Out of the 25 iron foundries, the PCDs installed in four foundries were not in good condition. For example, data was collected on PCDs that were effectively used in 21 iron foundries. These data are presented in Table 1. Even in these 21 iron foundries, some data could not be collected. For example, in Iron Foundry 4, the discharge rate prior to the installation of the wet plug manifold was not available. As this table shows, a dome is used in ten iron foundries. An induction furnace is used in the remaining 11 iron foundries. PCDs used in iron foundries equipped with cupola furnaces include cyclones, venturi wet scrubbers, energy-efficient scrubbers such as spray towers or wet cap and dry cap collectors 4,9. The PCDs used in iron foundries built into an induction furnace are the wet scrubber; the venturi wet scrubber, the bag filter, and the cartridge filter. An interesting observation is that so far, no researcher has treated the cartridge filter as a PCD used in iron foundries. Cartridge filter not found. Referring to the data presented in Table 2, the impact of PCDs used in Tamilnadu iron smelters is described in the following subsections.
Impact of dry cap collector
As shown in Table 2, three of the 21 iron foundries surveyed installed a dry plug manifold. The dry cap collector is a kind of pollution control equipment mounted on the dome pole. A spark arrester is fitted to the top of the dome. There is a cap with a deflector around the spark arrester. This assembly is called a dry plug collector. When dusty air enters the dry cap, particles settle at the bottom of the dry cap. Baffles are installed at the bottom of the dry cap. The baffles act as a barrier to prevent dusty air from escaping into the atmosphere. Clean air enters the atmosphere through the chimney. As shown in Table 1, a dry cap manifold equipped with a dome was found to reduce SPM from 1750 mg/nm3 to 496 mg/nm3 in foundry-3, 394 mg/nm3 in foundry-7, and 366 mg/nm3 in the smelter-9. In these three iron smelters, the particle concentration turned out to be higher than the specification of the CPCB, which is 150 mg/nm3 4,9
Table 2
PCDs installed in foundries of Tamilnadu state and their impact on pollution prevention
Iron
Foundry
number
|
Furnace
used
|
PCD
|
Stack temperature
(average) in degree Kelvin
|
Velocity
(m/sec)
|
Discharge rate
(liters/hour)
|
SPM
(mg/nm3)
(average)
|
The concentration of pollutants in (mg/nm3)
|
| |
|
Before
|
After
|
|
Before
|
After
|
Before
|
After
|
SO2
|
NOx
|
CO2
|
CO
|
| |
|
Installing the PCD
|
|
Installing the PCD
|
Installing the PCD
|
1
|
Cupola
|
Cyclone
|
200
|
39
|
7.4
|
8350
|
4099
|
300
|
67
|
2.7
|
1.2
|
-
|
-
|
2
|
Cupola
|
Wet cap
Collector
|
200
|
150
|
-
|
5670
|
4500
|
2500
|
110
|
10
|
17
|
-
|
0.2
|
3
|
Cupola
|
Dry cap
collector
|
250
|
200
|
-
|
-
|
-
|
1750
|
496
|
340
|
18
|
4.5
|
-
|
4
|
Cupola
|
Wet cap
collector
|
-
|
150
|
5.52
|
-
|
1060
|
-
|
110
|
31
|
21
|
-
|
0.2
|
5
|
Cupola
|
Venturi wet
Scrubber
|
-
|
37
|
11.4
|
-
|
2043
|
-
|
51
|
26
|
11
|
-
|
0.2
|
6
|
Cupola
|
Wet cap
Collector
|
-
|
150
|
11.28
|
-
|
1066
|
-
|
102
|
21
|
15
|
-
|
-
|
7
|
Cupola
|
Drycap collector
|
-
|
200
|
-
|
-
|
-
|
-
|
394
|
38
|
18
|
-
|
-
|
8
|
Cupola
|
Wet cap
Collector
|
-
|
150
|
11.4
|
-
|
1757
|
-
|
95
|
66
|
20
|
5
|
-
|
9
|
Cupola
|
Drycap collector
|
-
|
200
|
-
|
-
|
-
|
-
|
366
|
63
|
47
|
ND
|
-
|
10
|
Cupola
|
Wet cap
collector
|
-
|
160
|
6.2
|
-
|
1360
|
-
|
105
|
30
|
19
|
ND
|
-
|
11
|
Induction
|
Venturi wet scrubber
|
-
|
28
|
9.86
|
-
|
5588
|
-
|
31
|
19.2
|
3.1
|
5
|
ND
|
12
|
Induction
|
Venturi wet
scrubber
|
-
|
29
|
<10
|
-
|
4926
|
-
|
37
|
21
|
12
|
ND
|
ND
|
13
|
Induction
|
Wet scrubber
|
-
|
53
|
9.86
|
-
|
5588
|
-
|
52
|
19.2
|
31
|
ND
|
0.2
|
14
|
Induction
|
Wet scrubber
|
-
|
38
|
9.2
|
-
|
5260
|
-
|
51
|
12
|
7
|
ND
|
ND
|
15
|
Induction
|
Wet scrubber
|
-
|
32
|
10.2
|
-
|
4592
|
-
|
50
|
15
|
8
|
ND
|
ND
|
16
|
Induction
|
Wet scrubber
|
-
|
35
|
11
|
-
|
6120
|
-
|
51
|
12
|
6
|
ND
|
ND
|
17
|
Induction
|
Wet scrubber
|
-
|
26
|
9.8
|
-
|
4980
|
-
|
49
|
14
|
7
|
ND
|
ND
|
18
|
Induction
|
Wet scrubber
|
-
|
36
|
10.5
|
-
|
5950
|
-
|
55
|
10
|
5
|
ND
|
ND
|
19
|
Induction
|
Wet scrubber
|
-
|
33
|
10
|
-
|
3500
|
-
|
50
|
21
|
11
|
ND
|
ND
|
20
|
Induction
|
Wet scrubber
|
-
|
28
|
9.1
|
-
|
5120
|
-
|
48
|
18
|
10
|
ND
|
ND
|
21
|
Induction
|
Cartridge filter
|
200
|
<50
|
9
|
40000
|
5185
|
|
<20
|
ND
|
ND
|
ND
|
ND
|
Impact of wet cap collector
As shown in Table 2, the wet cap manifold is installed in iron foundries 2, 4, 6, 8, and 10. The wet cap manifold is another type of contamination control equipment. The function of the wet hood collector is the same as that of the dry hood collector. The additional feature of the wet cap is that water is sprayed into the housing, which is mounted on top of the dome with a water bike line. The dusty air is cleaned at high speed by water, and the solid particles settle in the settling tank. The water is recycled using a pump. As shown in Table 1, in iron smelter 2, when the wet cap manifold is equipped with a dome, the SPM concentration is reduced from 2500 mg/nm3 to 110 mg/nm3. In iron foundries 4, 6, and 10, no particulate matter concentration data were available before the installation of the wet plug manifold. The current concentration that occurred after the installation of the wet plug collector in iron smelters 4, 6, 8, and 10 was 110 mg/nm3, 102 mg/nm3, 95 mg/nm3, and 105 mg/nm3, respectively. These values are within the emission limit of 150 mg/nm3 4,9
Impact of Cyclone
As shown in Table 2, the cyclone is installed in iron foundry 1. A cyclone is a device used to filter particles with a diameter ranging from 1 to 1000 micrometers from a gas or liquid stream. The centrifugal force throws solid particles against the outer wall of the cyclone. After their fall, they are collected and separated in the deposition chamber. Table 1 shows that when the cyclone was used in an iron foundry, the SPM concentration reduced from 300 mg/nm3 to 67 mg/nm3. It was clear that the cyclone would be a suitable PCD to be installed in the dome to reduce contamination 4,9
Impact of wet scrubber
As shown in Table 2, the wet scrubber is installed in iron foundries 13, 14, 15, 16, 17, 18, 19, and 20. The wet scrubber is a term used to describe a variety. Devices that use a liquid to remove pollutants. In a wet scrubber, the contaminated gas stream comes into contact with the washing liquid. The particles of the contaminated gas stream are collected by the liquid droplets. This phenomenon is achieved by dissolving or absorbing the particles in the liquid. Any droplets in the flue gases must then be separated from the clean exhaust stream using a device called a mist separator.
Most foundries have used wet scrubbers. The wet scrubber is very effective in removing both particulate matter and gases. During the study reported here, three iron foundries equipped with a Venturi wet scrubber and eight foundries equipped with a normal wet scrubber of different types (see Table 1) were followed. Interestingly, a remarkable reduction in particle emission concentrations was achieved in the Iron 17 smelter and the Iron 20 smelter. The SPM concentrations were found to be 52, 51, 50, 51, 55, 50 mg / nm3 in iron-13 smelter, iron-14 smelter, iron-15 smelter, iron-16 smelter, iron-18 smelter, and iron-19 smelter respectively. These values show that the reduced particle emission magnitude obtained after installation of the wet scrubber is only 50 mg/nm3 4,9
Impact of Venturi wet scrubber
As shown in Table 2, the wet venturi scrubber is installed in iron foundries 5, 11, and 12. A wet venturi scrubber is essentially a channel with a converging venturi-shaped groove followed by a diverging cross-section. They are leading a stream of contaminated gas from the dome. The liquid is usually introduced in the form of jets, which atomize rapidly to form many tiny droplets (Goncalves et al., 2004). The wash liquid is injected perpendicular to the incoming gas stream, breaking the liquid down into small droplets that are then used to collect particulate and gaseous pollutants. The energy required for diffusion is provided by a high-velocity gas stream. The quality of the liquid dispersion depends on the speed of the feed gas. A decrease in the gas velocity will result in a decrease in collection efficiency. A venturi wet scrubber has high separation efficiency for removing contaminants from the air. Table 1 shows that when the Venturi wet scrubber was installed in the dome, the resulting reduction in SPM concentration was 51 mg/Nm3 in the iron foundry 5. When the venturi wet scrubber was installed in an induction furnace, the observed SPM concentrations were only 31 mg/nm3 and 37 mg/nm3, respectively, in iron foundries 11 and 12. Therefore, the control of the contamination depends on the nature of the SPM expelled from the stack and the type of furnace being used 4,9
Impact of Cartridge filter
As shown in Table 2, the cartridge filter is installed in foundry 21. It is pretty interesting to note that the use of the cartridge filter to control fouling from iron foundries has not yet been addressed by researchers. This is evidenced by the lack of papers stating that cartridge filters are installed in foundries. The cartridge filter equipped with an induction furnace in the iron foundry 21 reduced the concentration of SPM to less than 20 mg/nm3. This is the highest reduction in SPM concentration achieved as compared to that obtained by other PCDs discussed in the previous subsections (Freire et al., 2021; Sabour et al., 2021; Yazji et al., 2021).
The literature and field studies reported so far have revealed two facts. According to the first fact, the concentration of pollution caused by the induction furnace is lower than that caused by the cupola. The second fact is that of all PCDs, the cartridge filter is the most effective in controlling fouling from the iron foundry. While the construction, operation, and performance of the induction furnace are well documented, this is not the case with the cartridge filter. Therefore, the construction, operation, and performance of the cartridge filter are described in the following section (Wei et al., 2021; Zhang et al., 2021; Umezawa et al., 2021).
Construction and Working Principle of Cartridge Filter
Information regarding the construction, operation, and performance of the cartridge filter is collected from Foundry 21. This information is presented in this section. The schematic arrangement in which three sets of cartridge filters are used to control fouling in a foundry is shown in Figure 2. The detailed view of the cartridge filter is shown in Figure 3. As illustrated, flue gases enter from induction furnaces into the gravity separator through the inlet channels. Gravity separators separate heavy particles from the vapours. These heavy particles pass through cartridge filter assemblies. In the cartridge filter assembly, heavy particles are screened with a flat bag, and light particles of smaller sizes are released into the atmosphere. In this way pollution from combustion gases is reduced. Compared to other PCDs, the cartridge filter consumes less energy to control contamination from iron foundries. The construction of the cartridge filter assembly is so simple that it allows easy cleaning of the inner chamber and replacement of the flat bag. When installed in an induction furnace, the wet scrubber is known to generate secondary pollution. On the other hand, there is no possibility for the cartridge filter to generate secondary pollution during use. During the study reported here, in the iron 21 smelters using a cartridge filter, the contamination level was found to be less than 20 mg/nm3. This pollution level is the standard set in European regulations. A minor drawback of using the cartridge filter is that it requires technically trained personnel to operate it. This minor inconvenience can be overcome by providing professional training to iron foundry operators to operate and maintain the cartridge filter.