org/10.5772/intechopen.80678

Maspac, Intalox Saddle, Pall Ring, Tellerette, Raschig ring, and Berl Saddle. On the basis of our experience, the Raschig ring is appropriate for packing (popular, simple to make and maintenance, low-cost, etc.), and the optimum design velocity was 250 fpm for packed tower.

### **8.4. Cyclone collector**

The cyclone collector is commonly used for the removal of coarse dust from an air stream as a precleaner to more efficient dust collectors and/or as a product separator in air conveying systems. Principal advantages are low-cost, low maintenance, simple making, and relatively low-pressure drops. It is not suitable for the collection of fine particles.

#### *8.4.1. Low-efficiency cyclone*

In this collector, air velocity is 3200–4000 fpm with pressure drops 0.75–1.5 " wg. This cyclone can absorb with efficiency more than 900 / 0 the particle size more than 55 microns (see **Figure 8**).

**Figure 9.** High-efficiency cyclone.

#### *8.4.2. High-efficiency cyclone*

Water rates of 5–10 gpm per thousand cfm are typical for packed towers. Water is distributed over V-notched ceramic or plastic weirs. High-temperature deterioration is avoided by using brick linings, allowing gas temperatures as high as 1600 F to be handled directly from furnace

Maspac, Intalox Saddle, Pall Ring, Tellerette, Raschig ring, and Berl Saddle. On the basis of our experience, the Raschig ring is appropriate for packing (popular, simple to make and maintenance, low-cost, etc.), and the optimum design velocity was 250 fpm for packed tower.

The cyclone collector is commonly used for the removal of coarse dust from an air stream as a precleaner to more efficient dust collectors and/or as a product separator in air conveying systems. Principal advantages are low-cost, low maintenance, simple making, and relatively

wg. This cyclone

the particle size more than 55 microns (see **Figure 8**).

flues. Based on shapes, the packing is divided into the following types:

160 Air Pollution - Monitoring, Quantification and Removal of Gases and Particles

low-pressure drops. It is not suitable for the collection of fine particles.

In this collector, air velocity is 3200–4000 fpm with pressure drops 0.75–1.5 "

/ 0

**8.4. Cyclone collector**

*8.4.1. Low-efficiency cyclone*

**Figure 9.** High-efficiency cyclone.

can absorb with efficiency more than 900

In this collector, air velocity is 4000–4800 fpm with pressure drops 3–6" wg. This cyclone (see **Figure 9**) can absorb with efficiency more than 900 / 0 the particle size more than 13 micron. The diameter of this collector can be calculated based on Eq. (8):

$$\text{The diameter of high efficiency cylinder:} \text{d} = \left(\frac{0.083}{\text{hl}}\right)^{0.25} \sqrt{\text{Q}}, \text{ hl} = 3 \text{ to } 6 \text{ ('WG')} \tag{8}$$

where Q is the cyclone flow rate (cfm), hl is the cyclone pressure drop (" WG), and d is the cyclone diameter (in).

#### *8.4.3. Multiple cyclone*

These collectors (see **Figure 10**) consist of a chamber that some number of high-efficiency cyclone put on this chamber. Not only the inlets of cyclones are connected together but also

**Figure 10.** Multiple cyclone.

the outlets are connected together. This collector at list consist of four cyclones, and can more number cyclone put in this chamber and cyclones must have square array. The pressure drop in multi-cyclone is equivalent to each cyclone. The flow rate in each cyclone can be calculated based on Eq. (9) [1, 2]:

$$\text{Flow rate in each cylinder:} \begin{aligned} \mathbf{Q\_i} &= \frac{\mathbf{Q}}{\mathbf{N}} \\ \mathbf{N} &= \mathbf{n}^2 \end{aligned} \tag{9}$$

**References**

ed. 2013

pp. 1-315

Research. 2018

[1] Industrial Ventilation: A Manual of Recommended Practice For Design. In: ACGIH. 27th

[2] Matin AH.Industrial Ventilation Design and Calculation Guide for Industrial Hygienists.

[4] Jafari MJ, Matin AH, Rahmati AR, Azari MR, Omidi L, Hosseini SS, et al. Experimental optimization of a spray tower for ammonia removal. Journal of Atmospheric Pollution

[5] Rahmati AR. The influences of spray nozzles and water head on removal efficiency of ammonia from air in a spray tower [MSc thesis]. Tehran, Iran: School of Health, Shahid

[6] Jafari MJ, Nourian S, Zendehdel R, Massoudinejad MR, Sarbakhsh P, Rahmati AR, et al.

S from air. Safety Promotion and

Industrial Air Pollution Control

163

http://dx.doi.org/10.5772/intechopen.80678

[3] Matin AH, Bayatian M. Collection of Air Pollutants. Fanavaran; 1389

Beheshti University of Medical Sciences; 2015

Injury Prevention. 2015;**4**(2):321-328

The performance of a spray tower in scrubbing H2

where Q is the quota air for each cyclone, *Q* is the inlet or outlet air in cyclone (cfm), *N* is the number of cyclone in multi-cyclone, and n is the inlet eger number.
