# Current Issue

Asian Journal of Atmospheric Environment - Vol. 15 , No. 3

Abstract

For two bituminous coal-fired power plants with 500 MW and pulverized coal combustion type, the concentration of PMtotal, >PM10, PM2.5-10, PM2.5, NOx, and SO2 was measured, and their emission factors were calculated through field measurement. The measurement points started from the boiler downstream and continued to the air pollution control devices (APCDs) that are installed in series, namely, the selected catalytic reduction system (SCR), air preheater (APH), electrostatic precipitator (ESP) and wet flue gas desulfurization system (WFGD). The measurement was performed at one point for more than three times by using the Korean standard method for air pollutants. However, all measurement points, except for the stacks, were not representative of the standard test method. In addition, the PM concentration was too high to reduce the collection time due to isokinetic sampling. There is a limitation of how representative the measurement results can be. During the field measurement period, the power production rate of the two coal-fired power plants was 91.6% and 79.2% in the P-1 and P-2, respectively. Moreover, in the P-2, with a low power production rate, the concentration of PMtotal, PM10, PM2.5, and NOx was found to be low, and the emission factor calculated by dividing the measured concentration value by the fuel usage was also estimated to be low. Such results are due to the coal combustion chamber and various types of APCD being operated at a lower-load condition than the design capacity. In turn, the number of pollutants generated was less, and the removal efficiency of the pollutant became high. However, it was found that the concentration of SO2 generated and the emission factor are more significantly affected by the sulfur content of the coal than the load factor change. To this end, reducing the operation load of the coal-fired power plant improves the combustion efficiency and APCDs performance and decreases the emission factor, resulting in more reduction of the air pollutants than that based on the simple calculation.

 Keywords: Coal-fired power plant, Emission factor, Air pollution control devices, Particle size distribution, Upper limit restrictions

1. INTRODUCTION

The concentration of fine particulate matter (PM) is increasing, and in particular, the number of days in which high-concentration fine particulate matter occurred is also increasing (Wu et al., 2020; EEA, 2019). Fine particulate matter has an adverse effect on human health and visibility of the atmosphere and also induces climate change (Watts et al., 2015).

The ambient air quality standards for PM2.5 were strengthened in 2018 to 35 μg/m3 (daily average) and 15 μg/m3 (annual average) in Korea. To satisfy ambient air quality standards, governments, businesses, and the private sector are making air quality changes (Kim et al., 2017). It is important to identify the air pollution sources to effectively manage air quality (Ma and Gang, 2019; Han et al., 2018). Air quality management strategies are forced to focus on high emissions as a priority.

The capacity of the coal-fired power plants in South Korea is 34.7 GW (as of 2019) from 60 power production facilities, and approximately 98% of them use bituminous coal as fuel. The largest number of coal-fired power plants has a 500 MW class capacity (35 units). Recently, the six coal-fired power plants with a capacity of 1000 MW have been constructed. There are two main types of combustion for coal-fired power plants in Korea. One is the use of a pulverized coal combustion (PC) boiler, in which coal of 3 mm or less is mixed with air and injected into a combustion chamber. Another is the circulating fluidized bed combustion (CFBC) boiler, which burns by circulating particles (sand and limestone) and coal in the combustion chamber. Most coal-fired power plants use PC combustion systems in Korea.

The air pollutants emitted from the coal-fired power plants are PM, SOx, and NOx alongside hazardous air pollutants such as Hg and As. These air pollutants are removed by installing various types of air pollution control devices, and the most highly used air pollution prevention system in coal-fired power plants in Korea is the selected catalytic reduction (SCR) - electrostatic precipitator (ESP) - wet flue gas desulfurization (WFGD). The selected catalytic reduction is able to remove NOx. Furthermore, the low-NOx combustion burner is installed for suppressing the generation of NOx from the combustion process. The electrostatic precipitator removes PM and heavy metals. The wet flue gas desulfurization system is able to remove SOx, HCl, HF, and PM (Liang et al., 2020; IPPC, 2017; Saarnio, 2014).

In this study, when two coal-fired power plants with the same capacity and the same APCDs are installed to operate at different power production rates, the concentration of PM (PMtotal, >PM10, PM2.5-10, PM2.5), NOx, and SO2 in the air pollution prevention device installed based on the combustion exhaust gas flow was measured, and their emission factors were calculated and compared.

2. EXPERIMENTAL
2. 1 Facility

For the measurement targets, two PC type coal-fired power plants with the capacity of 500 MW were selected, which are the type and capacities that are used the most in the domestic coal-fired power plants. Based on the exhaust gas flow, the measurement was conducted at five points, as presented in Fig. 1. Specifically, the measurement was carried out at the SCR for De-NOx, an electrostatic precipitator that removes particulate matter; air preheater (APH) that reduces the temperature of the electrostatic precipitator; and the WFGD. Table 1 and Fig. 1 show a simple summary of the descriptions of the measurement target coal-fired power plants and the measurement points.

Fig. 1.
Measurement points of the coal-fired power plant.

Table 1.
Description of coal-fired power plant.
Item Speciation
Generation
facility
Capacity 500 MW
Type Pulverized coal combustion boiler, Low-NOx burner
Fuel Bituminous, biomass
APCD SCR V2O5-WO3/TiO2 catalyzer, Plate type, NH3 reagent
APH Rotary regenerative heat exchanger
ESP 5-field Dry ESP
WFGD Wet limestone-gypsum absorber

2. 2 Test Method

The measurement items are particulate matter, sulfur oxides, and nitrogen oxides. For the particulate matter, the concentration of total particulate matter (PMtotal) and particulate matter of different sizes (PM2.5, PM2.5-10, PM10 or more) was measured. The measurement equipment of the ES 01301.1 method (NIER, 2014) was used to measure the concentration of the total particulate matter, while the measurement equipment of the KS ISO 23210 method (KATS, 2012) was utilized to measure the concentration of the particulate matter with different sizes. For the field measurement, the PM sampler and cascade impactor were placed at the same point and conducted the measurement at the same time. The PMtotal was calculated based on the values measured with the PM sampler, the PM2.5/PMtotal and PM10/PMtotal ratios were calculated based on the concentration values obtained using the cascade impactor.

The PM10 and PM2.5 concentrations were estimated by applying these ratios to the total particulate matter concentration. The measurement equipment for each item is tabulated in Table 2. The measurement at each point could not be performed simultaneously for various reasons (multiple PM samplers and manpower required), and hence, it was conducted for the same facility for 1-3 days and repeated more than three times for each point.

Table 2.
Measuring equipment.
Item Method Instrument
>PM10, PM2.5-10, PM2.5 KS I ISO 23210 2-stage cascade impactor (Stage-X MS, X Ear Pro, Italy)
PMtotal ES 01301.1 PM sampler (KNJ-5, KNJ, Korea)
SO2, NOx, O2 ES 01204 Gas analyzer (Testo 350k, Testo, Germany)

The field measurement conducted in this study has limitations. In the boiler, SCR system, and APH points except for the stack, there were some points where the regulation of test methods for sampling of flue gas (ES 01114) could not be followed, i.e., where the fluid flow was unstable, according to the circumstances of the field. However, we measured the fluid velocity and static pressure using the pitot tube, selected the most stable point, and collected the sample in the field. Moreover, because the particulate matter concentration was high in the boiler, SCR system, and APH measurement points, the flow was lowered for the isokinetic sampling, and the sample collection time was shortened. Therefore, there is a possibility of issues regarding the representativeness of the measurement results.

3. RESULTS AND DISCUSSION
3. 1 Concentration of Air Pollutants

The measurement results of the PM (PMtotal, PM10, PM2.5), NOx, and SO2 concentrations for each coal-fired power plant and measurement point are presented in Fig. 2. The concentration of PMtotal generated at the boiler was 6,223.1±147.5 mg/Sm3 and 4,252.9±403.8 mg/Sm3 in the P-1 and P-2 facilities, respectively. After passing through the SCR, APH, ESP, and WFGD, it decreased to 5,233.5±63.1 mg/Sm3, 3,611.1±379.3 mg/Sm3, 14.4±0.8 mg/Sm3, and 6.5±0.2 mg/Sm3 in the P-1 facility and to 3,351.4±401.0 mg/Sm3, 2,158.3± 147.1 mg/Sm3, 6.5±0.6 mg/Sm3, and 3.2±0.39 mg/Sm3 in the P-2 facility, respectively. The nitrogen oxide concentration in the boiler and stack was 187.2 mg/Sm3 and 53.9 mg/Sm3 in the P-1 facility and 186.9 mg/Sm3 and 43.0 mg/Sm3 in the P-2 facility, respectively. The sulfur dioxide concentration in the boiler and stack was reduced to 794.3 mg/Sm3 and 36.5 mg/Sm3 in the P-1 facility and 833.7 mg/Sm3 and 43.9 mg/Sm3 in the P-2 facility, respectively. Here, the concentrations were converted to the oxygen concentration 6% condition. Except for the sulfur oxide concentration, the concentration of the PM (PMtotal, PM10, PM2.5) and NOx was found to be lower in the P-2 facility than in the P-1 facility.

Fig. 2.
PM, NOx, and SO2 concentration in APCDs of flue gas stream.

The removal efficiency of the air pollution systems is shown in Table 3. The final removal efficiency of the air pollutants, namely PMtotal, PM10, PM2.5, NOx, and SO2 when they passed through the APCDs and were emitted to the outside of the stack was found to be 99.91%, 99.76%, 99.67%, 74.11%, and 95.47%, respectively, which were obtained by taking an average of two coal-fired power plants. The removal efficiency of the PMtotal, PM10, PM2.5, and NOx appeared to be higher in the P-2 facility than in the P-1 facility, whereas the SO2 removal efficiency was higher in the P-1 facility than in the P-2 facility.

Table 3.
Removal efficiencies of air pollutants in APCDs of flue gas stream.
Efficiency (%) SCR APH ESP WFGD Stack
In Collection In Collection In Collection In Collection
P-1 >PM10 100 28.49 71.51 34.63 36.88 36.85 0.04 0.03 0.01
PM2.5-10 100 12.97 87.03 27.31 59.71 59.64 0.07 0.04 0.03
PM2.5 100 -8.81 108.81 3.52 105.29 104.30 0.99 0.53 0.46
NOx 100 72.57 27.43 0.00 27.43 0.00 27.43 -1.35 28.78
SO2 100 3.96 96.04 0.00 96.04 0.36 95.68 91.09 4.59
P-2 >PM10 100 36.50 63.50 42.77 20.73 20.71 0.02 0.01 0.01
PM2.5-10 100 19.06 80.94 24.84 56.10 56.06 0.04 0.02 0.01
PM2.5 100 -5.77 105.77 3.82 101.95 101.36 0.58 0.28 0.31
NOx 100 79.12 20.88 0.00 20.88 0.00 20.88 -2.12 23.00
SO2 100 4.39 95.61 0.34 95.27 2.74 92.53 87.27 5.26

In terms of PM2.5, it was found to be generated as it passed through the SCR system, and this suggests that NH3 sprayed as a reducing agent reacted with SO2, transformed into either (NH4)2SO4 or NH4HSO4 particles, and generated fine particulate matter (Ruan et al., 2019; Li, 2017; Shi et al., 2016; Li et al., 2015). The concentration of NOx also increased as it passed through the WFGD system, probably because of the leakage of the exhaust gas since the leakage type Gas-Gas Heater (GGH), i.e., a heat exchanger for adjusting to the adequate operating temperature of the WFGD system for De-SOx, is installed (Seong and Lee, 2017).

Fig. 3 presents the overall particle collection efficiencies for PMtotal (>PM10+PM2.5-10+PM2.5) at each measurement point. Although there is a slight difference between the P-1 and P-2 facilities, it was identified that the PMtotal is removed the most in the main collector, ESP. Moreover, it was found that PMtotal is removed in the SCR system for De-NOx, APH for the heat exchange, and WFGD system for De-SOx, and these results are in good agreement with the results of other studies (Ruan et al., 2019; Sui et al., 2016).

Fig. 3.
Overall particle collection efficiencies in APCDs of flue gas stream.

Fig. 4 shows the particle size distribution of the particulate matter at each measurement point. In terms of the size distribution of the particulate matter generated from the coal combustion, the PM2.5, PM2.5-10, and >PM10 accounted for 19.4%, 34.5%, and 46.1% in the P-1 facility and 22.5%, 33.2%, and 44.3% in the P-2 facility indicating a similar distribution in two facilities. Although the particulate matter size distribution was similar in the two facilities at the SCR system, APH, ESP, and WFGD system points, PM2.5 fraction in the P-1 facility was slightly higher than that in the P-1 facility.

Fig. 4.
Particle size distribution in APCDs of flue gas stream.

It was identified that the SCR system removes large-sized particulate matter and generates small-sized particulate matter. It was observed that the concentration ratio of >PM10 reduces, that of PM2.5-10 does not significantly change, and that of PM2.5 increases at the outlet of the SCR system. Such findings suggest that small-sized particulate matter is generated due to the reaction between SO2 and NH3, i.e., a reducing agent, and the large-sized particulate matter (>PM10) falls into the hopper below the catalyst layer by the soot blower and then is removed (Seo and Chang, 2012).

APH is a heat exchanger for decreasing the temperature of the exhaust gas that passed through the SCR system (340°C) to the adequate operating temperature of the electrostatic precipitator (about 130°C). In general, the specific resistivity of the particulate matter generated from the coal-fired power plant decreases with decreasing temperature of the exhaust gas, and hence, the generation of the back corona is inhibited (Cooper and Alley, 2002). Furthermore, with the decreasing temperature, the volume flowrate decreases, and the residence time within the ESP increases. Therefore, APH plays a role in improving the particle collection efficiency of ESP. However, even in such a heat exchanger, the flow decreases during the process of decreasing the temperature, the effect of gravity increases, and >PM10 is removed (Chen et al., 2017). In the measurement results of this study, the removal efficiency of >PM10 was found to be 30.7% and 20.1% in the P-1 and P-2 facilities, respectively.

ESP is the main equipment that removes the particulate matter, and it removes 57.8% and 50.69% of the PMtotal generated during the coal combustion in the P-1 and P-2 facilities, respectively. Furthermore, for PM2.5, it removes almost all of the PM2.5 generated during the coal combustion along with the one generated while passing through the SCR. The particle collection efficiency for PM2.5 was 95.9% and 96.4% in the P-1 and P-2 facilities, respectively. Although the WFGD system is usually used for De-SOx, the wet-scrubbing technology can generally remove the gaseous substance and particulate matter simultaneously and changes the design and operating conditions depending on the substances to be treated. The particulate matter is removed by the inertial impaction, diffusion, electrostatic attraction, and thermophoresis between the sprayed droplet and particulate matter (Kim et al., 2014; Jaworek et al., 2013; Copper et al., 2002). Based on the measurement results of this study, it was identified that particulate matter is removed, and the removal efficiency for PM2.5, PM2.5-10, and >PM10 was found to be 53.4%, 55.9%, and 72.4%, in the P-1 facility and 47.5%, 60.8%, and 71.4% in the P-2 facility, which is in line with the results of other studies showing higher removal efficiency for larger particulate matter (Chen et al., 2019; Wu et al., 2019; Li et al., 2017; Sui et al., 2016).

The SCR system installed to remove NOx is located downstream of the boiler, which is a good location to adjust the typical reaction temperature of the catalyst (300-400°C) (Li, 2017). The measurement target SCR of this study consists of three plate-type catalyst layers. The catalyst is composed of V2O5, and it is designed to use surface velocity of 3000-4,000 hr-1, and NH3 as a reducing agent. The NOx concentration was 187.2 mg/Sm3 and 51.3 mg/Sm3 at the SCR inlet and outlet in the P-1 facility, respectively, and the removal efficiency was measured as 72.6%. The NOx concentration was 186.9 mg/Sm3 and 39.0 mg/Sm3 at the SCR inlet and outlet in the P-2 facility, respectively, and the removal efficiency was measured as 79.1%. These NOx removal efficiencies appeared to be slightly lower than those of the typical SCR system (Sorrels et al., 2019; Li., 2017). The emission limit value of the measurement target coal-fired power plant is 102.7 mg/Sm3 (@ 6% O2), and the emitted concentration can conform with the emission limit value, suggesting it is not processed at high efficiency. Furthermore, because the low-NOx burner (LNB) is installed at this measurement facility, the concentration of NOx generated in the boiler is low, leading to a low removal efficiency (Zhang et al., 2021; Ti et al., 2014).

The WFGD system that removes SO2 is the desulfurization technique that is the most widely used in coal-fired power plants. By spraying the limestone slurry (CaCO3), SO2 is usually converted to gypsum (CaSO4) and then removed. The SO2 concentration was 794.3 mg/Sm3 and 36.5 mg/Sm3 at the WFGD inlet and outlet in the P-1 facility, respectively, and the removal efficiency was measured as 95.4%. In the P-2 facility, the SO2 concentration was 833.7 mg/Sm3 and 43.9 mg/Sm3 at the WFGD inlet and outlet, and the removal efficiency was measured as 94.7%. In this coal-fired power plant, the heat exchanger for the adequate operating temperature of the WFGD system, which is the leakage-type GGH, is installed upstream of the WFGD, and the leakage rate of GGH is between 3% and 5%. Therefore, the theoretical SO2 removal efficiency of WFGD would be slightly higher considering the leakage rate.

3. 2 Emission Factors

The emission factor of air pollutants is calculated using Eq. (1) (Wu et al., 2020; Jang et al., 2011).

 Emission factor kg/ton   =Concentration mg/Sm3×amount of flue gas         Sm3/hr×10-6/amount of coal feedington/hr (1)

Table 4 shows the information on the coal used in two coal-fired power plants during the measurement period. During this period, the P-1 facility generated 91.6% power, and the P-2 facility operated at 79.2%. During the measurement period of the P-2 facility, the power production rate of the power production facility was maintained at <80% due to the upper limit restrictions operated during the seasonal management system for highconcentration fine particulate matter.

Table 4.
Coal usage and contents of ash, sulfur in feed coal during sampling periods.
Power
plant
P-1 (500 MW) P-2 (500 MW)
Coal usage
(ton/hr)
(%)
Ash
(%)
Sulfur
(%)
Coal usage
(ton/hr)
(%)
Ash
(%)
Sulfur
(%)
Day 1 182.75 91.5 14.69 0.36 156.17 79.7 13.82 0.41
Day 2 190.50 91.7 12.03 0.44 153.58 78.8 15.05 0.33
Day 3 187.29 91.5 12.46 0.46 157.46 79.1 10.84 0.35

During the measurement period, the power production was kept at a constant level (maximum variance of 0.9%) in the two coal-fired power plants, but the coal consumption was found to change (maximum variance of 4%). This change is because of the calorific value change of the coal, and the calorific value of the coal changes depending on its composition, including carbon, moisture, and ash contents. For the stable operation of the power production facility, constant calorific value and quality of the coal are favorable; however, the calorific value is known to vary in the field. During the measurement period, the change in the ash and sulfur contents of the coal was 10.84-14.69% and 0.33-0.46%, respectively.

Using Eq. (1) and information tabulated in Table 4, the emission factors of PM (PMtotal, PM10, PM2.5), NOx, and SO2 at each spot of the coal-fired power plant were calculated based on the measurement data for each point and the same coal information data, and the results are presented in Table 5. The particulate matter (PMtotal, PM10, PM2.5) emission factors were lower in the P-2 facility with a lower load factor than in the P-1 facility with a higher load factor. The load factor of the P-2 is 84.4% of that of the P-1, but the emission factors of PMtotal, PM10, PM2.5, and NOx were found to be 56.0%, 56.7%, 58.8%, and 78.0%, respectively, suggesting that the reduction of the PMtotal, PM10, PM2.5, and NOx is more significant than the reduction of the coal consumption. However, although the load factor of SO2 decreased, its emission factor increased by about 1.5 times.

Table 5.
PM, NOx, and SO2 emission factor (kg/ton of coal) in APCDs of flue gas stream.
Emission factor (kg/ton) APCD PMtotal PM10 PM2.5 NOx SO2
This study P-1
Uncontrolled (LNB*) 3.310A 1.784A 0.642A 1.46* 17.2S
SCR 2.784A 2.088A 0.699A 0.63 16.6S
SCR+APH 1.921A 1.710A 0.676A 0.53 16.6S
SCR+APH+ESP 0.009A 0.009A 0.008A 0.42 13.2S
SCR+APH+ESP+WFGD 0.004A 0.0038A 0.0035A 0.41 0.61S
P-2
Uncontrolled (LNB*) 2.588A 1.441A 0.582A 1.57* 17.1S
SCR 2.039A 1.672A 0.616A 0.22 16.3S
SCR+APH 1.313A 1.183A 0.594A 0.31 16.3S
SCR+APH+ESP 0.0032A 0.003A 0.0028A 0.39 17.7S
SCR+APH+ESP+WFGD 0.0023A 0.0022A 0.0020A 0.32 0.94S
NAER (2020) Uncontrolled 50.00 29.10 10.14 7.50 19.0S
U.S. EPA AP-42 (1998) Uncontrolled 3.18A 1.18A 0.67A 4.99 17.7S
ESP 0.025A 0.019A 0.010A - -
Wu et al. (2018) Uncontrolled 6.9A 1.5A 0.4A - -
ESP 0.094A 0.065A 0.032A - -
ESP+WFGD 0.023A 0.0210A 0.0147A - -
*LNB: low-NOx burner
A: ash S: sulfur

Under the same operating conditions in the facility with the same capacity, if the coal consumption decreases, the exhaust gas flow (Q) becomes lower than the design value, and as a result, the fluid velocity of the combustion chamber and APCDs reduces and the retention time increases. In general, if the passage velocity decreases and, in turn, retention time increases, the removal efficiency of the SCR, ESP, and WFGD system is improved (Chen et al., 2019).

Therefore, the upper limit restrictions operated during the high-concentration fine dust generation period not only reduces the operating load of the power production facility and air pollutant emissions but also improves the efficiency of APCDs and reduces the dust emission factor. However, in the case of SO2, it is important to use coal with low sulfur content.

The LNB is installed in the two coal-fired power plants. Although the performance of LNB shows 80% efficiency in the two facilities considering NAER’s “uncontrolled” emission factor (7.5 kg/ton) (NAER, 2020), the efficiency of the SCR system was 58.2% and 86.0% in the P-1 and P-2 facilities, respectively, indicating lower emission factor in the facility with a lower load factor.

An SO2 emission factor is determined by the sulfur content of the fuel. Based on the measurement results, it was identified that the difference due to the different sulfur contents of the coal is more significant than the difference in the emission factor due to the load factor. In particular, the emission factor of the WFGD can be affected by the leakage rate of the GGH.

By comparing the “uncontrolled” emission factor of PMtotal, PM10, and PM2.5 with the existing emission factor, the “uncontrolled” emission factor of PMtotal, PM10, and PM2.5 used nationally is 50 kg/ton, 29.1 kg/ton, and 10.14 kg/ton, respectively. In the research of AP-42 (U.S. EPA) and Zhao et al., it is calculated as a function of the ash content included in coal. The emission factor of PMtotal, PM10, and PM2.5 calculated in this study was similar to that of AP-42 but lower than the PMtotal emission actor of Zhao et al. In terms of the emission factor for each prevention device, the emission factor of ESP and ESP+ WFGD appeared to be lower than that of the other studies, namely AP-42 and Zhao et al (Wu et al., 2018; Zhao et al., 2010; U.S EPA, 1998).

4. CONCLUSIONS

For the two bituminous coal-fired power plants with 500 MW and PC, the concentration of PMtotal, >PM10, PM2.5-10, PM2.5, NOx, and SO2 was measured through field measurement, and their emission factors were calculated. The measurement was carried out more than three times in the boiler downstream, SCR system, APH, ESP, and WFGD system (stack) by using the Korean standard test method for air pollutants.

During the field measurement period, the load factor was 91.6% and 79.2% in the P-1 and P-2 coal-fired power plants, respectively, and in the P-2 facility with a lower load factor, the measured concentration of PMtotal, PM10, PM2.5, and NOx was low. The emission factor obtained by dividing the measured concentration value by the fuel consumption was also calculated to be low. The load factor of the P-2 facility is only 84.4% of that of the P-1 facility, but the emission factor of PMtotal, PM10, PM2.5, and NOx was 56.0%, 56.7%, 58.8%, and 78.0%, respectively, suggesting the reduction of the PMtotal, PM10, PM2.5, and NOx emissions are more significant than the reduction of the coal consumption. However, although the load factor of SO2 decreased, its emission factor increased about 1.5 times, indicating no effect of the reduced load factor. Since the coal combustion chamber and various types of APCDs are operated at lower-load conditions than the design capacity, the number of pollutants generated decreases and the pollutant removal efficiency increases. However, it was identified that the SO2 concentration and emission factor are more significantly affected by the sulfur content of the coal rather than the difference in the load factor.

To this end, reducing the operating load of the coal-fired power plant improves the combustion efficiency and performance of several APCDs, and reduces the emission factor. It also leads to further decrease of the pollutants rather than the simply calculated reduction which is based on the reduction of power production rate. However, to decrease the SO2 emission, it is more effective to provide low-sulfur coal.

Acknowledgments

This study was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry, & Energy (MOTIE) of the Republic of Korea (grant no. 20161110100140), and Korea Environmental Industry & Technology Institute (KEITI) (grant Graduate School of Fine Particle Management Specialization).

REFERENCES
 1. Chen, H., Pan, P., Shao, H., Wang, Y., Zhao, Q. (2017) Corrosion and viscous ash deposition of a rotary air preheater in a coal-fired power plant. Applied Thermal Engineering, 113, 373-385. 2. Chen, Z., You, C., Wang, H., Liu, Q. (2019) Experimental study on the synergetic removal of fine particles by wet flue gas desulfurization tower with a flow pattern control device. Powder Technology, 343, 122-128. 3. Cooper, C.D., Alley, F.C. (2002) Air pollution control; A design approach. (3rd ED.), Waveland Press, Inc., pp. 155-159, 209-217. 4. EU/EEA (European Environment Agency) (2019) Air quality in Europe-2019 report. 5. Han, S., Lee, J.Y., Lee, J., Heo, J., Jung, C.H., Kim, E.S., Kim, Y.P. (2018) Estimation of the source contributions for carbonaceous aerosols at a background site in Korea. Asian Journal of Atmospheric Environment, 12, 311-325. 6. IPPC (Integrated Pollution Prevention and Control) (2017) Best Available Techniques (BAT) Reference Document for Large Combustion Plants, pp. 138-142. 7. Jang, K.W., Kim, H.C., Song, D.J., Jung, N.E., Hong, J.H., Lee, S.J., Han, J.S. (2011) Estimating PM emission factor from coal-fired power plants in Korea. Journal of Korean Society for Atmospheric Environment, 27(5), 485-493, (in Korean with English abstract). 8. Jaworek, A., Krupa, A., Sobczyk, A.T., Marchewicz, A., Szudyga, M., Antes, T., Balachandran, W., Natale, F.D., Carotenuto, C. (2013) Submicron particles removal by charged sprays. Fundamentals. Journal of Electrostatics, 71, 345-350. 9. KATS (Korea Agency for Technology and Standards) (2012) Stationary source emissions-determination of PM10/PM2.5 mass concentration in flue gas-measurement at low concentrations by use of impactor. 10. Kim, H.G., Kim, H.J., Lee, M.H., Kim, J.H. (2014) Experimental Study on the Enhancement of Particle Removal Efficiency in Spray Tower Scrubber Using Electrospray. Asian Journal of Atmospheric Environment, 8, 89-95. 11. Kim, S., Kim, O., Kim, B.-U., Kim, H.C. (2017) Impact of emissions from major point sources in Chungcheongnam-do on surface fine particulate matter concentration in the surrounding area. Journal of Korean Society for Atmospheric Environment, 33(2), 159-173, (in Korea with English abstract). 12. Li, X. (2017) Optimization and reconstruction technology of SCR flue gas denitrification ultra low emission in coal fired power plant. Materials Science and Engineering, 23, 012111. 13. Li, Z., Jiang, J., Ma, Z., Wang, S., Duan, L. (2015) Effect of selective catalytic reduction (SCR) on fine particle emission from two coal-fired power plants in China. Atmospheric Environment, 120. 14. Li, Z., Jiang, J., Ma, Z., Fajardo, O.A., Deng, J., Duan, L. (2017) Influence of flue gas desulfurization (FGD) installations on emission characteristics of PM2.5 from coal-fired power plants equipped with selective catalytic reduction (SCR). Environmental Pollution, 230, 655e662. 15. Liang, Y., Li, Q., Ding, X., Wu, D., Wang, F., Otsuki, T., Cheng, Y., Shen, T., Li, S., Chen, J. (2020) Forward ultra-low emission for power plants via wet electrostatic precipitators and newly developed demisters: Filterable and condensable particulate matters. Atmospheric Environment, 225, 117342. 16. Ma, C.J., Gang, G.U. (2019) Chemical property of the fly ash collected at an incinerator and its effects on near ambient particles. Asian Journal of Atmospheric Environment, 13, 136-143. 17. NAER (National Air Emission Inventory and Research Center) (2020) Air Pollutant Emission Calculation Manual IV, https://www.air.go.kr/jbmd/sub90_detail.do?tabPage=2&detailKey=62014P06&inputSchTxt=&typeSchOption=titleNm&menuId=undefined 18. NIER (National Institute of Environmental Research) (2014) Air pollution standard process test, Measurement method of total particulate matter, ES 01301.1. 19. Ruan, R., Liu, H., Tan, H., Yang, F., Li, Y., Duan, Y., Zhang, S., Lu, X. (2019) Effects of APCDs on PM emission: A case study of a 660 MW coal-fired unit with ultralow pollutants emission. Applied Thermal Engineering, 155, 418-427. 20. Saarnio, K. (2014) Chemical composition and size of particles in emissions of a coal-fired power plant with flue gas desulfurization. Journal of Aerosol Science, 74. 21. Seo, M.H., Chang, H.S. (2012) Computational Study on the Soot Blowing Method for Enhancing the Performance of the SCR System. Particle and Aerosol Research, 8(3), 99-110. 22. Seong, K.J., Lee, C. (2017) Operation and Improvement Cases of FGD Non-leakage Type Gas-Gas Heater (GGH) for Coal Fired Power Plants. Journal of the Korean Society of Combustion, 22(4), 35-42. 23. Shi, Y.-J., Shu, H., Zhang, Y.-H., Fan, H.-M., Zhang, Y.-P., Yang, L.-J. (2016) Formation and decomposition of NH4HSO4 during selective catalytic reduction of NO with NH3 over V2O5-WO3/TiO2 catalysts. Fuel Processing Technology, 150, 141-147. 24. Sorrels, J.L., Randall, D.D., Schaffner, K.S., Fry, C.R. (2019) Selective Catalytic Reduction, U.S. Environmental Protection Agency Research Triangle Park, NC 27711. 25. Sui, Z., Zang, Y., Peng, Y., Norris, P., Cao, Y., Pan, W. (2016) Fine particulate matter emission and size distribution characteristics in ultra-low emission power plant, Fuel, 185, 863-871. 26. Ti, S., Chen, Z., Li, Z., Xie, Y., Shao, Y., Zong, Q., Zhang, Q., Zhang, H., Zeng, L., Zhu, Q. (2014) Influence of different swirl vane angles of over fire air on flow and combustion characteristics and NOx emissions in a 600 MWe utility boiler. Energy, 74, 775-787. 27. U.S EPA (United States Environmental Protection Agency) (1998) Compilation of air pollutants emission factors AP-42. 28. Wang, C., He, B., Sun, S., Wu, Y., Yan, N., Yan, L., Pei, X. (2012) Application of a low pressure economizer for waste heat recovery from the exhaust flue gas in a 600 MW power plant. Energy, 48, 196-202. 29. Watts, N. et al. (2015) Health and climate change: policy responses to protect public health. The Lancet Commissions, 386, 1861-1914. 30. Wu, B., Bai, X., Liu, W., Zhu, C., Hao, Y., Lin, S., Liu, S., Luo, L., Liu, X., Zhao, S., Hao, J., Tian, H. (2020) Variation characteristics of final size-segregated PM emissions from ultralow emission coal-fired power plants in China. Environmental Pollution, 113886. 31. Wu, B., Tian, H., Hao, Y., Liu, S., Liu, X., Liu, W., Bai, X., Liang, W., Lin, S., Wu, Y., Shao, P., Liu, H., Zhu, C. (2018) Effects of wet flue gas desulfurization and wet electrostatic precipitators on emission characteristics of particulate matter and its ionic compositions from four 300 MW level ultralow coal-fired power plants. Environmental Science & Technology, 52(23), 14015-14026. 32. Wu, B., Tian, H., Hao, Y., Liu, S., Sun, Y., Bai, X., Liu, W., Lin, S., Zhu, C., Hao, J., Luo, L., Zhao, S., Guo, Z. (2020) Refined assessment of size-fractioned particulate matter (PM2.5/PM10/PMtotal) emissions from coal-fired power plants in China. Science of The Total Environment, 706, 135735. 33. Wu, Q., Gu, M., Du, Y., Zeng, H. (2019) Synergistic removal of dust using the wet flue gas desulfurization systems. Royal Society Open Science, 6: 181696. 34. Yao, S., Cheng, S., Li, J., Zhang, H., Jia, J., Sun, X. (2019) Effect of wet flue gas desulfurization (WFGD) on fine particle (PM2.5) emission from coal-fired boilers. Journal of Environmental Science, 77, 32-42. 35. Zhang, X., Chen, Z., Zhang, M., Zeng, L., Li, Z. (2021) Combustion stability, burnout and NOx emissions of the 300-MW down-fired boiler with bituminous coal: Load variation and low-load comparison with anthracite. Fuel, 295. 36. Zhao, Y., Wang, S., Nielsen, C.P., Lo, X., Hao, J. (2010) Establishment of a database of emission factors for atmospheric pollutants from Chinese coal-fired power plants. Atmospheric Environment, 44(12), 1515-1523.